title: Closed DHS system to prevent dissolved methane emissions as greenhouse gas in anaerobic wastewater treatment by its recovery and biological oxidation.
abstract: Anaerobic wastewater treatment has been focused on its eco-friendly nature in terms of the improved energy conservation and reduction in carbon dioxide emissions. However, the anaerobic process discharges unrecovered methane as dissolved methane. In this study, to prevent the emission of dissolved methane from up-flow anaerobic sludge blanket (UASB) reactors used to treat sewage and to recover it as useful gas, we employed a two-stage down-flow hanging sponge (DHS) reactor as a post-treatment of the UASB reactor. The closed DHS reactor in the first stage was intended for the recovery of dissolved methane from the UASB reactor effluent; the reactor could successfully recover an average of 76.8% of the influent dissolved methane as useful gas (containing methane over 30%) with hydraulic retention time of 2 h. During the experimental period, it was possible to maintain the recovered methane concentrations greater than 30% by adjusting the air supply rate. The remaining dissolved methane after the first stage was treated by the next step. The second closed DHS reactor was operated for oxidation of the residual methane and polishing of the remaining organic carbons. The reactor had a high performance and the influent dissolved methane was mostly eliminated to approximately 0.01 mgCOD L(-1). The dissolved methane from the UASB reactor was completely eliminated--by more than 99%--by the post-treatment after the two-stage closed DHS system.
authors.affiliation: Department of Environmental System Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan. matsuura@stn.nagaokaut.ac.jp
authors.forename: N
authors.initials: N
authors.lastname: Matsuura
authors.forename: M
authors.initials: M
authors.lastname: Hatamoto
authors.forename: H
authors.initials: H
authors.lastname: Sumino
authors.forename: K
authors.initials: K
authors.lastname: Syutsubo
authors.forename: T
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: A
authors.initials: A
authors.lastname: Ohashi
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000378:metabolism; D019149:Bioreactors; D005160:Facility Design and Construction; D017752:Greenhouse Effect; D008697:Methane / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D014865:Waste Disposal, Fluid / Q000295:instrumentation* / Q000379:methods*
chemical_list: D008697:Methane