Nanofiltration Unit Research Articles

Analysis of High Recovery Brackish Water Desalination Processes using Fuel Cells

The production and supply of potable water and the disposal of wastewater are among the major challenges of the 21st century. Inadequate supply of potable water, coupled with increasing water demand in developing countries due to rapid population growth and industrialization are among the major reasons for the worsening water situation (1). Desalination of brackish water by reverse osmosis (RO) and nanofiltration (NF) are the leading technologies used in supplying potable water. Typically, these plants operate at 75% product water recovery so that 25% of RO feed water is wasted as concentrated brine. However, the recovery can be increased by processing the primary RO reject water with the aid of selective membrane processes such as a secondary RO or NF unit. Hybrid RO/NF processes were modeled using the membrane manufacturer's software for various membranes and for two specific brackish waters studied (total dissolved solids, TDS = 1700 and 3700 mg/1). The analyses show that 90% product water recovery is achieved for the low TDS feed water and 88% recovery is achieved for the high TDS feed water using simple, state-of-the-art hybrid membrane systems, and with minimal feed water chemical pre-treatment. It is also shown that the specific energy consumption of the RO system is reduced when it is powered by a stand-alone, on-site fuel cell power plant.

Performance analysis of a trihybrid NF/RO/MSF desalination plant

The Saline Water Desalination Research Institute (SWDRI) of the Saline Water Conversion Corporation (SWCC), Saudi Arabia has been actively involved in developing the application of nanofiltration (NF) pretreatment to both seawater reverse osmosis (SWRO) and multistage flash (MSF) desalination processes. Full integration of NF, SWRO and MSF processes would result in enhancing the reliability, flexibility, plant productivity and ultimately reduce water production cost. Extensive experimental studies on a pilot-scale were conducted recently by SWDRI to establish the operational boundaries and constraints of the trihybrid NF/RO/MSF desalination system. The system was configured in such a way that the NF unit received seawater feed from the heat rejection of the MSF pilot plant and was able to operate at a fairly constant temperature of about 33°C which produced NF permeate (NFP) at a recovery ratio of about 64%. The SWRO unit which received the NFP as a feed yielded a permeate recovery of about 47%. Average chemical analysis of the RO reject (ROR) revealed that the sulphate and calcium concentrations were only 124 and 281 ppm, respectively, and was subsequently used as a make-up to the MSF pilot plant. The very low concentration of the sulphate and calcium ions in the brine recycle which were below the saturation limits enabled to operate the MSF unit safely up to a top brine temperature of 130°C (unit temperature design limit) and water recovery ratio of about 69%. In this paper, the operational performance of the trihybrid NF/RO/MSF desalination pilot plant will be presented. The established optimum operating conditions can be used as a guide to assess the techno-economic viability of the trihybrid desalination scheme.

Using reclaimed water as make-up water for a district heating system: a case study in Beijing

Make-up water used for a district heating system in Beijing is about 63 kg/m(2).a, so the total quantity of make-up water is over 10 million m(3) per year. Water deficiency is very serious in Beijing. Using reclaimed water as make-up water is one of the important measures to relieve water crises of the city. This study is mainly on nanofiltration (NF) process. The reclaimed water for the experiment is the effluent of The Sixth Water Plant, an urban reclaimed water plant in Beijing. Micro-filter (MF) and activated carbon filtration are used as pretreatment units to eliminate turbidity, organic matter in reclaimed water to avoid contamination and scale on the surface of NF membrane. Four SAEHAN NE-90 membrane elements with an array of 2-1-1 are selected for the NF unit and the flow rate is controlled around 1 m(3)/h. Through the test, it has been verified that NF membrane has high removal rate to the salt and impurity of reclaimed water. The average salt removal rate of the system is more than 94%, while the rejections of bivalent ions are more than 98%. The removal rates of organic matter, NH(3)-N and TP are 77%, 96% and 84% respectively. Temperature is a main influence of the process. When temperature is increasing, the permeate flux is increasing as well. The operating pressure is an important factor effecting membrane flux also. By the data comparison it is confirmed that the appropriate operating pressure and the water recovery of NF system are 0.75 MPa and 63.5% respectively.

