- Email: [email protected]
Combination of Different MSW Leachate Treatment Processes
10.5 COMBINATION OF DIFFERENT MSW LEACHATE TREATMENT PROCESSES Hans-Jürgen Ehrig and Rainer Stegmann
INTRODUCTION Many leachate treatment plants operate with a combination of different processes. Environmental and/ or economic boundary conditions and/or specific requirements can be the reason for such combinations. With the construction of large landfills in the second half of the 20th century the awareness and the knowledge of the high and relative complex leachate pollution investigations for appropriate treatment technology started. This search resulted in an adaption of different treatment processes for leachate treatment. Leachate analysis shows a wide range of different compounds (see Chapter 10.2). The treatment of the organic substances is not without problems also because the chemical composition of the organic pollution (measured as COD or TOC) is mostly unknown. One classification is the differentiation between the biodegradable and nonbiodegradable organics. The problematic of this differentiation is described in Chapter 10.2. Using biological treatment only the biodegradable and nitrogen compounds can be removed. If the required COD effluent limit values cannot be met by means of biological treatment additional treatment steps will be necessary. Unlike the publication of experiences from sewage treatment, experiences and results from full-scale biological and chemical physical leachate treatment plants are only scarcely published. It is also for this reason difficult to design a combination of different treatment processes. Different processes are available for the elimination of the same substances and there are great differences between treating raw or pretreated leachate. The execution of laboratory or better pilot scale tests is recommended to select the optimum treatment combination. Treatment processes require energy, sorbents, and/or additives as, e.g., external organic carbon, flocculation agents, and activated carbon. Flocculation agents and activated carbon, for example, react very differently when treating different leachate qualities; this may even be the case if leachate quality data seem nearly to be the same. Several processes produce residues which must be further treated or discharged what adds to the cost. Fig. 10.5.1 presents a selection of realized leachate treatment combinations.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
633
LEACHATE BIOLOGICAL TREATMENT
ADSORPTION (pulverised carbon)
PRECIPITATION & COAGULATION
ADSORPTION (granulated carbon)
BIOLOGICAL POST TREATMENT
CHEMICAL OXIDATION REVERSE OSMOSIS
EVAPORATION
DRYING
REED BED, CONSTRUCTED WETLANDS
LEACHATE DISCHARGE Possible vapour emissions Rarely used adsorpon and chemical oxidaon processes
Figure 10.5.1 Different combinations of leachate treatment technologies used in full scale plants.
Chemical oxidation generally is carried out by using ozone þ UV or ozone þ H2O2.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
UPGRADING BIOLOGICAL TREATMENT PLANTS In several cases biological treatment plants such as aerated lagoons or activated sludge plants can meet the required discharge limits. But due to the nature of the process aerated lagoons emit biomass with the effluent. Due to the existence of the clarifier in activated sludge plants this problem should be solved. But very often very light flocks of biomass may leave the plant via the effluent. If the temperature in the bioreactor decreases, the emissions may increase above given effluent requirements. For an artificially aerated lagoon the installation of a natural separation section for biomass sedimentation and effluent polishing is recommended. In nonaerated lagoons excess biomass becomes a sediment and stabilizes at the bottom of the lagoon. In most cases the sludge has to be removed in a time interval of several years (mostly >10 years). Operating a completely aerated lagoon the produced nitrate can in general not be reduced. During warm weather periods the nitrate leads to algae blooms with secondary water pollution. During cold weather periods the ammonium concentration in the effluent increases. During temperature changes high nitrite concentrations may be measured in the effluent. Installing a constructed wetland or reed bed as a posttreatment it may be possible to reduce nitrogen compounds also during cold periods. Although the suspended solids in the clarifier effluent of an activated sludge plant have a much lower concentration than in the effluent of aerated lagoons also in this case a polishing step may make sense. In Tables 10.5.1a and 10.5.1b results from activated sludge plants designed as a sequential batch reactor (SBR) with subsequent constructed reed beds are presented. Robinson et al. (2003b) reported that suspended solids and colloids in the effluent may be further reduced by using an air flotation step between SBR and reed bed.
Table 10.5.1a Leachate treatment in a sequential batch reactor with subsequent constructed reed
beds. Mean values at Efford Landfill (UK). From Robinson and Olufsen (2007). Parameter
Raw Leachate
SBR Effluent
Final Effluent
COD (mg/L)
942
462
309
BOD5 (mg/L)
72
22
3
NH4 (mgN/L)
820
1.6
0.5
NO3 (mgN/L)
0.21
423
384
NO2 (mgN/L)
0.04
0.56
0.87
Cl (mg/L)
1502
1442
1507
7.6
8.2
8.4
3830
1229
1138
PH Alkalinity (mgCaCO3/L)
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
635
Table 10.5.1b Leachate treatment in a sequential batch reactor with subsequent constructed reed
beds. Mean values at two different Landfills in South Africa (Robinson and Carville, 2007): A. Mariannhill (SBR approx. 78 m3; reed bed 300 m2; maximum flow rate 50m3/day). B. Vissershok Parameter
Raw Leachate
SBR Effluent
Final Effluent
A
B
A
B
A
B
Suspended solids (mg/L)
250
-
102
277
28
58
COD (mg/L)
760
4560
320
1470
435
1510
BOD5 (mg/L)
170
550
90
28
8
10
NH4 (mgN/L)
435
1554
1,9
0,2
<0,5
0,4
NO3 (mgN/L)
<0,1
9,2
443
1461
471
1471
NO2 (mgN/L) pH
<0,1
0,4
1
7,5
8,18
7,1
7,39
6,7
7,61
Alkalinity (mgCaCO3/L)
2422
9652
260
935
300
1133
Cl (mg/L)
1690
4626
1550
4545
1860
4455
Phosphate (mgP/L)
1,4
13
12
10,5
8,6
10,7
Sodium (mg/L)
590
2825
1113
3979
1469
3904
Magnesium (mg/L)
80
195
118
192
163
183
Calcium (mg/L)
105
198
118
123
170
115
ACTIVATED SLUDGE PLANTS WITH SUBSEQUENT PRECIPITATION AND ADSORPTION STEPS As a first development in the early 1980s in Germany to further reduce nondegradable or difficult to degrade organics, precipitation with subsequent pulverized activated carbon (PAC) adsorption was practiced (Plant “Pohlsche Heide”, Germany). Particularly for biologically treated leachate of landfills in the methanogenic phase precipitation of residual organics, e.g., using iron salts is a very effective and economic treatment step. To meet the required effluent standards a subsequent adsorption process using pulverized PAC was added which at that time was less costly than using granular activated carbon (GAC). This situation may be different in different countries. Treatment results of such plants are presented in Box 10.5.1.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Box 10.5.1 Leachate treatment in an activated sludge plant with subsequent post-treatment by precipitation and activated carbon adsorption (Albers and Mennerich, 1987; Mester, 1993) Landfill Plant Components (Volume in m3)
Heisterholz (1985/87)
Heisterholz (1990/91)
Pohlsche Heide
Denitrification tank Nitrification tank Clarifier 1 Fixed film reactor Adsorption tank Flocculation tank Clarifier 2 Neutralization tank Clarifier 3 Filtration Average flow rate (m3/d)
725
417 1670 146 460 80 30 277 48 e e 96
2 494 2 1446 180 88 81 10 267 21 e e 93 Effluent
19 e 36 36 60 131 60 e 96
Parameter
Wilsum 940 2 720 e e 50 2.5 e n.d. e Sand filter 90
Influent
Activated Sludge
After posttreatment
350 1375 0.742
n.d. n.d. 0.605
7 52 0.122
91 686 528 1.65
n.d. n.d. 4.6
2.1 51 0.7 0.23
410 1571 633 1.31
n.d. 614 0.81 n.d.
