Application of drinking water treatment residuals to green stormwater infrastructure for enhanced phosphorus removal

Background and Methods Bioretention systems are a form of green stormwater infrastructure that are becoming increasingly common for managing runoff from impervious surfaces by capturing stormwater flows and filtering pollutants. While bioretention systems function well for sediment removal, their phosphorus (P) removal performance is highly variable. Amending bioretention soil media with P sorbing materials, such as drinking water treatment residuals (DWTRs), has potential to greatly enhance P removal from stormwater and improve downstream water quality. Here, we aim to assess this potential by 1) quantifying the P sorption capacity of different DWTRs, 2) determining the contact time required for effective P removal and 3) measuring P removal by bioretention soil media amended with DWTRs. To do this, we conducted P sorption isotherm experiments, continuous-flow small column experiments and contact time experiments on three different sources of DWTRs. We then conducted large column experiments using various bioretention media blends with and without DWTRs. Finally, we measured a suite of physicochemical parameters in order to understand the drivers of P sorption by DWTRs at fine scales. Results and Conclusions The DWTRs used in this study demonstrated high but variable capacities for P sorption (8-40 g P kg-1). Specific surface area correlated strongly with P sorption, but the total abundance of metal oxides in DWTRs did not. Contact time experiments revealed that P sorption is very rapid and that over 95% of P can be sorbed after 1 minute of contact. Preliminary large column results show that P removal by DWTRs in bioretention media is effective (~95%) across all DWTRs, despite differences in maximum P sorption capacity. These results suggest that DWTRs have great potential to enhance the ability of bioretention soil media to remove P from stormwater