Mechanism of zero valent iron and anaerobic mesophilic digestion combined with hydrogen peroxide pretreatment to enhance sludge dewaterability: Relationship between soluble EPS and rheological behavior

This study proposed a novel two-step conditioning strategy to enhance activated sludge (AS) dewatering performance. The method involved a zero valent iron (ZVI), anaerobic mesophilic digestion (AMD) process, and hydrogen peroxide (H2O2) oxidation. Response surface methodology (RSM) was applied to achieve optimum dewatering conditions. After the combined conditioning, dewatering was significantly better in the treated sludge compared to the raw AS. The specific resistance of filtration (SRF) of the treated sludge decreased to 2.48 × 1011 m/kg; this SRF level was 93.60% lower compared to the raw AS. The bound water content (BWC) decreased to 1.19 g/g dry solid (DS); this BWC level was 15.2% lower compared to the raw AS. The water content of the treated sludge cake decreased to 44.18 ± 0.46%. An economic analysis shows that ZVI-AMD-H2O2 can be used in real-world settings. Investigations of the underlying mechanisms showed that small block structures were formed after conditioning; viscosity and the colloidal forces of the sludge decreased; and organic matter and BWC were released from inner extracellular polymeric substances (EPS) layers to form soluble (SB)-EPS. This study illuminated the relationship between SB-EPS and the rheological behavior of AS. There is a high correlation coefficient between rheological parameter τy and N-containing substances in SB-EPS (R = −0.993, p