Differential impact of acidic and alkaline conditions on hydrothermal Pre-treatment, fermentation and anaerobic digestion of sludge

Anaerobic digestion and fermentation processes in wastewater sludge treatment are limited by several factors, including the slow breakdown of complex organic matter and solubilization of solids. In this study, thermochemical pretreatment of TWAS using high temperature (> 170 degrees C) was investigated to understand the impact of the pretreatment on the volatile fatty acids (VFA) production and its fractions during the fermentation process. Furthermore, the influence the thermochemical pretreatment on sludge disintegration and methane recovery was investigated. A range of acidic and alkaline conditions over the pH range of 4.5 to 10 was examined. Sludge (pH adjusted) was exposed to hydrothermal pre-treatment (HTP) at a temperature of 170 degrees C for 30 minutes. Pretreated samples were then subjected to batch fermentation and methane potential tests that revealed that acidic and alkaline conditions resulted in increased sludge solubilization during HTP. Acidic conditions were associated with a higher VFA production yield of up to 185 mg COD/g TCOD. Alkaline conditions led to a higher methane production yield where the maximum yield (276 mL CH4/g TCOD added) was found to occur at pH 10. Therefore, alkaline sludge used for fermentation has shown technical and economic feasibility for sludge carbon recovery.