Water and Environmental Engineering Department of Chemical Engineering

NEW LEACHATE TREATMENT METHODS

Masters Thesis by 

Madu Jude Ifeanyichukwu

April 2008 

Vattenförsörjnings-och Avloppsteknik Water and Environmental Engineering Institutionen för Kemiteknik Department of Chemical Engineering Lunds Universitet Lund University, Sweden

New Leachate Treatment Methods

Master Thesis number: 2008-02 by

Madu Jude Ifeanyichukwu Water and Environmental Engineering

Department of Chemical Engineering April 2008

Supervisor: Professor Jes la Cour Jansen

Examiner: Associate professor Karin Jönsson

Picture on front page:

1. Spillepeng Landfill, Malmö, Sweden (Photo by: Jude Madu) PoP.SE S

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stal address: Visiting address: Telephone: O Box 124 Getingevägen 60 +46 46-222 82 85 -221 00 Lund. +46 46-222 00 00

weden, Telefax: +46 46-222 45 26

Web address: www.vateknik.lth.se

Abstract 

 This master’s thesis gives a brief background of leachate formation. It painstakingly reviewed the composition of leachate, factors affecting the composition and the treatment need. It also reviewed the leachate treatment methods, conventional as well as new methods and a comparison of the methods in terms of contamination removal efficiency, installation, operation and maintenance cost is made. Full scale installations of leachate treatment plants around the world were combed and recorded to give instances of where the various treatment methods and processes are in practise. More importantly, the thesis reviewed the composition of leachate generated in the Spillepeng landfill, Malmo which is managed by SYSAV AB a waste management company. It examined the efficiency of the treatment process in the pilot plant which is presently used for some of the leachate treatment and suggests processes that can be use for a full scale installation. The study concluded that there are tested, reliable and consistent conventional and new technologies for leachate treatment.

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Acknowledgements 

 I wish to express my sincere thanks to all who gave me the much desired assistance that saw me through the planning, development, production and presentation of this master’s thesis. My heartfelt gratitude is first to my supervisor, Professor Jes la Cour Jansen for his encouragement, expert advice and useful suggestions which was the driving force that propelled me to overcome this task. I would like to thank Associate Professor, Karin Jönson, my examiner for her positive contributions. My special thanks go to Associate Professor, Gerhard Barmen and Anna Carlqvist for their kind support, advice and encouragement during the difficult times. I acknowledge my gratitude to the management and staff of SYSAV AB especially to Erika Heander who expressed patience and provided me with answers for my numerous questions on the Spillepeng landfill as well as the SYSAV AB pilot plant for leachate treatment. Finally, I would like to thank my mother, Mrs Catharine Madu for her support, inspiration and

rayers. p

 Jude Madu Lund, April 2008

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Table of content Abstract ....................................................................................................................................... i 

Acknowledgements ...................................................................................................................iii 

Table o nte ........................................................................................................ iv f co nt.................

...  n

1  ......................................................................................................... 1 Background ........ductio

  ........................................................................................................ 2 1.1 Intro

  ........................................................................................................ 2 

........................................................................................................ 1 1.2 Objectives ....1.3 Aims .............

  ...................................................................................................... 2 1.4 Methodology .

  ................................................................ 3 2  p and treatment needCom osition of leachate, influencing factors

.....................  on

................................. 3 2.1 Age of Landfill ................

  .................................................................... 4 2.2 Climate /Seasonal weather variati ................................................................ 4 2.3 Kind of waste deposited .................2.4  Summary of leachate composition .................................................................... 6 2.4.1  ............ 6 Organic Substances ................................................................................

ces2.4.2  ............ 7 Inorganic Substan ..............................................................................  ave to be reduced and leachate discharge consent2.5 Substances that h  ................................................................................................. 8 2.6 Treatment needs

............ 7 

3  cri of leachate treatmentDes ption and evaluation ........................................................ 11 3.1  Biological methods ........................................................................................... 11 3.1.1  Biological nitrogen removal............................................................................. 11 3.1.2  oval of heavy metals

  ........................................................... 12 

Rem and sulphates .......................................................... 12 3.1.3  cipal biological processesPrin ........................................................... 12 ...............

....  r

3.1.3.1 The activated sludge...................g biological contracto

 3.1.3.2 The rotatin

  ............................................................... 16 3.1.3.3 Sequencing batch reactor (SBR)

s

........................................................... 13 .............................................................. 13 

3.1.3.4 Reed bed

  ................................................ 17 

....................................  ................................................ 16 3.1.3.5 Biologically aerated filter (BAF) ..............

..................................  ASB)

3.1.3.6 Lagoons ....................

........................................................ 18 3.1.3.7 Upflow anaerobic sludge blanket (U

..........BBR)

3.1.3.8  Anaerobic filter (AF) ...............eactor (Mrs (MBR)

............................................... 17 

3.1.3.9  Moving bed biofilm r3.1.3.10  Membrane Bioreacto

........................................................ 19 ................................................................. 19 

3.2  Physicochemical Method.................................................................................. 20 3.2.1  Coagulation-flocculation.................................................................................. 20 3.2.2  Precipitation ..................................................................................................... 20 3.2.3  Adsorption........................................................................................................ 21 3.2.4  Flotation ........................................................................................................... 21 3.2.5  (AOP)Chemical Oxidation and Advance Oxidation Process

..............................................  d Physicochemical Method

.......................... 21 3.2.6  ....................................... 22 Ammonia Stripping .....3.3 Combined Biological an ...................................... 23 3.4  Membrane Technology..................................................................................... 24 3.4.1  Microfiltration (MF)......................................................................................... 24 3.4.2  Ultra filtration (UF).......................................................................................... 24 3.4.3  Nanofiltration (NF) .......................................................................................... 24 3.4.4  Reverse Osmoses (RO) .................................................................................... 25 

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4  p ...................... 27 Com arison of the Methods ...................................................................4.1  ...................... 27 Merits and demerits of the treatment processes .....................

  conditions.4.2 Comparison of how good a process is for specific 

  ........ 37 

..................... 34 

5  ........ 37 Full scale installations. .........................................................................................5.1 Brief on the various full scale installations found. .................................

  te plants and treatment processes applied5.2 List of the full scale leacha

  ......................................... 51 

........ 48 

6  ......................................... 51 Leachate treatment in SYSAV AB, Malmo ............................................

  eng landfill6.1 Background on SYSAV AB ...................6.2 Composition of leachate in the Spillep ......................................... 52 6.3  Leachate treatment in the pilot plant.............................................................. 53 6.3.1  The pilot SBR process...................................................................................... 53 6.3.2  The pilot MBBR process.................................................................................. 54 6.3.3  Discharge limits from Miljödomstolen ............................................................ 55 6.3.4  Treatment results .............................................................................................. 55 6.3.5  Discussions....................................................................................................... 56 

7  Conclusion.................................................................................................................... 58 

8  Suggestion for further research .................................................................................... 60 

9  References .................................................................................................................... 62 

10  Abbreviations ............................................................................................................... 66 

 

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1 Background  1.1 Introduction  The importance of good health necessitated the deposition of domestic and industrial solid waste in landfills at remote areas. Decomposing waste within the landfills create major environmental problems as a result of the emission of the greenhouse gases (methane and carbon dioxide) as well as the production of a liquid known as leachate when precipitation infiltrates. Leachate is highly polluted due to high content of ammonium ions and organic compounds (Ulrika Welander, 1998). When leachate move downwards from landfill into ground-water table as a result of infiltrated precipitation, ground-water gets contaminated likewise if the waste is buried below the water table; ground-water becomes contaminated after leaching compounds from it (C.W Fetter, 2001). Once groundwater is contaminated it is very costly to clean-up. Figure 1 is a typical solid waste landfill in developing countries showing how leachate can contaminate groundwater if landfills have no leachate collection system. Figure 1: Typical solid waste landfill in Kuwait (A.F.Al-Yaqout and M.F.Hamoda, 2003)

Leachate plume

Water tableInfiltrating leachate

Variable level of water table

Landfill

No liner, no leachate collection system

Ground level

Solid waste

Liquid waste

Sludges

Hazardous waste

Landfill leachate can be toxic, acidic, and rich in organic acid groups. They can contain sulphate ions as well as high concentration of common metal ions especially iron. However, the type of material put into a landfill, landfill conditions such as pH, temperature, moisture, age, climate and the characteristic of the precipitation entering the landfill are some of the factors affecting the actual composition of a land fill leachate.

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Leachate consisting of mixtures of many chemicals is a potential risk to human health. As a result of the potential health effect of leachate, landfills have to be designed to minimize both the formation of leachate and the amount of leachate that leaks out from it. Landfill should therefore undergo design and construction procedures that will provide safeguards for control of leachate migration into groundwater. There should be the lining system (low permeable soil or synthetic materials) to ensure low-permeability of leachate into groundwater. Consequently, leachate collected through piping systems installed above the liners should be pumped out and treated before discharging to the environment, otherwise our reservoirs, waterways and underground water will be exposed to contaminants from leachate. Leachate are often discharged to local wastewater treatment plant in order to obtain sufficient treatment though it may be advantageous from an economic point of view to have final treatment of leachate on site. During the recent years many new methods- physicochemical, biological and combine biological with physicochemical have been proposed and tested. 1.2 Objectives  The objectives of this thesis are as follows:

• To identify the need for leachate treatment. • To identify the methods of leachate treatment • Give description of the various treatment methods • Evaluate the methods and make comparison of the methods • To find out treatment processes of some full scale leachate treatment plants • Describe leachate treatment in a specific site in Sweden (SYSAV AB, Malmö) • Propose a treatment method for SYSAV AB.

1.3 Aims  The aim of the study is to examine the various methods of leachate treatment, compare the methods, observe treatment processes and efficiency of existing full scale leachate plants, look at how SYSAV AB, Malmö, Sweden handles leachate treatment and proposes a full scale treatment method to them. 1.4 Methodology  The approach applied is a desktop and literature study of various aspects of the report. Reliable articles, journals and books were studied before and as the report were being written. Also a study visit was made to SYSAV AB to examine their treatment techniques.

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2 Composition of leachate, influencing factors and treatment need  

The composition of leachate is of interest because through it, leachate components that pollute surface and ground water bodies will be known and techniques of reducing or eliminating such components made. Leachate is composed of organic and inorganic substances. However, the chemical compositions of leachates differ owing to factors such as, age of landfill, climate/seasonal weather variation at the deposited site and the kind of waste deposited etc. 2.1 Age of Landfill   The age of a landfill greatly influences the chemical composition of a leachate. Landfills that are less than five years old are said to be in the acidogenic phase. In this phase, landfills contain large amount of biodegradable organic matter which normally undergoes anaerobic fermentation facilitated by water content of the landfill resulting in the production of volatile fatty acids (VFA). As the landfill gets beyond five years the methanogenic phase starts taking place. Methanogenic microorganisms develop in the waste, converting the VFAs to methane and carbon dioxides and the organic fraction of the leachate becomes mostly non-biodegradable (refractory) compounds e.g. humic substances. Generally, leachate from landfills less than five years old are said to be young leachates, those from landfills that are between five and ten years old are intermediate or medium age leachates as they may have both acidogenic and methanogenic features while those from landfills more than ten years old are said to be old or stabilized. Table 1 shows some chemical properties and composition of leachate at different age range. Table 1: Chemical properties and composition of leachate at different age range. ( S. Renou, J. G. Givaudan et al, 2007) Parameters Young( <5yrs) Medium Age (5-10yrs) Old (>10yrs) pH COD (mg/L) BOD5/COD Organic compound Biodegradability

6.5 > 10,000 > 0.3 80% volatile fatty acids (VFA) High

6.5-7.5 4,000-10,000 0.1-0.3 5-30% VFA+ humic and fulvic acid Medium

> 7.5 <4,000 < 0.1 Humic and fulvic Acid Low

pH, the hydrogen ion potential, is a measure of the acidity or basicity of a solution. The table shows that the pH of young leachate is acidic while the old one is basic. COD means Chemical Oxygen Demand. It is a measure of the concentration of contaminant in leachate that can be oxidised by a chemical oxidising agent. The table show high concentration of COD in young leachate than in the medium aged and the old. The same applies to the Biochemical Oxygen Demand (BOD) which is a measure of the concentration of biodegradable substances in the leachate or the quantity of oxygen consumed by microorganisms during the decomposition of organic matter in the leachate.

