Enhancing feammox-based perfluorooctanoic acid biotransformation using porous polyethylene-supported zeolite carriers

Abstract

Per-and polyfluoroalkyl substances (PFAS), such as perfluorooctanoic acid (PFOA), are persistent environmental contaminants that pose risks to human and ecological health. Traditional treatment methods for PFAS in drinking water are costly and often generate secondary waste, prompting interest in biological alternatives. Acidimicrobium sp. strain A6 conducts feammox, or anaerobic ferric iron reduction paired with ammonium oxidation, and has been shown to defluorinate PFOA and perfluorooctane sulfonate (PFOS) under acidic, anoxic conditions. Its practical application, however, is limited by slow growth, sensitivity to environmental conditions, and specific nutrient requirements. This study explored the potential of porous polyethylene-supported zeolite (PEZ) carriers as a nutrient-integrated support system to promote A6 growth and PFOA biotransformation. Iron-enhanced PEZ carriers were successfully synthesized and exhibited ammonium sorption capacities greater than normal PEZ, confirming their suitability for feammox nutrient delivery. Four unique culture environments were tested in batch incubation experiments spiked with 10 mg/L PFOA, and degradation was monitored over 100 days. Incubations revealed no significant differences in A6 growth or PFOA removal between cultures with carriers and controls. A6 was detectable on PEZ carriers (103 copies/carrier) at the end of the incubations, suggesting that they provided localized microenvironments supportive of A6 retention, though insufficient for measurable feammox activity or PFOA defluorination. The minimal activity observed may have been attributed to low initial A6 concentrations, suboptimal iron phase, or the presence of other bacteria outcompeting A6. While the PEZ carriers successfully retained ammonium and A6, future work should optimize culture conditions and reassess the performance of PEZ carriers in more active A6 cultures.