Pilot Testing Nutrient Recovery from WAS streams for Struvite Control and Recycle Load Reduction

The F. Wayne Hill Water Resources Center (FWHWRC) is Gwinnett County's largest and most advanced wastewater treatment facility with a capacity of 60 mgd. The FWHWRC uses EBPR and chemical trim to meet a total phosphorus (TP) limit of 0.08 mg/L. In 2009, Gwinnett County began adding magnesium hydroxide (Mag) to their collection system for odor and corrosion control. Struvite precipitation has since become a major issue at the FWHWRC. However, the digesters at the FWHWRC are now phosphorus limited with respect to struvite formation due to the Mag addition in the collection system. If Mag addition is halted, the P-recycle load will need to be addressed with increased metal salt addition and if it continues, the plant must address the struvite formation issues. This project evaluated nutrient recovery options compared with conventional metal salt addition to the digesters or centrate for both struvite control (if Mag continues) or recycle P load reduction (if Mag is stopped) using bench and pilot scale testing and process modeling.