Electrochemically activated persulfate combined with tannic acid significantly improved sludge-dewatering performance: Sludge floc weight structure, Fe(II)/Fe(III), and organic component conversion

Sludge-dewatering effect is a key factor in sludge disposal. In this study, the conditioning system of electrochemically activated persulfate combined with tannic acid (EF-PDS/TA) was used to improve sludge-dewatering performance. Results showed that the sludge water content (Wc) and Specific resistance to filtration (SRF) decreased by 29.4 % and 93.3 %, respectively, under the optimal operating conditions, which significantly improved the sludge-dewatering effect. Through research, we found that SO4•− and ·OH were the main factors promoting the improvement in sludge-dewatering performance. After the reaction, the physicochemical properties of the sludge changed significantly, and the floc structure effectively cracked. Further analysis of Fe2+/Fe3+ conversion, EEM and FTIR showed that in the process of sludge conditioning, on the basis of EF promoting Fe2+/Fe3+ conversion through electron transfer between cathode and anode plates, TA addition further improved the conversion efficiency of Fe2+/Fe3+. The conversion rate was as high as 90 %, which improved the oxidation ability of sludge. The thermal energy generated by the EF ohmic heat effect can promote the complexation and precipitation of proteins in EPS by TA, and the energy can be effectively utilized. Moreover, EF and TA exerted a synergistic effect in promoting Fe2+/Fe3+ conversion and protein cleavage. Finally, the economic cost of the combined conditioning system was calculated, and the practical application value of the conditioning system was evaluated. The findings laid a theoretical foundation for further research in the field of advanced sludge oxidation. •The EF-PDS/TA combined conditioning system significantly improved sludge dewatering performance.•The combination of EF and TA can improve the conversion efficiency of Fe2+/Fe3+ and enhance the oxidation ability.•The ohmic heat effect of EF and the complexation of TA to protein further enhanced the oxidative cracking effect of EPS.