Critical risk points of nanofiltration and reverse osmosis processes in water recycling applications

NF/RO membrane filtration processes have been recognized as an important technology to facilitate water recycling. Those processes are well-proven technologies, which can be used to remove a wide range of contaminants including trace contaminants that are of particular concern in water recycling. However, risk implications in association with brine or concentrate and membrane cleaning wastewater disposal have to date not been adequately understood. This study examines the adsorption and release process of several endocrine-disrupting chemicals (EDCs) during NF/RO filtration processes. Results reported here indicate that the membrane can serve as a large reservoir for EDCs and their release may be possible during membrane cleaning or erratic pH variation during operation. Treatment of membrane cleaning solution should be carefully considered when EDCs are amongst the target contaminants in NF/RO membrane filtration.     

Comparison of polyamide nanofiltration and low-pressure reverse osmosis membranes on As(III) rejection under various operational conditions

A nanofiltration (NF) membrane and a low-pressure reverse osmosis (LPRO) membrane both with aromatic polyamide selective layer from the same manufacturer were employed for the comparison of their performances in terms of As(III) rejection and filtration flux under a variety of operational conditions. In addition to the smaller membrane pore size, the LPRO membrane possesses much more dissociable functional groups than the NF membrane. When the feed pH was below the pKa₁ value (9.22) of H₃AsO₃, for which the steric hindrance is the only rejection mechanism, the removal efficiencies by NF and LPRO were about 10% and 65%, respectively. When the feed pH was higher, for which electrostatic effect began to take effect, the removal efficiencies could reach 40% and 90% for NF and LPRO, respectively. The rejection performance of LPRO was marginally affected by the feed As(III) concentration or ionic strength, although ionic strength had a strong effect on the filtration flux. In contrast, feed As(III) concentration and ionic strength had little effect on the filtration flux but great influence on the As(III) rejection performance of NF. The filtration flux was enhanced with the increase of transmembrane pressure for either NF or LPRO. The NF model could predict the general trend of the effects of the filtration flux, the feed water chemistry and its own concentration on As(III) rejection ratio by the NF membrane, but the rejection ratios were over-predicted.     

中空纤维纳滤膜与反渗透膜的研究

根据界面聚合反应成膜原理,以哌嗪(PIP)或间苯二胺(m-PD)水溶液为水相,均苯三甲酰氯(TMC)正己烷溶液为有机相,以聚砜中空纤维超滤膜为基膜,制备了一系列聚酰胺/聚砜纳滤或反渗透复合膜.研究了水相浓度、有机相浓度、界面聚合时间和温度等条件对复合膜性能的影响.结果表明:中空纤维纳滤复合膜在0.4 MPa、室温条件下,对2 g/L MgSO_4水溶液的通量可达36.64 L/(m~2·h),截留率为97.2%;中空纤维反渗透膜在0.7 MPa、室温条件下,对0.5 g/L的NaCl水溶液通量可达12.2 L/(m~2·h),截留率96.5%.     

Characterization of reverse osmosis and nanofiltration membranes by an automated system

Nanofiltration membranes have been characterized by computer controlled permeation experiments to provide certified results. This method records a real-time history of operating conditions and allows the incorporation of variations in the calculations of derived parameters. The effects of temperature and physical properties of feed on permeation have been evaluated and incorporated in models describing fluid flow trough membranes. As the influence of initial experimental conditions in nanofiltration is very significant, a method based on system mass-transfer coefficient is proposed in order to verify the accuracy of the results.     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Potential use of nanofiltration like-forward osmosis membranes for copper ion removal

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated. In this work, the performance of emerging nanofiltration(NF) like-forward osmosis(FO)membrane was evaluated for its efficiency to remove copper ion from water. Conventionally, copper ion is removed from aqueous solution via adsorption and/or ion-exchange method. The engineered osmosis method as proposed in this work considered four commercial NF membranes(i.e., NF90, DK, NDX and PFO) where their separation performances were accessed using synthetic water sample containing 100 mg·L~(-1) copper ion under FO and pressure retarded osmosis(PRO) orientation. The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force.The high removal rates were in good agreement with the outcomes of the membranes tested under pressuredriven mode at 1 MPa. The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process, achieving a relatively low reverse solute flux. The findings showed that the best performing membrane is PFO membrane in which it achieved N 99.4% copper rejection with very minimum reverse solute flux of 1 g·m~(-2)·h~(-1).     

