title: Biological oxidation of dissolved methane in effluents from anaerobic reactors using a down-flow hanging sponge reactor.
abstract: Anaerobic wastewater treatment plants discharge dissolved methane, which is usually not recovered. To prevent emission of methane, which is a greenhouse gas, we utilized an encapsulated down-flow hanging sponge reactor as a post-treatment to biologically oxidize dissolved methane. Within 3 weeks after reactor start-up, methane removal efficiency of up to 95% was achieved with a methane removal rate of 0.8 kg COD m(-3) day(-1) at an HRT of 2 h. After increasing the methane-loading rate, the maximum methane removal rate reached 2.2 kg COD m(-3) day(-1) at an HRT of 0.5 h. On the other hand, only about 10% of influent ammonium was oxidized to nitrate during the first period, but as airflow was increased to 2.5 L day(-1), nitrification efficiency increased to approximately 70%. However, the ammonia oxidation rate then decreased with an increase in the methane-loading rate. These results indicate that methane oxidation occurred preferentially over ammonium oxidation in the reactor. Cloning of the 16S rRNA and pmoA genes as well as phylogenetic and T-RFLP analyses revealed that type I methanotrophs were the dominant methane oxidizers, whereas type II methanotrophs were detected only in minor portion of the reactor.
authors.affiliation: Department of Social and Environmental Engineering, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashihiroshima, Hiroshima 739-8527, Japan. hatamoto@hiroshima-u.ac.jp
authors.forename: Masashi
authors.initials: M
authors.lastname: Hatamoto
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kindaichi
authors.forename: Noriatsu
authors.initials: N
authors.lastname: Ozaki
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Ohashi
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000235:genetics; D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology*; D008697:Methane / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010802:Phylogeny; D012150:Polymorphism, Restriction Fragment Length; D000644:Quaternary Ammonium Compounds / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012212:Rheology / Q000295:instrumentation*; D012995:Solubility; D014865:Waste Disposal, Fluid / Q000295:instrumentation*
chemical_list: D000644:Quaternary Ammonium Compounds; D012336:RNA, Ribosomal, 16S; D008697:Methane; D010100:Oxygen