Open Collections

Abstract

Bioretention systems are eco-friendly systems for treating wastewater and stormwater runoff and are primarily designed to remove suspended solids, nutrients, pathogens, etc. Recent studies indicate that these systems can also partially remove trace organic contaminants (TrOCs) via sorption to soil and biodegradation. However, hydrophilic compounds are poorly removed due to limited sorption, while persistent compounds resist biodegradation and may accumulate in the soil. These may result in soil contamination and subsequent entry of contaminants into waterways, posing environmental concerns. Soil amendments such as biochar have been investigated to enhance TrOC removal and degradation in such subsurface flow systems. Biochar, a carbon-rich material, adsorbs a wide range of contaminants present in runoff. To improve the degradation of TrOCs adsorbed on biochar, we hypothesized that redox-active amendments could generate reactive intermediates and trigger abiotic transformations. Iron amendments are potentially promising because the cycling of iron between Fe(II) and Fe(III) in subsurface soils where conditions vary between oxic and anoxic states produces reactive species like hydroxyl radicals (·OH) and ferryl iron (Fe(IV)), which facilitate TrOC degradation. To enhance TrOC sorption and degradation in soils, we developed an “iron-impregnated biochar” amendment by co-pyrolyzing biochar with an iron nitrate solution in a tube furnace at 800 °C. Material characterization methods revealed that the iron impregnation process into the biochar was successful. The resulting material had a high iron content, which decreased the measured specific surface area and increased surface roughness. This thesis discusses the characterization of the iron-biochar amendment and results from experiments designed to address three objectives: a) the adsorption of a suite of stormwater-derived TrOCs to the iron-biochar amendment, b) the amendment’s role in the production of ·OH and Fe (IV) in microcosm-scale experiments, and c) the amendment’s ability to enhance degradation of TrOCs via these reactive species. Experimental results demonstrated that the iron-biochar material effectively adsorbed a suite of stormwater-derived TrOCs, produced ·OH and Fe(IV) during redox fluctuations, and enhanced TrOC removal. These findings suggest that the iron-impregnated biochar amendment may serve as an effective approach for enhancing the ability of bioretention systems to remove harmful and persistent TrOCs from stormwater runoff.