Modeling of reverse osmosis flux of aqueous solution containing glucose

The aim of the paper is to model the permeate flux during reverse osmosis (RO) of a highly concentrated glucose solution using the osmotic pressure model. Such a model accounts for the effect of the concentration polarization phenomenon on the permeate flux. To apply this model the viscosity, the osmotic pressure of solution and the diffusion coefficient of glucose were estimated. Using mathematical simulation software, the values of mass transfer coefficient for different concentrations of glucose (5, 10, 15 and 20 wt%) and at different feed flow rate were determined. The experimental permeate flux values conducted on flat RO membranes (Type HR-99) agreed well with the values calculated by the osmotic pressure model, as shown by statistical analysis.     

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.     

Treatment of Leather Plant Effluent by Membrane Separation Processes

Abstract

A scheme is proposed for the treatment of the leather plant effluent using membrane based separation processes. The effluent coming out from the various upstream units of the leather plant (except chrome tanning) are combined and a two step pressure driven membrane processes involving nanofiltration (NF) and reverse osmosis (RO) are adopted after a pretreatment consisting of gravity settling, coagulation, and cloth filtration. The entire membrane separation scheme is validated by conducting experiments under a continuous cross flow mode. A detailed parametric study for cross flow experiments is investigated to observe the effects of the operating conditions, i.e., the transmembrane pressure drop and the cross flow velocity on the permeate flux and quality for both NF and RO. Using a combination of osmotic pressure and solution diffusion model for both NF and RO, the effective osmotic pressure coefficient, solute diffusivity, and the solute permeability through the membrane are obtained by optimizing the experimental permeate flux and concentration (in terms of total dissolved solids) values for this complex industrial effluent. The BOD and COD values of the finally treated effluent are well within the permissible limits (in India).     

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.     

Influence of colloidal fouling and feed water recovery on salt rejection of RO and NF membranes

The influence of colloidal fouling and feed water recovery (or concentration factor, CF) on salt rejection of thin-film composite reverse osmosis (RO) and nanofiltration (NF) membranes was investigated. Fouling experiments were carried out using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate the CF and recovery as commonly observed in full-scale RO/NF systems. For feed waters containing only salt (NaCl), permeate flux declined linearly as CF was increased and salt rejection was nearly constant for both RO and NF membranes. On the other hand, a sharp decrease in permeate flux and significant decline in salt rejection with increasing CF were observed under conditions where colloidal fouling takes place. For both RO and NF membranes, the marked permeate flux decline was attributed to the so-called “cake-enhanced osmotic pressure”. The decline in salt rejection when colloidal fouling predominated was much more substantial for NF than for RO membranes. In all cases, the decline in salt rejection was higher under conditions of more severe colloidal fouling, namely at higher ionic strength and initial permeate flux.     

垃圾渗滤液生化出水絮凝-纳滤处理及过程机理

垃圾焚烧发电厂渗滤液是一种含高浓度腐殖酸类物质和高盐含量的复杂有机废水, 传统生化处理后仍难达标排放。本工作围绕垃圾渗滤液生化出水的特性, 开展了Ca(OH)₂絮凝、臭氧氧化预处理与NF处理相结合的处理工艺, 并对处理过程的机理进行了探讨。研究表明, 渗滤液生化出水经过Ca(OH)₂絮凝处理, 可以有效地去除其中的杂环类化合物。生化出水经8 g·L^-1的Ca(OH)₂絮凝处理后, 比MBR出水产水通量提高达8.2%。对Ca(OH)₂絮凝出水进行臭氧氧化处理, 虽然降低了它的COD, 但并未进一步提高其NF膜通量, 其主要原因可能是臭氧氧化生成的硅氧烷类物质造成了膜的污染;与RO处理垃圾渗滤液生化出水相比较, NF膜无法分离废水中的酮类、胺和酰胺类、杂环类化合物, 使得NF产水的COD处在100~160 mg·L^-1。NF平均膜通量的增大可导致产水COD略有上升;垃圾渗滤液生化出水及其预处理水在NF处理过程中, 都没有表现出严重的膜污染。     

