Combination of electrochemical and Fe2+ -activated persulfate oxidation for improving the dewaterability of aerobically digested sludge

Abstract

This study uses two methods to condition aerobically digested sludge: electrochemical-Fe²⁺-activated PDS (E/Fe²⁺/PS) and Fe²⁺-activated PDS (Fe²⁺/PS). Due to the results of current studies, a comparison has been provided between these two methods to indicate the beneficial effect of applying electrical voltage on the generation of sulfate radicals and improving the dewaterability of sludge. TTF is measured to evaluate the efficiency of these conditioning methods. The Fe²⁺/PS process in the optimal retention time of 17 minutes decreased TTF by 50%. The E/Fe²⁺/PS process reduced TTF by 64% in the optimal retention time of 13 minutes and the voltage of 5V. In both methods, the optimal Persulfate concentration was 40mg/gDS. Sludge conditioning with both processes reduced compressibility and increased filtration yield, indicating that both methods can act as a physical conditioner (skeleton builder). Also, both pretreatments decreased the bound water of sludge, suggesting that both processes can serve as chemical conditioners, too. However, the E/Fe²⁺/PS process performs better in sludge conditioning when the concentrations of persulfate and iron are low. This phenomenon can be attributed to the regeneration of ferrous ions (Fe²⁺), acting as compensatory agents for the insufficiency of Fe²⁺, thereby ameliorating sludge dewatering efficiency.