Apparatus and method for recovering water from drain water containing organic matter

Abstract

To provide a water recovery apparatus which recovers water from drain water containing volatile organic matters and organic compounds of a low molecular weight in a closed system space of a spaceship interior or a lunar base or the like, and in which oxygen supply is unnecessary or a small amount thereof is sufficient, and further, which does not require consumables on the premise of exchange of activated carbon or the like.SOLUTION: A water recovery apparatus for recovering water by processing drain water containing volatile organic compounds or low molecular weight organic compounds of a molecular weight of 200 or lower, comprises a separation membrane module 2 for subjecting the drain water to pervaporation processing using a separation membrane with a pore size of 3.0-4.2 Å. The apparatus for recovering water from drain water containing organic compounds recovers treated water from which organic compounds have been removed by to the separation membrane module 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water recovery device and method for use in a closed space such as a spacecraft or a lunar base, and more particularly to a water recovery device and method for recovering water by treating wastewater containing volatile organic substances and low-molecular-weight organic substances using a pervaporation method using a separation membrane. [Background technology]

[0002] On the International Space Station, urine, air conditioning condensate, etc. are treated using a system that combines vacuum distillation, high-temperature catalytic oxidation, and adsorbents.

[0003] Vacuum distillation can remove inorganic ions and organic substances with relatively large molecular weights, but it cannot remove volatile organic substances or organic substances with low molecular weights. These organic substances are decomposed into carbon dioxide in a subsequent high-temperature catalytic oxidation process, but they cannot be completely decomposed, and some of them remain as harmful organic substances. The remaining organic substances are removed using adsorbents such as activated carbon and ion exchange resins.

[0004] However, activated carbon and ion exchange resin are consumables that must be periodically replenished from the ground and replaced by astronauts. Replenishment from the ground not only requires huge launch costs, but also poses a risk to drinking water supplies in the event of a rocket launch failure. It would also be desirable to minimize the need for replacement by astronauts.

[0005] In order to maintain a constant gas-liquid interface during vacuum distillation in a microgravity environment, a centrifuge is used to rotate a drum containing the water to be treated, forcibly creating a gas-liquid interface through centrifugal force. However, this method has the disadvantage of being prone to breakdowns due to its complex mechanical structure, and requires frequent maintenance of the sliding parts of the rotating body, etc.

[0006] In high-temperature catalytic oxidation, oxygen must be supplied to the catalyst column along with the water to be treated. Oxygen is an important resource on a spacecraft, and the amount consumed must be produced by electrolysis of water. Therefore, consuming oxygen increases the spacecraft's overall power consumption and indirectly leads to water loss.

[0007] In addition, conventional water recovery devices required a large number of units and associated equipment such as liquid storage tanks, pumps, valves, and meters, which made the devices large and difficult to install in the limited space on a spacecraft.

[0008] As another water treatment system for spacecraft, Patent Document 1 describes a system that combines a membrane distillation module, a reverse osmosis membrane unit, and a catalytic oxidation unit.

[0009] According to the space water treatment system of Patent Document 1, the organic load treated by catalytic oxidation is reduced by membrane distillation or reverse osmosis (RO) membrane treatment. However, the removal rate of volatile organic substances and low-molecular-weight organic substances is low using membrane distillation or RO membranes that use general polymer membranes, and they are not sufficient load reduction measures. In addition, there is a problem in that multiple types of organic treatment units must be combined, which requires a large installation space.

[0010] Furthermore, in membrane distillation, there are essentially no membranes that can be applied other than polymer porous hydrophobic membranes, but there is a risk that wastewater containing high concentrations of organic matter will flow directly into the water vapor side if it becomes hydrophilic due to contamination by organic matter in the wastewater.

[0011] Patent Document 2 describes a water treatment system that uses a pervaporation method using a separation membrane, in which a device is used to concentrate cesium-containing wastewater using a zeolite membrane.

[0012] The device in Patent Document 2 is a concentration device that uses a pervaporation method using a zeolite membrane. The concentration device in Patent Document 2 is intended to concentrate cesium, which has a boiling point much higher than that of water, and takes advantage of the properties of the zeolite membrane, such as its resistance to radiation, heat resistance, and resistance to membrane contamination by hydrophilic substances.

[0013] The pervaporation method using a zeolite membrane described in Patent Document 2 can remove water from high-concentration alcohol with a low water content and dehydrate and concentrate the alcohol. However, because the target product is dehydrated alcohol, the alcohol concentration in the permeate that permeates to the vapor side is so high that it does not meet water quality standards at all.

[0014] That is, the zeolite membrane used in Patent Document 2 has a pore size of 8 Å or less. Therefore, while it is suitable for separating cesium, which has a high boiling point and a relatively large atomic size, it cannot effectively remove volatile low-molecular-weight organic substances with small molecular sizes, such as ethanol (molecular size 4.5 Å), isopropanol (molecular size 4.6 Å), and acetic acid (molecular size 4.3 Å), to a level that is harmless to the human body. Furthermore, Patent Document 2 does not describe the use of the membrane to recover water vapor that has permeated the membrane in an environment with less gravity than Earth, or any means for gas-liquid separation of the condensed treated water from excess gas. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-188468 [Patent Document 2] Japanese Patent Application Publication No. 2013-202513 Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention aims to provide a water recovery device and method for recovering water from wastewater containing volatile organic compounds and low-molecular-weight organic compounds in closed spaces such as spacecraft and lunar bases, which does not require the supply of oxygen or only requires a small amount, and does not require consumables such as activated carbon that require replacement. [Means for solving the problem]

[0017] The water recovery device for organic-containing wastewater of the present invention is a water recovery device that treats wastewater containing volatile organic substances or low-molecular-weight organic substances with a molecular weight of 200 or less and recovers water, and is equipped with a separation membrane module that performs pervaporation treatment on the wastewater using a separation membrane with a pore size of 3.0 to 4.2 Å, and recovers treated water from which the organic substances have been removed by the separation membrane module.

