In situ generation of H2O2 for Fenton oxidation in electrochemical system for the enhancement of sludge dehydration

Fenton methods can effectively improve the dewatering performance of waste activated sludge (WAS). However, the explosive properties of H2O2 and demand of real-time dosing often incur transportation difficulties and high operational costs. It limits large-scale applications of Fenton processes on WAS dewatering. This study introduced the electro-Fenton technique by in-situ H2O2 generation into sludge dewatering for the first time. The responding surface methodology indicated that the yield of H2O2 could reach 10.11 mg/g DS (dry solids) at an optimal iron dose of 8 mg/g DS within 60 min. Compared to WAS, the capillary suction time (CST) and specific resistance to filtration (SRF) of treated sludge decreased from 87.7 ± 0.57 s and 3.67 × 1012 m/kg to 57.65 ± 0.92 s and 3.14 × 1012 m/kg, respectively. The mechanism investigations showed that electro-Fenton treatment reduced surface negative charge of WAS and caused disruption of extracellular polymeric substances and release of intracellular substances, which enhanced the flocculability and filtering performance, but decreased the moisture content, fractal dimension of WAS. Additionally, electro-Fenton treatment altered the secondary structure of proteins, which led to a loose structure of protein, benefiting the exposure of hydrophobic sites or groups in EPS proteins. Furthermore, the dewatering mechanisms involved in the electro-Fenton process were explored and the contribution of individual reactions in sludge dewatering was revealed. Overall, this work will provide both theoretical basis and practical knowledge for electro-Fenton sludge dewatering. [Display omitted] •In-situ generation of H2O2 for enhancing sludge dewatering is proposed.•Sludge dewaterability and filterability are demonstrated by water content, CST and SRF.•Fe3+ flocculation and ·OH oxidation are responsible for EPS disintegration.•Electro-Fenton process is the effective and inexpensive method for sludge handling.