m. sc. final report (md. nazmul haque, roll-1295)

A REVIEW ON THE TREATMENT TECHNOLOGIES OF INDUSTRIAL

WASTEWATER

A Project Report Submitted to the Department of Environmental Sciences,

Jahangirnagar University, in Partial Fulfillment of the Requirements for the Degree

of MASTER OF SCIENCE (M.Sc.) IN ENVIRONMENTAL SCIENCE

Course No. Env.530

SUBMITTED BY

Exam. Roll: Env. 060518

Reg. No: 17756

Session: 2005-2006

Department of Environmental Sciences

Jahangirnagar University

Savar, Dhaka-1342

September, 2008

i

DEDICATED

TO

MY BELOVED

PARENTS

ii

ABSTRACT

Different types of technologies used for the treatment of industrial wastewater were

summarized in this review paper and the removal efficiency of the technologies were

reviewed by collecting data from the treatment technologies used for the removal of

particular parameters. It was found that, internal circulation (IC) anaerobic reactor &

sequencing batch reactor (SBR) are efficient techniques for BOD5 removal, sequencing

batch reactor (SBR) is efficient technique for COD removal, predenitrification system is

efficient technique for TOC removal, circulating bioreactor is efficient technique for total

nitrogen (TN) removal and internal circulation (IC) anaerobic reactor & sequencing batch

reactor (SBR) are efficient techniques for ammonia nitrogen (NH3-N) removal, various

yeast species and sequencing batch reactor (SBR) are efficient techniques for

phosphorus removal. A large amount of untreated industrial wastewater is released into

surrounding areas of the industries daily in Bangladesh. So, these technologies can be

used for the treatment of industrial wastewater in Bangladesh to control industrial

pollution.

iii

List of Acronyms and Abbreviations

BOD Biochemical Oxygen Demand

COD Chemical Oxygen Demand

TOC Total Organic Carbon

TN Total Nitrogen

TP Total Phosphorus

PAH Polycyclic Aromatic Hydrocarbons

SS Suspended Solids

VOCs Volatile Organic Compounds

DO Dissolved Oxygen

DoE Department of Environment

EPA Environmental Protection Agency

AEPA Australian Environmental Protection Authority

iv

CONTENTS

Dedication ………………………………………………………………………………………………………. i

Abstract ………………………………………………………………………………………………………….. ii

List of Acronyms and Abbreviations ……………………………………………………………….. iii

Contents …………………………………………………………………………………………………………. iv-x

List of Tables …………………………………………………………………………………………………… viii

List of Figures …………………………………………………………………………………………………. ix-x

CHAPTER ONE: INTRODUCTION

01-25

1.1 General …………………………………………………………………………………….. 01

1.2 Wastewater…………………………………………………………………………….... 02

1.3 Composition of Wastewater …………………………………………………….. 02

1.4 Types of wastewater………………………………………………………………….. 03

1.5 Industrial wastewater ……………………………………………………………….. 04

1.6 Sources of industrial wastewater ……………………………………………… 05

1.6.1 Agricultural waste …………………………………………………………………….. 05

1.6.2 Iron and steel industry ………………………………………………………………. 08

1.6.3 Mines and quarries …………………………………………………………………… 08

1.6.4 Food industry ……………………………………………………………………………. 09

1.6.5 Complex organic chemicals industry …………………………………………. 10

1.6.6 Nuclear industry ……………………………………………………………………….. 10

1.7 Nature and Characteristics of industrial wastewater ………………… 10

1.7.1 Physical Characteristics …………………………………………………………….. 11

1.7.2 Chemical Characteristics …………………………………………………………… 13

1.7.3 Biological Characteristics …………………………………………………………… 17

v

1.8 Wastewater treatment ……………………………………………………………… 18

1.9 Industrial wastewater treatment ………………………………………………. 19

1.10 History of wastewater treatment ……………………………………………… 19

1.11 Necessity of wastewater treatment ………………………………………….. 20

1.12 Impacts of wastewater ……………………………………………………………… 21

1.12.1 Impacts of wastewater on human health …………………………………. 21

1.12.2 Effects of phosphorus on fish and other forms of aquatic life …… 22

1.12.3 Toxicity of heavy metals on microorganisms …………………………….. 22

1.13 Industrial scenario of Bangladesh ……………………………………………… 23

1.14 Objectives …………………………………………………………………………………. 25

CHAPTER TWO: MATERIALS AND METHODS

26-70

2.1 Wastewater Treatment Technologies ……………………………………….. 26

2.2 Wastewater Treatment Methods ……………………………………………… 26

2.2.1 Physical unit operations ……………………………………………………………. 27

2.2.1.1 Screening ………………………………………………………………………………….. 27

2.2.1.2 Comminution ……………………………………………………………………………. 29

2.2.1.3 Flow equalization ……………………………………………………………………… 29

2.2.1.4 Sedimentation ………………………………………………………………………….. 30

2.2.1.5 Flotation …………………………………………………………………………………… 32

2.2.1.6 Granular medium filtration ……………………………………………………….. 34

2.2.2 Chemical unit processes ……………………………………………………………. 34

2.2.2.1 Chemical precipitation ……………………………………………………………… 34

2.2.2.2 Adsorption with activated carbon …………………………………………….. 36

2.2.2.3 Disinfection ………………………………………………………………………………. 37

vi

2.2.2.4 Dechlorination ………………………………………………………………………….. 39

2.2.2.5 Other chemical applications ……………………………………………………… 39

2.2.3 Biological unit processes …………………………………………………………… 40

2.2.3.1 Activated-sludge process ………………………………………………………….. 41

2.2.3.2 Aerated lagoons ………………………………………………………………………… 43

2.2.3.3 Trickling filters ………………………………………………………………………….. 46

2.2.3.4 Rotating biological contactors …………………………………………………… 50

2.2.3.5 Stabilization ponds ……………………………………………………………………. 52

2.2.3.6 Completely mixed anaerobic digestion ……………………………………… 54

2.2.3.7 Biological nutrient removal ………………………………………………………. 56

2.2.3.7.1 Nitrification-denitrification ……………………………………………………….. 56

2.2.3.7.2 Phosphorus removal …………………………………………………………………. 57

2.3 Application of Treatment Methods …………………………………………… 58

2.3.1 Preliminary treatment ………………………………………………………………. 58

2.3.2 Primary treatment ……………………………………………………………………. 59

2.3.3 Secondary treatment ………………………………………………………………… 59

2.3.4 Tertiary/advanced wastewater treatment ………………………………… 59

2.4 Natural Treatment Systems ………………………………………………………. 60

2.4.1 Land treatment …………………………………………………………………………. 60

2.4.1.1 Slow rate …………………………………………………………………………………… 61

2.4.1.2 Rapid infiltration ……………………………………………………………………….. 62

2.4.1.3 Overland flow …………………………………………………………………………… 62

2.4.2 Constructed wetlands ……………………………………………………………….. 63

2.4.2.1 Free water surface systems ………………………………………………………. 63

2.4.2.2 Subsurface flow systems …………………………………………………………… 64

vii

2.4.3 Floating aquatic plants ……………………………………………………………… 64

2.5 Recent techniques ……………………………………………………………………. 65

2.5.1 Sequencing batch reactor …………………………………………………………. 65

2.5.2 Membrane Bioreactors (MBR) …………………………………………………. 66

2.5.3 Upward-flow Anaerobic Sludge Bed (UASB) ……………………………… 68

2.5.4 Expanded Granular Sludge Bed (EGSB) ……………………………………… 69

2.5.5 Reversing Anaerobic Upflow System (RAUS) ……………………………. 70

CHAPTER THREE: RESULTS AND DISCUSSIONS

71-83

3 Removal of Individual parameters …………….………………………………. 71

3.1 BOD5 removal ……………………………………………………..……………………. 71

3.2 COD removal ……………………………………………………………………..……… 73

3.3 Total Organic Carbon (TOC) removal ………………………………………… 77

3.4 Nitrogen (N) removal ………………………………………………………………… 78

3.5 Phosphorus (P) removal ……………………………………………………………. 80

3.6 Selenium (Se) removal ……………………………………………………………… 82

3.7 Lead (Pb) removal …………………………………………………………………….. 82

3.8 Manganese (Mn) removal …………………………………………………………. 82

3.9 Suspended Solid (SS) removal …………………………………………………… 82

3.10 Odor removal ……………………………………………………………………………. 83

3.11 Color removal …………………………………………………………………………… 83

CHAPTER FOUR: CONCLUSION

84-88

CHAPTER FIIVE: REFERENCES

89-97

viii

LIST OF TABLES

Table No. Table Names Page No.

Table 1.1 Typical pollutant concentrations in a variety of industrial

wastewaters ………………………………………………………………………..

03

Table 1.2 Types of wastewater …………………………………………………………… 04

Table 1.3 Typical range of BOD and SS load for industrial wastewater… 11

Table 2.1 Screen types ……………………………………………………………………….. 28

Table 2.2 Basic flow equalization processes ……………………………………….. 30

Table 2.3 Flotation methods ………………………………………………………………. 33

Table 2.4 Removal efficiency of plain sedimentation vs. chemical

precipitation ………………………………………………………………………..

35

Table 2.5 Characteristics of common disinfecting agents 38

Table 2.6 Other chemical applications in wastewater treatment and

disposal ……………………………………………………………………………….

40

Table 2.7 Advantages and disadvantages of activated-sludge process... 43

Table 2.8 Advantages and disadvantages of trickling filter …………………. 50

Table 2.9 Advantages and disadvantages of rotating biological

contactor (RBC) ……………………………………………………………………

52

Table 2.10 Types and applications of stabilization ponds ……………………… 53

Table 2.11 Advantages and disadvantages of stabilization ponds ………… 54

Table 2.12 Mechanisms of wastewater constituent removal by SR

systems ……………………………………………………………………………….

61

Table 3.1 Removal efficiency of BOD5 ………………………………………………… 71

Table 3.2 Removal efficiency of COD …………………………………………………. 73

Table 3.3 Removal efficiency of nitrogen ……………………………………………. 78

Table 3.4 Removal efficiency of phosphorus ………………………………………. 80

ix

LIST OF FIGURES

Figure

No.

Figure Names Page

No.

Fig. 1.1 Sources of wastewater …………………………………………………………………… 05

Fig. 1.2 Wastewater discharging from dying industries ………………………………. 23

Fig. 2.1 Settling basin with horizontal flow ……………………….………………………… 32

Fig. 2.2 Typical flotation unit ………………………………………………………………………. 33

Fig. 2.3 A once-through chemical treatment system …………………………………… 36

Fig. 2.4 A typical granular activated carbon contactor ………………………………… 37

Fig. 2.5 Diagram of a simple activated sludge system ……………………….………… 41

Fig. 2.6 Typical flow diagram for an activated-sludge process ………….…………. 42

Fig. 2.7 Typical flow diagram for aerated lagoons …………….………………………… 44

Fig. 2.8 A Typical Surface-Aerated Basing …………………………………………………… 44

Fig. 2.9 Diagram of aerobic (top) and facultative (bottom) aerated lagoons… 45

Fig. 2.10 A typical complete trickling filter system ………………………………………… 48

Fig. 2.11 Cutaway view of a trickling filter …………………………………………………….. 49

Fig. 2.12 Typical flow diagram for trickling filters …………………………………………. 50

Fig. 2.13 RBC system configuration ………………………………………………………………. 51

Fig. 2.14 Schematic diagram of a typical rotating biological contactor (RBC)…. 51

Fig. 2.15 Typical flow diagram for RBC units …………………………………………………. 52

Fig. 2.16 Typical flow diagram for stabilization ponds …………………………………… 53

Fig. 2.17 Diagram of an anaerobic digestion process ……………………………………. 55

Fig. 2.18 Biological phosphorus removal systems …………………………………………. 58

Fig. 2.19 Various treatment levels in a wastewater treatment plant flow

diagram ………………………………………………………………………………………….

60

Fig. 2.20 Rapid infiltration treatment system ……………………………………………….. 63

Fig. 2.21 Free water surface system ……………………………………………………………… 63

Fig. 2.22 Subsurface flow system ………………………………………………………………….. 64

Fig. 2.23 Floating aquatic plants system ……………………………………………………….. 64

Fig. 2.24 Typical schematic for membrane bioreactor system ………………………. 67

x

Fig. 2.25 The upward-flow anaerobic sludge bed (UASB) reactor concept ……. 69

Fig. 2.26 The expanded granular sludge bed (EGSB) reactor concept ……………. 70

Fig. 2.27 The RAUS System ……………………………………………………………………………. 70

Fig. 4.1 BOD5 removal efficiencies of various techniques ….………………………… 84

Fig. 4.2 COD removal efficiencies of various techniques …………….………………. 85

Fig. 4.3 TOC removal efficiencies of various techniques ……………………………… 85

Fig. 4.4.1 Total nitrogen (TN) removal efficiencies of various techniques ………. 86

Fig. 4.4.2 Ammonia nitrogen (NH3-N) removal efficiencies of various

techniques ……………………………………………………………….……………………..

86

Fig. 4.5 Phosphorus removal efficiencies of various techniques ….……………… 87

Fig. 4.6 Removal efficiencies of various techniques used for the removal of

selenium (Se), lead (Pb) and manganese (Mn) ………………………………..

87

Fig. 4.7 Removal efficiencies of various techniques used for the removal of

suspended solid (SS), odor and color ………………………………………………

88

CHAPTER ONE

INTRODUCTION

1

1.1 General

Water has been and will continue to be a major factor for the survival of humans

and human activities that needs certain concern and protection. Because of the limited

resources of fresh water, careful use and frequent reuse after appropriate treatment are

requirements for sustainable development and a healthy life.

Many industries use large volumes of water in their manufacturing operations. Industrial

waste water treatment systems treat wastewater from an industrial or manufacturing

process such as a cooling tower, food or animal processing plant or any type of

manufacturing process that generates wastewater.

As industrial development in the world, mostly in newly industrialized countries grew

significantly, amounts of industrial wastewater have been drastically increasing each

year. The amounts of heavy metals and synthesized organic compounds generated by

industrial activities have increased and some 10,000 new organic compounds are added

each year. Nevertheless, these compounds are complex, difficult and costly to treat by

conventional wastewater treatment processes. For example, wastes from manufacturing

plants contribute to pollution generation and environmental degradation e.g. textile,

semiconductor, palm oil mill and rubber processing plants (Sairan and Ujang, 2004).

Much of the water used by homes, industries, and businesses must be treated before it

is released back to the environment. Nature has an amazing ability to cope with small

amounts of water wastes and pollution, but it would be overwhelmed if we didn't treat

the billions of gallons of wastewater and sewage produced every day before releasing it

back to the environment. Treatment plants reduce pollutants in wastewater to a level

nature can handle. Wastewater is used water. It includes substances such as human

waste, food scraps, oils, soaps and chemicals. Pollution of water by industrial effluents of

process industries is a serious problem in most countries. The major aim of wastewater

treatment is to remove as much of the suspended solids as possible before the

remaining water, called effluent, is discharged back to the environment.

2

Increasing urban populations and production growth boost volumes of wastewater.

In large parts of the world, substantial amounts of the discharges of domestic sewage

and industrial effluents are still untreated. And in urban areas with sewage treatment

plants, treatment capacities are often far exceeded by the rapid pace of urban growth

and development.

1.2 Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic

influence. It comprises liquid waste discharged by domestic residences, commercial

properties, industry, and/or agriculture and can encompass a wide range of potential

contaminants and concentrations. In the most common usage, it refers to the municipal

wastewater that contains a broad spectrum of contaminants resulting from the mixing

of wastewaters from different sources.

1.3 Composition of Wastewater

The composition of wastewater varies widely. This is a partial list of what it may contain:

• Water ( > 95%) which is often added during flushing to carry the waste down a

drain

• Pathogens such as bacteria, viruses, prions and parasitic worms.

• Non-pathogenic bacteria (> 100,000 / ml for sewage)

• Organic particles such as faeces, hairs, food, vomit, paper fibers, plant material,

humus, etc.

• Soluble organic material such as urea, fruit sugars, soluble proteins, drugs,

pharmaceuticals, etc.

• Inorganic particles such as sand, grit, metal particles, ceramics, etc.

• Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide,

hydrogen sulphide, thiocyanates, thiosulphates, etc.

• Animals such as protozoa, insects, arthropods, small fish, etc.

• Macro-solids such as sanitary towels, nappies/ diapers, condoms, needles,

children's toys, dead pets, body parts, etc.

• Gases such as hydrogen sulphide, carbon dioxide, methane, etc.

3

• Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils,

etc.

• Toxins such as pesticides, poisons, herbicides, etc.

Industrial wastewater quality varies among industries. Table 1.1 summarizes the typical

wastewater composition from various industrial sources.

Table 1.1: Typical pollutant concentrations in a variety of industrial wastewaters

Pollutant Units Pulp and

Paper

Petroleum

Refinery

Paint

Production

Textile

Mills

Starch

Production

BOD5 mg/L 100–500 10–800 – 75–6,300 1,500–8,000

COD mg/L 600–1,000 50–600 19,000 220–31,300 1,500–10,000

TSS mg/L 500–1,200 10-300 – 25–24,500 100–600

VSS mg/L 100–250 16,000 100–400 –

TDS mg/L – 1,500–3,000 – 500–3,000 –

NH4+ mg/L – 0.05–300 – – 10–100

TN mg/L – 90 10–30 150–600

TP mg/L – 1–10 25 – –

pH 6–8 8.5–9.5 6.9 6–12 3.5–8

Sulfates/

sulfides

mg/L – Nondetect–

400

TOC mg/L – 10–500

Oil and

Grease

mg/L – 10–700

Phenols mg/L – 0.5–100

(Adapted from a table in Kadlec and Knight, 1996)

1.4 Types of wastewater

The strength of wastewater depends mainly on the degree of water dilution.

Wastewater can therefore be categorized as strong, medium and weak. Strong

wastewater has a higher BOD level than medium wastewater and so on.

4

Table 1.2: Types of wastewater

Parameters Concentration (mg/l)

Strong Medium Weak

BOD5 400 220 110

COD 1,000 500 250

Organic Nitrogen 35 15 8

NH – N 50 25 12

Total Nitrogen 85 40 20

Total Phosphorous 15 8 4

Total solids 1,200 720 350

Suspended solids 350 220 100

Source: Sri Anant Wanasen, Asian Institute of Technology.

1.5 Industrial wastewater

Industrial wastewater is water discharged after being used in, or produced by, industrial

production processes and which is of no further immediate value to these processes.

Many chemical products such as detergents, surfactants, plasticizers, mineral oils, dyes,

dye carriers and auxiliary products are used in textile mill operations. A large proportion

of these products does not figure in the finished fabric, but ends up instead in the

wastewater in the form of organic pollutants.

Wastewaters produced in textile industries originate in the process of dyeing and

washing the fabrics and during equipment cleaning. Wastewater compositions vary

widely, depending on the type of the fabrics currently treated and the type of

technological dyeing process. Textile wastewaters are generally characterized by a deep

color, high values of chemical oxygen demands (COD) and biological oxygen demands

(BOD) and a high content of surfactants, oil, grease, and nitrocompounds (Molga et al.,

2006).

5

1.6 Sources of industrial wastewater

The sources of industrial wastewater are given below. Figure 1.1 shows the Sources of

wastewater.

Figure 1.1: Sources of wastewater (Metcalf and Eddy, 2003).

1.6.1 Agricultural waste

Agricultural wastewater treatment relates to the treatment of wastewaters produced in

the course of agricultural activities. As agriculture is a highly intensified industry in many

parts of the world, the range of wastewaters requiring treatment can encompass at least

the following:

� Animals wastes - both liquid and solid

6

� Silage liquor

� Pesticide run off and surpluses

� Milking parlor wastes including milk

� Slaughtering waste

� Vegetable washing water

� Fire water

a) Animal wastes

The constituents of animal wastewater typically contain

� Strong organic content—much stronger than human sewage

� High solids concentration

� High nitrate and phosphorus content

� Antibiotics

� Synthetic hormones

� Often high concentrations of parasites and their eggs

� Spore of cryptosporidium - a bacterium resistant to drinking water treatment

processes

� Spore of Giardia

� Human pathogenic bacteria such as Brucella and Salmonella

Animal wastes from cattle can be as produced as solid or semisolid manure or as liquid

slurry. The production of slurry is especially common in housed dairy cattle.

b) Piggery waste

Piggery waste is comparable to other animal wastes except that many piggery wastes

contain elevated levels of copper that can be toxic in the natural environment. Ascarid

worms and their eggs are also common and can infect humans if wastewater treatment

is ineffective.

c) Silage liquor

Fresh or wilted grass or other green crops can be made into the semi fermented product

called silage which can be stored and used as winter forage for cattle and sheep. The

7

production of silage often involves the use of an acid conditioner such as sulfuric acid or

formic acid. The process of silage making frequently produces a yellow-brown strongly

smelling liquid which is very rich in simple sugars, alcohol, short-chain organic acids and

silage conditioner. This liquor is one of the most polluting organic substances known.

