specific moving bed biofilm reactor in nutrient removal from

Specific Moving Bed Biofilm Reactor in Nutrient Removal from Municipal

Wastewater

By

Asmita Shrestha

A thesis submitted in partial fulfillment of requirements

for the Degree of Master of Engineering

Submitted to the School of Civil and Environmental Engineering,

Faculty of Engineering and Information Technology, UTS

Supervisor: Dr. Wenshan Guo

Co-supervisor: A/Prof. Huu Hao Ngo

April 2013

ii

CERTIFICATE OF ORIGINAL AUTHORSHIP

I certify that the work in this thesis has not previously been submitted for a degree nor

has it been submitted as part of requirements for a degree except as fully acknowledged

within the text.

I also certify that the thesis has been written by me. Any help that I have received in my

research work and the preparation of the thesis itself has been acknowledged. In

addition, I certify that all information sources and literature used are indicated in the

thesis.

________________________

(Asmita Shrestha)

Signature of Student

Date: 01 – 08 – 2013

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ACKNOWLEDGEMENT

First of all, I would like to express my sincere gratitude to my principal supervisor, Dr.

Wenshan Guo, for her continuous guidance, support, discussion, suggestions,

understanding and encouragement and for taking me on as her master’s student by

believing on me. Without her guidance and suggestions this study would not be

possible. I would also like to thank my co-supervisor, A/Prof. Huu Hao Ngo, for his

valuable comments, suggestions, guidance and help throughout the research.

I am very grateful to Faculty of Engineering and Information Technology (FEIT), UTS

for providing a laboratory for my experimental works as well as nice environment for

my study without which it would not be possible. My special thanks to University

Graduate School for providing Thesis completion equity grant. I would like to thank all

the UTS staff for all the administrative and other supports.

I would like to extend my sincere thanks to Dr. Tien Thanh Nguyen, the senior technical

officer of Environmental Engineering Laboratory, FEIT Mr. Mohammed Johir and my

dear friend Ms Sima Adabju for all their help and support during my laboratory set up

and experiments. I would also like to thank all my fellow graduate students of UTS and

my good friends for the good time we shared together at UTS.

I would also like to thank all the Authors and researchers that I have listed in the

reference section of this thesis. Their materials were really valuable and useful for this

thesis writing.

Last but not least, I am grateful to my family for their unconditional love, courage,

support and understanding. Without them these accomplishments would not have been

possible. I am indebt to my husband Suman and our Daughter Sneha, who have given

me continuous encouragement, love and support in all the way. I have no words to

thank my beautiful daughter Sneha, who bear to stay at childcare for long hours when I

was busy in my study.

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TABLE OF CONTENTS

Certificate of Original Authorship…………………..…………………………….…… ii

Acknowledgement………………..………………………………………………….... iii

Table of Contents……..……………………………………………………………..… iv

List of Abbreviations..………………………………………………………………... vii

List of Figures……………..………………………………………………………..…. ix

List of Tables……..………………………………………………………………….... xii

Abstract………………..…………………………………………………………........ xiv

CHAPTER 1: INTRODUCTION……………………….....……………………1

1.1 Background of the Study…..……..………………………………..…………… 1

1.2 Objectives of the Study…………….………………...……………...………….. 3

1.3 Outline of the Thesis.………………………...…………………………………. 3

CHAPTER 2: LITERATURE REVIEW………...……...………………….... 5

2.1 Municipal Wastewater and its Impact on Environment……..…………………. 5

2.1.1 Wastewater characteristics and discharge standards.………….....……… 6

2.1.2 Wastewater treatment technologies…....…...…………………..……..…. 9

2.2 Low Pressure Membrane Processes.….………………………………………. 17

2.2.1 Microfiltration/ Ultrafiltration (MF/ UF)….………………………........ 19

2.2.2 Membrane bioreactor (MBR)…….…………………..………..….….… 20

2.2.3 Membrane fouling………….………..……………………….…..….… 25

2.3 Biological Nutrient Removal (BNR) from Wastewater..…...…..……………. 31

2.3.1 Nitrogen removal…….………………………..………………….......... 32

2.3.2 Phosphorus removal.……………………………..…………..……........ 33

2.4 Attached Growth Processes for Wastewater Treatment…….…..……..……... 34

2.4.1 Moving bed biofilm reactor (MBBR)………….………..……………... 38

2.4.2 Different types of media used in MBBR….………………..………...... 39

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2.4.3 Theory of attached growth processes….………………………..……… 43

2.4.4 MBR and MBBR for nutrient removal.….…………………..…………. 44

2.4.5 Application of MBBR for nutrient removal from wastewater……….… 46

CHAPTER 3: MATERIALS AND METHODOLOGIES…….……….. 56

3.1 Materials……………..…………………………………….……….………… 56

3.1.1 Wastewater……..…………………………………..…………….……. 56

3.1.2 Polyethylene (PE) carriers…..…………………………………………. 56

3.1.3 Membrane module…………..…………………………………………. 58

3.2 Methodologies………………………..…………………………..…………... 59

3.2.1 Experimental conditions……………………………………………….. 59

3.2.2 Analytical methods……………..………………………………….…... 65

3.2.3 Biomass growth rate calculation..………………………....…………… 65

3.2.4 Velocity measurement and circulation of……..………………………... 66

kinetic energy for moving media

3.2.5 Membrane resistance calculation…..…………………………………... 66

3.2.6 Membrane cleaning procedure…………………………………………. 68

CHAPTER 4: RESULTS AND DISCUSSIONS……..………..………….. 69

4.1 Determination of Optimum Operating Conditions for MBBR………………... 69

System in terms of Carrier Filling Rate, Aeration Rate and HRT

4.1.1 Evaluation of microbial growth in PE carriers and its..…..….…….…... 69

performance at different carrier filling rates, aeration rates and HRTs

4.1.2 Correlation between removal efficiency and total kinetic..……..……... 77

energy (KET) at different PE carrier filling rates and aeration rates

4.1.3 Nutrient and organic removal efficiency on…..……………………....... 79

MBBR at different PE carrier filling rates

4.1.3.1 PO4-P removal efficiency………………………………...……. 79

4.1.3.2 NH4-N removal efficiency……………...………………...……. 80

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4.1.3.3 DOC and COD removal efficiency…………….………...……. 82

4.1.4 Nutrient and organic removal efficiency...……..………………………. 83

on MBBR at different aeration rates




4.1.5 Nutrient and organic removal efficiency...……..………………………. 88

on MBBR at different HRTs




4.2 Evaluation of the Performance of MBBR-MF System......……….……..….… 93

4.2.1 Nutrient and organic removal..………….…..…..……..……………..… 93

4.2.2 Membrane resistance characteristics at.………….…………………….. 94

different permeate flux conditions

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS…...... 97

5.1 Conclusions………………………………………………………………..….. 97

5.2 Recommendations for Future Research……………………………………… 99

References………………………………………………………………………. 100

Appendix A…………………………………………..…………………………… 110

Appendix B……………………………………..………………………………… 114

Appendix C………………………………..……………………………………… 118

Appendix D…………………………..…………………………………………… 122

Appendix E……………………..………………………………………………… 126

Appendix F………………..………………………………………………………. 129

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LIST OF ABBREVIATIONS

AOB Ammonia oxidizing bacteria AOP Advanced oxidation process BF-MBR Biofilm membrane bioreactor BNR Biological nutrient removal BOD Biochemical oxygen demand CAS Conventional activated sludge C/N Carbon Nitrogen ratio CFMF Cross flow membrane filtration COD Chemical oxygen demand CP Cylindrical polypropylene CSTR Continuous stirred tank reactor DNA Deoxyribonucleic acid DO Dissolved oxygen DOC Dissolved organic carbon EPS Extracellular polymeric substance FBR Fluidized bed bioreactor FC Circulation frequency FS Flat sheet GAC Granular activated carbon h Hours HDPE High density polyethylene HF Hollow fiber HRT Hydraulic retention time H2SO4 Sulphuric acid J Permeate flux KE Kinetic energy KET Total kinetic energy LDPE Low density polyethylene MBBR Moving bed biofilm reactor MBBR-MF Moving bed biofilm reactor –Membrane filtration MBR Membrane bioreactor MF Microfiltration MLSS Mixed liquor suspended solid MLVSS Mixed liquor volatile suspended solid NaClO Sodium hypochlorite NaHCO3 Sodium carbonate anhydrous NaOH Sodium hydroxide NF Nanofiltration NH4-N Ammonium nitrogen NOB Nitrite oxidizing bacteria

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NOM Natural organic matter O3 Ozone OLR Organic loading rate OUR Oxygen uptake rate PAC Powdered activated carbon PAO Phosphate accumulating organism PB Polyethylene Bead PCL Polycaprolactone PE Polyethylene PG Polyethylene Granule PO4-P Ortho - phosphate PS Polyethylene sheet PTSE Primarily treated sewage effluent PUF Polyurethane foam PVA Polyvinyl alcohol RBC Rotating biological contactor RC Cake layer resistance RM Membrane Resistance RO Reverse osmosis RP Pore block resistance RT Total resistance S Sponge SBF Sponge biofilter SBR Sponge batch reactor SBR Sequencing batch bioreactor SMBR Submerged membrane bioreactor SMP Soluble microbial product SRT Sludge retention time SSMBR Sponge submerged membrane bioreactor SVI Sludge volume index T Temperature TMP Transmembrane pressure TN Total nitrogen TOC Total organic carbon TP Total phosphorus TSS Total suspended solid UASB Upflow anaerobic sludge blanket UCT University of Cape Town UF Ultrafiltration UTS University of Technology Sydney UV Ultraviolet VFA Volatile fatty acid ΔPT Transmembrane pressure μ Viscosity of water

ix

LIST OF FIGURES

Figure 2.1 Dead end filtration

Figure 2.2 Cross flow filtration

Figure 2.3 Configuration of MBR system; (A) Submerged MBR and (B) Side stream MBR configuration

Figure 2.4 Factors influencing fouling in membrane processes (Le-cleach et al., 2006, Chang et al., 2002)

Figure 2.5 Biomass growth systems in wastewater treatment systems (Jianlong et al., 2000)

Figure 2.6 Typical diagram for MBBR and fixed bed bioreactor

Figure 2.7 The physical appearances of the media used in attached growth processes

Figure 2.8 Schematic diagram of attached growth process

Figure 3.1 Polyethylene (PE) carriers

Figure 3.2 Flat sheet membrane module

Figure 3.3 Experimental arrangements of (A) MBBR and (B) MBBR-MF

Figure 3.4 Flow chart of the research activities

Figure 3.5 PE carriers acclimatization tank

Figure 3.6 Laboratory setup of MBBR

Figure 3.7 Laboratory setup of MBBR–MF system

Figure 4.1 Biomass growth in PE carriers (at different (A) filling rates and (B) aeration rates)

Figure 4.2 Variation of biomass concentration in the carriers at different filling rates

Figure 4.3 Variation of biomass concentration in the carriers at different aeration rates

Figure 4.4 Variation of biomass concentration in the carriers at different HRTs

Figure 4.5 Average DO consumption rate variation of the suspended biomass on the wastewater at different PE carrier filling rates

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Figure 4.6 Average DO consumption rate variation of the suspended biomass on the wastewater at different aeration rates

Figure 4.7 Average DO consumption rate variation of the suspended biomass on the wastewater at different HRTs

Figure 4.8 Average DO consumption rate variation of the attached biomass on PE carriers at different carrier filling rates, aeration rates and HRTs.

Figure 4.9 Correlation between the kinetic energy and (A) PE carrier filling rates and (B) aeration rates.

Figure 4.10 PO4-P removal efficiency at different PE carrier filling rates

Figure 4.11 Average PO4-P removal efficiency at different PE carrier filling rates

Figure 4.12 NH4-N removal efficiency at different PE carrier filling rates

Figure 4.13 Average NH4-N removal efficiency at different PE carrier filling rates

Figure 4.14 TN removal efficiency at different PE carrier filling rates

Figure 4.15 DOC removal efficiency at different PE carrier filling rate

Figure 4.16 COD removal efficiency at different PE carrier filling rates.

Figure 4.17 PO4-P removal efficiency at different aeration rates

Figure 4.18 Average PO4-P removal efficiency at different aeration rates

Figure 4.19 NH4-N removal efficiency at different aeration rates

Figure 4.20 Average NH4-N removal efficiency at different aeration rates

Figure 4.21 TN removal efficiency at different aeration rates

Figure 4.22 DOC removal efficiency at different aeration rates

Figure 4.23 COD removal efficiency at different aeration rates

Figure 4.24 PO4-P removal efficiency at different HRTs

Figure 4.25 Average PO4-P removal efficiency at different HRTs

Figure 4.26 NH4-N removal efficiency at different HRTs

Figure 4.27 Average NH4-N removal efficiency at different HRTs

Figure 4.28 TN removal efficiency at different HRTs

Figure 4.29 DOC removal efficiency at different HRTs

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Figure 4.30 COD removal efficiency at different HRTs

Figure 4.31 Effect of permeate flux on total membrane resistance (aeration rate: 1.35 m3/m2.h, membrane area: 0.2 m2)

Figure 4.32 Cake layer formations on the surface of flat sheet membrane module

Figure F1. Oven

Figure F2. Furnace

Figure F3. pH meter (HANNA instrument, model no. HI 9025)

Figure F4. DO meter (HORIBA Ltd. Japan, model no. OM -51E)

Figure F5. COD sample heater and a photometry

Figure F6. Analytikjena multi N/C 3100

Figure F7. Spectroquant® cell test (NOVA 60, Merck)

Figure F8. YSI 5300 Biological oxygen monitor

Figure F9. GFC Whatman’s 1.2 μm filter paper and syringe filters (0.45 and 1.20μ)

Figure F10. Ultrasonic cleaner (POWER SONIC 405, Thermoline scientific)

xii

LIST OF TABLES

Table 2.1 Health and environmental effects of nutrients

Table 2.2 Constituents present in domestic wastewater (Henze et al., 2002)

Table 2.3 Australian treated wastewater discharge standards (EPA, 2005)

Table 2.4 Different types of treatment processes used in wastewater treatment

Table 2 5 Advantages and disadvantages of MBR technology (Melin et al., 2006)

Table 2.6 Different types of attached growth systems (Odegaard, 1999)

Table 2.7 Characteristics of media used in the attached growth processes

Table 2.8 Characteristics data for the four different carriers used (Odegaard et al., 2000)

Table 3.1 Characteristics of synthetic wastewater

Table 3.2 Characteristics of PE carriers

Table 3.3 Characteristics of membrane

Table 3.4 Experimental conditions to determine effect of different aeration rates and HRTs in nutrient removal from wastewater

Table 4.1 Organic and nutrient removal efficiency at different filling rates of PE Carrier (aeration rate = 4.5 L/min, flow rate = 8 mL/min, HRT = 25 h)

Table 4.2 Organic and nutrient removal efficiency at different aeration rates (carrier filling volume = 20%, flow rate = 8 mL/min, HRT = 25 h)

Table 4.3 Organic and nutrient removal efficiency at different HRTs (carrier filling volume = 20%, aeration rate = 4.5 L/min)

Table 4.4 Calculation of total kinetic energy

Table 4.5 Comparison of organic and nutrient removal between MBBR and MBBR–MF Systems at different filtration fluxes (aeration rate: 1.35 m3/m2.h, membrane area: 0.2 m2)

Table 4.6 Rc, Rp, Rm and RT at different permeate fluxes (aeration rate: 1.35 m3/m2.h, membrane area: 0.2 m2)

Table A1. pH, DO and T in MBBR at different PE carrier filling rates (flow rate; 8 mL/ min, aeration rate; 4.5 L/min)

xiii

Table A2. MLSS and MLVSS in MBBR at different PE carrier filling rates (flow rate; 8 mL/min, aeration rate; 4.5 L/min)

Table A3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different PE carrier filling rates (flow rate; 8 mL/min, aeration rate; 4.5 L/min)

Table B1. pH, DO and T of MBBR at different aeration rates ( flow rate; 8 mL/min, PE carrier filling rate; 20%)

Table B2. MLSS and MLVSS in MBBR at different aeration rates (flow rate; 8 mL/min, PE carrier filling rate; 20%)

Table B3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different aeration rates (flow rate; 8 mL/min, PE carrier filling rate; 20%)

Table C1. pH, DO and T of MBBR at different HRTs (aeration rate; 4.5 L/min, PE carrier filling rate; 20%)

Table C2. MLSS and MLVSS of MBBR at different HRTs (aeration rate; 4.5 L/min, PE carrier filling rate; 20%)

Table C3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different HRTs (aeration rate; 4.5 L/min, PE carrier filling rate; 20%)

Table D1. NO2-N and NO3-N data for MBBR at different PE carrier filling rates (aeration rate; 4.5 L/min, flow rate; 8 mL/min)

Table D2. NO2-N and NO3-N data for MBBR at different aeration rates (PE carrier filling rate; 20%, flow rate; 8 mL/min)

Table D3. NO2-N and NO3-N data for MBBR at different HRTs (PE carrier filling rate; 20%, aeration rate; 4.5 L/min)

Table E1. Total membrane resistance at different fluxes

Table E2. DOC, COD, PO4-P and NH4-N removal efficiency in MBBR–MF at different HRTs

xiv

ABSTRACT

Wastewater treatment technology has been improved and modified to get higher

removal efficiency and to meet the stringent effluent regulations. However, from a

worldwide perspective, wastewater treatment process is facing many challenges,

especially nutrients removal, thereby resulting in the serious concern for enhancement

and modification of the existing wastewater treatment processes to achieve better

removal efficiency. Nutrient and organic removal from wastewater is becoming an

important priority for wastewater treatment plants due to the detrimental impact of these

components on the receiving bodies. Therefore my research study aims to evaluate a

moving bed biofilm reactor (MBBR) system for effective nutrient and organic removal

from municipal wastewater which has promising prospects in terms of achieving high

nutrient removal efficiency by reducing the operating cost. This study puts forward a

systematic study on the effect of polyethylene (PE) carriers filling rates, the influence of

aeration rate and different hydraulic retention time (HRT) on the organic and nutrient

removal from municipal wastewater using continuously operated MBBR system in

order to determine the optimum operating condition. To further verify the feasibility of

MBBR system operated at optimum condition, this system was combined with a

membrane filtration system to investigate the performance of the combined system in

terms of organic and nutrient removal efficiency. My research activities during my

research period were mainly focused on literature review in this field and lab scale

investigations. This report compiles introduction of the study, literature review,

materials and methodologies used, all the specific experimental results, findings and

conclusion drawn from the whole study period.

1

CHAPTER 1: INTRODUCTION

1.1 Background of the Study

It is expected that the Australian population in the major cities will increase by 35%, or

4.5 million people, by the year 2030 (ABS, 2006) and the water used by that population

will be 62% of all water extracted. The wastewater produced by the increasing

population and the huge economical cost for the treatment of this wastewater will be the

major problem in future. In early stage, when the population was very few, waste

generated by them was limited and they dumped those wastes directly into natural water

bodies to purify naturally by dilution and natural bacterial breakdown. With the

urbanization and the changing life style, the production of domestic and industrial

wastewater has been increased. The harmful constituents also have been discharged

together with the generated wastewater directly into the natural water bodies and have

affected the surrounding environment, human health and aquatic lives. Hence, in order

to prevent natural water bodies from pollution, basic wastewater treatment facilities

have been introduced to reduce organics, nutrients and other harmful constituents and

help to prevent environmental pollution.

It is a known fact that nutrients are very essential for the development of all the living

beings and plants. However, use of excess amount of these elements can cause adverse

effects. For example, excess nutrient discharge in natural water bodies affects the

aquatic lives, enhances eutrophication process and increases oxygen demand in the

receiving water bodies while excess nutrient to human being may cause different types

of health problems. The eutrophication in water bodies occurs due to discharge of

wastewater produced by human daily activities, which contains high concentration of

nitrogen and phosphorous. Therefore, it is a pressing issue on improving treatment

technology capable to achieve higher removal efficiency of nutrient, organic matter and

other harmful constituents. Standalone biological wastewater treatment systems such as

conventional activated sludge systems (CAS), Aerated lagoons have been able to treat

these harmful constituents, but at the expense of huge economical cost to achieve the

desired effluent water quality particularly at medium to large wastewater treatment

facilities. Similarly, in order to withstand in the present competitive market, membrane

2

bioreactor (MBR) process efficiency has been widely used due to its high treated water

quality and high productivity. However, the sludge production from solid retention time

(SRT) control, chemical waste from the membrane cleaning, membrane fouling, the

membrane life span are the main hindrance in the MBR application (Broeck et al., 2012;

Pal et al., 2012; Phattaranawik et al., 2011; Galil et al., 2009)

Moving bed biofilm reactor (MBBR) technology is one of the best options to overcome

these problems. At present, there are more than 500 large scale wastewater treatment

plants in 50 different countries all over the world based on MBBR processes in

operation. The technology has become popular in the field of wastewater treatment

because of its many advantages such as high capacity, high efficiency, relatively small

footprints compared with the conventional treatment systems. It also has capacity to

withstand the challenges of wastewater industry such as retrofitting the old treatment

plants, producing less sludge as a result of high biomass retention time, minimizing

process complexities and operators, eliminating the need of backwashing, and so on.

MBBR is a continuous flow process where higher concentration of active biomass can

be maintained for biological treatment without increasing the reactor size. The system is

mainly based on the aeration and special designed carriers to provide a surface

colonized by bacteria (Rahimi et al., 2011). The bioreactor provides favourable

condition to the microorganisms which are responsible for the sufficient removal and

conversion of harmful constituents from the wastewater. Aeration rate and carrier filling

rate play vital role to provide satisfied treatment efficiency (Jing et al., 2009). Odegaard

et al. (2000) stated in their study that the MBBR can be loaded with biofilm carrier up

to 70% of the reactor’s effective volume thus significantly reducing the required

footprint and allows carriers to move easily. However, experience has shown that

mixing efficiency decreased at higher percentage fills (Weiss et al., 2005) and the

performance efficiency of the reactor could vary with different types of biofilm carrier

used (Guo et al., 2010). As the biofilm carrier packing rate, aeration rate and hydraulic

retention time (HRT) have influence on the organics and nutrient removal efficiency,

and at the same time also increase the cost and energy consumption, it is an imperative

requirement to carry out a systematic study on the effect of carrier filling rates, aeration

rates and HRTs on the treatment efficiency in continuous MBBR system.

3

1.2 Objectives of the Study

Nutrient and organic constituents in wastewater are consumed by microorganisms that

lives within the wastewater in the process of there growth. These microorganisms, when

got suitable surface to attach, grow more rapidly in the presence of favourable condition

and perform effectively in wastewater treatment process. The suitable surface may be

the wood, sand, mud or plastic materials and the favourable condition for these

microbial growths depend on the factors like percentage of carrier filling rate, aeration

rate, HRT etc. Many researches have been carried out using MBBR but there is no

specific research on this particular carrier such as the effect of carrier filling rate,

aeration rate and HRT in nutrient and organic removal from municipal wastewater.

Therefore, this research aims to carry out series of lab scale experimental investigation

on the effects of the carrier filling ratio, aeration rate and HRT on the performance of

MBBR and optimize the operation conditions in a cost-effective way. In addition, the

specific objectives of this research are listed below.

Review wastewater treatment using MBBR related literature regarding its

performance in terms of nutrient and organic removal at smaller footprints, low

cost, easy operation, less burden to surrounding environment;

Establish an appropriate methodology for wastewater treatment using MBBR

system;

Evaluate optimum operating conditions for MBBR system in terms of carrier

filling rate, aeration rate and HRT.

Evaluate the MBBR system connected with membrane filtration (MBBR–MF)

for organic and nutrient removal and evaluate the membrane fouling behavior at

different fluxes.

1.3 Outline of the Thesis

This thesis is organized into 5 main chapters, and each chapter gives a particular aspect.

