BALTIMORE'S TWO-PHASE ANAEROBIC DIGESTION PROGRAM

The City of Baltimore is undertaking an expansion and upgrade of the anaerobic digestion system at its Back River Wastewater Treatment Plant. This works has a nominal capacity of 680,000 m3/day (180 mgd), and for the past few years has experienced an average daily flow of 540,000 m3/day (143 mgd). At present the sludge production rate averages 130 DMTPD (dry metric tons per day) (144 dry tons per day), and the 15-day rolling average production rate is 228 DMTPD (252 dry tons per day).The City has completed a preliminary engineering analysis that has demonstrated the technical and economic merits of the Two-Phase Anaerobic Digestion Process in the mesophilic temperature range for its digester project. The Two-Phase Anaerobic Digestion Process incorporates a volatile fatty acid (VFA) fermenter or acid phase reactor (APR), followed by a methane phase reactor (MPR) that can have one or more stages. The City's application will represent a 15-fold scale-up from a reference facility that has been operational in DuPage County, IL for over 10 years, and the City is implementing a Process Evaluation Facility (PEF) to verify performance, design and operational control assumptions for the full-scale facility.This paper reviews the scope of the City's project with the Process Evaluation Facility (PEF). The PEF includes the largest purpose-built VFA fermenter in the nation. The preliminary engineering work to upgrade the anaerobic digestion system was done by EarthTech, and the final engineering design work including consultation on the PEF program, now in process, is being done by the joint venture of RKK/Parsons. RKK/Parsons consists of the firms of Rummel, Klepper and Kahl LLP of Baltimore, MD and Parsons Corporation (formerly Parsons Engineering Science, Inc.) of Fairfax, VA.