The occurrence of per- and polyfluoroalkyl substances (PFAS) in groundwater has been consistently confirmed in the environment at µg/L to mg/L levels. Recently, there have been increasing concerns over the discharge of stormwater containing PFAS due to the historical use of aqueous film-forming foam (AFFF) and the possible intrusion and infiltration of AFFF-impacted groundwater into stormwater systems. PFAS have also been frequently detected in stormwater runoff from residential, commercial, and industrial areas. Notably, many reported values exceeded the Environmental Protection Agency's human health advisory level of 70 ng/L. Although biofilters are one of the widely used stormwater best management practices (BMPs), current knowledge suggests that these systems may fail to remove PFAS. As a result, there is an urgent need to develop sustainable BMPs to effectively prevent the introduction of PFAS from stormwater to receiving bodies of water. The objective of this project is to provide proof-of-concept evidence to show that tailored biochar can be employed as an amendment to augment the performance of biofilters for PFAS removal.

As a proof of concept, the project team will tailor biochar materials from metal rich waste feedstocks under a range of pyrolysis temperatures to alter their anion-exchange capacities, polyaromatic surfaces, and pore characteristics. The project team will also develop strategies to covalently graft quaternary ammonium groups on selected biochar to facilitate interactions with anionic PFAS. Throughout the biochar modification process, the project team will work closely with a biochar company to ensure method transferability and thus foster the market availability of the developed materials down the line. The efficacy of these materials will be evaluated under conditions relevant to field BMP operations using bench-scale batch and column tests. To better incorporate the complexities involved with field conditions, the project team will perform column tests using authentic stormwater collected from a DoD facility and assess the removal of PFAS under varying dissolved organic carbon contents as well as flow dynamics that allow the soil column to fluctuate between saturated and unsaturated conditions. Commercially available adsorbents will be included as a benchmark.

If this proof-of-concept study is successful, the next phase will be to scale the experiments up to larger biofilter mesocosms and eventually move to field studies to demonstrate the performance of the biochar-augmented biofilter BMP for DoD facilities. This project will generate critical data to fill the knowledge gap regarding the efficacy of biochar-augmented biofilter BMPs for stormwater PFAS removal under conditions that reflect the complexities in field operations. Biochar will be produced from various waste sources and modified to better retain a diverse set of PFAS, including short-chain PFAS. If successful, the project will inform the development of a passive stormwater treatment technology that effectively removes a suite of chemicals of concern, such as total suspended solids, metals, nutrients, and PFAS, and accommodates variable flows with a reduced need for regular media replacement. (Anticipated Project Completion - 2024).