Flow optimization and performance evaluation of bioreactors for municipal solid waste treatment

Abstract

ABSTRACTPerformance evaluation of the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was conducted in a laboratory scale test rig consisting of an upflow bioreactor with central substrate dispenser (UBCSD), an upflow anaerobic sludge blanket reactor (UASB) and a continuous stirred tank reactor (CSTR). An influent chemical oxygen demand (COD) concentration of 120,320 mg/l was utilized at steady state conditions. Hydraulic retention time (HRT) of 0–10 days were investigated throughout the experiment at a mesophilic temperature of 37 °C. Two kg of cow rumen content was used as inoculum (to improve microbial activities) and mixed with the organic waste at the initial stage before the reactors were loaded and allowed to run continuously for the stipulated range of HRT. During operation, substrate flow was observed to be more effective in the UBCSD than in the other reactors due to the action of the central substrate dispenser (CSD). The results obtained show the realization of a biogas production lag phase,, less than 24 hours. Cumulative biogas production for UBCSD, UASB and CSTR were 52915, 23550 and 28980 ml while their percentage COD reductions were calculated to be 95.2, 79.0 and 80.8% respectively. Modified Gompertz and Fenton's first order kinetic models were employed in the study for the analysis of the kinetic parameters. The values of the first order kinetic constant (k) of COD obtained for the reactors were 0.2857, 0.147 and 0.1708 respectively. UBCSD proved to be more efficient than the UASB and CSTR in terms of biogas production and COD reduction.