The volume of silage liquor produced is generally in proportion to the moisture content

of the ensiled material.

d) Pesticide runoff and surpluses

Inappropriate use of pesticides so that pesticide-containing wastewaters enter the

environment can give rise to severe and long-lasting ecological damage. This is

particularly true for insecticides used in sheep dips because of the volumes of pesticide-

containing wastewater requiring disposal and because of the persistent and damaging

nature of the pesticides.

e) Milking parlor wastes including milk

Although milk has a deserved reputation as an important and valuable food product, its

presence in wastewaters is highly polluting because of its organic strength, which can

lead to very rapid de-oxygenation of receiving waters. Milking parlor wastes also contain

large volumes of wash-down water, some animal waste together with cleaning and

disinfection chemicals.

f) Slaughtering waste

Wastewater from slaughtering activities is similar to milking parlor waste although

considerably stronger in its organic composition and therefore potentially much more

polluting.

g) Vegetable washing water

Washing of vegetables produces large volumes of water contaminated by soil and

vegetable pieces. Low levels of pesticides used to treat the vegetables may also be

present together with moderate levels of disinfectants such as chlorine.

8

h) Fire water

Although few farms plan for fires, fires are nevertheless more common on farms than on

many other industrial premises. Stores of pesticides, herbicides, fuel oil for farm

machinery and fertilizers can all help promote fire and can all be present in

environmentally lethal quantities in wastewater from firefighting at farms.

1.6.2 Iron and steel industry

The production of iron from its ores involves powerful reduction reactions in blast

furnaces. Cooling waters are inevitably contaminated with products especially ammonia

and cyanide. Production of coke from coal in coking plants also requires water cooling

and the use of water in by-products separation. Contamination of waste streams

includes gasification products such as benzene, naphthalene, anthracene, cyanide,

ammonia, phenols , cresols together with a range of more complex organic compounds

known collectively as polycyclic aromatic hydrocarbons (PAH).

The conversion of iron or steel into sheet, wire or rods requires hot and cold mechanical

transformation stages frequently employing water as a lubricant and coolant.

Contaminants include hydraulic oils, tallow and particulate solids. Final treatment of iron

and steel products before onward sale into manufacturing includes pickling in strong

mineral acid to remove rust and prepare the surface for tin or chromium plating or for

other surface treatments such as galvanization or painting. The two acids commonly

used are hydrochloric acid and sulfuric acid. Wastewaters include acidic rinse waters

together with waste acid. Although many plants operate acid recovery plants,

(particularly those using Hydrochloric acid), where the mineral acid is boiled away from

the iron salts, there remains a large volume of highly acid ferrous sulfate or ferrous

chloride to be disposed of. Many steel industry wastewaters are contaminated by

hydraulic oil also known as soluble oil.

1.6.3 Mines and quarries

The principal waste-waters associated with mines and quarries are slurries of rock

particles in water. These arise from rainfall washing exposed surfaces and haul roads

and also from rock washing and grading processes. Volumes of water can be very high,

9

especially rainfall related arisings on large sites. Some specialist separation operations

such as coal washing to separate coal from native rock using density gradients can

produce wastewater contaminated by fine particulate hematite and surfactants. Oils and

hydraulic oils are also common contaminants. Wastewater from metal mines and ore

recovery plants are inevitably contaminated by the minerals present in the native rock

formations. Following crushing and extraction of the desirable materials, undesirable

materials may become contaminated in the wastewater. For metal mines, this can

include unwanted metals such as zinc and other materials such as arsenic. Extraction of

high value metals such as gold and silver may generate slimes containing very fine

particles in where physical removal of contaminants becomes particularly difficult.

1.6.4 Food industry

Wastewater generated from agricultural and food operations have distinctive

characteristics that set it apart from common municipal wastewater managed by public

or private wastewater treatment plants throughout the world: it is biodegradable and

nontoxic, but that has high concentrations of biochemical oxygen demand (BOD) and

suspended solids (SS). The constituents of food and agriculture wastewater are often

complex to predict due to the differences in BOD and pH in effluents from vegetable,

fruit, and meat products and due to the seasonal nature of food processing and post

harvesting.

Processing of food from raw materials requires large volumes of high grade water.

Vegetable washing generates waters with high loads of particulate matter and some

dissolved organics. It may also contain surfactants.

Animal slaughter and processing produces very strong organic waste from body fluids,

such as blood, and gut contents. This wastewater is frequently contaminated by

significant levels of antibiotics and growth hormones from the animals and by a variety

of pesticides used to control external parasites. Insecticide residues in fleeces are a

particular problem in treating waters generated in wool processing.

10

Processing food for sale produces wastes generated from cooking which are often rich in

plant organic material and may also contain salt, flavorings, coloring material and acids

or alkali. Very significant quantities of oil or fats may also be present.

1.6.5 Complex organic chemicals industry

A range of industries manufacture or use complex organic chemicals. These include

pesticides, Pharmaceuticals, paints and dyes, petro-chemicals, detergents, plastics etc.

Waste waters can be contaminated by feed-stock materials, by-products, product

material in soluble or particulate form, washing and cleaning agents, solvents and added

value products such as plasticizers.

1.6.6 Nuclear industry

The waste production from the nuclear and radio-chemicals industry is dealt with at

radioactive waste treatment

1.7 Nature and Characteristics of industrial wastewater

It is only natural for industry to presume that its wastewater can best be disposed of in

the domestic sewer system. However, city authorities should not accept any wastewater

discharges into the domestic sewer system without first learning the facts about the

characteristics of the wastewater, the sewage system’s ability to handle them, and the

effects of the wastewater upon all components of the city disposal system. The following

table gives a comparison between the typical range of BOD and S.S. load for industrial

wastewater. A typical range of BOD and S.S. load for industrial wastewater is shown in

table 1.3.

11

Table 1.3: Typical range of BOD and SS load for industrial wastewater

Origin of waste

Biochemical oxygen

demand “BOD” (kg/ton

product)

Total Suspended solids

“TSS” (kg/ton product)

Dairy industry 5.3 2.2

Yeast industry 125 18.7

Starch & glucose industry 13.4 9.7

Fruits & vegetable canning

industry

12.5 4.3

Textile industry 30 - 314 55 - 196

Pulp & paper industry 4 - 130 11.5 - 26

Beverage industry 2.5 - 220 1.3 - 257

Tannery industry 48 - 86 85 - 155

Secondary treatment standards for wastewater are concerned with the removal of

biodegradable organics, suspended solids, and pathogens. Many of the more stringent

standards that have been developed recently deal with the removal of nutrients and

priority pollutants. When wastewater is to be reused, standards normally include

requirements for the removal of refractory organics, heavy metals, and in some cases

dissolved inorganic salts.

1.7.1 Physical Characteristics

The most important physical characteristic of wastewater is its total solids content,

which is composed of floating matter, settleable matter, colloidal matter, and matter in

solution. Other important physical characteristics include odor, temperature, color, and

turbidity.

a) Total Solids

Analytically the total solids content of a wastewater is defined as all the matter that

remains as residue upon evaporation at 103 to 105°C. Matter that has a significant vapor

pressure at this temperature is lost during evaporation & is not defined as a solid.

12

Settable solids are those solids that will settle to the bottom of a cone-shaped container

(called an Imhoff cone) in a 60 minute period.

The suspended solids are found in considerable quantity in many industrial wastewaters,

such as tannery and paper-mill effluents. They are screened and/or settled out at the

treatment plant. Solids removed by settling and separated from wash water are called

sludge, which may then be pumped to drying beds or filtered for extraction of additional

water (dewatering).

b) Odors

Odors are usually caused by gases produced by the decomposition of organic matter or

by substances added to the wastewater. Industrial wastewater may contain either

odorous compounds or compounds that produce odor during the process of wastewater

treatment.

c) Temperature

The temperature of water is a very important parameter because of its effect on

chemical reactions and reaction rates, aquatic life, and the suitability of the water for

beneficial uses. Increased temperature, for example, can cause a change in the species

of fish that can exist in the receiving water body. Industrial establishments that use

surface water for cooling-water purposes are particularly concerned with the

temperature of the intake water.

In addition, oxygen is less soluble in warm water than in cold water. The increase in the

rate of biochemical reactions that accompanies an increase in temperature, combined

with the decrease in the quantity of oxygen present in surface waters, can often cause

serious depletions in dissolved oxygen concentration in the summer months. When

significantly large quantities of heated water are discharged to natural receiving water,

these effects are magnified. It should also be realized that a sudden change in

temperature can result in a high rate of mortality of aquatic life. Moreover, abnormally

high temperatures can foster the growth of undesirable water plants and wastewater

fungus.

13

d) Color

Color of industrial wastewater varies according to the type of industry. Knowledge of

the character and measurement of color is essential. Since most colored matter is in a

dissolved state, it is not altered by conventional primary devices, although secondary

treatment units, such as activated sludge and trickling filters, remove a certain

percentage of some types of colored matter. Sometimes color matters need chemical

oxidation procedures for removal.

e) Turbidity

Turbidity, a measure of the light-transmitting properties of water, is another test used to

indicate the quality of wastewater discharges and natural waters with respect to

colloidal and residual suspended matter. In general, there is no relationship between

turbidity and the concentration of suspended solids in untreated wastewater. There is,

however, a reasonable relationship between turbidity and suspended solids for the

settled secondary effluent from the activated sludge process.

1.7.2 Chemical Characteristics

a) Organic Matter

Organic compounds are normally composed of a combination of carbon, hydrogen, and

oxygen, together with nitrogen in some cases. Other important elements, such as sulfur,

phosphorus, and iron, may also be present. Also, industrial wastewater may contain

small quantities of a large number of different synthetic organic molecules ranging from

simple to extremely complex in structure. Typical examples include surfactants, organic

priority pollutants, volatile organic compounds and agricultural pesticides. The presence

of these substances has complicated industrial wastewater treatment because many of

them either cannot be or are very slowly decomposed biologically.

Fats, Oils, and Grease: Fats are among the more stable of organic compounds and are

not easily decomposed by bacteria. Kerosene, lubricating oils reach the sewer from

workshops and garages, for the most part they float on the wastewater, although a

portion is carried into the sludge on settling solids.

14

Surfactants: Surfactants are large organic molecules that are slightly soluble in water

and cause foaming in wastewater treatment plants and in surface waters into which the

wastewater effluent is discharged. Surfactants tend to collect at the air-water interface.

During aeration of wastewater, these compounds collect on the surface of the air

bubbles and thus create very stable foam.

Phenols: Phenols and other organic compounds are also important constituents of

water. Phenols cause taste problems in drinking water, particularly when the water is

chlorinated. They are produced primarily by industrial operations and find their way to

surface waters via industrial wastewater discharges. Phenols can be biologically oxidized

at concentrations up to 500 mg/liter.

Volatile Organic Compounds (VOCs): Organic compounds that have a boiling point less

than < 100oC and/or a vapor pressure > 1 mm Hg at 25

oC are generally considered to be

volatile organic compounds (VOCs). The release of these compounds in sewers and at

treatment plants is of particular concern with respect to the health of collection system

and treatment plant workers.

Pesticides & Agricultural Chemicals: Trace organic compounds, such as pesticides,

herbicides, and other agricultural chemicals, are toxic to most life forms and therefore

can be significant contaminants of surface waters.

Parameters of Organic Content

Biochemical Oxygen Demand (BOD5)

The most widely used parameter of organic pollution applied to wastewater is the 5-day

BOD (BOD5). The BOD5 is usually exerted by dissolved and colloidal organic matter and

imposes a load on the biological units of the treatment plant. Oxygen must be provided

so that bacteria can grow and oxidize the organic matter. An added BOD5 load, caused

by an increase in organic waste, requires more bacterial activity, more oxygen, and

greater biological-unit capacity for its treatment.

15

The determination of the BOD5 involves the measurement of the dissolved oxygen used

by the microorganisms in the biochemical oxidation of organic matter. Several dilutions

of the wastewater are put into standard BOD5 bottles with water that has been

saturated with oxygen, and contains bacteria. A control bottle is also prepared with only

water and bacteria. The bottles are put into a standard incubator for five days; hence

this is called the “Five-Day BOD Test (BOD5).” The difference in oxygen levels between

the control bottle and the bottles with oxygen remaining is used to calculate the BOD5 in

mg/L.

Chemical Oxygen Demand (COD)

The COD test is used to measure the organic matter in industrial wastewater that

contains compounds that are toxic to biological life. It oxidizes the reduced compounds

in wastewater through a reaction with a mixture of chromic and sulfuric acid at high

temperatures. There is another COD test using permanganate as the oxidizing agent but

this test will give lower values and is not directly relatable to the standard COD test.

The COD of wastewater is, in general, higher than that of the BOD5 because more

compounds can be chemically oxidized than can be biologically oxidized. For many types

of wastewater, it is possible to correlate COD with BOD5. This can be very useful because

COD can be determined in 3 hours, compared with 5 days for the BOD5. Once the

correlation has been established, COD measurements can be used to good advantage

for treatment-plant control and operation.

The ratio of COD to BOD5 is usually 1.5:2 for industrial wastewater containing

biodegradable material (e.g. Food Industry). For wastewaters with ratios higher than 3,

it is assumed that some oxidizable material in the sample is not biodegradable.

Nonbiodegradable material sometimes is called refractory and found mainly in

wastewater from chemical and pulp & paper industries.

b) Inorganic Matter

Several inorganic components of wastewater are important in establishing and

controlling wastewater quality. Industrial wastewater has to be treated for removal of

16

the inorganic constituents that are added in the use cycle. Concentrations of inorganic

constituents also are increased by the natural evaporation process, which removes some

of surface water and leaves the inorganic substance in the wastewater.

pH: The hydrogen-ion concentration is an important quality parameter of wastewater.

The concentration range suitable for the existence of most biological life is quite narrow

and critical. Wastewater with an adverse concentration of hydrogen ion is difficult to

treat by biological means, and if the concentration is not altered before discharge, the

wastewater effluent may alter the concentration in the natural waters.

Alkalinity: Alkalinity in wastewater results from the presence of the hydroxides,

carbonates, and bicarbonates of elements such as calcium, magnesium, sodium,

potassium, or ammonia. Of these, calcium and magnesium bicarbonates are most

common. Borates, silicates, phosphates, and similar compounds can also contribute to

the alkalinity. The alkalinity in wastewater helps to resist changes in pH caused by the

addition of acids. The concentration of alkalinity in wastewater is important where

chemical treatment is to be used, in biological nutrient removal, and where ammonia is

to be removed by air stripping.

Nitrogen: Because nitrogen is an essential building block in the synthesis of protein,

nitrogen data will be required to evaluate the treatability of wastewater by biological

processes. Insufficient nitrogen can necessitate the addition of nitrogen to make the

wastewater treatable. Where control of algal growth in the receiving water is necessary

to protect beneficial uses, removal or reduction of nitrogen in wastewaters prior to

discharge may be desirable. The total nitrogen, as a commonly used parameter, consists

of many numerous compounds such as; NH3, NH4-N, NO3-N, NO2-N, urea, organic-N

(amines, amino acids etc.).

Phosphorus: Phosphorus is also essential to the growth of algae and other biological

organisms. The organically bound phosphorus is an important constituent of industrial

wastewater and sludge.

17

Sulfur: Sulfate is reduced biologically under anaerobic conditions to sulfide, which in

turn can combine with hydrogen to form hydrogen sulfide (H2S). Hydrogen sulfide

released to the atmosphere above the wastewater in sewers that are not flowing full

tends to accumulate at the crown of the pipe. The accumulated H2S can then be oxidized

biologically to sulfuric acid, which is corrosive to steel pipes and equipment.

Toxic Inorganic Compounds: Because of their toxicity, certain cations are of great

importance in the treatment and disposal of wastewater. Many of these compounds are

classified as priority pollutants. Copper, lead, silver, chromium, arsenic, and boron are

toxic in varying degrees to microorganisms and therefore must be taken into

consideration in the design of a biological treatment plant. Many plants have been upset

by the introduction of these ions to the extent that the microorganisms were killed and

treatment ceased. Other toxic cations include potassium and ammonium at 4000 mg/L.

Some toxic anions, including cyanides and chromates, are also present in industrial

wastewater. These are found particularly in metal-plating wastewater and should be

removed by pretreatment at the site of the industry rather than be mixed with the

municipal wastewater. Fluoride, another toxic anion, is found commonly in wastewater

from electronics manufacturing facilities. Organic compounds present in some industrial

wastewater are also toxic.

Heavy Metals: Trace quantities of Many metals, such as nickel (Ni), manganese (Mn),

lead (Pb), chromium (Cr), cadmium (Cd), zinc (Zn), copper (Cu), iron (Fe), and mercury

(Hg) are important constituents of some industrial wastewaters. The presence of any of

these metals in excessive quantities will interfere with many beneficial uses of the water

because of their toxicity; therefore, it is frequently desirable to measure and control the

concentration of these substances.

1.7.3 Biological Characteristics

Some industries have certain pathogenic organisms like slaughter houses others have

molds and fungi as starch and yeast factories. Biological tests on wastewater determine

whether pathogenic organisms are present by testing for certain indicator organisms.

Biological information is needed to assess the degree of treatment of the wastewater

18

before its discharge to the environment. The parameters setting the standards for the

discharge of different industrial wastewater effluents are outlined in table (2-4). Total

nitrogen is a commonly used parameter that includes a number of parameters, NH3,

NH4-N, NO3-N, NO2-N, urea, organic N such as amines, amino acids, proteins, etc.) and

process chemicals. The presence of these compounds depends on the production.

1.8 Wastewater treatment

Wastewater treatment is the process of removing contaminants from waste water, both

run-off (effluents) and domestic. It includes physical, chemical and biological processes

to remove physical, chemical and biological contaminants. Its objective is to produce a

waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or

reuse back into the environment. This material is often inadvertently contaminated with

many toxic organic and inorganic compounds.

The main function of a wastewater treatment plant is to remove biodegradable matter.

Thus, an important variable to record is the quantity of BOD in the influent entering the

plant and the quantity released by the plant in the treated effluent. The difference

constitutes an important measure of the treatment efficiency. Whereas a properly

functioning biological treatment plant may remove as much as 90% of BOD, a primary

treatment plant may remove only about 30% (Raddad, 2005).

Wastewater treatment plants act as the natural self-purification of water. The quality of

treated wastewater is largely depends on the type of treatment technology used. In

primary (mechanical) treatment, only settleable materials are separated from

wastewater, and the remainder is released again without further treatment. In

secondary (biological) treatment, organic material is mineralized through the action of

bacteria; the net result is that BOD is decreased. In advanced treatment, selected

minerals like phosphorus are removed by binding them into insoluble substances and

this treatment is more expensive than other methods.

19

1.9 Industrial wastewater treatment

Industrial wastewater treatment is a group of unit processes designed to separate,

modify, remove, and destroy undesirable substances carried by wastewater from

industrial sources. Industrial wastewater treatment covers the mechanisms and

processes used to treat waters that have been contaminated in some way by

anthropogenic industrial or commercial activities prior to its release into the

environment or its reuse.

The pattern of industrial wastewater treatment varies from country to country,

depending on prevailing economic and environmental policies and the penalties

incurred by industry for discharging polluted wastewater that fails to meet prescribed

standards (Hamer et al., 1985).

Industrial wastewater treatment can be either in form of pretreatment before discharge

into a public wastewater collecting system or as final treatment in an industrial

wastewater treatment plant before direct discharge to the environment.

