Method for recovering water and dyes from wastewater

Abstract

The invention relates to a method for recovering water and dyes, simultaneously, from wastewater, which comprises: - pretreating the wastewater using an ultrafiltration process; and - a step of concentrating the colourants present in the permeate stream obtained in the previous step, using a membrane contactor, which is selected from: - a step of membrane distillation of the permeate stream obtained in the previous step, using a membrane contactor, and - a step of osmotic membrane distillation of the permeate stream obtained in the previous step, using membrane contactors. The invention provides an innovative solution to address the treatment of textile industry effluents, promoting water reuse and colourant recovery in an efficient and sustainable manner.

Description

[0001] Procedure for recovering water and dyes from wastewater

[0002] DESCRIPTION

[0003] FIELD OF INVENTION

[0004] The present invention relates to a process for recovering dyes and clean water from wastewater from the textile industry using membrane contactors.

[0005] This process, based on emerging membrane technologies and employing membrane contactors, recovers dyes and clean water from textile industry wastewater, which has a very high environmental impact. This approach implements a circular economy within the textile dyeing process.

[0006] The process involves pretreatment with ultrafiltration to remove unwanted solids, followed by dye concentration using membrane contactors, applying either membrane distillation or osmotic membrane distillation. The result is clean water and concentrated dyes, ready for reuse in dyeing new garments. The invention offers an innovative solution for treating textile industry effluents, promoting efficient and sustainable water reuse and dye recovery. These dyes can be reused in a new dyeing stage, reducing costs and adding value to the industry's wastewater.

[0007] STATE OF THE ART

[0008] The textile industry plays a fundamental role in the global economy, as it is responsible for the production of a wide range of fabrics, garments, and other textile products.

[0009] The textile sector is one of the most polluting and environmentally damaging industries. During the dyeing, finishing, and washing processes of textiles, numerous and diverse chemicals are used, such as dyes, finishing agents, and auxiliary products, many of which can be toxic and persistent in the environment. Daily water consumption in a medium-sized textile plant can reach 1.6 million liters. Furthermore, a large quantity of highly colored wastewater is generated, which has a high organic load, high suspended solids content, high salinity (due to the presence of chlorides, nitrates, and sulfates), and a high pH. This wastewater also contains heavy metals and aromatic amines, which are known for their toxicity and carcinogenic potential. The article by Alventosa-De Lara et al.In 2012, a treatment for dyed water, such as water from the textile industry, was disclosed using ultrafiltration. However, it was not combined with a subsequent membrane distillation process.

[0010] Therefore, the textile industry is an ideal setting for the reuse of water and chemical compounds, as well as for the implementation of circular economy principles. The recovery of water and dyes from textile industry wastewater is a challenge of international importance, aligned with Sustainable Development Goal 6, "Clean Water and Sanitation," of the 2030 Agenda proposed by the United Nations.

[0011] Spain is a country where the textile industry is of great importance. Spanish textile companies generate €5.631 billion in revenue annually and create 46,498 jobs. In fact, Spanish textile companies contribute 2.9% of the gross domestic product (GDP). The Valencian Community is home to 24% of these companies, which has significant economic consequences, but also environmental ones, since a large volume of wastewater from textile processes is concentrated in this region.

[0012] Proper management of textile industry wastewater has become crucial for addressing the negative environmental impacts associated with this activity. Adopting more sustainable technologies and cleaner production practices are key to minimizing pollution from textile wastewater and promoting a more environmentally responsible approach. Conventional treatment of textile wastewater typically involves adsorption or biological treatment processes. Over the years, other conventional treatments, such as electrocoagulation and oxidation, have also been proposed. However, these processes do not achieve sufficient efficiency in removing color and other contaminants from textile effluents.

[0013] Alternatively, the use of conventional, pressure-driven membrane processes such as ultrafiltration, nanofiltration, or reverse osmosis has been proposed. In these cases, higher water recovery rates have been achieved compared to the previously mentioned techniques; however, some limitations exist during their application. Ultrafiltration and nanofiltration are highly susceptible to membrane fouling, leading to unavoidable cleaning processes that increase overall operating costs. Reverse osmosis, on the other hand, is an energy-intensive technology, as it requires the application of high transmembrane pressures.