BOD5/COD is a relationship between BOD and COD. It indicates the degree of biodegradability of the leachate.

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The table indicates that when BOD/COD ratio is greater than 0.3, it is a young leachate. When the ratio is between 0.1 and 0.3 it is a medium age leachate and when the ratio is less than 0.1 it is an old leachate. Volatile fatty acids (VFA) are products of the anaerobic degradation of organic matter. From table 1 they make up about 80% of the content of a young leachate while the organic content of old leachates mainly has humic and fulvic substances. 2 

.2 Climate /Seasonal weather variation  

Climate/seasonal weather variation influences the output of leachate a great deal in terms of quantity and quality. During the rainy season, there are lots of precipitations. This increases moisture content of landfills. Since moisture content enhances the anaerobic fermentation of organic matter, biodegradability in the rainy season will be faster and more than in the dry season. Thus hot and humid climate which favours microbial activities generates more leachate and biodegrades more organic matter than hot and arid climate. Also in dry season evaporation adversely affects moisture content decreasing leachate production and microbial activities. 2.3 Kind of waste deposited  The kind of waste deposited on a landfill is a factor that determines the chemical composition of leachate from the landfill. Organic materials in the waste are mostly kitchen waste while inorganic constituents are things like plastics, glass, metals etc. Waste from different sources e.g. municipal, industrial etc have different ratio of these organic and inorganic materials.

Below, the compositions of leachates from an active municipal solid waste landfill as well as that of a stabilised sanitary landfill are presented. a. Composition of leachate from an active municipal solid waste (MSW) landfill in arid climate. Arid climate describes regions with low rainfall. In such regions annual rainfall is less than 250 mm. One may think that no leachate will be generated in arid climate landfills but that is a wrong notion, arid climates do generate leachate as a result of improper disposal of liquid and sludge waste as well as rising of the groundwater table. Tables 2 and 3 show the composition of leachate in an active, municipal, solid waste landfill. The samples were taken from three different boreholes in the landfill which were labeled BH2, BH3 and BH4.

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Table 2: Chemical characteristics of leachate at an active landfill in Al-sulaybuja Kuwait (A.F.Al-Yaqout and M.F.Hamoda, 2003) Parameter Leachate sample BH2 BH3 BH4 pH TDS (mg/l) Conductivity( mS/cm) Alkalinity as CaCO3 (mg/l) Suspended solids(SS) (mg/l) Volatile SS (mg/l) BOD (mg/l) COD (mg/l) Sulphates (mg/l)

6.9 2900 5.9 1074 548 424 180 4688 1600

7.9 2895 11.6 4200 1092 648 600 2240 300

7 600 1.2 250 900 804 60 9440 1300

Table 3: Heavy metal concentration of the leachate in Table 2 (A.F.Al-Yaqout and M.F.Hamoda, 2003) Parameter Leachate sample BH2 BH3 BH4 Zn (mg/l) Pb (mg/l) Ni (mg/l) Fe (mg/l) Mg (mg/l) Ca (mg/l) Cu (mg/l) Al (mg/l)

0.1 0.0 0.0 2.9 20.8 43.8 0.0 1.9

0.2 0.1 0.0 18.1 9.2 8.8 0.0 2.2

0.1 0.1 0.0 2.4 11.8 67.6 0.0 4.0

From Table 2 it could be seen that the leachate is composed of organic substances and inorganic substances. From the values of the BOD and COD which is a measure of the organic content of the leachate, it could be said that the leachate is either a medium age leachate or an old leachate even though the landfill is still active. Inorganic substances in the leachate are sulphates and some heavy metals. The heavy metals are present in very small quantities. It might be as a result of the leachate coming from a MSW landfill. In MSW landfills the proportion of organic substances dumped is far greater than the inorganic substances. b. Composition of stabilized sanitary landfill leachate. In a study by Diamadopoulos E, 1994 on “Characterization and treatment of recirculated-stabilized leachate”, it was observed that the sanitary landfill leachate used, showed an average COD value of 1141 mg/l, an average BOD value of 85 mg/l, and a BOD:N:P ratio of 100:312:0.30. The study also showed the presence of heavy metal in the leachate.

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Looking at the kind and concentration of the leachate parameters in the above cases, it could be seen that they differ. While there is a presence of phosphorus in the stabilized sanitary landfill leachate, there is none in the leachate from the active municipal solid waste landfill. Also while there is a presence of sulphates in the leachate from the active municipal solid waste landfill, there is none in the leachate of the stabilized sanitary landfill. There is also wide difference in the concentration of composition parameters that was seen in both cases. Concentration of COD in borehole 2 of the active municipal solid waste landfill leachate was 4688 mg/l while in the stabilized sanitary landfill leachate it was 1141 mg/l. These differences indicate that leachate composition has a lot to do with the kind of waste deposited and also the point of collection. As it could be seen, the concentration of the leachate composition parameters in the different boreholes of the active municipal solid waste

fill all differs. land 2.4 Summary of leachate composition  A critical examination of leachate composition in the above mentioned cases confirms the statement that leachate differ in composition and it may be as a result of age of landfill, climate at the deposited site and kind of waste deposited etc. However, in general terms and using the above composition results, leachates are composed of organic substances as well as inorganic substances.

2.4.1 Organic Substances  Organic substances consist of micro organisms, their metabolic products and materials from recently living organism which are capable of decaying. They are carbon containing compound but CO2 and HCO3 which also contain carbon are exceptions. Since the determination of specific organic substances often is complicated and time consuming, the organic content of leachate is often measured through analyzing sum-parameters as COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand) and TOC (Total Organic Carbon). The concentration of these measures decrease as the waste degrades. Compounds such as phthalates, terpenes, monocyclic and polycyclic aromatic hydrocarbons and phenols also are some of the organic substances that have been identified in leachate (Ulrika Welander, 1998). The presences of phthalates are largely due to PVC plastics that are commonly dropped in landfills, while terpenes may originate from products such as soaps and cosmetics. Aromatic compounds which also form part of the organic substances in some cases indicate that the leachate might have come from a landfill where oil products were deposited. Phenols and some substituent are use as antioxidants in some products. So the presence of phenols as an organic substance in landfill leachate indicates that such products were deposited in the landfill.

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2.4.2 Inorganic Substances  The inorganic substances consist of ammonium, phosphorus, sulphate and metals. Though most often, the presence of phosphorus and sulphate depends on the source of the leachate. Ammonium is associated with biodegradable substrate. It influences oxygen demand and contributes nitrogen that can lead to eutrophication (oxygen- depletion). Phosphorus is found in the form of phosphates, which cause eutrification, growth of algae, and dissolve oxygen depletion. Some phosphates in leachate may come from phosphates in sewage sludge deposits in landfill which originated from phosphate detergents and human waste. It has to be removed to avoid algae growth, eutrification and dissolve oxygen depletion in receiving waters. Sulphates are chemical compounds containing the bivalent group SO4

2-. They are salts or ester of sulphuric acid. They are in leachate as a result of industrial waste. Most important heavy metals in leachate are Zn, Pb, Ni, Cu, Cd and Fe. The presence of some of them in water result to toxicity, turbidity, odour, bad taste and deposit etc as such they should be removed or their concentration reduced before discharging leachate into receiving waters. 2.5 Substances that have to be reduced and leachate discharge 

consent  Substances that make up leachates can either be useful or harmful to the environment. An example of a useful component of leachate is water. Water is essential in plant and animal life. Without water there will be no life. However, there several other components of leachate that have adverse effect to the environment as well as in plant and animal lives. The concentration of such substances in leachate has to be reduced before leachate is discharged to the environment. Table 4 contain a list of the major substances in leachate which may require concentration reduction before discharge. It also contains the discharge consent for treated leachate. The discharge consent was adopted from the Anglian Water Concent Limits (Barr M. J. and Robinson H. D, 1999) and was the discharge consent of leachate from the Sundon Landfill in the United Kingdom.

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Table 4: Substances in leachate requiring concentration reduction and discharge consent. Substances Discharge consent pH COD (mg/l) BOD (mg/l) Ammonium-N (mg/l) Chloride (mg/l) Sulphate (mg/l) Chromium (mg/l) Manganese (mg/l) Nickel (mg/l) Copper (mg/l) Zinc (mg/l) Lead (mg/l) Arsenic (mg/l)

6.0-10 700 10 23 1200 100 2 2 1 1 1 1 1

2.6 Treatment needs  Some of the above substances as well as high concentration of others in leachate are undesirable because of their negative effects on the environment and human life. Table 5 is example of the substances and their effects: Table 5: Substances in leachate and their negative effect. Substances Negative effects

a. Organic substances- humic substances, algae and some waste products from society.

b. Iron (Fe2+)

c. Calcium (Ca2+) and Magnesium (Ma2+) d. Ammonium e. Phosphorus

Impact colouration, odour and taste on water. Impact turbidity, odour and bad taste as well as causing deposit in pipes. Impacts hardness, causing deposits Contributes to nitrogen that can lead to eutrophication. Algae growth and eutrophication in receiving waters.

Some other studies have also shown that leachate is toxic and a serious concern for the environment. The studies are: (i) Genotoxicity of municipal landfill leachate on root tips of vicia faba (Nan Sang and Guangke Li, 2004). The result confirmed that leachate might be a genotoxic agent in plant cells and this implies that exposure to leachate in the aquatic environment may pose a potential genotoxic risk to organisms.

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(ii) Micronuclei (MN) induced by municipal landfill leachate in mouse bone marrow cells (Guangke Li, Nan Sang and Youcai Zhao, 2004). The results showed that mouse exposure via drinking water containing various concentrations of leachate caused a significant increase of MN frequencies in a concentration (Chemical oxygen demand measured with potassium dichromate oxidation, CODCr)-dependent manner. This implies that leachate is a genotoxic agent in mammalian cells and that exposure to leachate in an aquatic environment may pose a potential genotoxic risk to human beings. (iii) Oxidative damage induced in brains and livers of mice by landfill leachate was studied (Guangke Li, Nan Sang and Qian Wang, 2006). The results show that leachate caused lipid peroxidation and change of antioxidative status in brains and livers of mice. It suggested that leachate exposure can cause oxidative damage on brains and livers of mice. (iv) Leachates of municipal solid waste incineration bottom ash from Macao: Heavy Metal Concentration and genotoxicity (Feng SL, Wang XM, and Wei GJ et al, 2007). The study revealed that MSWIBA were genotoxic with the MN assay in vicia faba root tip cell. (v) Toxicological effects and reproductive impairments in female perch (Perca Fluviatilis) exposed to leachate from Swedish refuse dumps was studied (Erik Noakson, Maria Linderoth, Ulla Tjämlund and Lennart Balk, 2005). The result confirmed that leachate from a Swedish refuse dump caused toxicological effects, including endocrine disruption and reproductive failures in feral female perch (Perca Fluviatilis) from Molnbyggen. The study also showed that refuse dumps should be considered as potential point sources for environmental pollutants and that uncontrolled leachate contamination of lakes and freshwater reservoirs could be a serious environmental hazard for both wildlife and humans. The above are mostly the reasons why leachate has to be treated before being allowed to mix with surface and ground water.

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3 Description and evaluation of leachate treatment      methods  Once leachate is pumped out of a landfill, it can be discharged to a sewage treatment works, treated separately and then discharged or re-circulated back into the landfill. Treatment methods in this exercise have been limited to only that which is based on separate treatment. Methods whereby leachates are treated separately in stages can be classified in to biological, physicochemical as well as combine biological and physicochemical methods. 3.1 Biological methods  Biological methods are the use of microorganisms to degrade organic and nitrogenous matter from young leachates. It involves adapting an environment for growth of a microorganism that can remove the substances. Biological removals of organic substances are done through anaerobic and aerobic decomposition processes. Under anaerobic conditions (absence of oxygen or nitrate) e.g. digesters, lagoons, anaerobic filters etc, organic substances are converted to methane and carbon dioxide (biogas) as well as water and small fraction of new biomass (sludge). The non injection of oxygen in anaerobic systems greatly reduces their cost. In aerobic conditions (presence of oxygen) e.g. activated sludge reactors, aerated lagoons and bio rotors, organic substances are converted to carbon dioxide, water as well as biomass. However, biological methods cannot remove refractory organic compounds.

