Calcium hypochlorite assisted energetically efficient sonic hydrolysis of waste activated sludge for cost effective biogas production

The extracellular polymeric substances (EPS) in waste activated sludge (WAS) act as a protective barrier and limits the disintegration potential of the pretreatment process. In this study, an attempt was made to improve the disintegration potential of the pretreatment process by phase separating it into deflocculation and disintegration. In deflocculation, Calcium hypochlorite (Ca(ClO)(2)) was used to remove EPS, and in disintegration, ultrasonication was used to solubilize the WAS. An effective deflocculation was achieved at an optimum Ca(ClO)(2) dosage of 0.02 g/g SS and a time of 15 min. The results of calcium hypochlorite-induced ultrasonication (CH-UP) revealed a substantial enhancement in suspended solids (SS) reduction, with a remarkable 18.42 % reduction compared to 11.57 % of ultrasonic pretreatment (UP). Additionally, the biodegradability of the sludge was evaluated using the biochemical methane potential test. The results showcased a notable increase in methane production, with CH-UP exhibiting a methane yield of 92.5 mL/g COD, compared to 68.2 mL/g COD for UP alone. Energy analysis reveals a higher and positive net energy production of 171.5 kWh/ ton for CH-UP compared to UP (-13.9 kWh/ton).