Treatment of landfill gas with low methane content by biocover systems

Abstract

Landfills are significant sources of anthropogenic atmospheric methane (CH4), which contributes to climate change. Large amounts of CH4 are emitted from landfills in dilute form due to mixing with air in leachate collection systems, or during lateral migration away from landfills. The objective of this study was to investigate the CH4 oxidation efficiency of a compost material subject to LFG diluted with atmospheric air resulting in CH4 concentrations of 5-10 % v/v.. CH4 oxidation rates and carbon dioxide (CO2) production were measured through batch and dynamic column experiments where two laboratory scale biofilters were constructed. The columns were run at increasing flow rates. Column gas concentration profiles for each of five flow campaigns were compared to each other. This showed that oxygen (O2) was present through the entire column and elevated CO2 concentrations throughout the biofilters were found. Moreover, the oxidation process tended to be centred in the lower parts of both columns. It was observed that the biofilters performed better once they had adapted to the increasing loads of CH4. In both columns, the maximum removal rate of CH4 was found to be 98-100 %. Using CH4 mass balances the maximum oxidation rate was 238 g CH4 m-2 d-1 in Column 1 and 483 g CH4 m-2 d-1 in Column 2 (equal to the load). None of the biofilters reached their maximum CH4 oxidation capacity, hence they could have been exposed to a larger CH4 load. It was found that the retention time in the columns was not a factor limiting the oxidation process. High O2 consumption and carbon mass balances underlined the strong activity in the biofilters and it was not suspected that the methane oxidising bacteria were O2 limited. The results of this study suggest that biofilters have great potential for reducing CH4 in diluted LFG.

Mitigation of Methane, NMVOCs and Odor Emissions in Active and Passive Biofiltration Systems at Municipal Solid Waste Landfills

“…The oxidation efficiency with decreasing depth goes from 30% to 60% due to the high entry of atmospheric oxygen into the pores of the filter bed in the surface layers. As confirmed by some authors, O 2 is important for the oxidation of CH 4 , and a few studies have investigated actively aerated biofilters (mainly as lab-scale column tests), some with separate air injection at multiple levels [44] and some with CH 4 and ambient air or O 2 mixed in the inlet, thereby simulating diluted LFG [18,22,45,46]. Therefore, according to Scheutz et al (2009) [47], an oxygen concentration of less than 1% causes a total inhibition of the methanotrophic bacterial flora, while values between 1%-3% cause a reduced biological oxidation activity in methane.…”

Methane oxidation biosystem in landfill fugitive emissions using conventional cover soil and compost as alternative substrate—a field study

“…The oxidation pro les observed in Figure 4 are in agreement with Cabral et al (2007), who evaluated a methanotrophic population along the pro le of a biocover (mixture of compost and sand at a 5:1 ratio, respectively) and concluded that, in fact, the number of methanotrophic bacteria reduced with depth, and a reduction in the oxidation e ciency was seen with the depth of the cover layer. In addition, Hu and Long (2016) and Thomasen et al (2019) also reported that greater oxidation e ciencies were seen in the biocover upper layers, since methanotrophic bacteria are aerobic and need atmospheric oxygen to carry out the methane oxidation.…”

Landfill Impacts on the Environment—Review

“…Main factors affecting the amount of LFG are as follows: waste composition, moisture content, temperature, landfill age etc. LFG generation starts one to two years after waste disposal into the landfill and continues for (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) years [40][41][42]. Moreover, according to Directive 31/1999/CE: "LFG shall be collected from all landfills receiving biodegradable waste and the LFG must be treated and used.…”