Evaluation of potential inhibitors of methanogenesis and methane oxidation in a landfill cover soil

Biological methane (CH4) production is an anaerobic process, while CH4 consumption occurs predominantly under aerobic conditions; however, both processes can occur simultaneously in soil. Thus, field measurements of CH4 flux reflect the net result of both consumption and production reactions. Specific inhibitors of either CH4 consumption or production processes offer the opportunity for assessing the rates of these two processes independently. The objective of this work was to identify potential gaseous inhibitors of either CH4 oxidation or methanogenesis, and to evaluate the effect of inhibitor concentration on these two processes. For these studies, sieved cover soil from a municipal landfill was treated with a variety of compounds including acetylene (C2H2), ethylene (C2H4), ethane (C2H6), methyl chloride (CH3Cl) and methyl fluoride (CH3F). Each experiment consisted of six different treatments which included sterile soil, untreated soil and soil with test compound concentrations of 0.00%, 0.01%, 0.1% and 1%. Incubations were conducted under both aerobic and anaerobic conditions. Several compounds completely inhibited CH4 oxidation while not significantly influencing CH4 production; including C2H2 at 0.001%, C2H4 at 0.1%, and CH3F at 0.1%. One compound (CH3Cl) was unique; in that a concentration of 0.1% inhibited methanogenesis by 88.9% but CH4 oxidation was not significantly affected. We recommend the use of C2H2 or C2H4 for inhibition of CH4 oxidation, and CH3Cl for inhibition of methanogenesis.