Leachate quality from la x b ark, S tes, N genc 4 Feb nviro EU landfills that have received imports of MSOR and MBT wastes. Results are presented for sanitary analyses, heavy metals, and an extensive range of trace organic substances, from sites containing MBT wastes that have received different degrees of composting pre-treatment. Leachates produced from MSOR wastes have a very high polluting potential, but biological pre-treatment of these member states to draw up strategies to ensure that the Council�s Directive, on the quality of leachate that will tions of MBT wastes. A selection of analytical data is presented, including some conclusions on the effects of MBT on the fate of trace organic compounds, and the derivation of generic source term distributions that can be used in groundwater risk assessments, and in the q Disclaimer: The views expressed in this paper are not necessarily those of the EA. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of information, or reliance upon views contained herein. * Corresponding author. Tel.: +44 1743 284877. E-mail address:
[email protected] (H.D. Robinson). Waste Management 25 0956-053X/$ - see front matter � 2005 Published by Elsevier Ltd. amount of biodegradable municipal waste deposited at landfill progressively reduces over a 15-year period to only 35% of the total amount produced in 1995. The LFD also requires member states to only landfill wastes that have been subjected to treatment and incineration, leading to a reduction in their quantity or hazard to hu- man health or the environment. It is anticipated that mechanical and biological treatment (MBT), and incin- be produced in the future from UK landfills (Environ- ment Agency R&D Project P1-494). This paper presents results from investigations into the landfilling of municipal solid wastes (MSW) that have been subjected to mechanical biological treatment (MBT), and the impacts that this has on leachate qual- ity. Work has involved collection of data from published papers, and from European experts in this field, and also the collection of leachate samples from a number of European landfills that have received varying propor- wastes can avoid the peak acetogenic phase of decomposition, and produce leachates similar to, or weaker than, those from con- ventional methanogenic landfills. Effective MBT processes can also significantly reduce concentrations of trace organics, and of ammoniacal-N in leachates. However, further research is needed to examine the relative importance of nitrification/denitrification processes, generation of stable, organically based nitrogen forms, and other routes during MBT processing, in order that appropri- ate reactions to remove nitrogen can be encouraged and optimised. � 2005 Published by Elsevier Ltd. 1. Introduction The European Council Directive on the Landfill of Wastes 1999/31/EEC (LFD), places a requirement on eration of municipal waste will increase substantially in the UK, in order to achieve these objectives. In 2001, the UK Environment Agency began a re- search project to consider the potential impact of the H.D. Robinson a,*, K. Kno a Enviros Consulting Limited, Shrewbury Business P b Knox Associa c Environment A Accepted 1 Abstract A research project recently completed on behalf of the UK E doi:10.1016/j.wasman.2005.02.003 ndfilled MBT waste q , B.D. Bone c, A. Picken c itka Drive, Shrewsbury, Shropshire SY2 6LG, UK ottingham, UK y, Solihull, UK ruary 2005 nment Agency, has collected data and sampled leachates from www.elsevier.com/locate/wasman (2005) 383–391 composting processes, for many years in some European countries (notably Austria, Germany and Holland). Sev- The second phase of the project involved the detailed Man eral good papers and PhD theses (often not translated into English) have been published in these countries, provision of appropriate leachate management facilities at landfill sites. 2. Mechanical and biological treatment Mechanical and biological treatment of MSW has been required through national legislation in a number of EU member states for several years. The perceived benefits of such pre-treatment are: � Reduction in the strength of leachate produced, and the quantity of landfill gas generated; � Reduced clogging of leachate drainage systems; and � Improved waste settlement characteristics, and a shorter timescale to waste stabilisation. The desk study identified two broad categories of or- ganic residues from waste pre-treatment: mechanically sorted organic residues, and composted MSW or MSW fractions. 