Production of process water using integrated membrane processes

Application of ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, and integrated membrane processes for the preparation of process water from natural water or industrial effluents was investigated. A two-stage reverse osmosis plant enabled almost complete removal of solutes from the feed water. High-purity water was prepared using the membrane distillation. However, during this process a rapid membrane fouling and permeate flux decline was observed when the tap water was used as a feed. The precipitation of deposit in the modules was limited by the separation of sparingly soluble salts from the feed water in the nanofiltration. The combined reverse osmosis—membrane distillation process prevented the formation of salt deposits on the membranes employed for the membrane distillation. Ultrafiltration was found to be very effective removing trace amounts of oil from the feed water. Then the ultrafiltration permeate was used for feeding of the remaining membrane modules resulting in the total removal of oil residue contamination. The ultrafiltration allowed producing process water directly from the industrial effluents containing petroleum derivatives. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

反渗透膜微结构的调控及海水脱硼性能的提升

通过引入聚乙烯亚胺(PEI)链与对叠氮苯甲酸(ABA)分子对薄层芳香聚酰胺复合反渗透膜(TFC)进行接枝改性, 采用傅里叶衰减全反射红外光谱(ATR-FTIR)和X射线光电子能谱(XPS)分析了反渗透膜活性分离层的化学组成和结构, 用静态水接触角仪与Zeta电位仪测试了反渗透膜表面的亲疏水性和电荷性质, 并利用扫描电子显微镜(SEM)及原子力显微镜(AFM)观察其表面形貌, 测试了反渗透膜在苦咸水与海水条件下的分离性能. 实验结果表明, 使用PEI与ABA对反渗透膜改性后, 提升了其分离层的致密度, 使硼渗透通过反渗透膜时的传质阻力变大, 从而将改性反渗透膜(TFC-PEI-ABA)对硼的截留率提升至90.45%, 达到了世界卫生组织对水质的要求.     

Modeling permeation of volatile organic molecules through reverse osmosis spiral-wound membranes

Reverse osmosis is an interesting process to eliminate organic solutes from distillery condensates before recycling them into the fermentation step. However, organic solutes transport phenomena through reverse osmosis membranes are specific. Rejection and sorption of five compounds were studied on a brackish water membrane. Acetic acid and 2,3-butanediol were not sorbed on the membrane while furfural and 2-phenylethanol presented strong sorption following the Langmuir pattern. These sorption effects coupled with solute molecular weight (MW) led to low rejections of acetic acid and furfural (30–60%) and high rejections of 2,3-butanediol and 2-phenylethanol (80–98%). With intermediate sorption and MW, butyric acid showed rejections between 70 and 80%. A modified solution-diffusion model was developed to take into account the sorption pattern and predict the concentration profile along the membrane on the retentate and permeate sides. Equilibrium properties were determined experimentally while transport properties were identified with data obtained from a synthetic condensate. This model was validated for various operating conditions with the synthetic and the industrial condensates. It was then used to simulate the influence of the recovery rate on the retentate and permeate concentrations. It showed the behavior differences between solutes with a linear sorption and solutes with a saturating sorption.     

A study of selected phytoestrogens retention by reverse osmosis and nanofiltration membranes - the role of fouling and scaling

Fouling and scaling are common phenomena that accompany membrane filtration and are caused by the presence of organic and inorganic matter in water, which may affect the removal of low-molecular mass organic micropollutants. Comparative filtration of deionized water containing selected phytoestrogens (biochanin A, daidzein, genistein, and coumestrol) was carried out using one new membrane and one contaminated with organic or inorganic matter. Two commercial Osmonics DS membranes were selected for the research, reverse osmosis DS3SE and nanofiltration DS5DK. Filtration was carried out in the dead-end mode. Higher removal of phytoestrogens was caused by reverse osmosis and retention depended on the molar mass of the compound. The decrease in membrane efficiency associated with fouling or scaling brings about an increase in the retention coefficient of phytoestrogens during both reverse osmosis and nanofiltration. The highest increase in phytoestrogen retention was found for the nanofiltraton membrane which was more susceptible to fouling than the osmotic one. This confirms the effect of membrane porosity on the phenomenon studied. The increase in micropollutants removal observed after fouling or scaling was caused by the modification of the membrane surface, hindered diffusion of the compound, and intensified or limited adsorption of micropollutants on the membrane surface.     

