Pilot Scale Assessment of a Deployable Photocatalytic Treatment System Modified with BiPO4 Catalyst Particles for PFAS Destruction in Investigation-Derived Wastewaters
Ezra Cates | Clemson University
This project seeks to rapidly modify a packaged treatment system and demonstrate on a pilot-scale its ability to degrade and mineralize perfluoroalkyl substances (PFAS) in both real contaminated groundwater and synthetically prepared control water matrices. There is a need for deployable systems that achieve complete destruction of fluorinated contaminants (rather than adsorption to a solid medium or concentration via membrane processes). The Purifics Photo-cat is a fully contained and automated water treatment system that typical operates with titanium dioxide (TiO2) photocatalytic nanoparticles to mineralize a range of organic contaminants for wastewater, drinking water, groundwater, and industrial treatment applications; however, the redox potentials of TiO2 photogenerated charge carriers are insufficient for strong activity against PFAS. The research team at Clemson University has recently demonstrated rapid destruction of aqueous PFAS by a novel bismuth phosphate (BiPO4)-based photocatalytic material at the bench scale. The objective of this project is to evaluate the effectiveness of BiPO4 in the Purifics Photo-cat system for treatment of PFAS contaminated groundwater.
Bismuth phosphate is a polymorphic crystalline semiconductor material with photocatalytic properties under short-wavelength ultra violet irradiation. Over the past seven years, numerous studies have reported the ability of BiPO4 particles to induce rapid photocataytic advanced oxidation, as well as its complex crystal phase behavior relating to synthesis conditions. The research team at Clemson University has isolated a specific embodiment of mixedphase BiPO4 particles which were found to rapidly degrade perfluorooctanoic acid (PFOA) in bench-scale photoreactors under both acidic and neutral pH conditions. Mechanistic study is ongoing, though preliminary results suggest that PFOA undergoes both heterogeneous reductive and oxidative processes at the catalyst surface, resulting in mineralization and fluoride liberation.
The project tasks will comprise scaling-up BiPO4 synthesis capabilities in the research lab, and incorporating the material into a pilot-scale Photo-cat unit. This system functions by mixing the catalyst slurry with influent water which is then pumped under turbulent conditions through a serious of annular photoreactors containing low pressure mercury lamps. Catalyst particles are separated from the treated effluent by a crossflow ceramic ultrafiltration membrane unit and recycled back into the influent. Testing of the BiPO4-modified system at Clemson will first involve prepared influent waters containing PFAS in water matrices with varying pH, alkalinity, and dissolved organic carbon conditions. Degradation kinetics of high-initial concentration waters will be monitored with university analytical instruments, while analysis of lower concentrations (<10 ppb) and intermediate degradation products via accredited methods will be subcontracted to Battelle. Finally, the optimized unit will be tested with real water samples from Department of Defense PFAS sites in collaboration with the Naval Facilities Engineering and Expeditionary Warfare Center.
Combining the capabilities of a pre-engineered commercial photocatalytic system with a novel PFAS-active catalyst provides a unique opportunity for rapid development of a potentially transformative solution aligned with the relevant directives of the Strategic Environmental Research and Development Program. Upgrading of the Photo-cat system with BiPO4 is beneficial for PFAS remediation but is also anticipated to improve treatment efficiencies for a majority of synthetic and volatile organic compounds. Not only has BiPO4 been proven to result in degradation kinetics superior to TiO2, but its larger particle size may also allow use of larger-pore size microfiltration catalyst recovery with significantly lower pressure and energy requirements. These aspects align with the research team's goal of improving cost-effectiveness of practically applicable photocatalytic reactor systems. (Anticipated Completion - April 2019)