Significances of deflocculated sludge flocs as well as extracellular polymeric substances in influencing the compression dewatering of chemically acidified sludge

Abstract

Abstract Sludge extracellular polymeric substances (EPS) are frequently reported as a main factor determining sludge dewatering, but the role of sludge floc structure in influencing sludge dewatering has not been fully understood. The dewatering of chemically acidified sludge was investigated to reveal the respective role of sludge floc structure and sludge extracellular polymeric substances (EPS) in influencing the removal rate of moisture (i.e., dewatering rate) and the removal amount of moisture (i.e., dewatering extent) of acidified sludge. During the chemical acidification of sludge, serious lysis of microbial cells in sludge was induced to result in a decrease of moisture content in dewatered sludge cake, from 81.8% to only 66.7%, but both the significant increase of sludge outer layer EPS content and the deflocculated sludge flocs led to a serious deterioration of dewatering rate of acidified sludge. Further studies revealed that either decreasing sludge outer layer EPS content or modifying the deflocculated sludge flocs could improve both filtration and expression stages of compression dewatering of acidified sludge to enhance the dewatering rate of acidified sludge. Especially, only 5 mg/g dry solid of anionic synthetic organic polyelectrolyte polyacrylic acid (PAA) could condition acidified sludge to improve its dewatering rate at both filtration and expression dewatering stages through re-flocculating the deflocculated flocs in acidified sludge. Therefore, the deflocculated sludge floc structure is as significant as extracellular polymeric substances in influencing the compression dewatering of acidified sludge, and the treatment of sewage sludge through chemical acidification and followed conditioning using synthetic organic polyelectrolyte PAA can enhance the dewatering extent as well as dewatering rate.