[0014] The use of emerging membrane technologies represents an innovative approach to treating textile wastewater, as these technologies incorporate novel processes that enhance sustainability during treatment. The present invention comprises the integration of conventional and emerging membrane technologies, including the use of membrane contactors, to recover dyes from textile wastewater and subsequently use them in dyeing new garments.

[0015] Membrane contactors enable membrane distillation. This technique uses a hydrophobic membrane as a barrier between a high-temperature feed stream and a low-temperature feed stream (the carrier solution). The membrane prevents water from passing through, allowing only vapor to flow from the higher-temperature stream to the lower-temperature stream. Furthermore, membrane contactors allow for osmotic membrane distillation. In this method, the carrier solution has a high osmotic pressure and is maintained at a low temperature. Therefore, the driving force in osmotic membrane distillation is not only the temperature gradient but also the osmotic pressure gradient.

[0016] The doctoral thesis entitled “Treatment and Reuse of Textile Industry Effluents Using Membrane Techniques” by Valentina Buscio Olivera (2015) presents an analysis of the feasibility of combining traditional technologies (catalytic processes) with membranes for ultrafiltration or direct controlled membrane distillation (DCMD) for effluent treatment. This combination aims to achieve a higher dye recovery rate and subsequent reuse in the industrial process, as well as the recovery of some of the water used in the process. However, it neither presents nor suggests the combined use of ultrafiltration and distillation with membrane contactors.

[0017] Document CN110791123A discloses a method for dye treatment, desalination, and wastewater recycling using an integrated treatment based on membrane technology, which includes the following first steps: (1) dissolving a dye with a molecular weight of 900 Da or higher containing sodium sulfate in water, introducing the resulting liquid into an ultrafiltration membrane filtration system to remove suspended impurities and obtain a filtrate; (2) sending the filtrate to a dense nanofiltration membrane system to obtain raw dye water and produced water; (3) allowing the raw dye water to enter a reverse osmosis membrane concentration system for treatment to obtain raw dye water and produced water, and reusing the produced water in a dense nanofiltration membrane desalination system. It does not disclose a distillation step following an ultrafiltration stage.

[0018] Document CN 103420533 relates to a treatment method for high-concentration organic wastewater. The method comprises, first, conveying the water to an equalization tank and then subjecting it to a micro / ultrafiltration process. The stream obtained during micro / ultrafiltration is then subjected to a nanofiltration process, and finally, the nanofiltration permeate is sent to the distillation stage.

[0019] Therefore, between the ultrafiltration stage and the distillation stage, a nanofiltration stage is always carried out, according to CN 103420533.

[0020] The objective of the invention disclosed in CN 103420533 is to purify water. For this reason, several processes are linked together in which impurities are progressively removed. After nanofiltration, the permeate will be a highly purified stream, since nanofiltration rejects most chemical species.

[0021] The fact of interposing an additional membrane process, such as nanofiltration, implies several aspects compared to the present invention:

[0022] • Higher energy expenditure: in the case of nanofiltration, which can reach transmembrane pressures of up to 40 bar, the energy expenditure is very significant.

[0023] • Higher economic costs: Including another membrane process requires additional pumps, as well as the general equipment used in any membrane plant. Furthermore, in the case of nanofiltration, the necessary material must withstand high pressures.

[0024] • Increased waste generation: by introducing one more filtration, an additional reject stream is necessarily generated, which in the case of nanofiltration is characterized by a very small molecular cut, so the reject will contain many impurities.

[0025] The present invention presents the following differentiating characteristics with respect to the current state of the art:

[0026] • Use of membrane contactors as the main technology for the recovery of dyes and clean water from textile wastewater.

[0027] • The application of membrane distillation or osmotic membrane distillation using membrane contactors does not require the application of pressure as the driving force of the process. Therefore, the energy consumption of the technique is greatly reduced compared to currently used techniques such as biological treatment, nanofiltration, or reverse osmosis.

[0028] • Membrane contactors experience significantly less fouling than membranes used in conventional processes (ultrafiltration, nanofiltration, reverse osmosis), primarily because no pressure is applied during the process. Therefore, the consumption of reagents (and water) required for membrane cleaning is reduced.

