Pushing the Limits: 11.4-ML/D (3-mgd) Pilot Process Train at Brockton Achieves Low-Cost Nitrogen Removal to 3 mg/L TN

The 77.6 million liters per day (ML/D) [20.5 million gallons per day (mgd)] Brockton Advanced Water Reclamation Facility (AWRF) in Brockton, Massachusetts underwent a major capital upgrade program from 2004 through 2009. As part of the improvements, the plant’s previous two-stage nitrification process was transformed into a single-stage biological nutrient removal (BNR) process, without adding any new bioreactor or clarifier tankage. Though the plant’s National Pollutant Discharge Elimination System (NPDES) permit did not require nitrogen removal at that time, there was sufficient bioreactor volume available to employ a Modified Ludzack-Ettinger (MLE) process configuration to achieve year-round nitrification and denitrification, to a predicted average effluent total nitrogen (TN) concentration of 5.5 mg/L. Plant performance since commissioning of the upgrade in 2008-2009 is consistent with this anticipated level of performance, averaging 5.3 mg/L effluent TN.In 2013 – 2014, the City of Brockton was notified by the United States Environmental Protection Agency (EPA) that the Brockton AWRF discharge would be required to comply with a new average monthly TN limit of 3 mg/L with its next NPDES permit renewal, and this limit would likely be in effect seasonally from May through October. In preparation for this eventuality, Brockton evaluated process options and elected to construct modifications to one of the plant’s process trains to optimize nitrogen removal capability and determine if such low-impact modifications would enable the AWRF to achieve this level of nitrogen removal. After approximately one year of operation, the full-scale pilot process train has produced effluent averaging 1.45 mg/L total inorganic nitrogen (TIN).