Combined Electrochemical and Hypochlorite Pretreatment for Improving Solubilization and Anaerobic Digestion of Waste Activated Sludge: Effect of Hypochlorite Dosage

The electrochemical (EC) combined with hypochlorite (ClO-) pretreatment has been proven to be effective in improving disintegration of waste-activated sludge (WAS) and enhancing anaerobic digestion recently. The ClO- dosage had a significant impact on the performance of WAS solubilization and biogas production in terms of the disintegration degree (DDCOD), release of proteins (PNs) and polysaccharides (PSs), soluble nitrogen and phosphate, and subsequent anaerobic digestion. The results showed that a higher ClO- dosage was favorable to WAS solubilization and EC-ClO- pretreatment was able to rupture the floc structure and break cells apart. According to batch anaerobic digestion tests, the optimum ClO- dosage for EC-ClO- pretreatment was 0.6% (v/v), with up to 61.1% higher methane production compared to the unpretreated sludge after mesophilic anaerobic digestion for 40 days. Model-based analysis suggested that EC-ClO- pretreatment could enhance the hydrolysis process as well as methane potential. Moreover, EC-ClO- pretreatment at the ClO- dosage of 0.6% was economically feasible based on the economic evaluation.