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Landfilling of Mechanically Biologically Pretreated Waste
14.1 LANDFILLING OF MECHANICALLY BIOLOGICALLY PRETREATED WASTE Rainer Stegmann, Kai-Uwe Heyer and Karsten Hupe
INTRODUCTION The overall strategy of waste management in Europe is toward more material and energy recovery from waste and less landfilling. The European Union (EU) has, via the Landfill Directive, set a target for reducing the biologically degradable waste fraction going to landfills (see Chapter 4.1). In Austria, target values for the mechanical biological pretreatment (MBT) of municipal solid waste (MSW) as a prerequisite for landfilling are already in power from the beginning of 2005. This is also the case in Germany where through the implementation of the Landfill Directive in June 1, 2005 only thermally or mechanically biologically pretreated MSW are allowed to be landfilled (Anonymous, 2000). The disposal of MBT waste has to meet the requirements for a proper disposal described in the Abfallablagerungsverordnung (Anonymous, 2001) (German Waste Disposal Act, particularly Appendix 3). German limit values for waste going to landfills are presented in Table 14.1.1.
Table 14.1.1 Selection of limit values for the quality of waste going to landfills
(Anonymous, 2000) Parameter Respiration activitya (RA4) Gas formation potentialb (GF21)
Target Value 5 mg O2/g dry matter 20 Nl/kg dry matter
TOCeluatec
250 mg/L
TOCsolid
18 Mass-%
Gross calorific value
6000 kJ/kg
a
By means of bacteria in 4 days dependent on the amount of substrate available (indirect method to measure the biodegradable fraction of the waste sample). Gas formation potential (GF21): Gas formation of the waste sample in 21 days. c TOC in the eluate produced in an elution test (1:10 solid/liquid ratio and 24 hours shaking). b
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GENERAL ASPECTS OF MECHANICAL BIOLOGICAL PRETREATMENT WASTE LANDFILLING The incoming mechanically and biologically waste material heats up during transportation so that during the unloading of the material at the landfill temperatures around 50 C may be measured. Often water vapors escape from the waste. This phenomenon shows that this material is still biologically active. The existing easy degradable organic fractions in the MBT material may be partly produced during biological pretreatment from more difficult degradable organics. For a better long-term emission control, landfills in general should be built as a mound. To guarantee the mechanical stability of the landfill beyond others the water content and pore water pressures of the landfilled MBT material should be controlled and monitored. In addition, a landfill with intermediate layers of coarse material is recommended (Stegmann and Heyer, 2001). Aerobic conditions should be permanently achieved within the landfill body by means of suitable constructional and operational measures. Should anaerobic conditions restore, a rise in leachate concentrations and methane formationdhowever lowdcan be expected. To avoid problems during the emplacement, MBT material may be pressed to bales and landfilled using a forklift loader (Stegmann, 2005). To describe the emission behavior of biologically pretreated residual waste, landfill simulation experiments in the laboratory have been carried out (Stegmann, 1997). By choosing appropriate milieu conditions for the test, an enhanced biological degradation and elution process of the waste will be achieved. By these means, the emission quality and potentialdrepresented by gas quality and production as well as leachate concentrations and loadsdof the waste samples can be estimated within reasonable periods of time. Table 14.1.2 presents a summary of results from investigations using landfill simulation reactors (LSRs), which show that the emissions regarding organics and nitrogen as well as the gas production can be reduced by approximately 90%.