1.10 History of wastewater treatment

In earlier years, the natural treatment process in streams and lakes was adequate to

perform basic wastewater treatment. The provision of high quality piped drinking water

to households took a fast development during the second part of the 19th

century as a

response to the rapid expansion of cities and to the wide spread occurrence of cholera

epidemics (referred to as the Asian disease) in Europe and the USA. The origin of water

borne diseases was not well understood until the famous microbiologists Louis Pasteur

and Robert Koch discovered the concept of pathogenic bacteria and their transmission

via contaminated water.

From a historic perspective, as communities have grown, so has the need for quality

water. The need to supply safe water, remove wastes from water and to protect public

health, have been the endeavors and concern of many generations.

20

International cooperation and the free exchange of ideas have been very influential in

accelerating development, particularly between 1850 and 1950. At this time there was a

considerable exchange of ideas between London and east coast cities in the US such as

New York and Boston which were experiencing rapid growth and problems in controlling

sewage linked diseases. A similar exchange of ideas has been seen within Europe and

continues to this day.

The trend in Europe over the last thirty years has been to organize water and

wastewater treatment on a river basin basis by using river basin authorities rather than

by municipal councils, as happened in earlier times. This has benefited the areas and

population by improving environmental protection and possibly also by lowering costs.

1.11 Necessity of wastewater treatment

Treatment facilities simply compress the organic decomposition processes which take

place in nature. This is performed by a combination of physical, biological, and chemical

treatment stages. Nature (receiving waters) can only accept small amounts of sewage

before becoming polluted, that is, natural bacteria feed on the sewage organics and

create an abnormal amount of dissolved oxygen uptake. Dissolved oxygen which exists

in minute amounts (10 parts per million at 20°C), is required by all marine life for

survival. One of the principle objectives of wastewater treatment is to prevent as much

of this "oxygen-demanding" organic material as possible from entering the receiving

water.

In case wastewater is disposed off without being treated, it can either lead to pollution

of groundwater or surface water bodies; hence it is necessary to treat the wastewater

before it is finally released. Pollution of surface water bodies or groundwater can take

place because wastewater is either disposed off by surface spreading or sub-surface

disposal or by a dilution method (Srinivasan et al., 2007)

To prevent any health hazards caused by discharging wastewater to water streams, the

wastewater must be treated before discharge. Such treatment should comply with the

terms of the legislation defining the characteristics of the effluent discharging in water

21

streams. The concept of planning and development should be based on the criteria to

protect land, water resources, aquatic life in streams and rivers and marine life from

pollution and to safeguard public health as a high priority.

1.12 Impacts of wastewater

For the first half of the 20th century, pollution in the urban water ways resulted in

frequent occurrences of low dissolved oxygen, fish kills, algal blooms and bacterial

contamination. Lowering of the concentration of dissolved oxygen (DO) and formation

of sludge are most common environmental disturbances which may damage aquatic

biota.

Heavy metals in wastewater come from industries and municipal sewage, and they are

one of the main causes of water and soil pollution. Accumulation of these metals in

wastewater depends on many local factors such as type of industries in the region,

people’s way of life and awareness of the impacts done to the environment by careless

disposal of wastes. As the focal point, wastewater treatment plants are expected to

control the discharge of heavy metals to the environment (Chipasa, 2003).

EPA (1974) reported that the pollutional parameters in textile wastewater effluents are

suspended solids, BOD, COD, nitrogen, phosphate, temperature, toxic chemicals

(phenol), chromium and heavy metals, pH, alkalinity-acidity, oils and grease, sulphides,

and coliform bacteria. Textile effluents are high in BOD due to fiber residues and

suspended solids (AEPA, 1998). They can contaminate water with oils, grease, and waxes

while some may contain heavy metals such as chromium, copper, zinc and mercury (EPA

1974). Dyeing process usually contributes chromium, lead, zinc and copper to

wastewater (Benavides, 1992). Copper is toxic to aquatic plants at concentrations below

1.0 mg/l while concentrations near this level can be toxic to some fish (Sawyer and

McCarty, 1978).

1.12.1 Impacts of wastewater on human health

By nature, industrial wastewater is a mixture of hundreds of compounds. Water

contaminated by human, chemical or industrial wastes can cause a number of diseases

22

through ingestion or physical contact. Water-related diseases include dengue, filariasis,

malaria, onchocerciasis, trypanosomiasis and yellow fever (Volkman, 2003).

Effluent generated by the industries is one of the sources of pollution. Contaminated air,

soil, and water by effluents from the industries are associated with heavy disease

burden. Some heavy metals contained in these effluents (either in free form in the

effluents or adsorbed in the suspended solids) from the industries have been found to

be carcinogenic while other chemicals equally present are poisonous depending on the

dose and exposure duration. These chemicals are not only poisonous to humans but also

found toxic to aquatic life and they may result in food contamination.

1.12.2 Effects of phosphorus on fish and other forms of aquatic life

Phosphorus can be toxic, but toxicity occurs rarely in nature and is generally not a

concern. Of more concern are the indirect effects of phosphorus. All algae and plants

require phosphorus to grow. Elevated phosphorus levels, however, can increase a

freshwater system’s productivity and result in large amounts of organic matter falling to

the bottom. Bacteria and other organisms decompose this matter and in the process use

a lot of oxygen. In very productive freshwater systems, the oxygen levels can be in such

short supply that fish kills occur. A type of algae, called cyanobacteria, grows particularly

well in high levels of phosphorus. Cyanobacterial blooms can cause a range of water

quality problems, including summer fish kills, bad odors and tainted drinking water.

Some cyanobacteria produce toxins that can kill livestock and wildlife.

1.12.3 Toxicity of heavy metals on microorganisms

Toxicity of heavy metals to microorganisms is well documented (Nies, 1999; Lester et al.,

1979). At certain concentrations, heavy metals are toxic to higher organisms,

microorganisms and plants. Therefore, their presence in wastewater is not only of great

environmental concern but also strongly reduces microbial activity, as a result adversely

affecting biological wastewater treatment processes. Heavy metals are reported to

inhibit nitrification and denitrification processes (Braam and Klapwijk, 1981; Waara,

1992) and reduced microbial oxidation of organic compounds (Ajmal et al., 1982, 1983;

Madoni et al., 1996). More over, the toxicity of heavy metals in wastewater is shown to

depend on factors like metal

wastewater pollution load (Dilek

of the metal ions (Surittanonta and Sherrod,

1.13 Industrial scenario

Industrialization began at a very slow pace in

focus on agro-based industries such as jute, cotton and sugar. After independence in

1971, interest grew but it was not until the late 1970s that industrialization increased

rapidly, driven primarily by the RMG (Rea

government initiatives were also undertaken to promote industrial growth, including the

establishment of industrial estates and export processing zones (EPZ). By late 1990, 60

industrial estates and two EPZs had been est

wastewater from industries.

There are now over 24,000 registered small

1998) and it is generally accepted there are an equivalent number unregistered.

However, industrialization has also brought with it a range of problems. The industries

tend to be clustered together and are highly polluting. As a consequence of the rapid

and largely unregulated development of these industries, many aquatic ecosystems are

now under threat and with them the livelihood systems of local people (Chadwick and

Clemett, 2002).

Figure 1.2

metal species and concentration, pH, sludge concentration,

(Dilek and Yetis, 1992; Imai and Gloyna, 1990) and

ittanonta and Sherrod, 1981).

of Bangladesh

Industrialization began at a very slow pace in Bangladesh in the 1950s with the primary

based industries such as jute, cotton and sugar. After independence in


rapidly, driven primarily by the RMG (Ready-made garment) industry. Several



industrial estates and two EPZs had been established. Figure 1.2 shows discharge of

There are now over 24,000 registered small-scale industrial units in Bangladesh (SEHD,


zation has also brought with it a range of problems. The industries



and with them the livelihood systems of local people (Chadwick and

1.2: Wastewater discharging from industries.

23

concentration,

and solubility

Bangladesh in the 1950s with the primary

based industries such as jute, cotton and sugar. After independence in


made garment) industry. Several



shows discharge of

scale industrial units in Bangladesh (SEHD,


zation has also brought with it a range of problems. The industries



and with them the livelihood systems of local people (Chadwick and

24

The Department of Environment (DoE) in the early 1990s carried out a survey of

industries, principally tanneries. The report found that acidic emissions from effluents

had the potential to cause serious respiratory disorders to the employees and residents

of the area and damage to buildings. However as industrial expansion has continued

since the 1980s, acute localized pollution is now threatening the sustainability of the

resource base and increasingly impacting on the health of the population (Ullah et al.

2006)

The main industrial areas are Dhaka, Chittagong, Khulna, and Bogra districts. The

Department of Environment has listed 1,176 factories that cause pollution. These are

categorized into the following 9 types.

1) Chemical including pharmaceutical

2) Paper and pulp

3) Sugar

4) Food and tobacco

5) Leather

6) Industrial dyes

7) Petroleum

8) Metals

9) Power generation

Bangladesh maintained agro-based industries, such as jute mills, sugar mills and cotton

spinning mills until the 1970’s. Only the sugar mills, sporadically situated in the north

and north western part of Bangladesh, had localized pollution problems with its wastes.

The recent growth of garment industries with their backward linkage sectors like

composite textile mills (including dyeing printing & finishing units), and leather

processing units (under SMDs) use substantial quantities of highly toxic dyes and

chemicals. Some of these industries are situated close to the river and dispose of their

toxic wastes there. Tanneries and some other textile finishing units, situated in land

locked areas, pose increasing pollution problems to the surroundings. Some government

owned large industries like, urea fertilizer, pulp and paper, etc. are creating more

25

pollution problems with their gaseous emissions and untreated effluent discharge into

the adjoining rivers. This threatens the lives of both humans and animals, as many of the

rural communities and animals rely on this water for their drinking supply.

Lube oil and heavy metals enter the coastal area water from the ship-breaking industries

in Chittagong, and several accidents have occurred. However, there is no assessment

available on the amount of lube oil discharged from ship-breaking industries (Ireen, T.

A., 2006).

So, it is necessary to use cost-effective and efficient treatment techniques which have

greater removal efficiency of particular parameters (e.g. BOD5, COD, TSS, Color) for the

treatment of industrial wastewater in Bangladesh.

1.14 Objectives

The objectives of this review paper are as follows:

1. To describe the techniques used for the treatment of industrial wastewater.

2. To find out the removal efficiencies of various techniques used for the removal of

particular parameters.

3. To find out the efficient techniques which have maximum removal efficiency of

particular parameters.

CHAPTER TWO

MATERIALS AND METHODS

26

2.1 Wastewater Treatment Technologies

Physical, chemical and biological methods are used to remove contaminants from

wastewater. In order to achieve different levels of contaminant removal, individual

wastewater treatment procedures are combined into a variety of systems, classified as

primary, secondary, and tertiary wastewater treatment. More rigorous treatment of

wastewater includes the removal of specific contaminants as well as the removal and

control of nutrients. Natural systems are also used for the treatment of wastewater in

land-based applications. Sludge resulting from wastewater treatment operations is

treated by various methods in order to reduce its water and organic content and make it

suitable for final disposal and reuse. The various conventional and advanced

technologies in current use and how they are applied for the effective treatment of

municipal wastewater are discussed below.

2.2 Wastewater Treatment Methods

Wastewater treatment methods are broadly classifiable into physical, chemical and

biological processes.

Wastewater treatment unit operations and processes:

1. Physical unit operations

� Screening

� Comminution

� Flow equalization

� Sedimentation

� Flotation

� Granular-medium filtration

2. Chemical unit operations

� Chemical precipitation

� Adsorption

� Disinfection

� Dechlorination

� Other chemical application

27

3. Biological unit operations

� Activated sludge process

� Aerated lagoon

� Trickling filters

� Rotating biological contactors

� Pond stabilization

� Anaerobic digestion

� Biological nutrient removal

2.2.1 Physical unit operations

Among the first treatment methods used were physical unit operations, in which

physical forces are applied to remove contaminants. Today, they still form the basis of

most process flow systems for wastewater treatment. This section briefly discusses the

most commonly used physical unit operations.

2.2.1.1 Screening

The screening of wastewater, one of the oldest treatment methods, removes gross

pollutants from the waste stream to protect downstream equipment from damage,

avoid interference with plant operations and prevent objectionable floating material

from entering the primary settling tanks. Screening devices may consist of parallel bars,

rods or wires, grating, wire mesh, or perforated plates, to intercept large floating or

suspended material. The openings may be of any shape, but are generally circular or

rectangular (Metcalf and Eddy, 1991). The material retained from the manual or

mechanical cleaning of bar racks and screens is referred to as “screenings”, and is either

disposed of by burial or incineration, or returned into the waste flow after grinding

(Metcalf and Eddy, 1991; WEF & ASCE, 1992). The principal types of screening devices

are listed in table 2.1.

28

Table 2.1: Screen types

Screen

category

Size of openings

(millimeters)

Application Types of screens

Coarse

screens

≥ 6 Remove large solids,

rags, and debris.

� Manually cleaned bar screens/trash

racks

� Mechanically cleaned bar

screens/trash racks

o Chain or cable driven with front

or back cleaning

o Reciprocating rake screens

o Catenary screens

o Continuous self-cleaning screens

Fine screens 1.5-6 Reduce suspended

solids to primary

treatment levels

� Rotary-drum screens

� Rotary-drum screens with outward

or inward flow

� Rotary-vertical-disk screens

� Inclined revolving disc screens

� Traveling water screens

� Endless band screen

� Vibrating screens

Very fine

screens

0.2-1.5 Reduce suspended

solids to primary

treatment levels

Microscreens 0.001-0.3 Upgrade secondary

effluent to tertiary

standards

Source: (Adapted from Liu and Liptak, 1992)

The coarse screen category includes manually or mechanically cleaned bar screens and

trash racks. Bar screens consist of vertical or inclined steel bars distributed equally

across a channel through which wastewater flows. They are used ahead of mechanical

equipment including raw sewage pumps, grit chambers, and primary sedimentation

tanks. Trash racks, for their part, are constructed of parallel rectangular or round steel

bars with clear openings. They are usually followed by regular bar screens or

comminutes. Criteria used in the design of coarse screens include bar size, spacing, and

29

angle from the vertical, as well as channel width and wastewater approach velocity (WEF

& ASCE, 1992).

Fine screens consist of various types of screen media, including slotted perforated

plates, wire mesh, woven wire cloth and wedge shaped wire. Due to their tiny openings,

fine screens must be cleaned continuously by means of brushes, scrapers, or jets of

water, steam, or air forced through the reverse side of the openings. The efficiency of a

fine screen depends on the fineness of the openings as well as the sewage flow velocity

through that opening (Liu and Liptak, 1999).

2.2.1.2 Comminution

Comminutors are used to pulverize large floating material in the waste flow. They are

installed where the handling of screenings would be impractical, generally between the

grit chamber and the primary settling tanks. Their use reduces odors, flies and

unsightliness. A comminutor may have either rotating or oscillating cutters. Rotating-

cutter Comminutors either engage a separate stationary screen alongside the cutters, or

a combined screen and cutter rotating together. A different type of comminutor, known

as a barminutor, involves a combination of a bar screen and rotating cutters.

2.2.1.3 Flow equalization

Flow equalization is a technique used to improve the effectiveness of secondary and

advanced wastewater treatment processes by leveling out operation parameters such as

flow, pollutant levels and temperature over a period of time. Variations are damped

until a near constant flow rate is achieved, minimizing the downstream effects of these

parameters.

Flow equalization may be applied at a number of locations within a wastewater

treatment plant, e.g. near the head end of the treatment works, prior to discharge into a

water body, and prior to advanced waste treatment operations. There are four basic

flow equalization processes that are summarized in table 2.2.

30

Table 2.2: Basic flow equalization processes

Process Description Illustration

Alternating

flow

diversion

Two basins alternating

between filling and

discharging for successive

time periods.

Intermittent

flow diversion

An equalization basin to

which a significant

increase in flow is

diverted. The diverted flow

is then fed into the system

at a controlled rate.

Completely

mixed,

combined

flow

A basin that completely

mixes multiple flows at the

front end of the treatment

process

Completely

mixed, mixed

flow

A large, completely mixed,

holding basin located

before the wastewater

facility, leveling

parameters in influent

stream and providing a

constant discharge.

Source: Adapted from Liu and Liptak, 1992.

2.2.1.4 Sedimentation

Sedimentation, a fundamental and widely used unit operation in wastewater treatment,

involves the gravitational settling of heavy particles suspended in a mixture. This process

is used for the removal of grit, particulate matter in the primary settling basin, biological

floc in the activated sludge settling basin, and chemical flow when the chemical

coagulation process is used.

Sedimentation takes place in a settling tank, also referred to as a clarifier. There are

three main designs, namely, horizontal flow, solids contact and inclined surface (Metcalf

and Eddy, 1991). In designing a sedimentation basin, it is important to bear in mind that

the system must produce both a clarified effluent and a concentrated sludge. Four types

of settling occur, depending on particle concentration: discrete, flocculent, and hindered

and compression. It is common for more than one type of settling to occur during a

sedimentation operation.

Influent Treatment

facility Mixed basin Influent

Flow 2 Treatment

facility Mixed basin Influent

Flow 3

Flow 1

Influent Treatment

facility

Equalization basin

Influent

Influent

Equalization basin

Treatment

facility

Equalization basin Effluent

31

(i) Horizontal flow

Horizontal-flow clarifiers may be rectangular, square or circular in shape (figure 2.1). The

flow in rectangular basins is rectilinear and parallel to the long axis of the basin, whereas

in centre feed circular basins, the water flows radially from the centre towards the outer

edges. Both types of basins are designed to keep the velocity and flow distributions as

uniform as possible in order to prevent currents and eddies from forming, and thereby

keep the suspended material from settling. Basins are usually made of steel or

reinforced concrete. The bottom surface slopes slightly to facilitate sludge removal. In

rectangular tanks, the slope is towards the inlet end, while in circular and square tanks;

the bottom is conical and slopes towards the centre of the basin.

(ii) Solid contact clarifiers

Solid contact clarifiers bring incoming solids into contact with a suspended layer of

sludge near the bottom that acts as a blanket. The incoming solids agglomerate and

remain enmeshed within the sludge blanket, whereby the liquid is able to rise upwards

while the solids are retained below.

(iii) Inclined surface basins

Inclined surface basins, also known as high-rate settlers, use inclined trays to divide the

depth into shallower sections, thus reducing particle settling times. They also provide a

larger surface area, so that a smaller-sized clarifier can be used. Many overloaded

horizontal flow clarifiers have been upgraded to inclined surface basins. Here, the flow is

laminar, and there is no wind effect.

Figure 2.1

2.2.1.5 Flotation

Flotation is a unit operation used to remove solid or liquid particles from a

by introducing a fine gas, usually air bubbles. The gas bubbles either adhere to the liquid

or are trapped in the particle structure of the suspended solids, raising the buoyant

force of the combined particle and gas bubbles. Particles that ha

the liquid can thus be made to rise. In wastewater treatment, flotation is used mainly to

remove suspended matter and to concentrate biological sludge. The chief advantage of

flotation over sedimentation is that very small or light

completely and in a shorter time. Once the particles have been floated to the surface,

they can be skimmed out. Flotation, as currently practiced in municipal wastewater

treatment, uses air exclusively as the floating agent.

additives can be introduced to enhance the removal process

The various flotation methods are described in table

illustrated in figure 2.2.

2.1: Settling basin with horizontal flow

Flotation is a unit operation used to remove solid or liquid particles from a



force of the combined particle and gas bubbles. Particles that have a higher density than



flotation over sedimentation is that very small or light particles can be removed more



treatment, uses air exclusively as the floating agent. Furthermore, various chemical

additives can be introduced to enhance the removal process (Metcalf and Eddy, 1991).

he various flotation methods are described in table 2.3, while a typical flotation unit is

a) Parts of a rectangular basin

b) Parts of circular tank

32

Flotation is a unit operation used to remove solid or liquid particles from a liquid phase



ve a higher density than



particles can be removed more



Furthermore, various chemical

(Metcalf and Eddy, 1991).

, while a typical flotation unit is

Table 2.3: Flotation methods

Process Description

Dissolved

air flotation

The injection of air while wastewater is under the pressure of several

atmospheres. After a short holding time, the pressure is restored to

atmospheric level, allowing the air to be released as minute

Air

flotation

The introduction of gas into the liquid phase directly by means of a

revolving impeller or through diffusers, at atmospheric pressure.

