Evaluation of porous polyethylene-supported zeolite carriers to support feammox-based perfluorooctanoic acid biotransformation

Traditional treatment methods for removal of per- and polyfluoroalkyl substances (PFASs) from water are costly and often generate secondary waste, prompting interest in biological alternatives. Acidimicrobium sp. Strain A6 (A6) conducts feammox, or anaerobic ferric iron reduction paired with ammonium oxidation. These bacteria have been shown to defluorinate perfluorooctanoic acid (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 intended to promote A6 growth and PFOA biotransformation. It was hypothesized that the carrier would provide both ammonium and ferric iron to localize A6 bacteria growth and PFOA degradation. 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 (24 μM) PFOA, and degradation was monitored over 100 days. Incubations revealed no significant differences in ammonium removal or A6 growth between cultures with carriers and controls, and no PFOA removal was observed, even in the positive control. A6 was detectable on PEZ carriers (10 3 copies/carrier) at the end of the incubations, suggesting that these carriers provided localized microenvironments supportive of A6 retention, though insufficient for measurable feammox activity or PFOA defluorination, which limits assessment of the carrier design. The minimal activity observed may be attributed to low initial A6 concentrations, a suboptimal iron phase/limited availability of iron, or the presence of other bacteria outcompeting A6. This study indicates that PEZ carriers have potential to support the maintenance of A6 in engineered systems even though no clear support of feammox metabolism or PFOA degradation was observed and outlines parameters that require further optimization to improve anaerobic PFAS biotransformation.