High-efficiency solar water evaporator and preparation method and application thereof

Abstract

This invention belongs to the field of solar water evaporation technology, and discloses a high-efficiency solar water evaporator, its preparation method, and its application. The preparation method includes the following steps: (1) Clean and dry coconut fibers, take multiple coconut fibers and weave them into a rope, and then cut them into coconut fiber ropes of the same length; (2) Embed the above-mentioned coconut fiber ropes of the same length into a sponge in an m×n array, wherein the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while its upper end protrudes from the top surface of the sponge by a certain height; (3) Immerse the part of the above-mentioned coconut fiber rope array protruding from the top surface of the sponge in a sodium alginate solution containing carbon black for surface coating treatment, and then take it out and air dry naturally to obtain a high-efficiency solar water evaporator based on a coconut fiber array. This invention has the characteristics of wide material sources, low cost, simple evaporator construction method, and high water evaporation rate, and has better prospects for large-scale preparation and commercial application.

Description

Technical Field

[0001] This invention belongs to the field of solar water evaporation technology, specifically relating to a high-efficiency solar water evaporator, its preparation method, and its application. Background Technology

[0002] Solar-powered interfacial water evaporation technology can effectively convert seawater and wastewater into freshwater resources. Patent CN103964526B discloses a solar-powered micro-concentrating capillary evaporation seawater desalination membrane, comprising a hydrophilic porous material, a lower membrane, an upper membrane, and two or more desalination units. Each desalination unit utilizes a micro-concentrating lens to focus light and heat capillary carbon fiber bundles at the bottom. Due to capillary action, seawater is adsorbed onto the upper surface of the fiber bundles and evaporates under the heating effect of the solar spot. The water vapor condenses upon cooling, and the condensed water droplets are absorbed by hydrophilic fiber gaskets and stored in the hydrophilic porous material, ultimately achieving seawater desalination. Patent CN 114891266B discloses a method for preparing a composite hydrogel sponge, comprising a water supply layer and an evaporation layer arranged sequentially. The water supply layer is composed of polyacrylamide hydrogel, and the evaporation layer is composed of a polyacrylamide and graphene composite hydrogel. Under simulated sunlight, the water evaporation rate of this composite hydrogel sponge is 2.2 kg·m³. -2 ·h -1 Patent CN 117361673A discloses a method for preparing a solar water evaporator using polyethylene glycol-modified lignin-based loofah sponge as its core, and its application in seawater desalination and wastewater purification. Tests show that this solar water evaporator has a power output of 1.75 kg·m³. -2 ·h -1 The aforementioned water evaporators have driven the development of solar interface water evaporation technology, but they still suffer from one or more drawbacks, such as high cost of photothermal materials, complex evaporator structure, cumbersome preparation process, and low evaporation rate. Therefore, how to utilize low-cost photothermal materials to prepare a relatively simple solar water evaporator with high evaporation efficiency in a short process remains a significant challenge. Summary of the Invention

[0003] To address the shortcomings and deficiencies of the existing technologies, the primary objective of this invention is to provide a method for preparing a high-efficiency solar water evaporator. This method utilizes a composite material made from widely available sponges and natural coconut fibers to create a porous material capable of purifying seawater and wastewater, thereby achieving seawater desalination and wastewater purification and providing a new approach and solution to alleviate regional freshwater resource shortages.

[0004] Another objective of this invention is to provide a high-efficiency solar water evaporator based on a coconut fiber array prepared by the above method.

[0005] Another object of the present invention is to provide the application of the above-mentioned coconut fiber array-based high-efficiency solar water evaporator in seawater desalination and wastewater purification.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a high-efficiency solar water evaporator includes the following preparation steps:

[0008] (1) Clean and dry the coconut fiber, take multiple coconut fibers and weave them into a rope, then cut them into coconut fiber ropes of the same length.

[0009] (2) Embed the coconut fiber ropes of the same length into the sponge in an m×n array, wherein the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes from the top surface of the sponge by a certain height.

[0010] (3) The part of the above-mentioned coconut fiber rope array protruding from the top surface of the sponge is immersed in a sodium alginate solution containing carbon black for surface coating treatment, and then taken out and air-dried to obtain a high-efficiency solar water evaporator based on coconut fiber array.

[0011] Further, the coconut fiber mentioned in step (1) is coconut shell fiber with a diameter of 0.6 to 0.9 mm and a length of not less than 10 mm; the coconut fiber rope is woven from not less than 6 coconut fibers; and the cut length of the coconut fiber rope is not less than 7 mm.