Chapter 1 introduces the background of the study and objective of the study. Chapter 2

contains literature review which includes the information gathered during the study of

related literatures as a part of this research. This chapter mainly focuses on the different

types of wastewater treatment technologies specially MBR and MBBR and their

4

performance in terms of nutrient and organic removal efficiency. The literature review

is also integrated and related with the results of this research where relevant. The

materials, description of methodologies used for the study and the analytical methods

are presented in Chapter 3 under the title Materials and Methodology. Equations for

velocity measurement and circulation of kinetic energy for moving media, equations for

membrane resistance calculation, procedure for measurement of biomass growth on the

moving media and the procedure for the membrane module cleaning are also presented

in this chapter. The results obtained from the laboratory experiments are presented and

discussed in Chapter 4. The discussion focuses on the nutrient and organic removal

efficiency achieved from MBBR at different filling rates of PE carriers, different

aeration rates and HRTs so as to determine the optimum operating condition. The

evaluation of MBBR-MF are also included in Chapter 4. Conclusions of this research

and recommendations for future research are given in Chapter 5. References and

Appendices are included at the end of this thesis.

5

CHAPTER 2: LITERATURE REVIEW

2.1 Municipal Wastewater and its Impact on Environment

Municipal wastewater is the contents of sanitary waste collected from sewers and

households, waste from industries, commercial and institutional complexes and

sometimes the storm water. Municipal wastewater typically contains:

grit, debris and suspended solids,

disease-causing pathogens like bacteria and viruses,

human and other organic wastes which cause the oxygen depletion on a natural

water body,

nutrients such as nitrogen and phosphorus,

microorganisms and chemicals from household, institutions and industries.

All these constituents have wide range of potential impact to the surrounding

environment and the human health. Because of the complex composition and the high

amount of production, municipal wastewater management has become the major issue

worldwide. The escalating growth of commercial and industrial market and the lifestyle

affluent by these developments is one of the main factors that enhance the wastewater

production. After we use the supplied water for different activities such as laundry,

toilet, dishwashing, bathing, industrial purposes, commercial complexes, agricultural

lands, institutions and many others, the clean water receives many harmful constituents

such as pathogenic microorganisms, organic matters, nutrients, toxic compounds and

that wastewater can be mixed up with the valuable natural water resources (Metcalf &

Eddy, 2003). As water is a renewable resource and it does not affect by for what

purpose we are using it, however, the unsystematic and haphazard use of water and

contamination of the water resources knowingly or unknowingly by discharging the

polluted wastewater make renewal water resources to non-renewable. When the

wastewater containing harmful constituents accumulated, it impacts directly and

indirectly on the human health, environment and surrounding water sources. Once the

organic matters in the wastewater start decomposition, they produce foul-smelling gas.

Similarly, the numerous pathogenic microorganisms in untreated wastewater can

transfer into the human food chain. The nutrient in wastewater enhances the growth of

aquatic plants and toxic compounds in water bodies and can also harm the ecosystem

6

and human health. The ecosystem starts degrading in faster rate and the pollution affects

the ecosystem negatively. Some of the environmental and health effects of nutrient are

listed in Table 2.1.

In the scenario of limited source of appropriate water for drinking, farming, cleaning

etc. and raising problem of wastewater production and management, treating the

wastewater properly before it reaches the water bodies so that it will not hinder human

health and give extra burden to the surrounding environment and ecosystem is the main

alternative to support and preserve the limited water resources.

2.1.1 Wastewater characteristics and discharge standards

The identities and concentrations of different substances that need to be removed from

the wastewater need to be done beforehand so that it is convenient to choose the

appropriate treatment method. The constituents in wastewater vary according to the

source of its generation. Constituents of domestic wastewater are different from the

constituents of industrial wastewater (Henze, 2008). Wastewater constituents can be

divided into different categories as listed in Table 2.2.

Wastewater is characterised in terms of its physical, chemical and biological

composition. The wastewater characterization quality depends on the sample collection,

storage and laboratory analysis. If we fail to collect, store and analyse the wastewater

sample correctly then the wastewater characteristics may not be the same that it has to

be.

The wastewater discharged by the industrial and commercial operations must strictly

meet the standards that will help protect the environment, human health and reduce

operation cost for the wastewater treatment. Wastewater consists of different organic

and inorganic compounds either in dissolved or in suspended stage depending on for

what it was used which make the wastewater treatment difficult. Different treatment

technologies are used to remove such pollutants and pathogens from the wastewater

which helps to improve the wastewater quality and discharge it into the water bodies.

7

Table 2.1 Health and environmental effects of nutrients

Nutrients Environmental & Health Effects References Ammonia High concentrations cause the death of animals, birds

or fish, and death or low growth rate in plants, soil acidification, possibility of forest drought and fire.

Short term or moderate exposure to human cause severe burns to skin, eyes, throat, lungs, mouth and stomach

Long term exposure to human cause permanent blindness, lung disease, corneal disease, glaucoma or chronic respiratory diseases

Agency for Toxic Substances and Disease Registry, 2004;

Nitrogen High concentrations of nitrogen cause eutrophication process in water bodies which impact aquatic lives

In the animal stomach and intestines nitrates can form nitrosamines; dangerously carcinogenic compounds

High concentration of nitrite and nitrate cause the possibility of cancer, ingested nitrates and nitrites might result in mutagenicity, teratogenicity and birth defect, and coronary heart disease.

Very high level of nitrite causes methemoglobinemia, reactions with hemoglobin in blood, causing the oxygen carrying capacity of the blood to decrease

High level of nitrate increase the risk of gastric cancer with high concentration, decreased functioning of the thyroid gland, bladder and ovarian cancer

Nitrous oxide emission contributes to the climate change

Erisman et al., 2011; Camargo et al., 2006

Nitric acid High concentration of nitric acid cause soil acidification, alteration of plant species composition, affects the surface and ground water sources.

Concentrated nitric acid are highly corrosive to eyes and skin and produces deep painful burns, eye contact can cause severe burns and permanent damage

Inhalation of high concentrated HNO3 can cause irritation during respiration, ingestion of HNO3 cause burning and corrosion of the mouth, throat and stomach

Cisneros et al., 2010

Phosphorus High concentration of total phosphorus enhances to algal blooms that does not support the aquatic lives.

Higher amount of phosphate cause health problems like kidney damage and osteoporosis. Decrease in phosphate amount also cause health problems such as loss of appetite, fatigue, anxiety, bone pain, fragile bones, stiff joints, irregular breathing, irritability, numbness, weakness, and weight change. In children, decreased growth and poor bone and tooth development may occur.

White phosphorus is extremely poisonous and in many cases exposure to it will be fatal. It may cause nausea, stomach cramps and drowsiness. It can cause skin burns, liver, heart and kidney damage.

Coats et al., 2011; EPA, 2007

8

Table 2.2 Constituents present in domestic wastewater (Henze et al., 2002)

Wastewater constituents Examples Effects

Microorganisms Pathogenic bacteria, virus and worm eggs

Risk when bathing and eating shellfish

Biodegradable organic materials

Oxygen depletion in rivers, lakes and fjords Fish death, odours

Other organic materials

Detergents, pesticides, fat, oil and grease, colouring, solvents, phenols, cyanide

Toxic effect, aesthetic inconveniences, bio accumulations in the food chain

Nutrients Nitrogen, phosphorus, ammonium

Eutrophication, oxygen depletion, toxic effect

Metals Hg, Pb, Cd, Cr, Cu, Ni Toxic effect, bioaccumulation

Other inorganic materials

Acids, for e.g. hydrogen sulphide, bases Corrosion, toxic effect

Thermal effects Hot water Changing living conditions for flora and fauna

Odour (and taste) Hydrogen sulphide Aesthetic inconveniences, toxic effect

Radioactivity Wastewater from hospitals, laboratory which contains radionuclides, uranium etc.

Toxic effect accumulation.

All countries and regions have their own wastewater discharge standard and the treated

wastewater effluent has to meet with increasingly stringent discharge standard. Table

2.3 lists the Australian discharge standards of treated wastewater into the aquatic

ecosystem (EPA, 2005).

9

Table 2.3 Australian treated wastewater discharge standards (EPA, 2005)

Pollutants (mg/L) Discharge limits

Aquatic Ecosystem Fresh Water Marine

pH 6.5-9 ― TOC 15 10 BOD5 10 10 DO >6 >6 Turbidity (NTU) 20 10 SS 20 10 TN 5 5 NH4-N 0.5 0.2 PO4-P 0.1 0.1 TP 0.5 0.5 As (Total) 0.05 0.05 Cu (Total) 0.01 0.01 Cd (Total) 0.002 0.002 Cr (VI) 0.001 0.0044 Fe (Total) 1 ― Pb (Total) 0.005 0.005 Hg (Total) 0.0001 0.0001 Ni (Total) 0.15 0.015 Se (Total) 0.005 0.07 Ag (Total) 0.0001 0.001 Zn (Total) 0.05 0.05 Phenols (Total) 0.05 0.05 Toluene 0.3 0.80 Benzene 0.3 0.3 Polychlorinated biphenyls 0.000001 0.000004 Polyaromatic hydrocarbons 0.003 0.003

2.1.2 Wastewater treatment technologies

In previous years, until 1990, water authorities have kept pace with the growth in

population and its water requirements. However, in recent years the gap between supply

and demand has grown and the marginal costs of providing additional supplies are

rising sharply (Mekala et al., 2008). Many treatment technologies have been introduced

10

to fill this gap of demand and supply in an economical ways. Some of these

technologies are described in this section.

Wastewater can be treated by physical, biological, and chemical treatment methods in

different steps; preliminary, primary, secondary and tertiary. In preliminary treatment

stage, all the big particles like grit, rags, leaves which can damage the equipments are

removed. From the primary treatment stage, floating and settleable materials in

wastewater are removed by sedimentation process or by adding some chemicals to

enhance the removal of suspended and dissolved solids. In secondary treatment stage,

biological and chemical processes are used to remove most of the organic matters from

the wastewater. From the tertiary treatment stage, residual suspended solids and other

constituents that cannot be removed by secondary treatment are removed by using an

additional combination of physical and chemical processes (Metcalf & Eddy, 2003).

The type and order of treatment vary from one treatment plant to another according to

the wastewater type.

The advantages and disadvantages of some of the treatment technologies used in

wastewater treatment are described, including, but not limited to, in Table 2.4. Some of

these technologies are relatively easy, reliable and economical to construct and operate.

However, some of these simple and low cost treatment technologies may be unreliable

for the systems that require frequent inspections and constant maintenance to ensure

smooth operation. For this reason, and also because of the land requirements for

biologically based technologies, many communities prefer mechanically-based

technologies, which tend to require less land and permit better control of the operation.

However, these systems generally have a high cost and require more skilled personnel

to operate them.

11

Table 2.4 Different types of treatment processes used in wastewater treatment

Treatment process Brief description Advantages Disadvantages References

Physico-chemical treatment

Adsorption

Adsorption has been widely used in the removal of toxic or persistent organic pollutants from contaminated wastewater. It is also used sometimes to treat inorganic contaminants from wastewater. Most frequently used adsorbent in wastewater treatment is granular or powdered activated carbon (GAC or PAC).

Low initial cost, flexibility and simplicity of design, ease of operation and regeneration, insensitivity to toxic pollutants, avoids using toxic solvents and minimizes degradation.

High operation cost, this process just transfers pollutants from one phase to another rather than removing from the environment.

Soto et al., 2011; Jiuhui, 2008

Flotation

Flotation is a separation process widely used in wastewater treatment process and mineral processing industries. Flotation is very efficient for removal of humic acid, rapid sedimentation and comparatively cheaper than other processes. For many years, flotation has been extensively used and focused on the decrease of colloids, ions, macromolecules, microorganisms and fibers.

High selectivity to recover valuables (Au, Pt, Pd, etc.), high efficiency to remove contaminants, low operating costs with the use of upcoming flotation devices, less space needs,

Required higher power connection, less flocculation flexibility and performance are controlled by the strict hydraulic control.

Metcalf & Eddy, 2003;

Rubio et al., 2002

Chemical oxidation

For the treatment of wastewater containing toxic materials or soluble organic non-biodegradable substance, chemical oxidation treatment process is required. Chemical oxidation is a widely studied method for the treatment of effluents containing refractory compounds. Chemical oxidation modifies the structures of the pollutants in wastewater into similar but less harmful compounds by adding oxidizing agent.

Produces no significant wastes except Fenton, reduced operation and monitoring costs, compatible with post treatment monitored natural attenuation and can even enhance aerobic and anaerobic biodegradation of residual hydrocarbons.

Potentially higher initial and overall costs relative to other treatment processes, contamination in low permeability soils may not be readily contacted and destroyed by chemical oxidants, significant health and safety concerns are associated with applying oxidants.

Renou et al., 2008; EPA, 1998

12

Coagulation/ Flocculation

These processes are popular as a pre-treatment process for the removal of wastewater turbidity, organic matter, color, and microorganism. These processes are very essential component in wastewater treatment process. Coagulation process destabilizes colloidal particles by the addition of coagulant. The most popular coagulants are aluminum sulfate, ferrous sulfate, ferric chloride and ferric chloro-sulfate. To increase the particle size, coagulation is usually followed by flocculation of unstable particles into bulky floccules so that they can settle easily.

Helps to remove suspended particles from the wastewater and make colloids or floc particles settle faster and easier to dewater.

Required rapid mixing in the coagulation process to disperse coagulant throughout the liquid while flocculants must be added slowly and mix gently in the flocculation process to prevent agglomerated particles from broken apart. Excess coagulant and flocculant can cause a complete charge reversal and destabilize the colloid complex.

Zheng et al., 2011; Amokrane et al.,

1997

Air Stripping

Air stripping is widely used to treat the water contaminated specially with volatile organic compounds. In this process wastewater to be treated is brought into contact with air so that some toxic volatile substance present in the liquid phase can be released and carried away by the gas. Mechanical surface aeration, diffused aeration, spray fountains etc. is the air stripping processes in which large surface area of the wastewater is exposed to air which helps to transfer the contamination in wastewater from liquid phase to a gaseous phase.

Low cost, easy to install, operate and maintain, can be installed in a small area.

Air Stripping units can only take out chemicals that can evaporate, bulk items of pollution cannot be taken out.

Renou et al., 2008; Srinivasan et al.,

2008

13

Chemical Precipitation

Chemical precipitation is one of the methods for the wastewater treatment. This method is basically used to remove metals, fats, oils and greases, suspended solids and some organic and inorganic compounds. In this process of wastewater treatment, chemical is added into wastewater and allow mixing it homogeneously into the wastewater and finally the soluble toxic compounds present in wastewater become insoluble precipitates. Hydrogen sulfides or sodium sulfates are commonly used chemicals in this process.

Self-operating and low maintenance, requiring only replenishment of the chemicals used, a sophisticated operator is not needed frequently

Overdosing can diminish the effectiveness of the treatment, the addition of treatment chemicals like lime may increase the volume of waste sludge up to 50%, large amounts of chemicals may need to be transported to the treatment location.

EPA, 1998

Biological treatment

Aerobic treatment

Aerobic treatment is the biological process in which microorganisms use the free or dissolved oxygen in the biodegradation of organic pollutants. These treatment processes enhance the growth of naturally occurring aerobic microorganisms which are the main components in wastewater treatment processes. Aerobic treatment processes based on suspended-growth biomass, such as aerated lagoons, CAS. Suspended growth bioreactor, attached growth bioreactor, rotating biological contactor, trickling filter, sequencing batch reactor are the mostly used aerobic treatment processes.

Minimize odour, high biochemical oxygen demand (BOD) removal efficiency providing a good quality effluent; can treat the higher amount of influent even in small scale systems, the treated effluents may contain dissolved oxygen which reduces the immediate oxygen demand on receiving water and eliminates many pathogens present in agricultural wastes.

Requirement of energy and mechanical devices to aerate the basins and the effluents with a high suspended solids concentration results requirement of sludge disposal area raise the cost of the treatment requires skilled manpower for operation and maintenance.

Bae et al., 1999

14

Anaerobic treatment

Anaerobic treatment utilizes naturally-occurring bacteria to break down biodegradable material in wastewater. Reactors are enclosed or covered to prevent the introduction of air and the release of odors. The absence of oxygen leads to controlled anaerobic conversions of organic pollutants to carbon dioxide and methane, the latter of which can be utilized as an energy source. The anaerobic treatment processes include anaerobic suspended growth, upflow and downflow anaerobic attached growth, fluidized bed attached growth, upflow anaerobic sludge blanket (UASB), anaerobic lagoons, etc. They widely used to treat high strength wastewater having a warm temperature because they generate low amount of solids and requires and does not require aeration, thereby saving energy for the wastewater treatment.

Reduce CH4 & CO2 emissions, low sludge & odour production, low nutrient requirement, correspondingly low investment and operational costs.

Requires expert design, construction supervision, insufficient pathogen removal without appropriate post treatment, sensitivity towards toxic substances, lower microorganism growth rate

Ngo et al., 2008; Metcalf and Eddy,

2003

Advanced treatment processes

Membrane Technology

Membrane technology is easy and well-arranged process conductions. The membrane acts as a very precise filter that stops suspended solids and other substances to pass through, while it allows water to pass through. There are two factors that determine the effectiveness of a membrane filtration processes: retention and flux. Membrane filtration can be divided into micro and ultrafiltration (MF/UF), nano filtration (NF) and reverse osmosis (RO). When membrane filtration is used for the removal of larger particles MF/UF are applied. The pressure that is required to perform NF and RO is much higher than the pressure required for MF/UF, while productivity is much lower.

Higher treatment efficiency is obtained in smaller footprints compared to conventional treatment processes, higher biomass concentrations, no long sludge-settling periods, lower sensitivity to toxic compounds and both organic and high ammonia removals in a single process, flexible in terms of shape, load and volume, minimize labor costs, no need to add any chemicals.

High operating costs associated with the aeration process, membrane replacement costs are high and must be budgeted for appropriately, concentrate and waste stream disposal issue.

Sonune et al., 2004

15

Advanced Oxidation Processes (AOPs)

AOPs are the chemical treatment procedures considered to remove organic and inorganic materials in wastewater by oxidation. AOPs combine ozone (O3), ultraviolet (UV), hydrogen peroxide (H2O2) and/or catalyst to offer a powerful water treatment solution for the reduction or removal of residual organic compounds as measured by chemical oxygen demand (COD), BOD or total organic carbon (TOC). All AOPs are designed to produce hydroxyl radicals. It is the hydroxyl radicals that act with high efficiency to destroy organic compounds. AOPs are rapidly becoming the chosen technology for its many applications such as recalcitrant organic pollutant destruction in the form of toxicity reduction, Biodegradability improvement BOD/COD removal as well as odour and colour removal from the industrial and municipal wastewater. AOPs are recommended when wastewater components have a high chemical stability and/or low biodegradability.

Effectively degrade and remove specific pollutants having a high chemical stability and low biodegradability, a technologically efficient tool for the treatment of water with persistent residue, enhance the treatment performance of the system.

Relatively high operation cost due to use of expensive chemicals and increased energy consumption, formation of toxic compounds which resist attack by hydroxyl radicals.

Mandal et. al., 2010;

Poyatos et al., 2010;

Membrane bioreactor (MBR)

MBR systems have mostly been used to treat industrial wastewater, domestic wastewater and specific municipal wastewater, where a small footprint, water reuse, or stringent discharge standards were required. It is expected that the MBR system will increase in capacity and broaden in application area due to future, more stringent regulations and water reuse initiatives.

Higher and more consistent effluent quality can be achieved even in smaller footprints and smaller reactor volume, less dependent on mixed liquor suspended solid (MLSS) concentration and sludge volume index (SVI), less sludge production, no need of operators can operate automatically.

Relatively expensive to install and operate, required frequent monitoring and maintenance, limitations imposed by pH, temperature and pressure requirements to meet the membrane tolerance, less efficient oxygen transfer due to high MLSS concentration.

Melin et al., 2006; Cicek, 2003

16

Moving bed biofilm reactor (MBBR)

The MBBR has become popular on the broad range of wastewater treatment as an enhancement of biological nutrient removal. MBBR is a continuously operating, non–cloggable biofilm reactor with low head loss and high specific biofilm. For this process, Specially designed biofilm carrier is required in which microorganisms start growing while moving continuously with water in the reactor. This process improves reliability, simplifies operation and requires less space as compared to other conventional treatment processes.

Required small footprint and reactor volume, high effluent quality in terms of nutrient removal, good disinfection capability, higher volumetric loading, shock load protection and less sludge production, ease in upgrade of existing facilities.

High equipment and operation cost, fouling or biofouling of the membrane due to deposits of inorganic, organic & microbiological materials on the membrane surface and inside the pores. Extensive fouling leads to a pronounced decrease in permeate flux and can threaten the economic efficiency of the membrane plant.

Shore et al., 2012

17

2.2 Low Pressure Membrane Processes

The rapid consumption of limited waste resources and requirement of more stringent

water quality regulations and the need for reuse of water have been the main driving

forces for the development of membrane technologies (Guo et al., 2007). The positive

points of membrane technology are the facts that it can work without the addition of

chemicals, with a relatively low energy use and easy and well arranged process

conductions. Researches have revealed that membranes are commonly used for the

removal of dissolved solids, color, and hardness in drinking water. The main function of

all the membranes is to separate the unwanted particles and pathogens that are larger

than the membrane pore size and some particles smaller than the pore size from the

liquid coming through their way. In wastewater reclamation and reuse, water quality

requirement is measured in terms of the amount of suspended solids, total dissolved

solids and selected constituents such as nitrates, chlorides, and natural and synthetic

organic compounds present in treated wastewater. Membrane technology is the most

practical and reasonable treatment process to reach the required effluent quality levels.

There are two basic types of membrane separation processes, namely low pressure

membrane processes and high pressure membrane processes. Microfiltration (MF) and

ultrafiltration (UF) are the low pressure membrane processes while nanofiltration (NF)

and reverse osmosis (RO) are the high pressure membrane processes. These processes

use hydraulic pressure to force water molecules through the membranes. For these

processes, all the membranes require certain pressure, some membrane needs low while

the others need high pressure, for example MF need 1 - 2 bar pressure, UF need less

than 5 bar pressure, NF need about 5 bar and RO need 15 – 50 bar pressure for the

operation. Low pressure membrane processes are widely used in municipal wastewater

treatment plants to treat the secondary effluent and use that final product of high quality

for other purposes such as irrigation, release to natural water bodies, pretreatment for

RO feed water and for industrial applications. Low pressure membranes are economical

in terms of manpower and equipment, easy for retrofitting the conventional processes as

well as they have higher efficiency to remove harmful bacteria and viruses from the

wastewater. However, those harmful pathogens like bacteria and viruses may pass

through these membranes and make the water harmful to use if the membranes used are

18

broken or of low quality (Guo et al., 2010). Therefore it is very important to make sure

that the membranes used in the system pass the membrane reliability tests. The removal

efficiency of the membranes depends on its pore size and the performance of these

membranes can impact by the cake layer formation on and within the membrane surface

by the deposition of contaminants during the filtration process.

The principal of MF is physical separation. MF is used for the removal of larger

particles. Generally, the membrane pore size for MF is 0.1 – 10 μm. MF membranes can

remove most of the bacteria and can be implemented in many different water treatment

processes when particles with a diameter greater than 0.1 μm needs to be removed from

a liquid. MF is also used as pretreatment for another membrane process like UF, NF or

RO (Renou et al., 2008). For complete removal of viruses, UF is required. The pores of

UF membrane can remove particles of 0.001 – 0.1 μm from fluids. In UF process,

suspended solids and solutes of high molecular weight are retained, while water and

solutes of low molecular weight can pass through the membranes. UF offers higher

removals of solids than MF, but operates at higher pressures. UF in combination with

NF or RO in wastewater treatment can be a suitable treatment method which can

remove suspended solids and minimize the membrane fouling problems. UF membranes

have asymmetrical "skinned" surface structure and depth fouling does not occur with

this type of membrane, resulting in high and consistent membrane productivity

(Tchobanoglous et al., 1998). MF and UF can be used as the pre treatment process

before RO treatment in order to prevent the RO membrane from fouling problem due to

the suspended solids present in feed water.