Autopsy of high-pressure membranes to compare effectiveness of MF and UF pretreatment in water reclamation

A pilot-plant study was designed to compare the effectiveness of microfiltration (MF) and ultrafiltration (UF) as pretreatment for high-pressure membranes in reclamation of biologically treated wastewater effluent. Granular media, filtered secondary effluent from a full-scale wastewater treatment plant, was fed to MF and UF units that operated in parallel. Each of these filtrates served as the feedwater to two reverse osmosis (RO) units and one nanofiltration (NF) unit that operated in parallel. The decline in specific flux was substantially lower for high-pressure membranes receiving UF than MF pretreatment over the course of each of four pilot plant runs that lasted from 1 to 7 weeks. The removal of organic matter as measured by dissolved organic carbon (DOC) was somewhat higher by UF than MF pretreatment (about 15% by UF compared with 11% by MF). Addition of ferric chloride ahead of the UF unit, but not ahead of the MF unit, may account for this additional removal of organic matter. However, the additional DOC removal appeared insufficient to explain the differential in foulant accumulation between high-pressure membranes receiving UF and MF pretreatment. Extensive autopsy analyses of these high-pressure membranes showed from 35% to 56% less organic carbon on those receiving UF rather than MF pretreatment. A more specific indicator of a differential in organic fouling was the accumulation of polysaccharides and this showed from 27% to 38% less on UF- than on MF-pretreated membranes. Yet another possible source of foulants is inorganic material given that the inorganic and organic weight percentages were nearly equal (56% vs. 44%) on the membrane surface. One specific source was aluminum added for phosphorus removal. Less fouling of high-pressure membranes pretreated by UF than MF could be due to the following: (1) a small, but very important, colloidal fouling fraction may have passed through MF but was rejected by UF pretreatment; (2) organic fouling was not related to organics in either the MF or UF filtrates but rather to organics that are generated in situ by microbial activity on the membrane surface; and/or (3) less passage of colloidal Al–P that carried over from secondary wastewater treatment.

A membrane-based co-treatment strategy for the recovery of print- and beck-dyeing textile effluents

This paper describes the final part of a study on the recovery of print- and beck-dyeing wastewaters of the carpet manufacturing industry by membrane processes. These wastewaters had been previously treated separately where the print dyeing wastewaters were recovered by chemical precipitation followed by nanofiltration (NF) and beck-dyeing wastewaters were subjected to microfiltration (MF) and pH neutralization prior to NF. In this study, a co-treatment scheme after separate pre-treatment stages was adopted to simplify the overall process. The effect of mixing ratio on membrane fouling was also investigated. The co-treatment strategy was found advantageous since the number of NF units was minimized and the pH neutralization step in separate treatment of beck-dyeing wastewaters was eliminated, providing a reduction of chemical usage.

Influence of electrostatic interactions on the rejection with NF and assessment of the removal efficiency during NF/GAC treatment of pharmaceutically active compounds in surface water

The removal efficiency of several pharmaceutically active compounds from two different surface water types was investigated. Two different nanofiltration (NF) membranes (Trisep TS-80 and Desal HL) were first studied at low feed water recoveries (10%). In a second phase, the combination of an NF unit at higher feed water recovery (80%) with subsequent granular activated carbon (GAC) filtration of the permeate was investigated. Results indicate that removal of the selected pharmaceuticals with NF is mainly influenced by charge effects: negatively charged solutes are better removed, compared with uncharged solutes, which are, in turn, better removed compared with positively charged solutes. This latter trend is mainly due to charge attractions between the negatively charged membrane surface and positively charged solutes. Increasing feed concentrations of positively charged pharmaceuticals lead to increasing rejection values, due to membrane charge-shielding effects. The removal efficiency of pharmaceuticals with the combination NF/GAC is extremely high. This is mainly due to an increased adsorption capacity of the activated carbon since the largest part of the natural organic matter (NOM) is removed in the NF step. This NOM normally competes with pharmaceuticals for adsorption sites on the carbon.

Transport mechanisms of dissolved organic compounds in aqueous solution during nanofiltration

This paper investigates the relative contribution of convection, diffusion and charge effects during transport of dissolved organic compounds in aqueous solution using nanofiltration membranes. Measurements were carried out in a crossflow nanofiltration unit and in diffusion cells using four organic compounds (tryptophane, raffinose, benzylidene acetone and mandelic acid) in aqueous solution and five commercial nanofiltration membranes (UTC-20, Desal-HL-51, NTR-7450, NF270 and NF-PES-010). Diffusion was analyzed by the Donnan model for diffusion across a charged membrane. The charge effect was studied by changing the pH of the feed solution, which influences both the membrane and compound charge. It could be concluded that convection is the dominant transport mechanism for the organic compounds used. Furthermore, solute transport depends on the compounds properties. Uncharged compounds show a slight decrease of retention at high pH, which can be explained by an enlargement of the membrane pores due to an increased repulsion between the charged acidic groups. For charged compounds an increase of the retention is observed with increasing pH due to an increased repulsion between the charge of both compound and membrane. Finally, diffusion through membranes with tight pores (reflected by the MWCO) becomes more important as the molecular weight of the compound increases because steric hindrance in narrow pores mainly affects convective transport.

