Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark - PDF

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Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark Filippo Cassini Charlotte Scheutz Jan De Schoenmaeker Bent Skov Mou Zishen Peter Kjeldsen October 2014

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Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark Filippo Cassini Charlotte Scheutz Jan De Schoenmaeker Bent Skov Mou Zishen Peter Kjeldsen October 2014 Error! Reference source not found. Error! Reference source not found. Report [Nr.] 2014 By Filippo Cassini Charlotte Scheutz Jan De Schoenmaeker Bent Skov Mou Zishen Peter Kjeldsen Copyright: Cover photo: Published by: Request report from: ISSN: ISBN: ISSN: ISBN: Reproduction of this publication in whole or in part must include the customary bibliographic citation, including author attribution, report title, etc. [Text] Department of Environmental Engineering, Miljoevej, Building 113, DK-2800 Kgs. Lyngby, Denmark [ ] (electronic version) [ ] (electronic version) [ ] (printed version) [ ] (printed version) Preface This report is the result of a collaborative project between DTU Environment and AV Miljø carried out in the period from April 2011 until December We like to thank for the contribution by Svend Erik Christensen, Per Wellendorph and Finn R. Jensen from AV Miljø as well as Jonas Nedenskov from Amager Ressource Center, who all have actively contributed to the project and especially to the establishment of the pilot-scale biocover system at the AV Miljø Landfill. During the project several student projects have been carried out parallel to the on-going research project. I like to thank the students Christian Pilegaard Jespersen and Stefan Emil Danielsson (contributions to the tracer experiments) and Hans Henrik Jørgensen, Monika Margrethe Skadborg and Rune Skovsø Møller (contributions to the whole biocover methane oxidation measurements) for very valuable contributions to the project. Kgs. Lyngby, October 2014 Peter Kjeldsen Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark Content Summary... 5 Sammendrag Background and scope Pre investigation Gas flow rates from leachate wells Testing methane oxidation capacities of compost Overview of the biocover system Material and Methods Laboratory experiments: Methane oxidation and respiration Laboratory experiments for tracer influence evaluation on methanotrophic oxidation Monitoring of gas supply to biocover Moisture and temperature probes and measurements Surface screening of CH 4 and CO Surface emissions of CH 4, CO 2 and tracer (HFC-134a) Horizontal multi-port gas probes (HMPGP) design and sampling Tracer release experiment Single point CH 4 oxidation by the carbon mass balance method Single point CH 4 oxidation by the tracer mass balance method Whole biocover CH 4 oxidation based on CH 4 load and CH 4 surface emission Results and discussion Methane oxidation and respiration of compost material Temperature and moisture conditions in biocover Gas load to biocover Surface screening of CH 4 and CO Surface fluxes of CH 4, CO 2 and tracer (HFC-134a) Spatial evaluation of pore gas composition in biocover Evaluation of gas distribution by the tracer experiment Single point CH 4 oxidation comparison of the carbon balance and the tracer gas method Whole biocover CH 4 oxidation based on CH 4 load and CH 4 surface emission Evaluation of compost respiration by biocover carbon balance Conclusion and perspectives References Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark Summary Greenhouse gas mitigation at landfills by methane oxidation in engineered biocover systems is believed to be a cost effective technology but so far a full quantitative evaluation of the efficiency of the technology in full scale has only been carried out in a few cases. A third generation semi-passive biocover system was constructed at the AV Miljø landfill. The biocover was fed by landfill gas pumped out of three leachate wells. An innovative gas distribution system was used to overcome the often observed overloaded hot spot areas resulting from uneven gas distribution to the active methane oxidation layer consisting of garden compost. Performed screening of methane and carbon dioxide concentration at the surface of the biocover showed homogenous distributions indicating an even gas distribution. This was supported by result from performed tracer tests where the compound HFC-134a was added to the gas inlet over a period of up to12 days. Studies of the tracer movement within the biocover system showed very even gas distribution in gas probes installed in the gas distribution layer. Also the flux of tracer out of the biocover surface as measured by flux chamber technique showed a spatially even distribution. Compost samples were taken out at several occasions from the methane oxidation layer and tested in the laboratory for methane oxidation and respiration