[0018] One embodiment of the present invention is an apparatus for recovering water from organic matter-containing wastewater for use in a spacecraft or a lunar base.

[0019] In one embodiment of the present invention, the separation membrane is a zeolite membrane.

[0020] In one aspect of the present invention, the separation membrane module has a primary side and a secondary side separated by a separation membrane, and separates the wastewater introduced into the primary side into water vapor from which organic matter has been removed and concentrated water from which the organic matter has been concentrated; a gas suction device for reducing the pressure on the secondary side of the separation membrane module to less than the saturated water vapor pressure at the wastewater temperature on the primary side; and a pressure adjustment device for adjusting the pressure of the wastewater on the secondary side of the separation membrane module to equal to or greater than the saturated water vapor pressure; and treated water is obtained by condensing the water vapor from which organic matter has been removed from the secondary side.

[0021] In one aspect of the present invention, a gas-liquid separator is provided for removing bubbles from condensed water formed by condensation of water vapor from the gas suction device.

[0022] In one aspect of the present invention, a variable volume liquid storage tank whose volume changes in accordance with the amount of water stored is provided as a storage section for the wastewater, concentrated water, and treated water.

[0023] In one aspect of the present invention, a heating device for heating a fluid inside the separation membrane module is installed in the separation membrane module.

[0024] In one aspect of the present invention, the separation membrane module further includes a circulation means for circulating concentrated water from the secondary side of the separation membrane module to the wastewater inlet side.

[0025] In one aspect of the present invention, a condenser is provided that recovers latent heat from water vapor from the gas suction device.

[0026] In one aspect of the present invention, the separation membrane module further includes a heat exchanger for heating the wastewater supplied to the separation membrane module by heat exchange with the condensed water from the condenser.

[0027] In one aspect of the present invention, the separation membrane module further includes an ion removal device that removes ions from the wastewater supplied to the separation membrane module.

[0028] In one aspect of the present invention, a device for removing residual components remaining in the treated water is provided.

[0029] In one aspect of the present invention, the system includes a condenser for condensing water vapor from the separation membrane module, and a Peltier element for transferring latent heat recovered by the condenser to the separation membrane module and transferring cold heat from the separation membrane module to the condenser.

[0030] In one aspect of the present invention, the water vapor from the separation membrane module is introduced to the condenser without passing through a gas suction means.

[0031] In one aspect of the present invention, the cooling system further comprises a pump that sucks condensed water from the condenser.

[0032] In one aspect of the present invention, a concentrated water treatment device is provided that reduces the concentration of organic matter contained in the concentrated water discharged from the separation membrane module.

[0033] In one aspect of the present invention, the treated concentrated water discharged from the concentrated water treatment device is returned to the water-to-be-treated side of the separation membrane module.

[0034] In one embodiment of the present invention, the concentrated water treatment device is a UV oxidation device, a catalytic oxidation device, an electrolysis device, a wet oxidation device, a pervaporation membrane treatment device, or a distillation device.

[0035] In one embodiment of the present invention, water is recovered using the water recovery device for organic matter-containing wastewater of the present invention. [Effects of the Invention]

[0036] According to the present invention, by using a pervaporation method that utilizes a separation membrane such as a zeolite membrane with a pore size of 3.0 to 4.2 Å, it is possible to obtain treated water in which volatile organic compounds and low-molecular-weight organic compounds have been removed from the water to a level that is harmless to humans. Because a high organic compound removal rate can be achieved using the separation membrane module, it is not necessary to provide an organic compound removal means, such as a high-temperature catalytic oxidation treatment, downstream of the separation membrane module, or such a means can be small-scale. Therefore, it is possible to reduce the size and weight of the device without consuming large amounts of precious oxygen and with fewer consumables.

[0037] As mentioned above, vacuum distillation equipment used in space uses a centrifuge to separate wastewater and water vapor into gas and liquid, but regular maintenance of the rotor's sliding parts is required to prevent centrifuge breakdowns. Furthermore, membrane distillation is essentially limited to polymeric porous hydrophobic membranes, but there is a risk that wastewater containing high concentrations of organic matter may flow directly into the water vapor side if it becomes hydrophilic due to contamination by organic matter in the wastewater. The present invention uses a separation membrane with fine pores, allowing only water molecules that have turned into water vapor to pass through the membrane surface, allowing for long-term use without maintenance. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 2] FIG. 1 is an explanatory diagram of pervaporation. [Figure 3] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 4] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 5] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 6] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 7]FIG. 1 is a perspective view of a separation membrane module / condenser assembly. [Figure 8] FIG. 2 is a plan view of the separation membrane module-condenser assembly. [Figure 9] FIG. 2 is a front view of the separation membrane module-condenser assembly. [Figure 10] FIG. 2 is a left side view of the separation membrane module-condenser assembly. [Figure 11] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 12] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 13] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 14] FIG. 10 is a side view showing another example of a separation membrane module-condenser assembly. [Figure 15] FIG. 10 is a side view showing another example of a separation membrane module-condenser assembly. [Figure 16] FIG. 10 is a side view showing another example of a separation membrane module-condenser assembly. [Figure 17] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 18] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. [Figure 19] 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, an embodiment will be described with reference to the drawings.

