Enhancing modification of forward osmosis membrane for zwitterion-based surface using chemical structure of arginine to treat ammonium-rich wastewater

Intense ammonium transport passing through forward osmosis (FO) membranes is a critical problem in wastewater reuse because it deteriorates the permeate quality. Although conversion of the surface charge of the FO membrane to a positive charge improves ammonium rejection by electrostatic repulsion, severe membrane fouling is induced by electrostatic attraction. In this study, the zwitterion was applied to achieve the enhancing ammonium control and anti-fouling at the same time. The traditional method can connect only one zwitterion with one linker and initiator, and it has a limited capacity for membrane modification. Arginine was also used as the new linker to connect zwitterion on the membrane which has 4 pathways unlike the 1 pathway of traditional linker at the same spot. By applying an arginine linker, the quantitative initiator was increased by 50 times than the traditional method, and it induced improving zwitterion-based membrane modification. In addition, the maximum quaternary amine of zwitterion was increased by 2.3 times on the membrane surface by arginine than the traditional method, and the ammonium transport was also reduced by 3 times. In livestock wastewater treatment using arginine-zwitterion-based FO, the water flux was recovered by 20%, and the deposition of foulants was reduced by 55.7% than virgin FO because of the enhanced hydrophilic surface. Moreover, ammonium transport was reduced by up to 50.4%. This study proposed a new concept of FO membrane modification to improve ammonium selectivity, which can be used as a basis for further FO research in water treatment.