In the previous few years, a revolution has been made in conventional wastewater

treatment technology by combining the membrane separation technology and

conventional bioreactor technology which has most promising prospect in terms of high

quality effluent generation and led to a new focus on wastewater treatment. MBR is one

of this technology which not only removes the organic and nutrient from the wastewater

but also remove the biological pollutants such as bacteria, pathogens and viruses. It

contributes to very compact systems working with high biomass concentration and

achieving a low sludge production and high organic carbon removal with an excellent

effluent quality. This technology has become more popular, abundant, and accepted in

recent years for the treatment of many types of wastewaters mostly for BOD and

19

nutrient removal, whereas the CAS process cannot cope with either composition of

wastewater or fluctuations of the wastewater flow rate (Sutherland, 2010; Radjenovic et

al., 2008). MBR have been widely applied at pilot or full scale on industrial wastewater

treatment.

2.2.1 Microfiltration/ Ultrafiltration (MF/UF)

MF and UF are widely used low pressure membrane process to control pathogens as

well as to remove turbidity associated with higher water production in all types of water

treatment plants (Moon et al., 2009). Water and wastewater treatment plants are one of

the widely used areas of microfiltration process while, this process is also used in food

and agro industry, chemical industry, metallurgy, biotechnology, paper and pulp

industry, pharmaceutical industry. Most of the influents either colloidal or suspended

present in feed water having a particle diameter greater than 0.1 μm can be separated

from water by using MF process. Although, there is a possibility of the internal pore

clogging in MF membrane, it can be prevented by using membranes of appropriate pore

size, pre-treating the wastewater using the processes like screening, sedimentation etc.

and by backwashing the MF membranes. In MF, membrane fouling caused by

deposition of filtered constituents on the membrane surface and pore clogging are the

main drawbacks. These types of problems in MF membrane can reduce the filtration

capacity, permeate flux, life of the membrane by forming a permanent layer of deposit.

Deposits can be mechanically reversible but pore clogging is partially irreversible

(Vigneswaran et al., 1991). Cross flow microfiltration (CFMF) is effective process to

overcome these problems. In CFMF process, the feed water flow direction is parallel to

the membrane which helps to avoid the possibility of accumulation of suspended solids

on or inside the membrane. Back flushing or backwashing is used as a tool to remove

the deposits from the membrane surface and increase the permeate flux. Back flushing

is done by using highly pressurized permeate through the membrane and sometimes air

or gas are used for the back flushing. In wastewater reclamation, MF might provide a

suitable level of treatment and use of MF in conjunction with NF or RO might be

helpful to reduce the membrane fouling. Wang et al. (2009) reported experimental result

of MF operation which gives the removal efficiency of organic compounds from

20

laboratory simulated emulsified oily wastewater and factory wastewater over 95% and

the fouled membrane could be cleaned by using conventional cleaning methods.

UF is generally used in industrial and water reuse areas which can separate particles

smaller than 0.1 μm and the pathogens that cannot be separate by MF. Generally the

function of MF and UF are similar but UF is considered as more efficient than MF to

separate pathogens and suspended and colloidal particles from liquid. UF are combined

with other conventional treatment processes in order to increase the removal efficiency

of the system and helpful to remove microbial contaminants, turbidity, dissolved

organic matter etc. present in the wastewater. Mohammadi et al. (2005) studied the

treatment of the wastewater by UF-powdered activated carbon (UF-PAC) and their

experimental results showed that UF is better than the conventional biological method

and UF-PAC is better than UF. They used PAC in feed circulation loop for the UF

system with a concentration of about 0.1% in their experiment which improved water

quality and increased permeation flux. Their results showed that the wastewater treated

by UF-PAC has a removal efficiency of 94, 93, 100, 99 and 43% of chemical oxygen

demand (COD), TOC, total suspended solid (TSS), PO4 and Cl respectively.

The main problem in UF membranes are they start fouling with the accumulation of

organic materials on or within the pores of the membrane which reduce the filtration

capacity and the permeability of the membrane (Jarusutthirak et al., 2001). Because of

this problem, the operating costs of UF process become higher and impact its increasing

application in the field of wastewater treatment and reuse.

2.2.2 Membrane bioreactor (MBR)

A recent advancement in wastewater treatment technology involves the filtration of

wastewater through porous membranes. Specifically, MBR combine the activated

sludge process of a CAS system with a membrane submerged in the process water

capable of filtering particulate waste constituents from the mixed liquor solution

(Sharrer et al., 2007). These technologies have introduced a new cutting edge on

wastewater treatment. For concentrated wastewaters, like industrial streams and landfill

leachate, MBR has been applied at full scale successfully however this system requires

21

relatively high energy. Using new membrane techniques, like transfer flow modules,

creates the possibilities of a more widespread application. MBR technologies provide

the potential for reuse wastewater generated from industries or municipalities and

decrease in sludge production. Since the use of CAS process in wastewater treatment

has some disadvantage like lack of footprint, problem in secondary sedimentation due to

excess filamentous bacteria growth in the sludge, MBR can withstand these problems

and capable to produce high quality treated water and also can be reused (Drews, 2010;

Aryal et al., 2009). The MBR combines suspended growth unit responsible for the

biodegradation of the waste compounds and the membrane filtration module for the

physical separation of the treated water from the mixed liquor using a porous membrane

that helps to retain high microbial concentration in the reactor and increase the

biological operation capacity of the reactor. The MBR process was introduced by the

late 1960s, as soon as commercial scale UF and MF membranes were available (Le-

clech et al., 2006). The original process was introduced by Dorr-Olivier Inc. and

combined the use of an activated sludge bioreactor with a cross flow membrane

filtration loop (Smith et al., 1969). Although the research on MBR technology began

only few decades ago, it has developed quite rapidly and become one of the important

technologies in wastewater treatment process. Up to this date, MBR systems have

mostly been used to treat industrial wastewater, domestic wastewater and specific

municipal wastewater. Requirement of higher removal of organic matters, suspended

solids, nutrient and harmful bacteria from the wastewater and the requirement to meet

the strict effluent discharge quality in terms of nutrient and micropollutants, the main

cause for the eutrophication and decrease the water quality in the receiving water

bodies, are the important issues in the present wastewater treatment processes (Ersu et

al., 2008; Kraume et al., 2005). MBR technology have become a most promising

process to overcome these issues and the nutrient removal from the wastewater and

several studies have been focused on nutrient removal from wastewater using MBR

(Galil et al., 2009; Ersu et al., 2008; Yuan et al., 2008; Kraume et al., 2005; Song et al.,

2004; Adam et al., 2002; Lesjean et al., 2002).

The advantages and disadvantages of the MBR are listed in the Table 2.5.

22

Table 2.5 Advantages and disadvantages of MBR technology (Melin et al., 2006)

Advantages Disadvantages

Treatment system can be made automatic and operator requirements are reduced.

Relatively expensive to install and operate.

Decreased sludge production. Frequent membrane monitoring and maintenance.

Higher and more consistent effluent quality as a result of membrane filtration.

Limitations imposed by pressure, temperature and pH requirements to meet membrane tolerances.

Lower sensitivity to contaminant peaks. Membranes may be sensitive to some

chemicals.

Less dependent on the MLSS concentration and SVI. Less efficient oxygen transfer caused by

high MLSS concentrations.

Smaller footprints and smaller reactor volume as a consequence of higher mixed liquor concentration and loading rate.

Treatability of surplus sludge is questionable. Therefore there should be special consideration for additional treatment in emergency situations.

MBR System configurations

MBR operation can be classified into two operation modes; dead-end filtration and

cross-flow filtration (Radjenovic et al., 2008). The filtration of coarse particles down to

several micrometers is achieved by the conventional dead-end filtration. Particles

retained by the filter in dead-end filtration build up with time as a cake layer resulting in

an increased resistance to filtration. This requires frequent cleaning or replacement of

filters. This filtration is effective when the feed water contains low solid particles. In

cross-flow filtration, the feed water stream runs parallel to a filter media which

generates shear stress to scour the particles settled on the filter surface. Extra energy is

required in cross flow filtration, but it helps to control the cake layer formation on the

surface of the filter media. This type of filtration is effective when feed water carries

high level of foulants such as suspended solids and macromolecules. Figure 2.1 and 2.2

describes the dead end and cross flow filtration processes.

23

Figure 2.1 Dead end filtration Figure 2.2 Cross flow filtration

The breakthrough for the MBR came in 1989 with the idea of Yamamoto and co-

workers to submerge the membranes in the bioreactor which allowed the MBR to grow

faster (Sutherland, 2010). Until then, MBRs were designed with the separation device

located external to the reactor (side stream MBR) and relied on high trans-membrane

pressure (TMP) to maintain filtration. The resultant submerged membrane bioreactor

(SMBR) used two orders of magnitude less energy than the side stream version. In

submerged configurations, aeration is considered as one of the major parameters on

process performances both in hydraulic and biological. Aeration maintains solids in

suspension, scours the membrane surface and provides oxygen to the biomass, leading

to a better biodegradability and cell synthesis.

In MBR, membrane separation is carried out in two ways: 1) vacuum driven membranes

immersed directly into the bioreactor, which operates in a dead-end mode in submerged

MBRs and 2) pressure driven filtration in side stream MBRs (Radjenovic et al., 2008).

Submerged MBR configuration is very common and effective for wastewater treatment

because it consumes significantly less energy for the operations compared to side

stream MBR. The configuration of submerged and side stream MBR is shown in Figure

2.3 (A) and (B) respectively.

24

(A) (B)

Figure 2.3 Configuration of MBR systems: (A) submerged MBR and (B) side-stream

MBR configuration

Both configurations need a shear over the membrane surface to prevent membrane

fouling with the constituents of mixed liquor. In side stream MBR, this shear is

provided through pumping while in immersed MBR aeration is employed to provide

shear. Fouling is more pronounced in side stream MBR module due to its higher

permeate flux.

There are different types of membrane materials; polymeric (polyethylene,

polyethersulfone, polysulfone, polyethylene, polyethersulfone, polysulfone), ceramic

and metallic. Polymeric and ceramic membranes are mainly used while metallic

membrane filter has very specific applications which do not relate to MBR technology.

These membrane materials must be formed in such a way as to allow water to pass

through it (Judd, 2007). There are five principal membrane configurations currently

employed in practice, namely hollow fiber (HF), spiral–wound, plate-and-frame (i.e.

Flat sheet (FS), plated filter cartridge and tubular.

In HF module, large amounts of HF membranes of size 0.8 mm - 1.5 mm fine screen

make a bundle, and the ends of the fibers are sealed in epoxy block connected with the

outside of the housing. The water can flow from the inside to the outside of the

membrane and also from the outside to the inside, depends on the production of

different manufacturers. These membranes can work under pressure and vacuum

(Radjenovic et al., 2008).

25

The spiral-wound configuration is mostly used for the NF and RO process. The

membranes are wound around the perforated tube through which permeate goes out.

Many membrane modules can be installed together in series or parallel in plants with

high capacity. Plate-and-frame membrane modules comprise of FS membranes with

separators and/or support membranes. A fine screen of 2 mm – 3 mm is usually

employed for FS membrane systems. The pieces of these sheets are clamped onto a

plate. The water flows across the membrane and permeate is being collected through

pipes emerging from the interior of membrane module in a process that operates under

vacuum. Plated filter cartridge and tubular membrane configuration modules are not

widely used as the other three modules. Typically, tubular membranes are

predominantly used for side stream configurations (Radjenovic et al., 2008).

The MBR process can be configured in many different ways depending on project-

specific nutrient removal objectives. The commercial significance of this technology is

considerable, with applications in municipal and industrial wastewater treatment

becoming increasingly widespread. The market value of MBR technology was

approximately US $ 217 million in 2005, rising at an average annual growth rate of

10.9% that shows the MBR technology is growing significantly faster than the other

advanced wastewater treatment technologies (Judd, 2007). The MBR technology is

becoming more cost effective because of the decrease in cost of membrane and

membrane process and becoming more environmental friendly. The main driving factor

for the advancement of technological development, innovation and implementation of

membrane bioreactor technology in wastewater treatment to this extent is legislation

and the need of the industries which are working in this field. However, higher

operational costs due to membrane aeration, membrane fouling and the requirement of

chemicals for membrane cleaning which are harmful for the environment are the main

barriers in the widespread application of membrane bioreactor technology in wastewater

treatment (Drews, 2010)

2.2.3 Membrane fouling

In practice, the membrane filtration performance can change very much over time and a

continuous decline in the membrane permeability which is the result of membrane

26

fouling (Meng et al., 2010). The continuous deposition of unwanted microorganisms,

suspended solids, colloids and cell debris on the membrane surface or within the pores

of the membrane cause the membrane fouling. Membrane fouling has a great impact on

the process performance such as energy consumption or water production. The

concentration of all materials in the feed water either dissolved or suspended is highest

near the membrane surface. As permeate is drawn through the membrane, all impurities

are left on the membrane surface. The layer of water next to the membrane surface

(boundary layer) gets increasingly concentrated on the dissolved and suspended

materials. These concentrations reach a certain steady level depending on the feed

velocity, element recovery and membrane permeate flux. Maintaining proper operating

conditions for the membrane is the key preventative step to minimize membrane

fouling. The membrane fouling problem has narrowed the widespread application of

membrane despite of its many advantages. Control of membrane fouling and its

consequences in terms of plant maintenance, increased operating costs and the high cost

of membrane are the main inevitable obstacles encountered in the application of

membrane processes (Metzger et al., 2007).

Natural organic matter (NOM) plays an important role in membrane fouling (Zularisam

et al., 2006). As analytical techniques and knowledge of structural details of NOM

progress, identification of species responsible for fouling as well as understanding

membrane fouling mechanisms improve. For instance, today, it is well known that

humic substances as well as polysaccharides and proteins can be the major fouling

species for low- and high-pressure membranes (Jacquemet et al., 2005). While some

broad trends for simple colloids are valid for macromolecules like proteins, the labile

nature of proteins and the range of polydispersity of naturally occurring

macromolecules such as polysaccharides and some humic substances add a particular

complexity of the fouling mechanisms (Le-clech et al., 2006). Similarly, bound

extracellular polymeric substances (EPS) and soluble microbial products (SMP) are the

two important factors which affect the membrane fouling potential to mixed liquor.

Bound EPS, which is directly related to the fouling, is a complex mixture of

macromolecular polyelectrolytes such as proteins, humic compounds that determines

the most of the sludge characteristics. SMP can absorb onto the membrane surface

which can block the membrane pores forming a gel like structure on the membrane

surface and introduce the hydraulic resistance to permeate flow (Feng et al., 2012).

27

Membrane pore clogging and sludge cake formation on membranes can be attributed to

the membrane fouling. Membrane fouling leads to decline in permeate flux or increase

in TMP, necessary to frequent membrane cleaning and replacement (Baek et al., 2009).

Therefore, for the economical and efficient operation of membrane process, it is

becoming very important to take a remarkable step on membrane fouling control.

Membrane fouling mechanism can be described as (Guo et al., 2012; Meng et. al.,

2009):

1. Adsorption of solutes or colloids within/on membranes,

2. Deposition of sludge flocs onto the membrane surface,

3. Formation of a cake layer on the membrane surface,

4. Detachment of foulants attributed mainly to shear forces,

5. Biological fouling and

6. Pore blocking.

Membrane flux and TMP are the best indicators of membrane fouling; membrane

fouling occurs during an increase in TMP to maintain a particular flux or during

decrease in flux when the system is operated at constant pressure (Guo et al., 2012).

Under constant flux operation, TMP increases to compensate for the fouling. On the

other hand, under constant pressure operation, flux declines due to membrane fouling.

The TMP jump is believed to be the consequence of severe membrane fouling. The

sudden TMP jump is not only due to the local flux effect, but also caused by the sudden

change of biofilm or cake layer structure (Zhang et al., 2006). A more recent

investigation also confirmed that the sudden TMP jump is closely related to the sudden

increase in the concentration of EPS at the bottom of the cake layer, which might be

attributed to the death of bacteria in the inner of cake layer (Hwang et al., 2008). Thus,

to control membrane fouling, occurrence of TMP jump must be minimized.

Generally, membrane fouling can be classified as:

a. Removable and irremovable fouling

The removable fouling can be removed easily by physical processes such as

backwashing. The irremovable fouling cannot be removed by physical measures but by

28

chemical cleaning. The removable fouling and reversible fouling are the same. The

removable fouling is caused by loosely attached foulants or the cake layer formed on the

surface of the membrane while irremovable fouling is caused by pore blocking and

strongly attached foulants during filtration. The irreversible fouling is a perpetual

fouling and cannot be removed by any measures (Chang et al., 2002).

b. Biofouling, organic fouling and inorganic fouling

Biofouling is the deposition, growth and metabolism of undesirable bacteria cells or

flocs on the surface of the membranes, which has stimulated a significant concern in

membrane filtration processes. Biofouling is a major problem for low pressure

membranes like UF and MF because must foulants (microbial flocs) in MBRs are much

larger than the membrane pore size. The deposition of biopolymers (proteins and

polysaccharides) on the membranes causes the organic fouling. Due to small size, the

biopolymers can be deposited onto the membranes more readily due to the permeate

flow, but they have low back transport velocity due to lift forces in comparison to large

particles (colloids and sludge flocs) (Meng et al., 2009). The inorganic fouling can be

formed through two ways; chemical precipitation and biological precipitation. In

general, membrane fouling in MBRs is mainly governed by biofouling and organic

fouling rather than inorganic fouling, although all of them take place simultaneously

during membrane filtration of activated sludge (Meng et al., 2009; Chang et al., 2002).

All the parameters involved in the design and operation of membrane processes have an

influence on membrane fouling. The factors affecting membrane fouling can be

classified into four groups: membrane characteristics, biomass characteristics, feed

water characteristics and operating conditions as shown in Figure 2.4 below (Le-clech et

al., 2006; Chang et al., 2002). There are also some membrane fouling constituents

which determine the severity of fouling and technique needed to be used to control it.

These fouling constituents can be organic or inorganic particles which form a cake layer

on the membrane surface or microbiological organisms which can stick to the

membrane surface and hence produce biofouling. Some of these factors have a direct

influence on fouling while others enhance the fouling propensity. Therefore it is very

important to fully understand the biological, chemical and physical phenomena

occurring in membrane operation to evaluate fouling propensity and mechanisms.

29

Figure 2.4 Factors influencing membrane fouling in membrane processes (Le-cleach et al., 2006; Chang et al., 2002)

The techniques used to control membrane fouling in membrane processes are

categorized into the following groups (Yang et al., 2006):

Modification of membrane module design by optimizing the packing density of

hollow fibers flat sheets, the location of aerators, the orientation of fibers and

diameters of fibers.

Reduction of cake layer formation on membrane surfaces by controlling the

filtration process below the critical flux, by air-sparging in vicinity of membrane

and by operating in intermittent mode.

Improvement of the filtration characteristics of the mixed liquor by adding

adsorbents such as PAC.

Removal of the fouling materials after its formation by back-washing, back-

pushing and by chemical cleaning.

Although the above mentioned methods can effectively prevent the membrane fouling

to a certain extent, the decrease of membrane permeability is inevitable due to pore

clogging, sludge cake formation and biofouling. Once the membrane flux has decreased

below the design value, membrane cleaning needed to be done to recover the membrane

permeability. Pretreatment of the feed water is one approach to control membrane

fouling by reducing TSS and bacterial content of the feed water. Sometimes the feed

Pore size

Porosity

Hydrophobicity

Material

Configuration

Floc size

Dissolved matter

Floc structure

EPS

MLSS

TMP

HRT/SRT

Aeration

CFV

Configuration

Factors affecting fouling

Membrane Operating condition Biomass

30

water will be conditioned chemically to limit chemical precipitation within the units.

Back flushing with water and /or air is the most commonly used methods to improve the

membrane performance by moving colloidal particles and cell waste away from

membrane pores into the mixed liquor and eliminate the accumulated materials from

membrane surface. Chemical treatment is used to remove constituents that are not

removed during back washing (Metcalf & Eddy, 2003).

Several investigations have been performed to remove the membrane fouling and to get

more detailed information about it (Aryal et al., 2009; Baek et al. 2009; Metzger et al.,

2007; Le-clech et al., 2006; Jacquemet et al., 2005). Control of fouling is of utmost

importance. It can be reduced by maintaining turbulent conditions, operating at sub-

critical flux and /or by the selection of a suitable fouling resistance membrane material

(Liang et al., 2012). Chang (2011) did the critical review of previous researches and

concluded that the submerged hollow fiber membrane modules are effective membrane

module design for the MBR applications. However, the cost efficiency of the system

depends on the membrane properties, fiber diameter and configurations, aeration types

and the cassette design. For the long term stable operation of the membrane, it is

necessary to do the regular maintenance and recovery chemical cleaning of the

membranes. Sombatsompop et al. (2006) evaluated the biofouling phenomenon in

suspended and attached MBR systems during their research and found that MLSS

concentrations play vital role in the fouling process. They concluded that the membrane

fouling increased with increase in MLSS concentration and it is affected by the design

of operating system i.e. reactor with and without the media. They found out the attached

growth reactor has lower fouling and prolong filtration compared to the suspended

reactor due to the difference in particle size distribution of biomass between the two

reactors. Kim et al. (2008) conducted the experiment to control the membrane fouling

by changing the depth of membrane module in SMBR and concluded that if the

membrane module is elevated vertically to the upper zone of the reactor where MLSS

concentration is lower compared to the lower zone of the reactor, the membrane fouling

can be reduced and total nitrogen removal efficiency can also be improved. Park et al.

(2010) also carried out the experiment to reduce the membrane fouling by using a

vertically oriented hollow fiber membrane module equipped with a simultaneous

upward and downward air sparging. In this study, two different membrane air sparging

configurations; simultaneous upward and downward and single upward air sparging

31

were used to compare the fouling propensity in terms of TMP increasing rate,

membrane permeability decreasing rate, irreversible fouling coefficient and fouling

resistance values. This research concluded that the dual header vertically oriented HF

membrane module with simultaneous up and downward air sparging configuration was

more efficient than the single upward air sparging configuration in terms of reduced

membrane fouling rate and enhanced membrane permeability which means reduction in

the operating cost.

However, many researches have been done from more than decades in membrane

fouling and many advanced information have been achieved in this area, membrane

fouling in MBR is still complicated to understand because of its complex characteristics

and some of its phenomena which are difficult to understand. This complex nature of

membrane fouling cannot be explained by any single technique (Meng et al., 2010).

Improved aeration reduced MLSS concentration in the bioreactor, membrane

backwashing and improved membrane modules are some of the processes that have

been done to control membrane fouling. It is very important to carry out further research

in membrane fouling in order to expand the use of membrane technology in wastewater

treatment.

2.3 Biological Nutrient Removal (BNR) from Wastewater

It is very important to remove nutrient from wastewater before it reaches the natural

water bodies to prevent eutrophication process and protect the quality of water in water

bodies. Excess nutrients cause oxygen deficient, algal growth, increase in ammonia and

phosphorus, harmful algal blooms, high microbial activity and turbidity in the receiving

water bodies which is very harmful to the human health as well as aquatic lives. To

minimize such effects, more stringent effluent limit for nitrogen and phosphorus has

been setup to discharge the effluents into the water bodies. This leads the requirement of

improved wastewater treatment technology to achieve the lower limit of nutrient and

organic matters in effluent. Biological nutrient removal (BNR) processes remove total

nitrogen and total phosphorus from wastewater through the use of microorganisms

under different environmental conditions in the treatment process (Metcalf and Eddy,

2003). The biological nutrient removal processes require various combinations of

32

anaerobic, anoxic and aerobic conditions to remove nutrient. For nitrogen removal

aerobic-anoxic condition is favorable while alternating anaerobic-aerobic condition is

better for the phosphorous removal. Attached growth treatment technology has become

popular and promising method for the nutrient removal. Many successful researches

have been done using this technology for the successful biological nutrient removal

from different types of wastewater. Nowadays, specially designed biomass carriers such

as plastic media or polyurethane foam have been used in wastewater treatment process

to enhance the nutrient removal efficiency.

