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 m3 reactor. 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 g VSS/gCODremoved and a growth yield of 0.132 g VSS/g COD, determined by seasonal sludge profiling. The bacterial communities, based on bacterial 16 S 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.