potential performed in a temperature range of 4 to 60 C. The temperature range reflected the temperatures observed by installed temperature probes in the methane oxidation layer. The laboratory experiments showed high methane oxidation potential even at temperatures up to 60 C but also a significant respiration of the matured compost. Other performed batch experiments showed the adding concentrations of the tracer (HFC-134a) in a concentration range similar to the range observed in biocover pore gas during the tracer experiment did not have an influence on the methane oxidation process ie no inhibitory effects from the tracer was observed. The whole biocover CH 4 oxidation efficiency was determined by measuring the CH 4 inlet load and CH 4 surface fluxes using the static flux chamber technique. In addition CH 4 oxidation was determined for single points using two different methods; the carbon mass balance method (based on CH 4 and carbon dioxide (CO 2 ) concentrations in the deeper part of the cover and CH 4 and CO 2 surface flux measurements) and a trace gas mass balance method (based on CH 4 and tracer inlet fluxes and CH 4 and tracer surface flux measurements). Overall, the CH 4 oxidation efficiency of the whole biocover varied between 81 and 100% and showed that the pilot plant biocover installed at AV Miljø landfill was very efficient in oxidizing the landfill CH 4. The average CH 4 oxidation rate measured at seven campaigns was approximately 14 g m -2 d -1. The carbon mass balance approach compared reasonable well with the tracer gas mass balance approach when applied for quantification of CH 4 oxidation in single points at the biofilter giving CH 4 oxida- Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 5 tion efficiencies in the range of 84 to a 100%. CH 4 oxidation rates where however much higher using the tracer gas balance method giving CH 4 oxidation rates between 7 and 124 g m 2 d -1 compared to the carbon mass balance, which gave CH 4 oxidation rates and 40 g m 2 d -1. Extrapolation of the results from the laboratory experiments to field conditions showed that the biocover system may have a much higher methane oxidation potential and could be loaded with a larger flux of methane without losing much efficiency. A high emission of CO 2 was observed at the biocover. Analysis and calculation revealed that most of the emitted carbon dioxide originate from respiration of the compost contained in the methane oxidation layer. The carbon is however of biogenic nature and do not contribute to the greenhouse effect. 6 Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark Sammendrag Reduktion af drivhusgasser fra deponeringsanlæg ved mikrobiel metanoxidation i etablerede biocover systemer kan være en omkostningseffektiv teknologi. Der er imidlertid kun blevet gennemført kvantitative evalueringer af effektiviteten af teknologien i fuld skala i nogle få tilfælde. Et tredje generations semi-passivt biocover system er blevet etableret på lossepladsen AV Miljø. Biocoversystemet var udført i pilot skala med et samlet areal på 500 m 2 og behandlede lossepladsgas opsamlet fra tre perkolatbrønde. Et innovativ gasdistributionssystem blev brugt til at undgå metanudslip fra overbelastede hot spot områder opstået som et resultat af ujævn gasfordeling til det aktive metanoxidationlag (bestående af havekompost). Screeninger af metan- og kuldioxidkoncentrationen på overfladen af biocoveret viste homogene koncentrationsfordelinger, hvilket indikerer en jævn gasdeling til metanoxidationslaget. Dette blev yderligere understøttet af resultatet af udførte sporstofforsøg, hvor forbindelsen HFC-134a blev tilsat gastilløbet over en periode på op til 12 dage. Undersøgelser af sporstoftransporten i biocoversystemet viste at gassen forelte sig relativt jævnt i systemets gasfordelingslag. Målinger af fluxen af sporstof ud af biocoveroverfladen viste også en rumligt ensartet fordeling. Kompostprøver blev udtaget ved flere lejligheder fra metanoxidationlaget og testet i laboratoriet for metanoxidations- og respirationspotentiale udført i en temperatur mellem 4 og 60 C. Temperaturområdet afspejlede temperaturer observeret via installerede temperaturfølere i metanoxidationlaget. Laboratorie-forsøgene viste høj metanoxidationspotentiale selv ved temperaturer op til 60 C, men også en betydelig respiration i det modnede kompost. Andre udførte batchforsøg viste at tilførelse af sporstoffet (HFC- 134a) i det i sporstofforsøget benyttede koncentrationsområde ikke havde en indflydelse på metan oxidationsprocessen i komposten, dvs. ingen inhiberende virkninger fra sporstof blev observeret. Hele biocoverets metanoxidation blev bestemt ved måling af metantilførelsen i indløbet og metanfluxen i 50 målepunkter fordelt over biocoverets overflade målt ved hjælp af statiske fluxkamre. Desuden blev metanoxidationen bestemt for specifikke lokaliteter på biocoveret ved hjælp af to forskellige