2.3.1 Nitrogen removal

Wastewater generated from municipal, industrial and agricultural processes mostly

contain nitrogen. Total nitrogen in wastewater can be divided as organic nitrogen,

ammonium, nitrite and nitrate (Tchobanoglous et al., 2001). In domestic wastewater

60% of total nitrogen belongs to ammonium nitrite and nitrate while 40% of total

nitrogen belongs to organic nitrogen. Exposure to high concentration of ammonia or

nitrogen can cause many health effects such as; skin and eye irritation, disease related to

the respiratory tract, corrosive damage to mouth, throat and stomach and many other

risks. Nitrogen can be removed from wastewater by biological processes such as

nitrification and denitrification. Nitrification process required oxygen and in the

presence of oxygen ammonium nitrogen is converted into nitrite and nitrate with the

help of nitrosomonas or ammonia-oxidizing bacteria (AOB) and nitrobacter or nitrite-

oxidizing bacteria (NOB) respectively. This process can be explained by the following

equations;

2NH4+ + 3O2 2NO2

- + 2H2O + 4H+

2NO2- + O2 2NO3

-

Nitrification process requires adequate oxygen, long SRT, low food to microorganism

ratio, adequate temperature and pH. It reaches the maximum rate at dissolved oxygen

(DO) concentration of 1 mg/L or more, pH between 6.5 - 7.0, and temperature between

30ºC - 35ºC.

33

During denitrification Process, nitrate is reduced to gaseous nitrogen by denitrifying

microorganisms and this process occurs in the absence of oxygen as a result

microorganisms start consuming nitrate as a source of oxygen. Bacteria break nitrate to

nitrous oxide and then to nitrogen to gain oxygen which is very important for the

microorganisms to survive. The produced free nitrogen gas mix into the atmosphere as

it is a major component of air. The equation below can illustrate the denitrification

process;

6NO3- + 5CH3OH 3N2 + 5CO2 + 7H2O + 6OH-

Carbon, oxygen, pH, nitrate concentration and temperature play a major role in the

denitrification process. Optimum condition for denitrification occur at pH between 7 –

8.5, temperature between 5ºC – 30ºC and DO less than 0.5 mg/L, while readily

biodegradable COD is used as a source of organic carbon.

2.3.2 Phosphorus removal

Phosphorus is a vital factor for the growth of living organisms. It is a multivalent non-

metal of the nitrogen group and can be found in nature in several allotropic forms.

Phosphorus is useful for many applications such as; production of fertilizers,

pyrotechnics, pesticides, toothpaste, detergents productions. Phosphates are important

for human body because they are a part of deoxyribonucleic acid (DNA) materials and

they helps in energy distribution. However, the excess amount of phosphate can cause

health problems like kidney damage and less amount of phosphate also cause the health

problems. Similarly, excess amount of phosphorus in water bodies enhances the

eutrophication process. The treated effluent must have 0.10 – 2.0 mg/L of phosphorus

depending upon the potential impact on receiving water bodies (Metcalf and Eddy,

2003). Phosphorus is never found in the environment in its pure form, it appears only as

phosphates. Phosphorus can be found in wastewater as orthophosphate, polyphosphate

and organically bound phosphorus. Phosphorus is found as an ion in wastewater and can

be removed by converting it into insoluble solid fractions. This insoluble solid fraction

of phosphate can be recycled and used as a raw material in the phosphate industry.

Some part of phosphorus in wastewater is consumed by the microorganisms for cell

34

synthesis and energy transport. Normally, an anoxic reactor followed by anaerobic and

aerobic reactor is used for the phosphorus removal. Adam et al. (2002) carried out the

MBR bench scale pilot plant in parallel to the conventional plant under the similar

operation condition and their study showed that the MBR can remove phosphorus

effectively.

Phosphorus removal in wastewater is achieved mostly by phosphate accumulating

organism (PAO) which can store phosphorus within its cell. PAO store volatile fatty

acid (VFA) as intracellular products. For the biological phosphorus removal, VFA in

wastewater in anaerobic condition and DO in aerobic condition is required (Fuhs et al.,

1975).

2.4. Attached Growth Processes for Wastewater Treatment

The performance of biological wastewater treatment system depends on the total

biomass concentration on the system (Jianlong et al., 2000). Attached growth process is

a biological treatment process in which microorganisms grow and build a thin biofilm

layer in a specially designed inert materials such as gravel, sand, peat, or specially

woven fabric, plastic or sponges, moving freely in the whole volume of the reactor by

absorbing organic matter or other harmful constituents in wastewater. The basic

principle of the process is that the biomass grows on a specially designed mobile

carriers introduced in the reactor simultaneously with the oxidation of organic or

inorganic compounds in wastewater. Certain agitation is setup in the process to make

the carriers mobile by aeration in aerobic condition or mechanical mixing in anaerobic

and anoxic condition. The biofilm carriers provide a large protected surface area for the

aerobic biofilm and optimal conditions for the bacteria culture to grow and thrive. They

also improve volumetric nitrification rates and accomplish denitrification in the aeration

tanks by having anoxic zone within the biofilm depth. These microorganisms are

primarily aerobic and oxygen is a key requirement for their survival. Raw wastewater

must be treated before supplying into the attached growth system to remove the larger

solids and floating debris, because these solids can plug the filter. Attached growth

processes in wastewater treatment are very effective for BOD removal, nitrification, and

denitrification. The main advantage of the attached growth system is the high biomass

35

concentration, which enables stability under high organic and hydraulic loading, very

high sludge residence time, lower sensitivity to toxic effects, and easier adaptation to

feed pollutants. In addition, the compact size of these systems drastically reduces the

capital cost while operating cost is minimal in cases where natural aeration takes place

(trickling filters and RBCs) (Metcalf & Eddy, 2003). Disadvantages are a larger land

requirement, poor operation in cold weather, and potential odor problems. There are

many variations and combinations of these processes, sometimes referred to as hybrids

that use the attached growth process in combination with other technologies

(Sombatsompop et al., 2006). The biomass growth systems can generally be classified

as shown in Figure 2.5.

Figure 2.5 Biomass growth systems in wastewater treatment systems (Jianlong et al.,

2000).

Attached growth processes can be classified into two groups with regard to the carrier

status as; fixed bed and moving bed reactors. The moving bed reactors are defined as

the biomass growth on small carrier materials that move along with water in the reactor

(e.g. Rotating biological contactor). In the fixed film systems the media are held in

place, allowing the wastewater to flow over the bed (such as trickling filters). Figure 2.6

Biomass in wastewater

Suspended growth Attached growth/Biofilm Trickling filter Rotating biological contactor Biological activated sludge anaerobic Dispersed growth

Lagoons Flocculated growth Activated sludge Anaerobic sludge

Blanket reactor

Hybrid growth Fluidized bed reactor Expanded bed reactor Immersed media systems Porous support systems Carriers activated sludge

36

best illustrates these two types of reactors. In most cases, drains under the media collect

the effluent and either send it back through the filter or send it on for further treatment.

Different types of attached growth systems for wastewater treatment are summarized in

Table 2.6.

Figure 2.6 Typical diagram for MBBR and fixed bed bioreactor.

The attached growth bioreactor using specific materials is an alternative process to

overcome from the problem of fouling in MBR (Ngo et al., 2006). Combining a biofilm

reactor with membrane separation of the suspended solids may help to reduce the effect

of membrane fouling by high biomass concentrations (Leiknes et al., 2001). Biological

processes often required large land area due to the requirement for high HRT. They also

require high energy input for aeration and sludge management that is another problem

with these processes. Attached growth biofilm can form aerobic zone, anoxic zone and

anaerobic zone along the direction of mass transfer, providing a favourable environment

for simultaneous nitrification and denitrification. It could be presumed that the biofilm

can improve the total nitrogen removal in aerobic phase and inhibit the transfer of

nitrate into the anaerobic phase. As a result, simultaneous nitrogen and phosphorus

removal could be resolved in a single tank (Yang et al., 2010).

Air supply line

MBBR

Influe

Effluen

Air supply line

Fixed bed bioreactor

Influe

Effluen

37

Table 2.6 Different types of attached growth systems (Odegaard, 1999)

Type of attached growth systems

Comments

Tricking filter High surface area for biofilm attachment Require low power for operation Not volume effective

Rotating biological contactor (RBC)

High surface area for biofilm attachment Mechanical failure

Fixed media submerged biofilter

High surface area for biofilm attachment Simultaneous biological treatment and

suspended solid removal Poor distribution of the load on the hole carrier

Granular media biofilter Simultaneous biological treatment and

suspended solid removal Need backwashing

Fluidized bed reactor (FBR)

Highest volumetric rate for carbon and nitrogen removal

Stability for shock loading Hydraulic instability, expensive

Air lift Good mixing capacities and enhanced mass transfer

MBBR

Good oxygen transfer, Auto-regulation of biofilm thickness Simple distribution of liquid flow that enable

raw unsettled wastewater to be treated directly.

Hybrid bed Filter

No need for high rate effluent recirculation and concomitant pumping energy

Maximize biomass concentration in reactor Increase cost to the system due to added

support medias.

Loukidou et al. (2001) concluded on their experiment that the attached growth biofilm

treatment method can be an attractive another option to the CAS process for the

effective biological removal of carbon and nitrogen content from sanitary landfill

leachate. Khan et al. (2011) studied the performance of attached and suspended growth

process in membrane bioreactor. They found the presence of small bio particles having

a higher microbial activity and the growth of complex biomass captured within the

suspended sponge carrier resulted in improved total nitrogen and total phosphorus

removal efficiency in an attached growth membrane bioreactor. Attached growth

bioreactors having specific materials like sponge, polyethylene sheet has been used to

modify biological processes and to obtain effective nutrient removal efficiencies.

38

2.4.1 Moving bed biofilm reactor (MBBR)

The MBBR technology was developed in Norway in the late 1980’s and early 1990’s

when the nitrogen removal from the wastewater was the main focus and later on organic

matter removal has been more investigated (Odegaard, 1999). This technology adopts

the best from activated sludge processes and biofilter processes and can be operated as a

standalone process or it can be used to specifically enhance or upgrade the treatment

capacity of old plants which has limited space for the future extension. This process has

become popular in the field of wastewater treatment because it maximizes the capacity

and efficiency of the treatment plant while minimizing the footprints. It has the capacity

to withstand the challenges of wastewater industry like; retrofitting the old treatment

plants, higher nutrient removal capacity, produce less sludge as a result of high biomass

retention time, minimize process complexities and operators, no need of backwashing,

easy maintenance, economical, self regulating process with fluctuating organic loads

and so on. MBBR systems are mainly based on the aeration rate and reactors filled with

the specially designed carriers to provide a surface to colonize by bacteria (Rahimi et

al., 2011). When the suspended porous biofilm carriers are kept in continuously mixed

and operated aeration tank, active biomass grows as a biofilm on the surface of these

carriers having a density slightly less than the water (Kermani et al., 2008). MBBR

system is the efficient method to retain slow growing microorganisms such as nitrifiers

in the form of biofilm.

The MBBR system can be operated under aerobic conditions for BOD removal and

nitrification or under anoxic conditions for denitrification. During operation, the carriers

are kept in constant circulation. In an aerobic reactor, circulation is induced through the

action of air bubbles injected into the tank by a coarse bubble diffuser system. In an

anoxic reactor, a submerged mechanical mixer is typically supplied. Specific area of the

biomass carrier, flow and the mixing condition in the reactor and DO concentration are

the main factors that affect the operation of MBBR.

39

2.4.2 Different types of media used in MBBR

The media on which the biofilm develops are carefully designed with high internal

surface area having density slightly less than the water so that it can easily float. The

most commonly used solid surface for attached growth processes are; stones, clinker,

sand, activated charcoal, kieselguhr, metals, plastic sheets, and foams. There are

different types of media which can be used as a media for the microbial growth. The

physical appearance and characteristics of these media are shown in Table 2.7 and

Figure 2.7. The biofilm carrier is selected to have low density close to water (sponge or

plastic carriers), high specific surface area, good holding capacity, and it must avoid the

clogging by increased biomass.

By means of biomass carriers, it is possible to obtain a two fold increase in biomass

concentration in the aeration tanks compared to that in the conventional activated sludge

process (Jianlong et al., 2000). Tavares et al. (1995) stated that the microorganisms

produce a kind of natural polymer which helps them to attach to the surface of inert

carrier resulting the biofilm layer formation.

40

Polyethylene Polyethylene Cylindrical Polyethylene Sponges (S) KaldnesTM K1 KaldnesTM K3 beads (PB) granule (PG) polypropylene (CP) sheet (PS)

PVA-gel Poly propylene Polyethylene Ball Flocor RMP-HPS® Ceramic carriers Honeycomb ceramic Ceramic spheres

Tezontle grains HDPE grains LDPE grains polypropylene polyurethane Polyethylene tape Loofa sponge cubes SESSIL

Sand BioPortzTM WD-f10-4 bioMTM Natrix C10/10

Figure 2.7 The physical appearance of the media used in attached growth processes

41

Table 2.7 Characteristics of media used in the attached growth processes

Media Shape Size Specific Surface area (m2/g)

PB Beads 0.9 mm 2.54×10-3

PG Granules 3 mm 1.22×10-3

CP Cylindrical Int. 3 mm Ext 4 mm Length 5 mm

5.81×10-3

PS Sheet 11 cm 1.94×10-3

S Cubic 15×15×15 mm 0.91

K1 Cylindrical 10 mm Length 7mm 5.0×10-3

K3 Cylindrical 10 mm Length 7 mm 0.5×10-3

PVA-gel beads Spherical 4 mm -

BioPortzTM Cylindrical 20 mm Length 20 mm 0.58×10-3

poly propylene Cylindrical granules 0.35×10-3

Polyethylene Ball Circular 10 mm Length 7 mm 0.32×10-3

WD-F10-4bioMTM Cylindrical 25 mm 0.9×10-3

Flocor RMP-HSP® Cylindrical 10 mm

Length 10 mm 2.77×10-3

PVC plastic tubes Cylindrical 20.5 mm

Length 18.2 mm 0.15×10-3

Nonwoven hollow cylinder Cylindrical 20 mm

Length 15 mm 0.9×10-3

Ceramic spheres Spherical Outer 20 cm inner 18 cm Length 18 cm

1.032×10-3

Tezontle grains Cylindrical 3.25 mm 1.21×10-3

HDPE grains Granules 3.0 mm 1.177×10-3

LDPE grains Granules 4.5 mm 0.755×10-3

Polypropylene grains Granules 3.5 mm 1.001×10-3

Polyurethane cubes Cubes 25×25×25 mm 1.102×10-3

42

Polyethylene tape SESSIL Tapes 30×150 mm 1.098×10-3

Loofa sponge Cylindrical Length 36.25 cm -

Natrix C 10/10 Cylindrical 31-36 mm Length 32 mm

0.31×10-3

Sand Circular 3.0 mm 820 m-1

Polyether foam cube Cubes 5×5×5 mm -

The biofilm carrier should provide a suitable larger internal surface area and good

surface texture for quick biomass growth and to hold biomass against shear and

sloughing (Chaudhary et al., 2003). The design of biofilm carrier is important due to

requirements for good mass transfer and nutrients to microorganisms. The key

parameters of the biofilm carriers are its shape and the percentage of the tank filled with

it (Robescu et al., 2009). For the effective growth of biofilm and its performance in a

reactor we need to take special care while we design the specific surface area of the

carrier and the filling fraction of the carrier in the reactor (Odegaard et al., 2000). The

specific surface area of the carrier reflects the amount of surface area available for

biofilm development per unit volume of the carrier on a bulk volume basis. The reactor

specific surface area equals the specific surface area of the carrier multiplied by the

fraction of the total reactor volume that the carrier occupies (bulk volume basis) (Weiss

et al., 2005).

The attachment of microorganism to the surface and the subsequent growth of the

biofilm community depend upon the surface of the biofilm carriers that are rougher,

more hydrophobic, and coated with surface-conditioning films (Vayenas, 2011). Sponge

has been considered as a reasonable attached growth media because it can act as a

mobile carrier for active biomass resulting in improved organic and nutrient removal as

well as reduces fouling of the membrane by reducing the cake layers formed on the

surface of the membrane and retain microorganisms by incorporating a hybrid growth

system (Guo et al., 2009; Ngo et al., 2006).

43

2.4.3 Theory of attached growth processes

Biological wastewater treatment process has been performed as one of the most

effective treatment processes for the removal of organic pollutants from wastewater.

The biological process has been improved during the last few years and one of these

new improved process includes the addition of specially designed porous mobile

elements called carriers into the aeration tank that provide a surface for the biological

growth (Robescu et al., 2009). The basic principle of the process is that the biomass

grows on the specially designed carriers that move into the reactor by the agitation setup

by aeration in aerobic condition or mechanical mixing in anaerobic and anoxic

condition. It might take a few days or months to grow biofilm depending on the feed

water organic concentration and the biomass carrier types. It is very important to control

and maintain a healthy biomass on the surface of the media (Chaudhary et al., 2003). As

shown in the Figure 2.8, a biomass layer sticks to the surface of the solid media and

start growing. The liquid wastewater passes adjacent to the biomass layer forming a

liquid layer. During the passage of the wastewater in the liquid layer and its contacts

with the biofilm layer, the organic matter, ammonia, phosphate and DO in addition to

other dissolved materials penetrate into the biomass layer by diffusion. The biochemical

reactions such as organic matter oxidation, nitrification occurs inside the biofilm layer.

The end products such as CO2, H2O and NO3 leave the biofilm layer back to the liquid

layer and move out with the liquid flow of the effluent stream.

Figure 2.8 Schematic diagram of attached growth Process.

Organic matter, NH4, O2

End products (CO2 + H2O + NO3)

Liquid inflow

Liquid outflow Biofilm layer

Biofilm media

44

The bacteria in the biomass layer grow and some will die. The dead bacteria lose its

sticky characteristics and it is removed from the biomass layer by the action of the

moving liquid while the fixed bacteria within the media are very stable and active.

Denitrification can be achieved in the attached growth system in the lower parts of the

system where anoxic conditions exist (Ngo et al., 2006). In an aqueous environment,

microorganisms attach to wet surfaces, multiply, and embed themselves in a slimy

matrix composed of the EPS they produce, forming a biofilm. Attached cells metabolize

prevailing energy and carbon substrates, consume electron acceptors, grow, replicate,

and produce more insoluble extracellular polymers, predominantly polysaccharides,

thus accumulating a viable biofilm community. As the microorganisms grow, the

thickness of the biofilm layer in the carrier increases that results the consumption of

diffused oxygen and the metabolization of adsorbed organic matter before it can reach

the microorganisms near the carrier face. These results the microorganisms near the

carrier face enter into an endogenous phase of growth and lose their ability to cling to

the carrier surface. The liquid flow then washed away the biofilm from the carrier, and a

new biofilm layer starts to grow (Vayenas, 2011).

2.4.4 MBR and MBBR for nutrient removal

Although the activated sludge process has been used in biological treatment of

wastewater as one of the most economical and widely used method for more than 100

years, lots of modifications have been made because of the higher quality effluent

requirement and the more strict rules and regulations for discharging treated wastewater

into the natural water bodies. Compact wastewater treatment plants that produce an

effluent of high standard in the presence of smaller footprint and minimize waste is

increasingly become worldwide concern particularly in the densely populated areas

where limited space is available for the treatment plants (Leiknes et al., 2001).

Biological processes particularly MBBR is one of the advanced treatment processes in

wastewater treatment which offer compact treatment plant design to overcome the

drawbacks of CAS process and produce higher quality effluent even in smaller foot

print.

45

MBBR has been successfully applied to full-scale treatment of municipal and industrial

wastewaters (Pal et al., 2012). Specially designed biomass carriers having high specific

surface area, surface roughness, high durability, strength and porosity is one of the

important parts of MBBR. In MBBR system, the biofilm helps to maintain high

biomass age which gives favorable conditions for the specific slowly growing bacteria

(nitrifiers) (Rahimi et al., 2011). Many studies carried out for nutrient removal from

wastewater using MBBR found that MBBR technique is very useful to meet the recent

stringent rules of nutrient discharge limits. In this technique, simultaneous nitrification

and denitrification is possible in the continuously aerated bioreactor by introducing

biofilm carrier in the reactor. For example, Guo et al. (2010) did experiment on the

MBBR using Polyurethane foam (PU) cubes with different sizes as carrier and got

100% phosphorus removal. Similarly, Chu et al. (2011) investigated the performance of

MBBR using PU foam and biodegradable polymers including polycaprolactone (PCL)

as biofilm carriers separately and found that MBBR filled with PU carriers gave good

removal of TOC and ammonium (90% and 65% removal efficiency) while MBBR filled

with biodegradable PCL carriers are good for TN removal (58% removal efficiency).

Research to optimize wastewater treatment units has been demanding because of the

strict environmental standards to be faced in coming future. Integrated MBR with

MBBR is the most popular treatment configuration (Guo et al., 2008). MBR system is

widely used in the wastewater treatment by the improvements in membrane stability

and cost effectiveness. However, MBR is facing problem of membrane fouling which

lead to decrease in membrane performance by the deposition of foulants on the

membrane surface resulting decrease in flux and membrane area. From researches and

study, MBBR or addition of specially designed media in the MBR is proven as one of

the best option to minimize these problems and enhance the nutrient removal efficiency.

The use of media for attached growth in the MBR system become popular in the field of

biological nutrient removal from different types of wastewater. Khan et al. (2011)

carried out an experiment using suspended and attached growth MBR for nutrient

removal from synthetic wastewater and they concluded that the attached growth MBR

has higher efficiency for the nutrient removal compared to the suspended growth MBR.

Guo et al. (2009) investigated the effect of different sponge sizes on a submerged MBR

for improved nutrient removal from wastewater and concluded that the system is

effective for high nutrient removal. Similarly, Leiknes et al. (2007) investigated the

46

potential of biofilm membrane bioreactor (BF–MBR) combining the MBBR with

membrane separation and found that the BF–MBR is an alternative strategy to reduce

the effect of membrane fouling by high biomass concentrations, particularly under low

loading rates. They also concluded that the process has good treatment efficiencies and

produces a consistent high-quality effluent, irrespective of loading rates.

2.4.5 Application of MBBR for nutrient removal from wastewater

MBBR is one of the best solutions for Wastewater treatment plants to withstand the

high stringent legislation and improve the efficiency of organics and nutrient removal

from wastewater. To date, MBBR have been successfully employed to treat sewage and

industrial wastewater and to upgrade small wastewater plants (Loukidou et al., 2001).

Many successful investigations and researches have been done in MBBR for nutrient

removal from wastewater. Brief results of some of theses studies are described here.

Welander et al. (1998) did the experiment for treatment of leachate from municipal

landfill deposited both domestic and industrial waste using a pilot scale suspended

carrier biofilm reactors for the biological nitrogen and organic matter removal. They

carried out this investigation in two stage suspended carrier biofilm process. They used

Natrix model 6/6 C, ANOX AB, Lund plastic carrier with specific surface area of 210

m2/m3 and its performance was compared with a new carrier of model Natrix 12/12c,

ANOX AB, Lund with specific surface area of 390 m2/m3. They operated one reactor in

aerobic condition for nitrification and organic matter removal which was 5 m3 plastic

tank filled 60% of its volume with Natrix model 6/6 C, ANOX AB, Lund model carrier.

They operated the another reactor in an anorexic mode for denitrification with the

addition of external carbon source which was 900 L plastic tank filled 40% of its

volume with the same carrier as first reactor. They operated the third reactor in aerobic

condition for nitrification to compare the performance of the carrier used in both

reactors with the new carrier Natrix model 6/6 C, ANOX AB, Lund. The third reactor’s

volume was 900 L filled 60% of its volume with the new model carrier. From the study,

they showed that suspended carrier biofilm technology be useful process for the

biological nitrogen removal from landfill leachate. They achieved the highest

volumetric nitrification rate, 24 g/Nm3.h (16 ºC) in third reactor filled with the carriers

47

of largest surface area. The maximum denitrification rate with methanol as carbon

source was 55 gN/m3.h (17 ºC). They achieved around 90% removal of inorganic and

total nitrogen when the process reached the optimal operating condition. The

comparison between two carriers of different specific area showed that the carrier with

the largest surface area is better for the full scale nitrification of leachate.