[0029] DESCRIPTION OF THE INVENTION

[0030] The present invention relates to a process for simultaneously recovering water and dyes from wastewater, comprising:

[0031] - a pretreatment of wastewater through an ultrafiltration process

[0032] - a stage of concentrating the dyes, present in the permeate stream obtained in the previous stage, using a membrane contactor, which is selected from:

[0033] - a membrane distillation stage of the permeate stream obtained in the previous stage, mediated by a membrane contactor, and

[0034] - a membrane osmotic distillation stage of the permeate stream obtained in the previous stage, mediated by membrane contactors. In this document, the terms “dye” and “colorant” are used interchangeably.

[0035] In this document, the terms “membrane contactor” and “membrane contactors” are used interchangeably.

[0036] In the present invention, no intermediate step is carried out between the ultrafiltration stage and the dye concentration stage, in particular no nanofiltration stage is carried out.

[0037] In the wastewater pretreatment stage, the ultrafiltration process can be carried out with various membranes, such as a polyethersulfone, polysulfone, polyacrylonitrile, cellulose, cellulose acetate, polycarbonate, polyvinylidene fluoride polyamide, zirconium oxide or aluminum oxide membrane, with a molecular cutoff threshold located in the range 10 - 150 kDa, preferably located in the range 10 - 50 kDa.

[0038] The molecular cutoff threshold is the maximum molecular weight of molecules that can cross the membrane.

[0039] In this pretreatment stage, the reject stream is the only waste generated.

[0040] In the pretreatment stage, the higher molecular weight suspended solids are removed. These solids include unwanted polymers, such as silicones or fibrils, which can contaminate the dyes of interest. The permeate stream obtained in this stage is then directed to the membrane contactor to carry out the second stage.

[0041] In the ultrafiltration stage, a pressure between 1 and 5 bar can be applied, for example, 1.5 bar.

[0042] In the ultrafiltration stage, a tangential velocity of between 1 m / s and 3 m / s can be applied to the membrane module, for example, 1.5 m / s. This ultrafiltration process is maintained until a minimum concentration factor of 2 is reached, preferably 4, and more preferably 10. The concentration factor indicates how much the sample has been concentrated. That is, a concentration factor of 2 indicates that the sample on the permeate side is at half its initial volume after passing through the membrane.

[0043] The second stage of colorant concentration consists of a membrane distillation stage (which can be an osmotic distillation, if a saline solution is used as the carrier solution), using a membrane contactor equipped with a hydrophobic microporous membrane, for example, made of polypropylene, polytetrafluoroethylene or polyvinylidene fluoride.

[0044] According to this distillation stage, the permeate obtained during the ultrafiltration process is used as the feed solution and is heated to a temperature that depends on the exact composition of the wastewater being treated. This parameter is adjusted for each specific type of water. The temperature range is between 30 and 70 °C to promote water evaporation.

[0045] There are several configurations for carrying out this dye concentration stage, each of which is an alternative, including:

[0046] - direct contact,

[0047] - the air gap configuration,

[0048] - the sweeping gas configuration and

[0049] - the vacuum configuration.

[0050] A fifth alternative involves using the permeate gap configuration (Mohammadi Shamlou et al., 2022; Parani and Oluwafemi, 2021).

[0051] Up to this point, the information on the dye concentration stage refers to the two types indicated: membrane distillation and osmotic membrane distillation.

[0052] When the second stage is carried out by membrane distillation, a carrier solution is used, consisting of a stream of water flowing in the opposite direction to the feed solution. This carrier stream is maintained at a low temperature, below 20 °C, for example, between 5 and 15 °C. Thus, the concentration of the dye is achieved through a temperature gradient. A minimum concentration factor of 2 can be reached, preferably 3.5, and more preferably 4, and even more preferably 8.

[0053] Preferably, for this membrane distillation stage, direct contact distillation is selected. This generates a temperature gradient that drives the process. At the end of this stage, a dilute stream of clean water and a concentrated stream containing the recovered dyes are obtained.

[0054] If the second stage is a membrane osmotic distillation stage, membrane contactors with a microporous, hydrophobic membrane are used. The membrane material can be, for example, polypropylene, polytetrafluoroethylene, or polyvinylidene fluoride.

[0055] The feed stream is heated to a temperature that depends precisely on the composition of the wastewater. The minimum temperature is above 30 °C, and it can reach up to 70 °C to promote water evaporation. The permeate obtained from the ultrafiltration process is then brought into contact (via the membrane contactor) with a salt-rich saline solution at a low temperature, below 20 °C, for example, between 5 and 15 °C, as a carrier solution. This saline solution can have various origins; for example, it can be brine from desalination plants or any industrial wastewater with a high osmotic pressure (at least higher than the osmotic pressure of the ultrafiltered wastewater). It can even be a synthetic saline solution with an osmotic pressure higher than that of the ultrafiltered wastewater.