3.1.1 Biological nitrogen removal  Ammonification, nitrification/denitrification and anammox are major biological processes directly involved with biological nitrogen removal in leachate (J. Wiszniowski et al, 2005) Ammonification (aerobic process) is the conversion of organic nitrogen to ammonium. An example is the oxidation of C6H15O4NH2 which is the biomass that is built up when organic materials are degraded.

C6H15O4NH2 + 7.5O2 + H+→ 6CO2 + NH4

+ + 7H2O (1) Nitrification (aerobic process) is the oxidation of ammonium to nitrate NH4

+ + 1.5 O2 → NO2- + 2H+ + H2O (2)

NO2- + 0.5 O2 → NO3

- (3) In all it is as follows: NH4

+ + 2O2 → NO3- + 2H+ + H2O (4)

Denitrification (anoxic process) is the reduction of nitrate to nitrogen gas by microorganism while oxidising organic matter in the absence of oxygen. 2NO3

- + H+ + Organic matter → N2 + HCO3- (5)

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Anammox (anoxic process) is reduction of ammonium to nitrogen gas with nitrite as the electron acceptor. It is less expensive compared with denitrification. (J. Wiszniowski et al, 2005) NH4

+ + NO2- → N2 + 2H2O (6)

This process however has a long start-up time because the anammox bacterium (planctomycetes) grows slowly. It takes 100-150 days before an activated sludge reaches full capacity if inoculated with sludge from an anammox reactor. (J. Wiszniowski et al, 2005)

3.1.2 Removal of heavy metals and sulphates  Heavy metals and sulphates can be removed from leachate if subjected to anaerobic conditions (Ulrika Welander, 1998). The heavy metals precipitate as carbonates and sulphides.

3.1.3 Principal biological processes  Principal biological processes are the activated sludge, the rotating biological contractors, sequencing batch reactor (SBR), reed beds, biological aerated filters and lagoons. Others are upflow anaerobic sludge blanket (UASB) and anaerobic filters. There is also the moving bed biofilm rector (MBBR) and the membrane bioreactors (MBR) biological processes.

3.1.3.1 The activated sludge.  Activated sludge is one of the processes used in leachate treatment. The aeration tank is where oxygen is injected as the leachate flows along the system. Microorganisms develop in the tank forming biological flocs (mixed liquor). The microorganisms which are in suspension in the mixture then consume the organic matter in the leachate transforming it into new microbial biomass, carbon dioxide and water thereby reduces the organic content of the leachate. At the clarifier (settling tank), generated sludge settles at the bottom of the tank while the supernatant is runoff as effluent. Part of the settled material (sludge) is returned to the head of the aeration tank to re-seed incoming leachate with microorganism. The re-seeding part of the sludge is called return activated sludge while the excess sludge which accumulates beyond what is returned is removed and with that the ratio of biomass (microorganism) and food supplied (organic matter in leachate) i.e. F: M ratio will be in balance. The waste activated sludge is removed. Reactions that take place in the activated sludge are the absorption of soluble, colloidal and suspended organics on sludge flocs, biodegradation (oxidation) of organics, bacteria ingestion by protozoa, oxidation of ammonium to nitrite and nitrate as well as denitrification etc. Figure 2 is a generalized diagram of the activated sludge process.

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Influent Pre-sedimentation Clarifier Screen Aeration Grit Chamber Effluent Return sludge Waste sludge

Figure 2: A generalized diagram of the activated sludge process. Studies have shown that the activated sludge is a good process for COD and BOD removal from young leachates. COD removal is between 83% and 97% while BOD removal is over 90% (Ulrika Welander, 1998)

3 .1.3.2 The rotating biological contractor 

The rotating biological contractor also known as a biorotor is an attached growth technology. It has circular plastic discs mounted on a shaft which partially submerged in a tank containing the leached water. As the shaft is slowly rotated, microorganisms adhere to the disc as biological growth, assimilating and treating organics from the leached water as they pass over the surface of the disc. Aerobic conditions are maintained when the disc rotates out of the leachate where it is oxygenated. Thus the disc provides contact between biomass and the leachate, mixing the mixed liquor and aerating the leachate. However, performance is generally lower than with an activated sludge technique (J. Wiszniowski et al, 2005). A study by Castillo et al, 2006 showed a COD removal of about 52% at a HRT of 24 hrs and a rotational speed of 6 rpm.

3.1.3.3 Sequencing batch reactor (SBR)  In SBRs microorganisms are in suspension just like in the activated sludge. However, the major difference is that aeration and sludge settlement take place in the same tank in a batch mode based on cycle of operations. The SBR is therefore designed to operate under non-steady state condition unlike the conventional activated sludge which operates under a continuous flow process. The cycles comprise periods for leachate filling, aeration, settling and decanting. Leachate filling (loading) is the intake of influent leachate in the SBR tank where microorganisms will have contact with organic substances. In Figure 3, it falls within the first 30 min. of the SBR cycle as indicated in the horizontal time axis and is the initial part of the anoxic-anerobic phase which terminates after the first 150 min. of the cycle.

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Immediately after the anoxic-anerobic phase is the aerobic phase. In the graph it is a period of 150 min. which falls between the 150 and 300 min. mark. It is the period when oxygen is pumped into the system. The oxygen facilitates substrate consumption by microorganism (biodegradation) as well as nitrification. This period is also the reaction period and it ends when the tank is full or when the maximum time for filling is reached. The settling period is the period after aeration when solid-liquid separation takes place leaving clear treated effluent above the sludge blanket. In the graph, it is combined with extraction (decanting) and the both phases lie between the 300 and 360 min. mark, a period of 60 min. with decanting coming after settling. To avoid turbulent in the supernatant no liquid enters or leave the tank during this period. Decanting (extraction) is the withdrawal of treated effluent. It is done without disturbing the settled sludge. Figure 3 is a graph illustrating a typical SBR cycle. The duration of the cycle was 6hrs. 30 min for loading, additional 120 min for anaerobic/anoxic, 150 min for aerobic and 60 min for settling and decanting (extraction). Figure 4 is pie chart representation of the cycle.

Figure 3: A typical SBR cycle (S. Marsili-Libelli, 2006)

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Figure 4: Pie chart representation of the SBR cycle The loading period of 30 minute is the first 30 minutes of the anoxic-anaerobic cycle so it is within the blue segment. The graph is that of the concentration of ammonium-N, phosphate-P and nitrate-N verses time in an SBR cycle. From the graph it is seen that at time zero, nitrate concentration was 10 mg/l. As time progressed nitrate concentration declined until it came to zero. This period of about 30 minutes when the concentration of nitrate dropped from 10 mg/l to 0 mg/l is the anoxic period when denitrifying bacteria reduces nitrate to nitrogen gas while oxidising organic matter. Concentration of nitrate drops while concentration of ammonium rises. This period starts as loading progresses. The period when the concentration of phosphate rise from 0 mg/l to 32 mg/l (end of P-release) is the period when phosphorus accumulating organisms (PAO) uses their stored energy (phosphate) to utilise organic matter as food. Concentration of phosphate rises while organic matter content drops. From the graph this period falls within the anoxic-anaerobic period when the SBR is not aerated. After 150 minutes from the time of loading, the SBR was aerated for another 150 minutes. Within this period (aerobic) there was a sharp drop of phosphate from 25 mg/l to almost 0 mg/l (end of P-uptake). This is as a result of PAOs using their stored food to build biomass while storing away phosphate. Also from this period the concentration of nitrate starts rising and that of ammonium starts dropping as a result of nitrification by autotrophic bacteria which uses oxygen to oxidise ammonium. The oxidation of ammonium continued until its concentration came to zero (end of ammonium oxidation in graph). Settling and decanting comes after the aerobic phase. 60 minutes was allowed for that. From the graph the period was between time 300-360 minutes. By the end of this period the concentration of nitrate was 5 mg/l while ammonium and phosphate was zero. A study by Dorota K. Et al, 2006 on “BOD5 and COD removal and sludge production in SBR working with or without anoxic phase” showed high efficiency of SBR’s in the removal of organics from leachate.

15

BOD5 removal was over 98% with or without the anoxic phase while COD removal varied from 83.1% to 76.7% on shortening the hydraulic retention time (HRT) from 12 to 2 days with an anoxic phase of 3hrs and 79.6% to 75.7% without an anoxic phase.

3.1.3.4 Reed beds   Reed beds normally have gentle sloping beds lined with impermeable barrier and planted with emergent hydrophytes such as reeds (phragmites), bulrush (scirpus), or cattails (typha). Reed beds may have an inlet zone of crushed stone to distribute wastewater evenly over the bed with and an outlet zone of crushed stone to collect and discharge effluent. Leachate enters at the inlet and travels slowly through the bed following a horizontal flow path before leaving. As the leachate moves, oxygen diffuses into the beds then aerobic bacteria’s surrounding the rhizomes of reeds uses it to oxidise organic matter in leachate as it passes on through the bed. The gravel or soil in which the reeds are planted also acts as a filter medium.

In a study by Tjasa G. Bulc, 2006 on “Long term performance of a constructed wetland for landfill leachate treatment”, where three interconnected beds were used, two of vertical flow and one of horizontal flow, It was observed that COD removal was up to 50%, BOD5 (59%), ammonium nitrogen (51%), sulphides (49%), total phosphorus (53%), chloride (35%) and Fe (84%).

3 .1.3.5 Biologically aerated filter (BAF) 

A biological aerated filter is a treatment tank consisting of a submerged aerated fixed film biological filtration system which provides a surface for the biomass and also hold back suspended solids thus acting as a biological contactor as well as a filter, eliminating the need for a separate sedimentation step. In the system both the influent and the process air flow upward from the bottom. The highest biological activity takes place in the lower half of the filter and treated leachate remains above the media. In a study by Stephenson T. et al, 2004 on “Feasibility of biological aerated filters for treating landfill leachate”, it was seen that at a reduced pH of 7.2 from 9.2, the ammonium removal increased to 97% from 33%. Figure 5 is a typical BAF

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Effluent Air Wash Water Outlet Process air (oxygen) leachate Biolite Media Influent Scouring outlet Figure 5: A typical biologically aerated filter

3.1.3.6 Lagoons  A lagoon for leachate treatment is normally an artificial pond with microorganisms just like in an activated sludge reactor. Lagoons can be anaerobic or aerobic, artificially or naturally. A lagoon is anaerobic when it lacks dissolved oxygen throughout much of its depth (e.g. lagoons where liquid animal wastes are dumped) while an aerobic lagoon is one in which dissolved oxygen is present throughout much of its depth. Over the years, there have been studies of leachate treatment in anaerobic lagoons as well as in aerated lagoons. A study by Howard Robinson and Gary Grantham, 2003 on “The treatment of landfill leachate in on-site aerated lagoon plants: Experience in Britain and Ireland” showed a COD removal of about 97% together with excellent removal of ammonium, iron, manganese and zinc. Similarly, in a study of leachate treatment in an anaerobic lagoon an average of 60% BOD removal and 57% COD removal were reported (Cossu R, 1981)

3.1.3.7 Upflow anaerobic sludge blanket (UASB)  UASB technology is a form of anaerobic digester that is used in leachate treatment and for treatment of many other types of waste water. The process involves an upward passage of leachate through an anaerobic sludge bed in a tank. As the leachate passes through the sludge, microorganisms in the sludge degrade organic matter in the leachate producing biogas (methane and carbon dioxide). As the gas moves upwards to escape, hydraulic turbulence takes place in the reactor prompting mixing which result to more degradation as a result of more contact of microorganisms with substrate. At the top of the reactor the gas is collected and the liquid phase is separated from the sludge solid. The effluent is collected after the separation. Figure 6 shows a typical USAB.

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Gas cap Effluent Baffles Gas bubbles Influent Sludge bed Sludge granule Figure 6: A typical UASB

In a study by Neena C.et al, 2007 a UASB reactor in laboratory scale was used to treat leachate from coconut husk. The study showed that about 82% of total COD/kg coconut husk could be converted to biogas.