[0012] Furthermore, the sponge mentioned in step (2) is one of polyvinyl alcohol sponge, melamine foam, wood pulp sponge, and polyurethane sponge, and the thickness of the sponge is not less than 10 mm.

[0013] Furthermore, the coconut fiber rope described in step (2) is embedded in the sponge in an array of m≥3×n≥3.

[0014] Furthermore, the height of the upper end of the coconut fiber rope protruding from the top surface of the sponge in step (2) is 5 to 30 mm.

[0015] Further, the sodium alginate solution containing carbon black mentioned in step (3) refers to an aqueous solution with a sodium alginate mass fraction of 0.5% to 3% and a carbon black mass fraction of 2% to 8%.

[0016] A high-efficiency solar water evaporator was prepared by the above method.

[0017] The above-mentioned high-efficiency solar water evaporators are used in seawater desalination and wastewater purification.

[0018] The principle of this invention is as follows: To achieve the goal of preparing a relatively simple and efficient solar water evaporator using low-cost photothermal materials in a short process, this invention selects low-cost carbon black and coconut fiber as the photothermal material and water transport material, respectively. Carbon black has excellent photothermal conversion capabilities, effectively absorbing sunlight and converting it into heat, thereby accelerating water evaporation. Coconut fiber has numerous micropores both axially and radially. The presence of axial micropores facilitates the transport of water from the bottom to the top of the coconut fiber through capillary action, while the presence of radial micropores facilitates water evaporation on the surface of the coconut fiber. Pre-weaving the coconut fiber into ropes improves its mechanical properties and increases the surface area and the number of surface micropores, thus enhancing its water absorption capacity. Embedding the coconut fiber ropes into a sponge in an array, and coating the protruding part of the sponge top surface with a sodium alginate solution containing carbon black, forms a carbon black photothermal film on the surface of the coconut fiber, which is beneficial for improving the solar water evaporation capacity of the coconut fiber surface. Therefore, the three-dimensional water evaporator composed of coconut fiber and carbon black not only changes the structure of the conventional two-dimensional water evaporator, but also makes full use of the respective advantages of coconut fiber and carbon black, which is ultimately conducive to achieving efficient solar water evaporation.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The photothermal material carbon black, the water transport material coconut fiber, and the water evaporator substrate material sponge selected in this invention are all widely available, low in cost, and easy to obtain. By embedding coconut fiber ropes of the same length into the sponge and coating the protruding part of the sponge top surface with a sodium alginate solution containing carbon black, a carbon black photothermal film is formed on the surface of the coconut fiber. This method of constructing a three-dimensional high-efficiency solar water evaporator is simple, has a short process flow, and is easy to implement. This invention has the advantages of low cost, simple operation, and high water evaporation rate, and has better prospects for large-scale preparation and commercial application.

[0021] (2) The coconut fiber selected in this invention has unique structural features. The presence of axial micropores and radial (or surface) pores in the fiber together constitutes a natural and highly efficient water transport and evaporation system. The axial water transport channels inside the coconut fiber ensure rapid water transport from its root to its tip, while the pores on the surface of the coconut fiber greatly increase the contact area with water and air, thereby facilitating an increase in the water evaporation rate. This composite transport and evaporation mechanism makes coconut fiber an ideal material for preparing highly efficient evaporators.

[0022] (3) This invention assembles and constructs a three-dimensional evaporator by weaving coconut fibers into an array and embedding them into a sponge. Compared to the traditional two-dimensional pure sponge structure, this three-dimensional structure has a larger external surface area, providing more water evaporation interfaces. This characteristic is beneficial for increasing water evaporation efficiency because, under solar heating, more water can evaporate rapidly from the increased surface area. Therefore, this three-dimensional evaporator exhibits higher performance in solar water evaporation, which is beneficial for improving the water evaporation rate and overall evaporation efficiency. Attached Figure Description

[0023] Figure 1 The images show SEM images of the coconut fiber surfaces in step (2) of Embodiment 1 of the present invention without carbon black coating and in step (3) with carbon black coating (a in the image is the outer surface of the coconut fiber without carbon black coating, b is the outer surface of the coconut fiber with carbon black coating, c is the top surface of the coconut fiber without carbon black coating, and d is the top surface of the coconut fiber with carbon black coating).

[0024] Figure 2 This is a physical image of the high-efficiency solar water evaporator based on coconut fiber array obtained in Embodiment 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the high-efficiency solar water evaporator based on coconut fiber array obtained in Embodiment 1 of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0027] Example 1

[0028] (1) Thoroughly clean and dry the coconut fiber. Then, take 6 coconut fibers and weave them into a rope. Cut the woven coconut fiber rope into 30mm lengths for subsequent processing and use.

