Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

等离子体聚合及其聚合物的应用

本文着重综述了烃,含氮、氧的有机化合物,碳氟化合物以及有机硅化合物的等离子体聚合。同时还系统地介绍了等离子体聚合物在制备反渗透膜、分离膜、材料表面的涂层等方面的国内外的最新研究成果。     

羟丙基醋酸纤维素的合成及其膜的反渗透性

研究了羟丙基纤维素和羟丙基醋酸纤维素的合成。制备羟丙基纤维素的较佳反应温度为40℃左右和2小时或稍长,羟丙基含量随环氧丙烷浓度的增加而增加。在制备羟丙基醋酸纤维素时,随羟丙基含量的增加,所需醋化和水解的时间减少。以甘油-正丙醇或磷酸为添加剂,丙酮为溶剂经30～60s蒸发后制得了羟丙基醋酸纤维素反渗透膜。后者在20kg/cm~2下对氯化钠脱盐率可达95～98％,水通量1.0～2.1mL/cm~2·h,其使用温度上限比醋酸纤维素反渗透膜提高10℃以上。     

Mixed Polymer‐Coated Magnetic Nanoparticles as Forward Osmosis Draw Agents of Tuned Hydrophilicity

We recently reported a polymer‐coated magnetic nanoparticle (MNP) draw agent for the forward osmosis (FO) water desalination process. The water flux was found to increase when the polymer poly(sodium acrylate) (PSA) was anchored to the MNP surface as compared to the polymer (or polyelectrolyte solution) alone, due to the polymer chains being stretched out and most of the hydrophilic groups on the polymer contributing to water flux. We herein report the use of a secondary polymer poly(N‐isopropylacrylamide) PNIPAM to manipulate the PSA polymer conformation and influence inter‐ and intrachain interactions to enhance the efficiency of the FO draw agent. These PSA–PNIPAM‐coated MNPs generated a much higher water flux of ～11.66 LMH when compared to the 100 % PSA‐coated MNPs featuring a value of ～5.32 LMH under identical FO conditions. The osmotic pressure and water flux driven by the mixed polymer‐coated MNPs were found to be a strong function of the net polymer coverage on MNPs, that is, net available hydrophilic groups. Our new draw agent demonstrates potential for use in the water industry due to its improved efficiency and cost effectiveness as it uses only ～0.062 % (w/v) of the draw agent solution.     

Preparation,structure characteristics and separation properties of thin-film composite polyamide-urethane seawater reverse osmosis membrane

A novel thin-film composite (TFC) seawater reverse osmosis membrane was developed by the interfacial polymerization of 5-chloroformyloxyisophthaloyl chloride (CFIC) and metaphenylenediamine (MPD) on the polysulphone supporting membrane. The performance of the TFC membrane was optimized by studying the preparation parameters, which included the reaction time, pH of the aqueous-MPD solution, monomer CFIC concentration, additive isopropyl alcohol content in aqueous solution, curing temperature and time. The reverse osmosis performance of the resulting membrane was evaluated through permeation experiment with synthetic seawater, and the structure of the novel membrane was characterized by using SEM, AFM and XPS. Furthermore, the separation properties of the TFC membrane were tested by examining the reverse osmosis performances of various conditions, the boron rejection performance and the long-term stability. The results show that the desired TFC seawater reverse osmosis membrane has a typical salt rejection of 99.4% and a flux of about 35 L/m² h for a feed aqueous solution containing 3.5 wt.% NaCl at 5.5 MPa, and an attractive boron rejection of more than 92% at natural pH of 7–8; that the novel seawater reverse osmosis membrane appears to comprise a thicker, smoother and less cross-linking film structure. Additionally, the TFC membrane exhibits good long-term stability.     

Innovative beneficial reuse of reverse osmosis concentrate using bipolar membrane electrodialysis and electrochlorination processes

Reverse osmosis (RO) is a widely used and rapidly growing desalination technology. A major disadvantage of this process is that the concentrate from the RO process, which could be as much as 25% of the feed stream, represents a polluting stream. This waste stream could pose a significant challenge to the implementation of this process, particularly for inland communities which do not have the option of ocean disposal. An excellent environmentally benign approach to disposal could be beneficial reuse of the waste stream. This study presents two innovative beneficial reuse strategies for RO concentrate produced by an integrated membrane system (IMS) from a wastewater reclamation facility. The technologies evaluated in this study included bipolar membrane electrodialysis (BMED) for conversion of RO concentrate into mixed acid and mixed base streams, and electrochlorination (EC) for onsite chlorine generation. Bench-scale studies conducted with BMED demonstrated that RO concentrate could be desalted while producing mixed acids and mixed bases with concentrations as high as 0.2N. Similarly, the EC process was capable of producing a 0.6% hypochlorite solution from RO concentrate. The acids and bases as well as the hypochlorite produced could be directly applied to the RO process as well as upstream pre-treatment processes. A preliminary economic evaluation of the viability of these two approaches was conducted by conducting rough order of magnitude cost estimates based on the bench-scale performance of these processes on RO concentrate. A comparison of the overall costs of an Integrated Membrane System utilizing these innovative reuse strategies with conventional disposal options and thermal zero liquid discharge treatment is presented. This comparison indicates that a reuse approach might be economically viable for inland wastewater reuse facilities that utilize RO membranes and have limited options for concentrate disposal.     

