Comparison of start-up of an upflow anaerobic sludge blanket reactor and a polyurethane carrier reactor
The start-up and performance of an Upflow Anaerobic Sludge Blanket (UASB) reactor and a Polyurethane Carrier Reactor (PCR) was investigated under similar operational conditions. The presence of polyurethane cubes as a carrier material in the PCR resulted in fast reactor start-up due to quick immobilization of methanogenic associations. Start-up of the UASB was slower compared to the PCR, which was mainly reflected in a lower biogas production and acetate degradation efficiency. However, when enough biomass had accumulated in the UASB reactor after 15 weeks of operation, the performance of the two reactors was almost the same in terms of biogas production and volatile fatty acids degradation. Efficient VFA degradation (about 90%) and biogas production (5.2 l/l.d) were achieved at an organic loading rate of 13.2 g/l.d) and HRT of 6 h. When hydraulic retention time was subsequently reduced from 6 to 2 h, the performance of the UASB reactor was better than that of the PCR. The inferior performance of the PCR may have been attributed to channelling of the influent in the reactor at high liquid flow rate.