纳滤和反渗透组合回收盐湖提锂尾液中锂的研究

盐湖提锂后的尾液中仍含有大量的锂,直接外排至盐田会造成锂资源的浪费,并且会对盐湖系统造成破坏,而降低提锂尾液中的镁锂比是回收提锂尾液中锂的关键。采用纳滤和反渗透组合工艺成功地回收了提锂尾液中的锂。考察了7种型号的纳滤膜对提锂尾液中镁锂分离的效果,结果表明1号纳滤膜的分离效果最好。以1号纳滤膜为纳滤元件,考察了纳滤膜在不同的过滤压力、实验温度和提锂尾液稀释倍数条件下对提锂尾液中镁锂分离的效果,得到较优操作条件：过滤压力为4 MPa、提锂尾液稀释倍数为6倍、实验温度为35 ℃。以1号纳滤膜为纳滤元件,在较优操作条件下采用二级纳滤对提锂尾液进行镁锂分离,再通过反渗透对富锂液相进行浓缩,得到镁锂质量比为13.8、锂离子质量浓度为0.39 g/L的富锂液相。富锂液相经过浓缩除杂,然后与纯碱反应,可制备电池级碳酸锂。纳滤截留的镁离子含量较高的液相则外排至尾液池,经蒸发浓缩排入盐田再回收利用。     

Integration of reverse osmosis and membrane crystallization for sodium sulphate recovery

Reverse osmosis and membrane crystallization are evaluated in this work as stand-alone and integrated technologies for the recovery of Na₂SO₄ from aqueous solutions. When SO₂ is removed from flue gases by absorption in an aqueous solution and reacts with NaOH, a reusable product (i.e., Na₂SO₄) of industrial interest can be obtained.For stand-alone reverse osmosis, the effect of the concentration of the feed solution and pressure is studied. For membrane crystallization, the influence of the concentration and flow rate of the feed and osmotic solutions on the process performance has been determined. The characterization of the obtained crystals shows that Na₂SO₄·10H₂O is obtained. From the experimental results, the potential for integration of reverse osmosis and membrane crystallization is simulated. It was concluded that using a reverse osmosis unit prior to the membrane crystallization unit minimizes the total membrane area in comparison with the stand-alone processes.     

Chemical cleaning of reverse osmosis and nanofiltration membranes fouled by licorice aqueous solutions

The aim of this work was finding optimum cleaning agents and conditions for cleaning reverse osmosis (RO) and nanofiltration (NF) membranes fouled by licorice aqueous solutions. The effect of various chemicals on flux recovery (FR) and resistance removal (RR) of the fouled membranes was investigated. For both membranes the results indicate that a combination of ethylene diamine tetra acetic acid (EDTA), sodium dodecyl sulphate (SDS) and sodium hydroxide may be used as cleaning agents to achieve an optimum cleaning efficiency. Zeta potential and contact angle measurements indicate the changes in charge and hydrophilicity of the surface of RO and NF membranes at various pH solutions, respectively. The effect of surface characteristics is evident in efforts to select the optimal operating conditions. The effect of cleaning condition such as concentration, temperature, pH and cleaning time was studied. The optimum temperature, cleaning time, pH and concentration were found as 35 ± 1 °C, 20 min, 12 and 0.1 wt.%, respectively. SEM pictures showed the surface morphology of RO and NF membrane.     

Emergence of thermodynamic restriction and its implications for full-scale reverse osmosis processes

The production rate of permeate in a reverse osmosis (RO) process controlled by mass transfer is proportional to the net driving pressure and the total membrane surface area. This linear relationship may not be the only mechanism controlling the performance of a full-scale membrane process (typically a pressure vessel holding six 1-m-long modules in series) which utilizes highly permeable membranes. The mechanisms that control the performance of an RO process under various conditions were carefully examined in this study. It was demonstrated that thermodynamic equilibrium can impose a strong restriction on the performance of a full-scale RO process under certain circumstances. This thermodynamic restriction arises from the significant increase in osmotic pressure downstream of an RO membrane channel due to the accumulation of rejected salt within the RO channel as a result of permeate water production. Concentration polarization is shown to have a weaker influence on the full-scale RO process performance than the thermodynamic restriction. The behavior of the process under thermodynamic restriction is quite different from the corresponding behavior that is controlled by mass transfer. The transition pressure for an RO process to shift from a mass transfer controlled regime to a thermodynamically restricted regime was determined by the basic parameters of the full-scale RO process.     

