Enhanced Microbial Methane Oxidation in Landfill Cover Soil Amended with Biochar

Abstract

Biochar amendment to landfill cover soil is proposed as an economical solution to reduce methane (CH4) emissions from landfills without gas-recovery systems or in conjunction with gas recovery for near-complete CH4 removal. In this study, column experiments were conducted to simulate the effects of biochar amendment to landfill cover soil and investigate whether biochar amendment can promote the growth of methanotrophic bacteria able to oxidize CH4 into carbon dioxide (CO2). Acrylic columns were packed with coarse gravel (gas-distribution layer) and then filled with either soil or 20% biochar/80% soil. The columns were fed humidified synthetic landfill gas (25% CH4:25% CO2:50% N2) continuously for 4 months. Sampling ports along the length of the column were used to collect gas samples for measurement of the CH4 and CO2 concentrations. Additional isotopic analysis (δ13C) and temperature profiles were also used to evaluate the extent of CH4 oxidation as a function of depth. The deoxyribonucleic acid (DNA) extracted from the soil and biochar-amended soil samples collected at different depths of the columns were subjected to quantitative polymerase chain reaction (QPCR) analysis to determine the abundance of the particulate CH4 monoxygenase (pmoA) genes and infer methanotrophic activity. The pmoA results indicated that a higher number of CH4-oxidizing bacteria (methanotrophs) existed in the biochar-amended soil column, which also supported the observed higher rates of CH4 oxidation compared with soil alone. Batch incubation experiments were conducted using column soils retrieved from different depths to determine Michaelis-Menten kinetic parameters for CH4 oxidation. These results indicate that biochar amendment is effective in increasing methanotroph populations and promoting CH4 oxidation.