Enhanced Microbial Methane Oxidation in Landfill Cover Soil Amended with Biochar: Fid-Bau Portal

Enhanced Microbial Methane Oxidation in Landfill Cover Soil Amended with Biochar

Reddy, Krishna R. / Yargicoglu, Erin N. / Yue, Dongbei / Yaghoubi, Poupak

Abstract

Biochar amendment to landfill cover soil is proposed as an economical solution to reduce methane ( ${CH}_{4}$ ) emissions from landfills without gas-recovery systems or in conjunction with gas recovery for near-complete ${CH}_{4}$ 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 ${CH}_{4}$ into carbon dioxide ( ${CO}_{2}$ ). 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 ( $25 % {CH}_{4} : 25 % {CO}_{2} : 50 % N_{2}$ ) continuously for 4 months. Sampling ports along the length of the column were used to collect gas samples for measurement of the ${CH}_{4}$ and ${CO}_{2}$ concentrations. Additional isotopic analysis ( $δ^{13} C$ ) and temperature profiles were also used to evaluate the extent of ${CH}_{4}$ 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 ${CH}_{4}$ monoxygenase (pmoA) genes and infer methanotrophic activity. The pmoA results indicated that a higher number of ${CH}_{4}$ -oxidizing bacteria (methanotrophs) existed in the biochar-amended soil column, which also supported the observed higher rates of ${CH}_{4}$ oxidation compared with soil alone. Batch incubation experiments were conducted using column soils retrieved from different depths to determine Michaelis-Menten kinetic parameters for ${CH}_{4}$ oxidation. These results indicate that biochar amendment is effective in increasing methanotroph populations and promoting ${CH}_{4}$ oxidation.