Infiltration-based stormwater treatment systems such as biofilters are designed to remove a wide range of pollutants present in stormwater, but they are often inadequate to remove per- and poly-fluoroalkyl substances (PFAS). The ineffectiveness of biofilters has often been attributed to the surfactant-like structure of PFAS, the low adsorption capacity of biofilter media, the presence of co-contaminants in stormwater that compete with PFAS for adsorption capacity, and limited biodegradation potential of sequestered PFAS. Furthermore, biofilters naturally experience dry-wet and freeze-thaw cycles that release colloids and adsorbed PFAS back into the pore water. Biofilters need to be redesigned to overcome these challenges so that the PFAS removal capacity of biofilters remains consistent during its operational lifetime. Proper redesigning of biofilters involves understanding the processes that are unique to biofilters and affect PFAS removal and release due to their surfactant nature. This presentation provides insight into fundamental PFAS removal and release processes in stormwater biofilters, highlights some of the design concepts based on our and other recent studies, and discusses the challenges and opportunities in developing such designs on a large scale. Fundamental processes that are unique to stormwater biofilters include fluctuation of air-water and water-ice interfaces in biofilter in response to dry-wet and freeze-thaw cycles and their impact on adsorption and release of PFAS on filter media. The design concepts include the addition of novel adsorbents and in situ alteration of surface charge of filter media by application of ionic polymer and direct current. However, scaling up these designs from laboratory column scale to pilot or field scale presents many practical and operational challenges in addition to affecting the removal of other types of pollutants.

Developing regenerative biofilters to remove PFAS from stormwater: Challenges and opportunity

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ACS Fall 2022

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