STATE-OF-THE-PRACTICES AND IMPLEMETATION RECOMMENDATIONS FOR NON-HAZARDOUS WASTE MANAGEMENT USING

Transcription

1 STATE-OF-THE-PRACTICES AND IMPLEMETATION RECOMMENDATIONS FOR NON-HAZARDOUS WASTE MANAGEMENT USING BIOREACTOR LANDFILLS December 2007 Study realised for and FNADE Technical coordination: Isabelle HEBE - Département Gestion Optimisée des Déchets Direction Déchets et Sols Angers

2 AKNOWLEDGEMENTS FNADE (French Federation of Waste Management Services) and (French Environment and Energy Management Agency) have initiated and sponsored the following document. The creators of this guide have relied on the support and professional experience of landfill operators as well as on the scientific expertise of a team made up of the research labs that have worked on the subject. Authors Research, concept and writing by T.CHASSAGNAC (Cabinet 3C), with assistance from research consulting firm CSD AZUR. Close collaboration from : Isabelle HEBE : Philippe BELBEZE: VEOLIA PROPRETE Arnaud BUDKA : SITA Emmanuel COSTE: COVED Nadir CROS: CHEZE SA Jean-Michel MANDUIK : DELTA DECHETS Thomas LAGIER : VEOLIA ENVIRONNEMENT Alain ROSPARS : GROUPE SECHE Assistance from : Christian DUQUENOI : CEMAGREF Dominique GUYONNET : BRGM Sylvain MOREAU : CEMAGREF Jean-Pierre GOURC : LTHE Olivier BOUR : INERIS And financial support for this guide from :, FNADE, SITA, VEOLIA PROPRETE, COVED, SECHE ENVIRONNEMENT, and the GNPMED represented by BAUDELET ENVIRONNEMENT, BRANGEON ENVIRONNEMENT, CHEZE SA, CHARIER DV, DELTA DECHETS, GROUPE PIZZORNO ENVIRONNEMENT, MOULIN SA. 2/51

3 Any representation or reproduction of the contents herein, in whole or in part, without the consent of the author(s) or their assignees or successors, is illicit under the French Intellectual Property Code (article L 122-4) and constitutes an infringement of copyright subject to penal sanctions. Authorised copying (article 122-5) is restricted to copies or reproductions for private use by the copier alone, excluding collective or group use, and to short citations and analyses integrated into works of a critical, pedagogical or informational nature, subject to compliance with the stipulations of articles L L incl. of the Intellectual Property Code as regards reproduction by reprographic means." About The French Agency for the Environment and Energy Management () is a public agency under the joint supervision of the Ministry of Ecology and Sustainable Development and the Ministry of Industry and Research. It participates in the implementation of public policies in the fields of the environment, energy and sustainable development. The agency makes its expertise and consultancy skills available to business, local communities, public authorities and the general public and helps them to finance projects in five areas (waste management, soil preservation, energy efficiency and renewable energies, air quality and noise abatement) and to make progress with their sustainable development procedures. 3/51

4 SUMMARY French Federation of Waste Management Services (FNADE) and French Environment and Energy Management Agency () have created in 2007 a working group in order to realize a guide of which the objective is to facilitate the implementation of bioreactor landfill non-hazardous waste management. This guide comprises a state of the practices and implementation recommendations for bioreactor landfill. It is intended for professionals of non-hazardous waste landfill (operators, authorities, ). The creation of this guide is based on teamwork, a selected bibliography, visits to bioreactor landfill sites, operators feedbacks and interviews with researchers and technicians. This guide defines what is a bioreactor landfill. It consists in controlling and in accelerating aerobic degradation processes of waste within a protective containment liner by control of for instance moisture in waste mass. This waste management recognized by European (Council Decision n 2003/33/EC) and French (09/09/1997 ministerial decree) regulations, can have important environmental interests in comparison with traditional landfills: Acceleration of stabilization of waste by depleting their degradation potential, Reduction of greenhouse gas and bad smell emissions by earlier implementation of more effective containment, Reduction of quantity and biodegradable organic content leachates, Optimization of biogas energy recovery potential for a site. However, implementation of bioreactor landfill requires material and human means and depends on many parameters (configuration site, climate ). In order to provide professionals with environmental bioreactor landfill specifications, the guide FNADE/ describes: Implementation conditions and operational practices, System specifications (re-circulation systems ), Techniques and methods available for preparation of waste and leachate and biogas management, Advantages, drawbacks and application limits associated to these techniques and methods, Standards for monitoring and sampling programme, Risks and difficulties that may be encountered. Non-hazardous waste management in bioreactor landfill, when it is possible, allows a significant reduction of environmental impacts linked to the waste disposal. Indeed, it enables to limit and have a better grasp of long-term environmental impacts. Nevertheless, bioreactor landfill implementation has to respect some development and operational conditions detailed in the guidance and to be adapted to each site specifications. 4/51

5 Table of contents Aknowledgements 2 Summary 4 ACRONYMS 8 Foreword Goals and limits of this guide Methodology to create this guide 9 General description of the process General definition History Bioreactor landfilling: the stakes Environmental stake Technical expertise requirements Regulatory framework 11 DESIGN AND OPERATION OF A BIOREACTOR LANDFILL SITE Design Differences with a traditional landfill cell Pre-treatment of waste before disposal Leachate re-circulation network Impact on other leachate management working systems Biogas collection network Implementation of containment Specific monitoring equipment Operation Operational practices Conditioning waste before landfilling Collection and treatment of leachates Leachate re-circulation Biogas capture Monitoring of bioreactor operation 34 General recap of environmental impacts Impacts on leachate generation Impacts on biogas emission Impacts on speed of stabilization Impact on settlement 43 Technical and economic feasibility study Required human resources: skills and staff size Technical and economical approach: minimum tonnages and equipment level required to run bioreactor operations, costs Required equipment and incremental costs Potential benefits 46 Prospects 46 ANNEX 1 BIBLIOGRAPHY 47 ANNEX 2 THEORETICAL NOTIONS ON HOW LIQUIDS FLOW THROUGH WASTE 50 5/51

6 Table of illustrations Figure 1: theoretical variation of permeability to water in saturated conditions as a function of actual loading (100 kpa = about 10m of waste) according to Bleiker et al Figure 2: impact of liquid pore and gas pressure on hydraulic conductivity (Hudson et al. )15 Figure 3: diagram of typical re-injection system Figure 4: geophysical imaging using differential resistivity on an input pipe (CEMAGREF) Figure 5: diagram showing the principle and connection possibility of an automated re-circulation system (3C) Figure 6: partial view of automated re-circulation plant: buffer tank, distributor, pneumatic valves Loches landfill site, COVED Figure 7. left: view of surface installation of 5 injection lines with manual control valves and flowmeter Champlâtreux landfill site, COSSON Co. Right: pumping unit; La Vergne landfill site, VEOLIA PROPRETE Figure 8: view of injection automation unit controlling pumping time and frequency Champlâtreux landfill site, COSSON Co Figure 9: water level sensor at the tail end of the network controlling interruption of injection. 21 Figure 10: diagram and photo of a well featuring dual piping VEOLIA PROPRETE landfill site of Lavergne Figure 11: simulation of evolution of leachate injection through laterals Figure 12: cross-section of a dual leachate-injection and gas-capture trench (SITA s Busta site) Figure 13: cumulated volumes of methane output in control and bioreactor enhanced cells, Yolo County, California (Augenstein et al. 8 ) Figure 14: on-site fitting of a battery of electrodes (CEMAGREF) Figure 15: evolution of weight and volumetric moisture content of coarsely-ground domestic waste as a function of loading (Olivier et al. 2007) Figure 16: core samplings to measure moisture content at different distances from the injection well at the La Vergne bioreactor landfill cell VEOLIA PROPRETE Figure 17: core-sampling campaign to measure moisture and the state of degradation Figure 18: flux chamber measurement on biogas biofilter (CSD AZUR) Figure 19: mapping of flux chamber measurements of fugitive emission on La Vergne site (VEOLIA PROPRETE) Figure 20: comparison of states of waste stabilization from bioreactor and control cells of La Vergne site (VEOLIA PROPRETE) Figure 21: visual comparison of settlement on bioreactor and control cells at the Yolo site (USA) Figure 22: measurements of settlement on bioreactor and control cells, Yolo County site, USA44 Figure 23: effective action range of an injection system (Chassagnac. 2007) /51

7 ANNEX 1 BIBLIOGRAPHY 47 Table of annex ANNEX 2 THEORETICAL NOTIONS ON HOW LIQUIDS FLOW THROUGH WASTE 50 Table of charts Chart 1: statistical comparison of leachate composition between traditional and bioreactor landfill sites (Reinhart, D.R. and Townsend, T.G. 1998) Chart 2: waste monitoring parameters Chart 3: leachate monitoring parameters Chart 4: biogas monitoring parameters Chart 5: operational monitoring parameters Chart 6: cost structure of a bioreactor s set-up /51

8 ACRONYMS : Agence Nationale de l Environnement et de la Maîtrise de l Energie (French Environment and Energy Management Agency) FNADE : Fédération Nationale des Activités de la Dépollution et de l Environnement (French Federation of Waste Management Services) LIRIGM : Laboratoire Interdisciplinaire de Recherche Impliquant la Géologie et la Mécanique (Inter-disciplinary Lab for Research Involving Geology and Mechanics) LTHE : Laboratoire d étude des Transferts en Hydrologie et Environnement (Lab for Study of Hydrological Transfers and the Environment) US EPA : United States Environmental Protection Agency BRGM : Bureau de Recherches Géologiques et Minières CEMAGREF : Centre national du Machinisme Agricole, du Génie Rural, des Eaux et des Forêts MODECOM : Normalised method for waste caracterisation SWANA : Solid Waste Association of North America INERIS : Institut National de l Environnement et des Risques Industriels HDPE : High Density Polyethylene COD : Chemical Oxygen Demand BOD : Biological Oxygen Demand TDR : Time Domain Reflectométry EEDEMS : Evaluation Environnementale, Déchets, Matériaux et Sols pollués (environmental evaluation, wastes, material and polluted soils) INSA : Institut National des Sciences Appliquées (national institute of applied sciences) URGC : Unité de Recherche en Genie Civil (unit of research of civil engineering) ISPM : Institut Supérieur de Pétrole et Moteurs (institute of petroleum and motors) BMP : BioMethanogene Potential ANR : Agence Nationale de la Recherche (national research agency) R&D : Research and Development 8/51

