Quaternization-based graft modification of straw fibers for conditioning the sludge dewatering performance

Abstract

ABSTRACT Extracellular polymeric substances (EPS) are a critical influencing factor in sludge dewatering. Disrupting such EPS contributes to the release of bound water in sludge, enhancing the sludge dewatering performance. In this study, quaternized straw fibers that are destructive to the EPS structure and components in active sludge were prepared using heterogeneous free radical graft polymerization. Straw fibers, dimethyl diallyl ammonium chloride (DMDAAC), ammonium persulfate (APS), and acrylamide (AM) were taken as the substrate, grafting monomer, catalyst, and cross-linking agent, respectively. The optimal processing conditions determined for the DMDAAC-based quaternization and graft modification of straw fibers were as follows: reaction temperature of 60 °C, reaction time of 5 h, 0.1 g of catalyst APS dosage per g of straw, and 3 mL of DMDAAC dosage per g of straw. The optimal processing conditions yielded 1.335 g of modified straw fibers per g of straw, 33.5% grafting rate, and 31.70% substitution of the quaternary ammonium groups. They improved the filtering performance of the sludge. The capillary suction time was conditioned from 243.3 ± 22.6 s in the original sludge to 134.5 ± 34.45 s. The specific resistance to filtration was reduced from 8.82 ± 0.51 × 1012 m/kg in the original sludge to 4.59 ± 0.23 × 1012 m/kg.