Effect of microwave pretreatment in presence of NaOH on mesophilic anaerobic digestion of thickened waste activated sludge

► We evaluate the effect of microwave with NaOH treatment on digestibility of sludge. ► Our findings show better performance in the anaerobic digester with pretreatment. ► The solubilization in pretreated sludge was 18 times higher than in raw sludge. ► The relative improvement of digester properties increased as HRT was reduced. ► Microwave/alkali pretreatment is effective in anaerobic biodegradability of sludge.