Updating an Old Approach to Solve a Modern Problem to Remove Nitrogen (and Saving Money in the Process)

This project involves the upgrade of the 58,670 m3/d (15.5 mgd) Danbury, CT Water Pollution Control Plant (WPCP) to provide nitrogen removal using a creative approach that employed a modification of the Wuhrmann process, a nitrogen removal process dating back to the 1960's, that uses a post anoxic zone as the primary means to achieve nitrogen removal. Relatively low BOD and high dissolved oxygen in the influent to the WPCP's existing nitrification tanks posed a challenge to using a pre anoxic zone in a conventional MLE process modification for nitrogen removal. Moving the anoxic zone to the effluent end of the nitrification tanks (as a post anoxic zone) allowed the influent dissolved oxygen to be used for nitrification and BOD removal, eliminated the need for nitrate recycle, and the relatively low cost modification achieves lower effluent nitrogen (between 4 to 6 mg/l TN) than achievable by the MLE process.