[0040] FIG. 1 and FIGS. 3 to 6 each show an apparatus for recovering water from organic matter-containing wastewater according to an embodiment of the present invention.

[0041] Examples of wastewater that can be treated by the device of the present invention include condensed water derived from water vapor contained in human sweat or exhaled breath, and human urine, which are discharged from spacecraft, lunar bases, etc. Examples of volatile organic compounds contained in such wastewater include methanol, ethanol, isopropanol, phenol, formaldehyde, and acetone. Examples of low-molecular-weight organic substances (e.g., molecular weight of 200 or less) include formic acid, acetic acid, oxalic acid, citric acid, urea, glycine, and histidine.

[0042] In the water recovery system shown in Figures 1 and 3-6, raw water (wastewater containing volatile organic compounds and low-molecular-weight organic compounds) is sent to a separation membrane module 2 by a liquid transfer means including a pump 1 and pipes 1a and 1b. The pressure on the secondary side (suction side) 2b of a separation membrane 2m with a pore size of 3.0 to 4.2 Å is reduced to less than the saturated water vapor pressure at the water temperature on the primary side (raw water side) 2a of the separation membrane 2m by a gas suction device 3 such as a vacuum pump. As a result, as shown schematically in Figure 2, water molecules in the raw water permeate as water vapor from the primary side 2a of the separation membrane 2m to the secondary side 2b. The water vapor in the secondary side 2b is extracted through pipe 3a, gas suction device 3, and pipe 3b, condenses, and is recovered as treated water.

[0043] The concentrated water concentrated on the primary side 2a flows into a concentrated water line 4a and is taken out as concentrated water through a pressure regulator 4. This pressure regulator 4 sets the water pressure of the concentrated water to be equal to or higher than the saturated steam pressure at the maximum temperature of the wastewater, thereby preventing the concentrated water from boiling.

[0044] The water recovery device of Fig. 3 includes a condenser 10 for condensing the water vapor from the pipe 3b. The low-temperature fluid for cooling the water vapor in the condenser 10 of Fig. 3 is utility cooling water or the like.

[0045] 3 also includes a gas-liquid separator 5 for separating gas components from the condensed water. The condensed water from the condenser 10 is introduced into the gas-liquid separator 5 via a pipe 10a.

[0046] The gas separated by this gas-liquid separator 5 is taken out through a pipe 5a, and the water is introduced through a pipe 5b into a treated water tank 6b, which is a volume-variable liquid storage tank. A suitable example of the gas-liquid separator 5 is as described below.

[0047] In FIG. 3, a raw water tank 6a consisting of a variable volume liquid tank for storing raw water and a concentrated water tank 6c consisting of a variable volume liquid tank for storing concentrated water from the concentrated water line 4a are installed.

[0048] In addition, in FIG. 3, a heater 7 is provided integrally with the separation membrane module 2, for example, so as to surround the outer periphery of the separation membrane module, and water in the separation membrane module 2 is heated.

[0049] The other configurations of the water recovery device in FIG. 3 are the same as those in FIG. 1, and the same reference numerals denote the same parts.

[0050] In the water recovery device of Figure 4, the discharge water from the pump 1 is supplied to the separation membrane module 2 via a pipe 1c, a circulation pump 8, and a pipe 1d. A portion of the concentrated water from the concentrated water line 4a is introduced into this pipe 1c via a pipe 9.

[0051] In this way, in the water recovery apparatus of FIG. 4, part of the concentrated water from the separation membrane module 2 is circulated to the inlet side of the separation membrane module 2 and treated.

[0052] In the water recovery device of FIG. 4, a heater 7 is also provided in the separation membrane module 2, making it possible to heat the water in the separation membrane module 2.

[0053] The other configurations of the water recovery device in FIG. 4 are the same as those in FIG. 1, and the same reference numerals denote the same parts.

[0054] In the water recovery device of FIG. 5, a heat exchanger 11 for heating raw water is installed midway along the pipe 1c.

[0055] The raw water is passed through the low-temperature fluid flow path of this heat exchanger 11, and is heated while flowing through this low-temperature fluid flow path, and then sent to the circulation pump 8 together with the return concentrated water from the pipe 9.

[0056] In addition, in FIG. 5, the membrane permeation fluid (water vapor) from the pipe 3b is caused to flow into the high-temperature fluid flow path of the condenser 10, and is cooled and condensed while flowing through the high-temperature fluid flow path.

[0057] Concentrated water from the separation membrane module 2 is circulated through a pipe 10b in the low-temperature fluid flow path of the condenser 10. The condensed water generated by flowing through the high-temperature fluid flow path of the condenser 10 and being cooled is passed through a pipe 10c to a high-temperature fluid flow path of the heat exchanger 11, where it is cooled by heat exchange with raw water flowing through the low-temperature fluid flow path of the heat exchanger 11, and then taken out as treated water through a pipe 11a.

[0058] The concentrated water, whose temperature has increased while flowing through the low-temperature fluid flow path of the condenser 10, flows out into the concentrated water line 4a, and a portion of it is circulated via the pipe 9 to the pipe 1c upstream of the circulation pump 8 and downstream of the heat exchanger 11. The remainder of the water flowing into the concentrated water line 4a passes through the pressure regulator 4 and is extracted as concentrated water.

[0059] Other configurations in FIG. 5 are the same as those in FIG. 4, and the same reference numerals denote the same parts.

