Evaluation of thermal, thermal-alkaline, alkaline and electrochemical pretreatments on sludge to enhance anaerobic biogas production

• Thermal, alkali, thermo-alkali and electrochemical pretreatments were done to improve sludge AD.
• The electrochemical pretreatment was much more efficiency than other pretreatments.
• The highest biogas production (647 L/kg VS) was achieved after electrochemical pretreatment.
• The stabilization was achieved 15 days earlier than control after electrochemical pretreatment.

Anaerobic digestion was regarded as one of the ways to recover energy from waste activated sludge in this study. After applying thermal-, thermal-alkaline-, electrochemical- and alkaline-pretreatments to waste activated sludge to promote the digestion efficiency, biogas yield and volatile solid (VS) removal were investigated to evaluate the effectiveness of the pretreatments for the purpose. The highest biogas production (647 L/kg VS) was achieved after pretreatment by electrochemical method. The highest daily biogas production rate was obtained through alkaline pretreatment. Biogas production has no positive relationship with the solubilization degree of sludge. The highest VS removal rate could be got by the pretreatment of thermo-alkaline and electrochemical methods, and the sludge achieved the stabilization after the shortest digestion time with the treatment of electrochemical.