9 STATE-OF-THE-PRACTICES AND IMPLEMENTATION RECOMMENDATIONS FOR NON-HAZARDOUS WASTE MANAGEMENT USING BIOREACTOR LANDFILLS Foreword GOALS AND LIMITS OF THIS GUIDE At a time when the latest developments in regulations (amendment of September 1997 bill, government s budget, etc.), technology (numerous bioreactor landfill pilot experiments) and research have focused decision makers attention on landfill bioreactor waste management, and FNADE, which originated this guide, have thought it fit to take a good look at the current body of knowledge. This document by no means a design manual is meant to be concise, easy to use, addressed to operators, designers and government bodies, with a view to facilitate the implementation of this kind of waste management. Basic knowledge of traditional waste disposal techniques is assumed to be acquired. The guide is therefore intended for those in the know. Its aim is to review data on the subject, sorting out what is broadly accepted and what remains to be further researched. It offers a consensus on what can be called bioreactor landfill management and attempts to outline minimum thresholds without impeding future evolution. This guide proposes a state-of-the-art on what can be referred to as bioreactor management and tries to identify minimum requirements without precluding the opportunities for future developments METHODOLOGY TO CREATE THIS GUIDE The creation of this guide is based on teamwork, a selected bibliography, visits to bioreactor landfill sites and interviews with operators and/or research outfits that are involved in the relevant research and development programs. Attention was focused on the following landfill sites: La Vergne site (VEOLIA PROPRETE) Courlaoux-Les Repôts site (SYDOM of Jura) Champlâtreux site (COSSON) Labessière-Candeil site (TRIFYL) Drambon site (SITA) Loches site (COVED) The select bibliography is listed in annex 1 and will be referred to by numbers between brackets. General description of the process GENERAL DEFINITION Waste management using bioreactor landfill cells for non-hazardous waste is an innovative technique that consists in accelerating degradation and stabilizes the waste mass within a protective containment liner. Biodegradation rates can be increased through enhanced control of the main factors influencing microbial activity: moisture, temperature and waste content. Strictly speaking, bioreactor landfill operation is not necessarily linked to leachate re-circulation. In practice, however, effective organic matter degradation cannot occur without appropriate moisture 9/51

10 levels. That is why bioreactor landfills are often synonymous with leachate re-circulation. Another way of promoting stabilization consists in injecting air in the waste mass to boost aerobic degradation processes. The emphasis of this guide, however, remains on the technique that is better mastered: anaerobic leachate re-circulation HISTORY Pioneered in the USA, leachate re-circulation has been studied for almost 35 years. As early as the 1970s, US EPA partnered with the US Army Corps of Waterways Engineers and the Georgia Institute of Technology to carry out lab work on anaerobic bioreactor. Since the 1980s, US EPA has used those lab results to sponsor numerous larger-scale pilot experiments on test cells. One of the intentions was to avoid turning test sites increasingly weatherproofed into dry tombs, in other words putting off and potentially losing control of the waste degradation process discontinued for lack of moisture. One survey by SWANA (Solid Waste Association of North America) shows that numerous landfill sites carry out leachate recycling on a routine basis. This practice, however, used re-circulation mainly as a way to manage leachates i.e.: to reduce the quantities to be treated and maybe cut the organic content of leachates without bothering too much about uniform moisture distribution in the waste mass or about its stabilization. Researchers have been able to draw on the many existing experiments carried out in labs or test cells around the world and more or less monitored to highlight meaningful benefits but also potential troubles associated with the implementation of this concept. There has lately been a considerable increase in the number of enhanced pilot sites, whose data lays the groundwork for the sizing and quantitative forecasting of full-scale sites. Moreover labs base their experiments and modeling on real-life reactions observed in bioreactor landfills more and more faithfully. In the USA, about 70 bioreactor landfills using re-circulation are in operation. In France, a dozen sites have been granted permits BIOREACTOR LANDFILLING: THE STAKES While bioreactor landfill operation is undeniably a plus for the environment, it should be remarked that traditional landfills can be eco-friendly as well. Bioreactor landfill management requires higher initial financial investment and a better grasp of the technical issues involved Environmental stake The process s essential environmental gain stems from a reduction of long-term liabilities by speeding up waste degradation and ensuring noticeable decrease in greenhouse gas and in bad smell emissions. Earlier implementation of more effective containment better waterproofing of the top cover makes it possible to reach minimum capture rate of 90%. As a corollary it is worth pointing out: a reduction of long-term liabilities since degradation chiefly occurs during commercial operation of the site while protective containment systems are at their best; an increase in the number of potential landfill sites to take advantage of biogas production. This is especially relevant for landfill sites whose waste quantities are deemed if operated traditionally to be insufficient for gas extraction, but if run as a bioreactor landfill will generate enough gas to warrant extraction; a decrease in fossil fuel consumption that comes with electrical or thermal exploitation; new landfill space available sooner thanks to accelerated rates of settlement. 10/51

11 Technical expertise requirements The aforementioned goals cannot be achieved without human and material investment: additional equipment and requirements: re-circulation systems, high-efficiency capping, higher gas capture within a shorter timeframe, possible need to store and pump leachates up, monitoring; operators commitment to improve operational monitoring and check-ups means investment in operational staff (management of additional equipment, staff training) in order to upgrade supervisory operations. Environmental requirements can only be met as long as technical issues linked to hydraulics, biology and geo-mechanics are sufficiently well mastered to run the landfill as an effective bioreactor much more so than for a traditional landfill site. Operating objectives are as follows: hydraulics: effective monitoring devices for better management of liquid and gas flows, and purposeful layout especial attention to drainage layers, composite or not for uniform moisture throughout the waste mass to maximize gas extraction; biology: proper monitoring of degradation progress in the waste mass should enable fine-tuning by adjusting re-circulation; geo-mechanics: settlement of the waste mass and the stability of the sidewalls should be monitored. Uneven settlement of the waste mass and instability of the sidewalls related to waste moisture and possible mechanical conditioning should be carefully supervised. All this leads to reinforced need for monitoring landfill sites REGULATORY FRAMEWORK European directive 1999/31/EC on landfill waste disposal requires a cut in the disposal of biodegradable municipal waste and sets national targets for reduction in weight. Decision 2003/33/EC (annex B) mentions bioreactors as a landfilling option. Strategies to be implemented nationwide may include measures pertaining to recycling, composting, biogas generation or the utilization of various materials. For some countries such as Italy, Spain or the United Kingdom where landfill use is prevalent, falling in line with the EU directive inevitably leads to the development of techniques whose goal is to cut the amount of organic matter before disposal. Other countries like Germany, Austria and the Netherlands have opted to limit the amount of organic matter in landfills and have introduced restriction criteria at each site s gates. France which already meets the directive s targets to 2009 at least probably to 2016 if biological treatment and recycling continue to follow current trends does not enforce a limitation to the disposal of organic matter at each landfill s gates, therefore making it possible for sites to be run as landfill bioreactors. French regulation has besides introduced the possibility to re-circulate leachates January 19th, 2006 amendment of its 09/09/1997 ministerial decree. The first priority of French waste management policy is to promote waste prevention and recycling. Returning organic matter to the soil makes perfect sense from that perspective. Clearly bioreactor landfills should not supersede sorting out solid waste and composting organic matter. It should however be remarked that the impact of national waste management strategies does not noticeably change the global proportion of degradable matter in the various figures and that for now no impediment in that regard stands in the way of bioreactor landfill cells. A bioreactor landfill is not from a regulatory standpoint one way to reduce the amount of biodegradable waste to be buried: it remains a mode of waste disposal. Nevertheless, it enables to limit and have a better grasp of long-term environmental impacts, which is why this kind of 11/51

12 designated installation has become significantly more widespread. 12/51

13 DESIGN AND OPERATION OF A BIOREACTOR LANDFILL SITE DESIGN Differences with a traditional landfill cell While few visual clues help the casual observer tell a bioreactor landfill cell apart from a traditional one, experience shows that there may be more to turning a traditional cell into a bioreactor than meets the eye. Specific design before operation starts may help overcome such difficulties. The main differences may involve: conditioning of waste before disposal in the landfill to enhance its characteristics organic matter content, moisture, waste particle size. Such preliminary step might call for additional processing steps grinding, conditioning of the waste mass, etc. which in turn dictate their own demands on the way operation is run; leachate re-circulation requires specific equipment: re-injection plant, piping network, instrumentation, monitoring devices, storage pond; the expected elements to manage leachates and biogas: perforated pipes, main collection header, ponds, treatment and coverage which, depending on configuration, may all have to be adapted reinforced protection, over-sizing or more site-specifically designed Pre-treatment of waste before disposal Intention and benefits The desire to enhance control of waste characteristics enabling faster degradation after disposal has led some operators to introduce a preliminary step to condition the waste matter. The waste considered being meant for final disposal no utilization is sought at this preliminary stage. The parameters it is possible to act upon comprise: moisture content: moistening before or during disposal in the landfill may be an option to ensure uniform moisture distribution; content in easily-degradable organic matter by adding appropriate waste matter sludge for example to run-of-the-mill garbage; grading of the waste particles, so as to seek more uniform hydraulic characteristics of the waste; content in bioactive agents to accelerate degradation Techniques suggested Grinding Grinding enables more uniform and smaller grading of the waste than what is feasible under the shredding action of waste compactor blades. It enhances hydraulic properties by facilitating fluid infiltration through the waste mass and biological ones by making organic matter more readily available. Grinding can be carried out right on top of the disposal cell or in a building installation. In that case extra handling of the waste load is required, implying additional transportation, which makes it worthwhile for high-capacity landfills above all. The grading down of waste particles may also impact geo-technical properties increased rates of settlement and decrease of mechanical resistance capacity. It may thereby call for a site-based approach, especially with respect to the cell s geometry in order to ensure stability. In case grinding is implemented, compacting techniques may be re-examined and lighter means of compacting looked into. On the other hand, if waste particles are ground too fine, bio-degradation and leachate/biogas circulation might suffer. 13/51

14 A landfill s lifespan can be substantially extended often by more than 10% by grinding the coarser pieces of waste. Such gains result from breaking down the structure of this type of waste. Better inter-penetration of the broken-down waste almost immediately follows compacting and loading down of the waste under the weight of interim layers and coverage. Such practice is well suited to coarse and rigid refuse like solid industrial waste and bulky curbside refuse, etc. In some cases, grinding has been seen to make it less likely for garbage to be lifted off by wind. Among the sites visited while writing this report only one uses this technique of waste conditioning Pre-moistening and mixing In the USA pre-moistening may be carried out during landfilling to promote compacting of very dry garbage and better distribution of moisture possibly even to facilitate leachate management. The solutions implemented may involve moistening using sprinklers or automatic watering systems, as well as infiltration ponds. No such example turned up in the literature that was read, though. These processes are liable to trigger unwanted early gas generation leading to fugitive emission, bad smells and health hazards. They should not be implemented without specific precautions such as anticipated gas capture for instance. It is not implemented in France where few experiments of direct injection of water, leachate or sludge before disposal have been conducted Leachate re-circulation network Issues, intentions and benefits Controlling waste moisture levels is the key to successful bioreactor landfill programs. Once waste is stored in the landfill, the whole issue of stabilizing it revolves around optimal and uniform distribution of moisture within the waste mass. Recycling of leachates to boost waste moisture and therefore provide favorable conditions for bio-degradation also enables to: dilute the concentration of possible inhibitors; promote colonization of the waste by microorganisms; facilitate nutrient input; stir up biological activity in the bioreactor cell. The design of a bioreactor cell will have to take the following critical points into account: Reaching high moisture that is sufficiently well distributed The experiments originating from research done in France for the past few years have shown that leachate re-circulation systems do not always address the fundamental requirement of uniform distribution of moisture in the waste mass. As a result the intended accelerated degradation does not occur uniformly in the landfill, thereby limiting gas yield gains compared to a traditional landfill cell. Moreover settlement has turned out to be uneven. This outcome is primarily connected to insufficient flowrates/volumes injected and to inadequate action ranges of the systems implemented. The re-circulation system design will therefore have to provide the cell with appropriate and uniformly-spread flux using well-suited devices that are compatible with action ranges observed for the leachate re-circulation system used. The design will also have to take into account the permeability of waste matter. Such permeability naturally decreases as waste decomposes and drops significantly as depth increases, as is shown in the figure 1: 14/51

