An innovative biological process for the treatment of ammonium-rich plant recycle streams from the dewatering of anaerobically digested sludges ("centrate" or "rejection water") is being evaluated in North America in an unprecedented collaborative technology evaluation program between
the New York City Department of Environmental Protection, the District of Columbia Water and Sewer Authority and the Alexandria Sanitation Authority. The technology is being evaluated as part of a broader program to identify reliable, cost-effective technologies for total nitrogen removal. The
process consists of a single-sludge suspended growth sequencing batch reactor called DEMON®, which is operated with pH-controlled intermittent aeration to provide aerobic and anoxic/anaerobic periods for nitritation and anaerobic ammonium oxidation (ANAMMOX) reactions (the complete
process is referred to as "Deammonification"). The DEMON® process has been successfully implemented in full-scale facilities in Strass, Austria and Glarnerland, Switzerland; however, the collaborative project participants established a research program to understand the operating
conditions that contribute to the stability (or threaten the stability) of the process. Specifically, the focus of the work has been on operating ranges for dissolved oxygen, pH, pH bandwidth, temperature, nitrite concentration and the maximum ammonium-N loading rate. The results presented
in the paper are the product of one-and-a-half years of work by the collaborative research project participants and were assembled to provide the reader with the status of the DEMON® process development and operational characteristics of the process. This project will continue
into 2008 as further work is conducted on the defining procedures and/or technical options for recovering from operational upsets and accumulating a greater mass of anammox biomass for seeding larger systems for eventual full-scale implementation in North America.
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