2.1. Mechanically sorted organic residues Mechanically sorted organic residues (MSOR) (also termed ‘‘residual wastes’’) are the fine fraction residues from a mechanical sorting process, which cannot be re- used or recycled. The maximum size fraction of MSOR typically passes through a 40-mm or 100-mm screen, and the quality and proportion of MSOR will depend on the extent to which: � Wastes have been subject to source separation, e.g., of garden and kitchen wastes; and � Wastes have been separated for recycling at a MRF. Typically, the larger-size fractions discarded during the sieving process are of higher calorific value, and are diverted for either direct incineration (preferably with energy recovery), or for the production of refuse- derived fuels. The high organic content, high moisture content, and small particle size of the MSOR appears to give rise to much higher landfill gas production rates and stronger leachates. If this material is landfilled, particularly in isolation from other waste streams, then extremely strong leachates must be expected, that will persist for as long as, or longer than, those from conventional MSW landfills. With this very high pollution potential in mind, MSOR wastes have often been subjected to various 384 H.D. Robinson et al. / Waste and it was recognised that much could be learned chemical analysis of samples of leachate taken from ac- tual European landfills that have received a high propor- directly from researchers with more experience than was available in the UK. 3. Objectives and scope of the uk study The objectives of the study were to provide data and guidance for UK landfill operators, on the impact which the landfilling of MSW fractions, or composted MBT wastes, might have on leachate quality at their sites. This information is necessary to allow them to: � Define a leachate source term for groundwater risk assessments; � Assess the implications of waste pretreatment on the timescales, and long-term liabilities, of the landfilling of pretreated waste materials; � Make appropriate and adequate provisions for leach- ate management, treatment and off-site disposal; � Consider the effects of changes in leachate quality on landfill liners and leachate drainage blankets and systems. The project has been undertaken as two linked phases of work. Initially data were collected from EU experts and researchers in this field, who had undertaken studies using bench-scale experiments, and at operational land- fill sites. The assistance of these researchers has been ex- tremely valuable, in particular by their efforts to make available, by translation into English, many research re- sults not previously available to the UK. At several sites where research has been undertaken into the disposal of MBT wastes, leachate quality data runs of 20 years or more have been obtained. Nevertheless, in spite of these long periods of data, leachate quality results from MBT mono-landfills are limited, because typically MBT wastes are disposed of together with variable propor- tions of untreated MSW, MSOR or commercial and industrial wastes. The co-disposal of MBT waste and MSW or organic residues (MSOR) is likely to reflect the situation in the UK until significant infrastructure for MBT becomes available, at least locally. The quality of the MBT waste materials themselves will also vary as consequence of: � The extent of source-separation, for example of food and garden wastes; � The waste inputs (e.g., urban or rural source, summer or winter collection); � Type of mechanical treatment; and � Type and duration of biological treatment. agement 25 (2005) 383–391 tion of inputs of MBT wastes. Samples have been analysed for detailed sanitary parameters and major ions, heavy metals, and an extensive range of 65 trace organic compounds. Seven landfills in two EU member states were visited during 2002, and nine samples of leachate were obtained in conjunction with the operators and researchers. The detailed final report of the study has recently been com- pleted (Environment Agency, 2003a). 