15 Figure 1: theoretical variation of permeability to water in saturated conditions as a function of actual loading (100 kpa = about 10m of waste) according to Bleiker et al Liquid pore and/or gas pressure can also influence permeability, as is evidenced in the figure 2: low gas accumulation and low pore pressure (<10kPa) Hydraulic conductivity m.s -1 high gas accumulation and low pore pressure (<10kPa) low gas accumulation and high pore pressure (from 60 to 70 kpa) high gas accumulation and high pore pressure (from 60 to 70 kpa) Mean loading (kpa) Figure 2: impact of liquid pore and gas pressure on hydraulic conductivity (Hudson et al. ) Preventing clogging Because the re-injection system working parts are submitted to increased hydraulic use, the risk of clogging must be considered. Mainly affected are the systems and networks of leachate recirculation, interim and bottom drainage layers as well as the collection network. Several types of clogging must be taken into account for leachate re-circulation: physical clogging owing to the re-circulation of leachates with solid particles floating in suspension; chemical clogging that may result from either the precipitation of chemicals dissolved in the leachates or that originating from draining layers containing calcium carbonate. That is why calcium carbonate should be avoided in drainage layers in leachate re-circulation cells; biological clogging: clogging that has a biological cause may also occur owing to a development of biomass. There are nowadays tools to forecast and diagnose clogging (see III.17.5). They might serve to anticipate potential clogging by monitoring the composition of leachates. 15/51

16 On top of the usual remedial solutions to address clogging issues, bioreactors specific hydraulic configuration offers possibilities to act before problems arise: when applicable, by inflating the hydraulic parameters of the leachate re-circulation network: grade of piping, permeability of drainage layers, grading of perforated pipes, openings, protective filter netting, gradient of slopes, etc. by careful selection of materials, opting out drainage material with a susceptibility to clogging. By the same token waste particle size should be above 10 mm [33]; by preventing conditions of oxidation-reduction from varying throughout the collection network for instance by preventing outside air from intruding; by designing injection systems that allow pressurization of the network; by facilitating monitoring of the main networks Preventing overall or partial warping and avoiding instability Settlement The optimization of the degradation process results in accelerated settlement of the waste mass. This results from: the lubrication of particles in contact produced by the re-circulated liquid; enhanced softening of porous materials; increase in global density of the waste mass because of higher moisture; enhanced biodegradation. While it may yield excess space for additional waste lifts, settlement is not without having an impact on leachate re-circulation and biogas management systems, and on the top cover. Being able to forecast and control such settlement matters greatly. At stake are both: safety and the environment: extra attention to be paid to the capping, the integrity of the cover lest settlement should be unevenly distributed, effectiveness of biogas capture, stability of sidewalls, etc. the economics of the project: planning of the final height of waste, forecast of landfill capacity and corresponding optimization of operational lifespan. The final extent of settlement can safely be assumed to bear little relationship with re-circulation. Settlement rates, on the other hand, increase by a factor of 2 or more during the first years [8, 32]. Because of the accelerated rate of waste degradation in a bioreactor landfill cell, these elements take on acute dimension, and settlement in critical areas needs tracking. Information about the general settlement issue and relevant analytical tools can be found in Guide méthodologique pour le suivi des tassements des centres de stockage de classe II (Methodological Guide for the Monitoring of Settlement in Class II Landfills) by -LIRIGM. The Incremental Settlement Prediction Model, or ISPM, developed by LTHE (previously LIRIGM) can be used in this context. This kind of tool can be used in the designing stages in order to: predict ultimate settlement of a depth of waste so as to estimate the landfill capacity and provide an effective benchmark for the staging of landfill operation; predict settlement around various critical points areas where uneven settlement is predictable so as to estimate the predictable warping that installations will have to undergo in or on top of the waste mass; amongst others: leachate re-circulation and biogas recovery networks; wells, if applicable; top cover. 16/51

17 The causes of instability High moisture content in the landfill often leads to instability. This downside can be made worse by re-circulation. Leachate injection can indeed increase pore pressure and cut down useful friction between waste particles. The higher the injection pressure (pressure-enhanced injection, pressuregenerating fall in the wells, etc.) the more instability. The risk increases in the vicinity of sidewalls where top cover slippage can occur if the slope is too steep, as can seeping of leachates. In the case of re-circulation via lateral perforated pipes under a liner, the parameters of re-circulation (flowrate and pressure) will have to be re-calculated to avoid local upsurge in the liner, the more so as the latter is waterproof. The monitoring of pressure in the system could therefore be worth evaluating. Geo-mechanical modeling can be a tool for the design of landfill cell geometry and re-circulation network layouts Get liquid injection to co-exist with gas capture Even though gas extraction and leachate injection campaigns may neither be performed at the same time nor in the same sector of the landfill, re-circulation may sometimes alter gas output rates because of pressure variations within the landfill. Liquid flow pushing away gas flow, gas may be observed to accumulate in the upper parts of the injection drainage installations [36]. The choice of configuration of liquid re-circulation and gas drainage installations, the sequencing of the operational steps, the quantities re-circulated all matter then How to re-circulate and what performances to expect The re-circulation system is composed of 3 essential parts: input system: injection plant or gravitational installation, a pumping facility, and sometimes its automation; main injection header to convey leachates to the sectors of re-circulation; perforated injection pipes. Injection plant main header injection leachate pond perforated pipes Leachate re-circulation input system Figure 3: diagram of typical re-injection system The input flowrate is one of the fundamental parameters to take into consideration in order to ensure uniform distribution of moisture throughout the landfill. The flowrate should be set by taking into account the absorption capacity of the drainage layers used to spread leachates in the landfill cell and in situ configuration: loss of loading in the main headers, pressure amount corresponding to the height that the leachates have to be raised, etc. 17/51

18 Several re-circulation configurations are worth considering and are detailed thereafter. To optimize their action ranges, for each of them it is possible to: alternate phases of re-circulation and phases without leachate injection. Such an approach allows periods of rest, which enables to: spread distribution laterally (McCreanor. 1998); avoid saturation, therefore possible leaks; promote free circulation of the accumulated biogas. re-circulate less often (once a week for a given trench, for example), but using higher flowrates. The illustration 4 which was obtained using geophysical imaging along a sloping, gravitationallyfed input pipe shows that the area affected by re-circulation varies as a function of injection flowrates. Flowrates that are too weak impact only the down-flow end nov 15h35 6,6 m 3 /h nov 13h m 3 /h ! dif % 20! (%) Figure 4: geophysical imaging using differential resistivity on an input pipe (CEMAGREF) Leachate re-circulation may cause instability in the landfill if not properly performed or controlled rupture of the hydraulic circuit owing to increased liquid pore pressure, side seeps, etc. It is then necessary to: keep close track of injected volumes; move re-injection points sufficiently far away from slopes. Liquid addition can occur without pressurizing perforated injection pipes, which partially or completely maintain atmospheric pressure. Low-level pressurization may be considered (a few hundred millibars) to ensure even after warping and/or loss of the original incline complete loading of the re-circulation network. Moreover, as CEMAGREF has shown on the SYDOM landfill site (in the Jura area of France), pressurization of about 0.2 bar in the tail-end of the piping may contribute to unclogging. Little reporting is available on re-circulation experiments carried out at pressures exceeding these orders of magnitude. For higher pressures, it might be useful to assess the amount of excessive pressure that the unit formed by the perforated piping, drainage layer and nearby waste mass can accommodate, and the risk of formation of preferential flowpaths, etc. Such pitfalls call for very specific monitoring. In general a re-circulation network is made up of one or several injection lines per cell or sub-cell, 18/51

19 which are fed via a distributor (Figure 6). Re-circulation is then usually carried out in individual zones by opening one or more valves that each sets an injection line to work. Automation of the injection plant may be envisioned to make management of re-circulation episodes easier. Time input Pressure input Automation unit Out to valves Out to pump Flowrate data Main header Leachate pond Pump Flowmeter Distributor Pneumatic valves Lateral lines injection RE-CIRCULATION PLANT Landfill cell Figure 5: diagram showing the principle and connection possibility of an automated re-circulation system (3C) Figure 6: partial view of automated re-circulation plant: buffer tank, distributor, pneumatic valves Loches landfill site, COVED. 19/51

20 Figure 7. Left: view of surface installation of 5 injection lines with manual control valves and flowmeter Champlâtreux landfill site, COSSON Co. Right: pumping unit; La Vergne landfill site, VEOLIA PROPRETE. Given the complexity that such a network can have on an extensive site and the distances between its different components, it is highly recommended in these cases to implement automation of the installation s operation. The automation unit runs the management of the pneumatic valves and pump. It can be connected to one or several of the following monitoring instruments: a flowmeter to monitor leachate inflow placed down-flow from the pump; an internal clock to control operation time at constant flowrate; sensors integrated in the extremities of the network to monitor pressure there; system to track leachate levels reached in re-circulation installations. Figure 8: view of injection automation unit controlling pumping time and frequency Champlâtreux landfill site, COSSON Co. 20/51

21 Figure 9: water level sensor at the tail end of the network controlling interruption of injection Injection lines Theoretical principle ANNEX 2 summarizes the theory on how liquids percolate through waste matter. Many authors have highlighted the lack of homogeneity of waste landfill in terms of liquid transfers and the law of double porosity that rule such transfers. Double porosity consists of the overlapping of a micro-porosity at waste scale centimeters to decimeters range and a macro-porosity meter to several-meters range. The latter accounts for the appearance of preferential flowpaths that cause bypassing of intended drainage and that reduce the time water spends in the waste matter. This predicament makes it hard for a site to reach its maximum moisture potential and makes it necessary to input volumes slightly higher in practice than what should be required in theory i.e. calculated as the difference in initial moisture content of the waste and its expected capacity to soak up more moisture. In practice, the behavior of the water injected into the waste via an injection line can be represented as in the illustration shown in ANNEX 2. In the vicinity of the injection point waste absorption capacity is inferior to the unit flowrate i.e.: flow transiting through one volume unit of waste and water uses each pore available to flow out; such flow moistens waste effectively. Beyond a certain range that will be called effective action range the unit flowrate is insufficient to fill all the available gaps and the flow favors paths made up by macro-pores. Its moistening ability as a result is weak and the intended effect is no longer achieved. There is a lateral action range and a vertical action range that both depend on: the type of injection lines, and especially the size of the interface involved length, width, circumference of the drainage layer around the line; the flowrate itself dependent on the pressure in the re-circulation network. Such theoretical notions should be taken into account for designing the injection system The systems that can be used If operational imperatives require re-circulation, the latter should systematically go hand in hand with anticipated gas capture whose good performance has to be monitored. There are currently three types of techniques to ensure waste moisture during operation and post-closure of a nonhazardous waste landfill cell. vertical wells; horizontal infiltration trenches; injection blankets. 21/51

