Nitrogen Removal Performance in Roadside Stormwater Bioretention Cells Amended with Drinking Water Treatment Residuals.

Bioretention cells, a type of green stormwater infrastructure, have been shown to reduce runoff volumes and remove a variety of pollutants. The ability of bioretention cells to remove nitrogen and phosphorus, however, is variable and bioretention soil media can act as a net exporter of nutrients. This is concerning as excess loading of nitrogen and phosphorus can lead to eutrophication of surface waters, which green stormwater infrastructure is intended to ameliorate. Drinking water treatment residuals (DWTR), metal (hydr)oxide-rich byproducts of the drinking water treatment process, have been studied as an amendment to bioretention soil media due to their high phosphorus sorption capacity. However, very few studies have specifically addressed the effects that DWTRs may have on nitrogen removal performance within bioretention cells. Here, we investigated the effects of DWTR amendment on nitrogen removal in bioretention cells treating stormwater in a roadside setting. We tested the capacity for three different DWTRs to either retain or leach dissolved inorganic nitrogen in the laboratory, and also conducted a full-scale field experiment where DWTR-amended bioretention cells and experimental controls were monitored for influent and effluent nitrogen concentrations over two field seasons. We found that DWTRs alone exhibit some capacity to leach nitrate and ammonium, but when integrated into sand- and compost-based bioretention soil media DWTRs have little to no effect on the removal of nitrogen in bioretention cells. These results suggest that DWTRs can be used in bioretention media for enhanced phosphorus retention without risk of contributing to nitrogen export in bioretention effluent. This article is protected by copyright. All rights reserved.