Effect of zero-valent iron activated sodium hypochlorite on sludge dewatering performance

Abstract Zero-valent iron (ZVI) activated sodium hypochlorite (NaClO) was used to condition sludge to improve sludge dewatering, and the mechanism of its effect on sludge cracking and dewatering performance was systematically investigated. The dewatering performance of sludge was measured by detecting capillary suction time (CST) and sludge specific resistance (SRF). The evolution patterns of substances such as ammonia nitrogen (NH₄-N), chemical oxygen demand (COD), soluble phosphorus (SRP), extracellular polymeric substances (EPS) (including soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (LB-EPS)), the study quantitatively and qualitatively analysed the migration patterns of organic substances within and outside sludge cells, clarifying the intrinsic connection between sludge disintegration and dewatering performance. The results showed that under the optimal treatment conditions (pH = 3 + Fe powder 75mg/gDS+ NaClO100mg/gDS) the CST of ZVI-NaClO treated sludge decreased from 192.7 s to 51.3 s; the SRF decreased from 2.05×10 9 S 2 /g to 1.35×10 9 S 2 /g; and NH 4 -N in the supernatant increased from 4.14 mg/L to 8.64 mg/L; DP increased from 0.47 ug/mL to 1.12 ug/mL; and COD increased from 960.5 mg/L to 2323.8 mg/L. Additionally, the synergistic effect of acidified ZVI-NaClO can oxidise and degrade organic matter in sludge, reducing glutamic acid and humic acid components in the three types of EPS in sludge. Therefore, the acidified ZVI-NaClO system can disrupt the structure of sludge flocs and efficiently degrade extracellular polymers (EPS), significantly improving sludge dewatering efficiency and providing a physical-chemical foundation for subsequent sludge reduction and resource utilization.