Formatted Title
Impact of Organic Matter on PFAS Removal from Complex Water Matrices by Selective and Nonselective Adsorbents
Background/Objectives
This presentation focuses on the impact of organic matter presence on PFAS removal performance of selective and nonselective adsorbents during the treatment of complex water matrices such as groundwater and wastewater effluent. Employing different levels of pretreatment, such as ozonation (O3) and biologically active filtration (BAF), can alter the concentration/characteristics of the interfering organic matter, which ultimately impacts the PFAS removal performance and longevity of adsorption-based processes. Further, size exclusion chromatography (SEC) analysis could assist in unraveling the mechanisms behind organic matter interference with PFAS removal for selective versus nonselective adsorbents.
The objectives of this study were to: 1) evaluate the potential of selective adsorbents such as anion exchange resins (AER) and surface-modified clays (SMC) as an alternative to granular activated carbon (GAC) during the downstream sorption-based step in reverse-osmosis (RO)-free potable reuse treatment trains; 2) compare the impact of different pretreatment scenarios (i.e., O3, BAF, and O3-BAF in tandem) on the performance enhancement of AER and SMC with respect to both organic matter and PFAS removal compared to GAC; and 3) identify the mechanisms involved in the improvement of PFAS removal performance by GAC, AER, and SMC during each pretreatment scenario.
Approach/Activities
The pilot-scale O3-BAF system employed for pretreating the wastewater effluent/groundwater for different scenarios in this study was fed with treated wastewater effluent from a 30 m3/d pilot-scale sequencing batch membrane bioreactor (SBMBR). Raw wastewater from a student complex at Colorado School of Mines was discharged to the SBMBR with a total solid concentration of ~5.1 g/L and a solid retention time of 25 days. Rapid small-scale column tests (RSSCTs) were conducted with selective (AER, SMC) and non-selective adsorbent media (GAC) receiving wastewater effluent/groundwater that had undergone different levels of pretreatment. RSSCTs use ground adsorbent media with smaller particle size enabling the prediction of PFAS removal performance of an adsorbent in a fraction of the time required for full-sized particle scale tests. In addition to PFAS analysis, SEC was conducted to evaluate the interference mechanisms of organic matter with PFAS adsorption into selective and nonselective adsorbents.
Results/Lessons Learned
The results of this study demonstrated that AER outperformed both GAC and SMC for all the investigated pretreatment scenarios with respect to media use rates, particularly for the treatment of perfluoroalkyl sulfonic acids (PFSAs). For nonselective GAC, O3 and BAF resulted in similar PFAS removal improvements, while BAF alone performed better than O3 for AER and SMC. O3-BAF in tandem resulted in the highest PFAS removal performance improvement among pretreatments investigated for selective and nonselective adsorbents. Side by side evaluation of the dissolved organic carbon (DOC) breakthrough curves and size exclusion chromatography (SEC) for each pretreatment scenario suggested that despite the higher affinity of selective adsorbents towards PFAS, the competition between PFAS and organic matter (MWs ~100-1000 Da) negatively impacts the performance of these adsorbents. The SEC results also demonstrated that transformation of hydrophobic organic matter to more hydrophilic molecules during O3 and biotransformation of organic matter during BAF were the dominant mechanisms responsible for alleviating the competition between PFAS and organic matter, resulting in PFAS removal improvement.