Table 14.1.2 Effects of mechanical biological pre-treatment (MBT) on landfill emissions (results
from laboratory scale tests) (Stegmann and Heyer, 2001) Emission
Raw Waste
COD (mg/kg dry matter)
25.000e40.000
1.000e3.000
90%
1.500e3.000
150e300
90%
150e200
0e20
90%
Total nitrogen (mg/kg dry matter) Gas production GB21 (Nl/kg dry matter)
MBT-Waste
Reduction
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Since the gas formation potential is low, an active gas extraction may be considered; in any case the residual amounts of produced gas need to be biologically oxidized in the top area before leaving the landfill. Today in Germany there are already 10 years of experiences available regarding the operation of MBT-waste landfills, but there are not too many results from field investigations available. After MBT, also the landfilling characteristic of the waste is significantly different from raw MSW. Due to the separation of the high calorific value fraction refuse derived fuel (RDF) from the raw waste, MBT waste has a lower content of structural material. Due to the low amount of macropores the water and gas permeability are lower and water saturation of the landfilled material is reached at lower water contents. DESIGN AND OPERATION OF MBT LANDFILL Investigations of Mechanical Properties at Test Fields and in the Laboratory The results from investigations at test fields and laboratory analysis may not be representative and cannot be transferred directly to actual landfilling; in addition, due to the kind of mechanical (dependent also on the quality of the produced RDF) and the kind of biological treatment [aerobic or anaerobic (wet or dry AD process)] the quality of the MBT material may vary significantly. Eitner and Tiedt (2005) summarized investigations and experiences with the landfilling of MBT waste as follows: Shear strength (f: 27e36 ) and cohesion (C:11e62 kN/m2) of MBT waste is similar to raw waste, but the tensile strength is nearly zero. • It can be expected that slopes of 1:3.5e1:3 are probably sufficiently stable (f ¼ 35 , C > 15 KN/m2). This should be confirmed by waste mechanical calculations. • Densities in the surface areaddependent on the material qualitydcan be expected between 1.0e1.5 t/m3 wet weight (wwt) resp. 0.7e1.0 t/m3 dry weight (dwt). • Compaction may be difficult to achieve due to different quality and water content of the to-belandfilled MBT waste as well as a kind of “mattress” effect. Experiences From Landfill Operation Due to the homogeneity of the MBT material and a relatively high achievable density more even and lower settling rates can be expected. As a consequence a higher load may weigh on the bottom of the landfill and drainage pipes. Due to a low content in coarse material (e.g., plastic pieces, wood) and the resulting lower reinforcement of the material the sheer strength and friction are reduced (Bräcker, 2010). Based on present experiences the following procedures for the landfilling of an MBT material may be applied: • To achieve a low permeability the waste may be highly compacted in thin layers, (30e50 cm) by means of about 3e4 compaction runs (Figs. 14.1.1 and 14.1.2). Different kinds of machines for emplacement, compaction, and surface flattening can be used (compactor, roller, sheep’s foot roller).
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Figure 14.1.1 Distribution and compaction of mechanical biological pretreatment material (landfill Minden-Lübbecke).
Figure 14.1.2 Surface layer of a mechanical biological pretreatment landfill.
• Due to the more homogeneous character of the waste material as well its lower pore volume and higher disposal density, the permeability of the emplaced MBT material is between kf: 10e5 to 10e8 m/s; the great range reflects influences of the quality of the raw waste the kind of pretreatment (e.g., sieve size for RDF separation, kind of biological treatment) the initial emplacement density and the depth of the landfill (load of the overlaying waste mass). When gas fills part of the pores the density may further increase up to values of kf ¼ 10-10 m/s.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
• Maximum densities of 18 kN/m3 may be reached (Bräcker, 2010), which are in practical operation significantly lower (1015 kN/m3) (Entenmann and Wendt, 2005). • Settling rates in the area of in total 2.5% of the final height can be expected. • The working area should, in general, be small but can be extended when the waste has a higher incoming moisture content than recommended. In this case the pore water can decrease due to consolidation on the surface. • The Proctor water content should be between 25%e40% (wwt). No landfilling should be practiced during (intensive) rainfall. If the moisture content on the surface is too high the emplacement will become difficult because the machines and trucks will sink into the waste. If this is the case the incoming waste has to be intermittently stored and landfilled when it is dry weather again. During rain the working phase may be covered with a tarpaulin (reusable plastic foils that should be rolled and unrolled). By these means also the leachate production will be reduced. Areas that are not in operation and not yet cultivated should be intermittently lined with plastic foil (Stegmann and Heyer, 2002). • Precipitation of low intensity may be completely absorbed by the waste; if the upper waste layer is water saturated and the precipitation rate is higher than the infiltration, water may accumulate on the surface. If the surface is quite flat, significant surface water runoff can be expected. The amount of runoff depends on the intensity of the rain and the degree of the slope (e.g., at high precipitation rate and a slope of 1:2 about 2/3 of the precipitation became surface water runoff (observation at a test area) (Bräcker, 2010). • Therefore, the planning and operation of a surface water collection system is an important task. As already mentioned the plastic membranes used for temporary cover should be reused as far as possible after resuming operation of those areas. A collection (e.g., in a pond) and treatment of the surface water that had contact with the waste surface may be necessary where a significant pollution reduction can be achieved by removing particles by means of settling (Ziehmann et al., 2002). • During dry periods the surface may become dry, and dust may be produced. • Owing to the pretreatment, there will be no food for birds and mammals. • When the landfill is closed the installation of a final surface cover/liner