Vacuum

flotation

The saturation of wastewater with air either directly in an aeration tank

or by permitting air to enter on the suction side of a wastewater pump.

A partial vacuum is applied, causing the dissolved air to come out of

solution as minute bubbles which rise with the attached solids to the

surface, where they form a scum blanket. The scum

skimming mechanism while the settled grit is raked to a central sump for

removal.

Chemical

additives

Chemicals further the flotation process by creating a surface that can

easily adsorb or entrap air bubbles. Inorganic chemicals (aluminum

ferric salts and activated silica) and various organic polymers can be used

for this purpose.

Source: Adapted from Metcalf and Eddy, 1991.

Figure 2.2: Typical flotation unit

n methods



atmospheric level, allowing the air to be released as minute bubbles.




permitting air to enter on the suction side of a wastewater pump.



surface, where they form a scum blanket. The scum is removed by a



easily adsorb or entrap air bubbles. Inorganic chemicals (aluminum


for this purpose.

Metcalf and Eddy, 1991.

: Typical flotation unit (Source: Liu and Liptak, 1999)

33



bubbles.




permitting air to enter on the suction side of a wastewater pump.



is removed by a



easily adsorb or entrap air bubbles. Inorganic chemicals (aluminum and


Liu and Liptak, 1999)

34

2.2.1.6 Granular medium filtration

The filtration of effluents from wastewater treatment processes is a relatively recent

practice, but has come to be widely used for the supplemental removal of suspended

solids from wastewater effluents of biological and chemical treatment processes, in

addition to the removal of chemically precipitated phosphorus. The complete filtration

operation comprises two phases: filtration and cleaning or backwashing. The

wastewater to be filtered is passed through a filter bed consisting of granular material

(sand, anthracite and/or garnet), with or without added chemicals. Within the filter bed,

suspended solids contained in the wastewater are removed by means of a complex

process involving one or more removal mechanisms such as straining, interception,

impaction, sedimentation, flocculation and adsorption. The phenomena that occur

during the filtration phase are basically the same for all types of filters used for

wastewater filtration. The cleaning/backwashing phase differs, depending on whether

the filter operation is continuous or semicontinuous. In semi-continuous filtration, the

filtering and cleaning operations occur sequentially, whereas in continuous filtration

the filtering and cleaning operations occur simultaneously (Metcalf and Eddy, 1991).

2.2.2 Chemical unit processes

Chemical processes used in wastewater treatment are designed to bring about some

form of change by means of chemical reactions. They are always used in conjunction

with physical unit operations and biological processes. In general, chemical unit

processes have an inherent disadvantage compared to physical operations in that they

are additive processes. That is to say, there is usually a net increase in the dissolved

constituents of the wastewater. This can be a significant factor if the wastewater is to be

reused. This section discusses the main chemical unit processes, including chemical

precipitation, adsorption, disinfection, dechlorination and other applications.

2.2.2.1 Chemical precipitation

Chemical coagulation of raw wastewater before sedimentation promotes the

flocculation of finely divided solids into more readily settleable flocs, thereby enhancing

the efficiency of suspended solid, BOD5 and phosphorus removal as compared to plain

sedimentation without coagulation (table 2.4). The degree of clarification obtained

35

depends on the quantity of chemicals used and the care with which the process is

controlled.

Table 2.4: Removal efficiency of plain sedimentation vs. chemical precipitation

Parameter Percentage removal

Plain sedimentation Chemical precipitation

Total suspended solids (TSS)

BOD5

COD

Phosphorus

Bacteria loadings

40-90

25-40

5-10

50-60

60-90

40-70

30-60

70-90

80-90

Source: WEF and ASCE, 1992.

Coagulant selection for enhanced sedimentation is based on performance, reliability and

cost. Performance evaluation uses jar tests of the actual wastewater to determine

dosages and effectiveness. Chemical coagulants that are commonly used in waste-water

treatment include alum (Al2(SO4)3.14.3 H2O), ferric chloride (FeCl3.6H2O), ferric sulfate

(Fe2(SO4)3), ferrous sulfate (FeSO4.7H2O) and lime (Ca(OH)2). Organic polyelectrolytes are

sometimes used as flocculation aids (WEF and ASCE, 1992).

Suspended solids removal through chemical treatment involves a series of three unit

operations: rapid mixing, flocculation and settling. First, the chemical is added and

completely dispersed throughout the waste-water by rapid mixing for 20-30 seconds in a

basin with a turbine mixer. Coagulated particles are then brought together via

flocculation by mechanically inducing velocity gradients within the liquid. Flocculation

takes 15 to 30 minutes in a basin containing turbine or paddle-type mixers (Liu and

Liptak, 1992). The final step is clarification. A once through chemical treatment system is

illustrated in figure 2.3.

Figure 2.3: A once-through chemical treatment system

The advantages of coagulation include greater removal efficiency, the feasibility of using

higher overflow rates, and more

coagulation results in a larger mass of primary sludge that is often more difficult to

thicken and dewater. It also entails higher operational costs and demands greater

attention on the part of the operator.

2.2.2.2 Adsorption with activated carbon

Adsorption is the process of collecting soluble substances within a solution on a suitable

interface. In wastewater treatment, adsorption with activated carbon a solid interface

usually follows normal biological treatm

remaining dissolved organic matter. Particulate matter present in the water may also be

removed. Activated carbon is produced by heating char to a high temperature and then

activating it by exposure to an oxid

porous structure in the char and thus creates a large internal surface area. The activated

char can then be separated into various sizes with different adsorption capacities. The

two most common types of ac

has a diameter greater than 0.1 mm, and powdered activated carbon (PAC), which has a

diameter of less than 200 meshes

A fixed-bed column is often used to bring the waste

water is applied to the top of the column and withdrawn from the bottom, while the

through chemical treatment system (Source: Liu and Liptak, 1992).


higher overflow rates, and more consistent performance. On the other hand,



attention on the part of the operator.

Adsorption with activated carbon



usually follows normal biological treatment, and is aimed at removing a portion of the



activating it by exposure to an oxidizing gas at high temperature. The gas develops a



two most common types of activated carbon are granular activated carbon (GAC), which


meshes (Metcalf and Eddy, 1991).

bed column is often used to bring the waste-water into contact with GAC. The


36

Liu and Liptak, 1992).


consistent performance. On the other hand,





ent, and is aimed at removing a portion of the



izing gas at high temperature. The gas develops a



tivated carbon are granular activated carbon (GAC), which


ater into contact with GAC. The


carbon is held in place. Backwashing and surface washing are applied to limit head loss

build up. A schematic of an activated carbon contacto

bed and moving-bed carbon contactors have been developed to overcome the problem

of head loss build-up. In the expanded

bottom of the column and is allowed to expand. In the

is continuously replaced with fresh carbon. Spent granular carbon can be regenerated by

removal of the adsorbed organic matter from its surface through oxidation in a furnace.

The capacity of the regenerated carbon is slight

Figure 2.4: A typical granular activated carbon contactor

1991).

2.2.2.3 Disinfection

Disinfection refers to the selective destruction of disease causing micro

process is of importance in wastewater treatment owing to the nature of wastewater,

which harbors a number of human enteric organisms that are associated with various

waterborne diseases. Commonly used means of disinfection include the following:


build up. A schematic of an activated carbon contactor is shown in figure 2.4

bed carbon contactors have been developed to overcome the problem

up. In the expanded-bed system, the influent is introduced at the

bottom of the column and is allowed to expand. In the moving bed system, spent carbon



The capacity of the regenerated carbon is slightly less than that of the virgin carbon.

: A typical granular activated carbon contactor (Source: Metcalf and Eddy,

Disinfection refers to the selective destruction of disease causing micro-organisms. This

is of importance in wastewater treatment owing to the nature of wastewater,



37


2.4. Expanded

bed carbon contactors have been developed to overcome the problem

bed system, the influent is introduced at the

bed system, spent carbon



ly less than that of the virgin carbon.

Metcalf and Eddy,

organisms. This

is of importance in wastewater treatment owing to the nature of wastewater,



38

1) Physical agents such as heat and light;

2) Mechanical means such as screening, sedimentation, filtration, and so on;

3) Radiation, mainly gamma rays;

4) Chemical agents including chlorine and its compounds, bromine, iodine, ozone,

phenol and phenolic compounds, alcohols, heavy metals, dyes, soaps and

synthetic detergents, quaternary ammonium compounds, hydrogen peroxide,

and various alkalis and acids. The most common chemical disinfectants are the

oxidizing chemicals, and of these, chlorine is the most widely used (Qasim, 1999).

Table 2.5: Characteristics of common disinfecting agents

Characteristics Chlorine Sodium

hypochlorite

Calcium

hypochlorite

Chlorine

dioxide

Bromine

chloride

Ozone Ultraviol

et light

Chemical

formula

Cl2 NaOCl Ca(OCl)2 ClO2 BrCl O3 N/A

Form Liquid,

gas

Solution Powder,

pellets or 1

per cent

solution

Gas Liquid Gas UV

energy

Toxicity to

micro-

organisms

High High High High High High High

Solubility Slight High High High Slight High N/A

Stability Stable Slightly

unstable

Relatively

stable

Unstable,

must be

generated

as used

Slightly

unstable

Unstable,

must be

generated

as used

Must be

generate

d as used

Toxicity to

higher forms of

life

Highly

toxic

Toxic

Toxic

Toxic

Toxic

Toxic

Toxic

Effect at

ambient

temperature

High High High High High High High

Penetration High High High High High High Moderat

e Corrosiveness Highly

corrosive

Corrosive Corrosive Highly

corrosive

Corrosive Highly

corrosive

N/A

Deodorizing

ability

High Moderate Moderate High Moderate High None

Availability/

cost

Low cost Moderately

low cost

Moderately

low cost

Moderate

ly low cost

Moderate

ly low

cost

Moderate-

ly high cost

Moderat-

ely high

cost

39

Disinfectants act through one or more of a number of mechanisms, including damaging

the cell wall, altering cell permeability, altering the colloidal nature of the protoplasm

and inhibiting enzyme activity. In applying disinfecting agents, several factors need to be

considered: contact time, concentration and type of chemical agent, intensity and

nature of physical agent, temperature, number of organisms, and nature of suspending

liquid (Metcalf and Eddy, 1991 & Qasim, 1999). Table 2.5 shows the most commonly

used disinfectants and their effectiveness.

2.2.2.4 Dechlorination

Dechlorination is the removal of free and total combined chlorine residue from

chlorinated wastewater effluent before its reuse or discharge to receiving waters.

Chlorine compounds react with many organic compounds in the effluent to produce

undesired toxic compounds that cause long-term adverse impacts on the water

environment and potentially toxic effects on aquatic micro-organisms. Dechlorination

may be brought about by the use of activated carbon, or by the addition of a reducing

agent such as sulfur dioxide (SO2), sodium sulfite (Na2SO3) or sodium metabisulfite

(Na2S2O5). It is important to note that dechlorination will not remove toxic by-products

that have already been produced (Qasim, 1999).

2.2.2.5 Other chemical applications

In addition to the chemical processes described above, various other applications are

occasionally encountered in wastewater treatment and disposal. Table 2.6 lists the most

common applications and the chemicals used.

40

Table 2.6: Other chemical applications in wastewater treatment and disposal

Application Chemical used Remarks

� Treatment

Grease removal

BOD reduction

pH control

Ferrous sulfate oxidation

Filter - ponding control

Filter - fly control

Sludge-bulking control

Digester supernatant oxidation

Digester and Imhoff tank foaming

control

Ammonia oxidation

Cl2

Cl2, O3

KOH, NaOH,

Ca(OH)2

Cl2

Cl2

Cl2

Cl2, H2O2, O3

Cl2

Cl2

Cl

Added before preaeration

Oxidation of organic substances

Production of ferric sulfate and ferric

chloride

Residual at filter nozzles

Residual at filter nozzles, used during fly

season

Temporary control measure

Conversion of ammonia to nitrogen gas Source: Metcalf and Eddy, 1991.

2.2.3 Biological unit processes

Biological unit processes are used to convert the finely divided and dissolved organic

matter in wastewater into flocculent settleable organic and inorganic solids. In these

processes, microorganisms, particularly bacteria, convert the colloidal and dissolved

carbonaceous organic matter into various gases and into cell tissue which is then

removed in sedimentation tanks. Biological processes are usually used in conjunction

with physical and chemical processes, with the main objective of reducing the organic

content (measured as BOD, TOC or COD) and nutrient content (notably nitrogen and

phosphorus) of wastewater. Biological processes used for wastewater treatment may be

classified under five major headings:

a) Aerobic processes

b) Anoxic processes

c) Anaerobic processes

d) Combined processes

e) Pond processes.

These processes are further subdivided, depending on whether the treatment takes

place in a suspended-growth system

both. This section will be concerned with the most commonly used biological processes,

including trickling filters, the activated sludge process, aerated lagoons, rotating

biological contactors and stabilizatio

2.2.3.1 Activated-sludge process

The activated-sludge process is an aerobic, continuous flow system containing a mass of

activated microorganisms that are capable of stabilizing organic matter. The process

consists of delivering clarified wastewa

where it is mixed with an active mass of microorganisms, mainly bacteria and protozoa,

which aerobically degrade organic matter into carbon dioxide, water, new cells, and

other end products. The bacteria

gram-negative species, including carbon oxidizers, nitrogen oxidizers, floc formers and

nonfloc formers, and aerobes and facultative anaerobes. The protozoa, for their part,

include flagellates, amoebas an

Figure 2.5: Diagram of a simple activated sludge system

Figure 2.5 shows the layout of a typical activated sludge system. The most common

types of activated sludge are the conventional and the continuous flow stiffed tank

(Figure 2.5), in which the contents are completely mixed.


growth system an attached-growth system or a combination of



biological contactors and stabilization ponds.

sludge process

sludge process is an aerobic, continuous flow system containing a mass of


consists of delivering clarified wastewater, after primary settling, into an aeration basin



other end products. The bacteria involved in activated sludge systems are primarily

negative species, including carbon oxidizers, nitrogen oxidizers, floc formers and


include flagellates, amoebas and ciliates.

: Diagram of a simple activated sludge system

shows the layout of a typical activated sludge system. The most common


), in which the contents are completely mixed.

41


growth system or a combination of



sludge process is an aerobic, continuous flow system containing a mass of


ter, after primary settling, into an aeration basin



involved in activated sludge systems are primarily

negative species, including carbon oxidizers, nitrogen oxidizers, floc formers and


shows the layout of a typical activated sludge system. The most common


In a wastewater treatment plant, the activated sludge process can be used for one or

several of the following purpose:

� Oxidizing carbonaceous matter: biological matter.

� Oxidizing nitrogeneous matter: mainly

materials.

� Removing phosphate.

� Driving off entrained gases carbon dioxide, ammonia, nitrogen, etc.

� Generating a biological floc that is easy to settle.

� Generating a liquor low in dissolved or suspended material.

An aerobic environment is maintained in the basin by means of diffused or mechanical

aeration, which also serves to keep the contents o

completely mixed. After a specific retention time, the mixed liquor passes into the

secondary clarifier, where the sludge is allowed to settle and a clarified effluent is

produced for discharge. The process recycles a portion of the settled sludge back to the

aeration basin to maintain the required activated sludge concentration (figure

process also intentionally wastes a portion of the settled sludge to maintain the required

solids retention time (SRT) for effective organic removal.

Figure 2.6: Typical flow diagram for an activated

Control of the activated-sludge process

performance level under a wide range of operating conditions. The principal factors in

process control are the following:

1) Maintenance of dissolved oxygen levels in the aeration tanks


several of the following purpose:

Oxidizing carbonaceous matter: biological matter.

Oxidizing nitrogeneous matter: mainly ammonium and nitrogen

Removing phosphate.

Driving off entrained gases carbon dioxide, ammonia, nitrogen, etc.

Generating a biological floc that is easy to settle.

Generating a liquor low in dissolved or suspended material.

bic environment is maintained in the basin by means of diffused or mechanical

aeration, which also serves to keep the contents of the reactor (or mixed liquor)


arifier, where the sludge is allowed to settle and a clarified effluent is


aeration basin to maintain the required activated sludge concentration (figure

cess also intentionally wastes a portion of the settled sludge to maintain the required

solids retention time (SRT) for effective organic removal.

: Typical flow diagram for an activated-sludge process

sludge process is important to maintain a high treatment


process control are the following:

Maintenance of dissolved oxygen levels in the aeration tanks

42


in biological

bic environment is maintained in the basin by means of diffused or mechanical

f the reactor (or mixed liquor)


arifier, where the sludge is allowed to settle and a clarified effluent is


aeration basin to maintain the required activated sludge concentration (figure 2.6). The

cess also intentionally wastes a portion of the settled sludge to maintain the required

sludge process

is important to maintain a high treatment


43

2) Regulation of the amount of returning activated sludge

3) Control of the waste activated sludge.

The main operational problem encountered in a system of this kind is sludge bulking,

which can be caused by the absence of phosphorus, nitrogen and trace elements and

wide fluctuations in pH, temperature and dissolved oxygen (DO). Bulky sludge has poor

settleability and compactibility due to the excessive growth of filamentous

microorganisms. This problem can be controlled by chlorination of the return sludge (Liu

and Liptak, 1992 & Metcalf and Eddy, 1991).

Table 2.7: Advantages and disadvantages of activated-sludge process

Advantages Disadvantages

Flexible, can adapt to minor pH,

organic and temperature changes

High operating costs (skilled labor, electricity,

etc.)

Small area required Generates solids requiring sludge disposal

Degree of nitrification is controllable Some process alternatives are sensitive to

shock loads and metallic or other poisons

Relatively minor odor problems Requires continuous air supply

2.2.3.2 Aerated lagoons

An aerated lagoon is a basin between 1 and 4 meters in depth in which wastewater is

treated either on a flow-through basis or with solids recycling. The microbiology

involved in this process is similar to that of the activated-sludge process. However,

differences arise because the large surface area of a lagoon may cause more

temperature effects than are ordinarily encountered in conventional activated-sludge

processes. Wastewater is oxygenated by surface, turbine or diffused aeration. The

turbulence created by aeration is used to keep the contents of the basin in suspension.

Depending on the retention time, aerated lagoon effluent contains approximately one

third to one half the incoming BOD value in the form of cellular mass. Most of these

solids must be removed in a settling basin before final effluent discharge (figure 2.7).

Figure 2.7:

Wastewater treatment using PAC

the powder directly to the biological treatment effluent or the physiochemical

treatment process, as the case may be

contacting basin for a certain length of time. It is then allowed to set

the tank and removed. Removal of the powdered carbon may be facilitated by the

addition of polyelectrolyte coagulants or filtration through granular medium filters. A

major problem with the use of powdered activated carbon is that the

its regeneration is not well defined.

There are many methods for aerating a lagoon or basin:

• Motor-driven floating surface aerators

• Motor-driven submerged aerators

• Motor-driven fixed-in

• Injection of compressed air th

Figure 2.8: A Typical Surface

Figure 2.7: Typical flow diagram for aerated lagoons

Wastewater treatment using PAC (Powdered Activated Carbon) involves the addition of


treatment process, as the case may be. PAC is usually added to waste

contacting basin for a certain length of time. It is then allowed to settle to the bottom of



major problem with the use of powdered activated carbon is that the methodology for

its regeneration is not well defined.

There are many methods for aerating a lagoon or basin:

driven floating surface aerators

driven submerged aerators

in-place surface aerators

Injection of compressed air through submerged diffusers

A Typical Surface-Aerated Basing (using motor-driven floating aerators)

44

involves the addition of


. PAC is usually added to wastewater in a

tle to the bottom of



methodology for

driven floating aerators)

The aerated lagoons are basins, normally excavated in earth and operated without solids

recycling into the system. This is the major difference with respect to activated sludge

systems. Two types are the most common: the completely mixed lagoon (also calle

completely suspended) in which the concentration of solids and dissolved oxygen are

maintained fairly uniform and neither the incoming solids nor the biomass of

microorganisms settle, and the facultative (aerobic

lagoons. In the facultative lagoons, the power input is reduced causing accumulation of

solids in the bottom which undergo anaerobic decomposition; while the upper portions

are maintained aerobic (Figure

lagoons is the power input, which is in the order of 2.5

for aerobic lagoons while the requirements for facultative lagoons are of 0.8

Being open to the atmosphere, the lagoons are exposed to low temperatures which can

cause reduced biological activity and eventually the formation of ice. This can be

partially alleviated by increasing the depth of the basin. These units require a secondary

sedimentation unit, which in some cases can be a shallow basin excavated in earth, or

conventional settling tanks can be used.