Treatment of tanning effluent using nanofiltration followed by reverse osmosis

An investigation on the recovery of chromium from the effluent of a chrome-tanning bath has been performed using nanofiltration (NF) followed by reverse osmosis (RO). The experiments are conducted using a rectangular cross flow cell under laminar and turbulent regimes. Significant flux enhancement is achieved using thin wires as turbulent promoters. The performance criteria are evaluated in terms of the concentration of chromium, COD, BOD, TDS, TS, pH, and conductivity of the permeate. The effects of different operating parameters on permeate flux and observed retention of chromium are evaluated experimentally. The retention of chromium is found to be 91–98% for NF and 98.8–99.7% for RO for the experimental conditions of this study. Concentrations of chromium and COD of the final permeate are well within the permissible limits.     

Application of reverse osmosis to automotive electrocoat paint wastewater recycling

Field and bench-scale reverse osmosis experiments on wastewater derived from automotive electrocoat paint operations are reported. Field experiments were performed continuously over a six-month interval using a reverse osmosis unit equipped with cellulose acetate membranes. An operating pressure of 3100 kPa (450 psi) and a temperature of 24–27°C was maintained. These RO experiments were unusual for two reasons. First, certain solutes in the feedwater were allowed to permeate through the membrane along with water. This was done to permit solute recycling and reuse. Since these solutes (ethyl, butyl and hexyl glycol ethers) were present in a 3% total concentration in the feedstream, their permeation through the membrane eliminated a flux reduction mechanism. This would arise from the increased upstream osmotic pressure if these solutes were concentrated. Second, the experiments were performed under conditions where colloidal lead was present. This caused limited membrane fouling which was controlled via weekly cleaning with dilute lactic acid. Some supporting bench-scale RO experiments were carried out to probe factors influencing this RO application.     

An advanced treatment of high-strength opium alkaloid processing industry wastewaters with membrane technology: pretreatment, fouling and retention characteristics of membranes

This paper presents the results of the laboratory and pilot-scale membrane experiments of opium alkaloid processing industry effluents. Different types of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for membrane fouling, permeate flux and their suitability in separating COD, color and conductivity. Experiments demonstrated that membrane treatment is a very promising advanced treatment option for pollution control for opium alkaloid processing industry effluents. Almost complete color removal was achieved with NF and RO membranes. COD and conductivity removals were also greater than 95% and met the current local standards. Nevertheless, pretreatment was an important factor for the NF and RO membrane applications. Membrane fouling occurred with direct NF membrane applications without UF pretreatment. The total estimated cost of the UF and NF treatment system was calculated as $0.96/m³, excluding the concentrate disposal cost.     

Optimal design of split partial second pass reverse osmosis network for desalination applications

Reverse osmosis (RO) network design problem is presented in this study for seawater desalination. The RO pressure vessel is multiple spiral wound modules connected in series. We exploit in this study the RO pressure vessel operation by considering stream property variations within the pressure vessel itself. The design problem allows extraction of high‐quality permeates from different locations along the pressure vessel length. Superstructure optimization is adopted to model the RO network in order to find: (1) optimal arrangement of the process units, (2) optimal permeate extraction locations, and (3) production of several permeate streams with different qualities. Several case studies are presented to show the applications of the proposed mathematical programming model. In general, lower treatment cost and higher permeate recovery can be achieved by allowing permeate extraction streams from the RO pressure vessels. © 2013 American Institute of Chemical Engineers AIChE J 60: 520–532, 2014     

Recovery and recycle of tannins in the leather industry by nanofiltration membranes