3.5 76 0.69 0.17
207 1506
n.d. 709
1 94
LANDFILL HEISTERHOLZ (1985/87)
BOD5 COD AOX
mg/L mg/L mg/L
LANDFILL HEISTERHOLZ (1990/91)
BOD5 COD NH4 AOX
mg/L mg/L mgN/L mg/L
LANDFILL POHLSCHE HEIDE (1990/91)
BOD5 COD NH4 AOX
mg/L mg/L mgN/L mg/L
LANDFILL POHLSCHE HEIDE (1994)
BOD5 COD
mg/L mg/L
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
637
NH4 NO3 AOX Cl SO4
mgN/L mgN/L mg/L mg/L mg/L
579 44 1.45 1244 139
0.26 288 n.d. n.d. n.d.
0.09 296 0.182 1125 746
n.d. 896 459 0.12 7.1 1.04 3 1715 0.58 0.48
n.d. 401 0.34 0.04 149 0.48 n.d. n.d. n.d. n.d.
3 73 0.24 0.84 118 0.15 0.1 1950 0.03 0.15
LANDFILL WILSUM
BOD5 COD NH4 NO2 NO3 AOX Phosphate Cl Copper Nickel
mg/L mg/L mgN/L mgN/L mgN/L mg/L mgP/L mg/L mg/L mg/L
n.d., no data available.
Due to easier handling at a later stage at “Pohlsche Heide” the adsorption plant was operated as filters with GAC. Fig. 10.5.2 shows the relative strong relationship between both processes (Plant Heisterholz). Using an optimized precipitation process with increased COD elimination the dosing of PAC can be reduced, which resulted in a significant reduction of the treatment costs. The dewatering of iron sludge is greatly improved as a mixture of GAC and iron sludge.
ACTIVATED SLUDGE PLANTS WITH ACTIVATED CARBON FILTERS This combination is most commonly used for leachate treatment in Germany. Important reasons for this solution are the relatively low investment and low operation costs. In addition the required amount of carbon can be automatically adapted on the leachate quality. The higher costs of GAC compared to PAC can be partly compensated by higher carbon adsorption loading rates. Using GAC filters it is possible to reduce remaining organic and trace substances in the leachate. But it should be noted that trace substances are only adsorbed if the main portion of the organics are removed. In such cases a specific operation of two GAC filters in a row may be necessary. In the first filter the organics should
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
COD removal by precipitaon (mg/L)
600
500
400
300
200
100
0 0
100
200
300
400
500
600
COD removal by PAC adsorpon (mg/L)
Figure 10.5.2 Relationship between COD removal by precipitation and pulverized activated carbon
adsorption in a combined treatment system (Albers and Mennerich, 1987).
be reduced to the range of the required COD discharge limit values so that the in the subsequent filter trace substances can be adsorbed. Such a specific situation must be tested in laboratory or pilot scale tests. This is also necessary because a great number of different activated carbon qualities exist; the optimum quality can only be determined by performing tests. To avoid early clogging of the pores in the AC the effluent of the activated sludge plant should be filtered before entering the GAC filters. Sand filter, fabric filter, and ultrafiltration are methods that are available for fine particle removal. The higher the removal rate of suspended solids upfront the higher will be the adsorption capacity of the GAC; as a consequence costs may be reduced. The ultrafiltration process reduces fine particles to the highest extent. Results from different treatment plants using the combination of activated sludge and GAC filters are presented in Box 10.5.2. Some activated sludge plants in Germany with subsequent GAC filters are combined with nanofiltration as a third treatment step. The nanofiltration membranes are permeable for small molecules as chloride, but most inorganic and organic molecules are retained. The nanofiltration can be placed after the ultrafiltration of the activated sludge plant. The ultrafiltration is used to retain the suspended solids of the activated sludge plant. The permeate of ultrafiltration is fed in to the nanofiltration plant. The concentrate of the nanofiltration is fed to GAC filter, and its effluent is returned back to the activated sludge plant. The idea of this combination is to retain “all” organic substances and increase their concentrations. The consequence of higher organics (COD values) in the concentrate stream of the nanofiltration is an increase of adsorption capacity from 20% to 30% of GAC (by weight) to values up to
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
639
Box 10.5.2 Combination of an activated sludge plant with an activated carbon filter (ATV, 1996; Ehrig, 2001) Plant layout (plant A) of the combination activated sludge plant and activated carbon filter.