Ngo et al. (2006) developed a study to further enhance the performance of a novel

attached cultures sponge bioreactor and emphasize the approaches towards making an

alternative system that is compact, cost effective and low maintenance in a wide range

of applications. For this study, they used a laboratory scale attached cultures sponge

bioreactor consisting of a number of trays and selected the sponge type, shape and the

sponge tray inclination very specifically. Each tray was designed to hold sponge of

different shapes like semi circular, semi hexagonal and triangular. The sponge was

reticulated, flexible polyester polyurethane sponge having unique three dimensional,

uniform open cell structures. They used two types of wastewater: one was synthetic

wastewater and the other was biologically treated sewage effluent from a water

reclamation plant. The synthetic wastewater was fed to an influent channel that flows

under gravity onto the surface of the sponge bioreactor which was placed at different

inclination angles (0, 30, 45, 60 and 90). The suitable sponge type and shape for the

system was selected through the investigation on biomass growth onto the sponge at a

predetermined flow rate. The biologically treated wastewater was fed into the sponge

bioreactor system through the collection tank. This system was designed to run the trays

at a 10º inclination. The performance of this system was evaluated in terms of total

nitrogen, ammonia, ortho-phosphate and chemical oxygen demand. The results showed

that the highest NH4-N removal was about 90% in 18 days operation with an effluent

concentration of less than 0.04 mg/L. The COD removal efficiency varied in the range

of 20 - 100%. This study concluded that the selected triangular shaped sponge with a

sponge type of 70 - 90 cells/in2 and designated slope of sponge tray at 10º led to the

highest pollutant removal.

Yang et al. (2010) studied the biological nutrient removal in a sequencing batch moving

bed membrane bioreactor. They added carriers in the reactor instead of activated sludge

in order to advance the nutrient removal efficiency. For this study, they used a 30 L

reactor and divided the reactor into two parts with a volume ratio of 4:1 using a piece of

48

clapboard having bores in it. In the bigger part of the reactor, they filled 30% of the

volume of the reactor with a new kind of non-woven carriers having density 0.27 g/cm3

and specific surface area 900 m2/m3. To avoid the carriers accumulating around the

membrane module, they put the hollow fiber membrane made of polypropylene with a

pore size of 0.1μm and the filtration area 0.4m2 in the small part of the reactor. They

run the system continuously for about 5 months. They inoculated the system with

activated sludge taken from the secondary settlement tank of municipal wastewater

treatment plant and fed synthetic wastewater contained 400 mg COD/L, 30 mg NH4-

N/L and 4 mg PO4-P/L. The water was fed into the reactor in the anaerobic phase and

the discharging of water occurred in aerobic phase. This study showed good

performance on organic substance and nitrogen removal. The TN, ammonium nitrogen

and COD removal efficiencies were averaged at 82.6%, 95.6% and 93.5% respectively.

The total phosphorus removal was closely correlated with the length of aerobic and

anaerobic phase. The average TP removal efficiency reached to 84.1% when both

aerobic and anaerobic phases were operated at HRT of 2 hours (h). This study showed

that the sequencing batch operation mode was beneficial for improving membrane

fouling since filamentous bacteria was restrained in the reactor.

Guo et al. (2009) developed a study to investigate the performance of three different

sizes of reticulated polyester urethane sponge (S28-30/45R, S28-30/60R and S28-30/90R)

coupled with continuous aerated submerged membrane bioreactor to improve the

phosphorus and nitrogen removal, improving membrane fouling and enhancing

permeate flux. Synthetic wastewater containing glucose, ammonium sulphate,

potassium dihydrogen phosphate and trace nutrients was used in the experiment. 10% of

the volume of the reactor was filled with the sponge. The sponge submerged membrane

bioreactor was inoculated with sludge from the local wastewater treatment plant and

adapted to synthetic wastewater. The three different sizes of sponge were evaluated

depending upon the removal efficiencies of NH4-N, PO4-P, DOC, COD and biomass

concentration. The result of this experiment showed that the denser the sponge, the

more biomass can grow on the sponge. All three sizes of sponge performed well to

remove DOC, PO4-P whereas S28-30/45R and S28-30/60R can remove more than 99%

NH4-N from wastewater. The single size sponge submerged membrane bioreactor gave

good results in terms of organic and nutrient removal. Also mixed sponge in

conjunction with hollow fiber submerged membrane bioreactor and non-woven

49

submerged membrane bioreactor of ratio 1: 1: 1 showed superior removal of NH4-N

(over 99.8%) associated with over 99% removal of PO4-P and low TMP development

during 15 days of operation.

Guo et al. (2010) investigated the performance of sponge as an active carrier for

attached growth biomass in three typical types of aerobic bioreactors to treat a high

strength synthetic wastewater. They investigated the effect of sponge thickness on

sponge biofilter (SBF) using a low dense sponge (S45R) and high density sponge

(S90R), effect of the sponge volume on sponge batch reactor (SBR) using S45R and

S90R, and the effect of filtration rate and pH on sponge submerged membrane

bioreactor (SSMBR) using an intermediate dense sponge (S60R) in terms of

simultaneous organic, nitrogen and phosphorus removal. They used a SBF column

fitted with a single piece of sponge at the bottom of the column to study the effect of

sponge thickness. They compared three different thicknesses of sponges (1, 2 and 3 cm

respectively) to treat wastewater with COD of 0.4 kg/m3.d pumped upward through the

column at a flow rate of 20 mL/min. This study found that the organic and nutrient

removal decrease with the increase of sponge thickness. They found 15% less DOC

removal efficiency with 3 cm thickness of S45R and S90R sponges while the removal

efficiency was quite similar with 1 and 2 cm sponges. The system demonstrated that the

sponge itself has the function of simultaneous nitrification and denitrification and

verified the decreasing DO gradient occurring inside of the sponge cubes. This

experiment found the 1 cm sponge is best for high TN and TP removal (39.9% and

61.0% for S45R and 51.7% and 89.1% for S90R respectively) compared to 2cm and

3cm sponges. They used acclimatized 1 cm sponge as a moving bed media to determine

the effect of sponge volume using SBR equipped with air diffuser. Aeration rate was 8

L/min and HRT was 8 h. This experiment showed that the sponge volume played a

significant role in phosphorus removal while it has only little influence in organic and

TN removal. In this experiment they obtained high TP removal with S90R sponge

volume at 10 and 20% (99 and 100% respectively) within the short retention time (6 h

and 3 h respectively) while it was only 68.7 and 69.2% within 8 h with S45R sponge.

The DOC removal achieved more than 92% at all conditions while TN removal was

very low (around 10% for S45R and 20 - 30% for S90R). Therefore, from this

investigation they concluded that to get better TN removal, either high sponge volume

or the moving bed reactor coupled with suspended growth is required which helps to

50

improve the nitrification rate in the system. They also evaluated the system for

improved nitrogen removal in SSMBR using S60R sponge. They examined three

filtration fluxes (10, 15 and 20 L/m2.h) under pH values of 5, 5.5, 6, 6.5, 7, 7.5 and 8.

They maintained the MLSS of suspended growth at 10 g/L and used sponge volume of

10%. The result showed the more than 96% DOC removal efficiency when the filtration

flux and pH varied in the range of 10 - 20 L/m2.h and 5 - 8 respectively. While optimum

ammonium removal (100%) was achieved at pH of 6 - 7 and filtration flux of 10 and 20

l/m2h and more than 91% phosphorus removal was obtained at pH range of 6 - 7 at all

filtration flux range.

Odegaard et al. (2000) analyzed the influence of carrier size and shape on the

performance of moving bed biofilm process related to highly loaded plants working in

municipal wastewater. For this experiment, they used a pilot plant with one moving bed

bioreactor and a linked settling tank, operated in parallel on the same wastewater. They

carried out the comparison test at various COD loads using carriers of different size and

shape having same density and analyze the results on the basis of volumetric removal

rate as well as area removal rate. In the first part of the experiment, three parallel lines

each consisting of one moving bed reactor and one linked settling tank, were used. The

reactors were 20 L capacity for line 1 and 2 and 30 L capacity for line 3. The surface of

the settling tank was 0.068 m2 for line 1 and 2 and 0.102 m2 for line 3. The moving bed

bioreactors were filled with three different types of carriers (KMT, AWT and ANOX,

characteristics are described in the Table 2.8 below) made of high density polyethylene

having density 0.95 g/cm3. In the first period of the experiment of first part, all three

reactors were filled with different carriers with same filling fraction (60%) in order to

give same volumetric load while in the second period the filling fraction was varied to

give same effective area load at constant flow. Comparison of two kaldnes carriers K1

and K2 was carried out in the second part of the experiment using the same plant. The

two lines were operated in three periods at close to constant flow and the same

volumetric loading rate in each period. The filling fraction was 70% in both reactors.

51

Table 2.8 Characteristics data for the four different carriers used (Odegaard et al., 2000)

Specific surface area

KMT carrier K1

KMT carrier K2

AWT carrier

ANOX carrier

Estimated surface area (mm2/piece) Bulk carriers (number/liter) Specific surface area(m2/m3)

total: 670 effective: 490

1030


total: 3465 effect.: 1910

159


total: 2200 effect.: 1500

203



24


From this study, they concluded that the organic surface area loading rate (g COD/m2.d)

is the main component for the removal of organic matter in municipal wastewater using

moving bed biofilm reactor. The comparison test at various COD loads using carriers of

different size and shape having same density showed no significant variation. They also

concluded that the residence time of the bioreactor has only an influence at long

residence times and hydrolysis plays a major role. In short residence times, hydrolysis

play a minor role and the reactor should be designed for the removal of easily

biodegradable soluble organic matter. In order to increase the settleability of the

biomass in high rate system, there is a need of enhanced settling by coagulation or

alternative separation techniques.

Quan et al. (2012) demonstrated the MBBR performance for nutrient removal efficiency

from synthetic wastewater at different packing rates (20, 30 and 40%) of cubic shaped

PUF carriers. Their experimental results indicated that the PUF packing rate had a bit

influence on the COD removal and got 81% COD removal efficiency on average while

the ammonium removal and the biofilm structure had a high effect with the different

packing rates and COD loading rates. From this experiment, they proved that higher the

packing rate higher will be the ammonium removal efficiency. They achieved 96.3%

ammonium removal efficiency in 40% of the reactor packing rate at a HRT of 5 h while

only 37.4% ammonium removal efficiency at 20% of the reactor packing rate.

Chu et al. (2011) investigated the performance of MBBR for the removal of organics

and nitrogen from wastewater with a low C/N ratio using the two different materials as

52

a carrier for their research, namely PUF and biodegradable polymer PCL particles. This

study demonstrated the MBBR with PUF had good results in the TOC and ammonium

removal, 90% and 65%, compared with 72% and 56% for reactor filled with PCL

carriers at an average HRT of 14 h. This is because of the higher attached

microorganism on the PUF enhanced the nitrifiers to reside. The MBBR with

biodegradable PCL carrier showed good performance in terms of TN removal (59%

with PCL carriers and 14% with PU carriers) as these carriers are an effective substrate

providing reduced power for denitrification. However, the high cost of the

biodegradable PCL is the drawback for its application as external carbon source and

biofilm media.

Shore et al. (2012) examined the use of MBBR with BioPortzTM as carriers for tertiary

ammonia treatment in high temperature (35 – 45 ºC) industrial wastewater in their

experiment and found that the system was successful to remove more than 90% of the

influent ammonia from synthetic and industrial wastewater. At 45 ºC, nitrification could

not be sustained for more than 24 h. However, the MBBR was recovered within two

weeks once the temperature was lowered to 30 ºC. In this experiment they also

investigated the effect of temperature on the biomass in the reactor and they found

biomass reduction with increasing temperature, however values were not statistically

significantly different following the increase in reactor temperature. Therefore, they

mentioned the decrease in biomass may be decrease in bioavailable substrates which

affect the growth and some detachment of the heterotrophic organisms in the biofilm.

Kermani et al. (2008) evaluated MBBR filled with FLOCOR – RMP® in terms of

organics and nutrient removal efficiency from synthetic wastewater which showed that

the MBBR could be used as an ultimate and efficient option for the total nutrient

removal from municipal wastewater. In their study, they applied MBBR in series with

anaerobic, anoxic and aerobic units in four separate reactors and operated continuously

at different nitrogen and phosphorus loading rates. At the optimum condition (500 mg

COD/L, 62.5 mg NH4-N/L and 12.5 mg PO4-P/L), close to complete nitrification

99.72% of ammonium removal efficiency occurred in the aerobic reactor. Most of the

biodegradable organic matter was consumed during the denitrification process in the

anoxic reactor. The experiment showed that the system was a very effective process for

almost complete organic and nutrient removal, with average soluble COD, TN and TP

53

removal efficiencies of 96.9, 84.6 and 95.8% respectively during optimum operating

conditions.

Nguyen et al. (2011) used sponge tray bioreactor for wastewater treatment at different

operating conditions. In their experiment, they investigated the effect of different

organic loading rate (OLR), flow velocity and HRT on the performance of sponge tray

bioreactor. They use 0.6, 1.2, 2.4 and 3.6 kg COD/m3 sponge day OLR and concluded

that the optimal OLR of 2.4 kg COD/m3 sponge day was the most appropriate OLR in

terms of high COD and nutrient removal. They achieved more than 92% organic carbon

removal efficiency at OLR of 1.2 and 2.4 kg COD/m3 sponge day while the system

removed less than 86% at OLR of 0.6 and 3.6 kg COD/m3 sponge day. Similarly, at

OLR of 2.4 kg COD/m3 sponge day, the system could eliminate 56% of PO4-P and

40.2% NH4-N and 41.9% TN while these removal efficiencies decreased at other OLR.

Using the optimal OLR of 2.4 kg COD/m3 sponge day, Nguyen et al. (2011) also

investigated the effect of different flow velocities (4, 8, 20, 28 and 40 mL/min) and

concluded that the flow velocity has no significant effect on DOC removal as the

system could successfully achieve more than 90% of DOC removal at all the flow

velocities. However, it affects the PO4-P, TN and NH4-N removal. They achieved high

PO4-P, TN and NH4-N (87.4%, 54.8% and 52.9% respectively) removal efficiency at 28

ml/min flow velocity. Therefore, they concluded that 28 mL/min flow velocity is

optimum for higher pollutant removal and reducing membrane fouling. They conducted

experiments to investigate the effect of HRT on the performance of sponge tray

bioreactor using optimal OLR of 2.4 kg COD/m3 sponge day and Flow velocity of 28

ml/min at four different HRTs of 40, 80, 120 and 180 min. The result showed that at

increasing HRT, the system could give better performance in terms of reducing

membrane fouling and nutrient removal. They also concluded that at high HRT, there is

a chance of biomass growth in the sponge. From this experiment, they concluded that

the simple and compact sponge tray bioreactor system could remove nutrients and

organics efficiently from wastewater and to achieve excellent performance, the system

needs to operate at the optimal OLR flow velocity and HRT which helps to provide

suitable conditions for biomass growth on the sponge media.

Jing et al. (2009) did an experiment on the carrier effects on oxygen mass transfer

behavior by varying the suspended carrier filling rate and aeration rate to seek the

54

optimal operating conditions under which MBBR can be run at high efficiency and with

low power expense. In this experiment, they used a reactor of 2 L capacity and bio

carriers of model WD-f10-4 bioMTM having a specific surface area of 900 m2/m3 and a

density of 0.96 – 0.98 g/cm3 to investigate the effect of carrier filling rate and intensity

of aeration on the volumetric oxygen mass transfer (KLa) coefficient by the dynamic

oxygen dissolution method. They found that within the fluidizable flow rate, the

efficiency of oxygen mass transfer increased with the carrier filling rate and KLa reached

its highest when the carrier filling rate was 40% while it decreased by two fold when the

carrier filling rate was only 10%. They also found the increasing KLa trend with an

increase in aeration intensity but high aeration rate was not favorable for reactor

operation. Through their investigation, they concluded the aeration intensity of 0.3 m3/h

and the carrier filling rate of 30 - 50% is the favorable condition for the better oxygen

mass transfer effect and higher oxygen transfer efficiency. They also concluded that the

possible mechanisms that can account for carrier effect on oxygen mass transfer are the

changes in the gas-liquid interfacial area. They applied this experimental conclusion to

the NH4-N removal performance of the coking plant wastewater in MBBR for its proof

in practical performance and found satisfactory result with NH4-N removal efficiency of

93%.

Levstek and Plazl (2009) evaluated the effect of carrier type on nitrification in moving

bed biofilm process using two different types of carriers fundamentally different in size,

shape and structure. One of the carriers they used was a cylindrical high density

polyethylene ring shaped carrier (AnoxKaldnes, K1 carrier) and the other was a

spherical polyvinyl alcohol (PVA) gel bead shaped carrier (Kuraray, PVA-gel carrier).

For this investigation they used two separate continuously aerated lab scale continuous

stirred tank reactors (CSTR); one with 7.3 L capacity and the 37% volume of this

reactor was filled with K1 carrier taken from an oxic reactor of an industrial scale pilot

plant while the other reactor having 3.54 L capacity and the 9.6% volume of the reactor

was filled with PVA-gel bead carrier taken from an oxic reactor of the semi - industrial

scale pilot plant used for nitrogen removal. They operated the both reactors in the same

conditions and supplied synthetic wastewater which contains only ammonium,

phosphate and growth minerals. They used the carrier filling ratios less than the

recommended ratio by the manufacturers to achieve good mixing of carriers so that

there is the proper distribution of substrates to the biofilm in the reactor. They operated

55

the system continuously for six months at temperature of 20 ± 1 ºC and oxygen was

maintained at 8.0 ± 5 mg/L. Form this operation they achieved 93% nitrification

efficiency and average total biomass concentration in the reactor was 1.12 ± 0.14 gTS/L

in reactor filled with K1 carrier while the nitrification rate was 86.5% and average total

biomass concentration in the reactor was 0.83 ± 0.36 gTS/L in reactor filled with PVA-

gel bead carrier. Their experimental results showed that the process with PVA-gel

beads, however, had a lower carrier filling rate than that of K1 carriers, about the same

maximal nitrification rate were achieved from both systems. They concluded that the

reason for this appears to be the higher effective specific surface area of about 2,534

m2/m3 for PVA-gel beads versus the effective surface area of about 500 m2/m3 for the

K1 carrier. From their investigation they found the different carrier types does not affect

the concentration of the autotrophic biomass and nitrification rate in an attached growth

process.

Marques et al. (2008) demonstrated attached biomass growth and substrate utilization

rate in MBBR using synthetic wastewater and polyether form cubes of size 5×5×5 mm

and density of 0.65. They developed their study using 3.8 L MBBR filled with a

maximum content of polyester foam (0.13% by volume) and 2 L/min air was supplied

in the reactor. From their study they found that the biomass growth in the polyether

foam was quite fast most probably by the mechanism of entrapment of biomass flocks

instead of the attachment of microorganisms on the surface. In their experiment they

found the system saturation about 30 h of continuous operation. They also found the

increase in substrate utilization rate with the organic load due to the high biomass to

carrier ratios, whose maximum value was about 0.8 kg biomass/kg inert carrier. Form

this study they concluded that MBBR can withstand about 2 times the volumetric

organic loads experienced by the other modalities of activated sludge reactor processes

and by using MBBR the area required for the treatment process can be reduced and also

the capacity of the existing conventional plants can be increased by introducing inert

carriers in the system.

56

CHAPTER 3: MATERIALS AND METHODOLOGY

3.1 Materials

3.1.1 Wastewater

In order to provide a continuous source of completely biodegradable organic pollutants

and maintain the constant feed concentration, synthetic wastewater was used as an

influent in this experiment and prepared to represent the primarily treated sewage

effluent (PTSE). This wastewater contains glucose as the main carbon source and

ammonium sulphate and potassium phosphate as the main source of nutrient. The

synthetic wastewater consists of DOC of 120 – 130 mg/L, COD of 330 – 360 mg/L,

ammonium nitrogen (NH4-N) of 18 – 19 mg/L, ortho-phosphate (PO4-P) of 3.3 – 3.5

mg/L (COD: N: P = 100: 5: 1) and trace elements in tap water. The synthetic

wastewater having above mentioned concentrations is adequate to provide required

nutrients for the microorganism growth. The chemical composition of synthetic

wastewater used for this experiment is as shown in Table 3.1. The synthetic wastewater

was prepared everyday to avoid microbial growth on the feed tank and kept at room

temperature.

3.1.2 Polyethylene (PE) carriers

The PE carriers, circular in shape with the diameter of 4.50 cm were used as biofilm

carriers. These carriers consist of smaller dividers inside the carriers and fins outside

where microorganisms can attach and grow on. The characteristics of PE carriers used

in this experiment are summarized in Table 3.2. The specific surface area, density and

weight of each PE carriers were 6.22 cm2, 0.613 g/cm3 and 1.226 g respectively. The

picture of PE carriers is shown in Figure 3.1. These PE carriers were slightly lighter

than the density of water (1 g/cm3) and developed specifically for use in wastewater

treatment reactors.

57

Table 3.1 Characteristics of synthetic wastewater

Compounds Concentration (mg/L)

Organics and nutrients

Glucose(C6H12O6) 280

Ammonium sulfate((NH4)3SO4) 72

Potassium phosphate (KH2PO4) 13.2

Trace nutrients

Calcium chloride (CaCl2 2H2O) 0.368

Magnesium sulfate (MgSO4 7H2O) 5.07

Manganese chloride (MnCl2 4H2O) 0.275

Zinc sulfate (ZnSO4 7H2O) 0.44

Ferric chloride anhydrous (FeCl3) 1.45

Cupric sulfate (CuSO4 5H2O) 0.391

Cobalt chloride (CoCl2 6H2O) 0.42

Sodium molybdate dihydrate (Na2MoO4 2H2O) 1.26

Yeast extract 30

Table 3.2 Characteristics of PE carriers

Media Polyethylene

Shape Circular

Diameter 4.5cm

Specific surface area 6.22 cm2

Density 0.613 g/cm3

Weight 1.226 g

58

Figure 3.1 Polyethylene (PE) carriers

3.1.3 Membrane module

A flat sheet membrane module made of polyvinylidene fluoride (PVDF) was used in

this experiment for the membrane filtration process. The characteristic of the membrane

module used in this experiment is summarized in Table 3.3. This membrane module had

8 separate vertical sheets of filtration at an approximate interval of 1.1 cm. This type of

membrane module has the capacity to resist high and low pH, higher water permutation

rates and ability to withstand oxidizing agent such as sodium hypochlorite during

membrane cleaning (Johir et al., 2012). Figure 3.2 shows a picture of the flat sheet

membrane module used in this experiment.

Table 3.3 Characteristics of membrane

Item Characteristics

Module Membrane material Membrane configuration Dimension Pore size Surface area Manufacture

M70 PVDF Flat sheet 10.5×11.5×22.5 cm 0.14 μm 0.2 m2 A3 Water Solutions GmbH, German

59

Figure 3.2 Flat sheet membrane module

3.2 Methodology

3.2.1 Experimental conditions

Firstly, this study put forward a systematic study on the effects of PE carriers filling

rate, aeration rate and HRT on nutrient removal in a continuous MBBR system.

Afterwards, the system was combined with a MF membrane module to investigate the

performance of the combined system and evaluate the membrane fouling phenomenon.

In order to achieve these tasks, an acrylic reactor with a working volume of 12 L was

used. A sketch of the laboratory scale experimental setup is shown in figure 3.3 (A) and

(B) respectively.

60

(A)

(B)

Figure 3.3 Experimental arrangements of (A) MBBR and (B) MBBR-MF

The laboratory scale experiment was conducted in four different sets of experiments.

The flow chart in Figure 3.4 describes the order of different activities and their

interrelation which were carried out during the research time.

(A)

61

Figure 3.4 Flow chart of the research activities

The acclimatization of PE carriers is one of the essential components to provide

preferably active biomass growth on the carriers so that this biomass can perform well

in the wastewater treatment process. Therefore, about one month prior to starting

experiment in the reactor, the PE carriers were acclimatized in a separate aeration tank

(30 L) filled with synthetic wastewater and activated sludge from a wastewater

treatment plant in Sydney. Figure 3.5 shows the aeration tank used for the PE carriers

acclimatization in the University of Technology Sydney (UTS) laboratory. Everyday,

10 L synthetic wastewater was added in the aeration tank and pH was maintained to 7

by adding sulphuric acid (H2SO4) or sodium carbonate anhydrous (NaHCO3) to support

the microbial growth. MLSS in the tank was maintained to 8 - 10 g/L. The PE carriers

were acclimatized after 25 days. The acclimatization of these PE carriers was

determined by observing the biomass growth rate on the surface of PE carriers at every

5 days interval.

