Catalytic Defluorination of PFAS in Municipal Wastewater, Sludge, and Dewatering Filtrate at Mild Temperatures (≤ 80C)

INTRODUCTION
Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative 'forever chemicals' that pose significant environmental and public health challenges due to their resistance to traditional wastewater treatment processes. Current PFAS treatment technologies applied in full-scale water and wastewater treatment processes primarily rely on phase transfer methods, such as ion exchange, adsorption, membrane filtration, and foam fractionation [1, 2], or high-temperature (350-1000°C) destruction processes like incineration, pyrolysis, and supercritical water oxidation [3-5]. However, these approaches are limited by inherent drawbacks, such as high energy consumption, high capital investment and operating cost, and operational complexity, making full-scale, in situ implementation by utilities challenging.

This study for the first time introduces a novel, bio-inspired, transition metal oxide-based catalyst for PFAS destruction at a mildly heated temperature of 80°C, offering a potential energy-efficient alternative. Attributed to the catalyst's low-temperature nature, the process can be integrated into existing heated solids treatment processes, such as thermophilic anaerobic digestion, thermal hydrolysis pretreatment (THP), or pre-pasteurization. The objective of this study is to assess the effectiveness of this catalyst on the destruction of PFAS compounds within the PFAS-accumulating matrices, including municipal wastewater, sludge, and sludge dewatering filtrate. The goal of the current experimental phase is to provide proof of concept and to understand the extent of PFAS destruction in such complex matrices.

Methods and Materials
Samples of treated wastewater effluent, pre-dewatered raw sludge (THP feed sludge), and dewatering filtrate were collected from WSSC Water's Piscataway Bioenergy Facility, a centralized biosolids processing facility that is designed to receive biosolids from six regional water resource recovery facilities (WRRFs), representing a potential full-scale application site for this technology for destroying concentrated PFAS compounds. The experimental design, including the setup of different sample matrices, spiked PFAS concentrations, catalyst doses, reaction temperatures, and reaction time, is shown in Table 1. Briefly, the experiments (Samples 1-36) involved dosing wastewater and sludge samples with synthesized catalyst and performing reactions at 80°C for 24 hours. Additional experiments (Samples 37-42) utilized a pressure vessel (Parr Instrument Company, IL, USA) to simulate full-scale THP conditions at 165°C for 30 minutes. Post-reaction liquid and solid phases were separated and analyzed for PFAS concentrations by following EPA Method 1633.

Results and Discussion Preliminary results of this study, Samples 1-18, are shown in Figures 1 and 2. As can be seen in Figure 1, approximately 57.3% to 69.4% of the total PFAS spiked before the reaction was destroyed. The destruction can be corroborated by the defluorination during the reaction shown Figure 2. It is interesting to observe that the amount of fluoride ion released from the reactions for both types of samples were approximately more than 10 times the stoichiometric release of fluoride (Figure 2). It should be noted that rather than the target concentration of 500 ppb PFOS as shown in Table 1, the actual PFAS concentration spiked into the shown groups before reaction turned out to be approximately 1,100 ppb PFOS with a significant amount of impurities accounting for about 10% of the added PFOS. The average concentration of PFOA+PFOS after the treatment was surprisingly reduced to only about 8.3 ppb, marking a PFOA+PFOS destruction efficiency of over 99% ± 0.03% on average. Furthermore, approximately 10.1% to 19.0% of the total PFAS spiked was adsorbed onto the catalyst. In the liquid phase, approximately 17.2% to 26.5% of the total PFAS were either transformed to other PFAS species identified by EPA 1633 or remained undegraded. It is noteworthy that the PFAS destruction across the sample types were insignificantly different (T-test, p > 0.05), indicating that defluorination in WRRF effluent samples was not affected by the more complex characteristics.

These preliminary findings demonstrate the potential of the studied catalyst for efficient PFAS destruction in wastewater matrices and further provide the confidence for testing samples with more complex constituents. Results from more complex samples, including sludge dewatering filtrate and THP feed sludge (Samples 19-42), will be made available in early 2025 and incorporated in the manuscript.