Effects of Biochar on PFAS Destruction by Advanced Reduction Process

Abstract

The widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in water sources poses significant risks to human health and the environment. PFAS are highly persistent due to exceptional strength and stability of the carbon-fluorine (C-F) bonds present in their chemical structure, allowing them to remain in the environment for extended periods. Advanced reduction processes (ARPs), such as UV/sulfite systems, have shown great promise for PFAS remediation in water by generating highly reductive hydrated elections (eaq•−) capable of cleaving the C-F bonds. Incorporating cost-effective biochar into the UV/sulfite system has the potential to enhance PFAS removal by promoting adsorption, thereby facilitating the subsequent reductive defluorination of PFAS for enhanced PFAS destruction.  

This study investigated how different types of biochars affect PFAS defluorination in water by using the UV/sulfite system. Both long-chain (PFOA and PFOS) and short-chain (PFHxS and PFBS) PFAS were examined to represent commonly detected and recalcitrant PFAS compounds. Four biochars—Corn 500, Douglas Fir 500, Douglas Fir 900 (where the number represents pyrolysis temperature in °C for biochar production), and a commercial biochar were evaluated for their effectiveness in enhancing PFAS defluorination. Duplicate experiments were conducted under anoxic conditions with 1 mg/L of PFAS, 0.1 g/L of biochar, 40 mM of sodium sulfite (Na2SO3), and 1 mM of sodium chloride (NaCl) in a photochemical reactor equipped with UV lamps operating at 254 nm. At different time intervals (i.e., 5, 15, 30, 60, 90, 120, 150, and 180 min), samples were collected, filtered, and analyzed for fluoride release using an ion selective electrode (ISE) to determine the defluorination efficiency of PFAS.  

Our results showed that the presence of biochar significantly enhanced the defluorination of PFAS, compared to UV-only and UV/sulfite systems. These findings provide insights into designing the optimal operating conditions for PFAS degradation, demonstrating that integrating biochar with UV/sulfite ARPs may offer a cost-effective, efficient, and scalable strategy for combating PFAS pollution in water treatment systems.