22 Vertical wells The design of injection wells differs little from biogas collection wells classically implemented in traditional landfill cells, for which useful information can be found in s 2001 guide Gérer le gaz de décharge, techniques et recommandations (Management of Landfill Waste Gas, techniques and recommendations). These installations can be installed with pressure sensors connected to the re-circulation automation unit to ensure optimal conditions of re-circulation. Wells have been part of the first generation of injection installations on landfill sites that were turned into bioreactors after landfilling stopped. Reporting on those experiments reveals limited efficiency. restricted lateral action range, described in the literature as being between 5 and 10 meters [30]; poor performance over the injected elevation. Owing to the vertical nature of the installation injection pressure is highest at the bottom and nil at the top. As a result injection is above all effective in the bottom layers and much reduced in the upper layers of the installation. To mitigate this drawback, some operators have designed multiple-line installations, as Figure 10 illustrates, which might enable better vertical distribution; restricted draining surface compared to lateral systems. But this technique has the following benefits: easier access to bottom areas in cells that are already filled up; in cells where horizontal isolation is well marked resulting from interim coverage that allows little permeability, wells are the only types of installation that enable access to waste under such layering; injection parameters are less subjected to variations than for horizontal installations, and settlement does not affect the geometry of vertical installations, making it possible to avoid injection under pressure, though such installations might warp or even break apart. Bouchon Clay layer d argile crépine Draining pipe Figure 10: diagram and photo of a well featuring dual piping VEOLIA PROPRETE landfill site of Lavergne Horizontal infiltration trenches Nowadays most of the recently designed landfill sites that are run as bioreactors use infiltration trenches considered to be more effective [29]. These installations are made up of a trench dug right out of the waste mass, generally filled with gravel and fitted with an injection line. The length of the lines mainly depends on the flowrate to be injected, the cell s geometrical layout and does not exceed 100 meters on most sites. 22/51

23 The search for uniform unit flowrate per linear meter of injection pipe calls for variable perforation over the length of piping. The installation s orifice law (drain perforation plan) requires specific hydraulic calculations. Given the existence of lateral and vertical effective action ranges, several levels of perforated pipes must be laid as soon as the elevation to be managed exceeds 10 meters. Tests of geophysical monitoring of infiltration show that action ranges are about 5 to 7 m max given rather low injection unit flowrates: ca. 100l/ml*h. Usually, re-circulation is operated one injection line at a time. Benefits: good exchange surface compared to wells; higher efficiency since, unlike wells, the action range does not only extend around the well area, but over the whole length of the injection line. Drawbacks: liability to warp and sensitivity to settlement, which requires limiting the length of lines and operating injection under pressure; need to use a flowrate compatible with the size of the system, otherwise the perforated piping does not achieve full loading; higher risk of clogging than for wells. Figure 11: simulation of evolution of leachate injection through laterals (Aran. 2001) Injection blankets Draining blankets can be described as broad trenches. Their use currently remains restricted to some pilot experiments. Thanks to their very broad interface, they should guarantee better percolation of moisture laterally and enable to inject for the same amount of time higher volumes without risking excessive pressurization thanks to their high retaining capacity. The high volume of drainage material accounts for higher investment needs, partly offset by a lesser density in the piping. To preserve the economic viability of the project, the use of alternative and economical draining materials may be desirable Dual leachate/gas systems Re-circulating a volume of liquid in the waste mass is bound to shift an equivalent volume of gas in the injection area. It is possible to better manage the impacts of this phenomenon by alternating leachate injection and biogas collection piping to ensure respective optimal efficiency as was suggested by Barina et al. (), cf ref. 27. An equivalent solution consists in sequencing the use of a single line shared for gas capture and re-circulation. Such a configuration can be achieved by laying gas piping in the upper part of the drainage trench and re-circulation piping under it as the 23/51

24 figure 12 illustrates or the use of a single line for both gas capture and injection. Figure 12: cross-section of a dual leachate-injection and gas-capture trench (SITA s Busta site) Implementation requirements and constraints As was remarked above, re-circulation installations are liable to clog and warp/break apart because of settlement. Dealing with these liabilities involves adaptations in the designing stages. In regions which are exposed to cold temperatures, anti-frost protection will require the designing of systems which are mostly immune to cold: insulation of above-ground installations, burial of networks, coupling of system management to temperature parameters, etc Impact on other leachate management working systems Should current practices be altered? Leachate ponds As will be seen in the chart 1, re-circulation may require large quantities of leachates. The size of the leachate pond may vary in relationship with local rain patterns. Determining the filling capacity involves a hydrological forecast survey that allows for operational data input: retention capacity, build-up rate of the waste elevation, injection flowrate, etc. To avoid re-circulating leachates that are loaded with particles in suspension and increasing the risk of clogging, leachates can be made to transit via a settlement pond. Alternatively it might be just as simple to avoid pumping the dregs from the bottom Waterproofing of bottom liner Given the hydraulic stress bioreactor installations are subjected to owing to re-circulation in addition to sometimes high temperatures that result from enhanced degradation research in the USA has striven to determine the impact this strain has on the bottom liner. The outcome after long-term comparison between a bioreactor and a control standard landfill cell [29] is that temperatures and leachate build-ups remain comparable in either cell and that the risk of damage to the bottom liner namely creeping does not increase, no more than does the risk of leaks. Having said that, a gravitational leachate collection installation meaning no pumping is required remains preferable whenever it is feasible as it ensures low leachate build-up at the bottom of the cell and minimal leakage Impacts of re-circulation on the design of treatment units and on purging techniques to be implemented The impact of re-circulation on leachate composition has been extensively researched by labs as well as by the industry. 24/51

25 Generally speaking, excessive accumulation of pollutants in leachates stemming from recirculation is not observed. Re-circulated leachates undergo a series of evolutions similar to what traditional leachates undergo with sometimes, however, a more acute acidogenesis phase [5]. Several surveys on organic matter content of leachates, highlight a reduction in Chemical and Biochemical Oxygen Demands (COD & BOD) that is faster in bioreactor than in non-re-circulated cells see chart 1: Chart 1: statistical comparison of leachate composition between traditional and bioreactor landfill sites (Reinhart, D.R. and Townsend, T.G. 1998) Parameter Standard landfill site Bioreactor landfill site Iron (mg/l) BOD (mg/l) COD (mg/l) Ammonium (mg/l) Chloride (mg/l) Zinc (mg/l) ,1-66 When no complementary treatment is performed before re-circulation, conservative elements chloride and ammonium, namely remain at sustained concentration levels even after several years. After a likely peak in Chemical Oxygen Demand that is higher than in traditional cells in the initial stages of operation, a drop in both Chemical and Biochemical Oxygen Demands is then observed in bioreactor cells, and the figures become inferior to those of traditional landfill sites. Such variations in organic content make it harder for appropriate biological, physical and chemical treatment solutions to be found. Post-closure leachates might have lower Chemical Oxygen Demand than those of a traditional landfill, but might have as high or higher concentration in nonorganic matter. Careful monitoring of ammonium ion levels should be carried out. The extension of the period of leaching of conservative elements might call for prolonged treatment. And pre-treatment of nitrogen before re-circulation might be a good idea. R&D research work is being conducted to better grasp the fate of nitrogen in landfills Biogas collection network Issues, intentions and benefits Significantly higher instant production of biogas for the first years of operation is expected from bioreactor compared to traditional cells. So collection networks must be designed accordingly to avoid fugitive emission. This may be where the greatest gap in results is observed between small- and large-scale experiments. Pilots involving pit-shaped cells or cells under 100m3 may turn up very significant increases in instant or cumulated output 6 times and more but such gains have proven elusive on full-scale sites. The literature gives the following increase percentage points: +0% [28], + 30% [34], +69% [29], +70% [30], + 200% [33], +260% see figure 13: 25/51

26 Figure 13: cumulated volumes of methane output in control and bioreactor enhanced cells, Yolo County, California (Augenstein et al. 8 ) The pilot site of Yolo County see above clearly shows evidence that its waste material is particularly dry, and as a result fairly sensitive to moistening. However various contingencies make on-site evaluations delicate: on-site experiments seldom have unbiased basis of comparison namely, non-re-circulated control cell; pilot tests often benefit from high-efficiency top liner whose impact cannot be isolated; output gains vary with time e.g. higher output peak, but faster decrease so prolonged evaluation is necessary to outline re-circulation s impact clearly; in the absence of a control cell, an estimation of the impact on gas output is obtained by comparing the graph of observed output to that of estimated output based on theoretical data output potential, degradation constants extrapolated from existing sites, which remains imprecise. A specific survey using operational data could enable such theoretical biogas output estimation. Given the accumulated body of knowledge, gains ranging from 50% to 100% of added instant output depending on the type of waste and climate variables do not seem unreasonable for the first few years. Over the long run the decrease in production will also be more marked Spacing, gas collection strategies and rates Information on gas capture can be found in the guide Optimisation du captage du biogaz des installations de stockage by, 2007 (Optimizing the capture of landfill biogas). Most authors agree to say that increased biogas production requires an enhanced capture system and that waste containment forms an integral part of this system. Containment is dealt with in the following paragraphs Strategies and design The strategies of biogas collection with vertical wells or horizontal trenches, used in traditional landfills, are also used on bioreactor landfills. Horizontal strategies can however more often be found on recent or projected sites. The creation of separate biogas collection and leachate injection networks eliminates the risks of interference mentioned above. Nevertheless, even though the injection network should not be the most active part in the gas collection system, the two networks can be connected for optimal global capture rates. The risk of build-up of condensates should however be addressed. Enhancing the biogas collection system involves an increase in the density of installations, along 26/51

