Evaluation of Biochar as a Potential Filter Media for the Removal of Mixed Contaminants from Urban Storm Water Runoff

Urban storm water runoff can carry a wide range of contaminants, many of which exceed federal maximum contaminant levels, into surface water resources (e.g.,rivers and lakes). The use of filtration systems has received greater attention for its potential to remove particulate matter and other contaminants. Biochar is expected to have excellent potential as an adsorbent or filter given its large surface area and microporous structure. This study evaluated the potential use of biochar as a filter media through a series of column experiments. A column with an inner diameter of 7cm (2.75in.) and a length of 61cm (24in.) using biochar as filter media was constructed to examine its effectiveness for the removal of mixed contaminants [total suspended solids (TSS), nutrients, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and E. coli] from synthetic storm water. The results demonstrated that this filter reduced the TSS in the storm water effluent by an average of 86% and the concentrations of nitrate and phosphate by 86 and 47%, respectively. After filtration, the concentration of Cd, Cr, Cu, Pb, Ni, and Zn (heavy metals) decreased by 18, 19, 65, 75, 17, and 24%, respectively. The variation can be explained in terms of the chemical behavior of the different heavy metals as well as the properties of the biochar. Among the three PAHs tested, biochar successfully removed phenanthrene (almost 100% removal efficiency) and achieved 76% removal efficiency for naphthalene but resulted in no removal of benzo(a)pyrene; the average removal for the three PAHs was 68%. Biochar was not efficient in removing E. coli from storm water, and the concentration of almost 7,400MPN/100mL in the inflow was reduced to approximately 5,000MPN/100mL in the outflow, representing a mean removal efficiency of 27%. Overall, the biochar used in this study showed promise to be an effective filter media for the removal of selected contaminants from urban storm water runoff. However, additional research should be conducted using different types of biochars, produced from different feedstock and production conditions, to determine the most effective biochar that can simultaneously remove multiple contaminants from urban storm water.