Evaluation of Process Performance and Sludge Properties of an up-flow staged Sludge Blanket (USSB) reactor for Treatment of Molasses Wastewater

A combination of an acidification reactor and an up-flow staged sludge bed (USSB) reactor was applied to treatment of molasses wastewater. The USSB, equipped with three gas solid separators, was selected because of superior organic removal by means of good retention of granular sludge. The combined system was continuously operated at mesophilic (35°C) conditions for 600 days. The USSB achieved a high organic removal rate of 37 kgCOD/m 3 day (organic loading rate of 43 kgCOD/m 3 day with 86.2% COD removal). The USSB retained high sludge concentration of approximately 58 gVSS/L based on the reactor volume. The retained granular sludge had good settle-ability with a sludge volume index (SVI) of 4 to 20 ml/ gSS. The retained sludge possessed a sufficient level of methanogenic activities for acetate (1.2 gCOD/gVSS day) and for hydrogen (1.7 gCOD/gVSS day). Analysis of microbial community revealed that genus Methanobacterium as hydrogen utilizing methanogen and order Methanosarcinales as acetate utilizing methanogen were detected in the retained sludge of the USSB reactor. The superior performance of the USSB was attributed to good retention of a large amount of granular sludge with high methanogenic activity.