3.1.3.8 Anaerobic filter (AF)  Anaerobic filter is another form of anaerobic digester. The digestion tank contains a filter medium which anaerobic bacteria populations can establish upon and then degrade organic substances in leachate as it moves slowly across the medium. A filter medium can for example be a reticulated polyurethane foam, expanded shale, and voidage plastic medium or porous stone. Figure 7 shows a typical anaerobic filter. Gas Reservoir and recirculation tank Filter Medium Pump Influent Effluent Figure 7: An anaerobic filter (Z Wang and C.J.Banks, 2006)

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In a study by Z Wang and C.J.Banks, 2006 where leachate arising from the co-disposal of MSW with cement kiln dust was used, COD removal was in the range of 75-90% and sulphate removal was up to 88%.

3.1.3.9 Moving bed biofilm reactor (MBBR)  The MBBR process is an attached growth biological leachate treatment process. In a reactor with the MBBR process microorganism attach themselves and grow on a plastic biofilm carrier or biocarrier that are suspended and in continuous movement within the reactor on a specified volume resulting in uniform and highly effective treatment. The biocarriers are designed such that there is good mass transfer of substrate and oxygen to the microorganism. There can be a tank for nitrification and one for denitrification. At the settling tank, generated sludge settles at the bottom of the tank while the supernatant is runoff as effluent. Part of the settled material (sludge) is returned to the head of the aeration tank to re-seed incoming leachate with microorganism. Figure 8 presents a schematic diagram of the anaerobic-aerobic MBBR system (Sheng Chen et al, 2007) Mechanical stirrer Biofilm carrier Settler Anaerobic MBBR Aerobic MBBR Influent Air Pump Figure 8: A schematic diagram of the anaerobic-aerobic MBBR system (Sheng Chen et al, 2007) A laboratory scale study by Sheng Chen et al, 2007 showed that COD removal got up to 91% using anaerobic MBBR and when the resultant effluent was polished with aerobic MBBR the COD removal increased further to 94%. The ammonium nitrogen removal with the aerobic MBBR was more than 97% when the HRT was more than 1.25 days.

3.1.3.10 Membrane Bioreactors (MBR) Membrane Bioreactors combine membrane treatment technology with those of bioreactors in leachate treatment. The system is compact, it generates high biomass concentration, and turns out good effluent quality.

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Membrane Bioreactors were first built at full industrial scale for waste water treatment and when they were found to be highly efficient, some plants were then adapted to leachate treatment.

However, there have been some specific studies on leachate treatment by membrane bioreactors. An example is the treatment of leachate with ultrafiltration-biologically active carbon (UF-BAC). The process combined adsorption, biodegradation and membrane filtration. In the study, TOC removal was in the range of 95-98% while those of specific organic contaminants were greater than 97% (S.Renou, J. G. Givaudan et al, 2007).

3.2 Physicochemical Method   Physicochemical methods are non-biological methods applied in leachate treatment. The method achieves treatment by the oxidation of contaminants with chemicals after which physical separation processes are applied. The method is also used along with the biological method to improve treatment efficiency. It is applied when removing non-biodegradable or recalcitrant substances (humic substances or undesirable compounds) like heavy metals, absorbable organic halogens (AOXs) and polychlorinated biphenyls (PCBs) from leachate. The physicochemical methods can be coagulation-flocculation, precipitation, adsorption, flotation, chemical oxidation/ advance oxidation process (AOP) and ammonia stripping.

3.2.1 Coagulation­flocculation   This is a process of reducing the repulsion between particles thus enhancing their attraction, aggregation and formation of heavy flocs that can settle. In leachate treatment aluminium sulphate (alum), ferrous sulphate, ferric chloride and ferric chloro-sulphate have been used as coagulants. COD removal with this process for young leachates is between 25-38% and for stabilised leachate with low BOD/COD ratio it is about 75% (J. Wiszniowski et al, 2005).

3.2.2 Precipitation  In the precipitation process suitable chemicals are added to leachate to precipitate soluble contaminants as insoluble compounds which can be separated by sedimentation or filtration. Precipitation is use as pre-treatment to remove high strength ammonium nitrogen from leachate (S.Renou, J. G. Givaudan et al, 2007) Lime milk and sodium hydroxide also precipitates heavy metals from leachate (J. Wiszniowski et al, 2005). Table 6 is treatment effectiveness of landfill leachate with the use of chemical precipitation.

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Table 6: Treatment effectiveness of landfill leachate with the use of chemical precipitation ( S. Renou, J. G. Givaudan et al, 2007) COD (mg/l) BOD/COD pH Precipitant Removal (%) 1585 7511 35,000- 50,000

0.07 0.19 0.5-0.6

8.2 8.22 5.6- 7.0

Ca(OH)2 (1g/l) MgCl2.6(H2O)+ Na2HPO4.12(H2O) (Mg: NH4: PO4=1:1:1) Struvite (Mg:NH4: PO4=1:1:1)

27% COD 40% COD 98% N-NH4

+

50% COD

From the table it could be seen that as much as 98% ammonium nitrogen can be removed by precipitation while COD removal can be up to 50%. However, percentage removals of the contaminants depend on chemical type and dosage.

3.2.3 Adsorption  This is the adhesion of a substance to the surface of another. This process is used in leachate treatment. Granular or powdered activated carbon is a good adsorbent and is frequently used. It is use to reduce the concentration of hydrophobic substances which are difficult to remove by other methods (Ulrika Welander, 1998). It removes 50-70% of COD and ammonium nitrogen (J. Wiszniowski et al cited Amokrane et al 1997) as well as toxic heavy metals and organics like AOXs, PCB etc.

3.2.4 Flotation  Flotation exploits the ability of some substances to float on leachate surface on their own or with the aid of air bubbles from below. It has not been a common method in leachate treatment though widely used in the removal of colloids, ions, macromolecules, microorganism and fibres etc from waste water. However, an investigation of its effect on the removal of humic acid (non–biodegradable) from simulated landfill leachate after biological treatment showed an efficient treatment performance reaching almost 99% indicating that floatation is an alternative technology for the removal of humic acid (A.I. Zouboulis, Wu Jun et al, 2003).

3.2.5 Chemical Oxidation and Advance Oxidation Process (AOP)  Chemical oxidation is used when leachate contains refractory organic compounds i.e. soluble organics which cannot be remove by physical separation and biological oxidation. Oxidants directly react and mineralise contaminants. Oxidants can be chlorine, potassium permanganate, calcium hydrochloride, ozone as well as hydroxyl (·OH) radicals generated when hydrogen peroxide is added to leachate in the presence of ferrous salt as is the case in the Fenton Process (J. Wiszniowski et al, 2005). The hydroxyl radical rapidly oxidises recalcitrant organic molecules through carbon-centred radicals which are formed on the attack.

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The carbon-centred radicals rapidly react with O2 in water to form organic intermediate products which may continue to react with the hydroxyl radicals and O2 leading to final mineralization of the organics to water and carbon dioxide (Yang Deng et al, 2006). The Advance Oxidation Process enhances the chemical oxidation potentials as it increases the generation of the hydroxyl radicals. It can be non-photochemical (without light) e.g. ozonation at pH >8.5, ozone + hydrogen peroxide and Fenton process (H2O2/Fe2+) etc or Photochemical (with light) e.g. O3/UV, H2O2/UV, Photo- Fenton and Photocatalysis (UV/TiO2). In the Fenton Process (Yang Deng and D. Englehardt, 2006) the organic content, odour, colour and biodegradability of recalcitrant organic compounds was greatly improved. COD removal efficiencies range from 45% to 85% (Yang Deng et al, 2006). Photo-Fenton was investigated on leachate from used tires to obtain the maximum organic matter removal. At optimum conditions COD and TOC were reduced by 64% and 48% respectively (Judith Sarasa et al, 2006).

3.2.6 Ammonia Stripping  This is a physicochemical process which removes ammonia nitrogen (NH4

+-N) from leachate. High pH values are used by the addition of chemicals e.g. calcium hydroxide. As ammonium ion is converted to ammonia gas, the leached water is cascaded down to allow the gas come out of solution and escape into the air. The air and gas is then treated with H2SO4 which absorbs the gas. A study of the effectiveness of ammonia stripping at different air flow rate and lime (calcium hydroxide) dosage (Chung, K.C. et al, 1997) showed that ammonia nitrogen removal was 70% for free-stripping (i.e. air passage of zero litres per minute), 81% for air passage of 1 L/min, and 90% for 5 L/min at a temperature of 20oC after one day. Figure 9 is a schematic laboratory representation of ammonia stripping.

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Air Slurry Air + NH3 Air Thermostatic bath Ammonia trap Sulphuric acid solution Figure 9: A schematic laboratory representation of ammonia stripping (August Bonmati and Xavier Flotats, 2002) 3 .3 Combined Biological and Physicochemical Method 

The Combined Biological and Physicochemical Method is used to achieve better leachate treatment results due to their high content of NH4

+ -N and COD which is not likely to be obtained if only the biological or physicochemical method is applied. An example is when leachates contain refractory organic compounds; in this case the biological process alone will not be able to remove the COD to an acceptable level, in which case, the physicochemical method will be needed as well. A study by Koh et al, 2004 on leachate treatment by the combination of photochemical oxidation with biological process showed that as the leachate was treated in an additional step using an activated sludge plant after a photochemical oxidation stage which came after an initial biological pre-treatment, the values of COD, BOD, and AOX decreased further to an acceptable legislative level. In this particular case, the COD was 920 mg/l after the biological pre-treatment, 326 mg/l after the photochemical oxidation and 186 after the biological post-treatment. In a pilot-scale study on stabilised leachate treatment (Ulrika Welander cited Copa and Meidl 1986), the COD removal was more as the biological process was combined with adsorption onto powdered activated carbon (PAC). In the study final COD removal was 77%. Thus the combination of the physical adsorption with biological treatment increased the treatment efficiency. Also a study by Kargi F et al, 2003 where high COD leachate was pre-treated by coagulation-flocculation followed by air stripping at pH 12 and then biologically treated in an aeration tank operated in fed-batch (sequencing batch) mode, showed improved COD and ammonium nitrogen removal by 86% and 26% respectively when powdered activated carbon was further applied.

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3.4 Membrane Technology   Membrane technology in leachate treatment is the application of membrane materials for the physicochemical treatment process. The principle of the membrane process is the separation of two solutions with different concentrations by a semi permeable membrane. Pressure is induced to the more concentrated solution (leachate) to force water to the one of lower concentration while most of the leachate compounds are well retained. However, the degree of retention of the leachate compounds varies depending on the membrane. The microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and the reverse osmosis (RO) are some examples of membrane technology.

3.4.1 Microfiltration (MF)   Microfiltration is a membrane separation process with membrane pore size allowing particles up to 0.2um. The membrane configuration is usually cross-flow in which case leachate is circulated parallel or tangential to the membrane surface ensuring limited clogging unlike in a frontal or dead- end filtration.

As a result of the membrane pore sizes which allow the passage of some organic substances and minerals, MF cannot be use alone in leachate treatment as it will not give a high percentage reduction of COD. However it can be used as pre-treatment for other membrane processes e.g. UF, NF or RO. Using microfiltration alone, the COD removal is between 25-35% (S.Renou, J. G. Givaudan et al, 2007)

3.4.2 Ultra filtration (UF)  Ultra filtration is also a membrane separation process similar to microfiltration. The ultra filtration membranes have smaller pore sizes in the range of 0.01-0.1um and their configuration is usually cross flow as well. They can be use to fractionate organic matter that is achieving specific percentage retentate for organic molecules and minerals. Using the UF step alone 50% of organic matter can be separated (S.Renou, J. G. Givaudan et al, 2007). As the UF cannot also be use alone in leachate treatment due to the passage of low molecular weight compounds through its membrane, it can effectively be used in pre-treatment for reverse osmosis since it can be used to remove the larger molecular weight components of leachate that tend to disrupt(foul) the RO membrane.

3.4.3 Nanofiltration (NF)  Nanofiltration is yet another pressure driven membrane separation process with cross flow membrane configuration. In the NF treatment process only water and substances with molecular weight less than 200 Dalton (1Da = 1.66 E-27 kg) permeates the semi permeable separation layer.

NF membranes also have a selectivity of charge for dissolved components. Monovalent ions and water permeates while divalent and multivalent ions are retained.