[0060] The water recovery device of FIG. 6 is provided with an ion removal device 21 in the middle of the pipe 1 b to remove ions from the raw water, and the deionized water is supplied to the separation membrane module 2 .

[0061] In addition, in Figure 6, a residual component removal device 22 is installed in the pipe 5b through which the water from which gas has been separated in the gas-liquid separator 5 flows, and after removing the residual components, the treated water is introduced into a treated water tank 6b consisting of a volume-variable liquid storage tank.

[0062] Suitable examples of the ion removal device 21 and the residual component removal device 22 are as described below.

[0063] The other configurations in FIG. 6 are the same as those in FIG. 3, and the same reference numerals denote the same parts.

[0064] The separation membranes and other devices used in each of the water recovery devices shown in FIGS. 1 and 3 to 6 will be described in detail below.

[0065] [Separation membrane] The pore size of the separation membrane 2m is 3.0 to 4.2 Å, and does not allow organic substances with molecular sizes larger than water molecules (molecular size 2.7 Å), such as ethanol (molecular size 4.5 Å), isopropanol (molecular size 4.6 Å), and acetic acid (molecular size 4.3 Å) to pass through (Figure 2). Therefore, treated water with a sufficiently reduced organic matter concentration is obtained from the secondary side 2b of the separation membrane module 2.

[0066] On the primary side 2a of the separation membrane module 2, components such as organic matter, such as ethanol, in the raw water are concentrated to produce concentrated water. This concentrated water is discharged from a concentrated water line 4a. A pressure regulator 4 is installed on the concentrated water line 4a. This pressure regulator 4 sets the water pressure of the concentrated water to be equal to or greater than the saturated steam pressure at the maximum temperature of the wastewater, preventing the concentrated water from boiling.

[0067] To increase the amount of water treated by the separation membrane module 2, it is necessary to increase the water vapor transmission rate across the membrane surface of the separation membrane 2m. The water vapor transmission rate per membrane area of ​​the separation membrane 2m depends on the difference between the water vapor pressure on the primary side 2a and the water vapor pressure on the secondary side 2b. To increase the water vapor pressure on the primary side 2a, a higher wastewater temperature is preferable, but if the temperature is too high, it will require an improvement in the heat resistance of the device and will increase the energy consumption for heating. Therefore, the temperature range of the primary side 2a is preferably 80 to 150°C, and particularly 90 to 140°C.

[0068] To lower the pressure on the secondary side 2b, it is necessary to increase the suction capacity of the gas suction device 3. However, lowering the suction pressure requires increasing the size of the device or selecting equipment with high power consumption, which is not desirable for space equipment. Therefore, a pressure of 30 to 95 kPa-Abs is preferable for the secondary side 2b. Note that because the atmospheric pressure on a spacecraft or lunar base is different from that on Earth, the unit of pressure is expressed as absolute pressure, with an absolute vacuum being zero, rather than as gauge pressure, which is based on atmospheric pressure.

[0069] Increasing the water vapor permeation rate of the separation membrane 2m is also effective in improving the quality of treated water. Generally, even if the pore size of the crystalline structure of a separation membrane is 3.0 to 4.2 Å, a small number of pores larger than 4.2 Å exist due to defects, so organic matter cannot necessarily be completely removed. However, by increasing the vapor pressure difference between the primary side 2a and secondary side 2b of the separation membrane 2m, the increase in the permeation rate of smaller water molecules exceeds the increase in the permeation rate of organic matter, thereby reducing the concentration of organic matter in the treated water. Furthermore, since the ratio of the saturated vapor pressure of water to the saturated vapor pressure of volatile organic compounds such as ethanol increases at higher temperatures, performing membrane separation at higher temperatures allows for preferential water recovery, leading to improved water quality.

[0070] [Chabazite-type zeolite membrane] The separation membrane 2m must have a pore size that allows it to separate organic molecules such as water molecules (molecular size 2.7 Å) and organic molecules such as ethanol (molecular size 4.5 Å), isopropanol (molecular size 4.6 Å), and acetic acid (molecular size 4.3 Å). The separation membrane 2m must also be water-resistant and heat-resistant. A chabazite-type zeolite membrane is suitable as a separation membrane 2m that meets these requirements.

[0071] The pore size of zeolite membranes varies from approximately 3 to 8 Å depending on the type, but chabazite-type zeolite membranes have pore sizes (approximately 3.7 Å) that are intermediate between the sizes of water molecules and the organic molecules to be treated.

[0072] Generally, the crystalline structure of zeolite membranes other than chabazite-type membranes is destroyed by long-term immersion in water or a high-water-air mixture, but chabazite-type zeolite membranes are highly durable even in water or a high-water-air mixture. Furthermore, while increasing the membrane permeation rate requires increasing the liquid temperature and water vapor pressure, chabazite-type zeolite membranes do not deteriorate for long periods even at temperatures above 100°C.

[0073] [Heater 7] In a typical membrane distillation process, wastewater is circulated through a separation membrane module at a high flow rate to ensure a flow rate that prevents target substances from concentrating on the membrane surface. In this case, a heater is installed at the inlet of the separation membrane module to raise the wastewater temperature, reduce the viscosity of the liquid, and reduce pump power. Furthermore, heat is exchanged between the liquid at the outlet of the separation membrane module and the liquid upstream of the heater in a heat exchanger, reducing the power consumption of the heater.