[0056] The salt concentration determines the osmotic pressure of the carrier solution, which must be higher than that of the feed stream. Therefore, based on the osmotic pressure of the wastewater to be subjected to osmotic membrane distillation, the brine or industrial wastewater to be used as the carrier solution will be selected. If a synthetic saline solution is prepared as the carrier solution, a mass of salt will be added to achieve an osmotic pressure higher than that of the wastewater being treated. This generates a temperature gradient and an osmotic pressure gradient (generated solely by the difference in osmotic pressure between the feed solution and the carrier solution) that result in the concentration of the dye. A minimum concentration factor of 2, preferably 4, is achieved.

[0057] According to this alternative second stage, at the end of the procedure, a dilute saline stream (which can be returned to the sea) and a concentrated stream containing the recovered dyes are obtained. Osmotic membrane distillation is continued, preferably until a minimum dye concentration factor of 2 is reached.

[0058] The dyes obtained can be used for dyeing new garments.

[0059] The water can be subjected to the relevant quality control at the end of the procedure.

[0060] It is possible to purify and concentrate the dyes present in wastewater such as that from the textile industry, from the garment dyeing process, or from the leather treatment process.

[0061] BRIEF DESCRIPTION OF THE FIGURES

[0062] Figure 1: A schematic of the procedure is shown where the first pretreatment stage by ultrafiltration is designated as (A), the stage of concentrating the dyes using a membrane contactor, by membrane distillation or osmotic membrane distillation, is designated as (B), the use of the dyes obtained for dyeing new garments is designated as (C) and the relevant quality control is designated as (D).

[0063] The numerical references in the figure show:

[0064] 1: Wastewater from the textile industry

[0065] 2: textile wastewater pretreated by ultrafiltration (25 °C)

[0066] 3: current rich in concentrated dyes (30-70 °C)

[0067] 4: Carrier solution for the membrane contactor (water, <20 °C) 5: Clean water, in the case of membrane distillation, or dilute saline solution, in the case of osmotic membrane distillation

[0068] A: ultrafiltration

[0069] B: membrane contactor for performing membrane distillation or osmotic membrane distillation

[0070] C: dyeing tests with the recovered dyes and water

[0071] D: Quality control

[0072] Figure 2: A schematic of an example membrane distillation procedure for concentrating dyes from textile dyeing wastewater pretreated by ultrafiltration is shown. The numerical references in the figure indicate:

[0073] 1: textile wastewater pretreated by ultrafiltration (50 °C)

[0074] 2: Carrier solution for the membrane contactor (water, 10 °C)

[0075] 3: Clean water

[0076] 4: current rich in concentrated dyes (50 °C)

[0077] EXAMPLES

[0078] Example 1

[0079] A water and dye recovery test was carried out by performing the second stage through membrane distillation, and with the direct contact configuration.

[0080] The feed stream was 5 liters of wastewater from the dyeing stage of the textile industry. This wastewater contained the dye Remazol-Black at a concentration of 0.5 g / 100 mL. The objective of this experiment was to treat this textile wastewater, concentrating the Remazol-Black dye and recovering clean water from the wastewater of the textile dyeing stage.

[0081] First, the wastewater was treated by ultrafiltration. The ultrafiltration stage was carried out using an organic, polyethersulfone membrane with a molecular weight cutoff of 10 kDa. A pressure of 1.5 bar was applied. The tangential velocity across the membrane module was 1.5 m / s. During this stage, a permeate flow rate of 17 L / hm was obtained. 2 .

[0082] The permeate stream (2) obtained from the ultrafiltration stage was then fed to the membrane contactor (B). The volume of this permeate was 2.5 liters. A polypropylene membrane contactor (B) was used during the membrane distillation. The permeate (2) obtained during the ultrafiltration process was used as the feed solution. This feed solution was heated to 50°C, while the carrier stream (4) consisted of distilled water at 10°C. The procedure is shown in Figure 2. Both streams were pumped at a flow rate of 25 L / h through the membrane contactor module. The membrane contactor only allows the passage of water; therefore, at the end of this stage, a clean water stream (5) and a concentrated stream (3) containing the recovered dyes were obtained. Finally, a Remazol-Black concentration of 1.4 g / 100 mL was achieved.The water recovered at the outlet of the membrane contactor module (in the conveying solution) showed a chemical oxygen demand of less than 12 mg / L, which demonstrates that it contains a very low concentration of organic matter.

