Selecting the Effective Biochar for Removal of Pollutants from Highway Stormwater Runoff

Abstract

Biochar is a carbonaceous material with pollutant removal abilities due to its characteristics, such as high surface areas resulting from small and large pores for adsorption. Biochar can be incorporated into best management practices (BMPs) as a performance-enhancing device (PED), treating pollutants such as nutrients, heavy metals, and suspended solids in highway stormwater runoff. In this study, three (3) commercial biochar products were purchased from different manufacturers and studied. In the end, the effective one was selected based on its ability to remove pollutants from highway stormwater runoff. A batch experimental setup was utilized for each biochar product and highway stormwater runoff pollutant parameter tested. Three (3) major analyses [chemical oxygen demand (COD), color, and total dissolved solids (TDS)] were selected to represent the biochar’s ability to remove oxidizable pollutants, color, and ions such as sodium (Na+), magnesium (Mg2+) and chloride (Cl−) ions from the sampled highway stormwater runoff. Among the three (3) biochars studied, the Soil Reef Biochar showed relatively high and consistent removal of COD (82%), color (66%), and TDS (28%) from the highway stormwater runoff compared to the Wakefield Biochar and the Biochar Supreme products and therefore was selected as the effective one for further studies. The pH of the highway stormwater runoff treated with the three (3) biochar products was in the low basic range (7.95 to 9.01). The Wakefield Biochar showed a conductivity of 92.3 μs/cm compared to the Soil Reef Biochar and the Biochar Supreme at 156 and 160 μs/cm, respectively. This study presented a comprehensive yet simple analytical method for selecting the effective biochar for highway stormwater runoff pollutants removal. Biochar has properties that make it an efficient material for pollutant removal in highway stormwater runoff. Some of these properties include a large surface area, higher pore volume with a variety of sizes, and high carbon content, allowing pollutant removal through adsorption. The adsorption treatment process allows the attachment of solute molecules (pollutants) in the water to the biochar. The large surface area and pore volume allow for greater adsorption of pollutants and therefore greater pollutant removal. The readily available feedstock materials from waste for biochar production ensure less expensive and sustainable green material for highway stormwater runoff treatment. Biochar products in the market currently are produced using different raw materials and different production and quality assurance methods. The knowledge on selecting or screening biochar to ensure efficient highway stormwater pollutant treatment is limited. To ensure the applicability of a certain commercial biochar product in the removal of highway stormwater runoff pollutants in a specific location, traffic volume, and pollutant composition, this study provides a method of general performance testing of the biochar product before field implementation or model studies. Based on the methods developed and the results obtained from this study, stormwater managers and other stakeholders from several agencies will be able to make informative decisions on biochar product selection.