Water treatment system

Abstract

To provide a water treatment system capable of efficiently treating wastewater and enabling energy saving.SOLUTION: A water treatment system of an embodiment of this invention is assembled with a reaction tank which accommodates an active sludge including aerobic microorganism and to which wastewater is supplied; an oxygen supply-line for supplying an oxygen-containing gas having higher oxygen concentration than that in the atmospheric air to the reaction tank; and an exhaust gas line for exhausting a carbon dioxide-containing gas from the reaction tank. The water treatment system controls a supply amount of an oxygen-containing gas to the reaction tank depending on the oxygen concentration of the oxygen-containing gas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment system.

Background Art

[0002] It is known to purify sewage and other polluted water (wastewater) through biological treatment. For example, a polluted water treatment apparatus has been proposed that supplies air to perform aeration in the polluted water flowing into a treatment tank (see, for example, Patent Document 1). In the polluted water treatment apparatus, activated sludge in the treatment tank decomposes organic matter in the polluted water under aerobic conditions to purify the polluted water. In such water treatment field, energy saving has been desired along with the recent growing global awareness of environmental issues.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A main object of the present invention is to provide a water treatment system that can efficiently treat polluted water and achieve energy saving.

Means for Solving the Problems

[0005] [1] A water treatment system according to an embodiment of the present invention includes a reaction tank, an oxygen supply line, and an exhaust line. The reaction tank accommodates activated sludge containing aerobic microorganisms and is supplied with polluted water. The oxygen supply line supplies an oxygen-containing gas having an oxygen concentration higher than that of the atmosphere to the reaction tank. The exhaust line exhausts carbon dioxide-containing gas from the reaction tank. The water treatment system controls the supply amount of the oxygen-containing gas to the reaction tank in accordance with the oxygen concentration of the oxygen-containing gas. [2] The water treatment system described in [1] above may further include a measuring instrument, which is installed in the exhaust line and capable of measuring carbon dioxide concentration or oxygen concentration. [3] In the water treatment system described in [1] or [2] above, the oxygen supply line may supply oxygen-containing gas obtained by vaporizing liquefied oxygen to the reaction vessel. [4] In the water treatment system described in [3] above, the pressure of the oxygen-containing gas obtained by vaporizing the liquefied oxygen may be higher than the water pressure at the bottom of the reaction tank. [5] The water treatment system described in any of [1] to [4] above may further include a first heat exchanger. The first heat exchanger exchanges heat between liquefied oxygen and treated water treated in the water treatment system to vaporize the liquefied oxygen. [6] The water treatment system described in any of [1] to [5] above may further include a power generation device including a condenser and a cooling water supply line. The cooling water supply line supplies the treated water treated in the water treatment system to the condenser as cooling water for the condenser. [7] In the water treatment system described in [6] above, ammonia may be used as fuel for the power generation device. [8] In the water treatment system described in [7] above, liquefied ammonia may be used as the ammonia. The water treatment system may further include a second heat exchanger. The second heat exchanger vaporizes the ammonia by exchanging heat between the liquefied ammonia and the treated water treated by the water treatment system. [9] The water treatment system described in any of [1] to [8] above may further include a power generation device including a combustor. The exhaust line supplies the carbon dioxide-containing gas to the combustor after it has been combined with combustion air. The carbon dioxide-containing gas includes residual oxygen remaining in the reaction vessel without being consumed by aerobic microorganisms, nitrous oxide produced as a by-product in the reaction vessel, methane produced as a by-product in the reaction vessel, or a combination thereof.

[10] The water treatment system described in any of [1] to [9] above may further include a greenhouse gas recovery device for recovering greenhouse gases from the carbon dioxide-containing gas. Typical greenhouse gases include carbon dioxide, but are not limited to carbon dioxide; nitrous oxide or methane may also be used.

[11] The water treatment system described in

[10] above may further include a return line, which returns the recovered treated gas that has passed through the greenhouse gas recovery device to the reaction tank.

[12] The water treatment system described in

[10] above may further include a power generation device including a combustor and a recovered treatment gas supply line. The recovered treatment gas supply line supplies the recovered treatment gas that has passed through the greenhouse gas recovery device to the combustor after being combined with combustion air. The recovered treatment gas includes residual oxygen that remains in the reaction vessel without being consumed by aerobic microorganisms, carbon dioxide produced in the reaction vessel, nitrous oxide produced as a by-product in the reaction vessel, methane produced as a by-product in the reaction vessel, or a combination thereof. [Effects of the Invention]

[0006] According to embodiments of the present invention, a water treatment system can be realized that can efficiently treat wastewater and save energy. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of a water treatment system according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram of a water treatment system according to another embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram of a water treatment system according to yet another embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram of a water treatment system according to yet another embodiment of the present invention. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments.

