Nutrient Recovery at the F. Wayne Hill Water Resources Center: Wasstrip Design and Full Scale Start Up

Over the past five years, struvite precipitation has increasingly become a major maintenance issue at the 60-mgd F. Wayne Hill Water Resources Center (FWHWRC). In addition, the FWHWRC had a significant increase in influent phosphorus loading from sludge being transferred from the 22 mgd Yellow River WRF. To address the struvite issues and decrease the impacts of phosphorus recycle loads on the main liquid stream, Gwinnett County selected the OSTARA Pearl® nutrient recovery process along with the WASSTRIP process (Wasted Activated Sludge Stripping to Remove Internal Phosphorus) to remove phosphorus and ammonia from the thickening and dewatering recycle streams and to decrease struvite clogging while producing a slow-release fertilizer.Both the WASSTRIP and the Ostara Process was piloted to gain process information for a Business Case Evaluation (BCE). With just over 6-months of full-scale operational experience, a comparison of the pilot and full-scale performance is presented.The WASSTRIP process blends primary sludge and waste activated sludge in an anoxic condition causing the WAS to release phosphorus. The WASSTRIP bench scale testing showed that the phosphorus concentration in the thickening filtrate increased to 120 mg/L of orthro-P, which is currently being achieved by the full-scale process.The Ostara pilot achieved an average of 75 percent orthophosphate-P removal and an average of 25 percent ammonia-N removal. During the first six months of operation, the full-scale Ostara system is achieving between 60 and 75 percent orthophosphate-P removal and between 15 and 20 percent ammonia-N removal. Overall, the Ostara Nutrient Recovery System and the WASSTRIP process is producing about 1 ton of fertilizer a day. Ostara is continuing to optimize the process to increase removals and fertilizer production, while decreasing caustic usage.