Evaluation of a Sludge Homogenization Pre-Conditioning Process for Increased Biogas Cogeneration Potential and Reduced Sludge Yields from Anaerobic Digestion

Abstract

Recently several technologies and process innovations have been proposed to reduce or eliminate the waste activated sludge (WAS) fraction resulting from treatment, or to render it more amenable to anaerobic digestion, a common sludge stabilization step, in order to maximize biogas production and the corresponding potential for energy cogeneration. Under WERF's 05-CTS-3 Evaluation of Processes to Reduce Activated Sludge Solids Generation and Disposal, data collected from the full-scale demonstration of MicroSludge TM , a WAS reduction technology, at the Des Moines Water Reclamation Facility was independently evaluated. Results indicate that sludge pre-treatment ahead of mesophilic anaerobic potential did improve biogas production rates and yields as well as volatile solids reduction under most of the tested conditions. Results also indicated lower odor generation potential for the MicroSludge TM pretreated sludge before co-digestion of primary and WAS, and an ability to destroy filamentous organisms that could be precursors to foaming problems in anaerobic digesters. However this technology did not have a significant impact on pathogen reduction ahead of the anaerobic digestion process MicroSludge TM (developed by Paradigm Environmental Technologies) is a chemical and mechanical pre-treatment process that conditions thickened waste activated sludge (TWAS) to increase both the rate and the extent that TWAS is degraded in an anaerobic digester. The process uses caustic pre-treatment to weaken cell membranes, followed by a high-pressure homogenizer, or "cell disrupter", to provide a large and sudden pressure drop to burst the cells in TWAS. The premise of the process is that by rupturing cell membranes and releasing the cytoplasm of TWAS, the concentration of soluble solids from TWAS is greatly increased, potentially enabling anaerobic digesters to convert a larger portion of TWAS to biogas and at a faster rate (Stephenson and Dhaliwal, 2000). A process flow diagram of a typical installation of a MicroSludge TM cell disrupter and a central processing skid with the unit processes and pumps is illustrated in Figure 1. Control Feed Average % MicroSludge TM Feed Average % COD WEFTEC 2010