title: Effects of solids retention time on methanogenesis in anaerobic digestion of thickened mixed sludge.
abstract: When a bench-scale digester fed thickened mixed sludge was operated over an SRT range of 4-20 days, removal efficiencies for total chemical oxygen demand and volatile suspended solids declined with decreasing SRT (especially <10 days), but methanogenesis was stable for SRT as low as 5 days. Quantitative PCR analyses showed that methanogens declined steadily for SRT<10 days, with the acetate-cleaving Methanosaetaceae becoming more dominant. Clone-library analyses indicated significant shifts in bacterial population from 20 to 4 day SRT: declining Chloroflexi (28 to 4.5%) and Syntrophomonas (9 to 0%), but increasing Bacteroidetes (12.5 to 20%) and two acetogenic genera belonging to the phyla Firmicutes and Spirochaetales (6.3 to 12%). Thus, the decrease in the apparent hydrolysis constant (khyd-app) with higher SRT and the process limiting size of Methanosaetaceae with the lower SRT are proactive signs for defining rate limitation in anaerobic digestion.
authors.affiliation: Center for Environmental Biotechnology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, United States.
authors.forename: Il-Su
authors.initials: IS
authors.lastname: Lee
authors.forename: Prathap
authors.initials: P
authors.lastname: Parameswaran
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
mesh_terms: D000693:Anaerobiosis; D001105:Archaea / Q000254:growth & development; D001419:Bacteria / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D056804:Biofuels / Q000032:analysis; D057919:Biological Oxygen Demand Analysis; D019149:Bioreactors / Q000382:microbiology; D005232:Fatty Acids, Volatile / Q000032:analysis; D015723:Gene Library; D006868:Hydrolysis; D007700:Kinetics; D008697:Methane / Q000032:analysis*; D009930:Organic Chemicals / Q000302:isolation & purification; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012037:Refuse Disposal / Q000379:methods*; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology*; D012995:Solubility; D013997:Time Factors; D014835:Volatilization
chemical_list: D056804:Biofuels; D005232:Fatty Acids, Volatile; D009930:Organic Chemicals; D012336:RNA, Ribosomal, 16S; D012722:Sewage; D008697:Methane