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Nanofiltration removes up to 60-70% COD as well as about 50% ammonia from leachates (S.Renou, J. G. Givaudan et al, 2007) while its combination with physicochemical methods further improves leachate treatment bringing the COD removal (refractory COD inclusive) to a range of 70-80% (D. Trebouet et al,2001).

3.4.4 Reverse Osmoses (RO) 

The Reverse Osmoses process is also another membrane process like MF, UF and NF. The membrane configuration is cross flow and the separation is pressure driven. However, the membrane pore sizes are very very small compared with those of NF thus allowing only small amount of very low molecular weight solutes (ammonia and small chlorinated organic compounds) to pass.

Reverse Osmosis process has been reported to be a very efficient and promising method for leachate treatment. This process is in use in places like Germany, the Netherlands and Switzerland (Ulrika Welander, 1998)

With the RO process alone, COD and ammonium nitrogen removal are as high as 98% (K. Linda et al, 1995).

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4 Comparison of the Methods  Having discussed the various leachate treatment methods, it is pertinent to compare the methods. A comparison of the methods will help decision makers and designers to choose an appropriate method for specific leachate treatment. Comparison can be in the form of merits and demerits of a method or in a more specific form, how good a method is for a particular condition. In comparing the considered leachate treatment methods, their efficiency in terms of contaminant removal in the various leachate types, space consumption, skill personnel requirement, treatment effectiveness without pre-treatment as well as without secondary clarifier and installation/operation cost, are the major criteria used. 4.1 Merits and demerits of the treatment processes  Table 7 is a presentation of the merits and demerits of the leachate treatment processes. Table 7: Treatment processes, merits and demerits. S/No Treatment Process Merits Demerits 1. a. b.

Biological Method Activated sludge Rotating biological contactor (RBC)

-This process is good for treatment of young leachate. It remove over 90% of BOD and between 83-97% of COD -It can be adapted to any size of community (except very tiny ones) -It is good in eliminating most of the pollution parameters (SS, COD, BOD5, N by nitrification and denitrification.) -The energy consumption in this process is low and it is simple to operate, requiring less maintenance and monitoring than the activated sludge.

-The process is not so good (fair) in the treatment of medium leachate and is poor for the treatment of old leachate. -It attracts relatively high capital cost, high energy consumption and requires skilled personnel as well as regular monitoring. -It is not easy to control the settling property of the sludge and there is high sludge production that must be treated before disposal. -The performance of this method is generally lower than that with activated sludge. However, realistic dimensioning will allow satisfactory qualities of treated water to be reached.

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c. d.

Sequencing batch reactor (SBR) Reed Beds

-The attached growth system better retains microorganism unlike the suspended growth system that can lose them as a result of poor settling of sludge. -Energy is optimised through control of aeration rate and duration. -Secondary clarifiers are eliminated. -There is flexibility in adjusting reaction time and tank volume to meet variable loading. Also it does not occupy as much space as the activated sludge reactor. -It provides treatment with lower energy requirement, operational and maintenance cost. -Reed beds are green and aesthetically better than traditional plant equipments. They have attractive appearance which compensate for the poor images of landfill sites. They can re-introduce valuable bird life (biodiversity)

Its capital cost can be 20% higher than that of activated sludge (J. Wiszniowski et al, 2005) -Not good for acetogenic leachate because exess sludge growth can cause clogging of interstices within rotors -It requires skill personnel and regular monitoring. -Land area requirement may be greater than that of the conventional methods -Design procedures are not standardised.

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e. f. g.

Biological Aerated Filters (BAF) Lagoons Upflow anaerobic sludge blanket (UASB)

-They are capable of treating very low/intermittent flows Good for ammonium nitrogen removal. Can remove up to 97% -Submerged filters have high voidage and do not require backwashing because accumulated solids in the reactor are controlled occasional scouring removal. -Elimination of secondary clarifiers removing all the associated cost and operational problem -Treatment efficiency is high especially in aerated lagoons. COD removal can be up to 97% -The method is technically and economically viable at full scale. -This is an anaerobic process so it has the advantage of low energy consumption -There is biogas production -Low production of surplus sludge

-Not too good for COD removal because effluent will require COD polishing to meet discharge consent. -Energy cost especially in aerated lagoons may be high. -Lagoons occupy lots of space. -Heavy metals can impede digestion -High ammonium remains in effluent which results in ammonia toxicity -Vulnerable to pH and temperature changes.

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h. i. j. 2. a.

Anaerobic filters (AF) Moving bed biofilm rector (MBBR) Membrane Bioreactor (MBR). Physicochemical Methods Coagulation-Flocculation

-Elimination of secondary clarifiers removing all the associated cost and operational problem -As a result of the wide and uniform spread of the bio carries there is uniform and highly effective treatment. -MBRs turn out good effluent quality. BOD and COD removals are greater than 80% and 85% respectively. -This method is fair for removal of COD from medium and old leachate. It can remove up to 75% of COD.

-Backwashing is a complex operation that has to be controlled to ensure that a healthy biomass is retained on the support media. -Energy cost may be higher because of the mechanical stirrer that has to ensure that the beds are moving for uniform treatment. -Potential high cost of periodic membrane replacement especially membrane fouling which leads to high energy consumption and chemical requirement. -There is limited data on membrane life -There is also high capital and operating cost -This is a poor method for removal of COD from young leachate. COD removal is just between 25-38% -Buying chemicals for coagulation may be a drawback as they may be expensive.

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b. c. d. e.

Precipitation Adsorption Flotation Chemical Oxidation and Advance Oxidation Process.

-Good for pre-treatment to remove high strength ammonium nitrogen before the biological process. -Good for phosphorus and heavy metal removal. -This process is good to remove COD from old leachate. COD removal can be up to 70% -Very good in removal of hydrophobic substances especially if PAC is used. It can remove toxic heavy metals and organics like AOX and PCB. -Good method to remove humic acid after biological treatment. The removal is up to 99% -This process can be use to remove refractory organic compounds from leachate after biological treatment. COD removal efficiency can range from 45-85% -The Fenton Process in particular is a simple technology and the iron and hydrogen peroxide that are used are cheap.

-This process is poor in removing COD from leachate. COD removal is between 27-50% -Cost of chemicals may also be a drawback. The process is poor in removal of COD from young leachate. -Expensive process. -In some advance oxidation process, there are high demands for electrical energy for devices such as ozonizers and UV lamps, resulting in high treatment cost. -Also for complete degradation of pollutants, high oxidant doses are needed. - Some chemicals that are used e.g. hydrogen peroxide are very toxic and should be handled with care.

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f. 3. 4. a. b.

Ammonia Striping Combined Biological and Physicochemical Method. Membrane Technology Microfiltration (MF) Ultrafiltration (UF)

This process is good in eliminating high level of ammonia nitrogen from leachate. Removal efficiency for ammonium Nitrogen can be up to 90% -No pretreatment is required -This process can be very good as it combines both the biological and physico chemical processes. Treatment efficiency will definitely be higher than where either biological or physicochemical is used alone. -The process will be good for treatment of any type of leachate whether young, medium or stabilized. -Good in pre-treatment of leachate for other membrane processes. -This membrane process can be use to fractionate organic matter and can also be a good pre-treatment for reverse osmosis.

-The process does not work very efficiently in cold weather and requires high pH values for very good performance. -It is a very expensive treatment process. -It may be very expensive to build and operate. -Cannot be use alone in leachate treatment because COD removal is only 25-35%. -Membranes may develop fouling problems.

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c. d.

Nanofiltration (NF) Reverse Osmosis (OR)

-This process is good to treat all categories of leachate-young, medium or old. It removes up to 70% of COD and if combined with physicochemical will remove even more. -Very efficient in the treatment of young, medium and old leachate. COD removal can be up to 98%. -It is insensitive to variations in the concentrations of compounds to be removed

-Membranes may develop fouling problems and yield concentrate which need further treatment. -Membranes may develop fouling problems. -It is expensive to build and install compared with the biological methods.

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4.2 Comparison of how good a process is for specific conditions.  Table 8 and 9 is a comparison of how good the treatment processes are for specific conditions. Table 8: Comparison based on age of leachate, space and skill of personnel Treatment process

Treatment of young leachate

Treatment of medium leachate

Treatment of old leachate

Economy of space

Requiring less skilled personnel

Biological Activated sludge RBC SBR Reed beds BAF Lagoons UASB AF MBBR MBR Physicochemical Coag. & flocculation Precipitation Adsorption Flotation Chem. Oxidation Ammonia stripping Membrane process Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis

Good Good Good Fair Good Good Good Good Good Good Poor Poor Poor Poor Poor Poor Poor Fair Good Good

Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Fair Poor Fair Good Good

Poor Poor Poor Good Fair Poor Fair Fair Poor Fair Fair Poor Good Fair Fair Fair Poor Fair Good Good

Poor Good Good Poor Good Poor Good Good Poor Poor Fair Fair Good Poor Good Poor Good Good Good Good

No Yes No Yes Yes Yes Yes Yes No No No No No Yes No No Yes Yes Yes Yes

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Table 9: Comparison based on effect of secondary clarifier, pre-treatment and cost Treatment process

Effective without secondary clarifier

Effective without pre-treatment

Installation and operational cost

Biological Activated sludge RBC SBR Reed beds BAF Lagoons UASB AF MBBR MBR Physicochemical Coag. & flocculation Precipitation Adsorption Flotation Chem. Oxidation Ammonia stripping Membrane process Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis

No Yes Yes Yes Yes Yes Yes Yes No No No No Yes No No Yes No No Yes Yes

No Yes No No Yes Yes No Yes No No Yes Yes Yes No Yes Yes No No No No

Expensive Expensive Less expensive Less expensive Expensive Expensive Less expensive Expensive Expensive Expensive Less expensive Less expensive Less expensive Expensive Expensive Expensive Expensive Expensive Expensive Expensive

35

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5 Full scale installations.  Having discussed leachate formation, composition, treatment need and treatment methods as well as the merits, demerits, treatment effectiveness, installation and operational cost of the various treatment methods, this research study will not be well completed and appreciated if instances of where full scale installations of plants using the various treatment methods around the world are not cited. Also of significance is when the treatment plants applying the various processes became operational and how effective they have performed. To accomplish the above task, full scale installations of leachate treatment plants around the world were combed from available company home pages, articles and journals in internet websites and books. Through Google an ENVIROS home page which discussed mariannhill leachate plant of South Africa was found. On the same home page vissershok leachate treatment plant which was referred to as “leachate case studies 2” was also found. However, the page did not give enough information about the plant. In order to search for more information on the plant, “vissershok leachate treatment plant” was goggled. Then on clicking “case study 2” on that webpage, more information on the plant was seen. From then on other case studies were goggled, case study 1, case study 2, case study 3 and so on. That was how a lot of the treatment plants presented was found. Search was also done in science citation index expanded through ELIN@Lund. The search was useful as it revealed more full scale leachate treatment plants. The information from this search was more detailed than those from company home pages found in websites through the Google search engine because aside from the name of the full scale leachate plant, location, year commissioned and treatment processes applied, it also contained the substances removed, and in some cases the flow sheet. The search was time consuming but results obtained were very informative and revealing. It was time consuming in the sense that a lot of search was involved before a hit with full scale leachate treatment plant was located. It became even more difficult as detailed information of the plants were being looked for. In some instances out of twenty hits which a search produced, there may be only one full scale leachate treatment plant or there may be none at all. Some may not even have the required information that will make their inclusion in this thesis worthwhile, so they were left out. 5.1 Brief on the various full scale installations found.  This description is brief and therefore had focused mainly on the plant location, operational date and treatment processes applied. 1. Mechernich leachate plant Mechernich leachate plant is in Mechernich landfill near Cologne, Germany. The plant became operational in 1994. The plant capacity is 65 m3/d. Figure 10 is the process scheme for the leachate treatment plant (Anke H, et al, 1997).

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Rain landfill Storage pond Methanol Biological pretreatment 2 stage evaporation Concentrate RO 1st Stage Tub. modules Concentrate Fluidized bed dryer RO 2nd Stage Distillate Spiral mod. Granules Subsurface dumps Effluent control Receiving water Figure 10: Process scheme for the leachate plant at Mechernich From the process scheme, it is seen that the applied leachate treatment processes in the plant are the biological and reverse osmosis process. Evaporation application however, is to dry concentrates from the reverse osmosis process before taking them away to subsurface dumps. The biological process is a pretreatment process for full degradation of the carbon and nitrogen compounds in the leachate while the reverse osmosis is for thorough reduction of the concentration of the compounds to discharge consent limits. An activated sludge reactor for denitrification and a biological contactor with micro strainer for nitrification are the components of the biological process. Figure 11 is a flow sheet of the biological process.

