Biotic And Abiotic Characterization Of Biochar-Amended Landfill Covers Based On Column And Field Studies

Landfills contribute nearly one fifth of the human-derived methane emissions in the U.S., which together pose a significant negative impact on global climate. In order to mitigate the negative impacts of landfill CH4 emissions, alternate landfill covers are being investigated as a means to enhance microbial oxidation of CH4 into CO2 within cover soils. The objective of this research was to determine the feasibility and effectiveness of biochar amendment in enhancing the oxidation of methane in soil-based landfill covers under field-relevant settings. A pinewood-derived biochar was selected following characterization of six locally available biochars for column and field studies due to its high fixed carbon content, favorable adsorption properties, and low content of total and leachable heavy metals and polycyclic aromatic hydrocarbons (PAHs). Large column tests were conducted to simulate different biochar-amended soil covers constructed to evaluate their performance under simulated landfill cover conditions. Concurrent with column testing, a field study was carried out to evaluate the performance of three biochar-amended cover designs examined in column tests. Highest surface emissions across the field trial were positively correlated with average air and ground temperature. A strong positive correlation was observed among CH4 oxidation rates and CH4 concentrations in soil gas at 90 cm depth within the plots (R2 = 0.986). Oxidation rates were also positively correlated (R2 = 0.90) with the relative abundance of methanotrophic taxa as determined via 16SrRNA gene sequencing. In field samples, Type I methanotrophs (primarily Methylomonas and Crenothrix species) prevailed over Type II methanotrophs. This study showed that the activity of methanotrophic bacteria in landfill covers is strongly influenced by environmental factors, such as average air and ground temperature, soil moisture, methane exposure history, and characteristics of the landfill itself.