Black Carbon-Amended Engineered Media Filters for Improved Treatment of Stormwater Runoff

James Conrad Pritchard; Kathleen Mills Hawkins; Yeo-Myoung Cho; Stephanie Spahr; Scott D Struck; Christopher P Higgins; Richard G Luthy

doi:10.1021/acsenvironau.2c00037

Black Carbon-Amended Engineered Media Filters for Improved Treatment of Stormwater Runoff

ACS Environ Au. 2022 Sep 28;3(1):34-46. doi: 10.1021/acsenvironau.2c00037. eCollection 2023 Jan 18.

Authors

James Conrad Pritchard^{1

2}, Kathleen Mills Hawkins^{1

3}, Yeo-Myoung Cho^{1

2}, Stephanie Spahr^{1

4}, Scott D Struck⁵, Christopher P Higgins^{1

3}, Richard G Luthy^{1

2}

Affiliations

¹ Re-inventing the Nation's Urban Water Infrastructure (ReNUWIt), National Science Foundation Engineering Research Center, Stanford, California 94305, United States.
² Department of Civil & Environmental Engineering, Stanford University, Stanford, California 94305, United States.
³ Department of Civil & Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, United States.
⁴ Department of Ecohydrology and Biogeochemistry, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), 12587 Berlin, Germany.
⁵ Geosyntec Consultants, Los Angeles, California 90015, United States.

Abstract

Urban stormwater runoff is a significant driver of surface water quality impairment. Recently, attention has been drawn to potential beneficial use of urban stormwater runoff, including augmenting drinking water supply in water-stressed areas. However, beneficial use relies on improved treatment of stormwater runoff to remove mobile dissolved metals and trace organic contaminants (TrOCs). This study assesses six engineered media mixtures consisting of sand, zeolite, high-temperature gasification biochar, and regenerated activated carbon (RAC) for removing a suite of co-contaminants comprising five metals, three herbicides, four pesticides, a corrosion inhibitor, six per- and polyfluoroalkyl substances (PFASs), five polychlorinated biphenyls (PCBs), and six polycyclic aromatic hydrocarbons (PAHs). This long-term laboratory-scale column study uses a novel approach to generate reproducible synthetic stormwater that incorporates catch basin material and straw-derived dissolved organic carbon. Higher flow conditions (20 cm hr^-1), larger sized media (0.42-1.68 mm), and downflow configuration with outlet control increase the relevance of this study to better enable implementation in the field. Biochar- and RAC-amended engineered media filters removed nearly all of the TrOCs in the effluent over the course of three months of continuous flow (480 empty bed volumes), while sample ports spaced at 25% and 50% along the column depth provide windows to observe contaminant transport. Biochar provided greater benefit to TrOC removal than RAC on a mass basis. This study used relatively high concentrations of contaminants and low biochar and RAC content to observe contaminant transport. Performance in the field is likely to be significantly better with higher biochar- and RAC-content filters and lower ambient stormwater contaminant concentrations. This study provides proof-of-concept for biochar- and RAC-amended engineered media filters operated at a flow rate of 20 cm hr^-1 for removing dissolved TrOCs and metals and offers insights on the performance of biochar and RAC for improved stormwater treatment and field trials.