[0074] In this embodiment of the water recovery system, water molecules and organic molecules are separated by the molecular sieve effect of the separation membrane 2m. Therefore, the influence of the organic concentration on the upstream side of the separation membrane on the organic concentration in the treated water is smaller than in conventional membrane processes. Therefore, depending on the treatment conditions, such as the organic concentration in the raw water and the target water recovery rate, it is not necessary to increase the linear flow rate of the raw water to prevent membrane surface concentration. Therefore, it is possible to treat the raw water while supplying it to the membrane module at a minimum flow rate, taking into account the size of the liquid transfer equipment and power consumption reduction.

[0075] When water is passed through the membrane module at a low flow rate, the latent heat lost when the water evaporates is greater than the heat content of the raw water supplied to the separation membrane module. This results in a large temperature drop within the separation membrane module 2, making it impossible to ensure a sufficient water vapor pressure difference between the primary side 2a and secondary side 2b of the separation membrane 2m, resulting in a decrease in the treatment volume. Therefore, as shown in Figures 3 to 6, a heater 7 can be integrated into the separation membrane module 2, for example, surrounding the outer periphery of the separation membrane module 2. This heats the water within the separation membrane module 2 to compensate for the heat loss, enabling treatment without a decrease in the treatment volume. Furthermore, by not providing a heating device separately from the separation membrane module 2, the amount of equipment installed can be reduced and the size of the water recovery device can be kept small. Furthermore, the amount of heat dissipated from the water recovery device can be reduced.

[0076] [Gas-liquid separation device 5] The water vapor discharged from the secondary side 2b of the separation membrane module 2 is liquefied by being cooled in the condenser 10 or the like. However, it does not become completely liquid, and gases dissolved in the wastewater, such as oxygen and nitrogen, vaporize, and uncondensed water vapor are mixed with the treated water.

[0077] If air bubbles exist in the liquid inside a water treatment system in a microgravity environment, they can cause various problems, such as poor performance due to air entrapment in the pump and a decrease in the effective volume of the tank. Therefore, it is desirable to remove air bubbles from the treated water.

[0078] If sufficient gas-liquid contact time and gas-liquid contact area are obtained, the gas may dissolve back into water. However, in a limited space such as a spacecraft, there is a significant disadvantage to installing a buffer tank to ensure contact time, and it is not easy to control the gas-liquid contact area in a microgravity environment.

[0079] Therefore, in one embodiment of the present invention (Figures 3 and 6), a gas-liquid separation membrane that utilizes the gas pressure difference or a gas-liquid separation device 5 that utilizes the centrifugal force difference caused by the swirling flow is provided downstream of the gas suction device 3, thereby making it possible to obtain treated water that does not contain bubbles.

[0080] In a distillation processing system installed on land, water vapor is condensed in the stage preceding the gas suction device, and the gas and liquid are separated in a gas-liquid separator using gravity, after which only the gas is sent from the top of the gas-liquid separator to the gas suction device. However, in this case, the latent heat generated during the condensation of water vapor cannot be fully recovered. In the present invention, the water vapor before condensation is pressurized in the gas suction device 3 to increase the saturated vapor pressure, making it easier to recover latent heat.

[0081] [Variable volume liquid storage tank] In a microgravity environment, open liquid storage tanks cannot hold liquid, and closed constant-volume storage tanks pose a problem of changes in the internal pressure of the storage tank due to the flow of fluid in and out. To prevent such problems, in one embodiment of the present invention, variable-volume liquid storage tanks such as bags made of soft film or the like, cylinder tanks equipped with plungers, or elastic bellows tanks, whose volumes change depending on the amount of liquid flowing in and out, are used as water tanks 6a to 6c for storing raw water, concentrated water, and treated water (Figs. 3 and 6).

[0082] [Concentrated water circulation treatment] When the organic matter concentration in the raw water is high and there is a risk that the organic matter concentration in the treated water will become high, at least a portion of the concentrated water is circulated. The concentrated water from the separation membrane module 2 may be returned to the raw water tank 6a, or to the inlet pipe 1c of the circulation pump 8 as shown in Figures 4 and 5. Although not shown, when a circulation pump is not installed as in Figure 1, it is preferable to return the concentrated water to the inlet pipe 1a of the pump 1.

[0083] In this way, when concentrated water is circulated to the raw water side, the concentration of the target substances, such as organic matter, in the concentrated water returned to the raw water side is reduced by dilution caused by mixing with the raw water. This results in cleaner treated water. However, mixing of the raw water and concentrated water may cause large fluctuations in the temperature of the circulating liquid, or may increase heat loss due to heat radiation in the raw water tank 1.

[0084] When a liquid transfer device (pump) is installed independently, it is preferable to install a pressure regulator before the circulation line branches, or to install a new pressure regulator in the circulation line to set the pressure on the suction side of the liquid transfer device lower than the pressure in the raw water tank and higher than the saturated water vapor pressure at the circulating liquid temperature, thereby preventing cavitation in the liquid transfer device. However, doing so increases the constraints on pressure and temperature control, making the equipment configuration and control more complex. Therefore, it is preferable to configure the circulation line to return concentrated water to the inlet side of the circulation pump 8. This allows for circulating concentrated water with a simple configuration while suppressing heat radiation.

[0085] [Condenser 10 for latent heat recovery] In the present invention, since most of the raw water needs to be evaporated in the separation membrane module 2, recovering latent heat from water vapor is effective in reducing power consumption. As shown in Figure 5, by installing a condenser 10 for recovering latent heat downstream of the gas suction device 3, heat can be recovered from the water vapor heated by being compressed by the gas suction device 3, and the condensation temperature can be increased, thereby improving the latent heat recovery efficiency.

