Stormwater applications of zeolite-coated biofilm carriers for ammonium removal with possible applications to PFAS biotransformation

Stormwater can contain nitrogen and contaminants of emerging concern, including poly- and perfluorinated alkyl substances (PFAS). As such, stormwater treatment systems are important for mitigating pollution in urban waterways. We previously showed that zeolite-coated polyethylene carriers were able to concentrate ammonium, enhancing colonization and retention of anammox bacteria in a wastewater environment. In this study, we focused on whether such carriers could remove ammonium quickly enough to be useful in a stormwater treatment system and retain target nitrogen-cycling organisms in the field and the laboratory. Polyethylene carriers (controls) and zeolite-coated carriers were studied; the two types of carriers were used both in a clean state and after seeding them with bacteria, either with an anammox enrichment culture or with treatment pond water. Zeolite-coated carriers were capable of rapid abiotic ammonium removal. Seeded carriers were capable of retaining anammox bacteria (Amx) and aerobic ammonia oxidizers (measured as amoA gene numbers) over a 10-week field deployment. When field-deployed, few differences in the retention of target organisms on the two carrier types were observed, whether seeded or clean. When tested in the laboratory, zeolite-coated carriers seeded with pond microorganisms resulted in lower effluent ammonia concentrations compared to control carriers (P < 0.0001). There was no statistically significant difference observed in Amx and amoA gene quantities on the two carrier types, although Amx genes were detected on the zeolite-coated carriers but not on the control carriers. Reactors containing carriers seeded with the anammox enrichment removed similar quantities of ammonium (P = 0.14) and had similar quantities of Amx (P = 0.44) and amoA (P = 0.23). Zeolite particles and zeolite-coated carriers were also tested in the presence of an enrichment culture containing the feammox organism Acidimicrobium sp. strain A6 (A6), which is capable of PFOS and PFOA defluorination. Statistically significant A6 enrichment occurred in reactors containing zeolite particles (P < 0.0001) and on two of five sampling days in reactors containing zeolite-coated carriers (P = 0.007, P = 0.045). These results suggest that the use of zeolite-coated carriers, perhaps in a combination of seeded and clean, show promise for managing ammonium, and perhaps PFAS, in stormwater control systems.