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Micro strainer in biological contactor plant for nitrification Influent Clarifier Leachate Denitrification Transition aeration Sullage Return sludge Surplus sludge RO Recirculation Figure 11: Flow sheet for biological pretreatment in the Mechernich leachate plant In the flow sheet, there is the denitrification tank, the transition aeration tank, the clarifier and the biological contactors which are all connected such that leachate flows in, get treated and flows out, in a continuous manner. Table 10 contain the substances that are removed, the effect of the treatment processes and the Federal Republic of Germany (FRG) discharge standard for leachate. Table 10: Illustration of the operating result of the treatment plant (Anke H, et al, 1997). Parameter Influent leachate

((average conc.) Biological treatment (average conc.)

RO treatment (average conc.)

FRG standard

COD (mg/l) BOD5 (mg/l) Org. N (mg/l) NH4-N (mg/l) NO3-N (mg/l) NO2-N ( mg/l) Inorg. N (mg/l) Pb (mg/l) AOX (mg/l) Cl- (mg/l)

3561 1512 251 833 1.3 0.15 835 0.5 1199 1790

1301 23.7 82.1 0.1 84 1.2 85 0.142 669 1675

15.8 2 5.3 0.1 9.8 0.12 10.6 0.001 0.01 27

200 20 - 10 - 2 70 0.5 0.5 -

From the table, the effect of the treatment processes could be seen. The reverse osmosis process had great impact on COD removal. It reduced the concentration of COD to 15.8 mg/l (which is far below the 200 mg/l FRG discharge standard) from the 1301 mg/l concentration after the biological pretreatment. The biological treatment had great impact on ammonium nitrogen reduction. It do not even require the reverse osmosis process to meet the discharge limit of ammonium nitrogen. It reduced the concentration of ammonium nitrogen from 833 mg/l to 0.1 mg/l which is far below the discharge limit of 10 mg/l.

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Another interesting result is the effect of reverse osmosis process on the reduction of the concentration of absorbable organic halogens (AOX). It reduced their concentration from 669 mg/l after biological treatment to 0.01 mg/l which is almost 100% reduction and far below the discharge limit of 0.5 mg/l. 2. Gärstad leachate treatment plant Gärstad leachate plant is near Linkoping, Östergötland, Sweden. The plant became operational in 1997. The lagoon process is the leachate treatment technique. The plant consist one aerated outlevelling basin which is a former clay pit and three constructed ponds. The designs of the ponds are such that aerobic and anaerobic conditions apply. The retention time in the plant is 7 months and substances removed are nitrogen (78%), phosphorus (80%) and organic materials (60%). 3. Izola leachate treatment plant Izola leachate plant is located in Izola, a coastal region in Slovenia. The plant was constructed in 1992. It has a sedimentation basin (lagoon) and one reed bed with an area of 400 square metre planted with phragmites australis. Substances removed are COD and ammonium nitrogen. COD reduction met discharge standard while ammonium nitrogen reduction did not (O.Urbanc-Bercic, 1997). The flow sheet of the Izola leachate plant is similar to that of Mislinjska Dobrava leachate plant which is in northern Slovenia (O.Urbanc-Bercic, 1997). Figure 12 is the flow sheet of Mislinjska Dobrava leachate plant. Shaft for aeration Outlet regulator valve Inlet regulator valve Influent leachate Reed bed Effluent Sedimentation basin Aeration pipes Inlet stone distributor Outlet stone distributor Figure 12: Schematic arrangement of constructed wetland leachate plant at Mislinjska. 4. Fågelmyran leachate treatment plant. Fågelmyran leachate plant is in Fågelmyran municipal landfill site, ten kilometres north of Borlänge, Sweden. The plant became operational in 1991 and is operated by Borlänge Energi AB. Treatment process is the SBR technique.

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The SBR tank capacity is 148 m3 with fill time and aeration time varying with flow. The tank was capable of nitrifying 80 mg/l of ammonium. Substance removed is ammonium nitrogen (Tina SK et al, 1993) 5. Buckden leachate treatment plant. Buckden leachate treatment plant is located in Buckden landfill site near Peterborough, East Anglian, Huntingdon, UK. The operators are Waste Recycling Group Limited and it has been operational since 1995 to date. It has a capacity of 200 m3/d and was designed and commissioned by Aspinwall. The plant has two SBR fabric roofed aeration tank, a control room, reed beds planted with australis phragmites and an ozonation plant. The treatment process combines biological and physicochemical treatment. The biological treatment takes place in the aerated SBR tanks and the reed beds while the physicochemical process is the ozonation. The reed beds and the ozonation plant are for the effluent polishing in the secondary stage. Ozonation provides treatment for pesticides which include herbicides mecoprop and isoproturon found in the leachate which might not be fully removed by biological treatment (Robinson H. et al, 2003). Treatment at the two secondary stages therefore produces an effluent which satisfies the tight toxicity based discharge consent. Substances removed are COD, BOD and ammonium nitrogen which is treated to drop from 400 mg/l to 10 mg/l. 6. Bryn posteg leachate treatment plant Bryn posteg leachate treatment plant is in Bryn posteg landfill site, Montgomery shire, Wales, UK. The operator is Evans logistics and it has been operational from 1983 to date. It treats up to 150 m3/d by an aerated lagoon SBR system. Aspinwall carried out all design, construction supervision and process commissioning of the plant. Retention time in the plant is >10 days and substances removed are BOD which is reduced from 10,000 mg/l to 50 mg/l and COD which recorded 97% reduction. Other substances reduced are ammonium-N, iron, manganese and zinc (Robinson, H D and Grantham, G 1988) 7. Compton bassett leachate treatment plant The Compton bassett leachate treatment plant is in Compton bassett, England, UK. It treats leachate from old, closed district council landfill at Sands Farm and for a large adjacent containment site at Compton basset. It has been operational from 1985 to date. Leachate is treated in an aerated lagoon SBR plant. The lagoon has a capacity of 1500 m3 and it is lined with a heavy-duty polyethylene (HDPE). The capacity of the plant is 100 m3/d and it has a minimum hydraulic retention time of 15 days (H.D Robinson, 1990). Effluent is polished with reed bed and further treated in a small village sewage works before discharge into a tiny river. Substances removed are SS, COD, BOD, ammonium nitrogen, calcium, iron and zinc (H.D Robinson et al, 1992).

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8. Sonzay landfill leachate treatment plant Sonzay landfill leachate plant is in Sonzay landfill site outside Tours in the western part of France. The plant treats leachate using the membrane bio reactor (MBR) and the reverse osmosis (RO) process. Treatment in the plant with this process became operational in 2001. The treatment capacity of the plant is 72 m3/d. The MBR has a biological reactor which degrades biodegradable compounds and an ultrafiltration membrane which separates treated leachate from the sludge. As leachate is pumped into the plant, it enters the first tank which has been conditioned to be anoxic as it contains nitrate which has been recycled from the third tank where ammonium was nitrified and carbon compounds removed. The anoxic condition of the first tank therefore gives room for denitrification, resulting to nitrogen reduction. Next the leachate under the influence of pressure moves through the ultrafiltration membrane where it is separated from biomass and SS but retaining the non biodegradable COD. This pretreatment is followed by the reverse osmosis process where resting COD, metals and about 80% of soluble salts (chlorides, sulphates) are removed (Anna Akerman, 2005). There is also an evaporation facility which dry concentrate from the ultrafiltration and RO membrane. Substances removed are BOD, ammonium –N, COD, metals and soluble salts. 9. Mariannhill leachate plant. Mariannhill Leachate Plant is located in the Mariannhill landfill in Kwazulu-Natal South Africa. It belongs to the eThekwini Metropolitan Municipality, Department of cleansing and solid waste (DSW) and was commissioned in February 2004 (landfill leachate site supported by ENVIROS). The design and construction was done by ENVIROS. The new generation lined landfill receives between 550 to 700 tons of solid waste each day and generates about 30 m3 leachate per day. The plant is made up of a sequencing batch reactor (SBR), a control room and a reed bed. The SBR unit is a cylindrical reinforced concrete tank, 10 m diameter and 6 m deep built outside the control room. The treatment process is biological. There is a primary biological treatment which is aligned to the activated sludge process in the SBR and a secondary polishing treatment by lined reed beds. The SBR and reed bed biological treatment processes were both discussed in chapter 3. Substances removed are BOD, COD, ammonium nitrogen. 10. Bukit tagar landfill leachate treatment plant Bukit Tagar Landfill Leachate Treatment Plant is in the north of Kuala Lumpur, Malaysia. It was design and process commissioned by ENVIROS in 2006. The plant consist of constructed lagoons, floating aerators in the lagoons, control room, dissolve air floatation (DAF) plant, alkali dosing tanks, picket fence thickeners, decant chambers and reed beds. The treatment process is biological and physicochemical; there is a primary biological treatment in the aerated lagoons (aerobic process) and a secondary polishing treatment by reed beds and the DAF plant.

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At the aerated lagoons organics are converted to carbon dioxide, water and biomass. The DAF plant is use to remove non–biodegradables like humic acid from the leachate after the biological treatments in the lagoons after which the effluent is moved to the reed beds for final polishing where reeds absorbs nutrients and aerobic bacteria’s surrounding the rhizomes of reeds uses diffuse oxygen to further oxidise remaining organic matter in the leachate as well as further removal of COD. The alkali dosing tanks are use to store alkali materials (NaOH) for pH adjustment while the picket fence thickeners are use in sludge treatment. The plant achieves its design flow of 1000 m3/day and discharges to irrigation/watercourse (landfill leachate site supported by ENVIROS) 11. Vissershok leachate treatment plant Vissershok Leachate Treatment Plant is situated in Vissershok landfill which is near Cape Town in South Africa. The landfill receives about 2000 tonnes of Cape Town’s municipal solid waste and low medium hazardous waste every day leading to the generation of about 80 m3 of highly polluted leachate per day.

Environs worked with Arcus Gibb, a local contractor in South Africa to design, construct and commission the full-scale plant. The plant was commissioned in July 2003. The plant has a large lined storage lagoon, a control room, a 6 m deep by 16 m diameter buried concrete SBR tank and a subsurface flow reed bed on which phragmites australis grows. The treatment process is entirely biological. The storage lagoon provides buffering of flows and some pre-treatment for the plant. The SBR does the main biological treatment of nitrification and denitrification after which the effluents are passed to the subsurface reed beds for final polishing before discharge. Routinely, ammonical nitrogen are reduced from over 1200 mg/l to less than 1 mg/l and COD concentration are reduced by 50%-60% from values over 2000 mg/l (P. Novella, H. Robinson, et al, 2005) 12. Guangzhou xingfeng landfill leachate treatment plant. Guangzhou xingfeng landfill leachate treatment plant is in the Xingfeng landfill in Hong Kong. The landfill takes 5500- 6500 tonnes garbage per day and generates around 1,700 m3/d in leachate. Veolia Water Solution and Technologies (VWS) were awarded the project for the leachate treatment and recycle plant by Guangzhou Urban Appearance and Environmental Sanitation Bureau in 2002 and it is operational to date. The leachate recycle treatment process combined the biological and membrane techniques. The process units are an upflow anaerobic sludge blanket (UASB), sequential biological reactor (SBR), continuous microfiltration (CMF) and a reverse osmosis (RO). Removal efficiencies for CODcr, BOD5 and total nitrogen are 99.8, 99.8 and 99.5% respectively and effluent meet the nonpotable water use standard (Zhanjiag Li, et al, 2007)

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13. Efford leachate treatment plant The Efford Leachate Treatment Plant is located in Efford Landfill in Hampshire, England, UK. It was design by Environs and is operated by Hampshire Waste Services since being commissioned in 2003. Leachate treatment in the plant is entirely biological. The primary biological treatment is done in an aerated SBR tank while the polishing takes place in a horizontal flow reed bed. The reed bed removes residual solids, ammonium –N, BOD and COD in SBR effluent (Guidance for treatment of landfill leachate, a, 2007). The daily operations of the plant are monitored in a control room. The design flow rate of the plant is 150 m3 per day and the treated effluent is discharged to a public sewer (landfill leachate site supported by ENVIROS) Substances removed are COD, BOD and ammonium nitrogen the main contaminants in leachate. 14. Niemark landfill treatment plant Niemark landfill Leachate Treatment Plant is in Luebeck, Germany. The plant’s leachate treatment capacity is 350 m3/d and was commissioned in 1999 (Guidance for the treatment of landfill leachate, b, 2007). In its leachate treatment process the plant combines the biological and the membrane technique. It has an SBR tank for the biological process and a two-stage Reverse Osmosis (RO) unit for the membrane process. The SBR does the biological treatment of nitrification and denitrification after which the effluents are passed to the reverse osmosis unit where COD, metals and soluble salts (chlorides, sulphates) are removed. Substances removed are BOD, COD, ammonium –N, metals and soluble salts. 15. Tondela landfill leachate treatment plant Tondela landfill Leachate Treatment Plant is in Tondela, Portugal. The plant can treat 140 cubic metre of leachate per day and was commissioned in 2004 (Guidance for the treatment of landfill leachate, b, 2007). Leachate treatment in the plant is a combination of the biological process and the membrane process. The plant has a two-stage reverse osmosis unit for the membrane process and a permeate lagoon for the biological process. The lagoon is the pretreatment unit where organic substances are biologically degraded into carbon dioxide, water and biomass while the two-stage reverse osmosis unit for the membrane process removes COD, metals and soluble salts. Substances removed are BOD, COD, ammonium –N and soluble salts.

