evaluation of treatment characteristics and sludge properties in a uasb reactor treating municipal sewage at ambient temperature

the evaluation of treatment characteristics and sludge properties of an upflow anaerobic sludge blanket (uasb) process was investigated using a pilot-scale 1.15 m3reactor. the uasb, inoculated with digester sludge, was operated at a hydraulic retention time of 8 h at sewage temperatures ranging from 10.6 to 27.7 °c for more than 1100 days. the stable removal efficiencies for total codcr and ss were 63 ± 13% and 66 ± 20%, respectively. the average concentration of the retained sludge increased to more than 24.5 gss/l of the column volume after two years of operation. in summer, the water temperature increased above 20 °c, and biodegradation of solid organic matter was enhanced. the solid retention time was evaluated to be as long as 293 ± 114 days; this is sufficient for mineralisation of solid organic matter, as indicted by a low sludge conversion of 0.029 gvss/gcodremoved and a growth yield of 0.132 gvss/gcod, determined by seasonal sludge profiling. the bacterial communities, based on bacterial 16s rrna genes in the retained sludge, were significantly diverse. bacteroidetes and firmicutes were the dominant phyla of the decomposers of solid organic matter in the library. a ruminococcus-related clone detected in the firmicutes phylum acted as a cellulose decomposer.