27 with the laying of a waterproof cap geomembrane or equivalent. With regards to the density of the piping the literature gives lateral spacing figures of 10 to 60 meters and 15 to 30 meters for vertical spacing. All ranges of effective action can be controlled via the depression created by the extraction system. Instant operational capture rates classically range around 35%. Sites for which gas capture and dense injection lateral networks are built in the design see these rates improve measurably and exceed 50%. When surface coverage is included, instant capture gas rates can top 90% 98% for the La Vergne site, see Impact on income-generating operations A bioreactor landfill cell s ultimate purpose is not the commercialization of biogas. Nevertheless, given the potential impact of re-circulation on biogas collection, treatment and utilization facilities should be designed with some flexibility. The design of treatment and utilization operations should therefore take on board the various techniques available to date micro-turbines, small motors, etc. Owing to a site s normal variable output flowrates during operation, inelastic handling capacity of utilization facilities, the need to shut down the latter for maintenance, flares remain a necessity on all sites Implementation of containment Surface waterproofing requirements for bioreactor A useful discussion of this topic can be found in s guide Guide pour le dimensionnement et la mise en œuvre des couvertures de sites de stockage de déchets ménagers et assimilés (Guide for designing domestic solid waste landfills capping, March 2001). Ideally a bioreactor approach implies that accelerated biodegrading takes place under coverage that allows little permeability geomembrane or equivalent to ensure perfect control of all liquid and gas flows. But this option may not always be possible for some configurations especially landfill cells with a very thick waste column. What is more, the intended accelerated settlement and its impact on surface cover dictate other restrictions on installations Choice of containment, implementation requirements, capture and infiltration rate performance There are 3 main configurations: The site s configuration precludes the shutting down of an area single cell with a thick waste column and small surface area, for example. In that particular case, gas emission can be limited through dynamic containment by laying a dense collection and injection lateral network during the filling. Operation can start after the network has been covered with only a few meters of waste, as too great a depth is bound to impede re-circulation performance owing to decreased permeability. Good gas capture performance is possible and can be substantiated by measuring surface emission see chapter on monitoring. The impact of rain will be relatively low even nil because of the retention capacity of the upper layers of waste the faster the filling, the more so. On this type of site the waste column is thick and refuse is first buried vertically in the active face of the landfill. Operations then move laterally before coming back to the starting point. Physical containment as opposed to dynamic containment using a temporary cover that performs at least as well as a conventional final cover is an interesting solution to fit on lateral injection networks due to the control of gas emission and water infiltration that it allows. Re-circulation can quickly start after the temporary liner is laid. The liner being temporary it is possible to use economical materials that are still efficient over the short term, like thin synthetic film available for large surface areas or geomembranes held in place by ballast, a layer of low-permeability earth to be removed when filling resumes or yet a combination of both. Depending on the way they are laid welded or not, the geo-textiles may be used again. Capture rates can be close to 90%, and even more if synthetic film is implemented. Also water infiltration is reduced to levels generally observed when 27/51

28 geomembrane containment is implemented under a few percentage points, provided that its design enables the evacuation of rainwater steep-enough slope, fitting of outlets, etc. Particular attention should be paid to the laying of the liners, especially in a few trouble spots such as where liners meet at the sidewalls, water-tightness around wells, along welds, etc. The third configuration pertains to sites whose waste column is not very high or the previous configurations when filling is about to end. Two strategies are possible: the first strategy is necessary if the expected settlement is likely to cause serious damage to the top cover. It consists in laying a temporary cover that will be finalized after two or three years, as soon as most of the settlement has occurred. An efficient configuration involves laying a 20- to 30-centimeter-thick layer of clay covered with synthetic film held in place by ballast such as tires or earth on top of the waste and the injection system. This liner should limit water infiltration and above all prevent clay from drying out. Moistened clay is indeed a good barrier to stop gas emission and air infiltration. Besides it copes well with warping (self-repairing abilities). Its main failing resides in its propensity to dry up, which should be prevented by using a geosynthetic liner. After 2 or 3 years, the geosynthetic can be replaced by a welded geomembrane topped by a layer of compost that is well drained. The second approach can be implemented if the expected settlement can be accommodated by the installations. In which case the configuration differs from the previous one in that the geomembrane is laid directly after the clay layer without initial welding around the spots where settlement will differ from the surrounding areas ( junction with the sidewalls, wellheads, etc.). Also a few precautionary measures should be taken: anticipating future conditions of water evacuation drainage amongst others slack, etc. Welding can be finalized after 2 to 3 years. The laying of a geomembrane being more susceptible to geotechnical contingencies, the design of the covers should include a survey of landslide liability. To reduce this risk, a drainage layer is recommended above geomembranes Specific monitoring equipment Bioreactor landfill operators can use different solutions to collect monitoring and diagnostic data that are needed for bioreactor landfill management. Several strategies and techniques can be considered and will lead to the same results, albeit with measuring campaigns that differ in their frequencies and different degrees of spatial precision and representativity. The available technologies are evolving fast, especially owing to current research work that paves the way for the design of new tools. Those that are meant to measure various parameters within the waste mass moisture for instance have not yet become reliable enough over the long term and cheap enough for full-scale implementation to enable their operational use. Thus, within the range of available techniques and their implementation, three levels should be singled out: continuing monitoring required by regulations; monitoring parameters that are needed for efficient and reliable bioreactor landfill management and that can be measured overall using simple techniques mainly from outside the cell at the operator s initiative: biogas volume, methane concentration, hydrological balance, leachate and biogas temperatures, etc. diagnostic parameters and methods in case of malfunctioning, or possibly even methods that can be used for research purposes. A certain number of specific adaptations are useful from the design stages and during landfilling to facilitate site-specific monitoring later on, which takes into account existing conditions and constraints. While the following list may not be comprehensive, it is worth mentioning: facilities to measure leachate volumes collected for each cell, as well as facilities to take leachate samples with a view to analyzing them. facilities to take biogas samples and measurements: volume and quality, as well as the cell s temperature, as closely approximated as possible. 28/51

29 depending on the cell s configuration, various inspection facilities can be built in, but other steps can be considered to enable if necessary to diagnose clogging incidents (analysis of flowrate/pressure response per drain) that require troubleshooting or a change in recirculation management. Operators should also opt for a protocol to record and read information that facilitates the processing of the data that is required for running operations, tracking potential operational anomalies and diagnosis errors. Time frequencies and volume or spatial frequencies are parameters that also matter in deciding what specific equipment is needed. Other techniques are presented thereafter and might require specific equipment, but most of them are not implemented on operational sites and remain confined to the requirements of research programs Temperature of landfilled waste The temperature of landfilled waste is an important indicator of biological activity underway in the waste mass and can be monitored. For that purpose sensors should be embedded in the waste mass as the cell is being filled. The benefit of temperature sensors is that they give locationspecific data, but they must be numerous and are rather fragile. In case fixed sensors are wanted, protective piping should be installed as the waterproofing base liner is being laid along sidewalls, on or even under the membranes, so as to place the sensors in the best positions once the waste lift reaches the target depth. The sensors may also be located in the capture and injection installations to provide mechanical protection and measurements from within the waste mass. Mobile sensors of the thermocouple type might be preferable and can be fitted at different heights within a measurement-taking line temporary or permanent that is dug into the waste mass during or at the end of filling. The installation of HDPE piping enables the tube to slide in through the cover and accommodate settlement. Overall measurements on gas capture installations may also provide useful data Landfilled waste moisture One of the major goals of bioreactor waste management is achieving an even distribution of moisture content throughout the waste mass. During research work measurements are taken using sensors TDR, thermistor, using electrical conductivity but problems quickly appear as sensors may lose contact with the waste and corrode. Barring future improvements, those techniques cannot therefore be implemented for full-scale monitoring. Unable to monitor moisture directly, the method consisting in measuring electrical resistivity that is indirectly linked to moisture and its distribution in the waste mass has shown its potential see above to visualize areas impacted by re-circulation. This method known as the electric panel method calls for a network of electrodes up to several dozens fitted into the top layer in direct contact with the waste, along and/or through injection lines. The drawback of this costly technique is that it requires a dense network of sensors that are connected to each other and need powering. What is more, even though it appears to provide a good indication of the changes within the waste mass during re-circulation, a direct link between the measurement and the moisture is not clearly established. Geophysical instrumentation is currently a good tool to monitor injection live since it allows the visualization of what is occurring within the waste mass. The range of effective action can for example be estimated. On the other hand, this technique is not suited to operational monitoring due to costs. Given the lack of existing means to be able to track moisture directly within the waste mass, great emphasis must be placed on the moisture balance in order to estimate the amounts of leachates to be re-circulated. 29/51

30 Figure 14: on-site fitting of a battery of electrodes (CEMAGREF) Moisture balance The injected and produced amounts of leachates can be measured through flowmeters embedded in the injection and collection networks. Electro-magnetic flowmeters are relatively efficient but require for the piping to be completely filled. Prior to coverage, the influence of rain on waste moisture is high and impacts the amounts to be re-circulated. That can be monitored via a meteorological station or at least a rain gauge on site. 30/51

31 Biogas flux and composition These measurements are classically taken on most sites whether they are bioreactor enhanced or not from collection installations out of well heads or main headers or by assessing the overall treatment process see the 2007 guide by entitled Optimisation du captage du biogaz des installations de stockage (Optimization of Landfill Gas Management) Monitoring the risk of clogging Because leachate re-circulation puts the leachate collection network under a lot of stress, the risk of clogging has to be investigated, even though to this day few clogging problems have been reported in injection installations. Networks should therefore be designed so as to enable inspection of network as well as is possible sufficient grading of piping, adequate curving of the piping. Two techniques can be implemented to carry out an inspection the use of a camera-robot or an endoscope and the length of and easiness of access to the network should determine which to choose OPERATION Operational practices A bioreactor landfill cell is first and foremost meant to enable accelerated stabilization of waste matter by depleting their degradation potential. An important corollary from an environmental perspective is the potential this process offers to boost gas output and enable greater scope for utilization. Still it may not be productive to restrict the term bioreactor solely to utilization operations. When there is no utilization of the energy potential, operational practices are intended to speed up degradation without desiring uniformity of the quality or output of gas. When an economic value is put on energy output, particular care must be taken of the parameters used to assess economic potential: biogas quality and output flowrate, preventing re-circulation from interfering with gas collection Conditioning waste before landfilling Nature of waste to be taken in, methods to manage reception and screen waste The bioreactor approach is compatible with all the waste accepted by non-hazardous landfills. In order to secure accelerated rates of degradation operators tend to monitor received waste very closely and limit any waste liable to delay or inhibit biological reactions. One case in point is polluted soils. The development of the recycling of packaging and of composting residential and/or large scale does not for now seem to stand in the way of bioreactors. Bioreactor landfill management benefits extend to non-hazardous industrial waste, recyclables that are turned down by the recycling industry and industrial sludge, which are at least partly made up of biodegradable elements Operational organization Bioreactor landfill cell management may call for an adaptation in sites operational organization. Sub-cells may, for instance, be filled with less than 15 meters of waste, covered temporarily and then undergo re-circulation for 2 to 4 years, during which period operation moves to a nearby sector, which enables to: gain easier access and manage re-injection and capture installations more easily; take full advantage of accelerated settlement; implement capping in better conditions Landfilling of waste 31/51

