Device and method for recovering water from organic substance-containing drainage water

Abstract

This device for recovering water from organic substance-containing drainage water recovers water by treating drainage water that contains a volatile organic substance or a low-molecular-weight organic substance having a molecular weight of at most 200, and comprises a separation membrane module 2 for subjecting the drainage water to a pervaporation treatment by using a separation membrane having a pore diameter of 3.0-4.2 Å, wherein treated water from which the organic substance has been removed by the separation membrane module 2 is recovered.

Description

Apparatus and method for recovering water from wastewater containing organic matter

[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.

[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 compounds and low-molecular-weight organic compounds 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 using a pervaporation method that uses 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 utilizes 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, thereby dehydrating and concentrating 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 disclose 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.

[0015] JP 2014-188468 A JP 2013-202513 A

[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.

[0017] The water recovery system for organic-containing wastewater of the present invention is a water recovery system 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 pervaporates 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] The apparatus for recovering water from wastewater containing organic matter according to one embodiment of the present invention is 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 aspect 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.

[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 with 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.

[0038] FIG. 1 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 2 is an explanatory diagram of pervaporation. FIG. 3 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 4 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 5 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 6 is a perspective view of a separation membrane module and condenser assembly. FIG. 7 is a plan view of a separation membrane module and condenser assembly. FIG. 8 is a front view of a separation membrane module and condenser assembly. FIG. 9 is a left side view of a separation membrane module and condenser assembly. FIG. 10 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 11 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. FIG. 12 is a side view of another example of a separation membrane module and condenser assembly. FIG. 13 is a side view of another example of a separation membrane module and condenser assembly. FIG. 14 is a configuration diagram of an apparatus for recovering water from organic matter-containing wastewater according to an embodiment. 1 is a block diagram of an apparatus for recovering water from wastewater containing organic matter according to an embodiment of the present invention. 2 is a block diagram of an apparatus for recovering water from wastewater containing organic matter according to an embodiment of the present invention.

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

[0040] 1 and 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 devices shown in Figures 1 and 3 to 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 to the secondary side 2b of the separation membrane 2m. 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 via 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, for example, utility cooling water.

[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 the 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 variable volume 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 volume-variable liquid tank for storing raw water and a concentrated water tank 6c consisting of a volume-variable liquid tank for storing concentrated water from the concentrated water line 4a are provided.

[0048] 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 the 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 water discharged 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 the 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 apparatus of FIG. 4, a heater 7 is also provided in the separation membrane module 2 so that the water in the separation membrane module 2 can be heated.

[0053] The other configuration of the water recovery device in FIG. 4 is the same as that in FIG. 1, and the same reference numerals denote the same parts.

[0054] In the water recovery system 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 cryogenic fluid flow path of this heat exchanger 11 , and is heated while flowing through this cryogenic fluid flow path, and then sent to the circulation pump 8 together with the return concentrated water from the pipe 9 .

[0056] In FIG. 5, the membrane permeation fluid (water vapor) from the pipe 3b is passed through the high-temperature fluid passage of the condenser 10, and is cooled and condensed while flowing through the high-temperature fluid passage.

[0057] Concentrated water from the separation membrane module 2 flows 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 exchanges heat with raw water flowing through the low-temperature fluid flow path of the heat exchanger 11 to lower its temperature, and then is 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] Other configurations in FIG. 6 are similar to 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] The separation membrane 2m has a pore size of 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 substance 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, thereby 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, the heat resistance of the device will be improved and the energy consumption for heating will increase. 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 a device 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 in 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 rate of the permeation rate of smaller water molecules exceeds the increase rate of 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 matter such as ethanol increases at higher temperatures, performing membrane separation treatment at higher temperatures allows for preferential recovery of water, leading to improved water quality.

[0070] [Chabazite-type zeolite membrane] The separation membrane 2m is required to have a pore size that can 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) by size. The separation membrane 2m is also required to be water-resistant and heat-resistant. A chabazite-type zeolite membrane is suitable as the 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 a pore size (approximately 3.7 Å) that is intermediate between the size of water molecules and the size of the organic molecules to be treated.

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

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

[0074] In the water recovery system of this embodiment, 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 primary 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 is integrally provided with 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 treated water 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 suppressed. 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 a condenser 10 or the like. However, the water does not become completely liquid, and gases that have evaporated from dissolved gases such as oxygen and nitrogen contained in the wastewater 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 ground, 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. In this case, however, 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 the latent heat.

[0081] [Variable Volume Liquid Storage Tank] In a microgravity environment, open-type liquid storage tanks cannot hold liquid, and closed-type fixed-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 inflow and outflow of liquid are used as the water tanks 6a to 6c for storing raw water, concentrated water, and treated water (Figures 3 and 6).

[0082] [Circulation of concentrated water] 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. As a result, cleaner treated water can be obtained. 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 branching of the circulation line 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, this 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 and treating concentrated water with a simple configuration while suppressing heat radiation.

[0085] [Condenser 10 for recovering latent heat] In the present invention, since it is necessary to evaporate most of the raw water in the separation membrane module 2, recovering latent heat from water vapor is effective in reducing power consumption. By installing a condenser 10 for recovering latent heat downstream of the gas suction device 3 as shown in Figure 5, it is possible to recover heat from the water vapor whose temperature rises as a result of being compressed by the gas suction device 3, and the latent heat recovery efficiency can be improved due to the increased condensation temperature.