system will be necessary. An often-used system is the combination liner consisting of a clay liner and plastic membrane as well as a soil layer on top. Other systems, e.g., capillary barrier, may be encountered (see Chapter 11.1). • The stability of the landfill mound needs the highest attention. When the waste is watersaturated, pore water over pressure can build up, e.g., due to the weight of the overlaying waste. In addition, the produced gas (even at low rates) can be compressed in the pores and it adds to the positive pressure. This situation results in lower friction values of the landfilled waste, which means less stability. As a consequence pore water pressures should be measured also during landfill operation. With lower friction values the incline of the slope of the MBT landfill mounds has to be adapted. In any way it should be <1:3. Since the waste material is more homogeneous and therefore more similar to soil waste mechanical calculation should be used to determine the safe physical stability of the landfill. But it should be kept in mind that the MBT material can be quite different depending on the kind of mechanical and biological pretreatment. Also due to this situation geotechnical investigations of the material to be used should be obligatory. • In addition, it should be the intention to reduce the pore water pressure. As a measure the installation of intermediate layers of about 50 cm height consisting of course material (“no” carbonate
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passive stabilization system: 11 air access / release of exhausts 12 combinated horizontal drainage layers/pipes for air/exhausts and leachate from consolidation 13 combinated vertical drainage columns for air/exhausts and leachate 14 biologically stabilized MBP-residues
alternative surface sealing system: 7 equation layer 8 capillary block, capillary barrier 9 capillary layer, capillary barrier 10 recultivation layer
5 leachate collection system 6 collection of uncontaminated surface and drainage water
subsurface / geological barrier
base sealing system: 1 equation layer 2 mineral layer 3 PE membrane 4 drainage layer with drainage pipe
Figure 14.1.3 Concept of a mechanical biological pretreatment landfill (Stegmann and Heyer, 2001).
and sulfur content) should be encountered. These should be constructed about every 5 m with a slope to the outside of the landfill (Fig. 14.1.3). By these means water over pressure resulting from water and gas can be reduced and the total friction of the landfill will increase. This system could also support natural aeration of the landfill once forced air in situ aeration has been terminated. This system is used at several landfills in Germany. Emission Control MBT landfills still produce leachate and gas. Regarding long-term total gas production rates, it can be expected that still about 10e40 Nm3/t wwt. (10%e20% of the total gas potential of the raw MSW) will be produced. After a short active gas production period (due to a kind of aerobic breakdown of heavy degradable compounds during the biological pretreatment) the remaining organic substances are not easily degradable; as a consequence low gas production rates over long periods of time can be expected. Leachate production will still occur where it is difficult to predict leachate production rates. These will be dependent on the specific climatic conditions as well as the waste mechanics of the emplaced material and the landfill operation. Leachate production rates in the average of about 5% of the annual precipitation rate are predicted by Bräcker (2010). These values will depend very much on the surface water control of precipitation, the MBT quality and the kind and time period of landfill operation. The authors have no access to actual monitored leachate production rates; this is also due to the fact that in Germany in most cases MBT material is landfilled on the top of existing landfills.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
The leachate quality (see also Chapter 10.2) will be similar to the leachate quality from existing landfills in the stable methanogenic phase. The nitrogen content may be lower. To meet the German discharge standards for leachate discharge into natural waters treatment will still be required. Leachate concentrations from a study by Robinson et al. in 2005 are presented in Table 14.1.3. These data are difficult to judge, since the material parameters (achieved respiration rate: AT4, and gas production potential, GB21) as well as the kind of landfill operation are not known. In the view of the authors, these concentrations seem to be on the higher end of what can be expected, if the German requirements for MBT material are reached. In this case COD values in the range of 500e2000 mg/L, BOD5 values of <50 mg/L, and NH4eN values of <500 mg/L seem to be more realistic. Of course, anaerobically pretreated waste may result to somehow different leachate quality data than aerobically treated material; this is also due to the different amounts of water used during the different processes (elution factor). In addition the disposal height with time and the achieved density are of influence. In the first years of landfill operation the concentrations may be somewhat higher than with increasing age. Since no acidic phase is expected the concentration curves dependent with time are quite flat. A better understanding of leachate quality evolution along the time and the influence of the pretreatment typology will occur when more data from field experiences will be available. Table 14.1.3 Range of concentrations of leachate parameters from MBT
landfills (study by Robinson et al. in 2005). Leachate Composition
LoweMedium-General Range
pH value (-) Conductivity (mS/cm)
7.5e8.5 10,000e20,000
COD (mg/L)
1000e5000
BOD5 (mg/L)
20e200
TOC (mg/L)
500e2000
Chloride (mg/L)
4000e8000
Sulfate (as SO4) (mg/L)
1000e5000
Phosphate (as P) (mg/L)
1.0e15
Alkalinity (as CaCO3) (mg/L)
2000e6000
Ammonia-N (mg/L)
50e1000
Kjeldahl-N (mg/L)
100e1300
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The leachate should be treated if possible together with the municipal wastewater in sewage treatment plants or it has to be treated separately. Owing to the low content in biological degradable substances, activated carbon adsorption and membrane separation processes are suitable for a treatment to achieve, e.g., the German target values for the discharge of treated leachate (Anonymous, 1996). For further information on leachate treatment refer to Chapters 10.3 and 10.4.
