Theory of reverse osmosis and some other membrane permeation operations

The general permeation equations for various transport operations using membranes were correlated according to the solution-diffusion theory. It was shown that for some important conditions, the permeation properties for reverse osmosis can be generated from those of pervaporation. The use of reverse osmosis with pressure smaller than 2000 psi is calculated to be of limited use for the purification of water with small amounts of organic compounds.     

Removal of organic substances from aqueous solutions by reagent enhanced reverse osmosis

The reagent enhanced reverse osmosis treatment of aqueous solutions containing phenol and its derivatives has been studied. A combination of the reverse osmosis with the oxidation of organic substances by hydrogen peroxide in the presence of FeCl₂ salt as a catalyst was shown to lead to the effective removal of phenol and its derivatives from aqueous solutions. The phenol catalytic decomposition was believed to occur not only in the bulk solution but also on the membrane surface. This phenomenon is of particular interest, but additional studies are necessary. In the case of solutions containing lignosulphonates (LS), a combination of the reverse osmosis treatment with the LS oxidation by hydrogen peroxide was found to provide the high degree of solution purification from both organic substances and inorganic salts. Furthermore, it shows a possibility for the recirculation of water.     

Use of Liquid Chromatography for Studying Reverse Osmosis and Ultrafiltration

Abstract

A method of observing the preferential adsorption of solute or solvent onto a polymer surface by liquid chromatography is illustrated, and the results are discussed in relation to the solute separation by reverse osmosis and membrane fouling. This method shows the existence of a preferentially adsorbed water layer at the polymer-solution interface, where its amount and thickness depend on the polymer material. The adsorption data of undissociated organic solutes indicate that cellulosic materials are intrinsically less susceptible to fouling by such solutes than synthetic polymer materials. It is also shown that the steric repulsion involved in the solute's distribution between the interfacial water phase and the bulk water phase is not sufficient to describe the solute transport through the membrane, and an additional steric effect associated with the frictional force working on the solute molecule in the membrane pore has to be considered.     

Dyestuff effluent treatment by integrated sequential photocatalytic oxidation and membrane filtration

In the present work, the combined photocatalytic oxidation/membrane filtration system is evaluated by decolorization, organic content and salinity reduction of a synthetic dyestuff effluent (SDE) containing the dye Reactive Black 5, with the scope to produce water that is able to be reused in the dyeing processes. The heterogeneous photocatalytic oxidation, as well as the photo-Fenton reagent, in the presence of UV-A or visible light, have been employed under various experimental conditions, in order to achieve complete decolorization and a substantial organic content reduction of the SDE. The addition of a membrane filtration unit, that is able to significantly reduce the high salinity of the photocatalytically treated SDE, can promote water reuse. The comparison of the performance of a nanofiltration and a reverse osmosis membrane by using operating variables, like applied pressure and recovery ratio, concerning the further polishing of the treated effluent shows that reverse osmosis produces water with low organic content and electrical conductivity. The integration of either photocatalytic methods with a reverse osmosis unit, leads to complete decolorization of the SDE, as well as to a more than 95% reduction of the initial organic content and salinity, thus, yielding a permeate with the potential to be reused in the dyeing process.     

Membrane filtration of NSSC-waste liquor

The influence of fouling and gel formation on the concentration and separation of NSSC-waste liquor by reverse osmosis with CA-membranes have been investigated.In hyperfiltration the permeability decreases to about 40% of the water permeability due to fouling of the membranes. This is shown to be caused by small amounts of substituted phenols, which are concentrated by a factor 1000 within the membrane phase in proportion to water, Some of the phenols have been identified by combined gaschromatography and mass spectrometry.In ultrafiltration the permeability decreases to about 20% of the water permeability due to severe fouling of the membranes. Gel formation is only observed under extreme conditions. The fouling is believed to occur by a surface adsorption of medium MW organic molecules inside the pores of the membrane skin.     

Preparation of reverse osmosis membranes by plasma polymerization of organic compounds

The plasma polymerization of organic compounds was used to prepare a composite reverse osmosis membrane which consists of an ultrathin semipermeable membrane formed by plasma polymerization of an organic compound or compounds and a porous substrate. Many nitrogen-containing compounds (aromatic amines, heteroaromatic compounds, aliphatic amines, and nitriles) were found to yield excellent reverse osmosis membranes by plasma polymerization directly onto porous substrates such as Millipore filters, porous polysulfone filters, and porous glass tubes. Factors involved in the preparation of reverse osmosis membranes by plasma polymerization were investigated and discussed. The plasma polymerized membranes have the following unique features: (1) very stable performance independent of salt concentration and applied pressure (practically no water flux decline was observed with many membranes): (2) salt rejection and water flux both increase with time in the initial stage of reverse osmosis (consequently, the performance of the membrane improves with time of operation); (3) very high salt rejection (over 99%) with high water flux (up to 38 gfd) can be obtained with 3.5% NaCl at 1500 psi (membranes perform equally well under conditions of sea water conversion and brakish water treatment).     