16. Rebat landfill leachate treatment plant The Rebat Landfill Leachate Treatment Plant is located at Rebat Landfill in the district of Amarante also in Portugal. The plant has a capacity to treat 120 m3/d of leachate and was commissioned in 2001(Guidance for the treatment of landfill leachate, b, 2007).

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Leachate treatment in the plant is also a combination of the biological process and the membrane process. The plant has a two-stage reverse osmosis unit for the membrane process and an aerated lagoon for the biological process. The flow process and substances removed are similar to that of Tondela leachate plant. 17. Greengairs landfill leachate treatment plant Greengairs landfill leachate treatment plant is at Greengair, near Airdrie, Strathclyde, Scotland, UK. It became operational in spring 1991 and has worked to date. The operators are Shanks and McEwan (now Shanks waste services). The plant occupies an area of 280 ha and can treat up to 200 cubic meter of leachate per day (landfill leachate site supported by ENVIROS). It has a twin lagoon extended aerated biological treatment unit with reed beds for final polishing of effluent to standards suitable for discharge. It was design, tendered and construction supervised by Aspinwall (now Enviros). Substances removed are ammonium nitrogen, BOD, COD and chloride (M.J.Philpott, et al, 1992) 18. Summerston leachate treatment plant Summerston leachate treatment plant is located in Summerston landfill site, 4 km north of Glasgow, UK. Aspinwall prepared the drawing, specifications and supervised the construction and it became operational in spring 1990. Leachate treatment in the plant is biological. It is done with a HDPE lined lagoon–based SBR that has a floating surface aerator (Guidance for treatment of landfill leachate, a, 2007). Substances removed are BOD20 from 443 mg/l to 30 mg/l, BOD5 from 173 mg/l to 33 mg/l, COD from 2140 mg/l to 1020 mg/l and ammonium –N from 1120 mg/l to 0.5 mg/l (H.D Robinson and M.J. Barr, 1999). 19. Arthurstown landfill leachate treatment plant The Arthurstown landfill treatment plant is in Dublin, Ireland. It was commissioned in 1998 and has buried tank SBR for treatment of leachate (Guidance for treatment of landfill leachate, a, 2007). It treats up to 300 m3/d of leachate and discharges effluent to a drainage network leading to Ringsend Municipality WWTP. Substances removed are BOD, COD and ammonium-N 20. Llanddulas landfill leachate treatment plant Llanddulas landfill leachate treatment plant is in Conwy, Wales, UK. Commissioned 2002, it can treat up to 150 cubic meter of leachate per day (Guidance for treatment of landfill leachate, a, 2007). Treatment is biologically done by an above-ground SBR tank and effluent is discharged to sewer. Substances removed are BOD, COD and ammonium-N

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21. Arpley landfill leachate treatment plant Arpley landfill leachate treatment plant is located in Warrington, England, UK. Commissioned 2001, it treats up to 450 m3/d of leachate. Treatment is biologically done by an above-ground SBR tank, a small DAF unit and a terraced reed beds for effluent polishing (Guidance for the treatment of landfill leachate, b, 2007). Substances removed are BOD, COD, ammonium nitrogen, iron, sodium and chloride. 22. Pitsea leachate treatment plant The Pitsea leachate treatment plant is in Pitsea landfill site, Essex, UK. It was constructed in 1985 with a 30,000 m3 media volume and to treat up to 150,000 cubic meter of leachate per year. Treatment is biologically done by a rotating biological contactor (RBC). The RBC is a fixed –film aerobic biological system with plastic circular disc on horizontal shaft. As the shaft rotates, the upper area of the circular disc with the biofilm are exposed to oxygen which attached aerobic bacteria uses in degrading organic substances in the leachate at the lower area of the circular disc. Nitrification also takes place as the contact between the biofilm, oxygen and leachate progresses. The plant achieves full nitrification at loadings of up to 5gN/m2.d at 20 oC (Guidance for treatment of landfill leachate, a, 2007). The plant has 3 RBC units, each with a volume of 10,000 m3 and a settling tank. Substances removed are TOC, BOB ammonium-N and iron. 23. Harewood whin leachate treatment plant Harewood whin leachate treatment plant is located in Harewood whin landfill site, Ruffort, York, England, UK. It has been operational since 1990. Treatment of leachate is biologically done by an aerated SBR lagoon. The plant treats up to 200 m3/d of leachate and discharges effluent in sewer systems. It was design by ENVIROS. Major substances removed are COD, BOD, TOC, ammonium-N, chloride, sodium, magnesium, potassium, calcium and iron (H.D Robinson, et al, 1992) 24. Hempsted leachate treatment plant Hempsted leachate treatment plant is adjacent river Severn, Gloucester, Gloucestershire, UK. It became operational in 1996 and it treats up to 280 m3/d. Treatment is biological, by a twin covered SBR unit and a polishing lagoon. Substances removed are COD, BOD5, ammonium –N and iron (H.D Robinson and M.J.Barr, 1999)

25. Fiskerton leachate treatment plant Fiskerton leachate treatment plant is located near Southwell, 4 km south-west of Newark, Nothinghamshire, UK. It became operational in 1992. Treatment is biological by a tank-based SBR system that pretreats up to 30 m3/d of leachate (H.D Robinson and M.J.Barr, 1999). Effluent is discharged to rural sewage treatment works.

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Substances removed are COD from 1640 mg/l to 378 mg/l, BOD from 660 mg/l to 16 mg/l, TOC from 538 mg/l to 85 mg/l, ammonium-N from 414 mg/l to 0.08 mg/l, others are sodium, magnesium, potassium, calcium, iron and zinc. 26. Gairloch leachate treatment plant Gairloch leachate treatment plant is located in landfill Gairloch, Rose-shire (near ullapool) on the west coast of Scotland, UK. It treats 40 m3/d of leachate and has been operational from 1993 to date. Treatment is by a tank based extended aeration SBR unit. Effluent is polished by spraying over an area of peat nearby before disposal. Substances removed are COD from 830 mg/l to 162 mg/l, TOC from 213 mg/l to 33 mg/l, ammonium-N from 62.3 mg/l to 1.0 mg/l, others are chloride, sodium, magnesium, calcium and iron (H.D Robinson and M.J.Barr, 1999). 27. Brookhill leachate treatment plant Brookhill leachate treatment plant is located in Brookhill landfill, north Wales, UK. It pretreats up to 150 m3/d of leachate and is operational from 2001 to date. Treatment is by a tank-based SBR system and effluent is discharged to sewer (landfill leachate site supported by ENVIROS). Substances removed are COD, BOD and ammonium-N.

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5.2 List of the full scale leachate plants and treatment processes applied 

 The summary of the full scale leachate treatment plants and the treatment processes they use are given in table 11. Table 11: Plants and treatment processes applied Name of plant Year

operation began

Capacity Country of location

Substances removed

Treatment process applied

Fågelmyran LTP Gärstad LTP Izola LTP Niemark LTP Mechernich LTP Sonzay LTP Tondela LTP Rebat LTP Arthurstown LTP Bryn posteg LTP Compton Bassett LTP Buckden LTP Greengairs LTP Summerston LTP Efford LTP

1991 1997 1992 1999 1994 2001 2004 2001 1998 1983 1985 1995 1991 1990 2003

- - - 350 m3/d 65 m3/d 72 m3/d 140 m3/d 120 m3/d 300 m3/d 150 m3/d 100 m3/d 200 m3/d 200 m3/d - 150 m3/d

Sweden Sweden Slovenia Germany Germany France Portugal Portugal Ireland UK UK UK UK UK UK

BOD,COD and NH4-N BOD, COD, nitro- gen, phosphorus BOD,COD and NH4-N BOD,COD, NH4-N, metals and soluble salts COD, BOD, AOX NH4-N, and Cl-

BOD,COD, NH4-N, metals and salts BOD,COD, NH4-N, metals and soluble salts BOD,COD, NH4-N, metals and soluble salts BOD,COD and NH4-N BOD,COD and NH4-N, iron, manganese, zinc SS, BOD,COD NH4-N, iron, calcium, and zinc BOD,COD and NH4-N BOD,COD, NH4-N, chloride BOD,COD and NH4-N BOD,COD and NH4-N

SBR Lagoons Lagoon and reed bed SBR, RO Activated sludge, BC and RO MBR, RO Lagoon and RO Lagoon and RO SBR Lagoon -SBR Lagoon- SBR SBR, Ozonation, Reed bed Lagoon, reed bed Lagoon- SBR SBR, reed bed

48

Llanddulas LTP Arpley LTP Pitsea LTP Harewood whin LTP Hempsted LTP Fiskerton LTP Gairloch LTP Brookhill LTP Mariannhill LTP Vissershok LTP Guangzhou xingfeng LTP Bukit tagar LTP

2002 2001 1985 1990 1996 1992 1993 2001 2004 2003 2002 2006

150 m3/d 450 m3/d - 200 m3/d 280 m3/d 30 m3/d 40 m3/d 150 m3/d 30 m3/d 80 m3/d - 1000 m3/d

UK UK UK UK UK UK UK UK S. Africa S. Africa Hong Kong Malaysia

BOD,COD and NH4-N BOD, COD, NH4-N, iron, sodium and chloride. TOC, BOD, COD NH4-N and iron COD, BOD, TOC, NH4-N, chloride, sodium, magnesium, potassium, calcium and iron BOD,COD, NH4-N, and iron COD, BOD, TOC NH4-N sodium, magnesium, potassium, calcium, iron and zinc. COD, TOC, NH4-N, chloride, sodium, magnesium, calcium and iron BOD,COD and NH4-N BOD,COD and NH4-N BOD,COD and NH4-N BOD,COD and NH4-N BOD,COD and NH4-N

SBR SBR, DAF and Reed bed RBC Lagoon- SBR SBR and lagoon SBR SBR, and spraying effluent over area of peat SBR SBR, reed bed SBR, reed bed UASB, SBR, CMF, RO Lagoon, DAF, Reed bed

49

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6 Leachate treatment in SYSAV AB, Malmo 6.1 Background on SYSAV AB  SYSAV AB is a municipality owned waste management company which operates in fourteen municipalities in Scania, southern Sweden. SYSAV AB has an incineration plant in Malmo, close to the Spillepeng landfill. The incineration plant converts waste to energy by burning all combustible waste from households and industries generated by the municipalities. Heat, electricity and incineration residue are the products of the incineration. The heat and electricity are used at homes and offices while the incineration residue is landfilled in the Spillepeng landfill. The Spillepeng Landfill is an embankment on the Oresund and its intake of waste materials have been decreasing over the years due to the development of new waste management strategies. In year 2000 SYSAV AB handled a total of 320,000 metric tons of waste out of which 220,000 metric ton was landfilled while in 2006 it handled 340,000 metric tons out of which only 60,000 metric tons was landfilled (Andersson A, et al 2007). The landfill has three different types of lined cells, the bio cells for biodegradable waste, the special waste cells for hazardous waste and the inert cells for non-reactive waste materials. The cells generate leachates which have to be collected and treated before discharge in order to save surface and underground water from contamination. Figure 13 is a map of Scania showing Spillepeng landfill, Malmö.