Laboratory operations

Experimental investigation Experimental PE carrier acclimatization

Conclusion

Nutrient removal from municipal wastewater using MBBR - MF and evaluate the

membrane fouling Phenomenon at different flux rate

Effect of PE carrier filling rates in nutrient removal from municipal wastewater using

MBBR

Effect of aeration rates in nutrient removal from municipal wastewater using MBBR

Effect of hydraulic retention time in nutrient removal from municipal wastewater

using MBBR

62

Figure 3.5 PE carriers acclimatization tank

For the first set of experiment, the acclimatized PE carriers were transferred into the

reactor filled with synthetic wastewater. The filling volume of the PE carriers was

started from 10% and increased to 20%, 30% and 40% by volume of the reactor

respectively. The reactor was operated at least 20 days for each filling condition. The

reactor was positioned with certain inclination (10º) giving some support at the bottom

in order to create a uniform movement of PE carriers. The air was moving in the reactor

by supplying the air through air diffuser at the bottom of the reactor. Air bubbles also

supplied oxygen for the biological activity of biomass and kept the PE carriers floating

and moving throughout the reactor volume accurately. The pH of the reactor was

maintained to 7 everyday by adding H2SO4 or NaHCO3. The DO of the reactor was

observed 3.0 - 4.8 mg/L in all the cases. The synthetic wastewater was supplied from

the bottom of the reactor using a feeding pump. Everyday 11.52 L synthetic wastewater

was treated by the reactor with the constant aeration rate of 4.5 L/min and HRT of 25 h.

In order to promote microbial growth on the carriers, the HRT was kept higher as the

carriers were very sensitive and took long time for acclimatization. However, once the

microorganisms grow on the carriers, they performed well in nutrient removal from the

wastewater. MLSS concentration in the reactor was in the range of 0.19 – 0.32 g/L at all

the cycles. Everyday the influent and effluent sample was taken and stored in fridge by

adding adequate acid. The biomass growth rate in PE carriers and oxygen uptake rate

(OUR) of suspended and attached biomass in the reactor were measured at every 5 days

interval.

Similarly, Table 3.4 describes the experimental conditions for another set of

experiments. The second experiment was conducted to determine the effect of different

aeration rate on nutrient removal from wastewater while the third experiment was

63

conducted to determine the effect of different HRTs in nutrient removal from

wastewater.

Table 3.4 Experimental conditions to determine effect of different aeration rates and

HRTs in nutrient removal from wastewater

Experiment

No.

Carrier filling

rate (%)

Aeration

rate (L/min)

HRT

(h)

DO concentration

(mg/L)

MLSS

(g/L)

1

10

20

30

40

4.5

4.5

4.5

4.5

25

25

25

25

7.41-9.50

3.43-5.54

3.26-4.76

2.33-3.07

0.25- 0.45

0.25-0.20

0.20-0.25

0.20-0.15

2

20

20

20

2.5

4.5

6.0

25

25

25

3.5–4.0

3.0–4.8

3.75–4.16

0.15–0.30

0.15–0.30

0.15–0.30

3

20

20

20

20

20

4.5

4.5

4.5

4.5

4.5

25

12

8

5

2

3.0–4.8

3.35-3.66

3.28-4.19

3.6-4.24

2.5-3.64

0.15–0.30

0.10-0.20

0.10-0.30

0.10-0.30

0.30-0.40

After 20 days of continuous operation of MBBR at each HRT, the MBBR was then

connected with the membrane filtration tank. The effluent discharged from the MBBR

was introduced into the membrane filtration tank from the top of the tank. The

membrane filtration process was conducted without any relaxation or backwash

procedure. Permeate was pumped out using a pump at constant flux. The flow rate of

synthetic wastewater into MBBR and permeate flux into membrane filtration tank was

maintained same at all the time. Pressure transducer with online data acquisition was

used to monitor the TMP of the membrane. Figure 3.6 shows the pictures of a

laboratory setup for the MBBR and Figure 3.7 shows a picture of the laboratory setup of

MBBR-MF system.

64

Figure 3.6 Laboratory setup of MBBR

Figure 3.7 Laboratory setup of MBBR-MF system

Pressure sensor

Membrane filtration system Feed pump for

MBBR and MF

MBBR unit

Flat sheet membrane module

Air supply system

Permeate out flow

control pump

65

3.2.2 Analytical methods

The analysis of COD and the measuring of MLSS and mixed liquor volatile suspended

solid (MLVSS) were carried out according to Standard Methods (APHA, 1998). The

COD was measured using COD reagent and a photometry. The MLSS and MLVSS

were measured by filtering the mixed liquor sample through a GFC Whatman’s 1.2 μm

filter paper. The retained solid residue on the filter paper was dried by placing in an

oven at 105 ºC for 2 h followed by desiccation for 20 min and finally weighted to

calculate the MLSS. Then the dried residue on the filter paper was again heated in a

furnace at 550 ºC for 20 min followed by desiccation for 20 min and weighted to

calculate MLVSS. DOC of the influent and effluent was measured using the

Analytikjena Multi N/C 3100. PO4-P, NO2-N, NO3-N and NH4-N were measured by a

photometric method using Spectroquant® Cell Test (NOVA 60, Merck). YSI 5300

Biological Oxygen Monitor was used to measure the OUR. The oxygen consumption

measurement can be achieved through the use of oxygen electrode with oxygen

permeable Teflon membrane. The voltage generated from the reaction is proportional to

the oxygen concentration of the sample and produces oxygen uptake during a period of

2 – 30 min. pH and DO of the reactor were measured everyday using pH meter

(HANNA instrument, model no. HI 9025) and DO meter (HORIBA Ltd. Japan, model

no. OM -51E) respectively.

3.2.3 Biomass growth rate calculation

To determine attached biomass fixed in PE carriers, three pieces of the PE carriers were

taken out of the reactor and kept in three separate beakers with millique water. The

beakers were inserted into Ultrasonic cleaner (POWER SONIC 405, Thermoline

Scientific), until the attached biomass on the carriers were slugged off from the carriers.

Then the solution of biomass and milique water was filtered through a GFC Whatman’s

1.2 μm filter paper. The filter paper was then kept in the oven at 105 ºC at least for 1 h

followed by desiccation for 20 min and measured weight. The filter paper was again

kept in a furnace at 550 ºC for 20 min followed by desiccation for 20 min and measured

weight. The average biomass was calculated as the average MLVSS value of the

acclimatized carriers.

66

3.2.4 Velocity measurement and circulation of kinetic energy for

moving media

The following equation gives the kinetic energy (KE) of a moving object;

KE = ½×m×v2… (1)

Where, m is the mass of an object and v is velocity of the object. Velocity of an object

can be obtained from the following equation;

v = d / T ... (2)

To measures the wet mass of a carrier coated with biofilm layer, ten pieces of PE

carriers were randomly taken from the reactor and the mass of each piece was

measured. The average wet mass of a carrier was calculated to be 3.52 (± 0.21) g. The

mean velocity of a moving carrier at each operating condition was obtained by

multiplying the circulation frequency (Fc) by the circulation distance (circulating

distance per circulation) of a carrier respectively. The circulation distance of moving

carriers was fixed at 20 cm and the circulating frequency to travel 20 cm distance by the

carriers were observed five times and then the average value was taken as the

circulating frequency. The total kinetic energy (KET) is the sum of the kinetic energy of

all carriers in the reactor which can be obtained by the following formula (Lee et al.,

2006);

KET = KE×n... (3)

Where, n is the total number of PE carriers in the reactor. These numbers are 252, 504,

756 and 1008 PE carriers at the filling fractions of 10, 20, 30 and 40% by volume of the

reactor respectively.

3.2.5 Membrane resistance calculation

Characteristics of membrane fouling can be demonstrated by using Darcy’s Law

relating flux (J) to transmembrane pressure (ΔPT), Viscosity (μ) and total resistance to

water filtration (RT). According to this model, the permeate flux (J) took the following

form (Chang et al, 1998):

J= ΔPT / (μ. RT)… (4)

RT= Rm + Rc + Rp… (5)

67

In equation (4) flux (J) is inversely proportional to flow resistance (RT). Assuming

constant TMP, less water is filtered with increasing resistance to flow (RT).

Where,

J = Permeation flux

ΔPT = Transmembrane pressure

μ = Viscosity of the permeate,

RT = Total combined resistance across a membrane,

Rm = Membrane material resistance,

Rc = Cake resistance formed by cake layer deposited over membrane surface,

Rp, = The resistance caused by pore plugging and/or solute adsorption onto the

membrane pore and surface.

Rc = RT - (Rm + Rp)... (6)

Rm = ΔPT/ (μ. J)... (7)

Rp = RT – Rm – Rc… (8)

After completion of every cycle, the fouled membrane was taken out from the reactor

and submerged into distilled water and total resistance (RT = Rc + Rm + Rp) was

calculated by changing the flux. Then the membrane was cleaned with the distilled

water giving a gentle shake so that the deposited cake layer from the membrane surface

can be washed out. The washed membrane was again submerged into the distilled water

and membrane resistance and pore block resistance (Rm + Rp) was calculated by

changing the flux. Finally the membrane was cleaned with chemicals (sodium

hydroxide (NaOH), citric acid and sodium hypochlorite (NaClO)). The membrane

resistance (Rm) was calculated by submerging the clean membrane inside the distilled

water and the water was withdrawn through the membrane at different fluxes at least for

1 h at each flux. The pressure was measured through the pressure gauge.

68

3.2.6 Membrane cleaning procedure

After completion of each cycle, membrane module was taken out from the reactor and

washed with tap water by submerging it into a water tank to remove the sludge that

accumulated between the membrane sheets. Then, the module was soaked in 2 L of

NaOH solution (0.5%) for 20 h. Afterwards, the membrane was cleaned by submerging

into the citric acid (0.5%) solution for 5 h followed by NaClO solution (200 ppm) for

the next 5 h.

69

CHAPTER 4: RESULTS AND DISCUSSIONS

4.1 Determination of Optimum Operating Conditions for MBBR

System in Terms of Carrier Filling Rate, Aeration Rate and HRT

The optimum operating conditions for MBBR system in terms of PE carrier filling rate,

aeration rate and HRT was determined by considering the nutrient and organic removal

efficiencies of the MBBR at different filling rates, aeration rates and HRTs.

4.1.1 Evaluation of microbial growth in PE carriers and its

performance at different carriers filling rates, aeration rates and

HRTs

It is very important to select suitable biofilm carrier because it affect the mass transfer

of substrate and oxygen to the microorganisms within it which in turn affect the biofilm

growth rate in the carriers. Some important qualities of biofilm carrier materials are;

small size, large protected specific surface area such as; high porosity, low density, high

resistance to attrition and capacity for biofilm attachment and activity (Andersson et al.,

2008). Therefore, the PE carriers were selected as the biofilm carriers for this research

as these carriers exhibit the above mentioned qualities for instance low density and high

protected specific surface area. The PE carrier is designed specially to provide

interspaces for the suspended microorganisms so that these microorganisms can attach

into the voids of these carriers and grow effectively. The microorganisms entrapped in

the internal space of the carriers form a thin layer of biofilm which is very active and

play a vital role in the nutrient and organic removal from wastewater. For the growth of

the microorganisms on the PE carriers, the MBBR system should be operated at

favorable operating conditions by maintaining suitable carrier filling rate, aeration rate

and HRT. During this experimental study, at the 10% carrier filling rate and aeration

rate of 4.5 L/min, it was observed that the carriers were rapidly circulated in the reactor.

This rapid movement of the carriers caused huge collision among the carriers and led

the loss of microorganisms attached into the carriers. While at 20% carrier filling rate,

the carriers moved uniformly with less collision problem in the reactor, which resulted

in the favorable condition for the attached microorganisms on and inside the carriers to

70

adsorbed enough foods (nutrient and organic matters) and DO from the wastewater and

at the same time prevented the loss of the microorganisms from the carriers enhancing

growth of thin layer of biomass in the carriers and improved the nutrient and organic

removal efficiency. At 30 and 40% filling rates, due to the larger number of PE carriers,

the carriers moved slowly in the reactor and a dense layer of biomass was formed

around the carrier surface. These dense layer of biomass obstructed DO, nutrient and

organic matters to penetrate inside the carriers. As a result the nutrient and organic

removal efficiency at 30 and 40% filling rate was decreased. The attached biofilm layer

in PE carrier at different filling rates and aeration rates are shown in Figure 4.1 (A) and

(B) respectively. The average biomass concentration on PE carriers at different

percentages of filling rates is shown in Figure 4.2. At 20% carrier filling rate the

average biomass growth rate was 15.7 mg/g while the growth rate were 10.6, 22.4 and

24.4 mg/g at 10, 30 and 40% carrier filling rates, respectively. At 20% filling rate the

carriers moved uniformly and helped prevent the accumulation of excess biomass on the

surface of the carriers as well as loss of biomass due to collision of the carries. Thus, the

biomass in the carriers could consume the more organics and nutrients in the presence

of adequate DO level and their removals were the highest compared with the 10, 30 and

40% filling rates.

Figure 4.3 shows the relation between biofilm concentration on the PE carriers and

aeration rates. At a low aeration rate (2.5 L/min), DO concentration in reactor decreased

which enhanced the ratio of sloughing on biofilm growth and biomass was washed out

from the reactor. At the same time, nitrification process also affected because of low

DO. Meanwhile, there was more friction among the biofilm carriers because of the high

turbulence induced by the high aeration rates (6 L/min). Therefore, the PO4-P uptake

rate and nitrification rate declined at a higher aeration rate (6 L/min). Although it was

observed that the NH4-N removal was the highest at the aeration rate of 2.5 L/min, the

4.5 L/min aeration rate achieved the best TN and PO4-P removal. According to the

experimental results, it was concluded that the aeration rate of 4.5 L/min was favorable

for the growth of active and effective microorganisms in PE carriers and gave higher

nutrient and organic removal from wastewater.

Figure 4.4 demonstrated the biomass concentration on PE carriers at different HRTs.

The biomass concentration on PE carriers increased when the OLR of feed water

71

increased. In other word, the biomass concentration on the carriers increased with

decreasing HRT of MBBR. The results showed that when the HRT was decreased from

25 h to 2 h (increased OLR from 0.33 to 4.14 kg COD/m3.d), the biomass concentration

on PE carriers was increased from 15.7 to 21 mg/g and the carriers were fully covered

with the biofilm. This increased biomass concentration on the carriers enhanced the

organic and nutrient removal from the system.

(A)

(B)

Figure 4.1 Biomass growth in PE carriers

(at different (A) filling rates and (B) aeration rates)

72

Figure 4.2 Variation of biomass concentration in the carriers at different filling rates

Figure 4.3 Variation of biomass concentration in the carriers at different aeration rates

Figure 4.4 Variation of biomass concentration in the carriers at different HRTs

121314151617181920

0 2 4 6 8

Aeration rate (L/min)

Bio

mas

s con

cent

ratio

n (m

g/g)

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16 18 20 22 24

HRT (h)

Bio

mas

s con

cent

ratio

n (m

g/g)

0

5

10

15

20

25

30

0 10 20 30 40 50

Carrier filling rate (%)

Biom

ass c

once

ntra

tion

(mg/

L)

73

This research was completely focused on the attached biofilm and its growth on the PE

carriers provided in the reactor. To evaluate the contribution of attached biomass on the

organic and nutrient removal from the system, the MLSS concentrations of suspended

biomass in the reactor (with none retained in the PE carriers) were measured every day,

which was remained around 0.15 – 0.32 g/L in all the cases. The MLSS concentration in

the reactor was lower at higher packing rates and aeration rates, whereas the MLSS

concentration increased with increasing OLR. Average biomass growth rate and

average nutrient and organic removal efficiency at different operating conditions are

summarized in the Table 4.1, 4.2 and 4.3.

Table 4.1 Organic and nutrient removal efficiency at different filling rates of PE Carrier (aeration rate = 4.5 L/min, flow rate = 8 mL/min, HRT = 25 h)

PE carrier filling

volume (%)

DOC removal

efficiency (%)

COD removal

efficiency (%)

PO4-P removal

efficiency (%)

NH4-N removal

efficiency (%)

MLSS (g/L)

Biomass growth rate in

carriers (mg/g)

10 93.0 75.7 56.8 49.5 0.22 10.6

20 95.8 91.4 65.9 66.1 0.25 15.7

30 95.4 86 40.5 59.5 0.25 22.4

40 93.2 79.5 30.2 70.5 0.21 24.4

Table 4.2 Organic and nutrient removal efficiency at different aeration rates (carrier filling volume = 20%, flow rate = 8 mL/min, HRT = 25 h)

Aeration rate

(L/min)

DOC removal

efficiency (%)

COD removal

efficiency (%)

PO4-P removal

efficiency (%)

NH4-N removal

efficiency (%)

MLSS (g/L)


carriers (mg/g)

2.5 95.1 93.1 27.6 74.8 0.305 17.8

4.5 95.8 91.4 65.9 66.1 0.25 15.7

6.0 94.1 87.3 47.3 68.5 0.22 16.4

74

Table 4.3 Organic and nutrient removal efficiency at different HRTs (carrier filling volume = 20%, aeration rate = 4.5 L/min)

HRT (H)

DOC removal

efficiency (%)

COD removal

efficiency (%)

PO4-P removal

efficiency (%)

NH4-N removal

efficiency (%)

MLSS (g/L)


carriers (mg/g)

25 95.8 91.4 65.9 66.1 0.25 15.7

12 93.7 86.7 40.2 64.1 0.18 15.5

8 94.2 80.8 51.9 65.8 0.19 15.4

5 94.6 90.3 57.6 71.5 0.22 18.6

2 96.0 91.4 81.8 71.2 0.39 21.0

In addition, OUR tests of the suspended biomass taken from the reactor and the attached

biomass on the PE carriers were conducted periodically. As oxygen plays an important

role in nitrogen and phosphorus removal, DO consumed by the biomass should be

monitored. The results exhibited that the higher the DO consumption rate, the more

efficient of the bacterial biodegradation could be achieved. Guo et al. (2007) also

demonstrated this type of results in their experiment. The average DO consumption rate

of suspended biomass on wastewater were around 19.7, 13.8 and 22.9% at different

carrier filling rates, different aeration rates and HRTs, respectively. The average DO

consumption rate of the attached biomass on PE carriers at different carrier filling rates,

aeration rates and HRT were around 49, 52.6 and 98%, respectively. That means the

contribution of microbial activity from the attached biomass on the PE carriers was

much stronger than the suspended biomass on the wastewater. All these parameters

indicated that the removal efficiency achieved by the system was mainly due to the

attached growth biomass on the PE carriers. The trends of DO consumption rates at

different operating conditions are displayed in Figure 4.5, 4.6, 4.7 and 4.8, respectively.

75

Figure 4.5 Average DO consumption rate variation of the suspended biomass on the

wastewater at different PE carrier filling rates


wastewater at different aeration rates

70

75

80

85

90

95

100

0 5 10 15 20 25 30

Time (min)

DO

con

cent

ratio

n (%

)

2.5 L/min 4.5 L/min 6 L/min

60

65

70

75

80

85

90

95

100

0 5 10 15 20 25 30Time (min)

DO

con

cent

ratio

n (%

)10% filling 20% filling30% filling 40% filling

76


wastewater at different HRTs

Figure 4.8 Average DO consumption rate variation of the attached biomass on PE

carriers at different carrier filling rates, areation rates and HRTs.

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30Time (min)

DO

con

cent

ratio

n (%

)

filling rate aeration rate HRT

50

60

70

80

90

100

0 5 10 15 20 25 30

Time (min)

DO

con

cent

ratio

n (%

) 25 h 12 h 8 h 5 h 2 h

77

4.1.2 Correlation between removal efficiency and total kinetic energy

(KET) at different PE carrier filling rates and aeration rates

Table 4.4 shows the velocity and total kinetic energy at different conditions calculated

using the equations (1), (2) and (3) as derived in Chapter 3. For the stable and effective

biofilm process, there must be a proper balance between the biofilm growth and

detachment which can be maintained by proper carrier filling rate and the aeration rate.

The different carrier filling rates and aeration rates affect the collision frequency

between the carriers. At the higher aeration rates and carrier filling rates, stronger

turbulence is produced and led to the increase in circulation frequency (FC) and kinetic

energy (KE) of the PE carriers moving inside the reactor. These two operating

parameters are the important factors affecting the nutrient and organic removal

efficiency in MBBR system. In terms of mass transfer, a fast fluid flow can be

beneficial to biofilm developed in the PE carriers as it will assure more solute transport

through a thinner boundary layer, thus providing better solute exchange between

biofilm and bulk liquid. However, faster flows also exert larger forces on the biofilm,

which lead to larger stresses in the biofilm structure and eventually some loss of

biomass with the effluent, particularly from the exposed surface layer of the biofilm

(Taherzadeh et al., 2012; Henriksson et al., 2011). The biofilm are the complex

microbial community which has visco-elastic properties for their beneficial. These

biofilm have a small immobile base attached to the biofilm carriers and a flexible tail

elongated in the liquid flow direction which can vibrate in fast flow (Taherzadeh et al.,

2012). The increase in speed of these biofilm tail movements relatively to the

surrounding liquid significantly enhances the substrate uptake ( or removal efficiency).

As shown in Figure 4.9 (A), the KET of PE carriers depended on the percentage of

filling fraction. The high KET of the carriers was obtained at 20% PE carrier filling rate

which was 3.255×10-2 Joule while the KET of the carriers were comparatively less at 10,

30 and 40% filling rates and the substrate uptake were also less compared to the 20%

filling rate. It was because at 20% carrier filling rate, the microbial inhabitants of

biofilm got better transport of substrate which provided better solute exchange between

biofilm and bulk liquid thus enhanced the substrate uptake i.e. the removal efficiency.

At the same time, the aeration rates also had impact on the KET of the carriers and

hence the overall substrate uptake. As we can see in the Figure 4.9 (B), the KET was

directly proportional to the aeration rate that means higher the aeration rate is, higher

78

the KET will be. However, for better removal efficiency, there must be a optimum KET

for the biofilm carriers which can protect the healthy microbial community. From this

experiment, we determined 4.5 L/min aeration rate at 20% carrier filling rate gave

optimum condition to obtain the best removal efficiencies.

Table 4.4 Calculation of total kinetic energy

Velocity of PE carriers, V

(M/Sec)

Number of carriers (n)

Total kinetic energy, KET (x 10-2 Joule)

Remarks

0.210 252 1.949 10% Carrier filling rate




0.103 504 0.945 2.5 L/ min aeration rate

0.192 504 3.255 4.5 L/ min aeration rate

0.244 504 5.303 6 L/ min aeration rate

(A) (B)

Figure 4.9 Correlation between the kinetic energy and (A) PE carrier filling rates and

(B) aeration rates

y = -1E-05x2 + 0.012x - 0.558R2 = 0.995

00.5

11.5

22.5

33.5

0 500 1000 1500

Number of PE carriers (n)

Tot

al K

E (

X 1

0-2 J

)

y = 1.240x - 2.206R2 = 0.997

0123456

0 2 4 6 8

Aeration rate (L/Min)

Tot

al K

E (X

10-2

J)

79

4.1.3 Nutrient and organic removal efficiency on MBBR at different

PE carrier filling rates

4.1.3.1 PO4-P removal efficiency

As shown in Figure 4.10, it was observed that the PO4-P removal efficiency was

increased and then decreased at first few days of operation at 10% PE carrier filling

rate, whereas 20, 30 and 40% filling rate showed relatively stable removal. However,

20% filling rate gave the best overall PO4-P removal efficiency (Figure 4.11) with

average PO4-P removal efficiency of 65.9%, while the removal efficiency was 56.8,

40.5 and 30.2% for 10, 30 and 40% filling rates, respectively. This is because at 10%

filling rate, the carrier circulation frequency in the reactor was faster. Due to the faster

circulation, the attached biomass in the carriers sloughed off and the new

microorganism growth in the carriers consumed the phosphorus from the system. While

at 20 % filling rate, the carriers moved uniformly and freely throughout the reactor that

helped in the formation of thin layer of active biofilm inside and around the carriers. As

a result, the PO4-P removal efficiency was higher at 20% filling rate. On the contrary, at

30 and 40% filling rate, due to larger number of carriers in the reactor, their movement

throughout the reactor became slower resulting formation of thick layer of biomass on

the surface of the carriers. That dense biomass on the carriers obstructed the flow of

DO, nutrient and organic matter inside the carriers which led to decrease in the PO4-P

removal efficiency. As phosphorus is one of the essential nutrients for microbial

growth, biomass growth in this system enhanced the biological phosphorus removal.