[0029] (2) Embed the treated coconut fiber ropes into a 5×3 array inside a 20mm thick sponge. In this step, it is necessary to ensure that the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 10mm from the top surface of the sponge to form an effective path for moisture transfer and evaporation.

[0030] (3) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension. Next, immerse the portion of the coconut fiber rope array protruding from the top surface of the sponge in step (2) into the prepared carbon black suspension, ensuring that the surface of the coconut fiber is completely coated with carbon black. Finally, remove the impregnated coconut fiber array and air dry it naturally to obtain a coconut fiber array-based solar water evaporator.

[0031] The top and outer surfaces of the coconut fibers without carbon black coating in step (1) and the coconut fibers coated with carbon black in step (3) were observed using a scanning electron microscope (FESEM; Hitachi S-4800, Japan). The results are as follows: Figure 1 As shown in the figures (a is the outer surface of the coconut fiber without carbon black coating, b is the outer surface of the coconut fiber with carbon black coating; c is the top surface of the coconut fiber without carbon black coating, and d is the top surface of the coconut fiber with carbon black coating), after impregnation with carbon black suspension, it can be seen from Figures b and d that both the outer and top surfaces of the coconut fiber are uniformly covered with adhered carbon black, thus forming water evaporation channels and achieving efficient photothermal conversion.

[0032] The physical image and structural schematic diagram of the high-efficiency coconut fiber array-based solar water evaporator constructed in this embodiment are shown below. Figure 2 and Figure 3 As shown.

[0033] Using real seawater from a certain sea and simulated wastewater prepared by adding 3wt% FeCl3·6H2O, Cu(NO3)2·3H2O, NiCl2, and ZnCl2 to 500mL of pure water (the following examples and comparative examples are the same), the evaporation rate of the coconut fiber array-based solar water evaporator for the two different water bodies was tested using a xenon lamp light source. The equipment model was CEL-HXF300-T3; the mass loss due to evaporation was obtained using an electronic balance (JJ600). The test results showed that the indoor and outdoor seawater evaporation rates of the coconut fiber array-based solar water evaporator were 4.03 kg·m³. -2 ·h -1 and 3.99 kg·m -2 ·h -1 The evaporation rates of indoor and outdoor wastewater were 4.05 kg·m³, respectively. -2 ·h -1 and 4.01 kg·m -2 ·h -1 .

[0034] Example 2

[0035] (1) Thoroughly clean and dry the coconut fiber. Then, take 6 coconut fibers and weave them into a rope. Cut the woven coconut fiber rope into 25mm lengths for subsequent processing and use.

[0036] (2) Embed the treated coconut fiber ropes into a 20mm thick sponge in a 5×3 array. In this step, it is necessary to ensure that the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 5mm from the top surface of the sponge to form an effective moisture transfer and evaporation path.

[0037] (3) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension. Next, immerse the portion of the coconut fiber rope array protruding from the top surface of the sponge in step (2) into the prepared carbon black suspension, ensuring that the surface of the coconut fiber is completely coated with carbon black. Finally, remove the impregnated coconut fiber array and air dry it naturally to obtain a coconut fiber array-based solar water evaporator.

[0038] The water evaporation rate of the coconut fiber array-based solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the coconut fiber array-based solar water evaporator were 3.52 kg·m³. -2 ·h -1 and 3.33 kg·m -2 ·h -1 The indoor and outdoor wastewater evaporation rates were 3.57 kg·m³, respectively. -2 ·h -1 and 3.40 kg·m -2 ·h -1 .

[0039] Example 3

[0040] (1) Thoroughly clean and dry the coconut fiber. Then, take 6 coconut fibers and weave them into a rope. Cut the woven coconut fiber rope into 40mm lengths for subsequent processing and use.

[0041] (2) Embed the treated coconut fiber ropes into a 5×3 array inside a 20mm thick sponge. In this step, it is necessary to ensure that the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 20mm from the top surface of the sponge to form an effective path for moisture transfer and evaporation.

[0042] (3) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension. Next, immerse the portion of the coconut fiber rope array protruding from the top surface of the sponge in step (2) into the prepared carbon black suspension, ensuring that the surface of the coconut fiber is completely coated with carbon black. Finally, remove the impregnated coconut fiber array and air dry it naturally to obtain a coconut fiber array-based solar water evaporator.