Treatment of a textile effluent: application of a combination method involving adsorption and nanofiltration

A combination of adsorption and nanofiltration (NF) was adopted for the treatment of a textile dyehouse effluent containing a mixture of two reactive dyes. The effluent stream was first treated in a batch adsorption process with sawdust as an adsorbent to reduce the dye concentration of the effluent by about 83% for Dye 1 and 93% for Dye 2. The effluent from the adsorption unit was passed through an NF unit for the removal of the remaining small amount of dyes and to recover the associated chemicals (mainly salt) in the effluent stream. The dyes remaining after this step were less than 1 ppm. The percentage removal of COD was greater than 99%, and the salt recovery was on the order of 90%. Equilibrium studies were carried out with synthetic solutions of the dyes (both single component as well as two-component systems) at room temperature. The adsorption rates were studied in detail using varying amounts of the adsorbent. NF of the effluent was performed in a cross-flow system using a 400 molecular weight cut-off membrane. A detailed study was carried out to observe the effect of the process parameters, namely applied pressure and bulk velocity on the process outputs such as dye rejection, COD removal, permeate flux and salt recovery. Finally, direct NF of the effluent (with the original high concentration) was undertaken, and the performance of the process was compared with the combination method. The permeate flux for the proposed combined method was found to be about twice that for the direct NF method. The dye rejection improved significantly compared to adsorption.

Steady State Behavior of Coupled Nonlinear Reactor−Separator Systems: Effect of Different Separators

In a typical plant, downstream separators are coupled to upstream reactors through recycle streams. The bifurcation behavior of the coupled system is different from that of the individual units. The bifurcation diagram depicts the dependence of the steady state on an operating parameter. In this work, we analyze the behavior of three different coupled reactor-separator systems. Each system is characterized by a different separator. The three different separator units investigated are a flash unit, a nanofiltration unit, and an ultrafiltration unit. The reactor is modeled as a CSTR sustaining a cubic autocatalytic reaction. The stand-alone reactor can have a maximum of three solutions. The coupled system is investigated for the situation when the fresh feed is flow controlled and the reactor level is maintained constant using the reactor effluent flow stream. It is shown that the coupled reactor-flash system has a maximum of two steady solutions, while the two coupled reactor-membrane separation systems have a maximum of three solutions. Each coupled process is analyzed for two situations: (i) a binary system and (ii) ternary system. The physical cause for the difference in these behaviors is analyzed.

Treatment by Nanofiltration of the Bleed Stream of a Continuous Alcohol Fermentor

In continuous ethanol fermentation processes, which include product removal and recovery steps, to limit the concentration of secondary products, a bleed stream may be used. This stream contains several small molecular weight organic fermentation products and substrate sugars. To recover sugars and to minimize the amount of waste, the bleed stream is treated by nanofiltration. Three types of membranes were used in these experiments: 500 and 200 mwco (molecular weight cut off) polyamide and a thin‐film composite membrane with 99.2% NaCl rejection. Separation was achieved in two stages. First, separation of sugars was studied with 500 and 200 mwco membranes, and 84% total sugar rejection was obtained. Second, by‐products, which constitute the high total organic carbon (TOC) of the wastewater, were separated from the bleed stream by using the thin‐film composite membrane. The 95.1% of organics leading to TOC could be removed from the bleed by this method. Based on these results, a waste process, consisting of two nanofiltration units with a 500 mwco membrane and a thin‐film composite membrane, were suggested for the recovery of sugars and water.