[0086] [Heat exchanger 11 for recovering sensible heat from treated water] As shown in Figure 5, the treated water that has been condensed after latent heat recovery in the condenser 10 is introduced into the heat exchanger 11 and heat exchanged with the raw water, thereby recovering the sensible heat of the treated water and reducing the power consumption of the heater 7.

[0087] [Ion removal device 21] By installing an ion removal device 21 upstream of the separation membrane module 2, the properties of the raw water (wastewater to be treated) can be adjusted to a water quality suitable for membrane separation treatment, and precipitation problems in the separation membrane module 2, pumps, etc. can be prevented.

[0088] Zeolite membranes are known to be poorly resistant to alkaline liquids. If the wastewater is alkaline, an ion removal device 21, such as an ion exchange resin, electrodialysis, continuous deionization device, or RO membrane, can be installed upstream of the separation membrane module to remove cations from the wastewater to be treated, thereby adjusting the pH to a neutral to acidic range suitable for zeolite or silica membrane treatment.

[0089] When treating wastewater containing organic matter that contains ions that easily precipitate, such as calcium ions and magnesium ions, the wastewater may become concentrated in the separation membrane module, resulting in the formation of precipitates. Because precipitates can cause problems such as clogging of the separation membrane and malfunction of the circulation pump, it is preferable to remove scale components using an ion removal device 21 upstream of the separation membrane module 2 to prevent problems caused by precipitates.

[0090] [Residual component removal device 22] The separation membrane module 2 has extremely high organic substance removal performance, but trace amounts of organic substances such as methanol, ethanol, and acetic acid, as well as small molecular ammonia (molecular size 2.6 Å), permeate into the treated water. To remove these components, a residual component removal device 22 may be connected downstream of the gas suction device 3, as in the water recovery device of Figure 6.

[0091] Activated carbon, catalytic oxidation devices, RO membranes (reverse osmosis membranes), etc. are effective means for removing organic substances such as methanol, ethanol, and acetic acid. Ion exchange resins, electrodialysis, continuous deionization devices, RO membranes, etc. are effective means for removing ions such as acetic acid and ammonia. Separation membrane modules can also be installed as residual component removal devices.

[0092] [Embodiment in which the separation membrane module is heated by the condensation heat of the condenser] In the present invention, the separation membrane module may be heated by the heat of condensation of the condenser. In this case, the heat of condensation of the condenser may be transferred to the separation membrane module by a Peltier element.

[0093] 7 to 10 show a separation membrane module-condenser assembly 30 in which a separation membrane module 31 and a condenser 32 are integrally combined for this purpose.

[0094] Similar to the separation membrane module 2, the separation membrane module 31 has a primary side and a secondary side separated by a separation membrane (not shown) having a pore size of 3.0 to 4.2 Å, and has a raw water supply port 31a for supplying raw water to the primary side, a concentrated water outlet 31b for extracting concentrated water from the primary side, and a water vapor outlet 31c for extracting water vapor from the secondary side.

[0095] The condenser 32 has an inlet 32a for steam and an outlet 32b for condensed water.

[0096] The separation membrane module 31 and the condenser 32 are flat, rectangular plates with roughly the same size for their main plate surfaces. The separation membrane module 31 and the condenser 32 are stacked together with a Peltier element 33 interposed therebetween. It is preferable to interpose thermal transfer grease or a thermal transfer sheet between the Peltier element 33 and the separation membrane module 31 and between the Peltier element 33 and the condenser 32 to improve thermal conductivity.

[0097] According to this separation membrane module-condenser assembly 30, heat from the condenser 32 is transferred to the separation membrane module 31 via the Peltier element 33, thereby heating the separation membrane module 31. Therefore, the same effect as when the heater 7 described above is provided can be obtained. In addition, the low temperature of the separation membrane module 31 is transferred to the condenser 32, allowing for efficient condensation.

[0098] In addition, this separation membrane module / condenser assembly 30 uses multiple Peltier elements 33, and the size and arrangement of these Peltier elements 33 can be selected appropriately depending on the size of the separation membrane module 31 and the condenser 32.

[0099] Figure 11 shows an example of a water recovery system using this separation membrane module-condenser assembly 30. This water recovery system has a configuration equivalent to that of the water recovery system shown in Figure 4, except that the separation membrane module 2 and heater 7 are replaced with the separation membrane module-condenser assembly 30.

[0100] 11, the discharge water from pump 1 is supplied to separation membrane module 31 via pipe 1c, circulation pump 8, and pipe 1d. A portion of the concentrated water from concentrated water line 4a is introduced into pipe 1c via pipe 9, and a portion of the concentrated water from separation membrane module 31 is circulated to the inlet side of separation membrane module 31 for treatment. The remainder of the water flowing out to concentrated water line 4a is taken out as concentrated water via pressure regulator 4.

[0101] In FIG. 11, the membrane permeation fluid (water vapor) from the separation membrane module 31 is caused to flow into the condenser 32 by the gas aspirator 3, and is cooled and condensed while flowing through the condenser 32.

[0102] The heat of condensation in the condenser 32 is transferred to the separation membrane module 31 via the Peltier element 33, heating the separation membrane module 31. Also, the cold heat of the separation membrane module 31 is transferred to the condenser 32 by the Peltier element 33, cooling the condenser 32 and causing condensation. The condensed water generated by flowing through the condenser 32 and being cooled is taken out as treated water via pipe 13a. A steam pressure regulator 13 is provided on pipe 13a.

[0103] 11, a gas suction device 3 is installed, but it may be omitted as in the water recovery device of FIG. 12. In FIG. 12, water vapor is suctioned from the secondary side of separation membrane module 31 due to negative pressure generated by condensation of water vapor in condenser 32.