This operation proved that the biomass growth in the PE carriers could remove

phosphorus even in the absence of suspended and cell growth system in the MBBR

system. The elements for the enhancement of PO4-P removal is PAO which may also

have developed within the PE carriers and enhanced the better phosphorus removal in

the system.

80

Figure 4.10 PO4-P removal efficiency at different PE carrier filling rates

Figure 4.11 Average PO4-P removal efficiency at different PE carrier filling rates

4.1.3.2 NH4-N removal efficiency

NH4-N can be removed from wastewater in two ways: either assimilation into biomass

or biological nitrification and denitrification process under aerobic and anaerobic

conditions respectively. Figure 4.12 shows the NH4-N removal trend at different PE

carriers filling rates. The NH4-N removal achieved at 10, 20, 30 and 40% filling rate in

MBBR showed that the NH4-N removal was effective at 20% filling rate. In this

experiment, from the day first to the day 15, NH4-N removal efficiency fluctuated

around 60% at all the filling rates. As the nitrification process was not good during that

period because the microorganisms attached to the biofilm carriers required time to

0

10

20

30

40

50

60

70

10 20 30 40

PE carrier filling rate (%)

PO4-P

rem

oval

effic

iency

(%)

0102030405060708090

100

1 3 5 7 9 11 13 15 17 19 21Time (Days)

PO4-

P re

mov

al e

ffici

ency

(%) 10% carriers 20% carriers

30% carriers 40% carriers

81

acclimate into the new environment. After day 16 at 20% carrier filling rate, the NH4-N

removal efficiency increased to 75% and became constant while it was still fluctuating

at 10, 30 and 40% carrier filling rates. As the carriers moved freely and uniformly

throughout the reactor at 20% carrier filling rate, the nitrifiers got favorable condition to

grow more inside the biofilm and got enough oxygen for the nitrification. Figure 4.13

shows the average NH4-N removal efficiency at different PE carrier filling rates.

Similarly, as demonstrated in Figure 4.14, in terms of TN removal efficiency, it was

49.3% at 20% filling rate while it was 39.8, 36.5 and 52.7% at 10, 30 and 40% filling

rates respectively. Although at 40% filling volume, TN removal was achieved higher

compared to at other filling rates, the TN removal at 20% filling rate was quite uniform

and the PO4-P removal was not removed effectively at 40% filling volume. Therefore,

from the experimental results, the 20% carrier filling rate was considered as an effective

filling volume for nutrient removal.

Figure 4.12 NH4-N removal efficiency at different PE carrier filling rates

Figure 4.13 Average NH4-N removal efficiency at different PE carrier filling rates

0

10

20

30

40

50

60

70

80

10 20 30 40

PE carrier filling rate (%)

NH

4-N

rem

oval

effi

cien

cy (%

)

0102030405060708090

100

1 3 5 7 9 11 13 15 17 19 21Time (Days)

NH

4-N R

emov

al E

fficie

ncy

(%)

10% carriers 20% carriers 30% carriers 40% carriers

82

Figure 4.14 TN removal efficiency at different PE carrier filling rates

4.1.3.3 DOC and COD removal efficiency

The MBBR at different filling rates performed well in terms of DOC and COD removal

which are demonstrated in Figure 4.15 and 4.16 respectively. The DOC removal

efficiency was found above 92% at all filling rates and the average removal efficiency

at 20% PE carriers filling rate was found the highest and uniform (95.8%). Although the

removal efficiency at 30% filling rate was observed higher sometimes (around 98%),

the overall performance was very fluctuating owing to the no uniform movement of the

carriers in the reactor that obstructed the carrier fluidization. The average COD removal

efficiency at 10, 20, 30 and 40% filling rates were 75.7, 91.1, 85.5 and 79.6%

respectively. These results also showed that the MBBR system achieved higher DOC

and COD removal efficiency at 20% PE carrier filling rate under the same condition of

influent organic loading rate.

0

10

20

30

40

50

60

70

80

1 3 5 7 9 11 13 15 17 19 21Time (Days)

TN

rem

oval

eff

icie

ncy

(%)

10% carriers 20% Carriers30% carriers 40% carriers

83

Figure 4.15 DOC removal efficiency at different PE carrier filling rates

Figure 4.16 COD removal efficiency at different PE carrier filling rates


aeration rates

Aeration plays a vital role on the microbial growth and development, as well as its

stability on the carriers and its movement throughout the reactor. Aeration supplies the

microbial oxidation with oxygen and also enhances the turbulent intensity of fluid,

which are important for the efficiency of wastewater treatment (Li et al., 2011).

0102030405060708090

100

0 5 10 15 20Time (Days)

CO

D r

emov

al e

ffici

ency

(%)

10% carriers 20% carriers30% carriers 40% carriers

86

88

90

92

94

96

98

100

1 3 5 7 9 11 13 15 17 19 21

Time (Days)

DO

C r

emov

al e

ffici

ency

(%) 10% carriers 20% carriers

30% carriers 40% carriers

84

Therefore, it is important to provide suitable aeration rate for the stable operation of

MBBR.


Figure 4.17 shows the trend of PO4-P removal efficiency of MBBR at different aeration

rates during the time period of 19 days. As demonstrated in Figure 4.18, in the MBBR

filled with 20% carriers, the average PO4-P removal efficiency achieved were 27.6, 65.9

and 47.3% at aeration rates of 2.5, 4.5 and 6 L/min, respectively. The effective PO4-P

removal in MBBR with 20% filling rate at aeration rate of 4.5 L/min due to the

favorable condition that helped to move the PE carriers uniformly throughout the

reactor which led to sufficient transfer of DO, nutrient and organic components.

Figure 4.17 PO4-P removal efficiency at different aeration rates

Figure 4.18 Average PO4-P removal efficiency at different aeration rates

10

20

30

40

50

60

70

80

2.5 4.5 6

Aeration rate (L/min)

PO4-P

rem

oval

effic

iency

(%)

0

1020

30

4050

60

7080

90

1 3 5 7 9 11 13 15 17 19

Time (Days)

PO4-P

rem

oval

effic

ency

(%)

2.5 L/min. 4.5 L/min. 6 L/min.

85


The trend of NH4-N removal efficiency of MBBR at different aeration rates during the

time period of 19 days is presented in Figure 4.19 and 4.20. The average NH4-N

removal at aeration rates of 2.5, 4.5 and 6 L/min were 74.8, 66.1 and 68.5%

respectively. Similarly, the trend of TN removal efficiency in the MBBR at different

aeration rates is displayed in Figure 4.21. The average TN removal achieved at 2.5, 4.5

and 6 L/min aeration rates were 25.4, 49.3 and 43.9% respectively which indicated that

simultaneous nitrification denitrification (SND) took place in the reactor. The TN

removal rate at 4.5 L/min aeration rate was higher compared to 2.5 and 6 L/min aeration

rate at the constant HRT of 25 h. Since the reactor was operated continuously in an

aerobic condition, the TN removal might be obtained due to DO gradient in the biofilm

layer.

Figure 4.19 NH4-N removal efficiency at different aeration rates

0

10

2030

40

50

6070

80

90

1 3 5 7 9 11 13 15 17 19

Time (Days)

NH

4-N

rem

oval

effi

cenc

y (%

)

2.5 L/min 4.5 L/min 6 L/min

86

Figure 4.20 Average NH4-N removal efficiency at different aeration rates

Figure 4.21 TN removal efficiency at different aeration rates


It was observed in this experiment that the MBBR filled with 20% carriers at different

aeration rates demonstrated the best results in DOC removal (Figure 4.22). For an

influent DOC of around 120 – 130 mg/L, the effluent DOC was achieved around 5 - 6

mg/L at the influent flow rate of 8 mL/min. That means the average DOC removal was

above 94% at all three different aeration rates. Similarly, at all three aeration modes, the

20

30

40

50

60

70

80

2.5 4.5 6Aeration rate (L/min)

NH

4-N

rem

oval

effi

cien

cy (%

)

010

203040

5060

7080

1 3 5 7 9 11 13 15 17 19

Time(Days)

TN

rem

oval

effi

cenc

y (%

) 2.5 L/min 4.5 L/min 6 L/min

87

COD removals were more than 85% (Figure 4.23), which demonstrated that the

presence of sufficient DO (4 mg/L) did not affect the organic removal efficiency even at

the different aeration rates. Rahimi et al. (2011) also demonstrated this in their

experimental study.

Figure 4.22 DOC removal efficiency at different aeration rates

Figure 4.23 COD removal efficiency at different aeration rates

82

84

86

88

90

92

94

96

98

1 3 5 7 9 11 13 15 17 19Time (Days)

DO

C r

emov

al e

ffici

ency

(%)

2.5 L/min. 4.5 L/min. 6 L/min.

75

80

85

90

95

100

1 3 5 7 9 11 13 15 17 19Time (Days)

CO

D r

emov

al e

ffice

ncy

(%) 2.5 L/min. 4.5 L/min. 6 L/min.

88


HRTs


From this set of experiment it was found that the HRT had significant effect on the PO4-

P removal. It can be demonstrated from Figure 4.24 that the PO4-P removal increased

with decreasing HRT. As shown in Figure 4.25, the average PO4-P removal efficiency

obtained were 65.9, 40.2, 52.0, 57.6 and 81.8% at HRTs of 25, 12, 8, 5 and 2 h

respectively. At 25 h of HRT, the system consumed more phosphorus for the microbial

growth while the consumption rate decreased at HRT of 12 h and the consumption rate

again increased and reached its peak at HRT of 2 h. The high PO4-P removal at HRT of

25 h was because of the consumption of phosphorus by the attached microorganisms in

the carriers for their growth while at 12 h HRT, the biomass growth on the carriers

became constant which caused the decreased PO4-P removal. When the HRT again

reduced to 8, 5 and 2 h respectively the OLRs in the reactor increased and that led to the

increased biomass growth rate on the carriers. As a result, the PO4-P removal also

increased.

Figure 4.24 PO4-P removal efficiency at different HRTs

0102030405060708090

100

1 3 5 7 9 11 13 15 17 19Time (Days)

PO4-

P re

mov

al e

ffici

ency

(%) 25h 12h 8h 5h 2h

89

Figure 4.25 Average PO4-P removal efficiency at different HRTs


The trend of NH4-N removal efficiency at different HRTs during 20 days period is

shown in Figure 4.26. the ammonium loading rate in the system at the HRTs of 25, 12,

8,5 and 2 h were 18.2, 38, 57, 91.2 and 228 NH4-N/m3.d respectively. This experimental

results suggested that the increased ammonium loading rate led to the increase in

nitrification rate. It may be because of the presence of a thin layer of heterotrops biofilm

on the surface of the PE carriers and higher density of nitrifiers developed on the PE

carriers which enhanced the nitrification in the system. The oxygen concentration,

ammonium concentration and organic loading are the three main factors which

determine the nitrification rate (Kermani et al., 2009; Chen et al., 2008). As shown in

Figure 4.27, the average NH4-N removal efficiency at the ammonium loading rate of

18.2 g NH4-N/m3.d was 66.1% while it increased to 71.2% at an ammonium loading

rate of 228 g NH4-N/m3.d. The TN removals at different HRTs are given in Figure 4.28.

The results showed that at HRT of 2 h, the lab scale MBBR had an average TN removal

efficiency of 67.4% during the operation, while the TN removals were 49.3, 49, 52.5

and 63% at HRTs of 25, 12, 8 and 5 h respectively.

0

10

2030

40

50

6070

80

90

25 12 8 5 2HRT (h)

PO

4-P re

mov

al ef

ficien

cy (%

)

90

Figure 4.26 NH4-N removal efficiency at different HRTs

Figure 4.27 Average NH4-N removal efficiency at different HRTs

Figure 4.28 TN removal efficiency at different HRTs

0

10

20

30

40

50

60

70

80

1 3 5 7 9 11 13 15 17 19Time (Days)

TN re

mov

al ef

ficen

cy (%

)

25h 12h 8h 5h 2h

60

62

64

66

68

70

72

18.24 38 57 91.2 228NH4-N loading rate (G NH4-N/m3.D)

NH4-N

rem

oval

effici

ency

(%)

20

30

40

50

60

70

80

1 3 5 7 9 11 13 15 17 19Time (Days)

NH

4-N

rem

oval

effi

cien

cy (%

)

25h 12h 8h 5h 2h

91


As shown in the Figure 4.29, the DOC removal efficiency was evaluated at different

HRTs in the continuous aerobic MBBR. It was observed that the average DOC removal

efficiency was more than 94% at all the HRT conditions. However, the average DOC

removal efficiency was observed highest at HRT of 2 h which was 96% while the HRTs

of 25, 12, 8 and 5 h had 95, 94, 94 and 94% of removal, respectively. Similarly, the

experimental results indicated that the average COD removal efficiency at all the HRTs

was above 80% however the highest COD removal was achieved at HRT of 2 h (Figure

4.30). When the HRT was decreased from 25 h to 12, 8, 5 and 2 h with constant influent

COD concentration of 330 – 360 mg/L, the organic loading rate (OLR) started to

increase from 0.33 kg COD/m3.d to 0.69, 1.035, 1.66 and 4.14 kg COD/m3.d,

respectively. The average COD removal efficiency at 25, 12 and 8 h HRTs were

gradually declinded (91.9, 86.7 and 80.8%, respectively), while the removal efficiency

was again increased to 90.3 and 91.4% at the HRTs of 5 and 2 h respectively. The

results evidence that the organic removal was due to microbial metabolism in the

system. It was observed from the experimental results that HRT had little effect on the

performance of continuous aerobic MBBR in case of DOC and COD removal. As

shown in Table 3.1 in Chapter 3, the synthetic wastewater contains totally

biodegradable compounds, which is one of the factors for the high DOC and COD

removal from the system. Similarly, the high concentration of biomass accumulated in

the PE carriers and its high activity which were developed and increased respectively

due to decreasing HRT i.e. increasing OLR, is the other factor for the high DOC and

COD removal.

92

Figure 4.29 DOC removal efficiency at different HRTs

Figure 4.30 COD removal efficiency at different HRTs

In conclusion, the optimum operating conditions in terms of carrier filling rate, aeration

rate and HRT for MBBR system are 20% filling rate over effective volume of the

reactor, 4.5 L/min and 2 h respectively.

85

90

95

100

1 3 5 7 9 11 13 15 17 19Time (Days)

DO

C r

emov

al e

ffici

ency

(%)

25h 12h 8h 5h 2h

60

70

80

90

100

1 3 5 7 9 11 13 15 17 19Time (Days)

CO

D r

emov

al e

ffici

ency

(%

)

25h 12h 8h 5h 2h

93

4.2 Evaluation of the performance of MBBR-MF System

The concept of MBBR-MF system is that the biofilm in MBBR removes nutrient and

organic matters from the wastewater and the MF physically separates the biomass and

colloidal matters from the effluent. The removal efficiencies are described in detailed

below.

4.2.1 Nutrient and organic removal

After finalization of the optimum operating conditions for the MBBR in terms of PE

carrier filling rate and aeration rate the MBBR-MF system was operated at different

HRTs of 12, 8.5 and 2 h to evaluate the nutrient and organic removal efficiency. The

corresponding fluxes for these HRTs were 5, 7.5, 12 and 30 L/m2.h respectively. A

constant supply of aeration at the rate of 1.35 m3/m2.h was maintained to the membrane

filtration system all the time. Before connecting the MBBR with membrane filtration

unit at each flux, the MBBR was continuously operated for 20 days. After completion

of each cycle, the flat sheet membrane unit was subjected to chemical cleaning

procedure before starting the new cycle. The combined system was operated until there

occurred a sudden TMP jump or the TMP was constant or uniform even after 20 days of

the operation. The combined system was operated for 20, 20, 6 and 3 days at different

fluxes of 5, 7.5, 12 and 30 L/m2.h respectively. After operation of the system for the

above mentioned period, sudden rise in TMP i.e. membrane resistance of 4.0×1011,

5.1×1011 and 5.3×1011 m-1 were observed at fluxes of 7.5, 12 and 30 L/m2.h respectively

while the system was still at constant TMP of 0.61×1011 m-1at a flux of 5 L/m2.h.

The result of nutrient and organic removal from this combined system gave the DOC

and COD removal efficiencies of 94 - 96% and 89 - 95% respectively at all the flux

conditions. Which means the system was successful to remove organic compounds from

the wastewater. Similarly, the PO4-P removal efficiency were 38.9, 31.4, 38.7 and 86%

at fluxes of 5, 7.5, 12 and 30 L/m2.h respectively, while at the same fluxes, the

respective NH4-N removal efficiency obtained were 73.6, 76.6, 77.6 and 72.1%. These

results clearly indicated that system was successfully achieved higher PO4-P removal at

the flux of 30 L/m2.h while the same system achieved higher NH4-N removal at the flux

94

of 12 L/m2.h. The average concentration of NO2-N and NO3-N on the feed water was

0.01 and 1.7 mg/L respectively. After MBBR-MF treatment process from, the

concentration of NO2-N and NO3-N increased to 0.23 and 5.8 mg/L respectively. These

results indicated the nitrification process occurred in the treatment system.

When comparing the removal efficiencies after the MBBR treatment and after the

MBBR-MF treatment, it was observed that the organic removal efficiency was quite

similar but the nutrient removal efficiency was quite different. The comparative results

are tabulated in Table 4.5.

Table 4.5 Comparison of organic and nutrient removal between MBBR and MBBR–MF systems at different filtration fluxes (aeration rate: 1.35 m3/m2.h, membrane area: 0.2 m2)

Flux (L/m2.h)

After MBBR (%) After MBBR-MF (%)

DOC COD PO4-P NH4-N DOC COD PO4-P NH4-N

5.0 93.7 86.7 40.2 64.0 94.7 95.0 38.9 73.6

7.5 94.2 80.8 51.9 65.8 94.4 89.5 31.4 76.6

12.0 94.6 90.3 57.6 71.4 95.0 90.3 38.7 77.6

30.0 96.0 91.4 81.8 71.1 96.0 89.0 86.0 72.1

4.2.2 Membrane resistance characteristics at different permeate flux

conditions

MLSS concentration is one of the most important factors affecting membrane fouling or

membrane resistance (Rahimi et al., 2011). Membrane fouling not only reduces the

treatment quality and capacity of the system but also decreases the membrane life.

Therefore, the effect of MBBR permeate on MF fouling was studied by measuring the

membrane resistance at different permeate fluxes of 5, 7.5, 12 and 30 L/m2.h (the

corresponding fluxes for these HRTs were 5, 7.5, 12 and 30 L/m2.h respectively). The

membrane resistance was calculated as a function of the rate of change of TMP

development with flux. The calculated membrane resistance of the clean membrane was

3.96E+10 m-1.From this experiment, it was clearly demonstrated that the membrane

resistance increased with increased flux. During the experimental period, as

demonstrated in Figure 4.31, it was observed that at the flux of 5 L/m2.h, the total

95

membrane resistance was around 0 to 1.5×1011 m-1 during 20 days of operation and

there was no sign of rise in membrane resistance even after 20 days of operation while

there was a sudden rise in membrane resistance (from 0 to 5.3×1011 m-1) only after 3

days of operation at the flux of 30 L/m2.h. This could be because of high amount of

suspended solids accumulated on the reactor due to increase in OLR with increased flux

and its accumulation on the membrane surface. This accumulated solid in turn formed a

cake layer onto the membrane surface as shown in Figure 4.32. From these

experimental results, it was observed that permeate flux plays determining role in

membrane resistance control. It has been also demonstrated by Nguyen et al., 2012;

Johir et al., 2012; Zhang et al., 2006 in their research based on MBR.

Figure 4.31 Effect of permeate flux on total membrane resistance (aeration rate: 1.35 m3/m2.h, membrane area: 0.2 m2)

Figure 4.32 Cake layer formations on the surface of flat sheet membrane module

Cake layer formation

0.E+00

1.E+11

2.E+11

3.E+11

4.E+11

5.E+11

6.E+11

0 2 4 6 8 10 12 14 16 18 20Time (Days)

Mem

bran

e res

istan

ce (m

-1)

Flux 5 L/m2.h Flux 7.5 L/m2.h

Flux 12 L/m2.h Flux 30 L/m2.h

96

Therefore to reduce membrane resistance or membrane fouling, there should be lower

permeate flux rate in the system. This can be explained by the difference in suction

pressure produced on the membrane surface at different fluxes. However, the TMP

jump or higher membrane resistance at higher flux might not be only due to the flux but

also due to change in structure of cake layer developed on the membrane surface

(Zhang et al., 2006). From the literature, it is clear that the main factor in membrane

resistance is Rc (Le-Clech et al., 2006; Meng et al., 2008). It can be also seen in this

experimental result. As shown in Table 4.6, the membrane fouling occurred in the short

period when the Rc was higher. As we can see from the Table 4.6, with the increased

permeate flux, the RT also increased. It was because of the increased Rc and Rp due to

higher flux. It might be because at higher flux the deposition of suspended solids onto

the membrane surface should be faster and the cake layer developed should be stable

and stronger than that built at lower flux. Which ultimately cause the decreased

treatment quality and increased frequency of membrane cleaning (both physical and

chemical).

Table 4.6 Rc, Rp, Rm and RT at different permeate fluxes (aeration rate: 1.35 m3/m2.h,

membrane area: 0.2 m2)

Flux (L/m2.h)

Cake layer resistance (Rc)

Pore block resistance (Rp)

Membrane resistance (Rm)

Total resistance

(RT) (m-1) % of RT (m-1) % of RT (m-1) % of RT (m-1)

5.0 5.38E+10 35.63 5.76E+10 38.15 3.96E+10 26.22 1.51E+11

7.5 1.49E+11 53.91 8.76E+10 31.74 3.96E+10 14.35 2.76E+11

12.0 2.79E+11 54.23 1.96E+11 38.08 3.96E+10 7.70 5.15E+11

30.0 3.88E+11 73.16 1.03E+11 19.37 3.96E+10 7.47 5.30E+11

97

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

MBBR is gaining impetus around the world. Its application in Australia for wastewater

treatment is also growing. It is a leading edge wastewater treatment technology as this

system can operate at smaller footprints and give higher removal efficiency. Therefore

this research study mainly focused on determination of optimum operating conditions

for MBBR to enhance higher nutrient and organic removal efficiency. The research also

evaluated the MBBR-MF system for nutrient and organic removal efficiency and

membrane resistance behavior at different permeate fluxes. From this study, it was

demonstrated that the optimum operating condition for the effective nutrient and

organic removal efficiency at 12 L volume of the reactor were; 20% of PE carrier filling

rate by the volume of reactor, 4.5 L/min aeration rate and HRT of 2 h. At that condition,

the attached biomass developed on and inside the carriers can adsorbed enough foods

(nutrient and organic matters) and DO from the wastewater and at the same time

prevented the loss of the biomass from the carriers enhancing growth of thin layer of

biomass in the carriers and improved the nutrient and organic removal efficiency. The

supplied aeration produced the high kinetic energy and the PE carriers moved uniformly

inside the reactor. It was also demonstrated in this experiment that the DOC and COD

removal was not significantly affected by the different operating conditions.

The key findings during the study of the determination of optimum carrier filling rate

are listed below:

There was a relationship between the biofilm thickness on the PE carriers and its

filling rate on the reactor. The biofilm thickness on the PE carriers increased

with increased filling rates of PE carriers in the reactor.

Higher removal efficiency was observed with a thin biofilm layer on the

carriers. It was because in thin biofilm layers high rate of substrate diffusion

took place through the micro channels in the biofilm.

