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Insights into simultaneous ammonia-selective and anti-fouling mechanism over forward osmosis membrane for resource recovery from domestic wastewater

Bao, Xian, Wu, Qinglian, Shi, Wenxin, Wang, Wei, Zhu, Zhigao, Zhang, Zhiqiang, Zhang, Ruijun, Zhang, Xinyu, Zhang, Bing, Guo, Yuan, Cui, Fuyi
Journal of membrane science 2019 v.573 pp. 135-144
amines, ammonium, ammonium nitrogen, artificial membranes, electrostatic interactions, fouling, hydrophilicity, municipal wastewater, osmosis, polyethyleneimine
The inferior selectivity towards ammonia nitrogen (NH4+-N) and severe fouling of the forward osmosis (FO) membrane during the pre-concentration of domestic wastewater (DW) greatly hinder the practical realization of FO-based processes in DW reduction and resource utilization. Herein, surface amine functionalization strategy was, for the first time, adopted to explore the feasibility of fabricating FO membrane with simultaneous ammonia-selective and anti-fouling capacities. Polyethylenimine (PEI), owing to its abundant positively charged primary (-NH3+) and tertiary (-NR3+) amines, was introduced as a protective barrier to impose synergistic interactions of diffusion resistance and electrostatic repulsion to the external NH4+. Benefiting from this, the PEI-grafted membrane exhibited significantly enhanced NH4+-N selectivity with rejection rate of 95.88% over that of 70.36% for the pristine membrane. Besides, the incremental surface hydrophilicity and smoothness as well as the nearly neutral surface potential endowed the PEI-grafted membrane with robust anti-fouling capacity in the concentration of raw DW. Meanwhile, deriving from the reinforced NH4+-N selectivity and the alleviated membrane fouling, the grafted membrane with moderate PEI load possessed a superior NH4+-N removal efficiency of 86.11%. The maximum concentration experiment of DW indicated that the simultaneous ammonia-selective and anti-fouling capacities of the PEI-grafted membrane greatly leaned upon the inhibitions of both the PEI layer incapacitation and the NH4+-N cake-enhanced polarization. The presented strategy on surface amine functionalization enlightened the fabrication of ammonia-selective and anti-fouling FO membrane and significantly facilitated the development of FO-based technologies in resource recovery from DW.