Enhanced sludge dewaterability using a bifunctional hybrid coagulant.

The combination of coagulation and addition of skeleton builder is a popular pretreatment method to improve the dewaterability of sludge. In this study, a novel bifunctional inorganic/organic hybrid coagulant (CS-Si@ATP) was designed and obtained by chemically coupling a cationic starch (CS) with a popular clay, that is, attapulgite (ATP), via a silane coupling agent (APTES) for one-step conditioning of sludge. CS-Si@ATP can evidently enhance the sludge dewatering performance compared with CS, ATP, and their simple combination due to the distinct dual functions of this hybrid coagulant. The tentacle-like cationic CS in CS-Si@ATP shows efficient charge neutralization effect to aggregate and precipitate the suspended solids for further formation of compact sludge cakes. Meanwhile, the internal ATP with a stable and rigid structure acts as the skeleton builder to notably improve the filterability and permeability of the sludge cakes. The synergistic effects of CS and ATP in CS-Si@ATP, i.e., the charge neutralization of CS and the skeleton construction of ATP, cause the evidently enhanced sludge dewaterability, with a filter cake moisture content approximately 78.30% after the mechanical dewatering at 0.05 MPa. In comparison with the traditional two-step combination process by separated addition of CS and ATP, the one-step addition of CS-Si@ATP can reduce the required ATP dose nearly an order of magnitude. Thus, CS-Si@ATP has the notable advantages of simple operation, efficient utilization of ATP and evident reduction of disposal cost. This study provides an environmentally friendly and cost-effective coagulant to further improve the dewaterability of sludge.