The Thermal Hydrolysis Link to Anaerobic Digestion: The Heart of the DC Water Biosolids Program

The primary objectives of DC Water's Biosolids Management Program are to reduce the costs of solids processing and managing biosolids from the 1.4 million cubic meter per day (370-million-gallon per day (mgd))-capacity Blue Plains Advanced Wastewater Treatment Plant (BPAWTP), and to improve DC Water's sustainability profile. Costs will be reduced by largely replacing the current Class B lime stabilization process with a new Class A anaerobic digestion process that will reduce the quantity of solids hauled to beneficial use by more than 50 percent. Class A biosolids will be achieved through the use of the Thermal Hydrolysis Process (THP) preceding digestion. DC Water will further benefit through the recovery of biogas from the digestion process to generate electric power (reduce electric power purchases from the local utility) and produce steam to support the THP. This paper expands on the development of design concepts to meet the project objectives and the incorporation of these concepts within the Request for Proposals (RFP) for Design-Build (DB) services. Specifically, unique technical features that link the THP with the anaerobic digestion process for reliable operation will be presented and explained together with important design criteria. With the growing interest in thermal hydrolysis across the United States and internationally, this paper is intended to provide insight into important design considerations that are being incorporated into the DC Water thermal hydrolysis-anaerobic digestion process.The major solids processing elements of the Biosolids Program are included in a $210 million Design-Build project called the Main Process Train (MPT). Once in operation in 2014, the MPT will be the world's largest THP-anaerobic digestion installation.