Excess wastewater sludge collected from the recycling stream of the wastewater treatment process of the food industry is biomass that has a high potential to produce energy. This work examined the anaerobic digestion of wastewater sludge using a Clostridium strain isolated from the sludge as the seed sludge. Four pretreatments (acidification, basification, freezing/thawing, and sterilization) were applied on wastewater sludge, and their effects on biogas yields were examined. The suspension pH and the presence of strains in seed sludge and sludge substrate significantly affected the fermentation process for wastewater sludge. The pretreatment using basification, freezing and thawing, and sterilization enhanced methane production. A critical pH of above 5.5 was needed to initiate the methanogenesis stage. Acidification could yield control of the fermentation process of wastewater sludge to separate into two sequential stages.
