Anammox: a Sustainable Process to Remove Nitrogen from Reject Water Generated by Anaerobic Digestion Processes

EXTENDED ABSTRACT The City College of New York (CCNY) in collaboration with New York City Environmental Protection (NYCEP) is currently engaged in operating a 1700 gallon pilot single stage partial nitritation/anaerobic ammonium oxidation (anammox) moving bed biofilm reactor (MBBR) at the 26th Ward waste water treatment plant (WWTP) in Brooklyn, NY. The MBBR is designed to remove nitrogen from the anaerobic digester reject water (centrate) emanating from the dewatering facility at the 26 Ward WWTP. This study was initiated as a result of earlier extensive bench-scale studies conducted by CCNY over a 2-year period, where the process proved effective in treating centrate generated at the Wards Island WWTP. The current pilot study of Anammox using a MBBR is the first of its kind in the United States. The Anammox process is an anaerobic autotrophic biological process that can be used to remove nitrogen from centrate. The process has been used at several treatment plants in Europe where it demonstrated its effectiveness to remove nitrogen at a much lower cost than conventional nitrification/denitrification processes. The anammox process has the potential of being the most sustainable treatment process for centrate because of its reduced energy needs, elimination of any organic carbon source, and acting as a sink for carbon dioxide, one of the documented greenhouse gases. The objective of the study was to provide further kinetic and operating data, test alternate loading rates, and provide guidance to the City and its consultants to eventually design a full-scale anammox process to treat centrate. Startup of the pilot began in March 2011 with seeding from the activated sludge process only since an important objective was to develop “homegrown” anammox bacteria with real centrate and subject to all the variations in strength that the WWTP experiences. The startup challenges and the modes of operation implemented will be discussed in this paper that enabled enrichment of the biofilm with noticeable anammox activity observed by August 2011. Nitritation of the centrate is limited by the available alkalinity based on stoichiometry. An achievable target was then estimated to be in the range of 60 to 70% nitrogen removal at the operating temperature of 32-34C without any chemical additions. With the addition of alkalinity, the performance of the pilot reactor reached between 80 and 85% further reinforcing the fact that sufficient alkalinity will enhance removal.The operational and maintenance challenges and the various phases of operation will be discussed.