LAUSR

Abstract Dissolved methane in the effluent of anaerobic wastewater treatment processes is unrecovered and released into the atmosphere as methane, a greenhouse gas. To prevent methane emissions from effluent, a post-treatment system consisting of two closed downflow hanging sponge (DHS) reactors for the recovery and biological oxidation of dissolved methane was developed. More than 99% of the dissolved methane was completely eliminated using this system under ambient temperatures for 1 year. In this study, the methanotrophic community composition of the two closed DHS reactors was investigated. The performance of the closed DHS reactor was evaluated at different heights of the reactor in summer and winter. The clone libraries and T-RFLP analyses based on the pmoA gene revealed that type I and type II methanotrophs were present in the closed DHS reactors. Furthermore, type I methanotrophs showed wide diversity and contained uncultured phylogenetic clusters of methanotrophs (FWs and LWs), while type II methanotrophs were dominated by Methylocystis- and Methylosarcina-related clusters. The relative abundance of type II methanotrophs increased during winter. The type I methanotroph population dynamically changed with height of the reactor. These results demonstrate the important role of methanotrophs in removal of dissolved methane from upflow anaerobic sludge blanket effluent treating sewage.