Figure 2.9: Diagram of aerobic (top) and facultative (bottom) aerated lagoons

If excavated basins are used for settling, care should be taken to provide a residence

time long enough for the solids to settle, and there should also be provision for the

accumulation of sludge. There is a very high possibility of offensive

due to the decomposition of the settled sludge, and algae might develop in the upper

layers contributing to an increased content of suspended solids in the effluent.



systems. Two types are the most common: the completely mixed lagoon (also calle



microorganisms settle, and the facultative (aerobic-anaerobic or partially suspended)

. In the facultative lagoons, the power input is reduced causing accumulation of


are maintained aerobic (Figure 2.9). The main operational difference between these

is the power input, which is in the order of 2.5-6 Watts per cubic meter (W/m

for aerobic lagoons while the requirements for facultative lagoons are of 0.8


reduced biological activity and eventually the formation of ice. This can be



onventional settling tanks can be used.

Diagram of aerobic (top) and facultative (bottom) aerated lagoons



accumulation of sludge. There is a very high possibility of offensive odor


layers contributing to an increased content of suspended solids in the effluent.

45



systems. Two types are the most common: the completely mixed lagoon (also called



anaerobic or partially suspended)

. In the facultative lagoons, the power input is reduced causing accumulation of


). The main operational difference between these

6 Watts per cubic meter (W/m3)

for aerobic lagoons while the requirements for facultative lagoons are of 0.8-1 W/m3.


reduced biological activity and eventually the formation of ice. This can be



Diagram of aerobic (top) and facultative (bottom) aerated lagoons



development


layers contributing to an increased content of suspended solids in the effluent. Odors

46

can be minimized by using minimum depths of up to 2 m, while algae production is

reduced with liquid retention time of less than two days.

The solids will also accumulate, all along the aeration basins in the facultative lagoons

and even in comers, or between aeration units in the completely mixed lagoon. These

accumulated solids will, on the whole, decompose in the bottom, but since there is

always a non-biodegradable fraction, a permanent deposit will build up. Therefore,

periodic removal of these accumulated solids becomes necessary.

2.2.3.3 Trickling filters

The trickling filter is the most commonly encountered aerobic attached-growth

biological treatment process used for the removal of organic matter from wastewater. It

consists of a bed of highly permeable medium to which organisms are attached, forming

a biological slime layer, and through which wastewater is percolated. The filter medium

usually consists of rock or plastic packing material. The organic material present in the

wastewater is degraded by adsorption on to the biological slime layer. In the outer

portion of that layer, it is degraded by aerobic microorganisms. As the microorganisms

grow, the thickness of the slime layer increases and the oxygen is depleted before it has

penetrated the full depth of the slime layer. An anaerobic environment is thus

established near the surface of the filter medium. As the slime layer increases in

thickness, the organic matter is degraded before it reaches the microorganisms near the

surface of the medium. Deprived of their external organic source of nourishment, these

microorganisms die and are washed off by the flowing liquid. A new slime layer grows in

their place. This phenomenon is referred to as ‘sloughing’ (Liu and Liptak, 1992 &

Metcalf and Eddy, 1991).

Two types of trickling filters are applied to the treatment of sewage and industrial

wastewater.

i) Sewage treatment trickling filters

Onsite sewage facilities (OSSF) are recognized as viable, low-cost, long-term,

decentralized approaches to sewage treatment if they are planned, designed, installed,

operated and maintained properly.

47

Sewage trickling filters are used in areas not serviced by municipal wastewater

treatment plants (WWTP). They are typically installed in areas where the traditional

septic tank system are failing, cannot be installed due to site limitations, or where

improved levels of treatment are required for environmental benefits such as preventing

contamination of ground water or surface water.

Sites with a high water table, high bedrock, heavy clay, small land area, or which require

minimal site destruction (for example, tree removal) are ideally suited for trickling

filters.

All varieties of sewage trickling filters have low and sometimes intermittent power

consumption. They can be somewhat more expensive than traditional septic tank-leach

field systems, however their use allows for better treatment, a reduction in size of

disposal area, less excavation, and higher density land development.

All sewage trickling filter systems share the same fundamental components:

• a septic tank for fermentation and primary settling of solids

• a filter medium upon which beneficial microbes (biomass, biofilm) are promoted

and developed

• a container which houses the filter medium

• a distribution system for applying wastewater to be treated to the filter medium

• a distribution system for disposal of the treated effluent.

By treating septic tank effluent before it is distributed into the ground, higher treatment

levels are obtained and smaller disposal means such as leach field, shallow pressure

trench or area beds are required.

Systems can be configured for single-pass use where the treated water is applied to the

trickling filter once before being disposed of, or for multi-pass use where a portion of

the treated water is cycled back to the septic tank and re-treated via a closed-loop.

Multi-pass systems result in higher treatment quality and assist in removing Total

Nitrogen (TN) levels by promoting nitrification in the aerobic media bed and

denitrification in the anaerobic septic

Trickling filters differ primarily in the type of filter media used to house the microbial

colonies. Types of media most commonly used include plastic matrix material, open

polyurethane foam, sphagnum peat moss, recycled tires, clinker, gravel

geotextiles. Ideal filter medium optimizes surface area for microbial attachment,

wastewater retention time, allows air flow, resists plugging and does not degrade. Some

residential systems require forced aeration units which will increase maint

operational costs.

Third-party verification of trickling filters has proven them to be a reliable alternative to

septic systems with increased levels of treatment performance and nitrogen removal.

Typical effluent quality parameters are Biochem

suspended solids (TSS), Total Kjeldahl Nitrogen (TKN), and fecal coliforms.

Figure 2.10

ii) Industrial wastewater treatment trickl

Wastewaters from a variety of

Such industrial wastewater trickling filters consist of two types:

• Large tanks or concrete enclosures filled with plastic packing or other media.


denitrification in the anaerobic septic tank.


colonies. Types of media most commonly used include plastic matrix material, open

polyurethane foam, sphagnum peat moss, recycled tires, clinker, gravel



residential systems require forced aeration units which will increase maint

party verification of trickling filters has proven them to be a reliable alternative to


Typical effluent quality parameters are Biochemical Oxygen Demand (BOD), Total

suspended solids (TSS), Total Kjeldahl Nitrogen (TKN), and fecal coliforms.

2.10: A typical complete trickling filter system.

Industrial wastewater treatment trickling filters

Wastewaters from a variety of industrial processes have been treated in trickling filters.

Such industrial wastewater trickling filters consist of two types:

Large tanks or concrete enclosures filled with plastic packing or other media.

48



colonies. Types of media most commonly used include plastic matrix material, open-cell

polyurethane foam, sphagnum peat moss, recycled tires, clinker, gravel, sand and



residential systems require forced aeration units which will increase maintenance and

party verification of trickling filters has proven them to be a reliable alternative to


ical Oxygen Demand (BOD), Total

industrial processes have been treated in trickling filters.

Large tanks or concrete enclosures filled with plastic packing or other media.

• Vertical towers filled with plastic packing or o

The availability of inexpensive plastic tower packings has led to their use as trickling

filter beds in tall towers, some as high as 20 meters.

The treated water effluent from industrial wastewater trickling filters is very often

subsequently processed in a clarifier

microbial slime layer attached to the trickling filter media

Currently, some of the latest trickl

are essentially trickling filters consisting of plastic media in

inject air at the bottom of the vessels, with e

wastewater.

After passing through the filter, the treated liquid is collected in an under drain sy

together with any biological solids that have become detached from the medium (figure

2.11). The collected liquid then passes to a settling tank where the solids are separated

from the treated wastewater. A portion of the liquid collected in the unde

or the settled effluent is recycled to dilute the strength of the incoming wastewater and

to maintain the biological slime layer in moist condition (figure

Figure 2.1

Vertical towers filled with plastic packing or other media.


filter beds in tall towers, some as high as 20 meters.


subsequently processed in a clarifier-settler to remove the sludge that sloughs off the

microbial slime layer attached to the trickling filter media.

Currently, some of the latest trickling filter technology involves aerated biofilters which

filters consisting of plastic media in vessels using blowers to

air at the bottom of the vessels, with either downflow or upflow of the

After passing through the filter, the treated liquid is collected in an under drain sy


). The collected liquid then passes to a settling tank where the solids are separated

from the treated wastewater. A portion of the liquid collected in the under drain system


to maintain the biological slime layer in moist condition (figure 2.12).

2.11: Cutaway view of a trickling filter.

49



settler to remove the sludge that sloughs off the

filter technology involves aerated biofilters which

vessels using blowers to

ither downflow or upflow of the

After passing through the filter, the treated liquid is collected in an under drain system,


). The collected liquid then passes to a settling tank where the solids are separated

r drain system


Figure 2.12

Table 2.8: Advantages and disadvantages of trickling filter

Advantages

Good quality (80-90% BOD5 removal) for 2

stage efficiency could reach 95%

Moderate operating costs (lower than

activated sludge)

Withstands shock loads better than other

biological processes

2.2.3.4 Rotating biological contactors

A rotating biological contractor (RBC) is an attached

consists of one or more basins in which large closely spaced circular disks mounted on

horizontal shafts rotate slowly through wastewater (figure

made of high-density polystyrene or polyvinyl chloride (PVC), are partially submerged in

the wastewater, so that a bacterial slime layer forms on their wetted surfaces. As the

disks rotate, the bacteria are exposed alternately to wastewater, from which

adsorb organic matter, and to air, from which they absorb oxygen. The rotary movement

also allows excess bacteria to be removed from the surfaces of the disks and maintains a

suspension of sloughed biological solids. A final clarifier is needed to rem

solids. Organic matter is degraded by means of mechanisms similar to those operating in

the trickling filters process. Partially submerged RBCs are used for carbonaceous BOD

removal, combined carbon oxidation and nitrification, and nitrificati

effluents. Completely submerged RBCs are used for denitrification

1991).

2: Typical flow diagram for trickling filters

Table 2.8: Advantages and disadvantages of trickling filter

Disadvantages

removal) for 2-

stage efficiency could reach 95%

High capital costs

Moderate operating costs (lower than Clogging of distributors or beds

Withstands shock loads better than other Snail, mosquito and insect problems

Rotating biological contactors

A rotating biological contractor (RBC) is an attached-growth biological process that


horizontal shafts rotate slowly through wastewater (figure 2.13). The disks, which a

density polystyrene or polyvinyl chloride (PVC), are partially submerged in


disks rotate, the bacteria are exposed alternately to wastewater, from which



suspension of sloughed biological solids. A final clarifier is needed to remove sloughed



removal, combined carbon oxidation and nitrification, and nitrification of secondary

effluents. Completely submerged RBCs are used for denitrification (Metcalf and Eddy,

50

Clogging of distributors or beds

Snail, mosquito and insect problems

growth biological process that


). The disks, which are

density polystyrene or polyvinyl chloride (PVC), are partially submerged in


disks rotate, the bacteria are exposed alternately to wastewater, from which they



ove sloughed



on of secondary

(Metcalf and Eddy,

Figure 2.13: RBC system configuration

Figure 2.14: Schematic diagram of a typical rotating biological contactor (RBC). The

treated effluent clarifier/settler is not included in the diagram.

A typical arrangement of RBCs is shown in figure

divided into a series of indepen

single basin or separate basins arranged in stages. Compartmentalization creates a plug

flow pattern, increasing overall removal efficiency.

It also promotes a variety of conditions where different orga

degrees. As the wastewater flows through the compartments, each subsequent stage

receives influent with a lower organic content than the previous stage; the system thus

enhances organic removal.

RBC system configuration (Source: Qasim, 1999).

Schematic diagram of a typical rotating biological contactor (RBC). The


A typical arrangement of RBCs is shown in figure 2.15. In general, RBC systems are

divided into a series of independent stages or compartments by means of baffles in a

single basin or separate basins arranged in stages. Compartmentalization creates a plug

flow pattern, increasing overall removal efficiency.

It also promotes a variety of conditions where different organisms can flourish to varying



51

Schematic diagram of a typical rotating biological contactor (RBC). The


. In general, RBC systems are

dent stages or compartments by means of baffles in a

single basin or separate basins arranged in stages. Compartmentalization creates a plug-

nisms can flourish to varying



Figure 2.1

Table 2.9: Advantages and disadvantages of rotating biological contactor (RBC)

Advantages

Short contact periods

Handles a wide range of flows

Easily separates biomass from waste

stream

Low operating costs

Short retention time

Low sludge production

Low power requirements

Low sludge production and excellent

control

2.2.3.5 Stabilization ponds

A stabilization pond is a relatively shallow body of wastewater contained in an earthen

basin, using a completely mixed biological process without solids return. Mixing may be

either natural (wind, heat or fermentation) or induced (mechanical or diffused a

Stabilization ponds are usually classified, on the basis of the nature of the biological

activity that takes place in them, as aerobic, anaerobic, or aerobic

2.10). Aerobic ponds are used primarily for the treatment of soluble o

effluents from wastewater treatment plants. Aerobic

the most common type and have been used to treat domestic wastewater and a wide

variety of industrial wastes. Anaerobic ponds, for their part, are parti

bringing about rapid stabilization of strong concentrations of organic wastes. Aerobic

and facultative ponds are biologically complex. The bacterial population oxidizes organic

matter, producing ammonia, carbon dioxide, sulfates, water

Figure 2.15: Typical flow diagram for RBC units.


Disadvantages

Need for covering units installed in cold

climate to protect against freezing

flows Shaft bearings and mechanical drive units

require frequent maintenance

Easily separates biomass from waste

excellent process

Stabilization ponds



either natural (wind, heat or fermentation) or induced (mechanical or diffused a


activity that takes place in them, as aerobic, anaerobic, or aerobic- anaerobic (table

10). Aerobic ponds are used primarily for the treatment of soluble organic wastes and

effluents from wastewater treatment plants. Aerobic-anaerobic (facultative) ponds are


variety of industrial wastes. Anaerobic ponds, for their part, are particularly effective in



matter, producing ammonia, carbon dioxide, sulfates, water and other end products,

52


Need for covering units installed in cold

climate to protect against freezing

Shaft bearings and mechanical drive units

require frequent maintenance



either natural (wind, heat or fermentation) or induced (mechanical or diffused aeration).


anaerobic (table

rganic wastes and

anaerobic (facultative) ponds are


cularly effective in



and other end products,

which are subsequently used by algae during daylight to produce oxygen. Bacteria then

use this supplemental oxygen and the oxygen provided by wind action to break down

the remaining organic matter. Wastewater retention time ranges

days. This is a treatment process that is very commonly found in rural areas because of

its low construction and operating costs. Figure

stabilization ponds (Liu and Liptak, 1992

Figure 2.16: Typical flow diagram for stabilization ponds

Table 2.10: Types and applications of stabilization ponds

Type of pond Common name

Aerobic Low-rate pond

High-rate pond

Maturation

pond

Aerobic-

anaerobic

(supplemental

aeration)

Facultative

pond with

aeration



the remaining organic matter. Wastewater retention time ranges between 30 and 120


its low construction and operating costs. Figure 2.16 presents a typical flow diagram for

Liu and Liptak, 1992).

: Typical flow diagram for stabilization ponds.

ypes and applications of stabilization ponds

Common name Characteristics Application

rate pond

Designed to maintain aerobic

conditions throughout the liquid

depth

Designed to optimize the production

of algal cell tissue and achieve high

yields of harvestable proteins

Similar to low-rate ponds but very

lightly loaded

Treatment of soluble organic

wastes and secondary

effluents

Nutrient removal, treatment

of soluble organic wastes,

conversion of wastes

Used for polishing effluents

from conventional secondary

treatment processes such as Deeper than high-rate pond; aeration

and photosynthesis provide oxygen

for aerobic stabilization in upper

layers. Lower layers are facultative.

Treatment of screened

untreated or

wastewater or industrial

wastes.

53



between 30 and 120


presents a typical flow diagram for

Treatment of soluble organic

wastes and secondary

Nutrient removal, treatment

of soluble organic wastes,

conversion of wastes

Used for polishing effluents

from conventional secondary

treatment processes such as Treatment of screened

untreated or primary settled


54

Table 2.10: Types and applications of stabilization ponds (Continued)

Type of pond Common name Characteristics Application

Aerobic-

anaerobic

(oxygen from

algae)

Facultative

pond

As above, except without

supplemental aeration.

Photosynthesis and surface

reaeration provide oxygen for upper

layers.

Treatment of screened

untreated or primary settled


wastes.

Anaerobic Anaerobic

lagoon,

anaerobic

Anaerobic conditions prevail

throughout; usually followed by

aerobic or facultative ponds.

Treatment of municipal

wastewater and industrial

wastes.

Anaerobic

followed by

aerobic-

anaerobic

Pond system Combination of pond types described

above. Aerobic-anaerobic ponds may

be followed by an aerobic pond.

Recirculation frequently used from

aerobic to anaerobic ponds.

Complete treatment of

municipal wastewater and

industrial wastes with high

bacterial removal.

Source: Adapted from Metcalf and Eddy, 1991.

Table 2.11: Advantages and disadvantages of stabilization ponds

Advantages Disadvantages

Anaerobic stabilization ponds

Does not require external energy Occupies open and permanent space

Removes heavy metals as insoluble metal

sulphides

Can release foul odor

Simple in construction Can contribute to mosquito breeding

Flexible degree of treatment

Low maintenance

Aerobic/Facultative stabilization pond

Simple construction Large permanent space requirement

High pathogen removal rate Can lead to mosquito breeding and release

odor if too small

Reliable if properly designed Algae in the pond can increase effluent

BOD

Can generate revenue through fish farming

2.2.3.6 Completely mixed anaerobic digestion

Anaerobic digestion involves the biological conversion of organic and inorganic matter in

the absence of molecular oxygen to a variety of end-products including methane and

carbon dioxide. A consortium of anaerobic organisms work together to degrade the

organic sludges and wastes in three steps, consisting of hydrolysis of high

mass compounds, acidogenesis and methanogenesis.

Figure 2.17: Diagram of

The process takes place in an airtight reactor. Sludge is intro

intermittently and retained in the reactor for varying periods of time. After withdrawal

from the reactor, whether continuous or intermittent, the stabilized sludge is reduced in

organic and pathogen content and is nonputrescible. The

anaerobic digesters are standard rate and high

process, the contents of the digester are usually unheated and unmixed, and are

retained for a period ranging from 30 to 60 days. In the high

contents of the digester are heated and mixed completely, and are retained, typically,

for a period of 15 days or less. A combination of these two basic processes is known as

the two-stage process, and is used to separate the d

liquor. However, additional digestion and gas production may occur

1991).

Anaerobic digesters are commonly used for the treatment of sludge and wastewater

with high organic content. The disadvantage

compared to aerobic treatment, stem directly from the slow growth rate of

methanogenic bacteria. A slow growth rate requires a relatively long retention time in

the digester for adequate waste stabilization to

means that only a small portion of the degradable organic matter is synthesized into

new cells. Another advantage of this type of system is the production of methane gas,

ganic sludges and wastes in three steps, consisting of hydrolysis of high

mass compounds, acidogenesis and methanogenesis.

: Diagram of an anaerobic digestion process.

The process takes place in an airtight reactor. Sludge is introduced continuously or



organic and pathogen content and is nonputrescible. The two most widely used types of

anaerobic digesters are standard rate and high-rate. In the standard-rate digestion


retained for a period ranging from 30 to 60 days. In the high-rate digestion process, the



stage process, and is used to separate the digested solids from the supernatant

liquor. However, additional digestion and gas production may occur (Metcalf and Eddy,

Anaerobic digesters are commonly used for the treatment of sludge and wastewater

The disadvantages and advantages of a system of this kind, as



the digester for adequate waste stabilization to occur; however, that same slow growth



55

ganic sludges and wastes in three steps, consisting of hydrolysis of high-molecular-

duced continuously or



two most widely used types of

rate digestion


rate digestion process, the



igested solids from the supernatant

(Metcalf and Eddy,

Anaerobic digesters are commonly used for the treatment of sludge and wastewaters

s and advantages of a system of this kind, as



occur; however, that same slow growth



56

which can be used as a fuel source, if produced in sufficient quantities. Furthermore, the

system produces a well-stabilized sludge, which can be safely disposed of in a sanitary

landfill after drying or dewatering. On the other hand, the fact that high temperatures

are required for adequate treatment is a major drawback.

