Nutrient Removal from Salt-Laden Snowmelt by Salt-Tolerant Plant Bioretention Cells with Different Fillers

Abstract

The presence of deicing salt in winter runoff from snowmelt affects the efficiency of bioretention cells. To stabilize the performance of bioretention cells in winter, two common plants were tested for their ability to tolerate deicing salt. Next, the performance of four bioretention cells containing different fillers [red brick construction waste (RB), cement construction waste (CM), biochar-modified sand (MB), and sand (BG)] and salt-tolerant plants were compared for their ability to remove nutrients from salt-laden snowmelt runoff. Results showed that Ophiopogon japonicus exhibited higher salt tolerance than Iris tectorum, making it more suitable for planting in bioretention cells treating snowmelt runoff. Subjecting the bioretention cells to different deicing salt concentrations (0, 5, and 10 g/L) induced varying levels of salt stress, and therefore had differing effects on the nutrient removal performance of different bioretention fillers. The removal of NH4+-N and NO2−-N under deicing salt stress had no effect on the RB, MB, or BG fillers, although it did enhance the NO3−-N and total nitrogen (TN) removal performance of the systems. The TN removal rates of RB, MB, and BG were −65.3% to −38.4%, −24.3% to 10.6%, and −38.1% to 27.9% at deicing salt concentrations of 0, 5 and 10 g/L, respectively. In contrast, the NH4+-N and NO2−-N removal performance of the CM filler was significantly affected by salt stress, with the NO3−-N and TN removal rates decreasing with increasing deicing salt concentrations. Furthermore, deicing salt inhibited total phosphorous (TP) removal by the RB, MB, and BG filler systems, whereas the TP removal rate of CM filler was not significantly affected, remaining above 97%.