Plant
Parameter
Unit
Influent
Effluent Biological Treatment
Effluent Activated Carbon Filter
A
BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4
(mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L)
1500e6000 1000e12000 1.0e2.5 400e800 n.d. 3000e6000 0.8e2.0 400e800 280 1700 1.1 900 90e210 1100e1600 0.8e1.7 500e900 50e150 450e800 n.d. 250e400 500e800 2000e5600 0.6e2.2 600e1800
<5 500e800 0.5e2.0 <10 n.d. 500e900 0.6e1.4 <10 <20 900e1200 0.5e0.9 <10 <20 300e900 0.9e1.2 <10 <10 250e320 n.d. <50 <10 750e1200 0.5e1.5 3e52
<5 <200 0.1e0.7 <10 n.d. <110 0.1e0.48 <10 <20 <400 0.1 e< 0.5 <10 <20 <200 <0.5 <10 <10 <200 n.d. <50 <10 <200 0.1e0.87 <20
B
C
D
E
F
n.d., no data available.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
more than 50% of GAC (by weight). But some organic and most inorganic substances cannot be adsorbed. A small amount of these substances will be adsorbed at the surface of the suspended solids in the activated sludge plant. But the predominant part is enriched in the returned effluent of the GAC. To avoid too high accumulation in the activated sludge part of the effluent from the GAC has to be removed and further treated and/or disposed. Another idea is the treatment of the concentrate from the nanofiltration by chemical oxidation. But also in this case there may be a slight increase of the concentration of some compounds in the returned effluent from the GAC. In general it is not useful to install GAC adsorption as first step before the activated sludge leachate treatment plant. But in the case of leachate cotreatment in a sewage treatment plant it may be an option if low organic concentrations of biodegradable organic substances (measured as BOD or BOD5/ COD < 0,1) in the leachate (leachate of the methanogenic phase) are required. With the preadsorption also a part of biodegradable organic substances are adsorbed with the consequence of higher GAC costs. But these higher costs may be compensated with lower treatment costs in the sewage treatment plant. ACTIVATED SLUDGE PLANTS WITH OXIDATION PROCESS Another option for the further reduction of organics and particularly trace organics in the leachate is the chemical oxidation. As agents, hydrogen peroxide and ozone and, in some cases, Fenton reagent are used. In most cases, in Germany, ozone in combination with UV is mostly used. In principle it is possible to oxidize organic substances to the end products CO2 and H2O. But in the reality some organics are difficult to oxidize and other substances can only be oxidized to lower molecular organic substances. The oxidation products may be biodegradable or nonbiodegradable. With increasing oxidation rate the production of biodegradable substances decreases. But since the biodegradation of organic substances with air is less expensive than oxidation with ozone several plants in Germany have an additional biological posttreatment step. Since the degradable BOD concentration is mostly lower than 100 mg/L in most cases the biological plant is a fixed film reactor (e.g., RBC, rotating biological contactor) (Box 10.5.3). Robinson et al. (2003a) presented another posttreatment process with a constructed reed bed (Box 10.5.3). Some plants in Germany have very short contact time in the oxidation reactor and the effluent is directly returned into the nitrification tank of the activated sludge plant. With such an operation the ozone requirement could be reduced up to 50% because biodegradable compound are immediately eliminated in the bioreactor and cannot consume any more ozone. In a very few cases a partly oxidation can produce toxic trace compounds. This may be possible due a chemical reaction of oxidable organics and high chloride concentrations. In this case a nonsufficient oxidation could produce halogenated organic substances (AOX). In most cases this situation may be avoided by increasing the oxidation period. As a result lower effluent values than required may be produced and more ozone will be used resulting in a higher energy consumption. In principle it is not possible to oxidize ammonium with ozone. But at most oxidation plants an occasional oxidation of a varying part of ammonium could be observed. Considering the high oxygen
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
641
Box 10.5.3 Activated sludge plant with a subsequent oxidation with ozone (ATV, 1996; Robinson et al., 2003a,b) Plant layout (plant A) with activated sludge plant and oxidation with ozone.
Plant B: denitrification 950 m3, nitrification 3700 m3, clarifier, cloth filter, oxidation (3e12 kgO3/h, 6 UV-reactors), RBC (4400 m2 surface), cloth filter, flow rate 120 m3/d.
Plant
Parameter Unit
Influent
Effluent Biological Treatment
A
COD NH4 COD NH4 AOX BOD5
320e5796 125e1350 1200e4000 600e1900 1.0e3.8 n.d.
236e854 <1.2 300e1000 0.1e9 0.5e2.0 <20
B
(mg/L) (mgN/L) (mg/L) (mgN/L) (mg/L) (mg/L)
Effluent Oxidation With Ozone
Effluent Biological Posttreatment
66e176 <0.9 50e200 n.d. 0.08e0.25 20e40
e e 18e150 n.d. 0.04e0.18 <10
Plant C: Biological treatment with two parallel sequential batch reactor þ reed bed (2000 m2) þ ozonation (maximum 150 mgO3/L) þ reed bed (500 m2) (Robinson et al., 2003a). Parameter (mg/L)
Influent
Effluent Effluent SBR Effluent RB 1 Oxidation
Effluent RB 2
Suspended solids COD BOD5 NH4eN Mecoprop (mg/L) Isoproturon (mg/L)
96 600 35 405 w200 w300
26/14 424/399 4/6 1.6/<0.1 n.d. n.d.
4 350 5 1 <0.05 1.9
9 390 4 0.7 n.d. n.d.
54 395 11 0.8 <0.05 3
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Plant D: Plant similar to plant B with following additions: filtration with sand filter and 3 activated carbon filters. Parameter
Influent
Effluent Biological Treatment
Effluent Oxidation
Effluent RBC
Effluent Adsorption
COD NH4eN AOX
1045 660 1.41
563 n.d. n.d.
71 n.d. n.d.
15 n.d. n.d.
