Dewaterability of sewage sludge conditioned with a graft cationic starch-based flocculant: Role of structural characteristics of flocculant

Coagulation/flocculation is one of the most extensive and cost-effective pretreatments to improve the dewaterability of sludge in water treatment plants. In this study, three series of graft cationic starch (St)based flocculants with distinct structural characteristics including charge density (CD), graft-chain length (L), and graft-chain distribution (N) were synthesized by graft copolymerization of [(2-methacryloyloxyethyl) trimethyl ammonium chloride] and acrylamide onto St backbone. The structural effects of these Stbased flocculants on the sludge dewaterability have been quantitatively analyzed by using a second-order polynomial model according to phenomenological theory. The predicted dewatering performance and optimal dose were fully consistent with the experimental results. On the basis of this established model, the dewatering mechanisms were discussed in detail by combination of the analysis of the changes in filter cake moisture content, specific resistance of filtration, bound water content, compression coefficient, extracellular polymeric substances fractions and components, spatial distributions of proteins and polysaccharides, microstructures of sludge cake, and flocs properties in the dewatering process. This graft St-based flocculant, with the structural characteristics of high CD, long L, and low N, exhibited superior sludge dewaterability because of the enhanced charge neutralization and bridging flocculation effects. Among these three structural factors, CD played a more important role in improvement of sludge dewaterability than L and N due to the dominant effect of charge neutralization. This study provided a better understanding of structure-activity relationship of these grafting modified flocculants, which was of significant guidance for the exploit and design of novel and efficient flocculants for improvement of sludge dewaterability. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Coagulation/flocculation is an extensive and cost-effective pretreatment method to improve sludge dewaterability in water treatment plants. Three series of graft cationic starch-based flocculants were synthesized, and their structural effects on sludge dewaterability were analyzed quantitatively. Among the structural factors, charge density was found to play a more important role in enhancing sludge dewaterability.