Process intensification in the textile industry: the role of membrane technology

Process intensification is a concept that was recently introduced in the chemical industry for the purpose of reducing environmental emissions, energy consumption and materials consumption. The principle of process intensification can be used in related industries as well; textile finishing is an exemplary activity where it may have a significant long-term added value. Membrane technology can be a key factor in the recycling and reuse of energy, water and chemicals. In this paper, an integral approach for treatment of aqueous process streams in the textile finishing industry is proposed. The proposed process includes microfiltration pretreatment of used finishing baths, followed by a dual nanofiltration (NF) unit. These can be operated at elevated temperatures so that no further energy is needed for preheating of recycle streams. In the proposed treatment scheme, the first of the NF units uses a loose nanofiltration membrane that retains most of the organic fraction but not the dissolved salts. The second unit uses a tight nanofiltration membrane, which produces a permeate fraction that can be directly reused, and a concentrated brine that is fed to a membrane crystallizer. In this unit, salts are recovered and recycled for use in new dye baths. The concentrate stream from the first NF unit is fed to a membrane distillation unit, where the high temperature is advantageously used for further concentration. The remaining fraction is not reusable, given the fact that most dyes are hydrolyzed after exhaustion of the bath, but has a significant energetic value, which can be utilized for compensation of energy losses and preheating of suppletion water, by using an incineration process with energy recovery. The concept was not tested experimentally, but a simulation for a 500 m 3/d production unit shows that it is feasible, although modifications may be necessary depending on the nature of the finishing baths. Furthermore, the membrane choice in the first NF unit is a critical aspect.

Investigation of ultra- and nanofiltration for utilization of whey protein and lactose

Ultrafiltration is one of the most fascinating technologies, which has been introduced for application in the dairy industry. Ultrafiltration makes it possible to improve the quality of traditional dairy products, to create new food staffs, to utilize dairy by-products (such as whey) to a much greater extent for human nutrition and to prepare milk ingredients to be used in the entire food industry. In this study the application of ultrafiltration for milk and whey protein concentration, and research on nanofiltration for lactose concentration of the ultrafiltration permeate are detailed. The performance of ultra- and nanofiltration membranes can be characterized in terms of permeate flux, membrane retention and yield, which parameters are determined by pressure, recycle flow rate and temperature. The influence of these parameters on milk- and whey protein and lactose concentration was measured. The experiments were carried out using laboratory scale ultra- and nanofiltration units. The permeate flux, protein and lactose content in the permeate and in the concentrate fractions were measured during the experimental runs. Comparing the separation behavior of the membranes it was found that the investigated membranes are suitable for concentration of the milk- and whey proteins and lactose with high flux and retention. The filtration characteristics were obviously influenced by the process parameters. A new combination of membrane based cheese production procedure is proposed, which makes possible a significant increase in the cheese yield by incorporating the whey proteins.

Nanofiltration and adsorption on powdered adsorbent as process combination for the treatment of severely contaminated waste water

A new process combination for the treatment of severely contaminated waste water has been developed: powdered adsorbent is injected into the feed of a nanofiltration unit and removed from the concentrate subsequently by a thickener. The powdered adsorbent in the feed has a positive effect on permeate quality, permeate flux and fouling layer in the nanofiltration (NF) unit. Experiments with a semi-continuous pilot plant and biologically pre-treated landfill leachate have shown that a recovery rate of 97% is possible and that the AOX and COD rejection are considerably increased by the powdered adsorbent. Experiments concerning the fouling layer have shown that it can be controlled by a non-chemical flushing procedure consisting of a combination of feed cross flow, air flushing and permeate back flushing. In comparison to reverse osmosis the process combination has higher maximum recovery rate, lower operating pressure and energy consumption which results in lower treatment costs. On the other hand the permeate concentrations are higher than for reverse osmosis but nevertheless still below the legal standards.

Fouling of reverse osmosis and nanofiltration membranes by diary industry effluents

Fouling experiments of nanofiltration (NF) and reverse osmosis (RO) are reported for treatment of the effluent of chemical-biological treatment plant and the original effluent of dairy industry respectively. In the experiments, a thin film composite type of spiral wound was used and fitted with flowmeters and pressure sensors. The feed water was stored into a feed tank and passed a fine filter and was pumped to membrane. Brine and permeate were recirculated back to the feed tank. Membrane fouling was investigated with 16 and 30% water recovery of a single membrane at different pressures and flowrates for RO and NF membranes respectively. Fouling is evaluated with a relationship between relative flux (J/Jo) which is the ratio of the flux at any time during the fouling test to the initial flux and relative resistance (Rf/Rm) which is the ratio of fouling (cake) layer resistance to clean membrane resistance. Turbidity, conductivity, chemical oxygen demand (COD), total suspended solids (TSS) and total hardness were measured in the feed and permeate side of each membrane. The effluent total hardness concentrations of chemical-biological treatment plant were found greater than the influents. The results are presented in terms of the relative flux as a function of time related to hydrodynamic conditions and pollution characteristics of wastewater. The permeate water flux of RO membrane decreases more rapidly than NF membrane, the relative flux decreases with increasing the fouling layer resistance, Rf onto membrane surface. 50% the drop of permeate flux was observed for RO and NF membranes after 50 h and 80 h of operation, respectively. The fouling rate increases with an increase in the concentration of the wastewater constituents in the dairy industry. The relative flux decreased 10 and 20% with increasing chemical oxygen demand (COD) from 5,000 mgl-1 to 10,000 mgl-1 and from 45 mgl-1 to 450 mgl-1 for RO and NF membranes, respectively after 45 h of time. Fouling of membranes resulted in 100% increase of specific energy consumption as the relative permeate fluxes of NF and RO membranes decreased 30 and 40% respectively. The average of specific energy consumption was obtained at 6 and 10 kWhm-3; consequently, operational costs were estimated at U.S. $0.45 m-3 and U.S. $0.75 m-3 for NF and RO units respectively. Also, operational cost for chemical-biological treatment was found at U.S. $0.30 m-3.

