Nutrient Recovery From Was Streams for Struvite Control and Recycle Load Reduction

摘要

The F. Wayne Hill Water Resources Center (FWHWRC) is Gwinnett County’s largest and mostadvanced wastewater treatment facility with a capacity of 60 mgd. The FWHWRC usesenhanced biological phosphorus removal and chemical trim to meet a stringent total phosphorus(TP) limit of 0.08 mg/L. Solids handling consists of anaerobic digestion of combined primarysludge and WAS in egg-shaped digesters. In 2009, Gwinnett County began adding magnesiumhydroxide (Mag) to their collection system for odor and corrosion control. Over the past twoyears with the addition of Mag in the collection system, struvite precipitation in the solidshandling process has become a major issue at the FWHWRC. However, the digesters at theFWHWRC are now phosphorus limited with respect to struvite formation due to the Magaddition in the collection system, which results in a benefit of very low phosphorus (P)concentrations in the dewatering centrate. Therefore if Mag addition is halted, the P-recycle load(most P removal is now by EBPR) will become a major concern that must be addressed withincreased metal salt addition and if Mag addition continues, the plant must address the struviteformation issues of clogged centrate pipes, centrifuge impacts and potential catastrophic failures.In addition, the FWHWRC will begin to receive primary and WAS from the 22 mgd YellowRiver WRF, which will significantly increase the TP load into the FWHWRC and increase thestruvite formation or P recycle load. This project evaluated nutrient recovery options comparedwith conventional metal salt addition to the digesters or centrate for both struvite control (if Magcontinues) or recycle P load reduction (if Mag is stopped) using bench and pilot scale testing andprocess modeling.