Proper management of excess sludge resulted from wastewater treatment through waste activated sludge process is a big challenge to wastewater treatment plant operators in order to comply with the stringent disposal regulation. To meet this objective with co-benefit of bio-energy recovery, anaerobic technology is a promising technique. However, anaerobic digestion in particular hydrolysis phase is a rate-limiting process which requires a long digestion time to fully stabilize the sludge. Therefore, a numbers of pretreatments are usually applied to shorten the digestion time...