REMOVING NUTRIENT POLLUTANTS FROM URBAN STORMWATER RUN-OFF USING ADSORPTIVE SUBSTRATES

Urban stormwater run-off is a major contributor of non-point source pollution to surface waters in developed areas. In order to reduce the environmental impacts of urban development, several low impact development (LID) structures including bio-infiltration ponds and vegetated filter strips have been designed to sequester and remove harmful pollutants present in urban stormwater run-off. Although a variety of suspended and dissolved pollutants are readily removed by LID structures, certain nutrient pollutants including ammonia, nitrate, and phosphate are not consistently removed. Therefore, the objective of this study was to evaluate economically viable substrates that can be added to existing LID structures to enhance removal of nutrient pollutants. Replicated batch sorption experiments were conducted to evaluate the potential of nine substrates (pine biochar, mulch, peat moss, granular activated carbon, natural zeolite, exhausted coffee grounds, pet waste biochar, and coco coir) to adsorb nutrient pollutants from simulated stormwater run-off containing ammonia (0.30 mg-N/L), nitrate (1.25 mg-N/L), and orthophosphate (0.25 mg-P/L). Pre-weighed samples of each substrate were mixed with simulated stormwater at a ratio of 1 g per 100 mL and agitated for 96 h. Sorption values (mg/g) were determined for each substrate using simple mass balance calculations. Results indicate that some substrates worked well for certain constituents while others did not. Mean ammonia sorption values revealed that natural zeolite (0.025 mg-N/g), coco coir (0.023 mg-N/g) and mulch (0.022 mg-N/g) worked best for removing ammonia, while peat moss (-0.004 mg-N/g) and pet waste biochar (-0.004 mg-N/g) actually leached ammonia. Mean nitrate sorption values indicate that mulch (0.123 mg-N), exhausted coffee grounds (0.122 mg-N/g), and peat moss (0.114 mg-N/g) were most effective in removing nitrate, while natural zeolite (-0.062 mg-N/g) and pine biochar (-0.144 mg-N/g) leached nitrate. Only exhausted coffee grounds were effective in removing orthophosphate (0.012 mg-P/g). The results of this study suggest that LID structures can be amended to promote nutrient removal using adsorptive substrates; however, a mixture of substrates is recommended to remove multiple nutrient pollutants simultaneously.