Combination of membrane technology and limestone filtration to control drinking water quality

Certain areas in Finland have a problem of high fluoride and aluminium in groundwater because of soil properties. In 1999, the City of Laitila constructed a membrane filtration plant (16–25m 3/h) to control fluoride and aluminium concentration in drinking water. The plant has two trains, one with reverse osmosis (RO) and the other with nanofiltration (NF). Only a fraction (ca. 1/4) of water distributed is membrane filtered. The rest flows directly to alkalization. The alkalization process includes two limestone filters: one for membrane-filtered water (RO+NF) and the other for untreated groundwater. During the first year of operation, both RO and NF were shown applicable for fluoride removal from soft, high fluoride (ca. 4 mgF/l) ground water. The fluoride removals were on average > 95% in RO at 7.3 bar and 76% in NF at 5.7 bar. More than 78% of aluminium was also removed in membrane filtration. Temperature (2–16°C) affected permeated conductivities in the NF unit but not in the RO unit. Limestone filtration was shown applicable for alkalization of membrane filtered water. The alkalinity of membrane-filtered water rose back to the level it was before membrane filtration. However, alkalinity achieved with membrane-filtered water was lower than with groundwater while pH obtained was higher. This mainly resulted from the difference in carbon dioxide concentration of these waters. Since start-up of the RO/NF plant, fluoride and aluminium concentrations in the water distribution system have been at acceptable levels (≤1.5 mgF/l, ≤0.2 mgAl/l) while limestone filtration has ensured a stable alkalinity and pH. The cost of membrane filtration was ca. Euro 0.2/m 3 permeate.

A demonstration plant based on the new NF—SWRO process

Earlier work at Saline Water Conversion Corporation (SWCC) R&D Center showed that nanofiltration (NF) pretreatment of seawater feed to seawater desalination plants removed from its turbidity and microorganism, caused significant rejection of the scale forming hardness ions, reduced TDS in Gulf seawater and produced a new, partially desalinated seawater product, considerably different and superior to seawater in qualities and without the problems normally associated with seawater of high concentration of scale forming ions, high TDS, high turbidity and high bacteria count. Integration of the NF unit with one of the conventional desalination processes to form for example an NF-SWRO lead to a significant improvement in the seawater desalination processes, for example by doubling the SWRO product water output and recovery ratio and the production of high purity permeate (TDS <200 ppm) from one single stage SWRO. However, all previous works were done on a pilot plane scale by integrating NF spiral wound membrane elements in series, size 4″×40″, with a SWRO unit employing 2.5″×40″ membrane elements. In view of the positive and encouraging results obtained on a pilot plant scale, trial on an NF—SWRO demonstration unit was not only logical but essential to determine the operating conditions as well as to establish plant performance parameters for commercial size NF-SWRO plants. The demonstration unit built for this purpose consisted of 6 NF spiral wound membrane elements, size 8″×40″ arranged in series followed by a SWRO unit comprising 3 HFF SWRO elements 8″×40″ or 9″×40″ also arranged in series. The paper describes the NF—SWRO demonstration unit along with the experimental approach used in this investigation dealing with the performance of several selected NF membranes integrated with SWRO membrane to form an NF—SWRO desalination system. The results obtained from the demonstration unit confirm the earlier results which were obtained from the pilot plant study. The results shall be utilized in the operation of the now under construction NF—SWRO plant at Umm Lujj, Saudi Arabia.

