18 - Removal of Nutrients from Stormwater Using Biochar and BOF Slag Filter Media in Bioswales

Urban stormwater runoff often carries excessive nutrients like phosphate and nitrate, posing significant risks to both public health and the environment. The concept of bioswales has garnered significant attention in recent times, whose function is to avoid flooding while simultaneously removing various pollutants from the runoff. However, conventional filter media such as sand, used in bioswales, is inadequate in removing these harmful nutrients. Consequently, there is a growing need to develop innovative filter media capable of efficiently adsorbing various pollutants including nitrate and phosphate from stormwater runoff. In this study, biochar (resulting from the gasification of waste pinewood) and BOF slag (a byproduct of steel manufacturing) were investigated as filter media for the removal of nitrate and phosphate from stormwater runoff. A thorough physicochemical and geotechnical characterization was performed to inform bioswale design while batch and column tests were performed to assess the efficacy of these materials in adsorbing the nutrients. Results of batch tests showed that biochar is efficient in removing both the nutrients while BOF slag showed exceptional ability to adsorb phosphate. Subsequently, column tests were then performed to assess the efficiency of these materials under dynamic flow conditions. The results from the column tests closely aligned with the findings from batch tests. Overall, both biochar and BOF slag (both waste materials) show promise to be effective in nutrient removal as filter media in bioswales, while the actual performance in field scale scenario, with runoff containing wide-ranging contaminants, is yet to be assessed.