FINAL REMARKS Landfilling of MBT waste is quite different from landfilling of raw MSW. This implies modified landfill design and operation. Important aspect to consider is the mechanical stability of the landfill mound. MBT waste has a high sorption capacity; pore water overpressures have to be avoided. As a consequence the water content of the incoming MBT material has to be strictly controlled. If the landfill mound stability cannot be guaranteed, dams built of soil could be constructed at the landfill foot. There is still leachate produced and has to be treated. The quality is similar to leachate from an MSW landfill in the stable methanogenic phase. About 10%e20% of the total gas production is still produced and has either be captured and treated or oxidized in the specially designed landfill surface. There are advantages regarding landfill operation as less birds and rats, but during dry periods dust emissions may happen.
References Anonymous, 1996. Allgemeine Rahmen- Verwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwässer in Gewässer. Rahmen-Abwasser VwV-GMBI, Anhang 51: Ablagerung von Sielungsabfällen. www.bmu.de. Anonymous, 2000. Verordnung über die umweltverträgliche Ablagerung von Siedlungsabfällen und über biologische Behandlungsanlagen. www.bmu.de. Anonymous, 2001. 30.Verordnung zur Durchführung des Bundesemissionsschutzgesetzes (Verordnung über Anlagen zur biologischen Behandlung von Abfällen e 30. BImSchV) vom 31.01.2001. www.bmu.de. Bräcker, 2010. Deponietechnik für mechanism-biologisch behandelte Abfälle, Abfallwirtschaftsfakten 4.3, Staatliches Gewerbeaufsichtsamt Hildesheim, Zentrale UnterstützungsstelleAbfall, Gentechnik und Gerätesicherheit (ZUS AGG). Eitner, R., Tiedt, M., 2005. Konzepte zum Deponiebetrieb mit MBA-Output. In: Gallenkemper, Bidlingmaier, Doedens, Stegmann (Eds.), 9. Münsteraner Abfalltage, Münsteraner Schriften zur Abfallwirtschaft, Band 8. Labor für Abfallwirtschaft der Fachhochschule Münster. Entenmann, W., Wendt, P., 2005. Einbauversuche mit AbfAblV-konformen MBA-Output. In: Gallenkemper, Bidlingmaier, Doedens, Stegmann (Eds.), 9. Münsteraner Abfalltage, Münsteraner Schriften zur Abfallwirtschaft, Band 8, Labor für Abfallwirtschaft der Fachhochschule Münster. Robinson, H.D., Knox, K., Bone, B.D., Picken, A., 2005. Leachate quality from landfilled MBT-waste. Waste Management 25. Stegmann, R., 1997. Description of a laboratory scale method to investigate anaerobic degradation processes taking place in landfills. In: Christensen, Cossu, Stegmann (Eds.), Sardinia 97, Proceedings, CISA Publisher, Cagliari. Stegmann, R., Heyer, K.-U., 2001. Landfill Concept for mechanical-biologically treated residual waste. In: Christensen, Cossu, Stegmann (Eds.), SARDINIA 2001, 8th International Landfill Symposium, Proceedings. CISA Publisher, Italy. Stegmann, R., Heyer, K.-U., 2002. Konzept für eine nachsorgearme MBV-Deponie. In: Stegmann, Rettenberger, Bidlingmaier, Ehrig (Eds.), Deponietechnik 2002, Hamburger Berichte 18. Verlag Abfall aktuell, Stuttgart. Stegmann, R., 2005. Landfilling of mechanically biologically pre-treated waste. In: Christensen, Cossu, Stegmann (Eds.), SARDINIA 2001, 10th International Landfill Symposium, Proceedings, CISA, via Marengo 34, 09123 Cagliari, Italy. Ziehmann, G., Münnich, K., Fricke, K., 2002. Einbau von MBV-Materialien. In: Stegmann, Rettenberger, Bidlingmaier, Ehrig (Eds.), Deponietechnik 2002, Hamburger Berichte 18. Verlag Abfall aktuell, Stuttgart.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
INTRODUCTION The overall strategy of waste management in Europe is toward more material and energy recovery from waste and less landfilling. The European Union (EU) has, via the Landfill Directive, set a target for reducing the biologically degradable waste fraction going to landfills (see Chapter 4.1). In Austria, target values for the mechanical biological pretreatment (MBT) of municipal solid waste (MSW) as a prerequisite for landfilling are already in power from the beginning of 2005. This is also the case in Germany where through the implementation of the Landfill Directive in June 1, 2005 only thermally or mechanically biologically pretreated MSW are allowed to be landfilled (Anonymous, 2000). The disposal of MBT waste has to meet the requirements for a proper disposal described in the Abfallablagerungsverordnung (Anonymous, 2001) (German Waste Disposal Act, particularly Appendix 3). German limit values for waste going to landfills are presented in Table 14.1.1.