2.2.3.7 Biological nutrient removal

Nitrogen and phosphorus are the principal nutrients of concern in wastewater

discharges. Discharges containing nitrogen and phosphorus may accelerate the

eutrophication of lakes and reservoirs and stimulate the growth of algae and rooted

aquatic plants in shallow streams. Significant concentrations of nitrogen may have other

adverse effects as well: depletion of dissolved oxygen in receiving waters, toxicity to

aquatic life, adverse impact on chlorine disinfection efficiency, creation of a public

health hazard, and wastewater that is less suitable for reuse. Nitrogen and phosphorus

can be removed by physical, chemical and biological methods. Biological removal of

these nutrients is described below.

2.2.3.7.1 Nitrification-denitrification

Nitrification is the first step in the removal of nitrogen by means of this process.

Biological nitrification is the work of two bacterial genera: Nitrosomonas, which oxidize

ammonia to the intermediate product nitrite, and Nitrobacter, which convert nitrite to

nitrate. Nitrifying bacteria are sensitive organisms and are extremely susceptible to a

wide variety of inhibitors such as high concentrations of ammonia and nitrous acid, low

DO levels (< 1 mg/L), pH outside the optimal range (7.5-8.6), and so on. Nitrification can

be achieved through both suspended growth and attached-growth processes. In

suspended-growth processes, nitrification is brought about either in the same reactor

that is used for carbonaceous BOD removal, or in a separate suspended-growth reactor

following a conventional activated sludge treatment process. Ammonia is oxidized to

nitrate with either air or high purity oxygen. Similarly, nitrification in an attached-growth

system may be brought about either in the same attached growth reactor that is used

for carbonaceous BOD removal or in a separate reactor. Trickling filters, rotating

biological contactors and packed towers can be used for nitrifying systems.

57

Denitrification involves the removal of nitrogen in the form of nitrate by conversion to

nitrogen gas under anoxic conditions. In denitrifying systems, DO is a critical parameter.

Its presence suppresses the enzyme system needed for denitrification. The optimal pH

lies between 7 and 8. Denitrification can be achieved through both suspended and

attached growth processes. Suspended-growth denitrification takes place in a plug-flow

type of activated-sludge system. An external carbon source is usually necessary for

micro-organism cell synthesis, since the nitrified effluent is low in carbonaceous matter.

Some denitrification systems use the incoming wastewater for this purpose. A nitrogen-

gas-stripped reactor should precede the denitrification clarifier because nitrogen gas

hinders the settling of the mixed liquor. Attached-growth denitrification takes place in a

column reactor containing stone or one of a number of synthetic media upon which the

bacteria grow. Periodic backwashing and an external carbon source are necessary in a

system of this kind.

2.2.3.7.2 Phosphorus removal

Phosphorus appears in water as orthophosphate (PO4), polyphosphate (P2O7), and

organically bound phosphorus. Microbes utilize phosphorus during cell synthesis and

energy transport. As a result, 10 to 30 percent of all influent phosphorus is removed

during secondary biological treatment. More phosphorus can be removed if one of a

number of specially developed biological phosphorus removal processes is used. These

processes are based on the exposure of microbes in an activated-sludge system to

alternating anaerobic and aerobic conditions. This stresses the microorganisms, so that

their uptake of phosphorus exceeds normal levels. Typical biological processes used for

phosphorus removal are the proprietary A/O process, the proprietary PhoStrip process,

and the sequencing batch reactor (SBR) process (figure 2.18).

The A/O process is a single-sludge suspended growth system that combines aerobic and

anaerobic sections in sequence. Settled sludge is returned to the influent end of the

reactor and mixed with the incoming wastewater. In the PhoStrip process, a portion of

the return activated sludge from the secondary biological treatment process is diverted

to an anaerobic phosphorus stripping tank. There, phosphorus is released into the

supernatant, which is subsequently treated with lime or some other coagulant. The

phosphorus-poor activated sludge is returned to the aeration tank.

Figure 2.18: Biological phosphorus removal systems

2.3 Application of Treatment

In wastewater treatment plants, the unit operations and processes described in the

previous section are grouped together in a variety of configurations to produce different

levels of treatment, commonly referred to as prelim

tertiary or advanced treatment (figure

2.3.1 Preliminary treatment

Preliminary treatment prepares wastewater influent for further treatment by reducing

or eliminating non-favorable wastewater characteristics that might

operation or excessively increase maintenance of downstream processes and

equipment. These characteristics include large solids and rags, abrasive grit, odors, and,

in certain cases, unacceptably high peak hydraulic or organic loadings. P

treatment processes consist of physical unit operations, namely screening and

comminution for the removal of debris and rags, grit removal for the elimination of

poor activated sludge is returned to the aeration tank.

Biological phosphorus removal systems (Source: Metcalf and Eddy, 1991).

reatment Methods



levels of treatment, commonly referred to as preliminary, primary, secondary and

tertiary or advanced treatment (figure 2.19).

Preliminary treatment


favorable wastewater characteristics that might otherwise impede



in certain cases, unacceptably high peak hydraulic or organic loadings. P



58

: Metcalf and Eddy, 1991).



inary, primary, secondary and


otherwise impede



in certain cases, unacceptably high peak hydraulic or organic loadings. Preliminary



59

coarse suspended matter, and flotation for the removal of oil and grease. Other

preliminary treatment operations include flow equalization, septage handling, and odor

control methods.

2.3.2 Primary treatment

Primary treatment involves the partial removal of suspended solids and organic matter

from the wastewater by means of physical operations such as screening and

sedimentation. Pre-aeration or mechanical flocculation with chemical additions can be

used to enhance primary treatment. Primary treatment acts as a precursor for

secondary treatment. It is aimed mainly at producing a liquid effluent suitable for

downstream biological treatment and separating out solids as a sludge that can be

conveniently and economically treated before ultimate disposal. The effluent from

primary treatment contains a good deal of organic matter and is characterized by a

relatively high BOD.

2.3.3 Secondary treatment

The purpose of secondary treatment is the removal of soluble and colloidal organics and

suspended solids that have escaped the primary treatment. This is typically done

through biological processes, namely treatment by activated sludge, fixed-film reactors,

or lagoon systems and sedimentation.

2.3.4 Tertiary/advanced wastewater treatment

Tertiary treatment goes beyond the level of conventional secondary treatment to

remove significant amounts of nitrogen, phosphorus, heavy metals, biodegradable

organics, bacteria and viruses. In addition to biological nutrient removal processes, unit

operations frequently used for this purpose include chemical coagulation, flocculation

and sedimentation, followed by filtration and activated carbon. Less frequently used

processes include ion exchange and reverse osmosis for specific ion removal or for

dissolved solids reduction.

60

Biological

process

Chlorine

contact

chambe

Influent Effluent

Cl2

Screens &

Communition

Grit removal

Recycle

Waste sludge

2.4 Natural Treatment Systems

Natural systems for wastewater treatment are designed to take advantage of the

physical, chemical, and biological processes that occur in the natural environment when

water, soil, plants, microorganisms and the atmosphere interact (Metcalf and Eddy,

1991). Natural treatment systems include land treatment, floating aquatic plants and

constructed wetlands. All natural treatment systems are preceded by some form of

mechanical pretreatment for the removal of gross solids. Where sufficient land suitable

for the purpose is available, these systems can often be the most cost effective option in

terms of both construction and operation. They are frequently well suited for small

communities and rural areas (Reed et al., 1988).

Figure 2.19: Various treatment levels in a wastewater treatment plant flow diagram.

2.4.1 Land treatment

Land treatment is the controlled application of wastewater to the land at rates

compatible with the natural physical, chemical and biological processes that occur on

Secondary

settling

Primary

settling

Effluent

filtration Mixer

Tertiary treatment

Secondary treatment

Primary treatment

Preliminary treatment

Offline flow

equalization

Backwash wastewater

Sludge processing

facility

Flotation

thickening

Backwash

water

storage

61

and in the soil. The three main types of land treatment systems used are slow rate (SR),

overflow (OF), and rapid infiltration (RI) systems.

2.4.1.1 Slow rate

SR systems are the predominant form of land treatment for municipal and industrial

wastewater. This technology incorporates wastewater treatment, water reuse, crop

utilization of nutrients and wastewater disposal. It involves the application of

wastewater to vegetated land by means of various techniques, including sprinkling

methods or surface techniques such as graded-border and furrow irrigation. Water is

applied intermittently (every 4 to 10 days) to maintain aerobic conditions in the soil

profile. The applied water is either consumed through evapotranspiration or percolated

vertically and horizontally through the soil system. Any surface runoff is collected and

reapplied to the system. Treatment occurs as the wastewater percolates through the

soil profile (table 2.12). In most cases, the percolate will enter the underlying

groundwater, or it may be intercepted by natural surface waters or recovered by means

of underdrains or recovery wells (Metcalf and Eddy, 1991 & Reed et al., 1988).

Table 2.12: Mechanisms of wastewater constituent removal by SR systems

Parameter Removal mechanism

BOD Soil adsorption and bacterial oxidation

SS Filtration through the soil

Nitrogen Crop uptake, denitrification, ammonia volatilization, soil storage

Phosphorus Chemical immobilization (precipitation and adsorption), plant uptake

Metals Soil adsorption, precipitation, ion exchange, complexation

Pathogens Soil filtration, adsorption, desiccation, radiation, predation, exposure to

other adverse

Trace

organics

Photodecomposition, volatilization, sorption, degradation

Source: Reed et al., 1988.

SR systems can be classified into two types, Type 1 and Type 2, based on design

objectives. Type 1 systems are designed with wastewater treatment itself, rather than

crop production, as their main objective. Accordingly, in systems of this kind, the

62

maximum possible amount of water is applied per unit land area. Type 2 SR systems, in

contrast, are designed mainly with a view to water reuse for crop production, and

consequently the amount of water applied in a system of this kind is just enough to

satisfy the irrigation requirements of the crop being grown. SR systems have the highest

treatment potential of all natural treatment systems.

2.4.1.2 Rapid infiltration

Rapid infiltration (RI) is the most intensive of all land treatment methods. Relatively high

hydraulic and organic loadings are applied intermittently to shallow infiltration or

spreading basins (figure 2.20). The RI process uses the soil matrix for physical, chemical,

and biological treatment. Physical straining and filtering occur at the soil surface and

within the soil matrix. Chemical precipitation, ion exchange and adsorption occur as the

water percolates through the soil. Biological oxidation, assimilation and reduction occur

within the top few feet of the soil. Vegetation is not applied in systems of this kind. The

RI system is designed to meet several performance objectives including the following:

(a) Recharge of streams by interception of groundwater;

(b) Recovery of water by wells or underdrains, with subsequent reuse or discharge;

(c) Groundwater recharge;

(d) Temporary storage of renovated water in the local aquifer (Sanks and Asano

1976 & Metcalf and Eddy, 1991).

2.4.1.3 Overland flow

Overland flow (OF) is a treatment process in which wastewater is treated as it flows

down a network of vegetated sloping terraces. Wastewater is applied intermittently to

the top portion of each terrace and flows down the terrace to a runoff collection

channel at the bottom of the slope. Application techniques include high-pressure

sprinklers, low-pressure sprays, or surface methods such as gated pipes. OF is normally

used with relatively impermeable surface soils, since, in contrast to SR and RI systems,

infiltration through the soil is limited. The effluent wastewater undergoes a variety of

physical, chemical and biological treatment mechanisms as it proceeds along surface

runoff path. Overland flow systems can be designed for secondary treatment, advanced

secondary treatment or nutrient removal, depending on user requirements.

Figure 2.20: Rapid infiltration

2.4.2 Constructed wetlands

Wetlands are inundated land areas with water depths typically less than 2 ft (0.6 m) that

support the growth of emergent plants such as cattail, bulrush, reeds and sedges. The

vegetation provides surfaces for the attachment of bacteria films, aids in the filtration

and adsorption of wastewater constituents, transfers oxygen into the water column, and

controls the growth of algae by restricting the penetration of sunlight. Two typ

constructed wetlands have been developed for wastewater treatment, namely free

water surface (FWS) systems, and subsurface flow systems (SFS)

& Reed et al., 1988).

2.4.2.1 Free water surface systems

FWS systems consist of parallel shallow basins ranging from 0.3 to 2 feet (0.1

or channels with relatively impermeable bottom soil or subsurface barrier and emergent

vegetation (figure 2.21). As a rule, pre

treated as it flows through the stems and roots of the emergent vegetation.

Figure 2.21: Free water surface system

Rapid infiltration treatment system (Source: Metcalf and Eddy, 1991)

Constructed wetlands



egetation provides surfaces for the attachment of bacteria films, aids in the filtration


controls the growth of algae by restricting the penetration of sunlight. Two typ


water surface (FWS) systems, and subsurface flow systems (SFS) (Sanks and Asano 1976

Free water surface systems

FWS systems consist of parallel shallow basins ranging from 0.3 to 2 feet (0.1


). As a rule, pre-clarified wastewater is applied continuously to be


: Free water surface system (Source: Qasim, 1999).

63




egetation provides surfaces for the attachment of bacteria films, aids in the filtration


controls the growth of algae by restricting the penetration of sunlight. Two types of


(Sanks and Asano 1976

FWS systems consist of parallel shallow basins ranging from 0.3 to 2 feet (0.1-0.6 meter)


nuously to be


: Qasim, 1999).

2.4.2.2 Subsurface flow systems

SFSs consist of beds or channels filled with gravel, sand, or other

planted with emergent vegetation (figure

horizontally through the media

secondary or advanced levels of treatment.

Figure 2.22: Subsurface flow

2.4.3 Floating aquatic plants

This system is similar to the FWS system except that the plants used are of the floating

type, such as hyacinths and duckweeds (figure 2

the case of wetland systems, ranging from 1.6 to 6.0 feet (0.5

plants shield the water from sunlight and reduce the growth of algae. Systems of this

kind have been effective in reducing BOD, nitrogen, metals and trace organics and in

removing algae from lagoons and stabilization pond effluents. Supplementary aeration

has been used with floating plant systems to increase treatment capacity and to

maintain the aerobic conditions necessary for the biological control of mosquitoes

(Metcalf and Eddy, 1991).

Figure 2.23: Floating aquatic plants system

Subsurface flow systems

SFSs consist of beds or channels filled with gravel, sand, or other permeable media

planted with emergent vegetation (figure 2.22). Wastewater is treated as it flows

horizontally through the media-plant filter. Systems of this kind are designed for

secondary or advanced levels of treatment.

: Subsurface flow system (Source: Qasim, 1999).

Floating aquatic plants


type, such as hyacinths and duckweeds (figure 2.23). Water depths are greater than in

systems, ranging from 1.6 to 6.0 feet (0.5-1.8 meters). The floating



from lagoons and stabilization pond effluents. Supplementary aeration



: Floating aquatic plants system (Source: Metcalf and Eddy, 1991).

64

permeable media

). Wastewater is treated as it flows

plant filter. Systems of this kind are designed for


). Water depths are greater than in

1.8 meters). The floating



from lagoons and stabilization pond effluents. Supplementary aeration




65

2.5 Recent techniques

2.5.1 Sequencing batch reactor

Sequencing batch reactors (SBR) or sequential batch reactors are industrial processing

tanks for the treatment of wastewater. SBR reactors treat waste water such as sewage

or output from anaerobic digesters or mechanical biological treatment facilities in

batches. Oxygen is bubbled through the waste water to reduce biochemical oxygen

demand (BOD) and chemical oxygen demand (COD) to make suitable for discharge into

sewers or for use on land.

While there are several configurations of SBRs the basic process is similar. The

installation consists of at least two identically equipped tanks with a common inlet,

which can be switched between them. The tanks have a “flow through” system, with

raw wastewater (influent) coming in at one end and treated water (effluent) flowing out

the other. While one tank is in settle/decant mode the other is aerating and filling. At

the inlet is a section of the tank known as the bio-selector. This consists of a series of

walls or baffles which direct the flow either from side to side of the tank or under and

over consecutive baffles. This helps to mix the incoming Influent and the returned

activated sludge, beginning the biological digestion process before the liquor enters the

main part of the tank.

There are four stages to treatment, fill, aeration, settling and decanting. The aeration

stage involves adding air to the mixed solids and liquid either by the use of fixed or

floating mechanical pumps or by blowing it into finely perforated membranes fixed to

the floor of the tank. During this period the inlet valve to the tank is open and a returned

activated sludge pump takes mixed liquid and solids (mixed liquor) from the outlet end

of the tank to the inlet. This “seeds” the incoming sewage with live bacteria.

Aeration times vary according to the plant size and the composition/quantity of the

incoming liquor, but are typically 60 – 90 minutes. The addition of oxygen to the liquor

encourages the multiplication of aerobic bacteria and they consume the nutrients. This

66

process encourages the production of nitrogen compounds as the bacteria increase their

number, a process known as nitrification.

To remove phosphorus compounds from the liquor aluminium sulfate (alum) is often

added during this period. It reacts to form non-soluble compounds, which settle into the

sludge in the next stage.

The settling stage is usually the same length in time as the aeration. During this stage

the sludge formed by the bacteria is allowed to settle to the bottom of the tank. The

aerobic bacteria continue to multiply until the dissolved oxygen is all but used up.

Conditions in the tank, especially near the bottom are now more suitable for the

anaerobic bacteria to flourish. Many of these, and some of the bacteria which would

prefer an oxygen environment, now start to use nitrogen as a base element and extract

it from the compounds in the liquid, using up the nitrogen compounds created in the

aeration stage. This is known as denitrification.

As the bacteria multiply and die, the sludge within the tank increases over time and a

waste activated sludge pump removes some of the sludge during the settle stage to a

digester for further treatment. The quantity or “age” of sludge within the tank is closely

monitored, as this can have a marked effect on the treatment process.

The sludge is allowed to settle until clear water is on the top 20%-30% of the tank

contents. The decanting stage most commonly involves the slow lowering of a scoop or

“trough” into the basin. This has a piped connection to a lagoon where the final effluent

is stored for disposal to a wetland, tree growing lot, ocean outfall, or to be further

treated for use on parks, golf courses etc (Wikipedia).

2.5.2 Membrane Bioreactors (MBR)

The Membrane Bioreactor (MBR) process is an emerging advanced wastewater

treatment technology that has been successfully applied at an ever increasing number of

locations around the world. In addition to their steady increase in number, MBR

installations are also increasing in terms of scale.

The MBR process is a suspended growth activated sludge system that utilizes

microporous membranes for solid/liquid separation in lieu of secondary clarifiers. The

typical arrangement shown in Figure

aerated portion of the bioreactor, an anoxic zone and internal mixed liquor recycle (e.g

Modified Lutzack-Ettinger configuration). Incorporation of anaerobic zones for biological

phosphorus removal has been the focus of recent resear

scale facility of this type being designed presently in North America. As a further

alternative to Figure 2.24, some plants have used pressure membranes (rather than

submerged membranes) external to the bioreactor.

Figure 2.24: Typical sche

The advantages of MBR include:

• Secondary clarifiers and tertiary filtration processes are eliminated, thereby

reducing plant footprint. In certain instances, footprint can be

reduced because other process units such as digesters or UV disinfection

can also be eliminated/minimized (dependent upon governing regulations).

• Unlike secondary clarifiers, the quality of solids separation is not dependent

on the mixed liquor suspended solids concentration or characteristics. Since

elevated mixed liquor concentrations are possible, the aeration basin volume can

be reduced, further reducing the plant footprint.

• No reliance upon achieving good sludge settle

remote operation.



typical arrangement shown in Figure 2.24 includes submerged membranes in the


Ettinger configuration). Incorporation of anaerobic zones for biological

phosphorus removal has been the focus of recent research, and there is at least one full


, some plants have used pressure membranes (rather than

submerged membranes) external to the bioreactor.

pical schematic for membrane bioreactor system

The advantages of MBR include:

Secondary clarifiers and tertiary filtration processes are eliminated, thereby

reducing plant footprint. In certain instances, footprint can be



Unlike secondary clarifiers, the quality of solids separation is not dependent



be reduced, further reducing the plant footprint.

