Enhancing the methane potential of the liquor obtained from enzymatic pre-treatment of sewage sludge by the addition of glycerin

Abstract

Inverted Phase Fermentation is a method for thickening sewage sludge that results in a clarified phase beneath a thickened fraction. An increased hydrolysis rate is obtained in both phases. The liquid phase or liquor was digested in UASB reactors. The optimum methane yield was obtained for hydraulic retention time of 1 day (0.32 m3 CH4/kg VS, 2.31 m3 CH4/m3reactor day). When this liquor was co-digested with 1% (v/v) crude glycerin, the optimum methane yield was obtained when operating at hydraulic retention time of 2 days (0.67 m3 CH4/kg VS, 2.76 m3CH4/m3reactor day). Co-digestion of the liquor with crude glycerin not only improved specific methane yield, but also organic matter biodegradation (up to 89% total COD and up to 76% VS removal).