采用荷正电纳滤膜进行市政水体中低浓度氨氮（NH3-N主要以NH4+形式存在）去除性能研究，从离子微观理化参数的角度探究了共存阴离子Cl-和SO42-以及共存阳离子Mg2+和Na+对荷正电纳滤膜分离NH4+性能的影响。结果表明，由于Cl-与SO42-的微观理化参数区别很大，Cl-比SO42-更优先透过荷正电纳滤膜，为保持膜产水侧电中性，膜进水侧的低电荷、小水合半径、小平均离子势、大扩散系数的NH4+会比Mg2+优先透过膜。如果膜进水侧没有Na+，则会导致NH4+的负截留，反之，由于NH4+和Na+微观理化参数较为相近，均可以透过膜，则导致NH4+的优先透过失效。不同体系下的多级循环实验证明，MgCl2+NH4Cl体系和Na2SO4+(NH4)2SO4体系，利用荷正电纳滤膜均难以实现NH4+与Mg2+、Na+的完全分离。

A positively charged nanofiltration membrane was used to study the removal performance of low-concentration ammonia nitrogen (NH4+) in municipal water. The effects of co-existing anions Cl- and SO42- as well as co-existing cations Mg2+ and Na+ on performance of NH4+ separation by positively charged nanofiltration membrane were investigated from the perspective of ionic microscopic physicochemical parameters. The results showed that Cl- could preferentially permeated the positively charged nanofiltration membrane than SO42- , mainly due to the huge difference between the microscopic physicochemical parameters of Cl- and SO42-, and then NH4+ with lower charge, smaller hydration radius, smaller average ion potential and larger diffusion coefficient on the water inlet side of the membrane could preferentially permeate the membrane than Mg2+ in order to keep the water outlet side of the membrane electrically neutral. If there was no Na+ on the water inlet side of the membrane, the rejection rate of NH4+ would be negative. Conversely, since the microscopic parameters of NH4+ and Na+ were similar, both could permeate the membrane, leading to the failure of NH4+ preferential permeation. The multi-stage cycling experiments under different systems proved that it was difficult to achieve complete separation of NH4+ from Mg2+ and Na+ using positively charged nanofiltration membrane for MgCl2+NH4Cl system and Na2SO4+(NH4)2SO4 system.

[1]Korzenowski C, Minhalma M, Bernardes A M, et al. Nanofiltration for the treatment of coke plant ammoniacal wastewaters [J]. Separation and purification technology, 2011, 76(3): 303-307.
[2]Jafarinejad S. Cost estimation and economical evaluation of three configurations of activated sludge process for a wastewater treatment plant (WWTP) using simulation [J]. Applied Water Science, 2017, 7(5): 2513-2521.
[3]Bodalo A, Gomez J-L, Gomez E, et al. Ammonium removal from aqueous solutions by reverse osmosis using cellulose acetate membranes [J]. Desalination, 2005, 184(1-3): 149-155.
[4]张莉娜, 黄婕, 熊丹柳, et al. 纳滤膜脱盐及其在海水软化中的应用 [J]. 膜科学与技术, 2012, 32(01):97-101
[5]侯立安, 高鑫, 赵兰. 纳滤膜技术净化饮用水的应用研究进展 [J]. 膜科学与技术, 2012, 32(05): 1-7.
[6]杜巍, 刘学建, 于波, et al. 纳滤膜在北京阿苏卫填埋场渗滤液改扩建工程中的应用 [J]. 膜科学与技术, 2010, 30(1): 78-81.
[7]汪润慈, 袁中伟, 晏太红, et al. 硝酸铵-微量硝酸钙体系的纳滤过程研究 [J]. 膜科学与技术, 2017, 37(02): 72-77.
[8]Paugam L, Taha S, Dorange G, et al. Mechanism of nitrate ions transfer in nanofiltration depending on pressure, pH, concentration and medium composition [J]. Journal of Membrane Science, 2004, 231(1-2): 37-46.
[9]Garcia-aleman J, Dickson J M. Permeation of mixed-salt solutions with commercial and pore-filled nanofiltration membranes: membrane charge inversion phenomena [J]. Journal of Membrane Science, 2004, 239(2): 163-172.
[10]王大新, 廖卓丹, 伍灵, et al. 用纳滤膜分离混合无机电解质溶液的性能评价方法 [J]. 化工学报, 2007, 58(3): 673-678.
[11]Marcus Y. A simple empirical model describing the thermodynamics of hydration of ions of widely varying charges, sizes, and shapes [J]. Biophysical chemistry, 1994, 51(2-3): 111-127.
[12]Babu C S, Lim C. Theory of ionic hydration: Insights from molecular dynamics simulations and experiment [J]. The Journal of Physical Chemistry B, 1999, 103(37): 7958-7968.
[13]Rempe S B, Asthagiri D, Pratt L R. Inner shell definition and absolute hydration free energy of K+(aq) on the basis of quasi-chemical theory and ab initio molecular dynamics [J]. Physical Chemistry Chemical Physics, 2004, 6(8): 1966-1969.
[14]Richards L A, Sch Fer A I, Richards B S, et al. The importance of dehydration in determining ion transport in narrow pores [J]. Small, 2012, 8(11): 1701-1709.
[15]Dudev T, Lim C. Importance of metal hydration on the selectivity of Mg2+ versus Ca2+ in magnesium ion channels [J]. Journal of the American Chemical Society, 2013, 135(45): 17200-17208.
[16]Eiberweiser A, Nazet A, Hefter G, et al. Ion hydration and association in aqueous potassium phosphate solutions [J]. The Journal of Physical Chemistry B, 2015, 119(16): 5270-5281.
[17]Hong S, Constans C, Surmani Martins M V, et al. Scalable graphene-based membranes for ionic sieving with ultrahigh charge selectivity [J]. Nano letters, 2017, 17(2): 728-732.
[18]Kobayashi K, Liang Y, Murata S, et al. Ion distribution and hydration structure in the stern layer on muscovite surface [J]. Langmuir, 2017, 33(15): 3892-3899.
[19]Epsztein R, Shaulsky E, Dizge N, et al. Ionic charge density-dependent donnan exclusion in nanofiltration of monovalent anions [J]. Environmental Science & Technology, 2018, 52: 4108-4116.
[20]Yin N, Yang G, Zhong Z, et al. Separation of ammonium salts from coking wastewater with nanofiltration combined with diafiltration [J]. Desalination, 2011, 268(1-3): 233-237.
[21]姜迪, 徐异峰, 陆国太, et al. 低浓度范围内盐浓度对纳滤膜截留性能的影响 [J]. 膜科学与技术, 2017, 37(01): 64-68.