No reliance upon achieving good sludge settleability, hence quite amenable to

67



erged membranes in the


Ettinger configuration). Incorporation of anaerobic zones for biological

ch, and there is at least one full


, some plants have used pressure membranes (rather than

stem.

Secondary clarifiers and tertiary filtration processes are eliminated, thereby

reducing plant footprint. In certain instances, footprint can be further



Unlike secondary clarifiers, the quality of solids separation is not dependent



ability, hence quite amenable to

68

• Can be designed with long sludge age, hence low sludge production.

• Produces a MF/UF quality effluent suitable for reuse applications or as a high

quality feed water source for Reverse Osmosis treatment. Indicative output

quality of MF/UF systems include SS < 1mg/L, turbidity <0.2 NTU and up to

4 log removal of virus (depending on the membrane nominal pore size). In

addition, MF/UF provides a barrier to certain chlorine resistant pathogens such

as Cryptosporidium and Giardia.

• The resultant small footprint can be a feature used to address issues of visual

amenity, noise and odor. Example MBR plants exist where the entire process is

housed in a building designed to blend in with its surrounding land use. This can

reduce the buffer distance required between the plants and the nearest

neighbor and can increase the surrounding land values.

2.5.3 Upward-flow Anaerobic Sludge Bed (UASB)

Anaerobic granular sludge bed technology refers to a special kind of reactor concept for

the "high rate" anaerobic treatment of wastewater. The concept was initiated with

upward-flow anaerobic sludge blanket (UASB) reactor. A scheme of a UASB is shown in

figure 2.25 below. From a hardware perspective, a UASB reactor is at first appearance

nothing more than an empty tank (thus an extremely simple and inexpensive design).

Wastewater is distributed into the tank at appropriately spaced inlets. The wastewater

passes upwards through an anaerobic sludge bed where the microorganisms in the

sludge come into contact with wastewater-substrates. The sludge bed is composed of

microorganisms that naturally form granules (pellets) of 0.5 to 2 mm diameter that have

a high sedimentation velocity and thus resist wash-out from the system even at high

hydraulic loads. The resulting anaerobic degradation process typically is responsible for

the production of gas (e.g. biogas containing CH4 and CO2). The upward motion of

released gas bubbles causes hydraulic turbulence that provides reactor mixing without

any mechanical parts. At the top of the reactor, the water phase is separated from

sludge solids and gas in a three-phase separator (also known the gas-liquid-solids

separator). The three phase separator is commonly a gas cap with a settler situated

above it. Below the opening of the gas cap, baffles are used to deflect gas to the gas

opening.

Figure 2.25: The upward

2.5.4 Expanded Granular Sludge Bed (

An expanded granular sludge bed (EGSB) reactor is a variant of the UASB concept (Kato

et al. 1994). The distinguishing feature is that a faster rate of upward

designed for the wastewater passing through the sludge bed. The increased flux p

partial expansion (fluidization) of the granular sludge bed, improving wastewater sludge

contact as well as enhancing segregation of small inactive suspended particle from the

sludge bed. The increased flow velocity is either accomplished by utilizi

or by incorporating an effluent recycle (or both). A scheme depicting the EGSB design

concept is shown in figure 2.26.

wastewaters (less than 1 to 2 g soluble COD/l) or for wastew

poorly biodegradable suspended particles which should not be allowed to accumulate in

the sludge bed.

above it. Below the opening of the gas cap, baffles are used to deflect gas to the gas

The upward-flow anaerobic sludge bed (UASB) reactor concept

2.5.4 Expanded Granular Sludge Bed (EGSB)


. 1994). The distinguishing feature is that a faster rate of upward-flow velocity is

designed for the wastewater passing through the sludge bed. The increased flux p



sludge bed. The increased flow velocity is either accomplished by utilizing tall reactors,


2.26. The EGSB design is appropriate for low strength soluble

wastewaters (less than 1 to 2 g soluble COD/l) or for wastewaters that contain inert or


69

above it. Below the opening of the gas cap, baffles are used to deflect gas to the gas-cap

flow anaerobic sludge bed (UASB) reactor concept


flow velocity is

designed for the wastewater passing through the sludge bed. The increased flux permits



ng tall reactors,


The EGSB design is appropriate for low strength soluble

aters that contain inert or


Figure 2.26: The expanded granular sludge bed (EGSB) reactor concept

2.5.5 Reversing Anaerobic Upflow System (RAUS)

In principle, the reversing anaerobic upflow system (RAUS) is slightly similar to UASB

system. But it consists of two anaerobic reactors interconnected with one another

(Figure 2.27). When one reactor is fed upward with wastewater, the other one acts as

the settler. After a certain set period of time, the flow is reversed such that the second

reactor is fed with wastewater and the first one now acts as the settler.

Effluent

Influent

The expanded granular sludge bed (EGSB) reactor concept

2.5.5 Reversing Anaerobic Upflow System (RAUS)



). When one reactor is fed upward with wastewater, the other one acts as

e settler. After a certain set period of time, the flow is reversed such that the second

reactor is fed with wastewater and the first one now acts as the settler.

Figure 2.27: The RAUS System.

Gas

Effluent

fluent Phase 2 Phase 1

70

The expanded granular sludge bed (EGSB) reactor concept.



). When one reactor is fed upward with wastewater, the other one acts as

e settler. After a certain set period of time, the flow is reversed such that the second

CHAPTER THREE

RESULTS AND DISCUSSION

71

3 Removal of Individual parameters

3.1 BOD5 removal

The removal efficiencies of various techniques used for the removal of BOD5 is described

below.

Table 3.1: Removal efficiency of BOD5

Serial

no.

Removal techniques Type of

wastewater

BOD Removal

efficiency (%)

References

01 Upflow Anaerobic Sludge Bed

(UASB) & Expanded Granular

Sludge Bed (EGSB)

N/A 97 - 99 Saleh and

Mahmood,

2003

02 Activated sludge N/A 67 Yazdi et al.,

2001

03 Aerated lagoon Paper 85 Fonade et al.,

2000

04 Vertically Moving Biofilm

System (VMBS)

Synthetic

fiber

97.9 Rodgers et al.,

2004

05 Anaerobic Baffled Reactor

(ABR)

Food

processing

95 Stewart, 2004

06 Chemically Enhanced Primary

Treatment/Trickling filter

(CEPT-TF)

N/A ≥ 85 Ahmed, 2007

07 Submerged Aerated Fixed

Film Reactor (SAFF)

Textile ≥ 85 Saral et al.,

2006

08 Internal Circulation (IC)

anaerobic reactor &

Sequencing Batch Reactor

(SBR)

Swine 99.6 Deng et al.,

2006

*N/A – Not available.

01. The Installation of the upflow anaerobic sludge bed (UASB) and expanded granular

sludge bed (EGSB) for industrial wastewater treatment (anaerobic process) was

studied which has grown very rapid by over the past (15-20 years). These systems

provided highly efficient BOD removal. The BOD reduction was about 97-99% (Saleh

and Mahmood, 2003).

02. The treatment of industrial effluents by using laboratory activated sludge unit was

studied. The result obtained has indicated that the average influent 5-days BOD was

approximately 4,000 mg/l and an average reduction to 1,200 mg/l was obtained. The

percentage reduction of up to 67% was obtained (Yazdi et al., 2001).

72

03. The aerobic biological treatment of industrial wastewaters was studied by aerated

lagoons. A methodology was developed which gave the best fit between the

biological reactions and the ideal hydrodynamic behavior of the lagoon. The BOD

degradation was about 85% (Fonade et al., 2000).

04. A vertically moving biofilm system (VMBS) was developed to treat industrial

wastewater. Removal efficiency of biological oxygen demand (BOD) was up to 97.9%

(Rodgers et al., 2004).

05. Anaerobic Baffled Reactor (ABR) utilizes separate loading and unloading cells on a

continuous feed basis. This ABR design with a storage volume of over 100,000 m3

reduces the land requirement to treat the same wastewater (300 liters per minute at

average flow rates) by 50 hectares. The ABR reduces BOD by over 95% (Stewart,

2004).

06. Chemically Enhanced Primary Treatment/ Trickling Filter (CEPT-TF) system was used

for low cost treatment of industrial effluents. The results indicated that, major part

of BOD load was removed within the CEPT module. More than 85 % of BOD5

removed by the overall system is carried out in CEPT module (Ahmed, 2007).

07. An advance process Submerged Aerated Fixed Film Reactor (SAFF) was developed for

the biodegradation of textile wastewater. The BOD5 reduction was more than 85%

(Saral et al., 2006).

08. A combined system consisting of Internal Circulation (IC) anaerobic reactor and

Sequencing Batch Reactor (SBR) was used to treat swine wastewater in order to

establish a cost-efficient wastewater treatment system. The removal rate of BOD5

was 99.6%, in the IC–SBR system with total hydraulic retention time of 5–6 days

(Deng et al., 2006).

73

3.2 COD removal

The removal efficiencies of various techniques used for the removal of COD is described

below.

Table 3.2: Removal efficiency of COD

Serial

no.


wastewater

COD Removal

efficiency (%)

References

01 Upflow Anaerobic Sludge

Bed (UASB) & Expanded

Granular Sludge Bed

(EGSB)

N/A 80 - 95 Saleh and

Mahmood, 2003

02 Activated sludge N/A 85 Yazdi et al.,

2001

03 Upflow Anaerobic Sludge

Bed (UASB)

Petrochemical 42.1 - 85.9 Jafarzadeh et

al., 2006

04 Anaerobic digestion Winery 90 - 95 R. Moletta, 2005

05 Vertically Moving Biofilm

System (VMBS)

Synthetic fiber 93.2 Rodgers et al.,

2004

06 Sequencing Batch Reactor

(SBR)

Dairy ≥ 90 Bandpi and

Bazari, 2004

07 Salt tolerant bacterial

mixed consortia

Tannery 80 Sivaprakasam et

al., 2008

08 Anaerobic Baffled Reactor

(ABR)

Food

processing

60 Stewart, 2004

09 Reversing Anaerobic

Upflow System (RAUS)

Polyester 88 Joshi and

Polprasert, 1998

10 Submerged Aerated Fixed

Film Reactor (SAFF)

Textile ≥ 85 Saral et al., 2006

11 (a) Aerobic Sequencing Batch

Reactor (SBR)

Textile 60 (for total

COD)

Frounda et al.,

2001

11 (b) Aerobic Sequencing Batch

Reactor (SBR)

Textile 30 (for

soluble COD)

Frounda et al.,

2001


(SBR)

N/A 88 - 95 Ros and

Vrtovsek, 2004

13 Clarification Textile 91 Sapci and Ustun,

2003

14 (a) Anaerobic Sequencing

Batch Reactor (SBR)

Olive mill 80 Bashaar and

Ammary, 2004

14 (b) Aerobic Sequencing Batch

Reactor (SBR)

Pulp and paper

mill

75 Bashaar and

Ammary, 2004


(SBR)

Beef

processing

99 (for

soluble COD)

Thayalakumaran

et al., 2003


(SBR)

N/A 90-98 Akin and Ugurlu,

2003

74

Table 3.2: Removal efficiency of COD (Continued)

Serial

no.


wastewater

COD Removal

efficiency (%)

References


(SBR)

Synthetic 96 Uygur and Kargi,

2004

18 Continuous anaerobic

digestion (CAD)

Olive oil mill 81 Heredia and

Garcia, 2005

19 Internal Circulation (IC)

anaerobic reactor &


(SBR)

Swine 95.5 Deng et al.,

2006


(SBR)

Tannery 95 Lefebvre et al.,

2005

*N/A – Not available.

01. The Installation of the upflow anaerobic sludge bed (UASB) and expanded granular

sludge bed (EGSB) for industrial wastewater treatment was studied which has grown

very rapid by over the past (15-20 years). These systems provided highly efficient

COD removal. The UASB reactor achieved a loading rate 7.2 kg COD/m3/d HRT

(hydraulic Retention Time) 3-4 days. The best performance loading rate was 4 kg

COD/m3/d. The COD reduction was about 80-95% (Saleh and Mahmood, 2003).

02. The treatment of industrial effluents by using laboratory activated sludge unit was

studied. The amount of COD reduction was variable throughout the experiment. The

minimum reduction was about 72% and the maximum about 90%. The percentage

reduction of COD reached an average of up to 85% in effluent, a reduction from

20,000 mg/l to 3,000 mg/l (Yazdi et al., 2001).

03. The performance of an anaerobic hybrid reactor (UASB) treating petrochemical

wastewater was studied. The minimum and maximum COD reductions of the overall

reactor were 42.1 and 85.9% at influent COD concentration of 3,000 mg/l and 4,000

mg/l respectively (Jafarzadeh et al., 2006).

04. Anaerobic digestion is widely used for wastewater treatment, especially in the food

industries. With winery wastewaters (as for vinasses from distilleries) the removal

yield for anaerobic digestion was very high, up to 90–95% COD removal (R. Moletta,

2005).

75

05. A Vertically Moving Biofilm System (VMBS) was developed to treat industrial

wastewater. Removal efficiency of filtered chemical oxygen demand (COD) was up to

93.2% (Rodgers et al., 2004).

06. A bench scale aerobic Sequencing Batch Reactor (SBR) was investigated to treat the

wastewater from an industrial milk factory. The study demonstrated the capability of

aerobic SBR for COD removal from dairy industrial wastewater. The COD removal

efficiency was achieved more than 90%, whereas COD concentration varied from 400

to 2,500 mg/l (Bandpi and Bazari, 2004).

07. Tannery saline wastewater degradation studies were done as batch experiments

(incubated shaking flask) with pure monocultures of Pseudomonas aeruginosa,

Bacillus flexus, Exiguobacterium homiense and Staphylococcus aureus. The salt

concentrations were varied from 2–10% (w/v). A maximum degradation of 87.6%

was observed for P.aeruginosa. Analysis of results showed that E.homiense exhibited

a higher COD removal (90%). Salt tolerant bacterial mixed consortia showed

appreciable biodegradation at all saline concentrations (2%, 4%, 6%, 8% and 10%

w/v) with 80% COD reduction in particular at 8% salinity level, the consortia could be

used as suitable working cultures for tannery saline wastewater treatment

(Sivaprakasam et al., 2008).

08. Anaerobic Baffled Reactor (ABR) utilizes separate loading and unloading cells on a

continuous feed basis. This ABR design with a storage volume of over 100,000 m3

reduces the land requirement to treat the same wastewater (300 liters per minute at

average flow rates) by 50 hectares. The ABR reduces COD by over 60% (Stewart,

2004).

09. A new high rate anaerobic process, the reversing anaerobic upflow system (RAUS)

was used for the lowest cost wastewater treatment option for highly polluted

industrial wastewater. Results indicated that COD reduction was about 88% (Joshi

and Polprasert, 1998).

10. An advance process Submerged Aerated Fixed Film Reactor (SAFF) was developed

for the biodegradation of textile wastewater. The COD reduction was more than 85%

(Saral et al., 2006).

11. The biological treatment of a textile wastewater was investigated in an aerobic

sequencing batch reactor (SBR). The system was operated in 8-hour cycles. At

76

steady-state operation, which took 60 days to attain, the removal of total and

soluble COD was 60% and 30% respectively (Frounda et al., 2001).

12. Four different experiments in a sequencing batch reactor were carried out. In all

series COD removal was from 88 to 95% (Ros and Vrtovsek, 2004).

13. Waste pumice was chosen as an adsorbent to observe removal efficiency of COD

from textile wastewater. When the clarification of textile wastewater was

experimented by waste pumice, it had been observed that the pumice had a capacity

of adsorption. Consequently, the best COD removal efficiency was obtained by an

increase on the ratios of pumice, FeSO4 and Ca(OH)2. The combination of these

chemicals and adsorbent (e.g. 10 g pumice, 0.6 g/l FeSO4 and 0.6 g/l Ca(OH)2) was

given maximum COD removal efficiency as 91% (Sapci and Ustun, 2003).

14. Wastewaters from olive mills and pulp and paper mill industries in Jordan were

treated using laboratory scale anaerobic and aerobic sequencing batch reactors,

respectively. It was found that for anaerobic treatment of olive mills wastewater

COD:N:P ratio of about 900:5:1.7 was able to achieve more than 80% COD removal.

For extended aeration aerobic treatment of pulp and paper mill wastewater COD:N:P

ratio of about 170:5:1.5 was able to achieve more than 75% COD removal (Bashaar

and Ammary, 2004).

15. A laboratory scale sequencing batch reactor (SBR) was operated for the treatment of

a beef processing effluent from slaughtering and boning operations. An effective SBR

cycle was found for removal of COD at 22°C. Removal of biodegradable soluble COD

of greater than 99% was achieved in the SBR (Thayalakumaran et al., 2003).

16. A research was performed for the removal of COD in a laboratory scale sequencing

batch reactor (SBR) having a new operational mode. The SBR system had

simultaneous feeding and decanting conditions. High COD (90-98%) removal was

achieved by this system (Akin and Ugurlu, 2003).

17. Nutrient removal from synthetic wastewater was investigated using a four-step

sequencing batch reactor (SBR) at different 2,4 dichlorophenol (DCP) concentrations.

Adverse effects of dichlorophenol on COD removal were almost negligible for DCP

concentrations below 123 mg/L. About 96% COD removal was obtained at a DCP

concentration of 123 mg/L (Uygur and Kargi, 2004).

77

18. The purification of the olive mill wastewaters (OMW) was investigated by the

combination of an anaerobic digestion, followed by an ozonation treatment.

Continuous anaerobic digestion (CAD) was performed in a laboratory scale

bioreactor. The COD removal was 81% (Heredia and Garcia, 2005).



establish a cost-efficient wastewater treatment system. Performance of post

treatment using SBR with the addition of raw wastewater was good with effluent

COD less than 300 mg/L. The removal rate of COD was 95.5%, in the IC–SBR system

with total hydraulic retention time of 5–6 days (Deng et al., 2006).

20. A study was performed to treat tannery wastewater from soak pit in a lab-scale

Sequencing Batch Reactor (SBR) for the removal of organic matter. The soak liquor

was biologically treated in an aerobic sequencing batch reactor seeded with

halophilic bacteria and the performance of the system was evaluated under different

operating conditions with changes in hydraulic retention time, organic loading rate

and salt concentration. Optimum COD removal efficiency of 95% was reached with 5

days hydraulic retention time (HRT), an organic loading rate (OLR) of 0.6 kg

COD m−3

d−1

and 34 g NaCl l−1

(Lefebvre et al., 2005).

3.3 Total Organic Carbon (TOC) removal

A research was conducted to study biological processes for treating wastewaters

containing high concentrations (e.g., 400 mg/L) of Lauryl Alkylbenzene Sulfonate (LAS).

Initial experiments were carried out using a respirometry technique and subsequently,

three different laboratory-scale bioreactor systems. The three systems studied were a

Sequencing Batch Reactor (SBR), a Sequencing Batch Biofilm Reactor (SBBR) and an

Intermittent Cycle Extension Aeration System (ICEAS). The SBR and ICEAS were operated

on a five-day cycle basis with a hydraulic retention time of four days. The SBBR was

operated mainly in a two-day cycle having a hydraulic retention time of ten days as well.

At the end of the experiment, TOC removal was 84.4%, 75.2%, 70.6%, and 46.0% for

samples initially containing 30, 60, 150, and 300 mg/L SDS (Rodezno, 2004).

78

The biological treatment of wastewater from an aminoplastic resin producing industry

was studied in a predenitrification system. The total organic carbon (TOC) values in the

feed varied from 1,423.0 to 1,599.5 mg/l, corresponding to an organic loading rate of

about 0.20 kg TOC/m3/d. High TOC removal was achieved, around 92% (Eiroa et al.,

2006).