The aim of this work was the study of the application of membrane concentration to exhausted tanning baths from vegetable tannage operations in order to increase the tannin/non‐tannin (T/NT) ratio and obtain recyclable material. For this purpose four samples of tanning baths at different T/NT ratios (from 0.7 to 1.4) were processed using six different types of membranes which ranged from reverse osmosis (RO) to nanofiltration (NF). The membrane module Fluid Systems TFC S 2540 gave the best results in terms of permeate flux and also in terms of increased T/NT ratio in the retentate (from 1.4 to 1.7). In order to compare the permeate flux reduction with time (J_t) for the different modules, the osmotic pressure differences (Δπ) between permeate and retentate were estimated by electrical conductivity measures. The fouling phenomena for the different membranes in the processing of each sample were evaluated by comparing the pressures required to obtain the same VRF (volume reduction factor), NPF (normalized permeate flux) and membrane performances with tap water before and after tannin concentration. The retention of tannins, which are polyphenols capable of significant hydrogen bonding, was found to be governed by the chemistry of the interactions between their complexes and the polyamide membrane material. Copyright © 2004 Society of Chemical Industry     

Control of scale formation in reverse osmosis by membrane rotation

Scale formation of soluble salts is one of the major factors limiting the application of reverse osmosis (RO) membranes. In this study, rotating RO, which takes advantage of Taylor-Couette flow instabilities to reduce concentration polarization and membrane fouling, was investigated as a novel method to control CaSO₄ scale formation. The permeate flux for rotating RO at ω = 180 rpm remains constant up to a volume concentration factor (VCF) of 4.2, while the permeate flux declines steadily with increasing VCF for no rotation. This is probably because vortices in rotating RO induce bulk crystallization and prevent scale particle deposition on the membrane surface. The anti-scaling effect in rotating RO increases with increasing rotational speed and depends to some extent on transmembrane pressure.     

纺丝油剂废水处理工艺研究

纺丝油剂废水是高浓度的O/W型乳状液,具有相当的稳定性。采用“破乳-反渗透”处理工艺得到了良好的实验结果。以自配的DEMUL-B1作为破乳剂,试验并分析了破乳剂的用量、水样的pH值、加热温度和加热时间等因素对破乳效果的影响。以OSMONICS公司的SE反渗透膜对破乳后的水样进一步处理。结果表明,经“破乳-反渗透”处理净化后的水质,其COD的去除率达到99.96%,含油量和浊度的去除率均为100%,达到了污水综合排放一级标准(GB8978-1996),可以直接排放或回用。     

Processing of composite industrial effluent by reverse osmosis

Reverse osmosis (RO) is a well‐established process for water desalination and effluent treatment and it is anticipated that its application could be extended to complex mixtures of industrial effluents. Pilot‐scale experiments using a spiral‐wound thin‐film composite (TFC) polyamide membrane were carried out to investigate the potential of RO for processing a composite effluent, which was a mixture of various wastewaters from bulk drug and pharmaceutical factories. Separation performance was evaluated at various feed pressures (0–70 bar) and feed concentrations (2–30 gdm^?3), and was found to improve with increasing pressure. High rejection of dissolved solids (～98%), COD, BOD and almost complete removal of color were achieved with reasonable flux rates and water recovery. The effect of concentration polarization and fouling on flux and rejection rates as functions of time was evaluated. An approximate cost estimate for an aerobic process vis‐à‐vis a RO membrane process for treatment of the composite effluent is presented. Copyright © 2003 Society of Chemical Industry     

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.     

Effect of Cross-flow Velocity on the Critical Flux of Ceramic Membrane Filtration as a Pre-treatment for Seawater Desalination

Pre-treatment, which supplies a stable, high-quality feed for reverse osmosis (RO) membranes, is a critical step for successful operation in a seawater reverse osmosis plant. In this study, ceramic membrane systems were employed as pre-treatment for seawater desalination. A laboratory experiment was performed to investigate the effect of the cross-flow velocity on the critical flux and consequently to optimize the permeate flux. Then a pilot test was performed to investigate the long-term performance. The result shows that there is no significant effect of the cross-flow velocity on the critical flux when the cross-flow velocity varies in laminar flow region only or in turbulent flow region only, but the effect is distinct when the cross-flow velocity varies in the transition region. The membrane fouling is slight at the permeate flux of 150 L穖^-2穐^-1 and the system is stable, producing a high-quality feed (the turbidity and silt density index are less than 0.1 NTU and 3.0, respectively) for RO to run for 2922.4 h without chemical cleaning. Thus the ceramic membranes are suitable to filtrate seawater as the pre-treatment for RO.     