[0083] Example 2

[0084] A water and dye recovery test was carried out by performing the second stage through membrane distillation, and with the direct contact configuration.

[0085] The feed stream consisted of 9 liters of wastewater from the dyeing stage of the textile industry, obtained after rinsing the dyed garments. This wastewater contained the dye Remazol-Black at a concentration of 10 g / L. The objective of this trial was to treat this textile wastewater, concentrating the Remazol-Black dye and recovering clean water from the wastewater of the textile dyeing stage.

[0086] First, the wastewater was treated by ultrafiltration. The ultrafiltration stage was carried out using an organic, polyethersulfone membrane with a molecular weight cutoff of 10 kDa. A pressure of 1.5 bar was applied. The tangential velocity across the membrane module was 1.5 m / s. During this stage, a permeate flow rate of 11 L / hm was obtained. 2 .

[0087] The permeate stream (2) obtained from the ultrafiltration stage was then fed to the membrane contactor (B). The volume of this permeate was 5 liters. A polypropylene membrane contactor (B) was used during the membrane distillation. The permeate (2) obtained during the ultrafiltration process was used as the feed solution. This feed solution was heated to 60°C, while the carrier stream (4) consisted of distilled water at 10°C. Both streams were pumped at a flow rate of 40 L / h through the membrane contactor module. The membrane contactor only allows the passage of water; therefore, at the end of this stage, a clean water stream (5) and a concentrated stream (3) containing the recovered dyes were obtained. A Remazol-Black concentration of 14 g / L was ultimately achieved.The water recovered at the outlet of the membrane contactor module (in the conveying of the entrainment solution) showed a chemical oxygen demand of less than 50 mg / L, which is considered a very low concentration of organic matter.

[0088] Example 3

[0089] A water and dye recovery test was carried out by performing the second stage through membrane distillation, and with the direct contact configuration.

[0090] The feed stream was 12 liters of wastewater from the rinsing stage of freshly dyed denim garments. This wastewater contained the direct dye Sirius Yellow at a concentration of 2.2 g / L. The objective of this trial was to treat this textile wastewater, concentrating the dye and removing unwanted organic matter from the water so that it could be reused in the industry.

[0091] First, the wastewater was treated by ultrafiltration. The ultrafiltration stage was carried out using an organic, polyethersulfone membrane with a molecular weight cutoff of 100 kDa. A pressure of 0.5 bar was applied. The tangential velocity across the membrane module was 2 m / s. During this stage, an average permeate flow rate of 39 L / hm³ was obtained. 2 .

[0092] The permeate stream obtained in the ultrafiltration stage was then directed to the membrane contactor. The volume of this permeate was 6 liters.

[0093] During membrane distillation, a polypropylene membrane contactor (B) was used. The permeate obtained during the ultrafiltration process was used as the feed solution. This feed solution was heated to 60 °C, while the carrier solution consisted of distilled water at 10 °C. Both streams were pumped at a flow rate of 40 L / h through the membrane contactor module. The membrane contactor only allows the passage of water; therefore, at the end of this stage, a purified water stream (with a chemical oxygen demand below 400 mg / L) and a concentrated stream containing the recovered Sirius Yellow dye at a higher concentration were obtained. A final Sirius Yellow concentration of 3.9 g / L was achieved.

[0094] Example 4

[0095] A water and dye recovery test was carried out by performing the second stage through osmotic membrane distillation, and with the direct contact configuration.

[0096] The feed stream was 9 liters of wastewater from the dyeing stage of the textile industry. This wastewater contained the dye Indigo Blue at a concentration of 0.7 g / 100 mL. The objective of this experiment was to treat this textile wastewater, concentrating the Indigo Blue dye and recovering clean water from the wastewater of the textile dyeing stage.

[0097] First, the wastewater was treated by ultrafiltration. The ultrafiltration stage was carried out using an organic, polyethersulfone membrane (the active layer of which had been treated by the manufacturer to increase its hydrophilicity), with a molecular weight cutoff of 50 kDa. A pressure of 1 bar was applied. The tangential velocity in the membrane module was 1.5 m / s. During this stage, a permeate flow rate of 14 L / hm was obtained. 2 .

