Effect of Thermal Hydrolysis Temperature on Anaerobic Digestion, Dewatering and Filtrate Characteristics

Thermal hydrolysis is a digestion pretreatment process used to enhance digestion, increase loading rates and achieve a Class A product not subject to reactivation and regrowth of indicator bacteria. A study was performed to evaluate the effect of thermal hydrolysis temperature on subsequent digestion and the downstream parameters such as dewatering. Primary and secondary solids mixtures from the Blue Plains treatment plant in Washington, DC, was dewatered to about 16% solids, and thermally hydrolyzed at temperatures of either 130, 140, 150, 160, 170 °C. The thermally hydrolyzed solids were then fed to five separate, laboratory scale digesters using the same solids loading rate (10.5% TS) and an SRT of 15 days. The digesters were operated over a six month period to achieve steady state conditions. The higher thermal hydrolysis temperatures generally improved the volatile solids and COD reduction, but only by a few percentage points. The increased temperature did have a larger effect on viscosity of the solids and the dewaterability.