Operational performance of sludge blanket in clarification: effect of organic matter

Sludge blanket clarifiers (SBC) are presently an important unit of the water treatment process in Taiwan. Most studies concerning SBC have revolved around the treatment efficiency on turbidities. In Taiwan, most of the raw water sources for water treatment plants are contaminated with organic substances, which often interfere with the operation of SBC. In this study, the effects of organic materials on the formation of the sludge blanket and its performance were examined. Humic acid and salicylic acid were added in water to simulate natural waters polluted with organic materials of high and low molecular weights. The addition of humic acid accelerated the formation of a stable sludge blanket, however, the sludge blanket so formed contained less solid. Opposite effects were discovered with salicylic acid. Nevertheless, both organics enhanced the efficiency of turbidity removal by SBC. Large organic molecules were more easily removed by SBC. Coagulant addition had no significant effect on turbidity removal although the formation time for a sludge blanket was shortened. To successfully operate SBC, the occurrence and types of organic materials must be monitored.