[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 the ion removal device 21 upstream of the separation membrane module 2, it is possible to adjust the properties of the raw water (wastewater to be treated) to a water quality suitable for membrane separation treatment, and to prevent precipitation problems in the separation membrane module 2, pumps, etc.

[0088] Zeolite membranes are known to be poorly resistant to alkaline solutions. If the wastewater is alkaline, an ion removal device 21, such as an ion exchange resin, electrodialysis, a continuous deionization device, or an 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. Since 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 very high organic substance removal performance, but trace amounts of organic substances such as methanol, ethanol, and acetic acid, as well as ammonia with a small molecular size (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. A separation membrane module can also be installed as a residual component removal device.

[0092] [Embodiment in which the separation membrane module is heated by condensation heat of the condenser] In the present invention, the separation membrane module may be heated by condensation heat of the condenser. In this case, the condensation heat 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 31 a for supplying raw water to the primary side, a concentrated water outlet 31 b for extracting concentrated water from the primary side, and a steam outlet 31 c for extracting steam 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 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 sizes of the separation membrane module 31 and the condenser 32.

[0099] 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 FIG. 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 regulating device 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. In addition, 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] Although a gas suction device 3 is provided in Fig. 11 , it may be omitted as in the water recovery device in Fig. 12. In Fig. 12 , water vapor is suctioned from the secondary side of a separation membrane module 31 by negative pressure generated by condensation of water vapor in a 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 similar to 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 three or more stages of separation membrane modules 31 may be provided.

[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 by a treatment device for reducing the concentration of organic matter, etc. Examples of such treatment are 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, sweat, etc., and a urine treatment device 41 is used as the concentrated water treatment device. The urine treatment device 41 is used to treat urine, and the concentrated water from the separation membrane module 2 or 31 is treated using this urine treatment device 41.

[0112] Experimental Examples 1 to 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 having a tubular separation membrane module 2 equipped with a chabazite-type zeolite membrane (pore diameter: approximately 3.7 Å) as the separation membrane 2 m. The results are shown in Table 1.

[0113] <Experimental conditions> Separation membrane: chabazite-type zeolite membrane (membrane area 0.015 m ２ ) ZEBREX ZX1 manufactured by Mitsubishi Chemical Corporation Organic matter concentration in simulated wastewater: 100 mg / L-TOC (ethanol 50 mg / L, acetic acid 50 mg / L) Liquid temperature on the primary side 2a of 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 rate: 0.03 m / sec Water recovery rate: 85% (Experimental Examples 1 and 2) or 90% (Experimental Example 3)

[0114] <Results and 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]

[0116] Comparative Experimental 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 in Experiments 1 to 3 Liquid temperature inside the module: 45°C Suction pressure: 5 kPa-Abs Water recovery rate: 85%

[0118] As a result, in the membrane distillation treatment using this porous polymer membrane, the concentration of organic matter 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. 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 apparatus according to FIG.

[0121] In this water recovery device, in FIG. 4 , heater 7 is provided only on one side of separation membrane module 2, and water vapor from pipe 3 b 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> Liquid temperature on the primary side 2a of the separation membrane module 2: about 110°C Condenser pressure: 20 kPa-G Water flow rate: 6 mL / min Water recovery rate: 90%

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

[0124] [Example 2] Using a water recovery apparatus having the configuration shown in Figure 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] The following points were confirmed from Examples 1 and 2: (1) By recovering latent heat using a Peltier element, the power 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, and heat dissipation can also be suppressed.

[0126] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the effects of the invention. This application is based on Japanese Patent Application No. 2024-059643 filed on April 2, 2024 and Japanese Patent Application No. 2024-121271 filed on July 26, 2024, and is incorporated by reference in its entirety.

[0127] REFERENCE SIGNS LIST 1 Pump 2 Separation membrane module 3 Gas suction device 4 Pressure regulator 5 Gas-liquid separator 6a Raw water tank 6b Treated water tank 6c Concentrated water tank 7 Heater 8 Circulation pump 10 Condenser 11 Heat exchanger 13 Steam pressure regulator 13b Condensed water 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 system for treating wastewater containing volatile organic matter or low-molecular-weight organic matter of 200 or less and recovering water, comprising a separation membrane module that uses a separation membrane with a pore size of 3.0 to 4.2 Å to pervaporate the wastewater, and recovering treated water from which the organic matter has been removed by the separation membrane module.

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

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

4. A water recovery system from organic-containing wastewater as claimed in claim 1, comprising: 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 below 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 above the saturated water vapor pressure; and the water recovery system for organic-containing wastewater as claimed in claim 1, wherein treated water is obtained by condensing the water vapor from which organic matter has been removed from the secondary side.

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 the condensed water formed by condensation of water vapor from the gas suction device.

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

11. 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. The water recovery system for organic matter-containing wastewater according to claim 1, which is equipped with a device for removing residual components remaining in the treated water.

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

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. The apparatus for recovering water from wastewater containing organic matter 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 system according to claim 16, wherein the treated concentrated water discharged from the concentrated water treatment system is returned to the water-to-be-treated side of the separation membrane module.

18. The water treatment device according to 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 wastewater containing organic matter using the apparatus for recovering water from wastewater containing organic matter according to any one of claims 1 to 18.

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