[0104] In the present invention, a condensed water suction pump 13b may be installed in the pipe 13a to suck the condensed water, as shown in Figure 13. By installing the pump 13b in this manner, the pressure inside the condenser 32 is further reduced.

[0105] Other configurations in FIGS. 12 and 13 are the same as those in FIG. 11, and the same reference numerals denote the same parts.

[0106] 7 to 13, the condenser 32 is provided on only one side of the separation membrane module 31, but as shown in FIGS. 14 and 15, the condensers 32 may be provided on both sides of the separation membrane module 31, and the water vapor from the separation membrane module 31 may be condensed by each condenser 32. Note that FIGS. 14 and 15 differ in the arrangement of the Peltier elements 33. As described above, the number and arrangement of the Peltier elements 33 can be changed as appropriate depending on the sizes of the separation membrane module 31 and the condensers 32, etc.

[0107] 16 shows a configuration in which separation membrane modules 31 are arranged in two stages, with condensers 32 arranged between the separation membrane modules 31, on the upper side of the uppermost separation membrane module 31, and on the lower side of the lowermost separation membrane module 31. Water vapor from the separation membrane modules 31 is condensed in the adjacent condensers 32. Note that separation membrane modules 31 may be arranged in three or more stages.

[0108] [Treatment method of concentrated water from separation membrane module] In the present invention, the concentrated water from the separation membrane module 2 (or separation membrane module 31) may be treated in a treatment device for reducing the concentration of organic substances, etc. An example of such a treatment device is shown in Figures 17 to 19.

[0109] 17, the concentrated water from the separation membrane module 2 or 31 is introduced into a concentrated water treatment device 40 for treatment, and the treated water is taken out. The concentrated water treatment device may be an oxidation device such as a UV oxidation device, a catalytic oxidation device, an electrolysis device, or a wet oxidation device, or a pervaporation membrane treatment device or a distillation device.

[0110] In FIG. 18, the treated water from the concentrated water treatment device 40 is returned to the raw water side (the water to be treated side) of the separation membrane module 2 or 31.

[0111] 19, the raw water is derived from condensed water from exhaled breath or sweat, and a urine treatment device is used as the concentrated water treatment device 40. The urine treatment device is used to treat urine, and this urine treatment device is used to treat the concentrated water of the separation membrane module 2 or 31. [Example]

[0112] [Experimental Examples 1-3] A simulated wastewater solution containing ethanol and acetic acid as volatile organic compounds at the following concentrations was treated under the following conditions using a water recovery device with a tubular separation membrane module 2 equipped with a chabazite-type zeolite membrane (pore diameter: approximately 3.7 Å) as the separation membrane 2m. The results are shown in Table 1.

[0113] <Experimental conditions> Separation membrane: Chabazite-type zeolite membrane (membrane area 0.015 m 2 ) Mitsubishi Chemical ZEBREX ZX1 Organic matter concentration in simulated wastewater: 100 mg / L-TOC (Ethanol 50mg / L, acetic acid 50mg / L) Temperature of the primary side 2a liquid of the separation membrane module 2: approximately 100°C Suction pressure: 70 kPa-Abs (Experimental Example 1) or 30 kPa-Abs (Experimental Examples 2 and 3) Membrane surface flow velocity: 0.03m / sec Water recovery rate: 85% (Experimental Examples 1 and 2) or 90% (Experimental Example 3)

[0114] <Results / Discussion> As shown in Table 1, by passing the simulated wastewater through separation membrane module 2, the organic matter concentration in the simulated wastewater was 5 mg / L or less under all conditions, confirming sufficient removal performance. The water vapor transmission rate per membrane area was 5.2 to 8.5 mm / h. The lower the suction pressure and the greater the water vapor pressure difference, the lower the concentration of organic matter in the treated water, and the lower the water recovery rate, the lower the concentration of organic matter in the treated water.

[0115] [Table 1]

[0116] [Comparative Experiment Example 1] The same simulated wastewater as in Experimental Examples 1 to 3 was subjected to membrane distillation treatment under the following conditions using a membrane distillation module having the following porous polymer membrane.

[0117] <Experimental conditions> Separation membrane: Porous polymer membrane (PF-001D manufactured by DIC) Simulated wastewater: same as Experiments 1 to 3 Liquid temperature inside the module: 45℃ Suction pressure: 5kPa-Abs Water recovery rate: 85%

[0118] As a result, in the membrane distillation process using this porous polymer membrane, the organic matter concentration in the treated water was 68 mg / L, and most of the organic matter permeated into the treated water side.

[0119] The liquid temperature was lower than in Experimental Examples 1 to 3 because the polymer membrane had a lower heat resistance temperature, and the suction pressure was lower than in Experimental Examples 1 to 3 because the water vapor pressure at the test liquid temperature was low and a sufficient water vapor pressure difference could not be obtained unless the suction pressure was lower.

[0120] [Example 1] A simulated wastewater solution consisting of an aqueous solution containing 50 mg / L of ethanol and 50 mg / L of acetic acid as volatile organic substances was treated under the following conditions using a water recovery device similar to that shown in FIG.

[0121] In this water recovery device, in Figure 4, heater 7 is provided only on one side of separation membrane module 2, and water vapor from pipe 3b is guided to a water-cooled condenser for condensation, and the separation membrane module is the same as that used in Experimental Example 1.

