Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation

Abstract Flocculation is one of the most significant conditioning methods for sludge dewatering. In the present study, a novel flocculant CS-TA, which was prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve the performance of sludge dewatering. The findings indicate that the conditioning of CS-TA yielded the best dewatering performance at 30 mg g TS− 1 with water content of 59.78% and capillary suction time of 11.8s, compared to the Wsc of 98.2% and CST of 56.2s in raw sludge. The flocculation efficiency of different influencing factors were evaluated, indicating that CS-TA possessed the capacity for enhancing sludge dewaterability over a wide range of pH. Furthermore, the analysis of particle size implied that the addition of CS-TA favored the formation of larger particles. Meanwhile, the value of zeta potential of sludge was increased form − 24.29 ± 0.49 mV to -17.69 ± 0.35 mV after CS-TA conditioning, suggesting that CS-TA could improve sludge dewatering through charge neutralization, thus accelerating sludge filtration. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide (PS) and protein (PN) contents in EPS after CS-TA addition could increase the relative hydrophobicity of sludge, contributing to a decrease in water content. The results of FTIR reinforced the breakdown of hydrophic functional groups of PN and PS, leading to the sludge hydrophobicity. This study provides a comprehensive insights into the exploration of CS-TA for sludge dewatering and the maintenance of ecological security in an eco-friendly way.