Assessment of Removal Efficiency of Per- and Polyfluoroalkyl Substances (PFASs) in Industrial Wastewater Using Various Adsorbents

Abstract

Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals known for their resistance to heat, water, and oil, making them prevalent in various industrial and consumer products. PFASs are highly persistent in the environment due to their strong carbon-fluorine bonds and pose potential human health risks. Regulatory bodies of various countries have implemented guidelines to limit PFAS emissions and contamination in the environment including water. Adsorption has proven to be more effective for PFAS removal due to their persistence compared to other techniques like oxidation, bioremediation, and membrane filtration. Chitosan-based biosorbents have emerged as a promising solution due to the presence of functional amine groups that enhance electrostatic interactions with anionic PFASs. These biosorbents are environmentally friendly and cost-effective, making them advantageous compared to traditional activated carbons and ion-exchange resins. This study aims to evaluate the efficiency of PFAS removal from industrial wastewater using various adsorbents. Initially, selected adsorbents, including two types of activated carbon, two types of ion exchange resins, and the newly developed PG-CB biosorbent tailored for PFAS adsorption, underwent characterization to assess their surface area, structure, and chemical properties. Subsequently, PFAS concentration and composition in industrial wastewater were analyzed. The study also compared the efficiency of PFAS removal among these adsorbents, aiming to identify optimal solutions for mitigating PFAS contamination in industrial wastewater and provide insights into their comparative performance. PFAS quantification is challenging due to the wide variety of PFAS compounds and their precursors, along with their varying chemical properties and low environmental concentrations. In this study, PFAS quantification was carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS), total oxidizable precursor-liquid chromatography-tandem mass spectrometry (TOP-LC-MS/MS), and total oxidizable precursor-combustion ion chromatography (TOP-CIC). LC-MS/MS provided high sensitivity and specificity for individual PFASs, TOP-LC-MS/MS expanded detection to include oxidizable precursors, and TOP-CIC offered comprehensive quantification of total organic fluorine content. PFAS concentrations of industrial wastewater was found to be 2.6 ug/L using LC-MS/MS, 3.1 ug/L using TOP-LC/MS/MS, and 5.3 ug/L using TOP-CIC. LC-MS/MS analysis applied to 33 PFAS species detected 11 species, with PFBA showing the highest concentration and PFCA compounds being predominantly detected. Chitosan-based biosorbents (CB) and polyaniline grafted chitosan-based biosorbents (PG-CB) were synthesized and characterized using FE-SEM, BET, XPS, and FT-IR analyses. The characterization revealed that PG-CB had a higher number of functional amine groups due to polyaniline grafting, enhancing its adsorption capacity. This detailed characterization demonstrated that the structural and chemical modifications in PG-CB significantly improved its potential for effective PFAS remediation. Furthermore, the efficiency of various adsorbents in removing PFAS was evaluated. PAC and PG-CB demonstrated high removal efficiencies of 70-80% at an adsorbent dosage of 0.5 g/L. The incomplete removal was mainly due to the lower removal efficiency of short-chain PFAS, particularly PFBA. Ion exchange resins achieved a maximum removal efficiency of ~20%, possibly due to the lower adsorbent dosage used compared to other studies. PG-CB exhibited a high removal efficiency like activated carbon, particularly showing higher removal rates for short-chain PFAS compounds that are typically challenging to remove compared to activated carbon. This highlights the potential of PG-CB as a viable alternative to activated carbon for PFAS removal. Kinetic and isotherm studies on F400 and PG-CB for PFOA removal showed both adsorbents rapidly reaching 90% equilibrium within 6 hours, with PG-CB exhibiting higher capacity. Both followed the pseudo-second order model closely. PG-CB outperformed F400 with higher qm and K values, lower 1/n, confirming superior PFOA affinity and potential in water treatment. These findings underscore the efficacy of PG-CB as effective adsorbents for PFAS removal from industrial wastewater, highlighting the challenges in achieving complete removal, especially for short-chain PFAS compounds like PFBA.