New (First Ever) Site Specific PSRP–Equivalent Anaerobic Digestion Process Increases Digestion Capacity by Fifty Percent

A low mean cell residence time (MCRT), i.e., 10–15 days, complete-mix thermophilic anaerobic digestion process was tested to demonstrate compliance with the U.S. Environmental Protection Agency (EPA) equivalency criteria for a Process to Significantly Reduce Pathogens (PSRP). Full-scale tests show that the digestion process developed by the East Bay Municipal Utility District (EBMUD) consistently exceeded EPA's required vector attraction and pathogen reduction performance standards.After intensive review by the U.S. EPA, EBMUD's process was approved as a site-specific PSRP-equivalent process on November 29, 2010; the very first granted since the 40 CFR Part 503 rule was promulgated in 1993. The EPA's approval allows EBMUD to operate its digesters down to a 10-day MCRT, replacing the previous 15-day minimum, thus effectively increasing digester capacity by 50% and potentially saving about 60 million or more in future digester construction.This work has broad application to all wastewater treatment plants with anaerobic digesters.