Effect of inoculum concentration on start-up of UASB reactor

Three identical laboratory upflow anaerobic sludge blanket reactors were operated under various initial sludge concentrations (10, 30 and 60 gVSS/L-reactor) to determine the effect of sludge concentration on the start-up rate. It was hypothesised that increasing the sludge concentration would increase the formation of rapid settling granules or floes. A sludge concentration of 30 gVSSIL-reactor gave better COD removal of 88% (at COD loading of 5 g/L) than 10 gVSS/L -reactor (58%). Increasing the sludge concentration to 60 gVSS/L -reactor resulted in greater washout with a slight improvement in COD reduction (90%). When the COD loading was increased to 20 g/L (week 4) removal of 79% was still achieved in the reactor with high initial sludge concentration compared to low initial sludge concentration (51% removal). Washout detracted from reactor performance, so of the three concentrations tested 30 gVSS/L -reactor appeared to be optimal