高回收率膜法苦咸水淡化工艺的应用研究进展

膜法苦咸水淡化过程中,符合环境保护要求的浓排水处理方法成本高昂,所以只有当回收率达到较高值时,在实际运行中才具有经济可行性。目前,在不加剧膜污染的条件下进一步提高苦咸水淡化系统回收率的方法已成为该领域研究热点。本文详细综述了高回收率膜法苦咸水淡化工艺的应用研究进展,包括基于反渗透、纳滤、正渗透、膜蒸馏、电渗析和电容去离子化淡化工艺过程,以及这些过程面临的热点问题,并对此提出了建议。     

Membranes for power generation by pressure-retarded osmosis

A model has been developed for obtaining the projected performance of membranes in pressure-retarded osmosis (PRO) from direct osmosis and reverse osmosis measurements. The model shows that concentration polarization within the porous substrate of the membrane markedly lowers the water flux under PRO conditions. The model has been used along with experimental data obtained with a variety of reverse osmosis membranes to project PRO performance with several water—brine sources. Some literature data on PRO have been similarly examined. Based on these results and a simple economic analysis we conclude that membranes with significantly improved performance will be needed if PRO is to become an economically feasible method for power generation using seawater—fresh water as the salinity gradient resource. However, the economics of a brine/fresh water system appear competitive with conventional power generation technologies.     

Comparison of membrane processes with distillation for alcohol/water separation

The overall objectives of this study were to summarize and evaluate the performance of currently available membranes for purification of fermentation alcohol and to compare the economics of membrane processes with a modern-day energy-efficient distillation scheme.Literature survey showed that very little work had been done on the development of membrane processes for alcohol concentration.Based on laboratory work, it was found that the present-day thin-film composite desalination membranes can be used for partial concentration of beer solution to about 20 to 30% alcohol concentration. The water permeation coefficient for these membranes in reverse osmosis with 7.6% alcohol feed at 60 atm was about 10 kg/m²-day-atm (2 lb/ft²-day-atm).Due to the high osmotic pressures of ethanol/water mixtures, reverse osmosis can be used only for the initial concentration of beer solution and for the final dehydration of 95% alcohol to produce 199 proof alcohol. Thus, a distillation unit would have to be used for the intermediate concentration of alcohol solution. Membrane concentration schemes using distillation for intermediate concentration were prepared for comparison with a conventional distillation process. Based on preliminary analysis it was concluded that while the capital cost of the membrane-augmented distillation schemes can be significantly than that of the conventional system, the annualized cost of these schemes will be approximately equal to that for distillation. The capital and the annualized costs of the membrane process for the final dehydration of alcohol can be significantly lower than those for the conventional dehydration still.     

Ion-containing reverse osmosis membranes obtained by radiation grafting method

Cationic membranes obtained by radiation grafting of acqueous acrylic acid onto low density polyethylene films followed by alkaline treatment to confer ionic character in the graft chains, were tested for reverse osmosis desalination of saline water. Selected physical properties of such membranes were investigated. The grafted membranes prossess good mechanical and electrical properties. Water uptake for the alkali-treated membrane was much higher than that of the alkali-untreated one. The effect of operation time, degree of grafting, applied pressure and feed concentration on the water flux and salt rejection for the grafted membranes was investigated. Such cationic membranes showed good durability, thermal and chemical stability, acceptable water flux and salt rejection which may make them acceptable for practical use in reverse osmosis desalination of sea water.     

The effect of membrane potential on the development of chemical osmotic pressure in compacted clay

When clay soils are subjected to salt concentration gradients, various interrelated processes come into play. It is known that chemical osmosis induces a water flow and that a membrane potential difference develops that counteracts diffusive flow of solutes and osmotic flow of water. In this paper, we present the results of experiments on the influence of membrane potential on chemical osmotic flow and diffusion of solutes and we show how we are able to derive the membrane potential value from theory. Moreover, the simultaneous development of water pressure, salt concentration and membrane potential difference are simulated using a model for combined chemico-electroosmosis in clays. A new method for short-circuiting the clay sample is employed to assess the influence of electrical effects on flow of water and transport of solutes.     

Reverse osmosis filtration for space mission wastewater: membrane properties and operating conditions

Reverse osmosis (RO) is a compact process that has potential for the removal of ionic and organic pollutants for recycling space mission wastewater. Seven candidate RO membranes were compared using a batch stirred cell to determine the membrane flux and the solute rejection for synthetic space mission wastewaters. Even though the urea molecule is larger than ions such as Na+, Cl-, and NH4+, the rejection of urea is lower. This indicates that the chemical interaction between solutes and the membrane is more important than the size exclusion effect. Low pressure reverse osmosis (LPRO) membranes appear to be most desirable because of their high permeate flux and rejection. Solute rejection is dependent on the shear rate, indicating the importance of concentration polarization. A simple transport model based on the solution-diffusion model incorporating concentration polarization is used to interpret the experimental results and predict rejection over a range of operating conditions. Grant numbers: NAG 9-1053.     

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.     

