Polyvinyl Alcohol-Sodium Alginate-Zeolite Biofilm Carriers to Enhance Wastewater Deammonification

Abstract

Polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel biofilm carriers exhibit high biomass retention and porosity. In this study, novel composite PVA-SA carriers were synthesized for partial nitritation/anammox (PN/A) by encapsulating a zeolite mineral (chabazite) and anammox inside the carrier and growing ammonia oxidizing microorganisms (AOMs) on the carrier surface. Initial experiments were carried out in anaerobic sequencing batch reactors (SBRs) with an anammox-based feed. Limited ammonium removal was observed in abiotic controls, while SBRs containing carriers or suspended cultures simultaneously removed ammonium and nitrite, while generating nitrate. AOMs were subsequently inoculated into the SBRs and feed and aeration conditions were adjusted to promote PN/A. Nitrate generation was lower in the carrier SBR compared with suspended growth control, resulting in total inorganic nitrogen removal rates of 11.3 mg N/L/d and 8.9 mg N/L/d for carrier and suspended SBRs, respectively. Overall, the PVA-SA-chabazite carrier SBR exhibited enhanced PN/A performance, most likely because chabazite concentrated ammonium inside the carriers to promote mass transfer and enhance anammox activity. Chabazite was bioregenerated by AOMs and anammox, allowing the carriers to be reused for fifteen cycles over 185 days. The results underscore the potential application of novel PVA-SA-chabazite carriers to promote PN/A for wastewater treatment.