Membranes for the control of natural organic matter from surface waters

A range of nanofiltration (NF) modules was evaluated to determine rejection of disinfection by-product (DBP) precursors from low turbidity surface waters. Dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP), and chloral hydrate formation potential (CHFP) rejections averaged 90, 97, 94, and 86%, respectively. Rejections of bromide ion, an inorganic precursor, ranged from 40–80%. Pretreatment using microfiltration (MF) alone before NF provided some removal of turbidity but not enough to maintain the initial flux and recovery of the NF unit. NF runs were sustained over 30 days; however, some adverse changes in operational conditions were observed, and significant pressure increases were necessary to maintain flux. Precursor rejections by NF following MF varied little over time frames of up to 30 days. MF was only moderately effective in particle removals, with virtually no DBP precursor removal provided by MF. Ultrafiltration (UF) alone did not exhibit significant changes in operational conditions over a 30-day time frame; however, only modest precursor (<30% DOC) removal was observed.

Comparative evaluation of nanofiltration and reverse osmosis treatment of an effluent from dairy industry

Nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for the treatment of the effluent of chemical‐biological treatment plant and the original effluent of dairy industry, respectively. A thin film composite type of spiral wound membrane (2 m2 area) with the NF (TFC‐S) and the RO (TFC‐HR) was used. The runs were conducted at approximately 16 and 30 % water recovery of a single membrane at different pressures and flowrates for the RO and NF, respectively. Permeate flux declined rapidly at the beginning of the run and then appeared to remain approximately constant after 50 h of operation at different pressures. At a pressure of 10 bar, the permeate fluxes of the NF and RO decreased from 46 l/m2h to 23 l/m2h after 88 h of operation and from 21 l/m2h to 10 l/m2h after 68 h of operation, respectively. The specific energy consumption increased as a function of time and decreased with increasing pressure for each membrane. The average specific energy consumption was obtained at 6 and 10 kWh/m3 for the NF and RO units, respectively. Therefore, the NF and RO operational costs were estimated at U.S. $0.45/m3 and U.S.S 0.75/m3, respectively. Also, the operational cost for chemical‐biological treatment was found to be U.S. $ O.3O/m3. Consequently, the operational costs for the treatment of the dairy industry effluent with the chemical‐biological process followed by NF membrane and the RO membrane alone were nearly equal. Effluents with high hardness, the total hardness of the NF and RO feeds were reduced from 1425 to 280 mg CaCO3/l (80% removal) and from 480 to 15 mg CaCC3/l (97% removal), respectively. The conductivities of the NF feed, permeate were approximately equal to the RO feed, permeate. The COD of the NF feed and RO feed were also reduced from 470 to 9 mg/1 (98% removal) and from 10500 to 80 mg/1 (99% removal), respectively.

Integrated membrane operations in desalination processes

Today there are many reverse osmosis (RO) plants in operation all over the world for desalination processes. The operating costs for both seawater and brackish water desalination are already competitive with those of thermal operations. These costs are mainly related to the costs of the pretreatment steps, which for seawater desalination might reach 60% of overall costs. By introducing integrated membrane operations, a possible reduction might be possible with an increase of water quality. For example, cross-flow microfiltration (MF), ultrafiltration (UF) and eventually nanofiltration (NF) units might be introduced in the pretreatment line for purifying and clarifying the feed streams and for reducing bivalent ions concentration. If the removal of dissolved gases (CO 2, O 2, etc.) is suggested, the possibility of also introducing membrane contactors before the RO treatment might be considered. Moreover, the recovery factor of the RO process could be enhanced by introducing membrane distillation (MD) units to treat the RO brine. In the present work, integrated membrane operations such as the ones described above are analyzed for a seawater desalination system. Preliminary experimental results will be discussed confirming the possibility of reaching a seawater recovery factor of 87%.

Aplicaciones de la tecnología de membranas en la industria alimentaria/Applications of membrane technology in the food industry

Membrane technology has emerged as a useful tool for separations in the food industry over the last two decades. Ultrafiltration (UF), reverse osmosis (RO) and cross flow microfiltration (CFMF) are already well established technologies in the dairy industry. To a lesser extent the above unit opera tions are used in tomato juice concentration and clarification of juices and wine. Other important potential applications concern aroma recovery from fruit juices using pervaporation, treatment of food industry waste effluents such as brine/blanching/osmotic solution using nanofiltration and other unit operations and finally recovery of valuable compounds from food wastes aiming at their transformation to products of medical importance, using bioreactors coupled with unit operations. In addition to the applications, the limiting factors and guidelines for modelling are also given.