HYDROTHERMAL PRETREATMENT OF DEWATERD SLUDGE AND BIOGAS PRODUCTION IN AN ANAEROBIC MEMBRANE BIOREACTOR FOR CENTRALIZED DIGESTION

Abstract

 A new process for centralized anaerobic digestion of dewatered sludge is proposed in this study. Hydrothermal treatment of dewatered sludge was performed. Water was then added to the hydrothermally treated sludge and dewatering was performed to extract organic matter to the liquid phase. The resulting liquid was used as a substrate for an anaerobic membrane bioreactor (AnMBR) to produce biogas. The solubilization ratio of dewatered sludge was 20.9% after 1 hour of hydrothermal treatment at 150°C. The water content of the dewatered residue was 76.6%. The organic-rich liquid was recovered and fed to the AnMBR. The AnMBR was operated by shortening the HRT step by step. As a result, the HRT could be shortened to 5 days without accumulation of volatile fatty acids. The biogas production rate and the methane yield were 1.74 L/L/d and 0.25 L/g-COD, respectively, when the HRT was 5 days. When the HRT was shortened to 2 days, the transmembrane pressure reached 50 kPa due to membrane fouling. Membrane cleaning at the end of the AnMBR operation indicated that reversible fouling was dominant.