印染废水深度处理中纳滤和反渗透工艺的比较

采用纳滤和反渗透两种膜工艺对印染厂处理出水进行深度处理,以达到废水减排、再生回用的目的,主要考察膜性能、处理效果及经济性等方面的状况.结果表明,在性能方面,与反渗透膜相比,纳滤膜在较低压力下即可获得较高的通量,NF-2和NF-2#产水COD分别为150～180 mg/L和120～130 mg/L,产水电导率分别为2 900～3 200 μS/cm和2 000～2 300μS/cm.反渗透产水水质较好,COD可达到5 mg/L以下,BW30和CPA2的产水电导率分别稳定在38 μS/cm和63μS/cm.虽然对一价离子的去除率差异较大,但两种膜工艺对Mg2+、Ca2+等工业循环回用水中最关注离子的去除率相当.在经济性方面,反渗透和纳滤处理成本分别为1.82元/m3和1.53元/m3.膜工艺的经济优势相当明显.     

Impact of pH on the removal of fluoride, nitrate and boron by nanofiltration/reverse osmosis

The objective of this study was to evaluate the impact of pH on boron, fluoride, and nitrate retention by comparing modelled speciation predictions with retention using six different nanofiltration (NF) and reverse osmosis (RO) membranes (BW30, ESPA4, NF90, TFC-S, UTC-60, and UTC-80A). Retention was explained with regard to speciation, membrane properties, and ion properties such as charge, hydrated size, and Gibbs energy of hydration. Flux was independent of pH, indicating that pH did not alter pore size and hence permeability for all membranes except UTC-60. Membrane charge (zeta potential) was strongly dependent on pH, as expected. Boron and fluoride retention depended on membrane type, pH, which correlated closely to contaminant speciation, and was due both to size and charge exclusion. While retention at low and neutral pH was a challenge for boron, high boron retention was achieved (> 70% above pH 11). Fluoride retention was generally > 70% above pH 7. Nitrate retention depended on membrane, and was mostly pH independent (as was the speciation). The presence of a background electrolyte matrix (20 mM NaCl and 1 mM NaHCO₃) reduced nitrate and boron retention (at high pH) due to charge shielding, and enhanced the retention of fluoride in single feed solutions, suggesting preferential transport of Cl⁻ compared to F⁻ with Na⁺.     

Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment

Filtration performance and fouling of nanofiltration (NF) and reverse osmosis (RO) membranes in the treatment of dairy industry wastewater were investigated. Two series of experiments were performed. The first one involved a NF membrane (TFC-S) for treating the chemical-biological treatment plant effluents. The second one used a RO membrane (TFC-HR) for treating the original effluents from the dairy industry. The permeate flux was higher at higher transmembrane pressures and higher feed flowrates. The curves of permeate flux exhibited a slower increase while the feed flowrate decreased and the pressure increased. Membrane fouling resulted in permeate flux decline with increasing the feed COD concentration. Furthermore, the flux decline due to the COD increase was found higher at higher pressures for both NF and RO membranes.     

Recent advances in polymer and polymer composite membranes for reverse and forward osmosis processes

Semipermeable membranes are the core elements for membrane water desalination technologies such as commercial reverse osmosis (RO) process and emerging forward osmosis (FO) process. Structural and chemical properties of the semipermeable membranes determine water flux, salt rejection, fouling resistance, and chemical stability, which greatly impact energy consumption and costs in osmosis separation processes. In recent years, significant progress has been made in the development of high-performance polymer and polymer composite membranes for desalination applications. This paper reviews recent advances in different polymer-based RO and FO desalination membranes in terms of materials and strategies developed for improving properties and performances.     