4. Leachates from MBT landfills 4.1. Published data Many detailed studies have demonstrated the very strong leachates that are generated when untreated MSOR are landfilled. A typical research project under- from untreated residual waste stabilised at about 1000 mg/l, this value was below 200 mg/l for pre-treated wastes. Nevertheless, in terms of L/S ratio, a trial period of 250 days corresponds to a period of about 50 years for a 20-m deep landfill, with an annual infiltration rate of 250 mm, or significantly longer if the site was capped. Table 1 contains basic summary data, from published sources, for leachates from landfilled MSOR, and from MSOR that has been pretreated by various combina- tions of composting. The results are typical of many other data, showing the very high strength leachates generated by untreated MSOR when landfilled, and also demonstrating the improvement in leachate quality achieved by various de- grees of composting pre-treatment widely observed to be capable of removing the initial strong organic leachates generated during the acetogenic stage of degradation, conta Com Composting (weeks) Intensive 0 0 4 9 2780 52 197 11300 0.14 0.23 0.71 3.4 H.D. Robinson et al. / Waste Management 25 (2005) 383–391 385 Secondary 0 0 COD 172000 19400 BOD5 123000 9400 Ammoniacal-N 3965 4200 Chloride 9100 6500 Chromium 0.41 1.3 Nickel 2.10 0.45 Copper 1.41 0.33 Zinc 102 0.56 taken by Woelders and Oonk (1999) looked at the behaviour of MSOR in a large-scale flushing bioreactor cell, and found that although initial COD values in ex- cess of 60,000 mg/l had fallen to below 20,000 mg/l within 2 years (BOD5 from above 40,000 mg/l to below 10,000 mg/l), concentrations of Kjeldahl-N showed little change-remaining at about 4000 mg/l throughout the period, and chloride increased from 5000 to more than 6000 mg/l. Other studies have looked at the benefits of compo- sting MSOR, in terms of reductions in pollutant emis- sions. Leikam and Stegmann (1999) studied the behaviour of composted MSOR wastes in landfill simu- lation tests, in comparison to untreated MSOR. For treated MSOR, the acetogenic phase during which strong organic leachate is produced was absent, and after about 250 test days the COD of the leachate was below 1000 mg/l (BOD5 < 20 mg/l). A much more signif- icant benefit of pre-treatment becomes apparent when concentrations of total-N (primarily ammoniacal-N) are considered. Whereas the total-N content in leachate Table 1 Basic leachate quality summary for leachates from landfills/test cells regimes Waste inputs MSOR Notes. All results in mg/l. Table based on data from Danhamer and Jager ( leading to a more rapid onset of methanogenic conditions. It is clear that the degree of composting achieved, and the efficiency of individual composting processes, cannot be determined simply based on the duration of intensive and secondary composting being carried out at each location. For example, at one site only 2 weeks of inten- sive, and a further week of secondary composting are applied, on paper the least, but in practice this achieves substantial improvements in leachate quality. Key find- ings from these and other published studies on leachates from landfilled MBT wastes are therefore that: � Organic residues from mechanical sorting (MSORs) can produce leachates with higher pollution potential than both acetogenic and methanogenic leachates from conventional landfills; � Composting such residues can reduce the organic pol- lution potential from both leachate and landfill gas, through the avoidance of the peak acetogenic phase of decomposition; ining untreated MSOR, and MSOR subjected to various composting posted MSOR, various sources 4 2 16 3 43 1 8 19 1170 540 4000 1900 9 158 111 14 11 56 292 340 6900 5700 6200 4100 0.04 0.03 0.21 0.09 0.71 0.16 0.40 0.09 0.80 0.28 0.52 0.18 1.0 0.22 1.6 1.2 1999) and others. � Concentrations of ammoniacal-N in MBT leachates can be either similar to, or much lower than, metha- nogenic leachates from conventional landfills. This raises the possibility that a nitrogen removal or atten- uating process may operate, to varying extents, dur- ing composting; � Landfills receiving MBT wastes will pose a risk to groundwater similar to conventional MSW landfills that have become methanogenic, and are therefore likely to require a similar period of time before active management and treatment of leachates ceases to be necessary. 