[0043] The water evaporation rate of the coconut fiber array-based solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the coconut fiber array-based solar water evaporator were 3.51 kg·m³. -2 ·h -1 and 3.31 kg·m -2 ·h -1The indoor and outdoor wastewater evaporation rates were 3.61 kg·m³, respectively. -2 ·h -1 and 3.37 kg·m -2 ·h -1 .

[0044] Example 4

[0045] (1) Thoroughly clean and dry the coconut fiber. Then, take 6 coconut fibers and weave them into a rope. Cut the woven coconut fiber rope into 50mm lengths for subsequent processing and use.

[0046] (2) Embed the treated coconut fiber ropes into a 5×3 array inside a 20mm thick sponge. In this step, it is necessary to ensure that the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 30mm from the top surface of the sponge to form an effective path for moisture transfer and evaporation.

[0047] (3) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension. Next, immerse the portion of the coconut fiber rope array protruding from the top surface of the sponge in step (2) into the prepared carbon black suspension, ensuring that the surface of the coconut fiber is completely coated with carbon black. Finally, remove the impregnated coconut fiber array and air dry it naturally to obtain a coconut fiber array-based solar water evaporator.

[0048] The water evaporation rate of the coconut fiber array-based solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the coconut fiber array-based solar water evaporator were 2.98 kg·m³. -2 ·h -1 and 2.73 kg·m -2 ·h -1 The indoor and outdoor wastewater evaporation rates were 3.11 kg·m³, respectively. -2 ·h -1 and 2.83 kg·m -2 ·h -1 .

[0049] Comparative Example 1

[0050] Compared with Example 1, this comparative example directly utilizes a single pure sponge as a solar water evaporator. The specific steps are as follows:

[0051] A 20mm thick sponge was used directly as a solar water evaporator.

[0052] The water evaporation rate of the sponge was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the sponge solar water evaporator were 1.76 kg·m³.-2 ·h -1 and 1.68 kg·m -2 ·h -1 The evaporation rates of indoor and outdoor wastewater were 1.77 kg·m³, respectively. -2 ·h -1 and 1.73 kg·m -2 ·h -1 .

[0053] The comparison results between this comparative example and Example 1 show that if coconut fiber is not used as a water transport material and carbon black is not used as a photothermal material to construct a three-dimensional water evaporator on a sponge substrate, the water transport and photothermal conversion capabilities of a single sponge are poor, and therefore the measured evaporation rates of seawater and wastewater are low.

[0054] Comparative Example 2

[0055] Compared with Example 1, this comparative example directly utilizes a single sponge treated with sodium alginate solution containing carbon black as a solar water evaporator. The specific steps are as follows:

[0056] (1) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension.

[0057] (2) Immerse the 20mm thick sponge completely in the carbon black suspension obtained in step (1) above to ensure that the surface of the sponge is completely covered with carbon black. After immersion, remove the sponge and place it in the natural environment to dry.

[0058] The water evaporation rate of the carbon black coated sponge solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the carbon black coated sponge solar water evaporator were 2.04 kg·m³. -2 ·h -1 and 1.98 kg·m -2 ·h -1 The indoor and outdoor wastewater evaporation rates were 2.14 kg·m³, respectively. -2 ·h -1 and 2.03 kg·m -2 ·h -1 .

[0059] The comparison results between this comparative example and Example 1 show that although the sponge surface is covered with carbon black photothermal material, due to the two-dimensional structure of its water evaporator and the lack of the rapid water transport capability of coconut fiber, the measured evaporation rate of seawater and wastewater is still relatively low.

[0060] Comparative Example 3

[0061] Compared with Example 1, this comparative example used a coconut fiber array that had not undergone carbon black impregnation treatment as a solar water evaporator. The specific steps are as follows:

[0062] (1) Thoroughly clean and dry the coconut fiber. Then, take 6 coconut fibers and weave them into a rope. Cut the woven coconut fiber rope into 30mm lengths for subsequent processing and use.

[0063] (2) Embed the treated coconut fiber ropes into a 5×3 array inside a 20mm thick sponge. In this step, it is necessary to ensure that the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 10mm from the top surface of the sponge to form an effective path for moisture transfer and evaporation.

[0064] The water evaporation rate of the coconut fiber array-based solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the coconut fiber array-based solar water evaporator were 2.37 kg·m³. -2 ·h -1 and 2.23 kg·m -2 ·h -1 The indoor and outdoor wastewater evaporation rates were 2.43 kg·m³, respectively. -2 ·h -1 and 2.33 kg·m -2 ·h -1 .