Practical aspects of sea water desalination by reverse osmosis

The cost of reverse osmosis equipment for sea water desalination is now equal or lower than the cost of multistage flash evaporators up to 6000 MTD capacity, depending on conditions. The high temperatures and salinity of the sea in several locations where fresh water is in short supply are important in the design of reverse osmosis plants; high temperatures will increase the flux of the membranes but will also increase the rate of compaction and flux decline. As a consequence, the most rugged membranes are required for the desalination of warm sea water. Experience has shown that the addition of aluminum sulfate followed by dual media filtration will provide a suitable feed for reverse osmosis treatment.     

沸石/聚酰胺反渗透复合膜的制备

为了提高反渗透膜的通量,通过在界面聚合反应过程中添加NaA型纳米沸石分子筛制备了沸石/聚酰胺反渗透复合膜,采用SEM及复合膜性能测试的方法比较了沸石分子筛添加在水相或者油相中时对膜结构及分离性能的影响.SEM图谱结果表明:沸石分子筛添加在油相中时,沸石在聚酰胺基质中分散均匀,膜结构比较均一;但当沸石分子筛添加在水相中时...     

反渗透技术在钢铁工业废水处理和回用中的应用

针对原水水质情况和环保要求,确定采用反渗透膜技术处理该废水,介绍了系统工艺流程及主要设备,详细说明了反渗透膜技术处理钢铁工业废水的应用经验及效果。通过观察电导、产水量、压差的变化,分析了膜污染的成因,提出了清洗方案,并对反渗透系统的运行管理问题进行了论述。结果表明,酸-碱-酸的清洗方案对反渗透膜污染具有很好的控制效果。     

商业正渗透膜的改性及其用于处理焦化废水的研究

正渗透技术是一种新兴的膜分离技术,在处理有机废水方面具有广阔的应用前景。分别对Poten以及HTI商业正渗透膜进行改性,并用于对焦化废水中难降解毒性小分子(吲哚和吡啶)的截留测试。探究了水相单体PIP浓度、膜朝向、汲取液浓度对改性前后两种膜水通量、J_s/J_w比值、有机物截留率的影响,以及改性前后两膜特征参数的变化。结果表明：对Poten膜和HTI膜进行界面聚合改性后,膜水通量以及J_s/J_w比值都不同程度地降低;改性后的两正渗透膜水渗透系数A、盐渗透系数B均降低,而膜结构参数S以及对NaCl和有机物的截留率均提高;其中HTI-IP复合膜对有机物的截留率(81%)明显高于IP-2(改性Poten膜)复合膜;与FO模式相比,IP-2复合膜在PRO模式下(汲取液面向活性层)具有更高的水通量及反向盐通量。此外,在两种膜朝向下,水通量及反向盐通量都随汲取液浓度的增大而增大,但是在FO模式下(料液面向活性层),通量呈现非线性增长。     

Distillation and reverse osmosis energy consumption and costs

The paper compares the energy requirements of single and dual purpose MSF distillation with seawater reverse osmosis plant. Energy consumptions are given both as heat and power consumptions for distillation and as power consumption for R.O. To enable a true comparison to be made these inputs are referred back to the heat inputs from fuel needed at the boiler plant or appropriate thermal power plant.Energy recovery is also considered for reverse osmosis and it is shown that the energy input can be expected to decrease by some 35% for a typical example.Although the prime energy input needed for reverse osmosis is shown to be substantially lower than for dual purpose distillation, the overall costs taking account Of capital charges, energy, replacements and other operating costs, are found to be in a band width of about 5% for plants in the range of 5000 to 15000 m³/day. Reverse osmosis plant water costs are significantly less than distillation if membrane life increases from 3 years to 5 years, particularly with small plant capacities.     

反渗透技术在废水处理中应用的研究进展

反渗透技术是一种高效、易操作的液体分离技术,同传统的废水处理方法相比具有处理效果好,可实现废水的循环利用和对有用物质回收等优点。文章简要介绍了反渗透技术的基本原理,重点介绍了反渗透技术在垃圾渗滤液、矿区污水、钢铁工业废水、电厂废水处理中的应用研究进展状况。并讨论了反渗透膜技术的预处理、反渗透膜污染及清洗和反渗透技术的发展前景。     

Asymmetric polyimide membranes for filtration of non-aqueous solutions

The preparation of asymmetric polyimide ultrafiltration and reverse osmosis membranes has been described. The membranes have been characterized in terms of their filtration properties and chemical stability. They were found to be insoluble in almost any organic solvent, even at elevated temperatures. In aqueous solutions, however, their stability is rather poor and their use in reverse osmosis desalination of sea and brackish water will be limited, in spite of their good salt rejection.     

