Effect of extracellular polymeric substances on sludge reduction in the-humic-activated sludge anoxic-oxic-settling-anaerobic process

The wide utilization of the activated sludge process for treating domestic wastewater has resulted in the huge production of excess sludge, posing a serious disposal problem. In the present study, a humic-activated sludge-anoxic-oxic-settling-anaerobic (HS-A-OSA) process was used to study the function of humic activated sludge on the efficiency of sludge reduction. For this purpose, two-anoxic-oxic-settling-anaerobic (A-OSA) experimental devices were fabricated. Between the two devices, one device with the composite humic biological filler served as the HS-A-OSA process and the other device served as the comparison. The processes were operated with a mixed liquor suspended solids concentration of 3,000 mg/L for a period of 60 days. The sludge internal recycling was 100% from the sedimentation basin to the anaerobic sludge reaction basin, followed by the anoxic basin. The return sludge residence time was 5.5 h with both devices. During the operation period, 23.2% of excess sludge reduction was observed. The chemical oxygen demand and total nitrogen removal efficiencies improved in the HS-A-OSA process. Based on the variations in polysaccharide, protein, humic acid and extracellular polymeric substances concentrations in different basins, the main reason for improved sludge reduction was that the sludge disintegration velocity of the HS-A-OSA process was higher than the A-OSA process.