[0098] The permeate stream obtained in the ultrafiltration stage was then directed to the membrane contactor. The volume of this permeate was 4 liters.

[0099] During membrane distillation, a polypropylene membrane contactor (B) was used. The permeate obtained during the ultrafiltration process was used as the feed solution. This feed solution was heated to 40 °C, while the carrier solution was a synthetic NaCl solution at a concentration of 110 g / L and a temperature of 15 °C. Both streams were pumped at a flow rate of 25 L / h through the membrane contactor module. The membrane contactor only allows the passage of water; therefore, at the end of this stage, a clean water stream and a concentrated stream containing the recovered dyes were obtained. A final concentration of Indigo Blue of 2.2 g / 100 mL was achieved.The water recovered at the outlet of the membrane contactor module (in the conveying solution) showed a chemical oxygen demand of less than 9 mg / L, which demonstrates that it contains a very low concentration of organic matter.

Claims

CLAIMS 1. A process for simultaneously recovering water and dyes from wastewater, comprising: - a pretreatment of wastewater through an ultrafiltration process - a stage of concentrating the dyes present in the permeate stream obtained in the previous stage, using a membrane contactor, which is selected from: - a membrane distillation stage of the permeate stream obtained in the previous stage, mediated by a membrane contactor and - a membrane osmotic distillation stage of the permeate stream obtained in the previous stage, mediated by membrane contactors.

2. A process according to claim 1, wherein, in the wastewater pretreatment stage, the ultrafiltration process is carried out with a membrane selected from a polyethersulfone, polysulfone, polyacrylonitrile, cellulose, cellulose acetate, polycarbonate, polyvinylidene fluoride polyamide, zirconium oxide, and aluminum oxide membrane, with a molecular cutoff threshold in the range of 10 - 150 kDa.

3. Method according to claim 1 or 2, wherein, in the ultrafiltration process, a pressure between 1 and 5 bar is applied.

4. Method according to any one of claims 1 to 3, wherein the ultrafiltration process is applied at a tangential speed in the membrane module between 1 m / s and 3 m / s.

5. Method according to any one of claims 1 to 4, wherein the ultrafiltration process is maintained until a minimum concentration factor of 2, preferably 4, is reached.

6. A process according to any one of claims 1 to 5, wherein the second stage is a membrane distillation stage, in which a hydrophobic microporous membrane is used.

7. Method according to claim 6, wherein the membrane is selected from a polypropylene, polytetrafluoroethylene or polyvinylidene fluoride membrane as the membrane contactor material.

8. A process according to any one of claims 1 to 7, wherein the second stage is a membrane distillation stage, wherein the permeate obtained during the ultrafiltration process is used as the feed solution.

9. A process according to any one of claims 1 to 8, wherein the feed solution is heated to a temperature between 30-70°C.

10. A process according to any one of claims 1 to 9, wherein the second stage is a membrane distillation stage, in which an entrainer stream is used that flows in the opposite direction to the feed solution.

11. Process according to claim 10, wherein the carrier solution is maintained at a temperature below 20°C, preferably between 5-15°C.

12. A process according to any one of claims 7 to 11, wherein the dye concentration step is carried out using a technique selected from: - direct contact, - air gap configuration, - gas sweeping configuration - vacuum configuration and - permeate gap configuration.

13. A process according to any one of claims 1 to 7, wherein the second stage is a membrane osmotic distillation stage, wherein a microporous hydrophobic membrane is used as the membrane contactor material.

14. Process according to claim 13, wherein the microporous hydrophobic membrane is made of polypropylene, polytetrafluoroethylene or polyvinylidene fluoride.

15. A process according to claim 13, wherein the second stage is a membrane osmotic distillation stage, in which the permeate obtained in the pretreatment stage is contacted, by means of the membrane contactor, with a saline solution, as a carrier solution, which is at a temperature between 5- 15 °C.

16. A process according to claim 15, wherein the saline solution is selected from brine from desalination plants, an industrial wastewater with an osmotic pressure at least above the osmotic pressure of the ultrafiltered wastewater, and a synthetic saline solution with an osmotic pressure higher than that of the ultrafiltered wastewater.

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