27 0.1 0.34
n.d., no data available.
requirement for the oxidation of ammonium this is a very expensive oxidation. The resulting fluctuation of the ozone requirement can lead to the high increase of effluent organics. As a consequence the activated sludge plant should nitrify almost all of the ammonium as stable as possible. Remaining suspended solids in the effluent of the activated sludge plant can reduce the efficiency of the oxidation process and may result in problems (incrustation) in the oxidation reactor. These problems may increase if the oxidation process is intensified by using UV-light because the penetration depth of the UV-light will be further reduced. To prevent such problems, a prefiltration is necessary.
BIOLOGICAL TREATMENT WITH SUBSEQUENT REVERSE OSMOSIS In a number of leachate treatment plants in Germany reverse osmosis is used as a posttreatment step after biological treatment. Using reverse osmosis almost all molecules of the compounds in the leachate may be retained. Under given conditions with lower total solids concentrations in the leachate the permeate flow is higher or the required pressure may be lower. For this reason in most cases the reverse osmosis plant consists of several modules. The membrane of the first module has a wider pore diameter to handle low concentrations of suspended solids. In Box 10.5.4 and 10.5.5 treatment plants and the corresponding results are presented. Treating raw leachate with reverse osmosis produces a mixture of inorganic and reactive organic substances in the concentrate. If the influent of the reverse osmosis plant contains ammonium and nitrate, there is a potential risk of thermal reactions in the dried concentrate. The treatment/disposal of the concentrates is still a great problem. Further information is presented in Chapter 10.4.
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
643
Box 10.5.4 Biological treatment with subsequent reverse osmosis (concentrate treatment not shown) (ATV, 1996) Plant layout: biological treatment (activated sludge plant) for denitrification and rotating biological contactor (RBC for nitrification) and reverse osmosis.
Parameter
Unit
Influent
Effluent Biological Treatment
Permeate Reverse Osmosis
COD BOD5 NH4 AOX
(mg/L) (mg/L) (mgN/L) (mg/L)
446e872 10e220 80e396 0.4e1.4
353e697 5e110 0.02e25.2 n.d.
5.3e27 1e19 0.03e10.1 <0.01e0.05
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Box 10.5.5 Biological treatment with subsequent two-stage reverse osmosis (ATV, 1996; Ehrig and Robinson, 2011)
Plant
Parameter
Unit
Influent
A
COD NH4 BOD5
(mg/L) 1543e2305 (mgN/L) 230e659 (mg/L) 145e253
Effluent Biological Treatment
Permeate Reverse Osmosis I
Permeate Reverse Osmosis II
736e1145 0.1e48 21e40
36e55 0.1e9 1.7e6.7
4.3e22 0.1e4.2 0.8e4.8
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
645
Plant
Parameter
Unit
Average/ Maximum
Effluent Biological Stage Average/ Maximum
B
COD NH4 Organic N NO3 NO2 BOD5
(mg/L) (mgN/L) (mgN/L) (mgN/L) (mgN/L) (mg/L)
3561/4590 833/1651 251/1103 1.3/2.9 0.15/5.25 1512/2860
1301/1755 0.1/0.2 82/125 84/140 1.2/30.9 23.7/64
Permeate Reverse Osmosis Average/ Maximum 15.8/45 0.1/0.12 5.3/9.4 9.8/21 0.12/0.79 2/5.3
CONCLUSIONS Sanitary landfill leachate contains a very complex mixture of different compounds. To reduce the organic compounds (measured as COD, BOD5, and AOX), ammonium, and in specific cases other parameters, it is often necessary to combine different treatment steps. In some cases, a combination of processes could be helpful to increase the effectiveness of one or more treatment steps and/or result in a reduction of the leachate treatment costs. There are several combinations of treatment processes described that are operated in technical scale; in addition results from these plants are presented.
References Albers, H., Mennerich, A., 1987. Chemisch/physikalische Nachreinigung von Deponiesickerwasser in Minden-Heisterholz (Chemical/physical post-treatment of landfill leachate in Minden-Heisterholz). Müll u. Abfall, p. 326. ATV work-group 7.2.26 “Landfill Leachate”(ATV ¼ German Association for Water, Wastewater and Waste), 1996. 1st Supplement to the Work Report “Description of Leachate Treatment Plants”, vol. 43. Korrespondenz Abwasser, p. 1303. Ehrig, H.J., 2001. Sickerwasser aus Abfallablagerungen (Leachate from landfills). In: ATV-DVWK (Ed.), ATV-Handbuch Industrieabwasser, Dienstleistungs- und Veredelungsindustrie. Verlag Ernst & Sohn, ISBN 3-433-01468-X, pp. 347e380. Ehrig, H.J., Robinson, H.D., 2011. Landfilling: leachate treatment. In: Christensen (Ed.), Solid Waste Technology & Management. Wiley, ISBN 978-1-4051-7517-3, p. 858 (Chapter 10.11). Mester, T., 1993. Sickerwasserreinigungsanlage der Deponie Wilsum e Belebungsanlage, Flockung, Aktivkohle (Leachate treatment plant - activated sludge plant, precipitation, activated carbon adsorption), vol. 8. Veröffentlichungen des Zentrums für Abfallforschung, TU Braunschweig, p. 263. Robinson, H., Carville, M., Walsh, T., 2003a. Advanced leachate treatment at Buckden landfill, Huntingdon, UK. Journal Environmental Engineering and Science 2, 255. Robinson, H., Farrow, S., Last, S., Jones, D., December 2003b. Remediation of Leachate Problems at Arpley Landfill Site, Warrington, Cheshire, UK. CIWM Scientific & Technical Review, p. 18. Robinson, H.D., Carville, M., 2007. The Design, Commissioning and Operation of Leachate Treatment Plants at Large Landfills in Tropical Regions. Paper presented to “Waste a global resource”, the 2007 annual exhibition and conference of the UK Chartered Institution of Wastes Management, June 2007. Torbay, UK. Robinson, H., Olufsen, J., 2007. Full biological treatment of landfill leachate; a detailed case study at Efford landfill in the New Forest, Hampshire, UK. In: Proceedings Sardinia 2007, Eleventh International Waste Management and Landfill Symposium. S. Margherita di Pula, Cagliari, Italy.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
