title: The role of methanogens in acetic acid production under different salinity conditions.
abstract: In this study, a fed-batch acidogenic reactor was operated at a 3 d hydraulic retention time (HRT) and fed with alkaline pre-treated sludge to investigate salinity effects on methanogens' abundance, activities and their consumption of produced acetic acid (HAc) and total volatile fatty acids (VFAs). The salinity concentration was increased step-wise by adding sodium chloride. At 3‰ (parts per thousand) salinity, the average produced volatile fatty acids (VFAs) concentration was 2410.16 ± 637.62 mg COD L(-1) and 2.70 ± 0.36 L methane was produced daily in the acidogenic reactor. Further batch tests indicated methanogens showed a HAc degradation rate of 3.81 mg COD g(-1) VSS h(-1) at initial HAc concentration of 1150 mg COD L(-1), and showed tolerance up to 16‰ salinity (3.76 g Na(+) L(-1)) as indicated by a constant HAc degradation rate. The microbiological study indicated this can be related to the predominance of acetate-utilizing Methanosarcinaceae and Methanomicrobiales in the reactor. However, with salinity increased to 20‰ and 40‰, increases in VFAs and HAc production and decreases in methane production, methanogens population, acidogenic bacteria population and acidification extent were observed. This study demonstrated presence of acetate-utilizing methanogens in an acidogenic reactor and their high tolerance to salinity, as well as their negative impacts on net VFAs production. The results would suggest the presence of methanogens in the acidogenic reactor should not be ignored and the recovery of methane from the acidogenic reactor needs to be considered to avoid carbon loss.
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
authors.forename: Keke
authors.initials: K
authors.lastname: Xiao
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
authors.forename: Chenghong
authors.initials: C
authors.lastname: Guo
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
authors.forename: Yogananda
authors.initials: Y
authors.lastname: Maspolim
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore. Electronic address: ZhouYan@ntu.edu.sg.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore. Electronic address: WJNg@ntu.edu.sg.
authors.forename: Wun Jern
authors.initials: WJ
authors.lastname: Ng
mesh_terms: D019342:Acetic Acid / Q000032:analysis*; D000693:Anaerobiosis; D019149:Bioreactors / Q000382:microbiology*; D002244:Carbon / Q000032:analysis / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000032:analysis / Q000378:metabolism; D017018:Methanomicrobiales / Q000254:growth & development*; D054712:Salinity; D012722:Sewage / Q000737:chemistry / Q000382:microbiology*; D018508:Water Purification / Q000379:methods*
chemical_list: D005232:Fatty Acids, Volatile; D012722:Sewage; D002244:Carbon; D008697:Methane; D019342:Acetic Acid
keywords: Acclimation; Acetic acid; Acidogenic fermentation; Methanogens; Salinity inhibition