Table 14.1.1 Selection of limit values for the quality of waste going to landfills
(Anonymous, 2000) Parameter Respiration activitya (RA4) Gas formation potentialb (GF21)
Target Value 5 mg O2/g dry matter 20 Nl/kg dry matter
TOCeluatec
250 mg/L
TOCsolid
18 Mass-%
Gross calorific value
6000 kJ/kg
a
By means of bacteria in 4 days dependent on the amount of substrate available (indirect method to measure the biodegradable fraction of the waste sample). Gas formation potential (GF21): Gas formation of the waste sample in 21 days. c TOC in the eluate produced in an elution test (1:10 solid/liquid ratio and 24 hours shaking). b
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
799
GENERAL ASPECTS OF MECHANICAL BIOLOGICAL PRETREATMENT WASTE LANDFILLING The incoming mechanically and biologically waste material heats up during transportation so that during the unloading of the material at the landfill temperatures around 50 C may be measured. Often water vapors escape from the waste. This phenomenon shows that this material is still biologically active. The existing easy degradable organic fractions in the MBT material may be partly produced during biological pretreatment from more difficult degradable organics. For a better long-term emission control, landfills in general should be built as a mound. To guarantee the mechanical stability of the landfill beyond others the water content and pore water pressures of the landfilled MBT material should be controlled and monitored. In addition, a landfill with intermediate layers of coarse material is recommended (Stegmann and Heyer, 2001). Aerobic conditions should be permanently achieved within the landfill body by means of suitable constructional and operational measures. Should anaerobic conditions restore, a rise in leachate concentrations and methane formationdhowever lowdcan be expected. To avoid problems during the emplacement, MBT material may be pressed to bales and landfilled using a forklift loader (Stegmann, 2005). To describe the emission behavior of biologically pretreated residual waste, landfill simulation experiments in the laboratory have been carried out (Stegmann, 1997). By choosing appropriate milieu conditions for the test, an enhanced biological degradation and elution process of the waste will be achieved. By these means, the emission quality and potentialdrepresented by gas quality and production as well as leachate concentrations and loadsdof the waste samples can be estimated within reasonable periods of time. Table 14.1.2 presents a summary of results from investigations using landfill simulation reactors (LSRs), which show that the emissions regarding organics and nitrogen as well as the gas production can be reduced by approximately 90%.
