Inhibitory effects of acidic pH and confounding effects of moisture content on methane biofiltration

This study focussed on evaluating the effect of hydrogen sulfide (H₂S) on biological oxidation of waste methane (CH₄) gas in compost biofilters, Batch experiments were conducted to determine the dependency of maximum methane oxidation rate (V_max) on two main factors; pH and moisture content, as well as their interaction effects. The maximum V_max was observed at a pH of 7.2 with decreasing V_max values observed with decreasing pH, irrespective of moisture content. Flow-through columns operated at a pH of 4.5 oxidized CH₄ at a flux rate of 53g/m²/d compared to 146g/m²/d in columns operated at neutral pH. No oxidation activity was observed for columns operated at pH 2.5, and DNA sequencing analysis of samples led to the conclusion that highly acidic conditions were responsible for inhibiting the ability of methanotrophs to oxidize CH₄. Biofilter columns operated at pH 2.5 contained only 2% methanotrophs (type I) out of the total microbial population, compared to 55% in columns operated at pH 7.5. Overall, changes in the population of methanotrophs with acidification within the biofilters compromised its capacity to oxidize CH₄ which demonstrated that a compost biofilter could not operate efficiently in the presence of high levels of H₂S.