INTRODUCTION Many leachate treatment plants operate with a combination of different processes. Environmental and/ or economic boundary conditions and/or specific requirements can be the reason for such combinations. With the construction of large landfills in the second half of the 20th century the awareness and the knowledge of the high and relative complex leachate pollution investigations for appropriate treatment technology started. This search resulted in an adaption of different treatment processes for leachate treatment. Leachate analysis shows a wide range of different compounds (see Chapter 10.2). The treatment of the organic substances is not without problems also because the chemical composition of the organic pollution (measured as COD or TOC) is mostly unknown. One classification is the differentiation between the biodegradable and nonbiodegradable organics. The problematic of this differentiation is described in Chapter 10.2. Using biological treatment only the biodegradable and nitrogen compounds can be removed. If the required COD effluent limit values cannot be met by means of biological treatment additional treatment steps will be necessary. Unlike the publication of experiences from sewage treatment, experiences and results from full-scale biological and chemical physical leachate treatment plants are only scarcely published. It is also for this reason difficult to design a combination of different treatment processes. Different processes are available for the elimination of the same substances and there are great differences between treating raw or pretreated leachate. The execution of laboratory or better pilot scale tests is recommended to select the optimum treatment combination. Treatment processes require energy, sorbents, and/or additives as, e.g., external organic carbon, flocculation agents, and activated carbon. Flocculation agents and activated carbon, for example, react very differently when treating different leachate qualities; this may even be the case if leachate quality data seem nearly to be the same. Several processes produce residues which must be further treated or discharged what adds to the cost. Fig. 10.5.1 presents a selection of realized leachate treatment combinations.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
633
LEACHATE BIOLOGICAL TREATMENT
ADSORPTION (pulverised carbon)
PRECIPITATION & COAGULATION
ADSORPTION (granulated carbon)
BIOLOGICAL POST TREATMENT
CHEMICAL OXIDATION REVERSE OSMOSIS
EVAPORATION
DRYING
REED BED, CONSTRUCTED WETLANDS
LEACHATE DISCHARGE Possible vapour emissions Rarely used adsorpon and chemical oxidaon processes
Figure 10.5.1 Different combinations of leachate treatment technologies used in full scale plants.
Chemical oxidation generally is carried out by using ozone þ UV or ozone þ H2O2.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
UPGRADING BIOLOGICAL TREATMENT PLANTS In several cases biological treatment plants such as aerated lagoons or activated sludge plants can meet the required discharge limits. But due to the nature of the process aerated lagoons emit biomass with the effluent. Due to the existence of the clarifier in activated sludge plants this problem should be solved. But very often very light flocks of biomass may leave the plant via the effluent. If the temperature in the bioreactor decreases, the emissions may increase above given effluent requirements. For an artificially aerated lagoon the installation of a natural separation section for biomass sedimentation and effluent polishing is recommended. In nonaerated lagoons excess biomass becomes a sediment and stabilizes at the bottom of the lagoon. In most cases the sludge has to be removed in a time interval of several years (mostly >10 years). Operating a completely aerated lagoon the produced nitrate can in general not be reduced. During warm weather periods the nitrate leads to algae blooms with secondary water pollution. During cold weather periods the ammonium concentration in the effluent increases. During temperature changes high nitrite concentrations may be measured in the effluent. Installing a constructed wetland or reed bed as a posttreatment it may be possible to reduce nitrogen compounds also during cold periods. Although the suspended solids in the clarifier effluent of an activated sludge plant have a much lower concentration than in the effluent of aerated lagoons also in this case a polishing step may make sense. In Tables 10.5.1a and 10.5.1b results from activated sludge plants designed as a sequential batch reactor (SBR) with subsequent constructed reed beds are presented. Robinson et al. (2003b) reported that suspended solids and colloids in the effluent may be further reduced by using an air flotation step between SBR and reed bed.
Table 10.5.1a Leachate treatment in a sequential batch reactor with subsequent constructed reed
beds. Mean values at Efford Landfill (UK). From Robinson and Olufsen (2007). Parameter
Raw Leachate
SBR Effluent
Final Effluent
COD (mg/L)
942
462
309
BOD5 (mg/L)
72
22
3
NH4 (mgN/L)
820
1.6
0.5
NO3 (mgN/L)
0.21
423
384
NO2 (mgN/L)
0.04
0.56
0.87
Cl (mg/L)
1502
1442
1507
7.6
8.2
8.4
3830
1229
1138
PH Alkalinity (mgCaCO3/L)
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
635
Table 10.5.1b Leachate treatment in a sequential batch reactor with subsequent constructed reed
beds. Mean values at two different Landfills in South Africa (Robinson and Carville, 2007): A. Mariannhill (SBR approx. 78 m3; reed bed 300 m2; maximum flow rate 50m3/day). B. Vissershok Parameter
Raw Leachate
SBR Effluent
Final Effluent
A
B
A
B
A
B
Suspended solids (mg/L)
250
-
102
277
28
58
COD (mg/L)
760
4560
320
1470
435
1510
BOD5 (mg/L)
170
550
90
28
8
10
NH4 (mgN/L)
435
1554
1,9
0,2
<0,5
0,4
NO3 (mgN/L)
<0,1
9,2
443
1461
471
1471
NO2 (mgN/L) pH
<0,1
0,4
1
7,5
8,18
7,1
7,39
6,7
7,61
Alkalinity (mgCaCO3/L)
2422
9652
260
935
300
1133
Cl (mg/L)
1690
4626
1550
4545
1860
4455
Phosphate (mgP/L)
1,4
13
12
10,5
8,6
10,7
Sodium (mg/L)
590
2825
1113
3979
1469
3904
Magnesium (mg/L)
80
195
118
192
163
183
Calcium (mg/L)
105
198
118
123
170
115
ACTIVATED SLUDGE PLANTS WITH SUBSEQUENT PRECIPITATION AND ADSORPTION STEPS As a first development in the early 1980s in Germany to further reduce nondegradable or difficult to degrade organics, precipitation with subsequent pulverized activated carbon (PAC) adsorption was practiced (Plant “Pohlsche Heide”, Germany). Particularly for biologically treated leachate of landfills in the methanogenic phase precipitation of residual organics, e.g., using iron salts is a very effective and economic treatment step. To meet the required effluent standards a subsequent adsorption process using pulverized PAC was added which at that time was less costly than using granular activated carbon (GAC). This situation may be different in different countries. Treatment results of such plants are presented in Box 10.5.1.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Box 10.5.1 Leachate treatment in an activated sludge plant with subsequent post-treatment by precipitation and activated carbon adsorption (Albers and Mennerich, 1987; Mester, 1993) Landfill Plant Components (Volume in m3)
Heisterholz (1985/87)
Heisterholz (1990/91)
Pohlsche Heide
Denitrification tank Nitrification tank Clarifier 1 Fixed film reactor Adsorption tank Flocculation tank Clarifier 2 Neutralization tank Clarifier 3 Filtration Average flow rate (m3/d)
725
417 1670 146 460 80 30 277 48 e e 96
2 494 2 1446 180 88 81 10 267 21 e e 93 Effluent
19 e 36 36 60 131 60 e 96
Parameter
Wilsum 940 2 720 e e 50 2.5 e n.d. e Sand filter 90
Influent
Activated Sludge
After posttreatment
350 1375 0.742
n.d. n.d. 0.605
7 52 0.122
91 686 528 1.65
n.d. n.d. 4.6
2.1 51 0.7 0.23
410 1571 633 1.31
n.d. 614 0.81 n.d.