32 As the hydraulic behavior of the waste mass should be as homogeneous as possible, partitioning should be avoided because of periodical coverage. Technically speaking it is possible to avoid this situation by removing such cover before adding another lift of waste. Permeable and/or degradable interim covers can also be used, such as compost turned down by the recycling center, cellulose-based coverage material. Synthetic liners held in place by ballast may be used as well Collection and treatment of leachates Impacts on volumes to be treated Establishing a reliable hydrological balance for a bioreactor requires a long period of monitoring, because retention and restitution phenomena depend on levels of degradation and are long to get underway. On the bioreactor of La Vergne which has been operated for three years and whose re-circulation system via wells has revealed an effective action range that is inferior to what was estimated the leachate absorption rate is estimated to be 7%, based on gross figures. These findings, however, cover the whole landfill and may not therefore be representative of what is happening locally. Some results have shown that one area of the landfill may be absorbing leachates while another one is seeping them. In that case the hydrological data aggregates two offsetting trends. Furthermore, the longer leachates are re-circulated, the more waste matter decomposes, which results in a change of its composition as well as its physical characteristics such as porosity, permeability, etc. The change in hydraulic behavior of a waste mass depends on these characteristics. That must be the reason why the hydrological data of a bioreactor cell changes with time. Moisture content measurements taken from waste core samples from different depths and increasing distance from an injection well and the comparison with the volumes injected in the closest well evidence a moisture absorption rate of 33% for the sampled waste. Accordingly, the hydrologic balance is negative for that area of the sub-cell. To conclude, if short-term findings reveal noticeably lower leachate generation, long-term figures might have to be raised owing to a progressive release of retained water, itself linked to a reduced moisture potential of the waste mass. Furthermore, the waterproofing of the top cover laid on bioreactor landfill cells, which is better than the one used on traditional sites, leads to a decrease in overall leachate generation in the long run Impacts on re-circulation and nature of leachates A little reminder from paragraph III.1.4.2: re-circulation on leachates causes a decrease in organic content in the middle term, which leads to a higher content in conservative elements mainly ammonium Leachate re-circulation Quantities to be re-circulated Optimal degradation occurs when moisture levels are in the 50 to 80% range. In practice, though, it is not possible to reach such rates in landfill cells. The average maximum retention potential for landfilled domestic waste is around 40 to 50%. Regulation prohibits leachate build-up above 30 centimeters at the base of the cell, which implies that full saturation of the waste column is prohibited. The best compromise between optimal moisture to accelerate degradation and operational requirements therefore consists in re-circulating until maximum retention potential is reached. Such potential is strongly dependent on pressure and it follows that the maximum retention potential of waste at the base of the cell differs from that of waste at the top. 32/51

33 Content in water after draining (24h) Teneur en eau après drainage (24 h) 120% 100% 80% 60% 40% 20% Content Teneur in water en measured eau pondérale as a weight (w) (w) Teneur en eau pondérale (w') Content in water measured as a weight (w ) Teneur en eau volumique 0% Contraintes verticales (kpa) Vertical loading (kpa) Figure 15: evolution of weight and volumetric moisture content 1 of coarsely-ground domestic waste as a function of loading (Olivier et al. 2007) The degree of moisture to reach optimal bioreactor landfill performance varies depending on waste composition, its density, its content in organic matter, its temperature, and weather conditions. It is essential for a target level of moisture to be determined, based on site-specific waste characteristics. Even if the literature gives average figures for standard categories of waste, it is not unusual for non-hazardous industrial waste, amongst others to be confronted with widely differing moisture findings compared to national averages. The literature gives re-circulation rates of around a few deciliters per day and per ton of waste. Such figures tend to be underestimated. The Yolo County site, USA among the best-performing in the field uses a re-circulation figure of 1.5 liters/ton.day; i.e. 540 liters/t.year. All in all, given average moisture figures 30 to 35% and the minimum target figure of maximum moisture potential 40 to 50% minimal amounts to be re-circulated settle at around 100 to 200 liters per ton. Such estimate is given for an ideal configuration where the re-circulation system is fully efficient 100% of the waste undergoes re-circulation, which remains difficult to achieve. In other respects, it would seem important to carry on leachate re-circulation even after reaching field capacity in order to stir up the reactor that is the landfill cell, to input nutrients and dilute local inhibitors When and how to re-circulate The rate of re-circulation should also suit the stage of waste degradation. It is better not to re-circulate or to do it using small amounts of leachates during the acidogenesis phase to prevent the bacterial flora from being harmed by acid impeding biodegradation. Most of the research work agrees on the necessity to allow periods of rest. It is better to inject using high flowrates for short amounts of time than inject continuously using low flowrates. With regards to re-circulation cycles, the literature gives frequencies that are yet again rather variable and highly linked to the efficiency of the re-circulation system involved. Most often weekly to monthly frequencies are quoted. For waste to stabilize as soon as possible, optimal moisture has to be reached as fast as possible. Hydraulic characteristics of the waste, however, such as rate of moisture absorption and geo-mechanical stability of the waste mass also have to be taken into consideration to determine the re-circulation to be implemented. Finally, the temperature of the injected liquid may have quite an impact on bio-activity and leachates that are too cold should not be re-circulated. Depending on regions, this limitation can severely curtail operations in winter What leachates can be re-circulated Lab work shows that the re-injection of leachates rich in volatile fatty acids or ammonium ions concentration in NH4 + > 3000 mg/l corresponding to fresh leachates linked to an acid ph < 5 impedes methanogenesis. 1 w=m w /m d w =m w /m h with m w =being the mass of water, m d the mass of the dried waste matter and m h the mass of the moist waste 33/51

34 Research work [35] has sought to determine whether pre-treatment of this type of leachates for nitrification, mainly is useful for re-circulation purpose. Work on re-circulation s impact on nitrified leachates has evidenced that: the main reaction of nitrate conversion is heterotrophic denitrification provided there are sufficient amounts of carbonated matter. In the areas of denitrification, methanogenesis cannot occur because the two reactions clash. large amounts of H 2 S may lead to a reaction of nitrammonification and a re-concentration of ammonium ions in the leachates. If the source of carbon is depleted in the case of stable methanogenesis for instance autotrophic denitrification may ensue. Potential leaching of metals might take place, but has not been observed in lab work. According to lab work, re-circulation of nitrified leachates might not be a good idea in case of gas utilization before stable methanogenesis is achieved because the reaction might be impeded. It would not be very productive either to re-circulate on waste that is likely to generate H 2S fresh waste, for example, or rich in sulfur and gypsum. Such considerations have to be taken into account if putting an economic value on gas output is intended. Research work [32] demonstrates the importance of the quality of re-circulated leachates in the leaching of metals. During re-injection, exchanges occur and then balances are struck between the liquid and solid phases, which might lead to different rates of leaching of metals depending on the composition of leachates. On site, significant leaching of metals have however never been quoted in the literature Biogas capture With regards to this topic, paragraph III.2.6 provides useful information on monitoring as well as s guides already cited: Optimisation du captage du biogaz issu des ISDND et des anciennes décharges (Optimization of Biogas Capture in Non- Hazardous Landfill and Post-Closure) 2007, Gérer le gaz de décharge (Landfill Gas Management) The adjustment of the collection process (adjustment of valves and lowering pressure in the collection network) should be conducted in parallel with the adjustment of the re-circulation process, especially during the first re-injection trials. Particularly, a compromise has to be found between leachate injection and biogas collection in order for re-circulation to interfere as little as possible with the output flowrate, which can crash in case re-circulation is ill adjusted (in terms of flowrate or duration) Monitoring of bioreactor operation In order to monitor and control the accelerated degradation process that results from a bioreactor landfill approach, site-specific monitoring is required. It is important to collect information on the quality of the waste treated in a bioreactor landfill cell and on the amounts and quality of the generated leachates. The reason for that is that the latter are liable to change and are indicators of the conditions of degradation within the waste mass. Also, these parameters enable better management of the bioreactor cell. In the following paragraphs, suggestions of parameters and frequencies of monitoring campaigns are divided into three themes: for operational, detailed or research purposes. Operational monitoring corresponds to the minimum level of monitoring that is compatible with controlling the impact of re-circulation on the process and with available, tried and tested facilities (equipment and/or methods). Detailed monitoring corresponds to an in-depth approach and is well suited to diagnosing. Monitoring for research purposes should be implemented to study the impact of re-circulation on the biological, physical and chemical processes. 34/51

35 Waste Monitored parameters Monthly tonnage % Household waste,% Solid industrial waste, % Other categories Biogas generation potential Moisture Chart 2: waste monitoring parameters Frequency of Intention monitoring - Theoretical estimation of biogas production - Understanding the changes in parameters (permeability, hydrological balance, organic content of leachates ) Yearly survey for each cell Level of monitoring Operational 1 sample analyzed at the gate for each 50,000 m 3 of waste Detailed Settlements and density - Survey of settlement of the waste mass - Estimation of the speed of utilization of the extra space made available Every six months - Yearly Detailed - Operational Temperature of waste mass Monitoring of the enhancement of degradation Continuously (embedded sensors) Detailed - Research Moisture of waste mass Re-circulation management (volume, flux, to be recirculated) Continuously - Yearly survey Research - Operational Permeability - Determination of the speed of liquid flux through the waste mass - Adjustment of re-circulation protocol About every three years Detailed - Research 35/51

36 Monitored parameters Recovered volumes Injected Volumes Leachates Leachate build-of in injection wells ph, conductivity and particles in suspension COD and BOD Cl NH 4 Metals total (Pb, Cd, Cu, Ni, Hg, CrTot, CrVI, Mn, Sn, Zn, Fe, Al) Particles in solution (Na, K, Mg, SO 4, HCO 3 ) Absorbable organicallybound halogens, Carbolic acids Intention Chart 3: leachate monitoring parameters Frequency of monitoring Monitoring of the hydrological balance Knowledge, control and management of the re-injection - Regulatory monitoring of leachate levels - Prevent swamping of the waste mass - Management of re-circulation - Indicators. Information on leachate general content, their maturity - Monitoring to prevent the accumulation of mineral particles - Changes in oxidizable content (mineral or organic) biodegradable or non-biodegradable - Basic parameters to estimate the decrease in volume of the biodegradable part of the waste - Monitoring of Cl content owing to the risk of accumulation - Indicators of changes in Cl concentration levels in leachates Monitoring of NH 4 content owing to the risk of accumulation Indicators. Information on leachate general content, their maturity and the chemical form of some of their components Monitoring of particles in solution - Toxic above certain concentrations - Determination of the need for pretreatment before re-injection Systematic measurement campaigns each time pumps are activated and monthly balances Systematic measurement campaigns for each re-injection episode and monthly balances To be adjusted to the frequency of recirculation Every six months - Weekly Every six months - Weekly Every six months - Weekly Every six months - Weekly Every six months - Weekly Monthly Every six months - Weekly Level of monitoring Operational Operational Operational Operational - Research Operational - Research Operational - Research Operational - Research Operational - Research Research Operational - Research 36/51

37 Monitored parameter s Flux (Relative pressure, volume, temperatur e) Biogas Intention Chart 4: biogas monitoring parameters - Actual volumes to be compared to estimates of theoretical generation - Evaluation of the impact of leachate recirculation on rates of biogas generation Frequency of monitoring Weekly - Monthly Level of monitoring Detailed - Operational Applied suction - Monitoring of proper performance - Recording of variations to be correlated to flowrate variations to estimate biogas generation Weekly Operational CH 4, CO 2, H 2 and O 2 - Methane flux calculation - Adjustment on network using O 2 content - Indication of a return to acidogenesis using H 2 content Weekly Operational N 2 Humidity H 2 S - Validate stripping of the site in NH 4 content in case leachates oxidize in interim installations before re-circulation - Check for air infiltration More precise estimate of % of other components in case of analysis on humid gas In case of electric utilization of biogas (motor), monitoring of H 2 S because of its corrosive characteristic Every six months Research Weekly Weekly Research Detailed Research Such monitoring when it is operational should be extended to the whole site. For research or diagnostic purposes monitoring may have to be restricted to areas like one cell or one biogas recovery well or an injection line Operational data Monitored parameters Chart 5: operational monitoring parameters Frequency of Intention monitoring Level of monitoring Accumulation of water in the low points of biogas collection piping Correct measurement of biogas flux Monthly survey Operational Rain Atmospheric pressure Hydrological balance Beneficial rain Biogas flowrate calculation Nm3 Monthly / Daily Operational / Detailed 37/51