Table 14.1.2 Effects of mechanical biological pre-treatment (MBT) on landfill emissions (results
from laboratory scale tests) (Stegmann and Heyer, 2001) Emission
Raw Waste
COD (mg/kg dry matter)
25.000e40.000
1.000e3.000
90%
1.500e3.000
150e300
90%
150e200
0e20
90%
Total nitrogen (mg/kg dry matter) Gas production GB21 (Nl/kg dry matter)
MBT-Waste
Reduction
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
Since the gas formation potential is low, an active gas extraction may be considered; in any case the residual amounts of produced gas need to be biologically oxidized in the top area before leaving the landfill. Today in Germany there are already 10 years of experiences available regarding the operation of MBT-waste landfills, but there are not too many results from field investigations available. After MBT, also the landfilling characteristic of the waste is significantly different from raw MSW. Due to the separation of the high calorific value fraction refuse derived fuel (RDF) from the raw waste, MBT waste has a lower content of structural material. Due to the low amount of macropores the water and gas permeability are lower and water saturation of the landfilled material is reached at lower water contents. DESIGN AND OPERATION OF MBT LANDFILL Investigations of Mechanical Properties at Test Fields and in the Laboratory The results from investigations at test fields and laboratory analysis may not be representative and cannot be transferred directly to actual landfilling; in addition, due to the kind of mechanical (dependent also on the quality of the produced RDF) and the kind of biological treatment [aerobic or anaerobic (wet or dry AD process)] the quality of the MBT material may vary significantly. Eitner and Tiedt (2005) summarized investigations and experiences with the landfilling of MBT waste as follows: Shear strength (f: 27e36 ) and cohesion (C:11e62 kN/m2) of MBT waste is similar to raw waste, but the tensile strength is nearly zero. • It can be expected that slopes of 1:3.5e1:3 are probably sufficiently stable (f ¼ 35 , C > 15 KN/m2). This should be confirmed by waste mechanical calculations. • Densities in the surface areaddependent on the material qualitydcan be expected between 1.0e1.5 t/m3 wet weight (wwt) resp. 0.7e1.0 t/m3 dry weight (dwt). • Compaction may be difficult to achieve due to different quality and water content of the to-belandfilled MBT waste as well as a kind of “mattress” effect. Experiences From Landfill Operation Due to the homogeneity of the MBT material and a relatively high achievable density more even and lower settling rates can be expected. As a consequence a higher load may weigh on the bottom of the landfill and drainage pipes. Due to a low content in coarse material (e.g., plastic pieces, wood) and the resulting lower reinforcement of the material the sheer strength and friction are reduced (Bräcker, 2010). Based on present experiences the following procedures for the landfilling of an MBT material may be applied: • To achieve a low permeability the waste may be highly compacted in thin layers, (30e50 cm) by means of about 3e4 compaction runs (Figs. 14.1.1 and 14.1.2). Different kinds of machines for emplacement, compaction, and surface flattening can be used (compactor, roller, sheep’s foot roller).
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Figure 14.1.1 Distribution and compaction of mechanical biological pretreatment material (landfill Minden-Lübbecke).
Figure 14.1.2 Surface layer of a mechanical biological pretreatment landfill.
• Due to the more homogeneous character of the waste material as well its lower pore volume and higher disposal density, the permeability of the emplaced MBT material is between kf: 10e5 to 10e8 m/s; the great range reflects influences of the quality of the raw waste the kind of pretreatment (e.g., sieve size for RDF separation, kind of biological treatment) the initial emplacement density and the depth of the landfill (load of the overlaying waste mass). When gas fills part of the pores the density may further increase up to values of kf ¼ 10-10 m/s.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
• Maximum densities of 18 kN/m3 may be reached (Bräcker, 2010), which are in practical operation significantly lower (1015 kN/m3) (Entenmann and Wendt, 2005). • Settling rates in the area of in total 2.5% of the final height can be expected. • The working area should, in general, be small but can be extended when the waste has a higher incoming moisture content than recommended. In this case the pore water can decrease due to consolidation on the surface. • The Proctor water content should be between 25%e40% (wwt). No landfilling should be practiced during (intensive) rainfall. If the moisture content on the surface is too high the emplacement will become difficult because the machines and trucks will sink into the waste. If this is the case the incoming waste has to be intermittently stored and landfilled when it is dry weather again. During rain the working phase may be covered with a tarpaulin (reusable plastic foils that should be rolled and unrolled). By these means also the leachate production will be reduced. Areas that are not in operation and not yet cultivated should be intermittently lined with plastic foil (Stegmann and Heyer, 2002). • Precipitation of low intensity may be completely absorbed by the waste; if the upper waste layer is water saturated and the precipitation rate is higher than the infiltration, water may accumulate on the surface. If the surface is quite flat, significant surface water runoff can be expected. The amount of runoff depends on the intensity of the rain and the degree of the slope (e.g., at high precipitation rate and a slope of 1:2 about 2/3 of the precipitation became surface water runoff (observation at a test area) (Bräcker, 2010). • Therefore, the planning and operation of a surface water collection system is an important task. As already mentioned the plastic membranes used for temporary cover should be reused as far as possible after resuming operation of those areas. A collection (e.g., in a pond) and treatment of the surface water that had contact with the waste surface may be necessary where a significant pollution reduction can be achieved by removing particles by means of settling (Ziehmann et al., 2002). • During dry periods the surface may become dry, and dust may be produced. • Owing to the pretreatment, there will be no food for birds and mammals. • When the landfill is closed the installation of a final surface cover/liner system will be necessary. An