A pilot study of the pollutant removal in bioretention for urban runoff

Abstract

Urbanization has negative effects on the water quality of receiving waters due to high concentrations of pollutants in urban runoff. Bioretention systems, shallow vegetated depressions in the landscape, help reducing flow volumes as well as promoting removal of contaminants in stormwater. In this thesis field studies were performed to evaluate the hydraulic performance and pollutant removal efficiency of two installed bioretention cells for petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs), contaminants that have been rarely investigated in such systems. Two columns were filled with two different filter media and subsequently treated alternately with “natural” stormwater and with diesel-spiked stormwater for a period of three months. In the laboratory, influent and effluent pollutant concentrations were measured, and the filter media was analysed before and after the construction of the stormwater treatment plant. Overall the results showed consistent high reductions of TPHs and PAHs concentrations (> 99%) and minimized outflow volumes, as compared to inflow volumes in both bioretention cells. Due to the initial leaching of soil material out of the system, total suspended solids (TSS) could not be removed efficiently. It was found that an appropriate filter media is essential to attenuate runoff flow and reduce pollutant concentrations and that the bioretention system takes time to operate effectively. However, when designed and applied correctly, bioretention is a promising stormwater management practice to control pollutant concentrations and flow volumes of urban runoff.