Removal of reverse-fluxed ammonium by anammox in a forward osmosis system using ammonium bicarbonate as a draw solute

• Anammox is linked to forward osmosis for removing reverse-fluxed ammonium.
• Nitritation–anammox shows advantages over sole anammox in assisting FO.
• The osmotic anammox helps maintain osmotic pressure and thus water flux.
• This system prevents the release of ammonium contaminants to water body.

Reverse flux of ammonium draw solute is a serious problem for applying forward osmosis (FO) in water/wastewater treatment. In this study, anaerobic ammonium oxidization (anammox) was synergistically linked to FO for removal of reverse-fluxed ammonium, thereby creating an osmotic anammox system. The feasibility of this system was demonstrated through both batch and continuous operation, and the anammox process was developed in two stages: sole anammox and nitritation–anammox. With addition of nitrite, the sole anammox process achieved an effluent ammonium concentration of 9.9±9.5 mg N L−1. The nitritation–anammox maintained an ammonium concentration of 3.1±4.2 mg N L−1, and increased the water flux to 2.46±0.24 LMH (L m−2 h−1) compared with the sole anammox (1.90±0.14 LMH). The nitritation–anammox process exhibited advantages over anammox process in assisting the FO with respect to water flux improvement and chemical savings. The osmotic anammox system can be linked to previously developed microbial electrolysis cells that recover ammonium from high-strength wastes as a draw solute for FO operation. The results encourage further investigation of this system for effects of organic residues, decreasing nitrate accumulation, understanding biofilm on the FO membrane, and long-term performance with actual waste.

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