Professor Joseph W. McCutchan, 1918-1982

The paper compares the energy requirements of single and dual purpose MSF distillation with seawater reverse osmosis plant. Energy consumptions are given both as heat and power consumptions for distillation and as power consumption for R.O. To enable a true comparison to be made these inputs are referred back to the heat inputs from fuel needed at the boiler plant or appropriate thermal power plant.Energy recovery is also considered for reverse osmosis and it is shown that the energy input can be expected to decrease by some 35% for a typical example.Although the prime energy input needed for reverse osmosis is shown to be substantially lower than for dual purpose distillation, the overall costs taking account Of capital charges, energy, replacements and other operating costs, are found to be in a band width of about 5% for plants in the range of 5000 to 15000 m³/day. Reverse osmosis plant water costs are significantly less than distillation if membrane life increases from 3 years to 5 years, particularly with small plant capacities.     

Highly permeable reverse osmosis membranes incorporated with hydrophilic polymers of intrinsic microporosity via interfacial polymerization

Enhancing the water permeation while maintaining high salt rejection of existing reverse osmosis (RO) membranes remains a considerable challenge. Herein, we proposed to introduce polymer of intrinsic microporosity, PIM-1, into the selective layer of reverse osmosis membranes to break the trade-off effect between permeability and selectivity. A water-soluble a-LPIM-1 of low-molecular-weight and hydroxyl terminals was synthesized. These designed characteristics endowed it with high solubility and reactivity. Then it was mixed with m-phenylenediamine and together served as aqueous monomer to react with organic monomer of trimesoyl chloride via interfacial polymerization. The characterization results exhibited that more “nodule” rather than “leaf” structure formed on RO membrane surface, which indicated that the introduction of the high free-volume of a-LPIM-1 with three dimensional twisted and folded structure into the selective layer effectively caused the frustrated packing between polymer chains. In virtue of this effect, even with reduced surface roughness and unchanged layer thickness, the water permeability of prepared reverse osmosis membranes increased 2.1 times to 62.8 L·m^-2·h^-1 with acceptable NaCl rejection of 97.6%. This attempt developed a new strategy to break the trade-off effect faced by traditional polyamide reverse osmosis membranes.     

反渗透预处理系统问题的分析与措施

反渗透给水的预处理一般包括源水到反渗透给水泵之前的一切处理[1].良好的预处理是反渗透装置长期稳定运行的必要条件.通过对上海焦化有限公司除盐水二组反渗透及其预处理系统在开车初期污染频繁、保安过滤器滤芯寿命过短等异常情况进行分析,提出相应的预处理系统改进方案,实施后,消除和减少了给水污染,为反渗透系统的可靠运行打下良好基...     

Water and solute transport across cellulose acetate membranes in the treatment of soybean whey by reverse osmosis

In processing full-fat soy flour to produce an acid-precipitated lipid protein concentrate, there results a by-product whey fraction which, because of its high biological oxygen demand, represents a serious disposal problem. Processing of food waste streams by reverse osmosis has received considerable attention because of its low theoretical energy requirement, since no phase change is involved. A series of statistically designed and analyzed experiments were conducted on a pilot-plant reverse osmosis unit to study the effect of the operating parameters on solute and solvent transport in cellulose acetate membranes. Sucrose and sodium chloride solutions were tested in addition to soybean whey to relate the mixed solute system in whey to that of single-solute organic and inorganic feed solutions. Water flux was shown to have an Arrhenius dependency on temperature, and some membrane compaction was observed with the more porous membrane. Concentration polarization for sucrose and sodium chloride solutions increased linearly with water flux. Solute flux for soybean whey solutions decreased with molarity and was independent of pressure, whereas solute rejection increased with temperature and pressure and was independent of molarity. Good agreement was obtained using the derived parameters A, B, and τ for soy whey in the diffusion transport model when compared to the observed experimental values.     

Synergistic behavior between silica and alginate: Novel approach for removing silica scale from RO membranes

The formation of mineral scale deposits on membranes is a pervasive and expensive problem for the water treatment industry. A series of experiments run on a laboratory-scale reverse osmosis membrane system examined the fouling of membranes when the feed water was spiked with organic and inorganic foulants. Alginic acid was used as the organic foulant and silica was used as the inorganic foulant. Studies involving interactions of these two foulants have not previously been reported in literature. Experiments were run with each foulant individually to characterize fouling at different velocities and pressures. Experiments were then run using both foulants together to characterize the synergistic effects on membrane fouling. One set of experiments with both foulants demonstrated that alginic acid inhibits silica fouling on reverse osmosis membranes. Further experiments indicated that alginic acid added after silica fouling had already occurred was able to remove silica scale from the membrane and restore permeate flux.     

反渗透深度处理回用生活污水的试验研究

某厂生活污水站的出水经混凝-砂滤-UF处理后，用小型反渗透设备对UF产水进行了脱盐试验，测量了给水压力及浓水回流比对产水水质、水回收率、产水量的影响；对进水量为14250m^3/d的反渗透工程进行了计算机模拟。试验及模拟结果表明，用反渗透处理经混凝-砂滤-UF处理后的某厂生活污水是可行的，可以得到高质量的产水。     

浓水回收在化工企业的应用实践与探讨

介绍了反渗透浓水回收方法、流程及工程改造实施后的应用情况。通过对反渗透浓水及工艺废水的回收再利用,提高了水的资源利用率,具有广泛的经济性及推广价值。