often-used system is the combination liner consisting of a clay liner and plastic membrane as well as a soil layer on top. Other systems, e.g., capillary barrier, may be encountered (see Chapter 11.1). • The stability of the landfill mound needs the highest attention. When the waste is watersaturated, pore water over pressure can build up, e.g., due to the weight of the overlaying waste. In addition, the produced gas (even at low rates) can be compressed in the pores and it adds to the positive pressure. This situation results in lower friction values of the landfilled waste, which means less stability. As a consequence pore water pressures should be measured also during landfill operation. With lower friction values the incline of the slope of the MBT landfill mounds has to be adapted. In any way it should be <1:3. Since the waste material is more homogeneous and therefore more similar to soil waste mechanical calculation should be used to determine the safe physical stability of the landfill. But it should be kept in mind that the MBT material can be quite different depending on the kind of mechanical and biological pretreatment. Also due to this situation geotechnical investigations of the material to be used should be obligatory. • In addition, it should be the intention to reduce the pore water pressure. As a measure the installation of intermediate layers of about 50 cm height consisting of course material (“no” carbonate
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passive stabilization system: 11 air access / release of exhausts 12 combinated horizontal drainage layers/pipes for air/exhausts and leachate from consolidation 13 combinated vertical drainage columns for air/exhausts and leachate 14 biologically stabilized MBP-residues
alternative surface sealing system: 7 equation layer 8 capillary block, capillary barrier 9 capillary layer, capillary barrier 10 recultivation layer
5 leachate collection system 6 collection of uncontaminated surface and drainage water
subsurface / geological barrier
base sealing system: 1 equation layer 2 mineral layer 3 PE membrane 4 drainage layer with drainage pipe
Figure 14.1.3 Concept of a mechanical biological pretreatment landfill (Stegmann and Heyer, 2001).
and sulfur content) should be encountered. These should be constructed about every 5 m with a slope to the outside of the landfill (Fig. 14.1.3). By these means water over pressure resulting from water and gas can be reduced and the total friction of the landfill will increase. This system could also support natural aeration of the landfill once forced air in situ aeration has been terminated. This system is used at several landfills in Germany. Emission Control MBT landfills still produce leachate and gas. Regarding long-term total gas production rates, it can be expected that still about 10e40 Nm3/t wwt. (10%e20% of the total gas potential of the raw MSW) will be produced. After a short active gas production period (due to a kind of aerobic breakdown of heavy degradable compounds during the biological pretreatment) the remaining organic substances are not easily degradable; as a consequence low gas production rates over long periods of time can be expected. Leachate production will still occur where it is difficult to predict leachate production rates. These will be dependent on the specific climatic conditions as well as the waste mechanics of the emplaced material and the landfill operation. Leachate production rates in the average of about 5% of the annual precipitation rate are predicted by Bräcker (2010). These values will depend very much on the surface water control of precipitation, the MBT quality and the kind and time period of landfill operation. The authors have no access to actual monitored leachate production rates; this is also due to the fact that in Germany in most cases MBT material is landfilled on the top of existing landfills.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann
The leachate quality (see also Chapter 10.2) will be similar to the leachate quality from existing landfills in the stable methanogenic phase. The nitrogen content may be lower. To meet the German discharge standards for leachate discharge into natural waters treatment will still be required. Leachate concentrations from a study by Robinson et al. in 2005 are presented in Table 14.1.3. These data are difficult to judge, since the material parameters (achieved respiration rate: AT4, and gas production potential, GB21) as well as the kind of landfill operation are not known. In the view of the authors, these concentrations seem to be on the higher end of what can be expected, if the German requirements for MBT material are reached. In this case COD values in the range of 500e2000 mg/L, BOD5 values of <50 mg/L, and NH4eN values of <500 mg/L seem to be more realistic. Of course, anaerobically pretreated waste may result to somehow different leachate quality data than aerobically treated material; this is also due to the different amounts of water used during the different processes (elution factor). In addition the disposal height with time and the achieved density are of influence. In the first years of landfill operation the concentrations may be somewhat higher than with increasing age. Since no acidic phase is expected the concentration curves dependent with time are quite flat. A better understanding of leachate quality evolution along the time and the influence of the pretreatment typology will occur when more data from field experiences will be available. Table 14.1.3 Range of concentrations of leachate parameters from MBT
landfills (study by Robinson et al. in 2005). Leachate Composition
LoweMedium-General Range
pH value (-) Conductivity (mS/cm)
7.5e8.5 10,000e20,000
COD (mg/L)
1000e5000
BOD5 (mg/L)
20e200
TOC (mg/L)
500e2000
Chloride (mg/L)
4000e8000
Sulfate (as SO4) (mg/L)
1000e5000
Phosphate (as P) (mg/L)
1.0e15
Alkalinity (as CaCO3) (mg/L)
2000e6000
Ammonia-N (mg/L)
50e1000
Kjeldahl-N (mg/L)
100e1300
CHAPTER 14 j Landfilling of Mechanically Biologically Pretreated Waste
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The leachate should be treated if possible together with the municipal wastewater in sewage treatment plants or it has to be treated separately. Owing to the low content in biological degradable substances, activated carbon adsorption and membrane separation processes are suitable for a treatment to achieve, e.g., the German target values for the discharge of treated leachate (Anonymous, 1996). For further information on leachate treatment refer to Chapters 10.3 and 10.4.