自支撑NH2-MIL-125/聚噁二唑复合正渗透膜的制备及性能

合成了高强度亲水性含羧基聚噁二唑材料(POD-COOH)和含氨基金属有机框架材料(NH₂-MIL-125), 以NH₂-MIL-125为填料, 与POD-COOH基体材料进行溶液共混, 并通过溶液浇铸法制备系列新型自支撑复合正渗透膜, 研究NH₂-MIL-125的引入对复合正渗透膜结构和性能的影响. 研究结果表明, 所制备的系列复合正渗透膜均呈致密结构, 且随着NH₂-MIL-125含量的增加, 复合膜的表面亲水性增加、 电负性增强, 并保持良好的机械性能. 以去离子水为进料液, 1.5 mol/L硫酸钠溶液为汲取液, 对上述自支撑复合膜进行正渗透性能测试, 发现由于消除了传统正渗透膜支撑层的内浓差极化现象, 该新型复合正渗透膜在分离过程中具有优异的正渗透性能.     

一种新型聚酰亚胺-氨酯反渗透复合膜材料的合成及表征

采用关键功能单体N,N'-二甲基间苯二胺(DMMPD)和多元酰氯5-氯甲酰氧基-异肽酰氯(CFIC)聚合制备了一种耐氧化的聚酰亚胺-氨酯(DMMPD-CFIC)反渗透复合膜材料. 研究了水相溶剂、 多元胺浓度和组成及两相接触时间等因素对DMMPD聚合成膜的影响. 结果表明, 虽然DMMPD-CFIC膜的脱盐率不够理想, 但将4-甲基间苯二胺(MMPD)与DMMPD以2∶1(质量比)组合后制得的MMPD/DMMPD-CFIC膜的脱盐率得到显著提高, 并且对膜的耐氯性能影响不大. 采用傅里叶衰减全反射红外光谱(FTIR)和X射线光电子能谱(XPS)分析了2种膜的活性层的结构, 并利用扫描电镜(SEM)和原子力显微镜(AFM)对膜的表面形态进行了表征.     

基于海水淡化的正渗透膜分离技术的发展

近年来,水资源危机日益加重。在海水淡化技术中,与反渗透分离技术相比,正渗透分离技术作为一种低能耗、绿色的解决方案,具有明显优势,在国际上得到了广泛的重视,是膜分离技术的研究热点之一。本文从正渗透膜材料结构与性能关系的角度,对膜材料的最新进展进行了综述,同时分析了汲取液的常见类型,并简述了正渗透分离技术的新应用,展望了其未来的发展前景。     

Changes of antioxidative enzymes and cell membrane osmosis in tomato colonized by arbuscular Mycorrhizae under NaCl stress

Salinity toxicity is a worldwide agricultural and eco-environmental problem. Many literatures show that arbuscular mycorrhizal fungi (AMF) can enhance salt tolerance of many plants and some physiological changes occurred in AM symbiosis under salt stress. However, the role of ROS-scavenging enzymes in AM tomato is still unknown in continuous salt stress. This study investigated the effect of Glomus mosseae on tomato growth, cell membrane osmosis and examined the antioxidants (superoxide-dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; peroxidase, POD) responses in roots of mycorrhizal tomato and control under different NaCl stress for 40 days in potted culture. NaCl solution (0, 0.5 and 1%) was added to organic soil in the irrigation water after 45 days inoculated by AMF (Glomus mosseae). (1) AMF inoculation improved tomato growth under salt or saltless condition and reduced cell membrane osmosis, MDA (malonaldehyde) content in salinity. So the salt tolerance of tomato was enhanced by AMF; (2) SOD, APX and POD activity in roots of AM symbiosis were significantly higher than corresponding non-AM plants in salinity or saltless condition. However, CAT activity was transiently induced by AMF and then suppressed to a level similar with non-AM seedlings; (3) higher salinity (1% level) and long stress time suppressed the effect of AMF on SOD, APX, POD and CAT activity; (4) this research suggested that the enhanced salt tolerance in AM symbiosis was mainly related with the elevated SOD, POD and APX activity by AMF which degraded more reactive oxygen species and so alleviated the cell membrane damages under salt stress. Whereas, the elevated SOD, POD and APX activity due to AMF depended on salinity environment.