Anammox Polishing in Mainstream Wastewater Treatment to Meet Stringent Ammonia and Total Nitrogen Limits

The anammox polishing MBBR was in operation for almost one and a half years. The study was separated into a start-up phase plus five additional phases. High nitrogen removal rates were measured, with TIN removal rates ranging from 0.053 – 0.26 g TIN/m2/day, with the system being typically limited on influent nitrite concentrations. Throughout the entire study due to limiting nitrite conditions, effluent nitrite values remained less than 0.25 mg NO2--N/L, with the last phase of the study producing an average effluent of 0.09 mg NO2--N/L. Batch activity tests were conducted on a weekly basis to determine maximum anammox removal rates. A maximum TIN activity removal of 1.5 g TIN/m2/day was observed at 24°C. Nitrite breakthrough performance was conducted during Phase II to determine the maximum nitrite removal that could be sustained by the system. A maximum value of 15.4 mg NO2--N/L was fed to the system and an effluent of less than 1 mg NO2--N/L was measured in the effluent. Near the end of the data collection period, a limited amount of acetate (2.8 ± 1 mg/L COD) was fed to the reactor to reduce nitrate in the system to nitrite. This produced significant results that added to even more TIN removal in the system with an average ratio of COD added/TIN removed of 0.9 ± 0.4. This study effectively shows how the use of an anammox MBBR as a polishing process can assist plants in cost-effectively meeting their future more strict permit limits, such as an ammonia limit or a total nitrogen limit.