Enhancement of biogas production efficiency using appropriate low‐temperature pretreatments of municipal treatment plants' excess sludge

Excess sludge in municipal plants normally contains high amounts of organic compounds (chemical oxygen demand [COD] of about 60,000 mg/L) and is capable of producing biogas. Anaerobic digestion is one of current methods to produce biogas. Municipal treatment plants' excess sludge contains high amounts of microbial cells with robust walls which inhibit microorganisms' access to the cells' organic content. This decreases biogas production efficiency as well as prolongs the time of anaerobic digestion process. In this study, a combination of the low‐temperature pretreatment techniques was used to increase biogas production efficiency in Isfahan South treatment plant. Through the mentioned techniques, which involve chemical, alkaline, microwave, and mechanical pretreatments, the cells' external structure is decomposed, and microorganisms' access to organic content is facilitated. All the experiments were carried out in two stages. The results of the first stage show that the highest amount of biogas efficiency is 365 mL/g COD for the sample under alkaline pretreatment by NaOH at 20 °C and pH = 12. The results of the second stage demonstrate that the highest rates of biogas production efficiency are obtained in samples under chemical pretreatment by KOH on secondary sludge at an ambient temperature (22 °C), and under 2400 H2O2 oxidation, respectively. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13072, 2019