Pilot-scale study of enhanced anaerobic digestion of waste activated sludge by electrochemical and sodium hypochlorite combination pretreatment

• Effects of electrochemical and NaClO treatment on anaerobic digestion was studied.
• Sludge got stabilization 9 d earlier with electrochemical pretreatment compared with control.
• 48.97% of VS reduction treated by electrochemical is high compared to the control of 42.64%.
• The biogas yield increased by 1.83 times compared to that of unpretreatment digester.

A pilot-scale study was carried out to evaluate the sludge anaerobic digestion in Qingpu wastewater treatment plant in Shanghai, China. This performance of sludge anaerobic digestion with electrochemical and sodium hypochlorite combination pretreatment was assessed by VS removal and biogas production. The results showed that the system with the pretreatment of electrochemical and sodium hypochlorite combination method performed better than the control. Electrochemical and sodium hypochlorite combination pretreatment significantly enhanced the biogas yields from sludge anaerobic digestion and shortened the stabilization period. The changes of the sludge composition resulted in an increase in both biogas and methane production by 1.83 times and 1.89 times, respectively. Up to 48.97% of VS reduction could be obtained with the electrochemical and sodium hypochlorite combination pretreatment compared to the control of 42.64%. Furthermore, sludge anaerobic digestion with the electrochemical and sodium hypochlorite combination pretreatment could reach stabilization 9 days earlier than that without pretreatment. Processes showed that the electrochemical and sodium hypochlorite combination pretreatment was feasible and had the potential to provide environmental and economic benefits for wastewater treatment plants in China.