3.4 Nitrogen (N) removal

Table 3.3: Removal efficiency of nitrogen

Serial no. Removal techniques Nitrogen

Removal

efficiency (%)

References

01 Sequencing Batch Reactor (SBR) 80-84 (TN) Ros and Vrtovsek,

2004

02 BioBalance 84.6 (TN) Vaboliene et al.,

2005

03 (a) Various yeast species 22-93 (TN) Thanh and Simard,

1973

03 (b) Various yeast species 27-90 (NH3-N) Thanh and Simard,

1973

04 Fungi 49-77 (NH3-N) Hiremath et al.,

1985

05 Sequencing Batch Reactor (SBR) 99 (NH3-N) Thayalakumaran et

al., 2003

06 Sequencing Batch Reactor (SBR) 90-95 (NH3-N) Akin and Ugurlu,

2003

07 Sequencing Batch Reactor (SBR) 46 (NH3-N) Uygur and Kargi,

2004

08 (a) Internal Circulation (IC) anaerobic

reactor and Sequencing Batch

Reactor (SBR)

99.4 (NH3-N) Deng et al., 2006

08 (b) Internal Circulation (IC) anaerobic

reactor and Sequencing Batch

Reactor (SBR)

94.3 (TN) Deng et al., 2006

09 Sequencing Batch Reactor (SBR) 96 (TKN) Lefebvre et al.,

2005

10 (a) Circulating bioreactor 90-98 (TN) Hirata et al., 2001

10 (b) Circulating bioreactor 80-92 (NH3) Hirata et al., 2001

* TN- Total Nitrogen; NH3-N-Ammonia Nitrogen; TKN-Total Kjeldahl Nitrogen

1. Four different experiments in a Sequencing Batch Reactor (SBR) were carried out.

Different COD:N:P and BOD5:N:P ratios were studied. The optimal COD:N:P was

79

100:11:2 and BOD5:N:P was 100:15:3. In all series nitrogen removal was from 80 to

84% (Ros and Vrtovsek, 2004).

2. Biological nitrogen removal was evaluated and compared by using the “BioBalance”

technology for biological nitrogen removal. Evaluating Utena Wastewater Treatment

Plant before and after the reconstruction, it was estimated that 84.6 % of total

nitrogen was removed by using the ”BioBalance” technology and total nitrogen (TN)

in the effluent was not higher than allowable norms (Vaboliene et al., 2005).

3. Treatment of wastewater by various yeast species was studied. The study screened

27 yeast strains for their ability to produce a high biomass, while maximizing

reduction of ammonia. Reported total nitrogen (TN) removal from 22 to 93%,

ammonia nitrogen (NH3-N) from 27 to 90% (Thanh and Simard, 1973).

4. Recently fungi have been recognized to perform denitrification at greater rates than

bacteria. Seven fungal species was isolated from a wastewater stabilization pond.

The study reported ammonia nitrogen (NH3-N) removal between 49 and 77%

(Hiremath et al., 1985).

5. A laboratory scale Sequencing Batch Reactor (SBR) was operated for the treatment

of a beef processing effluent from slaughtering and boning operations. An effective

SBR cycle was found for removal of nitrogen at 22°C. Removal of ammonia nitrogen

(NH3-N) of greater than 99 % was achieved in the SBR (Thayalakumaran et al., 2003).

6. A research was performed for the removal of nitrogen in a laboratory scale

Sequencing Batch Reactor (SBR) having a new operational mode. The SBR system

had simultaneous feeding and decanting conditions. High ammonia nitrogen (NH3-N)

removal of 90-95% was achieved by this system (Akin and Ugurlu, 2003).



About 46% ammonia nitrogen (NH3-N) removal was obtained at a DCP concentration

of 123 mg/L (Uygur and Kargi, 2004).



establish a cost-efficient wastewater treatment system. The removal rates of

ammonia nitrogen (NH3-N) and total nitrogen (TN) were 99.4% and 94.3%,

80

respectively, in the IC-SBR system with total hydraulic retention time of 5–6 days

(Deng et al., 2006).






and salt concentration. Optimum Total Kjeldahl Nitrogen (TKN) removal efficiency of

96% was reached with 5 days hydraulic retention time (HRT), an organic loading rate

(OLR) of 0.6 kg COD m−3

d−1

and 34 g NaCl l−1


10. Biological nitrogen removal from industrial wastewater was attempted by using a

circulating bioreactor system equipped with an anaerobic packed bed and an aerobic

three-phase fluidized bed. As a result of acclimating microorganisms with change of

the hydraulic residence time, this system effectively removed nitrogen from diluted

wastewater. The removal ratio of total nitrogen (TN) was 90% to 98% and that of

ammonia (NH3) was 80% to 92% (Hirata et al., 2001).

3.5 Phosphorus (P) removal

Table 3.4: Removal efficiency of phosphorus

Serial no. Removal techniques Phosphorus

Removal

efficiency (%)

References

01 BioBalance 97 (TP) Vaboliene et al.,

2005

02 Various yeast species 100 (PO43−

) Thanh and Simard,

1973

03 Fungi 77 (PO43−

) Hiremath et al.,

1985

04 Sequencing Batch Reactor (SBR) 99 (PO43−

-P) Thayalakumaran et

al., 2003


-P) Akin and Ugurlu,

2003


-P) Uygur and Kargi,

2004


) Lefebvre et al.,

2005

* TP- Total Phosphorus; (PO43−

-P)- Phosphate Phosphorus; (PO43−

)- Phosphate.

81

1. Biological phosphorus removal was evaluated and compared by using the

“BioBalance” technology for biological phosphorus removal. Evaluating Utena

Wastewater Treatment Plant before and after the reconstruction, it was estimated

that up to 97 % of total phosphorus (TP) was removed by using the ”BioBalance”

technology and Total-P in the effluent was not higher than allowable norms

(Vaboliene et al., 2005).

2. Treatment of wastewater by various yeast species was studied. The study screened

27 yeast strains for their ability to produce a high biomass, while maximizing

reduction of phosphate. Reported phosphate (PO43−

) removal ranged from 12 to

100% (Thanh and Simard, 1973).

3. Recently fungi have been recognized to perform denitrification at greater rates than

bacteria. Seven fungal species was isolated from a wastewater stabilization pond.

The study reported phosphate (PO43−

) removal from 34 to 77% (Hiremath et al.,

1985).

4. A laboratory scale sequencing batch reactor (SBR) was operated for the treatment of

a beef processing effluent from slaughtering and boning operations. An effective SBR

cycle was found for removal of phosphorus at 22°C. Removal of phosphate

phosphorus (PO43−

-P) of greater than 99 % was achieved in the SBR (Thayalakumaran

et al., 2003).

5. A research was performed for the removal of phosphorus in a laboratory scale

sequencing batch reactor (SBR) having a new operational mode. The SBR system had

simultaneous feeding and decanting conditions. High phosphate phosphorus (PO43−

-

P) removal of 77-100% was achieved by this system (Akin and Ugurlu, 2003).



About 22% phosphate phosphorus (PO43−

-P) removal was obtained at a DCP

concentration of 123 mg/L (Uygur and Kargi, 2004).






82

and salt concentration. Optimum phosphate (PO43−

) removal efficiency of 93% was

reached with 5 days hydraulic retention time (HRT), an organic loading rate (OLR) of

0.6 kg COD m−3

d−1

and 34 g NaCl l−1


3.6 Selenium (Se) removal

Biological treatment is an emerging technology for removing selenium (Se) from

wastewaters due to its cost-effectiveness and high specificity. It has been found that

certain microorganisms, especially anaerobic ones, have the ability to reduce Se into less

toxic forms or into forms that can be more easily removed, such as elemental selenium.

The Chevron Company invested in a system of biological treatment of refinery effluents

with the construction of a wetland obtaining a removal of, at least, 70% of the selenium

fed to the treatment system (Hansen et al., 1998).

3.7 Lead (Pb) removal

Removal of lead (Pb) from solution was studied using growing cells and washed cells of

Bacillus Cereus M1

16. The removal of Pb(II) ions with growing cells was maximum (85%)

when initial lead concentration was 50 mg/L. The highest value of lead uptake was 96%,

with 1.8 g/L washed biomass (dry basis) at 20oC and 92% at 30

oC (Ray et al., 2005).

3.8 Manganese (Mn) removal

A study was conducted for biological removal of manganese (Mn) from wastewater. The

result indicated that, manganese removal efficiency up to 94% was achieved for

sufficiently high (Retention Time) RT in a sequential batch reactor (Seguret, 2000) and

(Gouzinis, 1998).

3.9 Suspended Solid (SS) removal

A study was performed to treat tannery wastewater from soak pit in a lab-scale

Sequencing Batch Reactor (SBR) for the removal of organic matter. The soak liquor was

biologically treated in an aerobic sequencing batch reactor seeded with halophilic

bacteria and the performance of the system was evaluated under different operating

conditions with changes in hydraulic retention time, organic loading rate and salt

concentration. Optimum suspended solid (SS) removal efficiency of 92% was reached

83

with 5 days hydraulic retention time (HRT), an organic loading rate (OLR) of 0.6 kg

COD m−3

d−1

and 34 g NaCl l−1


3.10 Odor removal

Biological treatment of odor at wastewater treatment plants was studied using biofilters

and biotrickling filters for the treatment of complex air streams containing multiple

pollutants. Both the biofilter and biotrickling filter consistently removed Hydrogen

Sulfide (H2S) at greater than 97 % efficiency. Volatile Organic Carbon (VOC) removal in

the biotrickling filter was dependent on the pH (1.5-2). 35 to 45% removal was observed

for easily biodegradable VOCs such as toluene and benzene when a neutral pH was

maintained in the biotrickling filter. The results demonstrated that some organic sulfur

compounds were removed, in particular by the biofilter, but others not. Analyses of inlet

and outlet streams revealed that the odor reduction was greater than 97% in both pilot

units (Cox et al.).

A single-chamber microbial fuel cell (MFC) was used to reduce 10 chemicals associated

with odors by 99.76% (from 422 ± 23 µg/ml) and three volatile organic acids (acetate,

butyrate and propionate) by >99% (Kim et al., 2008).

3.11 Color removal

Synthetic textile wastewater and real wastewater from batik dyeing process were

decolorized by immobilized white-rot fungus Coriolus versicolor RC3 in repeated-batch

system. It was found that three cycles of repeated-batch decolorization were obtained

with more than 90% decolorization in 24 hours when a half of wastewater was removed

and replaced with new fresh dye. The immobilized fungal cell decolorized up to 80% was

reduced (Srikanlayanuku et al., 2006).

Waste pumice was chosen as an adsorbent to observe removal efficiency of color from

textile wastewater. When the clarification of textile wastewater was experimented by

waste pumice, it had been observed that the pumice had a capacity of adsorption.

Consequently, the best color removal efficiency was obtained by an increase on the

ratios of pumice, FeSO4 and Ca(OH)2. The combination of these chemicals and adsorbent

(e.g. 10g pumice, 0.6 g/l FeSO4 and 0.6 g/l Ca(OH)2) was given maximum color removal

efficiency as 87 % (Sapci and Ustun, 2003).

CHAPTER FOUR

CONCLUSION

The treatment technologies of the various industrial wastewaters were reviewed by

collecting data of the various treatment methods used for treatment of industrial

wastewater.

In this study, the parameters used for the treatment of industrial wastewater such as

biochemical oxygen demand (

carbon (TOC), nitrogen (N),

suspended solid (SS), odor,

efficiencies of particular parameters are given below.

For BOD5 removal, the efficiency of various techniques

anaerobic sludge bed (UASB) &

sludge – 67%, aerated lagoon

anaerobic baffled reactor (ABR)

filter (CEPT-TF) – 85%, submerged

circulation (IC) anaerobic reactor &

Figure 4.1: BOD

For COD removal, the efficiency of various techniques used are as follows:

anaerobic sludge bed (UASB) &

sludge – 85%, upflow anaerobic

vertically moving biofilm system (VMBS)

0

10

20

30

40

50

60

70

80

90

100




emand (BOD5), chemical oxygen demand (COD),

, phosphorus (P), selenium (Se), lead (Pb), manganese (Mn),

dor, color etc were analyzed. The results for the removal

efficiencies of particular parameters are given below.

removal, the efficiency of various techniques used are as follows:

ed (UASB) & expanded granular sludge bed (EGSB) – 99%, a

erated lagoon – 85%, vertically moving biofilm system (VMBS)

eactor (ABR) – 95%, chemically enhanced primary treatment/

ubmerged aerated fixed film reactor (SAFF) – 85% and i

irculation (IC) anaerobic reactor & sequencing batch reactor (SBR) – 99.6% (figure

BOD5 removal efficiencies of various techniques.


ed (UASB) & expanded granular sludge bed (EGSB) – 95%,

naerobic sludge bed (UASB) – 85.9%, anaerobic digestion

ystem (VMBS) – 93.2%, sequencing batch reactor (SBR)

Upflow Anaerobic Sludge Bed (UASB) &

Expanded Granular Sludge Bed (EGSB)

Activated sludge

Aerated lagoon

Vertically Moving Biofilm System (VMBS)

Anaerobic Baffled Reactor (ABR)

Chemically Enhanced Primary

Treatment/Trickling filter (CEPT-

Submerged Aerated Fixed Film Reactor (SAFF)

Internal Circulation (IC) anaerobic reactor &

Sequencing Batch Reactor (SBR)

84




, total organic

anganese (Mn),

The results for the removal

used are as follows: upflow

99%, activated

ystem (VMBS) – 97.9%,

reatment/trickling

85% and internal

6% (figure 4.1).

removal, the efficiency of various techniques used are as follows: upflow

95%, activated

naerobic digestion – 95%,

eactor (SBR) – 99%,

Upflow Anaerobic Sludge Bed (UASB) &

Expanded Granular Sludge Bed (EGSB)



-TF)




salt tolerant bacterial mixed consortia

reversing anaerobic upflow s

(SAFF) – 85%, clarification –

sequencing batch reactor –

circulation (IC) anaerobic reactor &

Figure 4.2: COD

For TOC removal, the efficiency of various techniques used are as follows:

technique and bioreactor systems

4.3).

Figure 4.3: TOC removal efficiencies of various techniques.

0

10

20

30

40

50

60

70

80

90

100

80

82

84

86

88

90

92

alt tolerant bacterial mixed consortia – 80%, anaerobic baffled reactor (ABR)

system (RAUS) – 88%, submerged aerated fixed

– 91%, anaerobic sequencing batch reactor –

75%, continuous anaerobic digestion (CAD) –

irculation (IC) anaerobic reactor & sequencing batch reactor (SBR) – 95.5% (figure

OD removal efficiencies of various techniques.

For TOC removal, the efficiency of various techniques used are as follows:

bioreactor systems – 84.4% and predenitrification system –

TOC removal efficiencies of various techniques.

Upflow Anaerobic Sludge Bed (UASB) & Expanded

Granular Sludge Bed (EGSB)Activated sludge

Upflow Anaerobic Sludge Bed (UASB)

Anaerobic digestion



Salt tolerant bacterial mixed consortia


Reversing Anaerobic Upflow System (RAUS)


Clarification

Anaerobic Sequencing Batch Reactor

Aerobic Sequencing Batch Reactor

Continuous anaerobic digestion (CAD)



Respirometry

technique and

bioreactor systems

Predenitrifica-tion

system

85

eactor (ABR) – 60%,

ixed film reactor

80%, aerobic

81%, internal

95.5% (figure 4.2).

For TOC removal, the efficiency of various techniques used are as follows: respirometry

– 92% (figure

Upflow Anaerobic Sludge Bed (UASB) & Expanded

Upflow Anaerobic Sludge Bed (UASB)


Salt tolerant bacterial mixed consortia

Reversing Anaerobic Upflow System (RAUS)


Anaerobic Sequencing Batch Reactor

Aerobic Sequencing Batch Reactor

Continuous anaerobic digestion (CAD)


For total nitrogen (TN) removal, the efficiency of various techniques used are as follows:

sequencing batch reactor (SBR)

internal circulation (IC) anae

and circulating bioreactor – 98% (

Figure 4.4.1: Total nitrogen

For ammonia nitrogen (NH3-

follows: sequencing batch reactor (SBR)

internal circulation (IC) anaerobic reactor and

and circulating bioreactor – 92% (figure

Figure 4.4.2: Ammonia nitrogen

75

80

85

90

95

100

0

20

40

60

80

100


eactor (SBR) – 84%, bioBalance – 84.6%, various yeast species

irculation (IC) anaerobic reactor and sequencing batch reactor (SBR)

98% (figure 4.4.1).

nitrogen (TN) removal efficiencies of various techniques.

-N) removal, the efficiency of various techniques used are as

eactor (SBR) – 99%, various yeast species – 90%,

irculation (IC) anaerobic reactor and sequencing batch reactor (SBR)

92% (figure 4.4.2).

mmonia nitrogen (NH3-N) removal efficiencies of various techniques.


BioBalance

Various yeast species

Internal Circulation (IC)

anaerobic reactor and

Sequencing Batch Reactor (SBR)Circulating bioreactor



Fungi

Internal Circulation (IC)

anaerobic reactor and

Sequencing Batch Reactor (SBR)Circulating bioreactor

86


arious yeast species – 93%,

eactor (SBR) – 94.3%

removal efficiencies of various techniques.

removal, the efficiency of various techniques used are as

90%, Fungi – 77%,

eactor (SBR) – 99.4%




For phosphorus removal, the efficiency of various techniques used are as follows:

bioBalance – 97%, various yeast species

reactor (SBR) – 100% (figure

Figure 4.5: Phosphorus

For selenium (Se) removal, the efficiency of a

lead (Pb) removal, the efficiency of c

(Mn) removal, the efficiency of s

Figure 4.6: Removal efficiencies of various techniques used for the removal of

(Se

For suspended solid (SS) removal, the efficiency of s

92%. For odor removal, the efficiency of

color removal, the efficiency of

90% (figure 4.7).

0

20

40

60

80

100

0

20

40

60

80

100


arious yeast species – 100%, fungi – 77% and sequencing

100% (figure 4.5).

hosphorus removal efficiencies of various techniques.

removal, the efficiency of anaerobic microorganisms was 70%. For

removal, the efficiency of cells of Bacillus Cereus M1

16 was 96%. For m

removal, the efficiency of sequencing batch reactor (SBR) was 94% (figure

emoval efficiencies of various techniques used for the removal of

(Se), lead (Pb) and manganese (Mn).

removal, the efficiency of sequencing batch reactor (SBR

removal, the efficiency of biofilter and biotrickling filter was 9

removal, the efficiency of immobilized white-rot fungus Coriolus versicolor

BioBalance


Fungi


(SBR)

Selenium (Se)

Lead (Pb)

Manganese (Mn)

87


equencing batch


was 70%. For

was 96%. For manganese

) was 94% (figure 4.6).

emoval efficiencies of various techniques used for the removal of selenium

eactor (SBR) was

was 99.76%. For

Coriolus versicolor RC3 was

Figure 4.7: Removal efficiencies of various techniques used for the removal of

suspended solid (SS), odor and color.

Finally it is found that, internal circulation (IC) anaerobic reactor & sequencing batch

reactor (SBR) are efficient techniques

is efficient technique for COD

for TOC removal, circulating bioreactor

removal and internal circulation (IC) anaerobic reactor

are efficient techniques for

and sequencing batch reactor (SBR)

In Bangladesh, a large amount of untreated industrial wastewater is releasing into

surrounding areas of the industrial areas daily. This type of wast

environmental pollution locally as well as the whole country.

effective techniques found from the review work

should be used for the treatment of industrial wastewater in Bangladesh

industrial pollution.

85

90

95

100


suspended solid (SS), odor and color.


techniques for BOD5 removal, sequencing batch

OD removal, predenitrification system is efficient

irculating bioreactor is efficient technique for total nitrogen

irculation (IC) anaerobic reactor & sequencing batch

for ammonia nitrogen (NH3-N) removal, various yeast species

eactor (SBR) are efficient techniques for phosphorus


surrounding areas of the industrial areas daily. This type of wastewater is causing

environmental pollution locally as well as the whole country. So, the efficient

found from the review work have higher removal efficiency

be used for the treatment of industrial wastewater in Bangladesh

Suspended solid (SS)

Odor

Color

88



atch reactor (SBR)

is efficient technique

nitrogen (TN)

atch reactor (SBR)

arious yeast species

phosphorus removal.


ewater is causing

efficient and cost-

have higher removal efficiency and

be used for the treatment of industrial wastewater in Bangladesh to control

CHAPTER FIVE

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