metoder, en kulstofmassebalancemetode (baseret på metan- og kuldioxidkoncentrationer i den dybere del af biocoveret og metan- og kuldioxid-overflade fluxmålinger ) og en sporgasmassebalance metode (baseret på metan- og sporstof indløbsbelastning og metan- og sporstoffluxmålinger målt på biocoveroverfladen). Den totale virkningsgrad for metanoxidation for hele biocoveret varierede mellem 81 og 100% og viste, at pilotskalaanlægget var meget effektivt til at oxidere metan indeholdt i lossepladsgas. Den gennemsnitlige CH4 oxidationsrate målt ved syv kampagner var cirka 14 g m -2 d -1. Der var relativt god overensstemmelse mellem kulstofmassebalancemetoden og sporgasmassebalancemetoden, når metoderne anvendes til kvantificering af lokale metanoxidationsrater. Oxidationseffektiviteter målt med de to metoder Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 7 blev observeret i intervallet 84 til 100%. Metanoxidationrater observeret ved hjælp af sporgasbalancemetoden gav metanoxidationrater mellem 7 og 124 g m 2 d -1 i forhold til kulstofmassebalancemetoden, som gav metanoxidationrater mellem og 40 g m 2 d -1. Ekstrapolation af metanoxidationspotentialer målt i laboratorieforsøg til felt viste, at biocoversystemet formentlig har en meget større evne til at reducere metanudslip og vil kunne belastes med en større flux af metan uden at effektivitet af biocoveret reduceres nævneværdigt. En høj udledning af kuldioxid fra biocoveret blev observeret. Analyser og beregninger viste, at størstedelen af den emitterede kuldioxid stammer fra respiration af komposten indeholdt i metanoxidation lag. Kulstof er dog af biogen natur og bidrager ikke til drivhuseffekten. 8 Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 1. Background and scope Landfills containing organic wastes produce biogas containing methane (CH 4 ). Landfills are significant sources of methane, which contributes to climate changes. At some landfills utilization of landfill gas (LFG) is not or cannot be carried out, and the gas is either flared with risk of producing toxic combustion products or just emitted to atmosphere. Landfills may be covered with biological active materials, so-called biocovers. Experiments have documented that a very high methane oxidation rate can be obtained in bio-covers, high enough to significant reduce the methane emission from the landfill. Documentation of the efficiency of bio-covers has so far only been carried out in full scale in a few cases for instance the newly finalized project at Fakse Landfill where a new-developed protocol for biocover establishment and monitoring were presented (Scheutz et al., 2011a, b) and the second generation biocover system established at the Klintholm Landfill (Kjeldsen et al., 2013). Some of the lessons learned from these two full-scale biocover systems were that avoiding point releases of methane from the leachate collection system is very difficult. Beside, a major challenge in any biocover system is to obtain an even gas distribution to the active methane oxidation layer to avoid hot spot loading, which results in significant methane emissions. AV Miljø is a modern waste disposal site situated in Avedøre Holme, approx. 10 km south of Copenhagen, Denmark. The disposal site was established in 1989 and has a total disposal capacity of 2 mill. m 3 divided into 22 disposal cells. The landfill receives waste from approx. 1.2 mill. inhabitants and 80,000 larger and smaller enterprises. Since 1997 it has been forbidden in Denmark to use landfills for disposal of combustible waste. AV Miljø therefore mostly deals with non-combustible waste, i.e., waste with low organic content such as, e.g., shredder waste, asbestos waste, contaminated soils, construction waste, residues from street cleaning, slag, and fly ashes from waste incineration. Previous studies have shown that significant quantities of landfill gas are produced at the landfill, where a considerable amount is emitted from the leachate collection system via inspection and collection wells, (Scheutz et al., 2011c, Fredenslund et al., 2010)). The planned study and establishment of the pilot scale biocover system was focused on the western part of the landfill where several gas leaking wells previously were identified. The scope of the project was: To construct and get experience with a semi-passive biocover system fed by a gas load extracted from the existing leachate collection system for reducing methane emissions from landfills To give special emphasis on the gas distribution system to obtain an evenly distributed gas load for avoidance of hot spot emission areas on the biocover Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 9 To quantify the efficiency of CH 4 oxidation in the biocover system. The CH 4 oxidation efficiency was determined for single points as well as for the whole biocover 10 Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 2. Pre investigation Prior to the establishment of the biocover system two rounds of pre investigations were carried out. The first round of field investigations focused on one of the waste cells at the AV Miljø Landfill intended for hosting the pilot-scale biocover test (Pedersen et al., 2010). The second round performed gas pump tests in several potential contributing leachate wells and made preliminary tests of potentially usable compost materials for the methane oxidation layer (Pedersen et al., 2011). A short summary of the latter report is given in this chapter. 