Fouling of reverse osmosis and nanofiltration membranes by humic acid—Effects of solution composition and hydrodynamic conditions

Fouling of reverse osmosis (RO) and nanofiltration (NF) membranes by humic acid, a recalcitrant natural organic matter (NOM), was systematically investigated. The membrane flux performance depended on both hydrodynamic conditions (flux and cross-flow velocity) and solution composition (humic acid concentration, pH, ionic strength, and calcium concentration), and was largely independent of virgin membrane properties. While increasing humic acid concentration and ionic strength, and lowering cross-flow velocity affected flux performance moderately, severe flux reduction occurred at high initial flux, low pH, and high calcium concentration. At a calcium concentration of 1 mM, all the membranes exhibited an identical stable flux, independent of their respective intrinsic membrane permeabilities. The effect of solution composition was more significant at higher fluxes. Improved salt rejection was observed as a result of humic acid fouling, which was likely due to Donnan exclusion by humic material close to membrane surfaces. Greater rejection improvement was observed for membranes with rougher surfaces.     

Power generation with pressure retarded osmosis: An experimental and theoretical investigation

Pressure retarded osmosis (PRO) was investigated as a viable source of renewable energy. In PRO, water from a low salinity feed solution permeates through a membrane into a pressurized, high salinity draw solution; power is obtained by depressurizing the permeate through a hydroturbine. A PRO model was developed to predict water flux and power density under specific experimental conditions. The model relies on experimental determination of the membrane water permeability coefficient (A), the membrane salt permeability coefficient (B), and the solute resistivity (K). A and B were determined under reverse osmosis conditions, while K was determined under forward osmosis (FO) conditions. The model was tested using experimental results from a bench-scale PRO system. Previous investigations of PRO were unable to verify model predictions due to the lack of suitable membranes and membrane modules. In this investigation, the use of a custom-made laboratory-scale membrane module enabled the collection of experimental PRO data. Results obtained with a flat-sheet cellulose triacetate (CTA) FO membrane and NaCl feed and draw solutions closely matched model predictions. Maximum power densities of 2.7 and 5.1 W/m² were observed for 35 and 60 g/L NaCl draw solutions, respectively, at 970 kPa of hydraulic pressure. Power density was substantially reduced due to internal concentration polarization in the asymmetric CTA membranes and, to a lesser degree, to salt passage. External concentration polarization was found to exhibit a relatively small effect on reducing the osmotic pressure driving force. Using the predictive PRO model, optimal membrane characteristics and module configuration can be determined in order to design a system specifically tailored for PRO processes.     

Stability and transport characteristics of reverse osmosis membranes using cyanide rinse waters

The recovery of cyanide rinse water using commercially available membranes (DESAL 3, MS10, SW30HR) is the objective of this work. Accordingly, flux, rejection, pretreatment and stability studies were carried out with these thin-film, composite, reverse osmosis membranes. The transport properties of membrane sections were tested using both cyanide rinse waters and NaCl solutions for flux and rejection on a flat-sheet test module after long term exposure to copper cyanide solutions. While SW30HR exhibited good chemical stability, DESAL3 and MS10 were not stable after exposure to high pH solutions for up to 6 months. Pretreatment studies were carried out on SW30HR membranes for flux enhancement in order to improve the recovery of the reverse osmosis system. SW30HR pretreated with ethanol exhibited a five-fold increase in water flux accompanied by an increase in ion rejection. Similar high fluxes and high rejection of principal bath constituents were exhibited by the SW30HR membrane when copper cyanide rinse water solutions were employed as the feed. These results indicate that this type of pretreated reverse osmosis membranes may have significant utility for reprocessing of copper cyanide rinse waters.     

添加共试剂改善聚酰胺复合反渗透膜的性能

将N,N′-二甲基乙酰胺(DMAc)作为共试剂添加在间苯二胺水溶液中参与界面聚合反应, 以改善聚酰胺复合反渗透膜(PA-RO-x, x代表添加DMAc的质量分数)的性能. X射线光电子能谱(XPS)和衰减全反射傅里叶红外光谱(ATR-FTIR)分析表明, 随着DMAc含量的增加, 复合膜结构中交联聚酰胺含量相对于线性羧基部分有所增加; 场发射扫描电子显微镜(FE-SEM)和原子力显微镜(AFM)表征结果显示, 随着DMAc含量的增加, 膜表面的粗糙程度逐渐增大; 静态水接触角测试结果表明, 添加DMAc后, 膜的亲水性增强. 结合上述测试结果发现, 添加DMAc可以有效降低水油两相的不相溶性, 提高水相中间苯二胺向正己烷中扩散的速率, 这有助于加快间苯二胺与均苯三甲酰氯反应; 同时, 聚酰胺结构中交联酰胺含量的增加可以提供更多的氢键位点, 有助于水分子快速渗透通过复合膜而不损失截盐率; 膜表面的粗糙程度变大, 有助于提高水通量. 在2 g/L的氯化钠溶液和1.6 MPa测试压力条件下, PA-RO-5.2(DMAc添加质量分数为5.2%)的渗透通量和截盐率分别为66.1 L/(m²·h)和98.7%, 与未添加DMAc的聚酰胺复合反渗透膜相比, 通量增加115%, 截盐率仅下降0.9%.     