38 Monitoring equipment and method Waste as received Composition of waste and methane-generation potential Knowing the methane-production potential enables to work out an estimated gas generation schedule and as a result to size the gas capture and utilization operations. The discrepancies that may be observed between the estimated production schedule and the actual measurements during operation will serve as a means to assess the site s performance. Ideally, regular and representative samplings of the waste as it is received using a method such as MODECOM is necessary to establish the methane-generation potential in a lab. Such a test known as a BMP (Bio-methane Potential) test consists in measuring the gas production of a waste sample placed in optimal conditions of degradation. The test should last a minimum of 3 months for the potential to be properly estimated extrapolating results from shorter periods of time is often tricky. This type of test should be carried out every 2 to 3 years or more often in case the waste brought in varies significantly. In practice, the aforementioned measures being relatively costly, an approach based on waste composition could be implemented. Each category of waste entering the mix having its own methane-generation potential, it is possible to assess the global potential by estimating the proportional composition of the waste mass visually or by weight of especial importance for domestic waste is the proportion paper/cardboard which is responsible for most of the gas generation Moisture content The moisture content in the received waste is one fundamental parameter that operators need to know in order to determine the amount of leachates to re-circulate. For domestic waste, it is possible to estimate this figure based on French waste averages (about 30 to 50 weight percent). But it is more difficult to do so for non-hazardous industrial or mixed waste. Precise measurement requires a sampling of the waste following the aforementioned MODECOM standard procedure, after which the waste is dried and weight measurements are taken if possible by representative types of waste. This sampling should be carried out every 3 to 5 years or whenever there are noticeable changes in the waste received Landfilled waste Moisture content This measurement has been mentioned in III and in III and illustrated using a geoelectrical method to display the pattern of moisture distribution around the injection lines. Operators should use such a method when the re-circulation system that they implement goes beyond the standards set by this guide. A method of overall evaluation using the hydrological balance and re-circulated quantities can also be used provided moisture is evenly distributed in the waste mass. This theoretical result can further be checked by taking weight measurements and samples from the waste mass. 38/51

39 Figure 16: core samplings to measure moisture content at different distances from the injection well at the La Vergne bioreactor landfill cell VEOLIA PROPRETE Temperature The measurement of temperature is dealt with in III Measurements using probes provide an uninterrupted data stream. In case a mobile probe is used measurements should be done on a monthly basis State of degradation Monitoring the state of degradation of waste matter undergoing re-circulation is essential to make sure the installation performs well. Besides the use of indirect parameters temperatures, gas generation, nature of leachates, this estimation can only be achieved by taking samples from the waste mass, which are then tested for their methane-generation potential as mentioned before. Operators can also use simpler tests such as: volatile materials; the dosage of cellulose and lignin, the ratio of cellulose + hemicelluloses / lignin, depending on the state of degradation; the dosage of oxidizable organic matter; the AT4-dosage that corresponds to a microbial aerobic test indicative of the content in oxidizable organic matter. These costly procedures may be carried out only every few years. 39/51

40 Figure 17: core-sampling campaign to measure moisture and the state of degradation Hydrological balance Amounts injected The amounts injected are controlled continuously thanks to the injection plant flowmeter or by adjusting the amounts injected gravitationally Meteorological parameters The basic meteorological parameter is the amount of rainfall, obtained by using daily readings from an on-site rain gauge of from the nearest met station Leachate production Leachate production can be measured by placing flowmeters down-flow from the cell or by knowing how long the pumps work and what their flowrates are if collection is not gravitational. Ideally production should be figured out for each cell. Leachates Content The determination of leachate content is a standard regulatory requirement that is requested every month or term. In the case of bioreactors more in-depth measurements are required owing to the data that it provides pertaining to the degradation process. The COD and BOD parameters, ammonium, volatile fatty acids should be measured on a monthly basis while ph can be monitored continuously as well as conductivity at least for a week at a time Temperature In general leachate temperature varies little. Its monitoring matters less than temperatures of the landfilled waste. Monthly measurements enable to ensure there is no risk of damage namely creeping to the bottom geomembrane liners Biogas Flux and content A site s overall gas flux is generally well measured often continuously via devices that are embedded in the gas destruction / utilization installations or through the check-ups that are carried out on the site. The same goes for the major content parameters: CH 4, CO 2, O 2. Oftentimes in order to adjust the network s configuration and fine-tune gas collection measurements are carried out at the network s various key points or at the injection line main headers. These are essential in a bioreactor s case to evaluate performance area by area especially with regards to the impact of re-circulation, or possibly even the impact of changes in the re-circulation patterns Fugitive emission 40/51

41 Compared to a traditional landfill approach, the major advantage of a bioreactor is its low level of fugitive emission. This can be evidenced by carrying out measurement campaigns using a surface flux chamber or other techniques such as the tracing of gas leaks, an overall weight balance, etc., when conditions are right as soon as capping is completed. This technique consists in measuring the accumulation of gas within a volume at atmospheric pressure laid on the top coverage. Depending on the type of coverage, the measurement grid can vary or even focus on the usually sensitive areas because of settlement amongst others like wellheads, subdivision lines, connection with the sidewalls, etc. Once the survey is completed, the performance of the top cover may be checked only from time to time. Settlement Figure 18: flux chamber measurement on biogas biofilter (CSD AZUR) Extent The monitoring of settlement using topographical measurements is requested on an yearly basis in permits to operate. Settlements are telltale indicators of changes in the state of the waste. When monitoring a bioreactor, regular measurement of settlement via a network of topographical posts or using a laser survey at ground level to correlate areas of settlement, areas moistened via recirculation and biogas generation area by area. In this respect, leachate re-circulation is liable to cause uneven settlement in case moisture is not evenly distributed throughout the waste mass Clogging Inspection Video inspection to check for clogging is not a routine measure but can be decided in case of a suspected malfunction in the piping (unexplained low fluxes, unexpected build-up of leachates at the base of the cell, suspicious re-injection pressure increase,...). General recap of environmental impacts IMPACTS ON LEACHATE GENERATION At this stage it may be useful see III.1.4, III & III to remind readers that bioreactors: do not increase the risk of leachate emission at the base of landfill cells; enable to decrease the biodegradable organic content of leachates, but may trigger concentration of some chemicals such as chloride and ammonium. Depending on the quality of the re-circulated leachates, lab experiments have shown some heavy metals might be leached; 41/51

42 reduce the quantity of leachates to be treated in the short run depending on the type of management and climate. Over the long run, the waterproof cover prevents water infiltration IMPACTS ON BIOGAS EMISSION Bioreactors curb long-term risks of biogas fugitive emission. By enhancing degradation they shorten the time frame for landfill gas generation and focus it during the period when the protective containment system is at its best. This approach is the disposal method that has the lowest rate of greenhouse gas emission into the atmosphere. Overall efficiency for the capture of gas generated is estimated to be above 90%. This performance is evidenced in the figure 19 which represent the findings of a measurement campaign of fugitive surface emission through the cover of the La Vergne site. To the right of the bioreactor landfill cell fitted with waterproof coverage, the traditional cell with traditional coverage flares up as a series of colored areas marking emission. Bioreactor cell Control cell Figure 19: mapping of flux chamber measurements of fugitive emission on La Vergne site (VEOLIA PROPRETE) By focusing gas production and collection over a shorter period of time, bioreactors help improve energy recovery from landfill sites or even allow such recovery on sites where it could hardly have been considered prior to this approach. The currently expected increase in instant production is around twice what is generated using a traditional approach. The current improvements in performance for this type of installation lead operators to hope for further significant progress in the field. For the sites that receive waste that is already moist and that are located in areas where rains are heavy, boosts in production might be more limited compared to non-re-circulated landfill cells. Nevertheless, depending on efficiency and implemented coverage, the capture flux therefore the control of fugitive emission can still be optimized. 42/51

43 IMPACTS ON SPEED OF STABILIZATION The more efficient a bioreactor s re-circulation system is with regards to moisture percolation into the waste mass, the less time is needed to stabilize waste. The literature gives estimated periods for stabilization of 10 to 15 years for current installations. Figure 20: comparison of states of waste stabilization from bioreactor and control cells of La Vergne site (VEOLIA PROPRETE) IMPACT ON SETTLEMENT The major impact of bioreactor landfill management lies in the acceleration of settlement over the first years of operation. Compared to traditional management the increase in settlement speed can be twofold. The comparison of settlement volume between the bioreactor test cell and the traditional control cell of Yolo County, which had the same initial volume, clearly illustrates the gain in space generated through bioreactor management see figure /51

44 Figure 21: visual comparison of settlement on bioreactor and control cells at the Yolo site (USA) Measurements of compared settlement volumes on the 2 cells above illustrated in figure 22 outline the excellent performance of this site where the bioreactor cell s settlement volume is 5 times higher than the one observed for the control cell. Settlement in % Tassements en % Figure 22: measurements of settlement on bioreactor and control cells, Yolo County site, USA 44/51

45 Technical and economic feasibility study REQUIRED HUMAN RESOURCES: SKILLS AND STAFF SIZE Bioreactor landfill management makes it necessary to hire extra personnel to staff the extra operations; i.e.: extra monitoring; monitoring injection operation and biogas recovery management. Extra staffing needs can be estimated to be between 0.5 and 1 extra staff depending on sites size or capacity. The level of motivation and training of this personnel in charge of monitoring and running re-circulation must be high: either a young engineer or an experienced technician TECHNICAL AND ECONOMICAL APPROACH: MINIMUM TONNAGES AND EQUIPMENT LEVEL REQUIRED TO RUN BIOREACTOR OPERATIONS, COSTS Environmental performance comes with an impact on economics: avoided costs and added costs, whose balance is to this day not clearly established. Avoided costs mostly become apparent in the long run. The main point of bioreactor landfill management being environmental friendliness, this approach is not restricted to high tonnages but can be used for smaller sites. As the chart 6 points out, incremental investment costs are mostly proportional to tonnage and economies of scale are rather limited, which only mildly penalizes low-capacity sites Required equipment and incremental costs Incremental investment and operation costs for a bioreactor can be estimated to be between 3 and 10 (before VAT) per ton depending on the site. They finance essentially: investment-wise: the re-circulation installations; the upgraded containment. operation-wise: additional monitoring; operation staff. A bioreactor set-up can be analyzed as follows: costs that are little proportional to tonnage (fixed) are to be differentiated from costs that are (quasi-) proportional to tonnage (variable), the number of X s representing the relative importance of costs. Chart 6: cost structure of a bioreactor s set-up Category Details Fixed Variable cost cost Re-circulation. plant pump, automation X. network grid of drainage trenches to fit action ranges of XXXXXXXX utilized systems, drainage layer, main headers XXX Biogas extra wells XXXX Cover high-performance containment XXXXXXXX Monitoring flowmeters, sensors X Operation. staff X. monitoring analysis, sampling, etc. X 45/51