2.1 Gas flow rates from leachate wells Pump tests were carried out in six inspection/collection wells in the western part of the landfill. Each test had duration of about three days where a gas pump rate of 47 L/min extracted gas from the well. The accumulative pumped volume was monitored by a gas meter and the content of methane was measured continuously by a Photoacoustic Gas Monitor INNOVA 1412i (LumaSenseTechnologies, 2012). The results showed that especially three out of the six wells could maintain a significant and constant methane supply. The total extracted methane from the three wells was calculated to be 26 kgch 4 /day. 2.2 Testing methane oxidation capacities of compost Two producers of garden waste compost were identified in the vicinity of the AV Miljø landfill, (Solum and RGS90). Representative sampling of the two compost types was carried out and batch test were performed to measure the respiration activity and the methane oxidation capability of the two composts. The tests were carried out in 500 ml containers each containing 100 grams of moist compost. For the respiration tests 120 ml of the head space air was exchanged with pure oxygen (O 2 ) and the decrease of oxygen and increase of carbon dioxide (CO 2 ) contained in the head space was monitored over a period of 250 hours. For the methane oxidation similar tests were set up. Here 30 grams of moist compost was used and 200 ml of the head space air was exchanged with 120 ml oxygen and 80 ml methane followed by monitoring of the gas composition of the head space for 100 hours. More details of material and methods are given in Kjeldsen et al. (2013). The results of the batch incubation tests showed that the compost from RGS90 had the lowest respiration (xx-xx g O 2 /g/d) and also the highest methane oxidation rate (xx-xx g CH 4 /g/d), so the compost from RGS90 was chosen as the active methane oxidation medium for the biocover. Besides, the compost was also produced very close to the AV Miljø Landfill. Based on previous experiences from the Fakse and Klintholm biocover systems (Scheutz et al., 2011a, Kjeldsen et al., 2014), where both batch incubations, column experiments and in situ determination of me- Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 11 thane oxidation capacities of compost layers were carried out, a conservative expected in situ capacity of the RGS90 compost was set to 50g CH 4 /(m 2 and day). With an expected methane load from extracting gas from the three most productive wells of 26 kgch 4 /day, the area of the pilot scale biocover system was set to 500m Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark 3. Overview of the biocover system The biocover system (12 m x 42 m) consisted of a gas distribution layer (30 50 cm) overlain by a compost layer (80 90 cm). The biocover system was designed with the three supply wells mentioned above connected with underground piping to a mixing chamber where gas from the three wells was efficiently mixed. The three landfill gas emitting leachate wells were enclosed in air tight sheds to improve gas extraction. To obtain a controlled loading to the biocover the landfill gas was pumped from the enclosed wells to the inlet mixing chamber of the biocover. The pumped gas, reached the inlet mixing chamber trough 3 PVC pipes(120 mm diameter). The cylindrical mixing chamber had an external and internal diameter respectively of 115 and 100 cm, respectively and was made of HDPE material. Pumping rates from each of the three sheds were continuously monitored and the content of methane in the mixing chamber was continuously monitored with a CH 4 -sensor and data logger. Knowing the gas flow and the CH 4 content in the mixing chamber, the CH 4 load to the biocover could be determined. Other gases (O 2, CO 2 and nitrogen (N 2 )) were monitored manually in gas tubes connected to the interior of the mixing chamber. The interface between the methane oxidation layer (MOL) (consisting of compost) and the coarse gravel gas distribution layer (GDL) was zig-zag-shaped to minimize continuous water locking due to capillary effects (which has been identified as a major problem in other biocover systems) see Figure 3.1a. An unslotted gas pipe - distributing gas to 20 slotted gas pipes (see Figure 3.1b and c) - was equipped with small outlet holes to obtain an even gas dis
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