[0065] The comparison results between this comparative example and Example 1 show that without carbon black impregnation and coating treatment of coconut fiber, the photothermal conversion capacity of the coconut fiber array-based solar water evaporator is poor, which is not conducive to water evaporation. Therefore, the measured evaporation rates of seawater and wastewater need to be improved.

[0066] Comparative Example 4

[0067] Compared to Example 1, this comparative example uses sisal fiber instead of coconut fiber in the solar water evaporator. The specific steps are as follows:

[0068] (1) Thoroughly clean and dry the sisal fibers. Then, take 6 sisal fibers and weave them into a rope. Cut the woven sisal fiber rope into 30mm lengths for subsequent processing and use.

[0069] (2) Embed the treated sisal fiber ropes into a 20mm thick sponge in a 5×3 array. In this step, it is necessary to ensure that the lower end of the sisal fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes 10mm from the top surface of the sponge.

[0070] (3) Add 1 wt% sodium alginate to deionized water and stir magnetically for 1 hour. Then, add 4 wt% carbon black and continue stirring magnetically for 24 hours to prepare a carbon black suspension. Next, immerse the sisal fiber array portion protruding from the top surface of the sponge in step (2) into the prepared carbon black suspension, ensuring that the surface of the sisal fibers is completely coated with liquid. Finally, remove the impregnated sisal fiber array and air dry it naturally to obtain a sisal fiber array-based solar water evaporator.

[0071] The water evaporation rate of the sisal fiber array-based solar water evaporator was tested using a xenon lamp light source. The test results showed that the indoor and outdoor seawater evaporation rates of the sisal fiber array-based solar water evaporator were 3.11 kg·m³. -2 ·h -1 and 2.93 kg·m -2 ·h -1 The indoor and outdoor wastewater evaporation rates were 3.13 kg·m³, respectively. -2 ·h -1 and 3.06 kg·m -2 ·h -1 .

[0072] The comparison between this comparative example and Example 1 shows that sisal fibers also have many micropores along their axial direction, which facilitates the capillary transport of water from bottom to top. However, sisal fibers lack obvious pores in their radial direction, which hinders the rapid evaporation of water on the fiber surface. Consequently, the evaporator constructed from sisal fibers has a lower solar water evaporation rate than the coconut fiber array-based evaporator constructed under the same conditions. In other words, the presence of micropores in both the axial and radial directions of natural fibers is a necessary condition for their array-based solar evaporators to achieve superior water evaporation rates.

[0073] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-efficiency solar water evaporator, characterized in that, The preparation steps include the following: (1) Clean and dry the coconut fiber, take multiple coconut fibers and weave them into a rope, then cut them into coconut fiber ropes of the same length. (2) Embed the coconut fiber ropes of the same length into the sponge in an m×n array, wherein the lower end of the coconut fiber rope is flush with the bottom surface of the sponge, while the upper end protrudes from the top surface of the sponge by a certain height. (3) The part of the above-mentioned coconut fiber rope array protruding from the top surface of the sponge is immersed in a sodium alginate solution containing carbon black for surface coating treatment, and then taken out and air-dried to obtain a high-efficiency solar water evaporator based on coconut fiber array.

2. The method for preparing a high-efficiency solar water evaporator according to claim 1, characterized in that, The coconut fiber mentioned in step (1) is coconut shell fiber with a diameter of 0.6 to 0.9 mm and a length of not less than 10 mm; the coconut fiber rope is woven from not less than 6 coconut fibers; the cut length of the coconut fiber rope is not less than 7 mm.

3. The high-efficiency solar water evaporator and its preparation method according to claim 1, characterized in that, The sponge mentioned in step (2) is one of polyvinyl alcohol sponge, melamine foam, wood pulp sponge, and polyurethane sponge, and the thickness of the sponge is not less than 10mm.

4. The high-efficiency solar water evaporator and its preparation method according to claim 1, characterized in that, The coconut fiber rope described in step (2) is embedded in the sponge in an array of m≥3×n≥3.

5. The high-efficiency solar water evaporator and its preparation method according to claim 1, characterized in that, The height of the upper end of the coconut fiber rope protruding from the top surface of the sponge in step (2) is 5 to 30 mm.

6. The high-efficiency solar water evaporator and its preparation method according to claim 1, characterized in that, The sodium alginate solution containing carbon black mentioned in step (3) refers to an aqueous solution with a sodium alginate mass fraction of 0.5% to 3% and a carbon black mass fraction of 2% to 8%.

7. A high-efficiency solar water evaporator, characterized in that, It is prepared by the method described in any one of claims 1 to 6.

8. The application of the high-efficiency solar water evaporator as described in claim 7 in seawater desalination and wastewater purification.

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