Waste activated sludge (WAS) produced from municipal
wastewater treatment plant is a problem with growing
importance because of its huge production, potentially
environmental risk and high cost for disposal. Anaerobic
digestion is considered to be the most energy efficient
method for destroying and stabilizing waste sludge and
methane byproduct as a form of fuel may reduce treatment
cost (Wang et al., 2013). Three stages are involved in the
anaerobic digestion of sludge, e.g. (i) hydrolysis of biological