Abstract
This research was focused on assessing the effect of pH on methane oxidation by methanotrophs in compost biofilters. The batch experiments were run to study the dependency of maximum methane oxidation rate (Vmax) on pH. In addition, the impact of moisture content on CH4 oxidation at different pH values was evaluated. The results from batch experiments confirmed that pH 4.5 is the lowest pH in which methanotrophs are still able to oxidize methane. Laboratory column experiments were performed to investigate the behaviour of compost biofilters operating at different pHs. The results confirmed that columns operated at pH 4.5 were found to oxidize methane at a rate of 53 g/m2/d compared to 146 g/m2/d in the columns operated at pH 7.5 (neutral). Observing no oxidation activity for columns operated at pH 2.5 leads to the fact that too acidic condition was suspected to be the cause for inhibiting methanotrophs ability to oxidize methane. Also, DNA sequencing analysis on the samples from column experiments indicated that the more acidic environment tends to inhibit the growth and activity of methanotrophs type I while being ineffective to the growth of methanotrophs type II. Biofilter columns operated at pH 2.5 contained only 2% methanotrophs type I, compared to 55% of the total microbial population in columns operated at pH 7.5. This study has revealed that the MOB population changes in the biofilter with acidification compromised its capacity to oxidize methane demonstrating that compost biofilter cannot operate efficiently under acidic conditions.