4.2. The sampling exercise undertake determination of Red List Substances, as part of a large sampling and review exercise into leachate quality at UK Landfill Sites, undertaken during the per- iod 1990–1996 on behalf of the UKDoE/EA (Robinson, 1996). They had also undertaken specialised analyses as part of major studies to look at Pollution Inventory dis- charges to sewer or surface waters from landfill leach- ates (Environment Agency, 2001, 2003b). In fact, following preparation of that report, and completion of this sampling work, the list of substances to be re- ported under the UK Pollution Inventory was subse- quently increased from 65, to nearly 100 (Environment Agency, 2003b). Samples for trace analyses were taken into various prepared sample bottles, and despatched by courier to eacha n us arily puts. 386 H.D. Robinson et al. / Waste Management 25 (2005) 383–391 Results from the sampling of leachates at EU landfills have been summarised below, full results being con- tained in the final report of the study (Environment Agency, 2003a). Samples were obtained in two separate visits, during February and July 2002, and sites have not been identified. In all instances, samples of leachate were obtained from boreholes, sumps, or pipelines which were frequently and routinely pumped, to avoid sam- pling of stagnant leachates. No samples were filtered or specifically settled in any way – the intention being to represent, as fairly as possible, the overall quality of leachate that might realistically be discharged from such a site. In practice, levels of suspended solids were rela- tively low in all samples. At each sample point, various subsamples were ta- ken. A range of sanitary parameters and metals was determined in samples delivered rapidly to laboratories in the UK in PET bottles, metal samples being preserved by on-site addition of hydrochloric or nitric acids as appropriate. For determination of trace compounds and elements, the UK Pollution Inventory List was used as a basis for an analytical suite to be determined by the laboratories of SAC Scientific (SAC) in Biggleswade, Bedfordshire, UK. SAC had previously been used to Table 2 General description of the categories of landfill site from which MBT l Waste input type Young wastes (50% MBTc No samples >90% MBT Sample #7 Sample #6 Sample #5 Sample #3 a Extent of historic leachate quality data available at sampling locatio waste disposal began in that cell. NA = not available. b No sample of leachate available from freshly emplaced MSOR. Prim recent years. c Sites receiving more than 50%, but less than 90%, of MBT waste in receiving 50–60% MBT. SAC, to arrive within 48 h of having been obtained. Subsamples were also taken on behalf of the laborato- ries of the UK Environment Agency, to assist them in progressing a GCMS water sample rapid screening methodology, to be used in the application of Regula- tion 15 of the UK Waste Management Licensing Regu- lations, 1994. Landfills selected were inevitably constrained by available sites, which could be included within the two short and intensive sampling visits. Nevertheless, a great deal was achieved, with help from many landfill opera- tors and researchers from different countries. The categories of site from which leachate samples could be obtained are presented in Table 2. The table also indicates the extent of historic data for basic leach- ate chemistry that was available from the site operator, at each location where a sample was obtained. Analytical results for sanitary parameters and metals are presented in Table 3, and a general summary of data for trace organic compounds is presented in Table 4. Historic leachate quality data, where available, were useful in placing the single leachate samples obtained in a context of the history of leachate quality at the site, since wastes were initially emplaced. For example, Fig. 1 presents historic data for leachate quality at the location te samples were obtained Old wastes (>5 years) Period of historic dataa Sample #1 14–23 years Sample #4 5–27 years Sample #2 10–18 years NA 0–3 years NA NA ed. Not always covering a period to date. Years represent period since because direct landfill of untreated MSOR has rarely been practised in Sample #4 from a site receiving 80% MBT, and Sample #2 from one g this us so s Man Table 3 Results for sanitary parameters and metals in leachates sampled durin Waste inputs MSOR Composted MSOR, vario Composting processes None Passive windrows Passive windrow Sample number 1 2 3 Period (weeks) Intensive 0 0 0 Secondary 0 12 30 COD 15590 582 4670 BOD20 7840 >157 843 BOD5 4240 46 202 TOC 4694 180 1480 Fatty acids (as C) 707 . . Tur 4 388 H.D. Robinson et al. / Waste