Poster 237 – Click on poster below to view presentation from author.
Washington State University
Co-Authors: Anand Jayakaran, Jenifer McIntyre
We evaluated the treatment of Polycyclic Aromatic Hydrocarbons (PAHs) and Fecal Indicator Bacteria (FIB) in highway runoff by bioretention. We compared treatment performance by Washington’s standard bioretention mix of 60% sand, 40% compost (by volume), and by three other blends amended with biochar and fungi. Biochar-amended mixtures contained 60% sand, 20% compost, and 20% biochar. Fungi-amended mixtures were inoculated with Stropharia rugosoannulata. Twelve bioretention columns were constructed in a greenhouse, each containing 18” of bioretention mix planted with Carex oshimensis overlaying a 20” gravel drainage layer. Columns were initially conditioned with clean water and then dosed with stormwater collected from a highway downspout in Tacoma, WA during 8 events over a 14-month period. Effluents for each column were analyzed for 23 PAHs, E. coli, Fecal coliform, dissolved organic carbon (DOC), and total suspended solids (TSS). To track the fate and transport of PAHs within the bioretention columns, soil cores were taken four time throughout the study. TPAHs were almost completely removed by all treatments across all storms, with removal rates ranging from 97-100% for 94 out of 96 samples. Compost appears to be a source of PAHs in bioretention soils, as biochar-amended soils initially contained half the soil TPAHs as columns with the standard 60:40 sand:compost mixture. We observed a net loss of TPAHs between 44-76% in bioretention soils which could not be explained by PAHs in effluent alone, suggesting that microbial bioremediation and/or plant uptake attenuated soil PAHs. Fungi amended bioretention soil showed higher TPAH losses (70-73%) than bioretention soil alone (60-71%). Influent concentrations of FIB spanned 3 orders of magnitude. E. coli and fecal coliform were initially exported, but all columns achieved some treatment after the first dosing event. DOC was exported from all columns, but export was reduced in biochar-amended columns.
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