The interactive effect of environmental factors on methane oxidation in a continental landfill bio-cover

Abstract

In the current study, the interactive effect of environmental factors was studied in an active bio-cover after two years of operation and experiencing a wide range of temperatures across the seasons (<0 ℃ to >45 ℃) in a continental climate condition. The studied environmental factors includes moisture content (MC), temperature, and initial CH4 concentration that were observed to have the most controlling effect on the CH4 oxidation in the bio-cover over two years of field-scale measurements. Therefore, selected environmental factors were modeled to determine their interactive effect on CH4 oxidation potential in the bio-cover material including Yard Waste and Leaf Compost (YWLC) and Biosolids Compost (BSC) (1:4). The compost was taken from the active bio-cover in October 2018 with a compost temperature between 10 and 15 ℃. The expectation was that the methanotrophic biomass would be adapted to the seasonal in situ conditions. While the effects of individual environmental factors on biological CH4 oxidation have been described in a previous long term study, their interactive effects in the bio-cover compost materials had not been explored. Therefore, interactive effects of environmental factors were investigated with a Box–Behnken Design adopting a Response Surface Methodology to develop a statistical model and determine the optimal conditions for the CH4 oxidation in the compost mixture sampled. To do so, 17 batch incubations were conducted at the MC of 20 %, 40 %, and 60 %, temperatures of 15, 30, and 45 ℃, and initial CH4 concentrations of 10 %, 20 %, and 30 %. The maximum value of CH4 oxidation rate obtained from the model was 2.20 mgCH4.gdw−1.d−1 with optimum MC of 47.4 %, temperature of 32.7 ℃, and initial CH4 concentration of 23.8 %. A parabolic curve for MC and temperature was observed simultaneously, and there was no significant difference between CH4 oxidation rates at 20 % and 30 % initial CH4 concentration. The model was then validated experimentally. The results of this study showed that the current compost mixture, collected from this bio-cover accustomed to fluctuations in temperature and MC, selected for a community of methanotrophs capable of effective operation over a wide range of summer compost temperatures and MCs, but was ill-adapted to spring and fall temperatures when the bio-cover temperature descends below 15 ℃, including when the bio-cover sample was taken for the current analyses.