Spillepeng landfill

Figure 13: Map of Scania showing Spillepeng landfill, Malmö (MapQuest, 2007)

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Approximately 175,000 m3 of leachate is produced as the waste in the landfill degrades (Anderson A, et al 2007). A local municipal WWTP use to handle treatment of the leachate but according to new regulations, treatment now has to be done on site by SYSAV AB. In line with the regulation, on 2nd March 2007 SYSAV AB started treating part of its leachate in a pilot-plant with a sequencing batch reactor (SBR) process which had prior been tested in a laboratory scale. Later on, a moving bed biofilm reactor (MBBR) process at pilot scale was also introduced. The general efficiency of these pilot plants will enable SYSAV AB select a process for its full scale leachate treatment plant. 6.2 Composition of leachate in the Spillepeng landfill  The leachate that is treated in the pilot plant is from the bio cell which contains biodegradable waste such as household waste which was deposited 5-15 years ago (Erika Heander, 2007 cited Anderson, 2007a). Table 12 is the composition of the leachate. Table 12: Average composition of the leachate P2/P6, spring 2007 and measurement from 2002 till 2007 (Erika Heander, 2007) Parameter P2/P6 pH Conductivity, mS/cm Chloride, mg/l Alkalinity, meq/l CODcr, mg/l BOD7, mg/l BOD7 /COD TOC, mg/l Total N, mg/l NH4-N, mg/l NO3-N, mg/l NO2-N, mg/l Total P, mg/l PO4-P, mg/l Suspended Solid, SS, mg/l VSS , mg/l

7.4 11 2769 45 655-718 56 0.08 297 325-344 265-273 3.7 0.5 2 1.2 81-95 48

The table shows that the leachate contains high concentration of chloride, COD and ammonium nitrogen. Since the CODcr is in the range of 655-718 which is less than 4000 mg/l, the BOD7 /COD ratio 0.08 which is less than 0.1 and the pH, 7.4 which is in the neighbourhood of 7.5, the leachate can be categorize as an old or stabilised leachate ( S. Renou, J. G. Givaudan et al, 2007).

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6.3 Leachate treatment in the pilot plant.  Leachate treatment in the pilot plant is done in two separate processes, the SBR and the MBBR processes. Most of the equipment of these processes are placed or installed inside the pilot plant building. Figure 14 is a picture of the building.

Figure 14: Picture of building for leachate treatment pilot plant (Photo by: Jude Madu)

6.3.1 The pilot SBR process.  The equipment for the SBR process consists of a 3m3 cylindrical reactor tank with aeration and stirring device. There is an inlet pipe for influent leachate, outlet for excess sludge and a funnel outlet for decanting. There are storage containers for ethanol, phosphor, the effluent and the excess sludge. There is also a pump, an aeration generator and a computer for monitoring. Figure 15 is a picture of the SBR.

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Figure 15: A picture of the SBR (Photo by: Jude Madu) Treatment of leachate in the SBR is in three cycles each day, eight hour per cycle. A cycle comprise periods for filling, aeration and stirring (nitrification), stirring without aeration (denitrification) and a period of aeration to oxidize any excess carbon source. In addition, each cycle also has a period of sedimentation and decanting. 500 liters of leachate is treated per cycle in the SBR unit.

6.3.2 The pilot MBBR process.  Equipment for the MBBR process consists of two serially connected 1.5 m3 cylindrical tanks. One is for nitrification and the other for denitrification. The tank for nitrification has a stirring device, some quantity of moving bed (plastic biofilm carrier) and an aeration devise while the tank for denitrification has only a stirring device and some quantity of biofilm carriers. Figure 16 is a picture of the MBBR

Figure 16: A picture of the MBBR (Photo by: Jude Madu)

The treatment process is a continuous one involving nitrification and denitrification and without a sedimentation unit but in full scale there should be one. 500 liters of leachate is treated per day in the MBBR process.

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6.3.3 Discharge limits from Miljödomstolen  Miljödomstolen is the organization that set the discharge levels of parameters in leachates from the Spillepeng landfill. Table 13 is their discharge consent limits. Table 13: Discharge consent limit in the SYSAV pilot plant for leachate treatment. Substance Limits Total Nitrogen (mg/l) CODcr (mg/l) BOD7, (mg/l) Total Phosphorus (mg/l) Mercury (mg/l) Cadmium (mg/l) Vanadium (mg/l) Chromium (mg/l) Lead (mg/l) Nickel (mg/l) Copper (mg/l) Zinc (mg/l)

15 500 10 0.5 0.001 0.001 0.05 0.05 0.05 0.5 0.5 0.5

6.3.4 Treatment results   The concentration of polluting parameters in the leachate composition which are higher than their concentration for discharge, justifies the treatment which the leachates are subjected to. The treatment therefore aims at reducing the concentration of the pollutants to their required discharge limits or even below. Table 14 shows the result of the concentration reduction of pollutants in the leachate by the SBR and MBBR process. Table 14: Concentration reduction of pollutants by SBR and MBBR process. Parameters Composition of

leachate from the biocell

Concentration after SBR treatment

Concentration after MBBR treatment (mg/L)

COD (mg/L) BOD (mg/L) TOC (mg/L) Total Nitrogen (mg/L) NH4-N (mg/L) Total Phosphorus (mg/L) SS (mg/L)

655-718 56 297 325-344 265-273 2 81-95

Mean value 535 App. 8 Mean value 150 Mean value 31 < 2 Mean value 1.5 Mean value 60

Mean value 553 Mean value 206 Mean value 162 Mean value 58 < 2 Mean value 2.86 Mean value 106

From the table it can be seen that the SBR process reduced the recalcitrant organic substances in the leachate by only about 18.32% (120 mg/L). However it should be noted that it is the mean value that was used in calculating the percentage reduction. The minimum concentration value after the SBR treatment was lower than the mean value and if it was use, the percentage reduction would have been higher.

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The BOD was greatly reduced by the SBR process. Its concentration after treatment was approximately 8 mg/L, which implies that the reduction was about 85.71% The SBR process reduced the Total Organic Carbon (TOC) by 50%. This calculation is also based on the mean value and may therefore not be the actual reduction. Total Nitrogen and NH4-N were both greatly reduced by the SBR process. Their concentration after the treatment was 31 mg/ l and 2 mg/l respectively, a reduction of 90.46% and 99.24% respectively. Result of the SS reduction by SBR was not impressive. The reduction was only about 25.93%. In the pilot plant the MBBR process is mainly for the reduction of nitrogen and there is no sedimentation step. From table 12 it is seen that total nitrogen as well as ammonium nitrogen were greatly reduced by the MBBR process. Their reductions were up to 82.15% and 99.24% respectively. However, higher values of BOD and SS concentrations were noticed in the effluent of the MBBR. This might be as a result of the lack of a sedimentation process.

6.3.5 Discussions   The generation of solid waste is unavoidable as humans, animals and plants lives on. Solid wastes that cannot be converted to useful materials are landfilled. Landfills generate leachate when precipitation, groundwater or liquid waste infiltrates in. Leachate is not environmentally friendly as it contains pollutants which contaminate surface and underground water the very source of potable water for humans and most animals. It is a challenge today to optimally treat leachate so as to fully reduce its negative impact in our environment. The variation and complexity of its composition is a cogent reason. Many processes are use in leachate treatment. The processes are classified as biological, physicochemical and membrane. Some processes are conventional while others are new e.g. the membrane processes. The choice of treatment processes for any leachate depends on the initial leachate quality and the desired purification level. In most cases there is a local discharge water standard given by water authorities. However, other factors such as efficiency of a process in terms of contamination removal, availability of space, installation, operation and maintenance cost are also considered.

There are so many full scale plants using the biological processes, a combination of the biological and physicochemical processes or a combination of the biological and membrane processes for leachate treatment.

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In Europe for instance the Buckden Leachate Treatment Plant located in Buckden landfill site near Peterborough, East Anglan, UK was identified. In Africa there is the Mariannhill leachate Plant located in Mariannhill landfill, Kwazulu-Natal South Africa while in Asia for instance there is the Bukit Tagar Landfill Leachate Treatment Plant in the north of Kuala Lumpur, Malaysia. Both the SBR and MBBR processes did very well in the reduction of Total nitrogen and ammonium nitrogen though however, the SBR had an edge over the MBBR. The leachate from the Spillepeng landfill in Malmo managed by SYSAV AB can be classified as an old leachate with recalcitrant organic substances. The sequencing batch reactor (SBR) process that is use at pilot scale to treat the leachate from the biocell (stream P2/P6) is not good enough as it does not sufficiently beat the COD discharge limit of 500 mg/l recommended by Miljödomstolen. The same applies to the moving bed biofilm reactor (MBBR) process which even requires a sedimentation step to meet up the efficiency of the SBR. COD removals by the processes were below 30%. If the MBBR process is to be use in the full scale treatment plant, it will be necessary to incorporate a sedimentation process that will greatly improve its COD, BOD and ammonium nitrogen removal by so doing its efficiency may get very close to that of the SBR. However, as a result of the compact nature of the SBR, its ability to treat wide range of influent volume and optimize energy through control of aeration rate/duration, it may be preferable to the MBBR process. The Spillepeng landfill is an embankment on the Oresund lacking adequate space for expansion. A combination of the SBR process and a secondary polishing treatment by a two stage reverse osmosis (RO) process as is the case in Niemark landfill Leachate Treatment Plant, Luebeck, Germany will be a good treatment technique for Spillepeng landfill leachate treatment if a full scale plant is to be built. The RO process has the ability to effectively remove recalcitrant organic substances which might have escape removal by the SBR process. Again since both processes are compact, they will fit in at the Spillepeng landfill site which lacks adequate space for expansion. Otherwise a combination of the SBR with a reed bed process as is the case in Mariannhill Leachate Treatment Plant, South Africa, would be a preferred option if space can be created for reed beds since they have some unique advantages over other treatment techniques. For instance they provide treatment with lower energy requirement, operational and maintenance cost. They are green and aesthetically better than traditional plant equipment as their attractive appearance compensates the poor images of landfill sites.

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7 Conclusion  The conclusion of this study on leachate composition and its treatment techniques as well as using the pilot plant at the Spillepeng landfill as a case study is as follows:

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1. There are tested, reliable and consistent conventional and new technologies for leachate treatment.

2. Within the biological and physicochemical leachate treatment methods, twenty different techniques was found and described.

3. From recorded removal efficiencies of some of the techniques or combination of

some of the techniques, discharge consent levels for landfill leachate are achievable.

4. The use of the sequencing batch reactor (SBR) technology for primary biological treatment of landfill leachate has proved to be a reliable and robust strategy.

5. A total of twenty-seven full scale operational leachate treatment plants using one,

two or three of the described twenty different techniques in leachate treatment was found out of which one started operation as far back as 1983.

6. The combination of the SBR biological technique with the membrane reverse

osmosis technique has proven to be very effective in leachate treatment.

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8 Suggestion for further research  

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Treating the effluent from the pilot scale SBR process with a laboratory scale two stage reverse osmosis process will be an interesting area for further research. It will expose how effective the RO process can be in removing recalcitrant organic substances. Another study can be done to find out the effectiveness of reed bed when the reeds are under adverse seasonal conditions.

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10    Abbreviations 

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AOP: Advance oxidation process AOX: Absorbable organic halogens BOD5: Five day biochemical oxygen demand COD: Chemical oxygen demand Discharge consent: discharge limit F: M ratio: Ratio of food (organic substance) supplied in a reactor against microorganism present GAC: Granular activated carbon PAC: Powdered activated carbon PCB: Polyvinyl chloride biphenyl pH: Hydrogen ion potential PVC: Polyvinyl chloride SS: suspended solids TDS: Total dissolves solids VAF: Volatile fatty acids VSS: Volatile suspended solids

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