Management 25 (2005) 383–391 Table 4 Results for trace organic compounds in leachates sampled Waste inputs MSOR Composted MSOR, various sources. Composting processes None Passive windrows Passive windrows Sample number 1 2 3 contaminants from landfilled products, is not a simple matter. It is not clearly defined, simply by measures of the periods during which waste fractions are subjected to intensive and secondary treatment, but depends on the specific nature of these treatments, as well as on the original MSOR waste stream. Period (weeks) Intensive 0 0 0 0 Secondary 0 12 30 25 Trace organics AOX 6064 366 790 213 Mecoprop 120 13 7.9 < Triazine herbicides < 1.1 < < Uron herbicides < 0.69 < < PCBs < < < < BTEX < < < < PAH < < 2.6 1.8 Organo P pesticides < < < < Organo Cl pesticides 0.33 < < < VOCs < < < < Phenols 210 1.3 < < Notes. Results in lg/l; 6below detection limit. 0 5000 10000 15000 20000 25000 30000 35000 1992 1993 1994 1995 1996 19 T CO D & BO D (m g/l ) B O D COD 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 1992 1993 1994 1995 1996 19 T Am m on ia ca l-N & C hl or id e (m g/l ) Ch loride Ammoniacal-N Fig. 1. History of leachate quality data where Sample 1 was taken in 2002, fo ned windrows Turned windrows Container Container + windrows 5 6 7 Representative leachate samples, obtained from various landfills, nevertheless demonstrated that when effective state-of-the-art composting processes are undertaken on residual wastes, the landfilling of such products can produce a substantial reduction in bioreac- tivity, and consequently the generation of more stable 0 16 2 8 0 30 1500 180 370 0.47 < < < < < < < < < < < < < < < < < < 0.34 0.27 0.29 < < < < < < < < 97 1998 1999 2000 200 1 2002 ime 97 1998 1999 2000 2001 2002 ime llowing emplacement of untreated MSOR during the period 1979–1991. Year Half COD Ammoniacal-N 1997 I – – H.D. Robinson et al. / Waste Man and weaker leachates. BOD5 values can be as low as importance of nitrification/denitrification, generation of stable, organically-bound forms of nitrogen, and other routes during MBT of waste fractions, in reducing long-term emissions of ammoniacal-N from landfilled wastes, in order that appropriate processes can be encouraged and optimised during waste pre-treatment. 6. Conclusions This project has confirmed existing knowledge related to the very high strength organic leachates generated when MSOR fractions of household wastes are land- filled without pre-treatment – these can typically be from twice to four times as strong as equivalent leach- ates from MSW landfills, and high organic strengths can persist for at least several decades. Efficient MBT of the MSOR fraction can considerably reduce the or- ganic strength of leachates, avoiding the acetogenic phase, and more rapidly producing leachates similar to those from MSW landfills in methanogenic phases of decomposition. Nevertheless, levels of ‘‘hard’’ COD in these leach- ates, not readily biodegradable by aerobic or anaerobic processes, are typically at least as strong as, and often stronger than those found in methanogenic leachates – often in the range 1000–4000 mg/l, in spite of BOD val- ues which are frequently less than 100 mg/l. Concentrations of ammoniacal-N and Kjeldahl-N in MBT leachates may be significantly lower than those from conventional MSW landfills, but the extent to which this occurs is variable, and not easily related to the design of specific composting and pretreatment pro- cesses. The biochemical transformations involved are not well understood, and the influence of nitrification/ denitrification, incorporation within stable organic frac- tions (possibly related to the elevated ‘‘hard COD’’ val- ues), and other processes, require further research. An outline source-term spreadsheet, for concentra- tions of sanitary parameters and metals in leachates from MSOR and MBT wastes, has been prepared (see Table 6), to be used as a generic database for groundwa- ter risk assessments, and as a tool to allow appropriate leachate management schemes to be developed at land- fills that will receive MBT wastes. Few data are available on the presence of potentially harmful trace organic substances in leachates fromMBT waste landfills, to allow these to be compared with data from conventional MSW sites. This study has obtained preliminary results, based on a programme of sampling at EU landfills. As at MSW sites, few trace organic com- pounds