3.5 76 0.69 0.17
207 1506
n.d. 709
1 94
LANDFILL HEISTERHOLZ (1985/87)
BOD5 COD AOX
mg/L mg/L mg/L
LANDFILL HEISTERHOLZ (1990/91)
BOD5 COD NH4 AOX
mg/L mg/L mgN/L mg/L
LANDFILL POHLSCHE HEIDE (1990/91)
BOD5 COD NH4 AOX
mg/L mg/L mgN/L mg/L
LANDFILL POHLSCHE HEIDE (1994)
BOD5 COD
mg/L mg/L
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
637
NH4 NO3 AOX Cl SO4
mgN/L mgN/L mg/L mg/L mg/L
579 44 1.45 1244 139
0.26 288 n.d. n.d. n.d.
0.09 296 0.182 1125 746
n.d. 896 459 0.12 7.1 1.04 3 1715 0.58 0.48
n.d. 401 0.34 0.04 149 0.48 n.d. n.d. n.d. n.d.
3 73 0.24 0.84 118 0.15 0.1 1950 0.03 0.15
LANDFILL WILSUM
BOD5 COD NH4 NO2 NO3 AOX Phosphate Cl Copper Nickel
mg/L mg/L mgN/L mgN/L mgN/L mg/L mgP/L mg/L mg/L mg/L
n.d., no data available.
Due to easier handling at a later stage at “Pohlsche Heide” the adsorption plant was operated as filters with GAC. Fig. 10.5.2 shows the relative strong relationship between both processes (Plant Heisterholz). Using an optimized precipitation process with increased COD elimination the dosing of PAC can be reduced, which resulted in a significant reduction of the treatment costs. The dewatering of iron sludge is greatly improved as a mixture of GAC and iron sludge.
ACTIVATED SLUDGE PLANTS WITH ACTIVATED CARBON FILTERS This combination is most commonly used for leachate treatment in Germany. Important reasons for this solution are the relatively low investment and low operation costs. In addition the required amount of carbon can be automatically adapted on the leachate quality. The higher costs of GAC compared to PAC can be partly compensated by higher carbon adsorption loading rates. Using GAC filters it is possible to reduce remaining organic and trace substances in the leachate. But it should be noted that trace substances are only adsorbed if the main portion of the organics are removed. In such cases a specific operation of two GAC filters in a row may be necessary. In the first filter the organics should
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
COD removal by precipitaon (mg/L)
600
500
400
300
200
100
0 0
100
200
300
400
500
600
COD removal by PAC adsorpon (mg/L)
Figure 10.5.2 Relationship between COD removal by precipitation and pulverized activated carbon
adsorption in a combined treatment system (Albers and Mennerich, 1987).
be reduced to the range of the required COD discharge limit values so that the in the subsequent filter trace substances can be adsorbed. Such a specific situation must be tested in laboratory or pilot scale tests. This is also necessary because a great number of different activated carbon qualities exist; the optimum quality can only be determined by performing tests. To avoid early clogging of the pores in the AC the effluent of the activated sludge plant should be filtered before entering the GAC filters. Sand filter, fabric filter, and ultrafiltration are methods that are available for fine particle removal. The higher the removal rate of suspended solids upfront the higher will be the adsorption capacity of the GAC; as a consequence costs may be reduced. The ultrafiltration process reduces fine particles to the highest extent. Results from different treatment plants using the combination of activated sludge and GAC filters are presented in Box 10.5.2. Some activated sludge plants in Germany with subsequent GAC filters are combined with nanofiltration as a third treatment step. The nanofiltration membranes are permeable for small molecules as chloride, but most inorganic and organic molecules are retained. The nanofiltration can be placed after the ultrafiltration of the activated sludge plant. The ultrafiltration is used to retain the suspended solids of the activated sludge plant. The permeate of ultrafiltration is fed in to the nanofiltration plant. The concentrate of the nanofiltration is fed to GAC filter, and its effluent is returned back to the activated sludge plant. The idea of this combination is to retain “all” organic substances and increase their concentrations. The consequence of higher organics (COD values) in the concentrate stream of the nanofiltration is an increase of adsorption capacity from 20% to 30% of GAC (by weight) to values up to
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
639
Box 10.5.2 Combination of an activated sludge plant with an activated carbon filter (ATV, 1996; Ehrig, 2001) Plant layout (plant A) of the combination activated sludge plant and activated carbon filter.
