Microwave treatment effectively regenerated PFAS-laden exhausted granular activated carbons from water treatment plants

This study tested microwave (MW) regeneration of PFAS-laden field-spent GACs collected from four U.S. treatment plants with different operational histories. This work provides new insights into the application-specific performance and challenges of MW regeneration for exhausted, aged GAC, accounting for changes in surface chemistry, porosity, and PFAS adsorption capacity before and after MW treatment. MW treatment significantly increased the surface area (8–34%) and pore volume (7–34%) of spent GACs to levels comparable to those of virgin F400 GAC, showing improved PFAS adsorption capacity. Batch adsorption tests showed an 85 to 100% increase in PFAS removal efficiency after MW regeneration, comparable to virgin F400. Results from batch tests and RSSCTs consistently demonstrated the effectiveness of MW regeneration in recovering the PFAS adsorption performance of GAC. PFAS extraction results showed that PFAS concentrations decreased from 39–670 ng/g (field-spent GACs) to below method detection limits after MW-regeneration, indicating a substantial reduction in extractable PFAS concentrations and the accumulation of fluoride following regeneration. This accumulation demonstrated extensive PFAS defluorination, which was further enhanced by increased GAC moisture content. Overall, the findings showed the effectiveness of MW treatment in removing PFAS from field-spent GACs and in regenerating GACs.