Gel immobilization: A strategy to improve the performance of anaerobic ammonium oxidation (anammox) bacteria for nitrogen-rich wastewater treatment.

Anaerobic ammonium oxidation (anammox) process appears a suitable substitute to nitrification-denitrification at a lower C/N ratios. Anammox is a chemolithoautotrophic process, belong to phylum Planctomycetes, and they are slow growing bacteria. Different strategies, e.g., biofilm formation, granulation and gel immobilization, have been applied to maintain a critical mass of bacterial cells in the system by avoiding washout from the bioreactor. Gel immobilization of anammox appears the best alternative to the natural process of biofilm formation and granulation. Polyvinyl alcohol-sodium alginate, polyethylene glycol, and waterborne polyurethane are the most reported materials used for the entrapment of anammox bacteria. However, dissolution of the gel beads refrains its application for long term bioprocess. Magnetic powder could coat on the surface of the beads which may increase the mechanical strength and durability of pellets. Application and problem of immobilization technology for the commercialization of this technology also addressed.