South Platte Renew (SPR) is the third largest water resource recovery facility (WRRF) in Colorado, with a capacity of 50 million Gallons per day (MGD). SPR’s discharge to the South Platte River is regulated by the Colorado Department of Public Health and Environment (CDPHE). CDPHE set a regulatory roadmap for nutrient removal with intermediate steps for compliance including a 10-year Voluntary Incentive Program (VIP). This program allows the SPR to voluntarily treat nitrogen and phosphorus to levels below permit requirements and to earn compliance credits (i.e., years) towards future more stringent regulations.
To take full advantage of the VIP, SPR is implementing a chemical phosphorus removal (Chem-P) process to achieve effluent total phosphorus below 0.7 mg/L. SPR took a comprehensive approach to evaluate design options for Chem-P implementation including full-scale piloting. The pilot used existing ferric sulfate storage/dosing facilities. The ferric sulfate dose was varied in three phases through five months: (I) initial baseline, (II) ramp-up, (III) stabilization at optimum dose. The pilot was conducted by a team of operators and engineers. Close collaboration and monitoring were critical for the successful completion of the pilot. Plant profiles of phosphorus, nitrogen, total suspended solids, alkalinity, and pH were monitored. Spot sludge samples were collected for vivianite analysis through x-ray diffraction.
The full-scale pilot demonstrated that a dose of 40 mg/L is required to reach the desired effluent total phosphorus concentration of 0.7 mg/L as P. It also indicated an increase in solids production of over 10 percent for the current 18 MGD average flow. Furthermore, the results indicated that depending on the overall plant operation, the impact in alkalinity may be significant to meeting effluent pH limits. Nitrification was not significantly affected during the full-scale pilot, however a small reduction in performance during high load hours of the day was observed.
Conversion to full biological phosphorus removal can be a costly option depending on the overall existing facility process design. Chem-P is still a common and cost-effective alternative to many WRRFs. This presentation will describe the approach and lessons learned in the full-scale chemical P removal pilot at the SPR WRRF.