Plant
Parameter
Unit
Influent
Effluent Biological Treatment
Effluent Activated Carbon Filter
A
BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4 BOD5 COD AOX NH4
(mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L) (mg/L) (mg/L) (mg/L) (mgN/L)
1500e6000 1000e12000 1.0e2.5 400e800 n.d. 3000e6000 0.8e2.0 400e800 280 1700 1.1 900 90e210 1100e1600 0.8e1.7 500e900 50e150 450e800 n.d. 250e400 500e800 2000e5600 0.6e2.2 600e1800
<5 500e800 0.5e2.0 <10 n.d. 500e900 0.6e1.4 <10 <20 900e1200 0.5e0.9 <10 <20 300e900 0.9e1.2 <10 <10 250e320 n.d. <50 <10 750e1200 0.5e1.5 3e52
<5 <200 0.1e0.7 <10 n.d. <110 0.1e0.48 <10 <20 <400 0.1 e< 0.5 <10 <20 <200 <0.5 <10 <10 <200 n.d. <50 <10 <200 0.1e0.87 <20
B
C
D
E
F
n.d., no data available.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
more than 50% of GAC (by weight). But some organic and most inorganic substances cannot be adsorbed. A small amount of these substances will be adsorbed at the surface of the suspended solids in the activated sludge plant. But the predominant part is enriched in the returned effluent of the GAC. To avoid too high accumulation in the activated sludge part of the effluent from the GAC has to be removed and further treated and/or disposed. Another idea is the treatment of the concentrate from the nanofiltration by chemical oxidation. But also in this case there may be a slight increase of the concentration of some compounds in the returned effluent from the GAC. In general it is not useful to install GAC adsorption as first step before the activated sludge leachate treatment plant. But in the case of leachate cotreatment in a sewage treatment plant it may be an option if low organic concentrations of biodegradable organic substances (measured as BOD or BOD5/ COD < 0,1) in the leachate (leachate of the methanogenic phase) are required. With the preadsorption also a part of biodegradable organic substances are adsorbed with the consequence of higher GAC costs. But these higher costs may be compensated with lower treatment costs in the sewage treatment plant. ACTIVATED SLUDGE PLANTS WITH OXIDATION PROCESS Another option for the further reduction of organics and particularly trace organics in the leachate is the chemical oxidation. As agents, hydrogen peroxide and ozone and, in some cases, Fenton reagent are used. In most cases, in Germany, ozone in combination with UV is mostly used. In principle it is possible to oxidize organic substances to the end products CO2 and H2O. But in the reality some organics are difficult to oxidize and other substances can only be oxidized to lower molecular organic substances. The oxidation products may be biodegradable or nonbiodegradable. With increasing oxidation rate the production of biodegradable substances decreases. But since the biodegradation of organic substances with air is less expensive than oxidation with ozone several plants in Germany have an additional biological posttreatment step. Since the degradable BOD concentration is mostly lower than 100 mg/L in most cases the biological plant is a fixed film reactor (e.g., RBC, rotating biological contactor) (Box 10.5.3). Robinson et al. (2003a) presented another posttreatment process with a constructed reed bed (Box 10.5.3). Some plants in Germany have very short contact time in the oxidation reactor and the effluent is directly returned into the nitrification tank of the activated sludge plant. With such an operation the ozone requirement could be reduced up to 50% because biodegradable compound are immediately eliminated in the bioreactor and cannot consume any more ozone. In a very few cases a partly oxidation can produce toxic trace compounds. This may be possible due a chemical reaction of oxidable organics and high chloride concentrations. In this case a nonsufficient oxidation could produce halogenated organic substances (AOX). In most cases this situation may be avoided by increasing the oxidation period. As a result lower effluent values than required may be produced and more ozone will be used resulting in a higher energy consumption. In principle it is not possible to oxidize ammonium with ozone. But at most oxidation plants an occasional oxidation of a varying part of ammonium could be observed. Considering the high oxygen
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
641
Box 10.5.3 Activated sludge plant with a subsequent oxidation with ozone (ATV, 1996; Robinson et al., 2003a,b) Plant layout (plant A) with activated sludge plant and oxidation with ozone.
Plant B: denitrification 950 m3, nitrification 3700 m3, clarifier, cloth filter, oxidation (3e12 kgO3/h, 6 UV-reactors), RBC (4400 m2 surface), cloth filter, flow rate 120 m3/d.
Plant
Parameter Unit
Influent
Effluent Biological Treatment
A
COD NH4 COD NH4 AOX BOD5
320e5796 125e1350 1200e4000 600e1900 1.0e3.8 n.d.
236e854 <1.2 300e1000 0.1e9 0.5e2.0 <20
B
(mg/L) (mgN/L) (mg/L) (mgN/L) (mg/L) (mg/L)
Effluent Oxidation With Ozone
Effluent Biological Posttreatment
66e176 <0.9 50e200 n.d. 0.08e0.25 20e40
e e 18e150 n.d. 0.04e0.18 <10
Plant C: Biological treatment with two parallel sequential batch reactor þ reed bed (2000 m2) þ ozonation (maximum 150 mgO3/L) þ reed bed (500 m2) (Robinson et al., 2003a). Parameter (mg/L)
Influent
Effluent Effluent SBR Effluent RB 1 Oxidation
Effluent RB 2
Suspended solids COD BOD5 NH4eN Mecoprop (mg/L) Isoproturon (mg/L)
96 600 35 405 w200 w300
26/14 424/399 4/6 1.6/<0.1 n.d. n.d.
4 350 5 1 <0.05 1.9
9 390 4 0.7 n.d. n.d.
54 395 11 0.8 <0.05 3
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Plant D: Plant similar to plant B with following additions: filtration with sand filter and 3 activated carbon filters. Parameter
Influent
Effluent Biological Treatment
Effluent Oxidation
Effluent RBC
Effluent Adsorption
COD NH4eN AOX
1045 660 1.41
563 n.d. n.d.
71 n.d. n.d.
15 n.d. n.d.
