Review on the Effects of Hydrothermal Pre-treatment of Thickened Waste Activated Sludge for Fermentation and Anaerobic Digestion Process

Municipal solid waste treatment and disposal have become one of the major concerns in waste management due to the excessive production of waste and higher-level of pollution. To address these challenges and protect the environment in sustainable ways, the hydrothermal pre-treatment technique coupled with anaerobic digestion becomes a preferred alternative technology that can be used for municipal solid waste stabilization and production of renewable energy. Hence this study was conducted to review the effect of hydrothermal pre-treatment of thickened waste activated sludge for fermentation and anaerobic digestion process. Accordingly, the majority of the results confirmed that there is a positive effect on the fermentation/acidification process and biogas production. Fermentation of TWAS at pre-treatment temperature ranges from 1600C to 1800C resulted up to 50% increase in VFAs yield compared to the raw sample. Whereas, for AD process, HTP in the range of 1750C to 2000C with 60 minute retention time was considered as the optimal condition for higher biogas production. 30% increase in biodegradability of waste activated sludge and higher than 55% of biogas production was obtained at the optimal range. Even though there is a direct relationship between increased HTP and the hydrolysis of WAS, a pre-treatment temperature range beyond 2000C alters the biogas production.