To reinvent their urban water supply systems, water-stressed cities are expanding the use of locally available water through actively capturing urban stormwater for aquifer recharge. Stormwater harvesting projects such as the Rory M. Shaw Wetlands Park in Los Angeles are designed to augment groundwater supplies, prevent flooding and beach pollution, and improve water quality. However, conventional green infrastructure might fail to remove the numerous hydrophilic organic chemicals present in urban stormwater. In a 1.5-year long column study, we demonstrate the beneficial effect of biochar amendments to conventional sand filters and reveal the impact of (i) biochar amount, (ii) compost-biochar combination, and (iii) infiltration rate on redox conditions and contaminant removal. The performance of nine different configurations of sand, biochar, and compost was assessed at two different flow rates of 1 and 3 in/h. The filter materials were conditioned for four months with actual stormwater collected in Los Angeles. Subsequently, we introduced 19 hydrophilic organic compounds including pesticides, flame retardants, veterinary drugs, and wastewater indicators to investigate sorption and biotransformation processes on the strongly matured filter materials. While removal of organic compounds was negligible in sand-only systems, biochar amendments of 5 percent by weight effectively retained all of the target chemicals for more than 500 pore volumes. The presence of compost reduced sorption of organic contaminants onto biochar, but promoted biotransformation of highly water soluble and anionic species such as dicamba, which was least retained by biochar. Concentration profiles over the depth of the filter columns allowed the prediction of breakthrough times and an assessment of the long-term performance of biochar-amended filters under different flow regimes.

Enhanced removal of hydrophilic organic contaminants from urban stormwater in biochar-amended biofilters

2019 Fall National Meeting

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