Effect of adding alum sludge from water treatment plant on sewage sludge dewatering

Alum sludge from water treatment plant contained residual polyaluminum chloride (PACl) and large amount inorganic matters. Alum sludge acted as chemical conditioner and physical conditioner improved the sewage sludge dewatering. It indicated that the addition of alum sludge reduced the dosage of polyacrylamide (PAM) and decreased the moisture content of sewage sludge. The moisture content was 64% when the blend ratio was 1 kg/kg (dry alum sludge/dry sewage sludge) with plate-and-frame filter press. The 3D-excitation–emission matrix (3D-EEM) was used to analyze the sludge dewatering process. A mechanism hypothesis of adding alum sludge in sewage sludge for improving the sludge dewatering was proposed. Alum sludge implements the charge neutralization and adsorption bridging effect, provides friction and squeeze for crushing sludge particles even cell, and acts as skeleton builders in the sludge to improve the sludge dewatering.