At 20% filling rates of PE carriers by volume of the reactor, the average NH4-N

and PO4-P removal obtained were 66.1 and 65.9% respectively.

98

The key findings during the study of the determination of optimum aeration rate follow

as below:

The different aeration rates influenced the biofilm development on the carriers,

its stability on the carriers and movement of the carriers throughout the reactor.

At higher aeration rate (6 L/min), the biomass on the carriers was easily washed

off due to the stronger turbulence.

At lower aeration rate (2.5 L/min), the thick biomass layer was formed on the

carriers which were not effective and did not enhance the nutrient removal

efficiency. It was because thick biofilm layers could block the micro channels in

the biofilm through which substrate diffusion took place. Thus, the substrate

diffusion was reduced and caused a reduction in removal efficiency.

Following findings were extracted from the study of the effect of different HRTs on

nutrient removal from MBBR:

HRT had significant effect on nutrient removal. The NH4-N and PO4-P removal

increased with decreased HRT.

The low HRT enhanced the high nitrification process in the system and gave

higher NH4-N removal efficiency mianly due to the development of higher

density of nitrifiers on the PE carriers.

The results of OUR for suspended biomass on the reactor and the attached biomass on

the PE carriers at different operating conditions demonstrated that the microbial activity

by the attached biomass on the PE carriers was stronger than the suspended biomass on

the wastewater. These findings indicated that the removal efficiency achieved by the

system was because of the attached biomass layer developed on and inside the PE

carriers.

Similarly, the experiment on the MBBR–MF at different fluxes was conducted to

evaluate nutrient and organic removal efficiency. From the experimental results it was

found that the organic and nutrient removal particularly NH4-N removal after MBBR–

MF system was significantly higher compared to treatment after MBBR. Therefore, it

was concluded that the MBBR–MF is suitable for the higher organic and nutrient

removal efficiency. At the same time, it was also observed that the flux had a strong

effect on membrane fouling or membrane resistance. It was noticed that with the

99

increased flux, membrane fouling also increased. Therefore, the system should operate

at an optimum flux condition which helps to reduce the membrane fouling and increase

the membrane life.

5.2 Recommendations for Future Research

The following recommendations have been made for the future research in order to

achieve higher nutrient and organic removal from this type of system:

The further research on MBBR system to improve PO4-P removal efficiency

would be interesting. Enhanced biological treatment (providing oxic, anoxic and

anaerobic environment in the system) or chemical removal techniques using

metal salts (e.g. iron, aluminium etc.) can be helpful to improve PO4-P removal.

This study was carried out using PE carriers as biofilm carriers. It would be

interesting to compare the removal efficiency using different types of biofilm

carriers at different filling volumes.

As this study was carried out on synthetic wastewater similar to PTSE, it will be

worth to carry out the same investigation using real municipal wastewater and

industrial wastewater such as oil recovery wastewater to verify the effectiveness

of this system and implement this type of system in practical field.

Further detailed investigation on the MBBR–MF system is recommended.

Aeration is the most costly factor in terms of energy consumption. Therefore the

investigation area on this system can be extended to varying aeration rate in MF

reactor and its influence on the fouling behavior. In-depth study of foulants will

be also helpful in order to develop biofouling control strategies.

The detailed investigation on effect of different organic loading rate on MBBR–

MF system can also be the useful investigation for this type of system.

100

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110

Appendix A

pH, DO, T, MLSS, MLVSS, COD, DOC, NH4-N, PO4-P and TN data for MBBR at

different PE carrier filling rates

111

Table A1. pH, DO and T in MBBR at different PE carrier filling rates ( flow rate; 8

mL/min, aeration rate; 4.5 L/min)

pH DO (mg/L) T (⁰C) Days Remarks 7.35 9.50 20.30 1

10% PE carrier filling rate by volume of reactor

6.65 9.50 21.40 3 4.80 9.50 21.00 5 6.78 9.28 20.40 7 6.92 9.07 21.70 10 6.67 8.58 22.20 12 6.68 8.57 22.00 14 6.31 7.96 21.60 16 6.58 7.41 22.30 18 6.55 7.48 21.10 20 5.38 5.54 21.60 21 20% PE carrier filling

rate by volume of reactor

5.12 5.24 21.10 24 4.67 5.08 20.90 26 4.87 5.11 20.60 28 4.77 4.24 19.90 30 4.69 4.08 20.50 32 4.64 4.04 20.50 37 4.63 3.43 22.00 40 4.51 4.36 22.40 41 30% PE carrier filling


4.66 4.76 22.3 44 4.80 5.22 22.40 46 4.80 5.24 22.40 48 4.88 4.72 20.50 50 4.75 4.61 19.80 53 4.75 4.29 19.90 55 5.53 3.42 22.30 57 5.42 3.26 21.70 60 5.15 3.07 20.80 61 40% PE carrier filling


5.33 2.99 20.30 65 5.22 2.71 20.70 67 4.80 2.67 21.20 69 5.22 2.54 19.20 70 3.91 2.38 19.60 73 4.78 2.36 19.70 75 4.52 2.33 20.10 80

112

Table A2. MLSS and MLVSS in MBBR at different PE carrier filling rates (flow rate;

8 ml/min, aeration rate; 4.5 L/min)

MLSS (g/L) MLVSS (g/L) Days Remarks

1.30 1.30 1

10% PE carrier filling rate by

volume of reactor

0.70 0.70 3 0.35 0.35 5 0.30 0.30 7 0.20 0.20 10 0.20 0.20 12 0.25 0.25 14 0.20 0.15 16 0.25 0.35 18 0.20 0.20 20 0.25 0.70 21


volume of reactor

0.25 0.30 24 0.20 0.30 26 0.20 0.00 28 0.20 0.05 30 0.20 0.20 32 0.25 0.25 37 0.25 0.30 39 0.25 0.20 40 0.25 0.05 41


volume of reactor

0.25 0.25 44 0.15 0.30 46 0.25 0.30 48 0.20 0.30 50 0.15 0.25 53 0.20 0.55 55 0.25 0.20 56 0.30 0.30 57 0.20 0.10 59 0.20 0.05 60 0.25 0.35 61


volume of reactor

0.10 0.35 62 0.20 0.15 65 0.25 0.20 67 0.20 0.15 69 0.10 0.25 70 0.20 0.25 73 0.15 0.15 75 0.10 0.20 77 0.25 0.20 80

113

Table A3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different

PE carrier filling rates (flow rate; 8 mL/min, aeration rate; 4.5 L/min)

DOC removal efficency

(%)

COD removal efficency

(%)

PO4-P removal efficency

(%)

NH4-N removal efficency

(%)

TN removal efficency

(%)

Days Remarks

96.11 73.50 28.38 6.25 55.48 1


94.07 61.35 84.52 67.68 54.39 5 93.45 68.90 73.89 72.13 64.46 7 91.90 81.70 56.63 47.37 42.70 10 91.34 84.75 50.00 56.41 50.33 12 94.22 81.36 44.30 65.79 56.64 14 93.99 83.88 35.14 47.31 33.71 16 92.36 87.17 45.72 38.98 24.11 18 91.64 87.04 44.82 44.44 31.34 20 94.12 89.29 62.15 54.29 9.56 21


95.03 91.92 63.96 54.02 25.44 24 95.31 92.24 68.63 50.46 34.22 28 95.79 96.36 67.08 55.37 41.00 30 95.89 91.98 67.83 72.85 63.35 32 96.10 92.20 66.08 77.14 61.63 37 96.65 81.34 63.16 76.47 57.81 39 96.80 95.07 76.17 81.06 61.60 40 95.22 83.53 29.81 72.00 55.48 41


94.97 85.71 31.05 66.67 56.79 46 96.17 80.40 43.92 66.67 57.05 48 95.56 87.30 57.99 54.29 42.70 50 97.92 86.27 55.75 50.89 35.14 53 97.97 93.20 47.99 59.09 23.01 55 95.18 88.10 30.50 57.79 33.71 56 92.87 87.30 15.97 25.74 6.60 57 95.61 83.94 41.99 48.10 38.80 59 95.15 86.45 40.75 60.59 31.34 60 95.09 88.05 54.42 75.61 27.64 61


95.17 79.60 49.70 68.45 36.12 62 96.16 75.81 36.86 73.00 48.10 65 93.74 69.44 25.34 72.73 34.50 67 90.41 78.46 33.96 60.61 18.59 69 90.23 86.64 30.09 61.54 61.46 70 92.84 86.40 25.32 68.42 68.33 73 91.89 65.48 22.26 70.81 70.72 75 94.71 81.30 24.76 70.00 53.48 77 94.58 79.84 23.72 73.13 73.05 80

114

Appendix B


different aeration rates

115

Table B1. pH, DO and T of MBBR at different aeration rates( flow rate; 8 mL/min, PE

carrier filling rate; 20%)

pH DO(mg/L) T (⁰C) Days Remarks 5.10 4.16 22.80 1 6 L/min aeration rate 3.84 4.12 22.80 3 4.73 3.96 23.30 5 4.48 3.75 21.50 7 4.25 4.04 22.50 9 4.64 4.00 20.60 11 4.25 4.15 18.80 14 4.43 4.23 22.00 15 3.99 4.12 20.30 18 4.01 3.97 20.80 20 4.08 3.95 21.40 21 2.5 L/min aeration

rate 4,.17 3.78 22.00 22 4.02 3.88 21.50 25 4.11 4.00 21.10 27 4.04 3.90 20.60 30 4.19 3.77 21.00 32 4.40 3.57 20.70 34 4.14 3.53 20.90 35 3.90 3.54 20.10 39 4.14 3.50 20.80 40

116

Table B2. MLSS and MLVSS in MBBR at different aeration rates (flow rate; 8

mL/min, PE carrier filling rate; 20%)

MLSS (g/L) MLVSS (g/L) Days Remarks 0.10 0.15 1

at 6 L/min

0.30 0.35 3 0.15 0.25 5 0.10 0.05 7 0.15 0.30 10 0.15 0.15 12 0.15 0.10 14 0.05 0.25 16 0.25 0.25 18 0.30 0.45 20 0.35 0.30 21

at 2.5 L/min

0.20 0.20 24 0.30 0.20 25 0.10 0.40 26 0.20 0.20 28 0.20 0.25 30 0.20 0.55 32 0.30 0.35 34 0.05 0.10 35 0.10 0.20 37 0.25 0.70 40

117

Table B3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different

aeration rates (flow rate; 8 mL/min, PE carrier filling rate; 20%)

DOC removal efficency (%)

COD removal efficency (%)

PO4-P removal efficency (%)

NH4-N removal efficency (%)

TN removal efficency (%)

Days Remarks

87.59 85.45 65.31 35.71 5.11 1

6 L/min

93.85 86.67 56.45 70.89 49.13 3 94.38 86.03 54.17 70.89 45.07 5 95.34 85.71 49.62 70.89 43.40 7 94.28 86.22 44.28 68.35 41.53 9 95.46 88.21 44.80 70.89 47.56 11 94.56 88.89 37.73 74.68 48.69 13 94.29 88.79 38.83 75.95 50.18 15 94.37 88.05 39.49 75.95 51.33 17 94.20 88.89 42.12 70.89 40.99 19 94.47 90.87 40.36 70.89 37.75 21

2.5 L/min

94.19 90.39 30.74 73.33 24.92 23 95.03 90.95 26.85 73.33 27.08 25 95.51 90.83 21.45 76.00 43.19 27 95.11 91.91 22.01 75.34 15.37 29 95.03 92.14 33.24 75.34 13.57 31 95.72 94.74 29.79 76.00 15.83 33 95.69 95.28 25.00 75.48 21.64 35 94.73 96.41 21.93 77.22 25.85 37 94.82 98.21 24.47 75.32 28.96 39

118

Appendix C


different HRTs

119

Table C1. pH, DO and T of MBBR at different HRTs ( aeration rate; 4.5 L/min, PE

carrier filling rate; 20%)

pH DO(mg/L) T ( C) Days Remarks 4.07 3.66 21.60 1

12 h

3.76 3.41 21.30 5 3.67 3.35 21.70 6 3.72 3.48 21.40 7 3.70 3.40 21.60 8 3.55 3.58 20.40 10 4.08 3.50 21.00 15 3.99 3.47 21.20 20 3.89 3.40 21.70 35 4.19 3.56 22.60 40 4.11 3.44 23.20 41

8 h

4.13 3.28 21.80 44 4.04 3.61 21.10 50 4.25 3.85 20.90 54 4.30 4.06 20.90 55 4.22 4.23 21.10 60 4.15 4.13 21.60 63 4.22 4.00 22.30 65 4.07 4.18 21.90 70 4.30 4.13 21.80 75 3.85 4.19 21.50 79 3.78 4.15 22.10 80

5 h

4.35 4.17 22.50 85 4.16 4.24 22.30 90 4.10 4.13 22.60 92 3.90 3.76 23.00 95 4.01 3.60 23.00 97 3.99 3.75 23.70 99 4.00 3.96 21.90 100 3.25 3.71 22.40 102 3.99 4.16 22.10 105 4.59 3.64 22.30 107

2 h

4.05 2.23 22.60 110 4.19 2.54 21.80 112 4.29 2.64 21.60 115 4.13 2.54 22.80 118 4.16 2.54 22.30 120 4.10 2.50 22.60 122 3.90 2.66 23.00 125 4.10 2.54 21.50 127 4.13 2.64 21.60 130

120

Table C2. MLSS and MLVSS of MBBR at different HRTs (aeration rate; 4.5 L/min,

PE carrier filling rate; 20%)

MLSS (g/L) MLVSS (g/L) Days Remarks 0.20 0.55 1

12 h

0.20 0.10 5 0.10 0.10 7 0.20 0.20 9 0.15 0.40 15 0.10 0.10 21 0.20 0.30 25 0.10 0.10 35 0.10 0.15 40 0.25 0.55 41

8 h

0.15 0.35 47 0.10 0.05 51 0.25 0.05 55 0.10 0.10 61 0.10 0.25 63 0.30 0.30 65 0.30 0.35 75 0.30 0.25 79 0.30 0.30 80

5 h

0.20 0.15 85 0.05 0.05 87 0.10 0.10 90 0.25 0.05 92 0.20 0.25 95 0.15 0.20 97 0.10 0.25 100 0.25 0.20 102 0.25 0.20 105 0.30 0.30 107

2 h

0.30 0.20 110 0.35 0.25 112 0.40 0.40 115 0.30 0.25 118 0.35 0.35 120 0.30 0.25 122 0.30 0.30 125 0.40 0.35 127 0.35 0.30 130

121

Table C3. DOC, COD, PO4-P, NH4-N and TN removal efficiency in MBBR at different

HRTs (aeration rate; 4.5 L/min, PE carrier filling rate; 20%)

DOC removal

efficiency (%)

COD removal

efficiency (%)

PO4-P removal

efficiency (%)

NH4-N removal

efficiency (%)

TN removal

efficiency (%)

Days Remarks

93.49 76.47 49.25 62.50 46.22 1

12 h

93.84 82.72 48.59 56.67 45.82 5 94.86 80.00 50.93 65.05 44.95 7 95.00 92.00 46.38 71.05 53.91 9 92.66 86.09 41.16 68.23 45.75 11 93.12 92.15 20.36 68.13 56.57 13 94.58 89.88 29.33 60.53 50.27 15 94.51 91.57 41.87 71.67 61.28 18 93.06 93.55 33.33 65.00 45.13 20 95.16 75.08 50.84 78.31 62.57 41

8 h

95.38 72.09 42.00 56.46 37.52 45 93.78 83.08 45.94 59.72 35.98 47 94.01 75.20 56.09 67.74 52.11 49 92.68 84.15 52.17 67.86 57.09 51 94.37 86.07 45.99 53.70 46.93 53 94.12 80.82 45.95 56.60 50.08 55 94.29 87.57 55.22 70.64 63.13 57 94.22 87.37 63.32 71.46 65.28 59 95.52 87.57 63.32 71.46 65.28 80

5 h

94.87 89.37 58.96 63.95 54.41 83 94.10 89.43 55.36 72.76 62.30 85 93.92 90.95 53.42 73.08 64.38 87 94.31 89.80 63.32 71.46 61.08 89 93.82 91.32 58.96 63.95 53.08 91 95.32 91.63 55.36 72.76 60.68 93 95.32 90.91 53.42 73.08 59.31 95 94.88 90.79 55.67 75.86 75.86 97 94.57 91.02 57.93 76.11 76.11 99 94.90 73.08 53.42 73.08 59.62 107

2 h

95.66 67.06 90.23 67.06 62.70 111 95.27 65.00 92.44 65.00 60.92 113 95.42 69.51 90.99 69.51 64.07 115 96.77 70.51 84.94 70.51 65.32 117 96.81 75.86 82.00 75.86 75.86 119 96.37 74.19 81.61 74.19 74.19 121 96.78 75.08 83.61 75.08 75.08 123 96.81 74.13 83.65 74.13 74.13 125

122

Appendix D

NO2-N and NO3-N data for MBBR at different PE carrier filling rates, aeration rates

and HRTs

123

Table D1. NO2-N and NO3-N data for MBBR at different PE carrier filling rates

(aeration rate; 4.5 L/min, flow rate; 8 mL/min)

NO2-N (mg/L) NO3-N (mg/L) Days Remarks Influent Effluent Influent Effluent

0.01 0.24 2.70 17.80 1


0.01 0.03 2.80 6.70 3 0.01 0.08 2.40 3.20 5 0.01 0.06 2.40 2.20 7 0.01 0.21 1.10 2.20 10 0.01 0.57 2.00 2.80 12 0.01 1.05 2.00 3.30 14 0.00 0.39 1.60 3.20 16 0.01 0.35 1.20 3.20 18 0.00 0.39 1.70 2.90 20 0.01 0.05 0.70 11.90 21


0.02 0.07 1.10 7.30 24 0.02 0.02 1.40 3.90 26 0.09 0.02 1.60 4.00 28 0.03 0.01 1.10 3.20 30 0.03 0.01 0.90 3.20 32 0.00 0.00 2.40 3.10 39 0.01 0.01 1.70 4.20 40 0.01 0.01 1.40 3.10 41


0.00 0.01 1.50 24.30 44 0.00 0.01 1.30 9.60 46 0.01 0.01 2.50 5.60 48 0.00 0.04 1.10 5.20 50 0.00 0.03 2.00 4.80 53 0.01 0.02 2.00 5.30 55 0.01 0.02 1.60 5.60 56 0.02 0.02 1.90 6.20 57 0.01 0.01 1.40 4.70 60 0.01 0.01 1.20 10.70 61


0.01 0.02 1.80 5.90 65 0.01 0.02 1.90 8.80 67 0.01 0.02 2.00 10.90 69 0.01 0.02 2.30 4.90 70 0.01 0.02 1.90 5.90 73 0.01 0.23 2.30 7.20 75 0.01 0.01 2.30 7.20 77 0.01 0.02 1.90 7.10 80

124

Table D2. NO2-N and NO3-N data for MBBR at different aeration rates (PE carrier

filling rate; 20%, flow rate; 8 mL/min)


0.01 0.02 1.00 7.90 1

6 L/min

0.03 0.02 1.90 4.40 3 0.03 0.02 1.50 4.90 5 0.02 0.02 1.00 4.90 7 0.03 0.04 1.00 4.80 9 0.02 0.02 1.00 4.20 11 0.01 0.03 1.40 4.80 13 0.01 0.02 1.40 2.00 15 0.01 0.02 1.90 4.80 17 0.02 0.02 1.50 5.60 19 0.02 0.03 1.90 6.40 21

2.5 L/min

0.01 0.02 0.60 7.70 23 0.01 0.01 0.50 7.30 25 0.02 0.01 2.60 6.40 27 0.01 0.01 1.00 9.60 29 0.01 0.01 1.60 10.40 31 0.02 0.01 2.10 10.80 33 0.01 0.02 2.00 9.90 35 0.02 0.02 1.20 9.00 37 0.02 0.02 1.10 8.10 39

125

Table D3. NO2-N and NO3-N data for MBBR at different HRTs (PE carrier filling rate;

20%, aeration rate; 4.5 L/ min)


0.01 0.02 1.50 4.70 1

12 h

0.01 0.02 1.70 4.10 3 0.03 0.02 1.20 3.90 5 0.02 0.00 1.00 4.30 7 0.02 0.02 1.20 3.80 9 0.01 0.01 0.90 4.80 11 0.01 0.01 1.40 4.30 13 0.03 0.01 1.40 4.60 15 0.02 0.01 1.20 4.20 18 0.01 0.06 0.90 6.40 20 0.01 0.03 1.60 6.50 41

8 h

0.01 0.29 1.20 6.70 43 0.00 0.26 1.80 4.80 45 0.02 0.07 1.80 5.90 47 0.01 0.05 1.70 5.60 49 0.01 0.02 1.70 3.70 51 0.01 0.01 1.80 4.60 53 0.00 0.01 1.30 4.10 55 0.00 0.01 1.90 3.40 59 0.00 0.01 1.90 3.10 80

5 h

0.00 0.01 1.90 3.90 83 0.01 0.01 1.90 3.40 85 0.01 0.01 2.30 3.30 87 0.01 0.01 2.30 5.00 89 0.01 0.01 2.00 4.40 91 0.00 0.01 2.30 4.00 93 0.00 0.01 1.90 4.70 95 0.01 0.02 1.90 4.60 107

2 h

0.00 0.01 1.70 4.90 109 0.00 0.01 1.90 4.40 111 0.01 0.01 1.90 4.00 113 0.01 0.01 1.80 5.10 115 0.01 0.01 1.90 4.70 117

126

Appendix E

Total membrane resistance (RT), DOC, COD, PO4-P and NH4-N data for MBBR–MF

system at fluxes

127

Table E1. Total membrane resistance at different fluxes

Flux (L/m2.h)

RT x1011 (m-1) Days Remarks

5

0.61 1 0.90 4 0.90 7 1.12 10 1.01 12 1.19 15 0.61 19

7.5

0.26 1 0.50 4 1.15 7 2.09 10 3.07 12 3.82 15 3.96 19

12

0.21 1 0.42 2 0.56 3 0.67 4 1.28 5 5.15 6 6.44 7

30 0.19 1 3.77 2 5.30 3

128

Table E2. DOC, COD, PO4-P and NH4-N removal efficiency in MBBR-MF at different

HRTs

DOC removal

efficiency (%)

COD removal

efficiency (%)

PO4-P removal

efficiency (%)

NH4-N removal

efficiency (%)

Days Remarks

95.64 94.51 39.16 66.67 1

12 h

94.52 96.39 38.82 69.23 4 94.07 95.48 40.63 63.93 7 93.49 95.15 42.64 63.33 10 93.70 94.28 42.31 83.46 12 94.92 94.84 37.58 86.18 15 94.08 94.19 32.00 83.33 19 94.83 88.08 42.50 73.46 1

8 h

95.26 88.43 35.26 76.13 4 93.38 84.15 34.45 74.64 7 94.06 93.61 31.42 83.00 10 94.43 93.61 30.74 79.25 12 94.01 93.20 21.55 75.07 15 95.08 92.10 23.20 74.75 19 94.78 87.04 55.36 85.31 1

5 h 94.82 90.94 48.97 79.50 2 94.60 91.32 62.45 74.29 3 95.57 92.24 33.56 70.71 4 95.07 92.00 33.78 77.05 5 96.27 85.20 84.59 65.03 1

2 h 95.74 89.50 83.50 77.50 2 96.17 92.20 91.00 74.12 3

129

Appendix F

Figure of all the equipments used in this experiment

130

Figure F1. Oven

Figure F2. Furnace

131

Figure F3. pH meter (HANNA instrument, model no. HI 9025)

Figure F4. DO meter (HORIBA Ltd. Japan, model no. OM -51E)

132

Figure F5. COD Sample heater and a photometry

Figure F6. Analytikjena multi N/C 3100

133

Figure F7. Spectroquant® cell test (NOVA 60, Merck)

Figure F8. YSI 5300 Biological oxygen monitor

134

Figure F9. GFC Whatman’s 1.2 μm filter paper, and syringe filters (0.45 and 1.20μ)

Figure F10. Ultrasonic cleaner (POWER SONIC 405, Thermoline scientific)

specific moving bed biofilm reactor in nutrient removal from

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