27 0.1 0.34
n.d., no data available.
requirement for the oxidation of ammonium this is a very expensive oxidation. The resulting fluctuation of the ozone requirement can lead to the high increase of effluent organics. As a consequence the activated sludge plant should nitrify almost all of the ammonium as stable as possible. Remaining suspended solids in the effluent of the activated sludge plant can reduce the efficiency of the oxidation process and may result in problems (incrustation) in the oxidation reactor. These problems may increase if the oxidation process is intensified by using UV-light because the penetration depth of the UV-light will be further reduced. To prevent such problems, a prefiltration is necessary.
BIOLOGICAL TREATMENT WITH SUBSEQUENT REVERSE OSMOSIS In a number of leachate treatment plants in Germany reverse osmosis is used as a posttreatment step after biological treatment. Using reverse osmosis almost all molecules of the compounds in the leachate may be retained. Under given conditions with lower total solids concentrations in the leachate the permeate flow is higher or the required pressure may be lower. For this reason in most cases the reverse osmosis plant consists of several modules. The membrane of the first module has a wider pore diameter to handle low concentrations of suspended solids. In Box 10.5.4 and 10.5.5 treatment plants and the corresponding results are presented. Treating raw leachate with reverse osmosis produces a mixture of inorganic and reactive organic substances in the concentrate. If the influent of the reverse osmosis plant contains ammonium and nitrate, there is a potential risk of thermal reactions in the dried concentrate. The treatment/disposal of the concentrates is still a great problem. Further information is presented in Chapter 10.4.
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
643
Box 10.5.4 Biological treatment with subsequent reverse osmosis (concentrate treatment not shown) (ATV, 1996) Plant layout: biological treatment (activated sludge plant) for denitrification and rotating biological contactor (RBC for nitrification) and reverse osmosis.
Parameter
Unit
Influent
Effluent Biological Treatment
Permeate Reverse Osmosis
COD BOD5 NH4 AOX
(mg/L) (mg/L) (mgN/L) (mg/L)
446e872 10e220 80e396 0.4e1.4
353e697 5e110 0.02e25.2 n.d.
5.3e27 1e19 0.03e10.1 <0.01e0.05
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Box 10.5.5 Biological treatment with subsequent two-stage reverse osmosis (ATV, 1996; Ehrig and Robinson, 2011)
Plant
Parameter
Unit
Influent
A
COD NH4 BOD5
(mg/L) 1543e2305 (mgN/L) 230e659 (mg/L) 145e253
Effluent Biological Treatment
Permeate Reverse Osmosis I
Permeate Reverse Osmosis II
736e1145 0.1e48 21e40
36e55 0.1e9 1.7e6.7
4.3e22 0.1e4.2 0.8e4.8
CHAPTER 10 j Combination of Different MSW Leachate Treatment Processes
645
Plant
Parameter
Unit
Average/ Maximum
Effluent Biological Stage Average/ Maximum
B
COD NH4 Organic N NO3 NO2 BOD5
(mg/L) (mgN/L) (mgN/L) (mgN/L) (mgN/L) (mg/L)
3561/4590 833/1651 251/1103 1.3/2.9 0.15/5.25 1512/2860
1301/1755 0.1/0.2 82/125 84/140 1.2/30.9 23.7/64
Permeate Reverse Osmosis Average/ Maximum 15.8/45 0.1/0.12 5.3/9.4 9.8/21 0.12/0.79 2/5.3
CONCLUSIONS Sanitary landfill leachate contains a very complex mixture of different compounds. To reduce the organic compounds (measured as COD, BOD5, and AOX), ammonium, and in specific cases other parameters, it is often necessary to combine different treatment steps. In some cases, a combination of processes could be helpful to increase the effectiveness of one or more treatment steps and/or result in a reduction of the leachate treatment costs. There are several combinations of treatment processes described that are operated in technical scale; in addition results from these plants are presented.
References Albers, H., Mennerich, A., 1987. Chemisch/physikalische Nachreinigung von Deponiesickerwasser in Minden-Heisterholz (Chemical/physical post-treatment of landfill leachate in Minden-Heisterholz). Müll u. Abfall, p. 326. ATV work-group 7.2.26 “Landfill Leachate”(ATV ¼ German Association for Water, Wastewater and Waste), 1996. 1st Supplement to the Work Report “Description of Leachate Treatment Plants”, vol. 43. Korrespondenz Abwasser, p. 1303. Ehrig, H.J., 2001. Sickerwasser aus Abfallablagerungen (Leachate from landfills). In: ATV-DVWK (Ed.), ATV-Handbuch Industrieabwasser, Dienstleistungs- und Veredelungsindustrie. Verlag Ernst & Sohn, ISBN 3-433-01468-X, pp. 347e380. Ehrig, H.J., Robinson, H.D., 2011. Landfilling: leachate treatment. In: Christensen (Ed.), Solid Waste Technology & Management. Wiley, ISBN 978-1-4051-7517-3, p. 858 (Chapter 10.11). Mester, T., 1993. Sickerwasserreinigungsanlage der Deponie Wilsum e Belebungsanlage, Flockung, Aktivkohle (Leachate treatment plant - activated sludge plant, precipitation, activated carbon adsorption), vol. 8. Veröffentlichungen des Zentrums für Abfallforschung, TU Braunschweig, p. 263. Robinson, H., Carville, M., Walsh, T., 2003a. Advanced leachate treatment at Buckden landfill, Huntingdon, UK. Journal Environmental Engineering and Science 2, 255. Robinson, H., Farrow, S., Last, S., Jones, D., December 2003b. Remediation of Leachate Problems at Arpley Landfill Site, Warrington, Cheshire, UK. CIWM Scientific & Technical Review, p. 18. Robinson, H.D., Carville, M., 2007. The Design, Commissioning and Operation of Leachate Treatment Plants at Large Landfills in Tropical Regions. Paper presented to “Waste a global resource”, the 2007 annual exhibition and conference of the UK Chartered Institution of Wastes Management, June 2007. Torbay, UK. Robinson, H., Olufsen, J., 2007. Full biological treatment of landfill leachate; a detailed case study at Efford landfill in the New Forest, Hampshire, UK. In: Proceedings Sardinia 2007, Eleventh International Waste Management and Landfill Symposium. S. Margherita di Pula, Cagliari, Italy.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann