Four Million Pounds of Nitrogen - Successful Startup and Operation of a 114-mgd BNR Facility

The Metro Wastewater Reclamation District (Metro District) in Denver, Colorado, recently completed significant improvements to the 220 million gallon per day (mgd) (833 ML/d) Robert W Hite Treatment Facility (RWHTF) for ammonia, nitrate, and phosphorus removal. These improvements began construction in March 2011 and the new 114-mgd (432 ML/d) South Secondary Complex (SSEC) began partial operation in September 2014 and the entire facility in October 2015.The facility provided successful results that maintained permit compliance from day one of operation. In fact, the overall reductions in ammonia and total inorganic nitrogen concentrations in the plant effluent resulted in approximately 4 million pounds per year of nitrogen (1,800,000 kg/year) diverted from the South Platte River. Figure 1 shows overall plant effluent ammonia and Figure 2 shows overall plant effluent nitrogen trends from prior to, during, and after the upgrades. Plant flows during this period averaged 140 mgd (530 ML/d).The successful operation of the new facility can be attributed to the planning and training efforts that were conducted prior to start-up. This paper includes an introduction to the SSEC biological nutrient removal (BNR) facility and reviews the start-up planning process and procedures, actual process start-up conditions, and the subsequent process performance evaluation. These process start-up approaches were successful for the Metro District and are applicable to other utilities preparing to bring new treatment technologies online.Figure 1: Trends in RWHTF combined effluent ammonia concentrations.Figure 2: Trends in RWHTF combined effluent total inorganic nitrogen (TIN) concentrations.