Treatment of Fumaric Acid Wastewater Using Integrated Process of Hollow-Fiber Supported Liquid Membrane-Strip Dispersion with Reverse Osmosis

In this paper, the integrated process of series connected hollow-fiber supported liquid membrane-strip dispersion (HFSLM-SD) with reverse osmosis (RO) was designed and used to recover fumaric acid (FA) from waste effluents and treat FA wastewater. The results showed that FA could be almost completely recovered by this integrated process, and TOC of wastewater finally decreased to the environment acceptable level. In addition, the continuous operation of wastewater treatment was implemented by the integrated process. After FA wastewater was extracted by six series connected HFSLM-SD modules, its TOC decreased from 35625 mg/L to 1000 mg/L, and the TOC removal rate reached 97.17%. Then the effluent from HFSLM-SD was further treated by RO, and TOC of permeate in RO was below 100 mg/L. The total TOC removal rate of the integrated process was as high as 99.7%. Furthermore, the effect of the osmotic pressure of RO process on TOC in the feed was obtained. The investigation of RO membrane fouling revealed that washing process was necessary because of the serious fouling in RO system.     

Impact of Protein Removal by an Upstream Ultrafiltration on the Reverse Osmosis of Skim Milk and Sweet Whey

Concentration of milk and whey by ultrafiltration and reverse osmosis (RO) in cascade mode is an amendment of evaporation for high volume reduction ratios (VRR) prior to drying. This study investigated the impact of a prior protein removal and the transmembrane pressure (TMP) on the RO stage, compared to skim milk and sweet whey. It could be found that removal of the protein fraction of both skim milk and sweet whey improved the efficiency of the RO. An upstream ultrafiltration resulted in higher VRR as well as an increased permeate flux.     

Optimization of solar-powered reverse osmosis desalination pilot plant using response surface methodology

A solar thermal and photovoltaic-powered reverse osmosis (RO) desalination plant has been constructed and optimized for brackish water desalination. The central composite experimental design of orthogonal type and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of different responses such as the salt rejection coefficient, the specific permeate flux and the RO specific performance index that takes into consideration the salt rejection coefficient, the permeate flux, the energy consumption and the conversion factor. The considered input variables were the feed temperature, the feed flow-rate and the feed pressure. Analysis of variance (ANOVA) has been employed to test the significance of the RSM polynomial models. The optimum operating conditions have been determined using the step adjusting gradient method. An optimum RO specific performance index has been achieved experimentally under the obtained optimal conditions. The RO optimized plant guarantees a potable water production of 0.2 m³/day with energy consumption lower than 1.3 kWh/m³.     

Bench-scale evaluation of seawater desalination by reverse osmosis

In bench-scale tests of seawater reverse osmosis desalination it is important to carefully consider osmotic pressure effects and determine the extent of concentration polarization so that sources of flux variation—whether from fouling, compaction, or osmotic pressure changes—can be properly assessed. Rigorous modeling of concentration polarization is difficult because of the complex geometries and flow regimes in RO modules; typically, concentration polarization must be measured. However, concentration polarization measurement usually requires knowledge of membrane permeability, which can vary from coupon to coupon. In this study a method is presented to determine both the membrane permeability and the concentration polarization regime in a single test. The key to the test is to allow the salt concentration to vary over time in a predictable way and extract parameters from a model fitted to the flux data. The usefulness of this technique is highlighted by evaluating results from several seawater experiments. It was found that specific flux decline in the experiments was caused by changes in osmotic pressure and membrane compaction. RO fouling by seawater organic-matter was not significant for the several seawater samples tested.