[Sludge Conditioning Performance of Polyaluminum, Polyferric, and Titanium Xerogel Coagulants]

The sludge conditioning performance of inorganic Al, Fe, and Ti coagulants were systematically compared in terms of specific resistance to filtration (SRF), the content of protein and polysaccharide in extracellular polymeric substances (EPS), the change in three-dimensional excitation emission matrix fluorescence (3D-EEM), the molecular weight of organic matter in EPS, and the floc size and surface morphology. The sludge conditioning ability and the mechanism were systematically analyzed. The results showed that the sludge conditioning ability of the three inorganic coagulants was in the order of polyaluminum chloride (PAC) > titanium xerogel coagulant (TXC) > polymeric ferric sulfate (PFS). After conditioning, the contents of protein and polysaccharide in the EPS were greatly reduced, especially in the loosely bound EPS (LB-EPS). The combined capacity for coagulation between TXC/PFS and organic matter was stronger than that of PAC. The content of polysaccharide in LB-EPS was the key factor affecting the sludge dewatering performance but not the coagulated floc size. The surface charge and the chelating ability with organic matter co-determined the sludge dewatering ability. The organic cationic polymer, polyacrylamide (PAM), made the sludge aggregate via charge neutralization. However, the use of PAM alone was not a good choice owing to the low dewatering ability and the loose sludge structure. The results here are helpful for the selection of suitable coagulants for sludge conditioning.