46 Potential benefits It is difficult to put a definite value on avoided benefits because they vary so much from site to site. They can however be structured as follows: new landfill space created that can represent a few percentage points of the cell s volume; increase in the utilization potential thanks to accelerated biogas generation and to the income generated by selling the produced energy; decrease in post-closure costs due to faster waste stabilization, thereby reducing the need for extended monitoring or even for financial guarantees; a decrease in external costs related to real or perceived long-term risks [31] loss of value, etc. Prospects There is consensus in the industry to say that the bioreactor solution represents real progress in landfill management. With an eye on continued improvement of landfilling processes, operators are even willing to commit themselves to raising the environmental performance of bioreactors and to pursuing the following goals: 90% of overall methane capture over the site s lifespan; 90% of initial methanogenesis potential realized within 15 years to reach a maximum of 15 Nm3 of CH 4 per ton dry waste mass. With a view to improving knowledge, research work in this field must go on. Cases in point include: ANR s 4-year project on waste conditioning to optimize biodegradation through methanization of non-hazardous waste BIOTIME, coordinated by VEOLIA PROPRETE, which has just been launched with the partnership of CEMAGREF, IMFT, LSEE, LTHE and LISBP. Another noteworthy project is ANR s PRECODD on a new generation of bio-active landfills, coordinated by the INSA institute of Lyon and EEDEMS with assistance from the following partnerships (1) University of Grenoble & LIRIGM/LTHE, (2) CEMAGREF & the University of Research on Hydrosystems and Bioprocesses, (3) INSA of Lyon & LAEPSI, (4) INSA of Lyon & URGC, (5) BRGM & Technical and Scientific Center of Orleans, and contributions from VEOLIA PROPRETE and SUEZ Environnement. supports the continuation of research programs to compare different landfilling approaches and to optimize bioreactor landfill management. Various private initiatives of operators who have developed full-scale bioreactor landfill management, having benefited from permits to operate (COVED in Loches, SITA in Sonzay, VEOLIA PROPRETE in La Vergne). 46/51

47 ANNEX 1 BIBLIOGRAPHY The reports and guides by quoted in this work are available online at: www2.ademe.fr. The * sign indicates that the article refers to an on-site experiment. Source N Title Author Sardinia Sardinia 2003 Sardinia SITA- 4 Programme R&D Sardinia Sardinia Sardinia Sardinia Sardinia 10 Sardinia Sardinia Sardinia Sardinia Sardinia Carbon and nitrogen mass balance in some landfill models for sustainability assessment Numerical evaluation of granular blankets for leachate recirculation in MSW landfills Discussion of different landfill concepts - from open dump to MBP-landfill Influence de la recirculation des lixiviats sur la stabilisation des déchets et la production de biogas des CSD non dangereux: Document de synthèse (*) Centre de Stockage du Jura, Recirculation des lixiviats programme de recherche et de développement. Résumé(*) Engineered landfill versus in-vessel processes for anaerobic composting and methane recovery from MSW Dutch sustainable landfill research program: 4 years experience with the bioreactor test cell Landgraaf (*) Yolo county, California controlled landfill program: a summary of results since 1994 (*) Predicting the storage capacity of deep landfills: Ferques bioreactor case study (*) Landfill gas production and energy recovery in bioreactor landfill (*) Investigation of water flow in a bioreactor landfill using geoelectrical imagining techniques (*) Commercial-scale aerobic-anaerobic bioreactor landfill operations (*) Aerobic-anaerobic treatment of MSW organic fraction in landfill: a bridge to bioreactor technology (*) ReactiveTransport in bioreactors: Development of a multiphase flow model Organic matter stabilization of sorted MSW under leachate recirculation R. COSSU, R. RAGA, G.VETTORAZZI, M.V. KHIRE, M.M. HAYDAR, 2003 D. AUGENSTEIN et al, G. BARINA, 2003 CEMAGREF, RIQUIER, LAEPSI, LIRIGM, 2002 / D. AUGENSTEIN, R. YAZDANI, J. BENEMANN, H. WOELDERS, L.LUNING, F. VAN VELTHOVEN, H. HERMKES, H. OONK, D. AUGENSTEIN, R. YAZDANI, J. BENEMANN, J. KIEFFER, F. OLIVIER, JP. GOURC, C. COQUANT, A. CORTI, L. LOMBARDI, L.PUGLIERIN, H. ROSQVIST, T. DAHLIN, C. LINDHE, R.B. GREEN, G.R. HATER, C.D. GOLDSMITH, F. KREMER, T. TOLAYMAT; M. MAGNANI, P. MAGNANI, S. PINAMONTE, D. CHENU, N. SKHIRI, L. BLETZACKER, M. QUINTARD, R. BAYARD, C. GACHET, F. ACHOUR, C. de BAUER, R. GOURDON, 47/51

48 Sardinia 16 Sardinia 17 Sardinia 18 Sardinia Sardinia Sardinia Sardinia Sardinia Sardinia Sardinia 25 Waste Managment World (revue) mars TSM 08 Nitrate injections during municipal solid waste anaerobic digestion Evolution and fate of nitrogen compounds in scale bioreactor landfills Codigestion of MSW and septic tank sludge in bioreactor landfill simulators Evolution of bio-physical and mechanical characteristics of MSW after 2 years incubation in a laboratory-scale bioreactor Implementation of bioreactor technology at a Northern Canadian landfill Performance results from the tucuman solid waste bioreactor (*) A strategy to achieve optimal performance at full-scale operationnal bioreactor landfill Observed benefits and problems associated with leachate recirculation Bioreactor landfills in northern regions - Diagnostics and outlook for operation and performance Bioreactor landfills lysimeter studies on indian urban refuse V. VIGNERON, M. PONTHIEU, G. BARINA, JM. AUDIC, N. BERNET, T. BOUCHEZ, L. MAZEAS, R. VALENCIA, W. VAN DER ZON, H. WOELDERS, H.J LUBBERDING, H.J. GIJZEN, R. VALENCIA, W. VAN DER ZON, E. ELPIDO, H.J. LUBBERDING, H.J. GIJZEN, F. OLIVIER, JP. GOURC, F. ACHOUR, J. MORAIS, R. BAYARD, C. FELSKE, U. WOLF, EA McBEAN, F.A. ROVERS, E. DEL ROSSO, T. GIDDA, Y. MOREAU-LE GOLVAN, T. LAGIER, L.SMITH, M. LANE, R. THIEL, C. ZIESS, M. SWATI, J. KURIAN, R. NAGENDRAN, 26 Bioreactor landfill T. REINHART, 27 Solagro 28 Waste Managment Vers une nouvelle génération de centres de stockage bioactifs (*) Recirculation des lixiviats dans un casier de stockage de DMA (*) Practice revue of 5 bioreactor/recirculation landfills (*) T. BOUCHEZ, G. BARINA, C. DUQUENNOI, A. BUDKA, J.M. AUDIC, V. VIGNERON, C. COUTURIER, 2000 C.H. BENSON et al., VEOLIA CEMAGRE F Bioréacteur de La Vergne: bilan de 3 années de recherche (*) Contribution à une gestion durable du risque environnemental du stockage des déchets ménagers et assimilés : l évaluation du coût externe des fuites de lixiviat des décharges Note de synthèse du programme de recherche sur la gestion des Installations de Stockage de Déchets ménagers et assimilés (dits aussi non dangereux) en bioréacteur N. SKHIRI, 2007 J. MERY, I. HEBE, /51

49 - SITA - SITA - CEMAGRE F-SITA Sardinia 33 Le concept du bioréacteur Note de synthèse : Influence de la recirculation sur la stabilisation des déchets et la production de biogaz des CSD non dangereux (*) Voies de réduction des oxydes d'azote lors de leur injection dans un massif de déchets ménagers et assimilés Investigation of water flow in a bioreactor landfill using geoelectrical imagining technics (*) T. DELINEAU, A. BUDKA, 2000 G. BARINA, 2003 V. VIGNERON, H. ROSQVIST, T. DAHLIN, C. LINDHÉ, 49/51

50 ANNEX 2 THEORETICAL NOTIONS ON HOW LIQUIDS FLOW THROUGH WASTE To complement the presentation on the different types of injection systems, it is important to explicit a few notions relative to liquid transfers in a heterogeneous environment and especially the notion of efficient action ranges in infiltration installations. Many authors have highlighted the lack of homogeneity of waste landfill in terms of liquid transfers and the law of double porosity that rule such transfers. Double porosity consists of the overlapping of a micro-porosity at waste scale centimeters to decimeters range and a macro-porosity meter to several-meters range. The latter accounts for the appearance of preferential flowpaths that cause bypassing of intended drainage and reduces the time water spends in the waste matter. As a result waste matter undergoing re-circulation produces leachates before it reaches its natural maximum moisture physical potential. The proportion of outflow of the preferential type might reach up to 40% of the flows transiting through the waste mass (Maloszewski et al. 1995). The origin of preferential paths may be related to the interconnection of micro-pores and the leaching of fine particles, which creates low-discharge channels or hairline cracks resulting from movements in the waste mass. This predicament makes it hard for a site to reach its maximum moisture potential and makes it necessary to input volume slightly higher in practice than what should be required in theory calculated as the difference in moisture potential and initial moisture content of the waste. It is to be noted however (Zeiss et Uguccioni. 1995) that waste, which undergoes repeated episodes of recirculation, sees its maximum moisture potential increase slowly but regularly. This is evidence of secondary absorption capacities, which are likely to be related to capillary forces that redistribute water from the macro-pores to the waste matter. With time macro-porosity tends to decrease significantly and evolves toward a more homogeneous environment. In practice, the behavior of the water pumped into the waste out of a pond can be represented as in the figure 23: Figure 23: effective action range of an injection system (Chassagnac. 2007) In the vicinity of the injection point waste absorption capacity is inferior to the unit flowrate i.e.: flow transiting through one volume unit of waste and water uses each pore available to flow out. The outflow gives out a lot of moisture and consequently moistens waste effectively. Moving away from the point of injection, the expected outflow paths gradually move away from each other and the unit flowrate decreases. Beyond a certain range that will be called effective action range the unit flowrate is insufficient to fill all the available gaps and the flow favors paths where discharge is minimum and which are made up by macro-pores. Its moistening ability as a result is weak and the intended effect is no longer achieved. The figure 23 not only evidences the presence of a lateral action range self-evident, intuitively, but also that of a vertical action range much more counter-intuitive. These action ranges depend on: the type of injection lines, and especially the size of the interface involved length, width, circumference of the drainage layer around the line; the flux itself dependent on the pressure in the re-circulation network. 50/51