Peroxide/Zero-valent iron (Fe0) pretreatment for promoting dewaterability of anaerobically digested sludge: A mechanistic study

Peroxide/Zero-valent iron (Fe-0) was reported to promote dewaterability of anaerobically digested sludge (ADS), but the mechanism of how Peroxide/Fe-0 facilitates ADS dewatering is unknown. This study therefore aims to uncover the details of how Peroxide/Fe-0 elevates ADS dewaterability. Experimental results showed that with 0.6 g Fe-0/g TSS and 0.08 g peroxide/g TSS, capillary suction time, specific resistance to filtration, and time to filtration of ADS was 50.7 %, 41.4 %, and 54.4 % of that in the control, respectively. In this condition, water content of sludge cake decreased from 91.2 % +/- 0.5 % (the control) to 68.6 % +/- 1.3 %. The mechanism explorations revealed that the elevated dewaterability was mainly caused by role of H-center dot and Fe(II)/Fe(III) species during Peroxide/Fe degrees pretreatment. (OH)-O-center dot decreased the polysaccharides and proteins in extracellular polymeric substance (EPS), then injured the cytoderm & cytomembrane through the releases of lactate dehydrogenase and N-acetylglucosamine, and further facilitated the decrease of intracellular substances, which disengaged the water trapped in ADS. In addition, the cell lysis caused by (OH)-O-center dot facilitated forming macro-pores. Moreover, (OH)-O-center dot converted the conformational structure of extracellular proteins, which may strengthen the ADS hydrophobicity, promoting the discharge of unbound water and ADS flocculation. Meanwhile, Fe(II)/Fe(III) benefited aggregating the denatured ADS particulates.