Comparison of ultrafiltration characteristics between activated sludge and BAC sludge

The effects of powdered activated carbon (PAC) addition on the ultrafiltration characteristics of activated sludge were investigated. Particle size distribution of biological activated carbon (BAC) sludge shifted to the lower region compared with that of normal activated sludge due to the relatively smaller size of the added PAC. Although the total suspended solid (SS) of BAC sludge was higher than that of normal activated sludge and the floc size was reduced, the membrane permeability of BAC sludge was greatly enhanced compared with that of normal activated sludge. It is because the addition of PAC led to the decrease of not only the compressibility of sludge floc but the content of extracellular polymeric substances (EPSs) inside the microbial floc, which increased porosity of cake layer and thus enhanced the membrane flux. The flux increase in BAC sludge was more pronounced with the increase in the nitrification extent.