Evaluation of Nitrate and Phosphate Removal in Bioswale Using BOF Slag and Biochar

Urban stormwater has a significant problem because it contains excessive nutrients harmful to the environment. According to the United States Environmental Protection Agency (2012), phosphate and nitrate are the most polluted nutrients in the United States. It harms the ecosystem, biodiversity, and human health. One way to prevent these nutrients from entering the body of water is through a system called bioswale, which consists of porous media such as BOF slag and biochar. These materials are tested to find their capacity to filter nitrate and phosphate. The methods used to test the capacity of BOF slag and biochar are column tests, batch tests, and swelling tests of BOF slag. The column tests results for nitrate removal are 63 mg/kg for BOF slag and 229 mg/kg for biochar. The results show a similar trend for phosphate removal in column test with 25 mg/kg for BOF slag and 150 mg/kg for biochar. In contrast, the batch tests results are 60 mg/ kg for BOF slag and 437 mg/kg and biochar for nitrate removal, and the results for phosphate removal are 317 and 232 mg/kg for BOF slag and biochar, respectively. Finally, the swelling tests found that the overburden stress from the topsoil is sufficient to overcome the swelling with 0.31 percent of volumetric strain in 84 days. It is recommended to test field stormwater using batch tests and column tests with similar nutrients. Furthermore, a pilot-scale study is needed to test the performance of BOF slag and biochar under real-world conditions.