Sorption and biodegradation of stormwater trace organic contaminants via composite alginate bead geomedia with encapsulated microorganisms†

Urban areas generate high volumes of stormwater runoff that frequently contains complex mixtures of hydrophilic trace organic contaminants (TOrCs) and dissolved nutrients. Green stormwater infrastructure is becoming increasingly adopted as a nature-based solution for improving water quality but is typically inefficient for removing dissolved-phase contaminants. We recently developed and characterized novel bioactive composite alginate bead media (BioSorp Beads) containing encapsulated PAC and iron-based water treatment residuals [FeWTR] as sorbents and white rot fungi as model biodegrading organisms to effectively capture and biodegrade stormwater-relevant TOrCs. We created multiple abiotic (no fungi) and biotic beads (containing Trametes versicolor or Pleurotus ostreatus fungi) to investigate sorption removal of a suite of representative dissolved-phase stormwater relevant pollutants (a neonicotinoid/metabolite, phosphate, three PFAS, and one tire-wear compound [acetanilide]). We also measured coupled sorption and biodegradation of acetanilide as a proof-of-concept demonstration of encapsulated biodegrading organisms. Alginate encapsulation increased desnitro-imidacloprid sorption onto PAC, likely due to the interactions between compound altered insecticidal functional groups and alginate. The sorption capacity of imidacloprid and desnitro-imidacloprid was up to 29.1 mg g⁻¹ and 16.8 mg g⁻¹, respectively, and impacted by PAC presence and the partial charge distributions of the compounds. The encapsulated FeWTR and Fe³⁺-alginate beads drove phosphate sorption (42.1 mg phosphate per g beads). Long-chain PFAS removal in the beads (13.1 mg PFOA per g) was greater than short-chain PFAS removal capacity (5.2 mg PFBA per g, 5.1 mg PFBS per g). Encapsulated fungi were not inhibited by exposure to azide that typically kill fungi in laboratory experiments, indicating the potential for encapsulation to protect organisms from harsh conditions. Furthermore, biodegradation of acetanilide by encapsulated fungi beyond sorption controls demonstrated that coupled sorption and biodegradation with the beads occurred. BioSorp Beads successfully capture and biodegrade representative hydrophilic stormwater TOrCs and thus hold potential as a green stormwater infrastructure geomedium and bioaugmentation tool.