反渗透系统中难溶盐极限回收率的解析分析

基于反渗透系统给水三类难溶盐饱和度的解析计算,计及了温度、pH、回收率、阻垢剂及浓差极化等因素的影响,导出了用系统给水参数解析表达的反渗透系统浓水难溶盐饱和度,得出了反渗透系统给水参数决定的系统难溶盐极限回收率．从而为反渗透系统的极限收率指标提供一个简捷而清晰的求取方式。     

Influence of temperature and permeate recovery on energy consumption of a reverse osmosis system

A model permits analysis of the influence of temperature on permeate recovery and energy consumption. The proposed model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) membrane rejection and other transport characteristics of membranes are position-independent; (3) specific water permeability of membranes was based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence depembrane rejection is assumed to be linear. This allows for analyzing the influence of channel geometry, feed concentration, flow rate and temperature on permeate recovery and energy consumption. Calculated data are included. The solutionpresented can be segmented andbuilt into systems for comprehensive techno-economic evaluation of the RO-based process where temperature-dependence of process characteristics has to be considered.     

地下水反渗透除盐预处理工艺的优化

地下水基本没有悬浮物,污染指数SDI低,比较适宜做反渗透的水源,但硬度高,容易引起反渗透膜结垢,故地下水反渗透除盐,预处理的重点是防止膜表面结垢。软化法预处理操作繁琐,设备复杂,讨论了在地下水中加入阻垢剂防止反渗透膜表面结垢的方法,结果表明此法有效可行。     

Rotating reverse osmosis for water recovery in space: influence of operational parameters on RO performance

Rotating reverse osmosis (RO), which is based on Taylor-Couette flow, offers a means to minimize flux decline due to concentration polarization and membrane fouling. However, the operating conditions play a significant role in determining the effectiveness of the system. In this study, the effect of operating conditions on system performance was explored using a theoretical model. Flux, rejection, recovery, and theoretical power consumption were calculated for a wide variety of operating parameters including transmembrane pressure, rotational speed, and concentrate flow rate. Flux and rejection increase with increasing transmembrane pressure and rotational speed. Operating in the vortical flow regime enhances the filtration performance. Higher concentrate flow increases flux, but decreases recovery. The power consumption for rotating RO is similar to that for conventional RO except at very high rotational speeds.     

Evaluation of the suitability of groundwater quality for reverse osmosis desalination

In this study the suitability of brackish ground water quality for reverse osmosis (RO) desalination is evaluated. The results of initial laboratory and field analysis of 41 production wells were used to determine the hydrochemical properties of groundwater for both the Dammam limestone aquifer and the clastic Kuwait Group aquifer in the southwestern part of the State of Kuwait. The core samples of these wells were collected and analyzed in order to determine the hydrogeological properties of the same aquifers in the Umm Gudair area. Hydrochemical data of these aquifers were analyzed to help describe relations between hydrochemically distinct bodies of water and elucidate links between hydrochemical data and hydrogeological parameters. During this study, the Expanded Durov diagram was simplified and linked with the Sulin classification method in order to give more interpretation values. The results show that the aquifer materials influence the quality of ground water in each aquifer. The Kuwait Group aquifer water is characterized by ClMg and ClCa genetic water types with an average TDS of 4008 mg/l and belongs to the chloride water type. The Dammam limestone aquifer water characterized by the NaSO₄ and ClMg genetic type with an average TDS of 3480 mg/l belongs to the sulphate type. Both aquifers contain suitable water for RO desalination since they have a high concentration of chloride and monovalent ions, which reduces the requirements of antiscalant additives.     

Cost effective recovery of lithium from lithium ion battery by reverse osmosis and precipitation: a perspective

Production of lithium from primary resources is lagging behind demand (12% versus 16% in 2016), cost of lithium is increasing (between 40 and 60% in 2016), battery energy density rapidly increasing versus declining cost, and estimated lithium ion battery (LIB) markets size ($77.42 billion by 2024) driven by projected demands for plug‐in electric vehicles (PEVs) clearly justifies recycling. PEV technology and projected demand raise several challenges, including lithium demand/scarcity and future technology to recover lithium from LIB waste. To address the circular economy, steady supply chain security, self‐reliance, environment safety, environment directive, energy security, resources conservation, futuristic carbon footprint, WEEE directives and waste crime, recycling of LIB is an absolute essential. During the last decade, LIB recycling research and industrial recycling of LIB have attracted the interest of researchers, industrialists, and environmentalists. All have reported progress in the recovery of valuable metals like Co, but have rarely focused on lithium recovery. Hence, this paper addresses logical hypothesis and application of available technology in a fashion where lithium recycling from LIB can be addressed. © 2017 Society of Chemical Industry