[0122] <Experimental conditions> Separation membrane module 2 primary side 2a liquid temperature: approximately 110°C Condenser pressure: 20kPa-G Water flow rate: 6mL / min Water recovery rate: 90%

[0123] As a result, treated water with a TOC concentration of 4 mg / L was obtained, and the power consumption of the heater 7 was 240 W.

[0124] [Example 2] 11, the same raw water as in Example 1 was treated under the same conditions. The separation membrane module 31 was the same as that used in Example 1. As a result, treated water with a TOC content of 4 mg / L was obtained, and the power consumption of the Peltier element was 110 W.

[0125] From Examples 1 and 2, the following points were observed. (1) By recovering latent heat using a Peltier element, the electricity required for heating can be reduced by more than half. (2) When the outer surface of a separation membrane module is heated with a heater, the outer surface temperature rises and the amount of heat dissipation also increases. However, in the case of a module equipped with a Peltier element, the outer surface becomes a condenser with a relatively low temperature, which reduces heat dissipation. [Explanation of symbols]

[0126] 1 pump 2 Separation membrane module 3 Gas suction equipment 4. Pressure Regulating Equipment 5 Gas-liquid separator 6a Raw water tank 6b Treatment tank 6c Concentrated Water Tank 7 Heater 8 Circulation Pump 10 Condenser 11 Heat exchanger 13 Steam pressure regulator 13b Condensate suction pump 21 Ion removal device 22 Residual component removal device 30 Separation membrane module / condenser assembly 31 Separation membrane module 32 Condenser 33 Peltier element

Claims

1. A water recovery apparatus for treating wastewater containing volatile organic substances or low-molecular-weight organic substances having a molecular weight of 200 or less and recovering water, The water recovery device for organic-containing wastewater includes a separation membrane module that performs pervaporation treatment on the wastewater using a separation membrane having a pore size of 3.0 to 4.2 Å, and recovers treated water from which organic matter has been removed by the separation membrane module.

2. 2. The apparatus for recovering water from organic matter-containing wastewater according to claim 1, which is for use in a spacecraft or a lunar base.

3. 2. The apparatus for recovering water from wastewater containing organic matter according to claim 1, wherein said separation membrane is a zeolite membrane.

4. a separation membrane module having a primary side and a secondary side separated by a separation membrane, which separates the wastewater introduced into the primary side into water vapor from which organic matter has been removed and concentrated water in which the organic matter has been concentrated; a gas suction device for reducing the pressure on the secondary side of the separation membrane module to less than the saturated water vapor pressure at the wastewater temperature on the primary side; a pressure adjusting device for adjusting the pressure of the wastewater on the secondary side of the separation membrane module to a saturated water vapor pressure or higher; 2. The apparatus for recovering water from wastewater containing organic matter according to claim 1, wherein the treated water is obtained by condensing the water vapor from which the organic matter has been removed from the secondary side.

5. 5. The apparatus for recovering water from wastewater containing organic matter according to claim 4, further comprising a gas-liquid separator for removing bubbles from condensed water formed by condensation of water vapor from the gas suction device.

6. 5. The apparatus for recovering water from wastewater containing organic matter according to claim 4, further comprising a volume-variable liquid storage tank, the volume of which changes in accordance with the amount of water stored, as a storage section for the wastewater, concentrated water, and treated water.

7. 2. The apparatus for recovering water from organic matter-containing wastewater according to claim 1, wherein a heating device for heating the fluid inside the separation membrane module is installed in the separation membrane module.

8. 5. The apparatus for recovering water from wastewater containing organic matter according to claim 4, further comprising a circulation means for circulating concentrated water from the secondary side of said separation membrane module to the wastewater inlet side.

9. 5. The apparatus for recovering water from wastewater containing organic matter according to claim 4, further comprising a condenser for recovering latent heat from the water vapor from the gas suction device.

10. 10. The apparatus for recovering water from organic matter-containing wastewater according to claim 9, further comprising a heat exchanger for heating the wastewater supplied to the separation membrane module by heat exchange with condensed water from the condenser.

11. 2. The apparatus for recovering water from wastewater containing organic matter according to claim 1, further comprising an ion removal device for removing ions from the wastewater supplied to the separation membrane module.

12. 2. The apparatus for recovering water from wastewater containing organic matter according to claim 1, further comprising a device for removing components remaining in the treated water.

13. a condenser for condensing water vapor from the separation membrane module; a Peltier element that transfers the latent heat recovered by the condenser to the separation membrane module and transfers the cold heat of the separation membrane module to the condenser; 2. The apparatus for recovering water from organic matter-containing wastewater according to claim 1, comprising:

14. 14. The apparatus for recovering water from wastewater containing organic matter according to claim 13, wherein the water vapor from the separation membrane module is introduced to the condenser without passing through a gas suction means.

15. 14. The apparatus for recovering water from organic matter-containing wastewater according to claim 13, further comprising a pump for sucking condensed water from the condenser.

16. The water recovery system according to claim 1, further comprising a concentrated water treatment device for reducing the concentration of organic matter contained in the concentrated water discharged from the separation membrane module.

17. The water recovery apparatus according to claim 16, wherein the concentrated treated water discharged from the concentrated water treatment apparatus is returned to the water-to-be-treated side of the separation membrane module.

18. 17. The water treatment device of claim 16, wherein the concentrated water treatment device is a UV oxidation device, a catalytic oxidation device, an electrolysis device, a wet oxidation device, a pervaporation membrane treatment device, or a distillation device.

19. A method for recovering water from organic matter-containing wastewater using the water recovery device from organic matter-containing wastewater according to any one of claims 1 to 18.

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