Improvement in biomass characteristics and degradation efficiency in modified UASB reactor treating municipal sewage: a comparative study with UASB reactor

Abstract Low strength wastewaters (LSWs) are difficult to degrade efficiently in the upflow anaerobic sludge blanket (UASB) reactor. The possible reasons for poor treatment of LSWs in UASB are: (i) low mixing due to low biogas production (ii) frequent biomass washout at higher hydraulic loading rate due to low settleability of biomass. In the present study, lab scale UASB reactor and modified upflow anaerobic sludge blanket (MUASB) reactor were operated with municipal sewage containing chemical oxygen demand (COD) in range of 180–210 mg L−1 as LSW at three different hydraulic retention times (HRTs) of 8, 6, and 4 h. The changes in the biomass characteristics as well as degradation efficiency were compared with respect to time. During this operation, samples of biomass were taken from both reactors to measure total suspended solids (TSS), settling velocity, granular size and specific methanogenic activity (SMA). The overall COD removal in MUASB reactor was higher compared to UASB (84 and 67% respectively). After 150 days of operation, the settling velocity and SMA of MUASB biomass increased, but no significant change in settling velocity and SMA of UASB biomass was observed. The study shows that MUASB could be preferred over UASB for the treatment of municipal sewage as LSW. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.