A Perfect Synergy of Pathogen Reduction and Renewable Energy – The Columbus Water Works CBFT³ and Cogeneration System Project

Abstract

Brown and Caldwell and Columbus Water Works (CWW) located in Columbus, Georgia, have led the development of a new Class A digestion process named Columbus Biosolids Flow-Through Thermophilic Treatment (CBFT 3 ). The new process offers a low-cost option -as compared to other EPA approved processes -for upgrading existing anaerobic digestion facilities from Class B to Class A Biosolids. To achieve Class A pathogen reduction, an existing completely-mixed mesophilic digester was converted to operate at thermophilic temperature and is followed by two plug flow reactors (PFRs) operated in series to achieve a minimum contact time of 30-minutes. Sludge is then further digested in the two existing mesophilic digesters to achieve additional volatile solids destruction.This project also incorporates a combined heat and power (CHP) or cogeneration system that will generate about 40-percent of the plant's electricity demand as renewable green power using digester gas that would otherwise be flared. Heat recovered from the cogeneration system will be used to heat the digestion process in its entirety. Construction of the CBFT 3 and Cogeneration System Project is complete and process start-up activities are underway. This paper presents a summary of project goals and benefits, background information regarding project research and engineering evaluation results, and a description of the construction elements and facility improvements.