Understanding the synergistic mechanism of PAM-FeCl3 for improved sludge dewaterability

Hybrid flocculant polyacrylamide-ferric chloride (PAM-FeCl3) was developed to improve the dewaterability of sewage sludge and the dewatering performance, properties of treated sludge, composition and morphology distribution of extracellular polymeric substance (EPS) were investigated. The physicochemical properties of the PAM-FeCl3 were characterized, and its effectiveness as a sludge conditioner was evaluated. The results indicated that PAM-FeCl3 conditioning was able to promote sludge dewaterability. Simultaneously, PAM-FeCl3 neutralized the negative charges on the surface of sludge particles and increased the sludge floc size. Besides, PAM-FeCl3 also formed a rough and porous floc structure that reduced sludge compressibility. Meanwhile, the exciting emission matrix analysis suggested that PAM-FeCl3 can effectively disintegrate of EPS fraction in sludge and decompose the aromatic protein-like substances as well as the humic acid-like substances in EPS. Additionally, the larger sludge floc formation, electrostatic interaction and adsorption bridging effect resulted in compression of sludge structure and the decomposition of EPS fractions and improved sludge dewatering performance.