Formatted Title
Using Colloidal Gas Aphrons to Remove PFAS from Water: Technology Development Status
Background/Objectives
Background/Objectives. Colloidal gas aphrons are unique microstructures composed of layers of surfactant and water around a gaseous core that are produced by mixing air, surfactant, and water under high shear environments. Due to their large interfacial area and electrostatic interactions, aphrons have shown the ability to separate dyes, proteins in the food industry, heavy metals, and contaminants from water with high performance levels. While conventional foam fractionation processes rely on air bubbles to remove PFAS from water, aphrons are a dramatically different because: 1) aphrons are not simple air bubbles, but three-layer microstructures with charged outer surfaces; 2) aphrons are much smaller than typical flotation air bubbles, greatly increasing the active surface area for PFAS removal; and importantly 3) air bubbles rely on air-water partitioning to remove PFAS while aphrons rely on electrostatic interactions to separate PFAS from water.
Approach/Activities
Approach/Activities. A full-scale PFAS removal process using aphrons is now being conducted with results expected in early 2023. Design flowrates are at the 10-gallon per minute range for a ~600-gallon flotation vessel. Key process design variables include the aphron removal technology (mechanical skimmers versus vacuum lift) and the aphron/influent flowrate ratio. A commercial-scale aphron generator is being used to provide aphrons in full-scale testing quantities. While key elements of the design are generally based on conventional dissolved air flotation technology, several key modifications have been made to adapt the process for aphron-based PFAS removal technology. In addition, ESTCP demonstration of aphrons for removing PFAS will start in late summer 2023, focusing on testing of aphron removal alone and integrating aphrons into the DMAX plasma process for destroying PFAS.
Results/Lessons Learned
Results/Lessons Learned. Because the aphron PFAS removal process likely relies primarily on electrostatic interactions rather than hydrophobic sorption, aphrons have been shown to treat a wider range of PFAS than existing activated carbon or air-bubble foam fractionation technologies, specifically exhibiting significantly improved removal of short-chained PFAS. Single-stage bench-scale tests using PFAS-impacted groundwater from a remediation site showed aphrons removed >96% of PFBS, 82% of all short-chained PFAS, and 79% of long-chained PFAS. Single-stage foam fractionation tests which use air bubbles alone to tests in the scientific literature using air bubbles alone showed 33% removal of PFBS and only ~50% removal of all short-chained PFAS because of the low level of air-water partitioning for PFBS and other short-chained species. Removal of long-chained PFAS was high (79%), but slightly lower for aphrons versus foam fractionation (~92%) in single-stage bench-scale tests.
Performance results for a full-scale single-stage aphron PFAS separation process are expected in early 2023. Key design results will: 1) reveal PFAS removal in a full-scale single stage reactor, particularly focusing on removal of both long- and short-chained PFAS; 2) confirm that residual surfactant in the process effluent is not present or is within risk-based levels; 3) be used to design high removal efficiency multi-stage aphron reactors that can effectively removal all PFAS, not just long-chained PFAS.
With these data, the aphron PFAS removal process can be customized for various applications, such as stand-alone process for treating drinking water treatment, groundwater, and surface water using multiple stages and as polishing step for foam fractionation and activated carbon PFAS removal processes to the remove difficult-to-treat short-chained PFAS.