Removal of organics from produced water by reverse osmosis using MFI-type zeolite membranes

Separation of an organics/water mixture was carried out by reverse osmosis using an α-alumina-supported MFI-type zeolite membrane. The organic rejection performance is strongly dependent on the ionic species and dynamic size of dissolved organics. The membrane showed high rejection efficiency for electrolytes such as pentanoic acid. An organic rejection of 96.5% with a water flux of 0.33 kg m⁻² h⁻¹ was obtained for 100 ppm pentanoic acid solution at an operation pressure of 2.76 MPa. For non-electrolyte organics, separation efficiency is governed by the molecular dynamic size; the organics with larger molecular dynamic size show higher separation efficiency. The zeolite membrane gives an organic rejection of 99.5% and 17% for 100 ppm toluene and 100 ppm ethanol, respectively, with a water flux of 0.03 kg m⁻² h⁻¹, 0.31 kg m⁻² h⁻¹ at an operation pressure of 2.76 MPa. It was observed that organic rejection and water flux were affected by the organic concentration. As pentanoic acid concentration increased from 100 ppm to 500 ppm, both organic rejection and water flux decreased slightly.     

Continuous water purification system for Langmuir film studies

A system for continuous purification of water to make it suitable for use in Langmuir film studies has been designed and implemented in our laboratory. The system incorporates particulate filtration, activated carbon adsorption, deionization by reverse osmosis, and continuous distillation under a nitrogen sweep. Surface tension in excess of 99% of theoretical and resistivity of 18 Megohm-cm at 25°C have been achieved without the use of organic ion exchange resins.     

苦咸水反渗透淡化中膜面结垢预测及防垢进展

苦咸水反渗透（BWRO）中的防垢过程,首先取决于给水水质,而根据水质条件和垢在膜面的形成机理采取相应的防垢措施是非常重要的。 显然,有效地管控膜面无机结垢及抑制膜面污染需要开展无机结垢趋势的预测、防垢措施和非破坏性无机垢监控等方面的技术研究。 一系列传统和新兴的分析技术,包括摩尔比率法、直接目测法和光谱法等已应用于BWRO过程中膜面防垢研究。 本文详细综述了该过程中无机结垢趋势的预测、防垢方法和非破坏性无机垢监控技术等方面的研究进展。 此外,针对目前的研究方向提出了建议。     

A critical flux to avoid biofouling of spiral wound nanofiltration and reverse osmosis membranes: Fact or fiction?

The relation between biofouling and membrane flux in spiral wound nanofiltration and reverse osmosis membranes in drinking water stations with extensive pretreatment such as ultrafiltration has been studied. The flux – water volume flowing through the membrane per unit area and time – is not influencing the development of membrane biofouling. Irrespective whether a flux was applied or not, the feed spacer channel pressure drop and biofilm concentration increased in reverse osmosis and nanofiltration membranes in a monitor, test rigs, a pilot scale and a full-scale installation. Identical behavior with respect to biofouling and feed channel pressure drop development was observed in membrane elements in the same position in a nanofiltration installation operated with and without flux. Calculation of the ratio of diffusive and convective flux showed that the diffusive flux is considerably larger than the convective flux, supporting the observations that the convective flux due to permeate production is playing an insignificant role in biofouling. Since fouling occurred irrespective of the actual flux, the critical flux concept stating that “below a critical flux no fouling occurs” is not a suitable approach to control biofouling of spiral wound reverse osmosis and nanofiltration membranes.     

Separation of aromatic substances from aqueous solutions using a reverse osmosis technique with thin,dense cellulose acetate membranes

Investigations were made of the water flux rate and rejection characteristics of aromatic substances in aqueous solutions using a thin, dense cellulose acetate membrane in reverse osmosis experiments. The aromatic substances used were phenol, aniline, hydroquinone and p-chlorophenol. The permeate became more enriched in aromatic compounds as compared to the feed solution as the water content of the membrane increased. By considering both the effects of pressure on the chemical potential of a component and the contribution of viscous flow to the overall transport of that component in the hydrated membrane, a theoretical relationship was developed to predict the negative solute rejection of the membrane. Based on this proposed theory, the permeability coefficients of water and organic solute were estimated from experimental solute rejection data, including negative values. The permeability coefficients of components were in good agreement with previously established correlations in measurements of partition and diffusion coefficients.