6PPD-Quinone Removal in Decant Facility

River Wan and Jeff Rudolph, Pierce County; Shelby Giltner, Washington State Department of Ecology

Stormwater catch-basin cleaning can reduce 6PPDq loadings to receiving streams. However, the concentrations of 6PPDq in the generated waste and the mechanisms by which different methods remove 6PPDq remain largely unknown. Pierce County’s decant facility presents an opportunity to address these knowledge gaps. The facility employs a multi-stage treatment process involving gravitational settling, flocculation, and granular activated carbon (GAC) filtration. This Ecology-funded project demonstrated that the waste contains 6PPDq at concentrations lethal to coho salmon. Gravitational settling and flocculation removed the insoluble fraction of 6PPDq through solid-liquid separation, while GAC filtration removed the soluble fraction effectively. The combined treatment processes consistently reduced 6PPDq levels to below 3 ng/L, achieving an average removal efficiency of over 95%. These findings underscore the effectiveness of advanced treatment methods in mitigating 6PPDq contamination in stormwater and suggest that similar principles should be considered in developing Best Management Practices (BMPs) for stormwater management.