FINAL REMARKS Landfilling of MBT waste is quite different from landfilling of raw MSW. This implies modified landfill design and operation. Important aspect to consider is the mechanical stability of the landfill mound. MBT waste has a high sorption capacity; pore water overpressures have to be avoided. As a consequence the water content of the incoming MBT material has to be strictly controlled. If the landfill mound stability cannot be guaranteed, dams built of soil could be constructed at the landfill foot. There is still leachate produced and has to be treated. The quality is similar to leachate from an MSW landfill in the stable methanogenic phase. About 10%e20% of the total gas production is still produced and has either be captured and treated or oxidized in the specially designed landfill surface. There are advantages regarding landfill operation as less birds and rats, but during dry periods dust emissions may happen.
References Anonymous, 1996. Allgemeine Rahmen- Verwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwässer in Gewässer. Rahmen-Abwasser VwV-GMBI, Anhang 51: Ablagerung von Sielungsabfällen. www.bmu.de. Anonymous, 2000. Verordnung über die umweltverträgliche Ablagerung von Siedlungsabfällen und über biologische Behandlungsanlagen. www.bmu.de. Anonymous, 2001. 30.Verordnung zur Durchführung des Bundesemissionsschutzgesetzes (Verordnung über Anlagen zur biologischen Behandlung von Abfällen e 30. BImSchV) vom 31.01.2001. www.bmu.de. Bräcker, 2010. Deponietechnik für mechanism-biologisch behandelte Abfälle, Abfallwirtschaftsfakten 4.3, Staatliches Gewerbeaufsichtsamt Hildesheim, Zentrale UnterstützungsstelleAbfall, Gentechnik und Gerätesicherheit (ZUS AGG). Eitner, R., Tiedt, M., 2005. Konzepte zum Deponiebetrieb mit MBA-Output. In: Gallenkemper, Bidlingmaier, Doedens, Stegmann (Eds.), 9. Münsteraner Abfalltage, Münsteraner Schriften zur Abfallwirtschaft, Band 8. Labor für Abfallwirtschaft der Fachhochschule Münster. Entenmann, W., Wendt, P., 2005. Einbauversuche mit AbfAblV-konformen MBA-Output. In: Gallenkemper, Bidlingmaier, Doedens, Stegmann (Eds.), 9. Münsteraner Abfalltage, Münsteraner Schriften zur Abfallwirtschaft, Band 8, Labor für Abfallwirtschaft der Fachhochschule Münster. Robinson, H.D., Knox, K., Bone, B.D., Picken, A., 2005. Leachate quality from landfilled MBT-waste. Waste Management 25. Stegmann, R., 1997. Description of a laboratory scale method to investigate anaerobic degradation processes taking place in landfills. In: Christensen, Cossu, Stegmann (Eds.), Sardinia 97, Proceedings, CISA Publisher, Cagliari. Stegmann, R., Heyer, K.-U., 2001. Landfill Concept for mechanical-biologically treated residual waste. In: Christensen, Cossu, Stegmann (Eds.), SARDINIA 2001, 8th International Landfill Symposium, Proceedings. CISA Publisher, Italy. Stegmann, R., Heyer, K.-U., 2002. Konzept für eine nachsorgearme MBV-Deponie. In: Stegmann, Rettenberger, Bidlingmaier, Ehrig (Eds.), Deponietechnik 2002, Hamburger Berichte 18. Verlag Abfall aktuell, Stuttgart. Stegmann, R., 2005. Landfilling of mechanically biologically pre-treated waste. In: Christensen, Cossu, Stegmann (Eds.), SARDINIA 2001, 10th International Landfill Symposium, Proceedings, CISA, via Marengo 34, 09123 Cagliari, Italy. Ziehmann, G., Münnich, K., Fricke, K., 2002. Einbau von MBV-Materialien. In: Stegmann, Rettenberger, Bidlingmaier, Ehrig (Eds.), Deponietechnik 2002, Hamburger Berichte 18. Verlag Abfall aktuell, Stuttgart.
SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann