Microwave-assisted Catalytic Membrane Filtration for PFOA degradation

Abstract:

Per- and poly fluorinated alkylated substances (PFASs) have been increasingly studied as a new class of global pollutants due to the broad historic uses in diverse industrial products. PFASs are extremely resistant to natural weathering and degradation processes such as hydrolysis, photolysis, and microbial degradation. Microwave-assisted membrane (MWM) filtration was explored to facilitate the degradation of refractory PFASs from wastewater. Microwave-absorbing catalyst (e.g., BiFeO₃) coated on the ceramic membrane produced hydroxyl radicals that enhance oxidative degradation of perfluorooctanoic acid (PFOA) as a model PFAS. MW irradiation was selectively absorbed by catalysts and hydrogen peroxide to produce ‘‘hotpots” on membrane surface that promoted generation of nanobubbles, which prevented membrane fouling and assisted degradation of PFASs. This presentation will introduce the results of degradation of PFOA in microwave-assisted catalytic membrane filtration including the influences of microwave irradiation on performances of membrane filtration. First, water permeation of the pristine and catalyst-coated membranes were examined under the influence of microwave irradiation to analyse the impacts of the coating layer and water temperature increase on permeate flux, which were well interpreted by the Carman-Kozeny and Hagen-Posieulle models. Then, the PFOA removal was first assessed in a continuous filtration model with and without microwave irradiation. Our results show that PFOA adsorbed on membrane and catalyst materials and fully penetrated the membrane filter after reaching adsorption equilibrium. Under microwave irradiation (7.2 watt·cm^-2), approximate 65.9% of PFOA (25 μg·L^-1) in the feed solution was degraded within a hydraulic time of 2 min (at the permeate flow rate of 43 LMH) due to the microwave-Fenton like reactions. In addition, low flow rates and moderate catalyst coating densities are critical for optimizing PFOA removal. Finally, potential degradation mechanisms of PFOA were proposed through the analysis of degradation by-products (e.g., PFPeA). The findings may provide new insight into the development of reactive membrane-enabled systems for destruction of refractory PFAS.

Keywords: microwave-assisted membrane (MWM), PFASs, degradation