are present, but for those which have been mea- Table 6 eters thano 00 00 0 0 0 00 0 0 0 0 Iron 300 5 Nickel 1 0.5 001 1 01 esult 390 H.D. Robinson et al. / Waste Management 25 (2005) 383–391 Copper 0.5 0.5 Zinc 10 0.5 Cadmium 1 sured at significant concentrations (e.g., mecoprop), evi- dence from this study is that effective composting pro- cesses are able to reduce concentrations significantly. In the case of mecoprop, this is generally present at significant levels in leachates from MSW, and was pres- ent at up to 120 lg/l in leachates from landfilled MSOR. However, it was absent, or present at very much lower concentrations, in leachates from composted residues. In practice, the extent of removal of mecoprop from leachates, may well be a good surrogate measure of the efficiency of the composting process itself, to which waste fractions have been subjected. Similarly, AOX values were very much lower in leachates from composted wastes, although there is doubt as to whether this is of any value in assessing risk from any specific trace organic compounds in these leachate samples. In general terms, many landfills receiving MBT release of these and other contaminants. However, even at such landfills, the extent to which timescales over funded as part of the UK Environment Agency�s Waste Regulation and Management Research programme. References Danhamer, H., Jager, J., 1999. Sickerwasseremissionen von mecha- nisch-biologisch und thermisch vorbehandelten siedlungsabfallen. EP (9), 31–35. Environment Agency, 2003a. Improved definition of the leachate source term for landfill: Phase 1 Report. Contract Report produced jointly by Enviros and Knox Associates. Project P1-494 (formerly P2-236). Environment Agency, 2003b. updating the landfill leachate pollution inventory reporting tool. R&D Technical Report No. PI496/TR(2) prepared for the UK Environment Agency by Enviros and Knox Associates, March 2003, 55pp. Environment Agency, 2001. Pollution inventory discharges to sewer or surface waters from landfill leachates. Report REGCON 70 H.D. Robinson et al. / Waste Management 25 (2005) 383–391 391 which leachates will require management can be reduced significantly, remains to be determined. Acknowledgements The assistance of European landfill operators and researchers, in providing data, discussion of results and arranging access to the landfills is gratefully acknowledged. This research (R&D Project P1-494) was wastes will continue to pose risks to groundwater, and require aftercare periods similar to conventional MSW landfills that have become methanogenic. There is no doubt that MBT processes have potential to reduce both organic strength, and concentrations of ammoniacal-N in leachates from such landfills, as well as the total mass prepared for the UK Environment Agency by Enviros and Knox Associates, May 2001, 15pp plus Appendices. Heiss-Ziegler, C., Lechner, P., 1999. Behaviour of stabilised organic matter under anaerobic landfill conditions. In: Margherita di Pula, S. (Ed.), Paper presented to Sardinia 1999, the Seventh International Landfill Symposium, Cagliari, Italy, vol. I, pp. 511– 518. Leikam, K., Heyer, K.U., Stegmann, R., 1997. In situ stabilisation of completed landfills and old sites. In: Margherita di Pula, S. (Ed.), Paper presented to Sardinia 1997, the Sixth International Landfill Symposium, Cagliari, Italy, vol. IV, pp. 451–462.. Leikam, K., Stegmann, R., 1999. Influence of mechanical–biological treatment of municipal solid waste on landfill behaviour. Waste Management and Research 17, 424–429. Robinson, H.D., 1996. A review of the composition of leachates from domestic wastes in landfill sites. Technical Report CWM 072/95, produced for the UK Environment Agency, 1996, 550pp (available from EA R&D Dissemination Centre, c/o WRC, Tel.: +10793 865 000). Woelders, H., Oonk, H., 1999. Full-scale demonstration of treatment of MSOR in a bioreactor at VAM in Wijster. In: Margherita di Pula, S. (Ed.), Proceedings of Sardini 1999, the Seventh Interna- tional Waste Management and Landfill Symposium, Cagliari, Italy, 4–8 October 1999, vol. V, pp. 375–382. Leachate quality from landfilled MBT waste Introduction Mechanical and biological treatment Mechanically sorted organic residues Objectives and scope of the uk study Leachates from MBT landfills Published data The sampling exercise Behaviour of nitrogen compounds during MBT processes Conclusions Acknowledgements References