[0009] A. Overview of the water treatment system Figure 1 is a schematic diagram of a water treatment system according to one embodiment of the present invention. A water treatment system according to one embodiment of the present invention is a system for biologically treating wastewater. As shown in Figure 1, the water treatment system 1 comprises a reaction tank 2, an oxygen supply line 3, and an exhaust line 4. The reaction tank 2 contains activated sludge containing aerobic microorganisms. The aerobic microorganisms are typically heterotrophic bacteria. Wastewater is supplied to the reaction tank 2. The oxygen supply line 3 supplies oxygen-containing gas to the reaction tank 2 at a higher oxygen concentration than that of the atmosphere. The exhaust line 4 exhausts carbon dioxide-containing gas from the reaction tank 2. The water treatment system 1 is configured to control the amount of oxygen-containing gas supplied to the reaction tank 2 according to the oxygen concentration of the oxygen-containing gas. In this configuration, the oxygen supply line delivers oxygen-containing gas with a higher oxygen concentration than the atmosphere to the reaction tank at a rate corresponding to that oxygen concentration. As a result, aerobic microorganisms contained in the activated sludge consume the supplied oxygen to decompose organic matter in the wastewater. Therefore, wastewater can be treated efficiently with a smaller gas supply (i.e., aeration rate) compared to when the oxygen supply line supplies air. Consequently, energy savings can be achieved.

[0010] In one embodiment, the water treatment system 1 further includes a measuring instrument 20. The measuring instrument 20 is located in the exhaust line 4. The measuring instrument 20 is capable of measuring carbon dioxide concentration or oxygen concentration. More specifically, the measuring instrument 20 is capable of measuring carbon dioxide concentration or oxygen concentration in carbon dioxide-containing gas passing through the exhaust line 4. The carbon dioxide-containing gas typically includes carbon dioxide emitted by aerobic microorganisms as a result of the decomposition of organic matter. The carbon dioxide-containing gas may also include residual oxygen that remains in the reaction vessel without being consumed by aerobic microorganisms. With this configuration, the measuring instrument can measure the carbon dioxide concentration or oxygen concentration in the carbon dioxide-containing gas, allowing for monitoring of the wastewater treatment status in the reaction tank and appropriate adjustment of the oxygen-containing gas supply to the reaction tank. For example, if the carbon dioxide concentration in the carbon dioxide-containing gas is below a predetermined threshold, it is predicted that the decomposition of organic matter by aerobic microorganisms is not progressing sufficiently. In this case, increasing the supply of oxygen-containing gas to the reaction tank can promote the decomposition of organic matter by aerobic microorganisms. Also, if the oxygen concentration in the carbon dioxide-containing gas exceeds a predetermined threshold, it is predicted that the supply of oxygen-containing gas to the reaction tank is excessive. In this case, reducing the supply of oxygen-containing gas to an appropriate range can lead to more efficient wastewater treatment and further energy savings. The thresholds for carbon dioxide concentration and oxygen concentration are set in advance, for example, based on the organic matter concentration (typically, biochemical oxygen demand; BOD) in the wastewater supplied to the reaction tank.

[0011] In one embodiment, the oxygen supply line 3 supplies oxygen-containing gas obtained by vaporizing liquefied oxygen to the reaction vessel 2. In this case, the oxygen concentration in the oxygen-containing gas is typically between 25% and 100% by volume. Therefore, compared to the case where the oxygen supply line supplies air, the amount of oxygen-containing gas supplied (aeration rate) can be reduced to approximately 4 / 5 to 1 / 5.

[0012] In one embodiment, the pressure of the oxygen-containing gas obtained by vaporizing liquefied oxygen is higher than the water pressure at the bottom of the reaction vessel 2. Therefore, the oxygen-containing gas can be smoothly supplied (blown) to the reaction vessel without the need to separately install mechanical components such as a blower in the oxygen supply line. Furthermore, since the pressure of the oxygen-containing gas obtained by vaporizing liquefied oxygen is higher than the discharge pressure of the blower normally used when blowing oxygen-containing gas into the reaction vessel, the bubble-refining components such as diffusers used when blowing oxygen into the reaction vessel can be changed to those that can generate finer bubbles. As a result, the dissolved oxygen concentration increases, and the amount of oxygen required for blowing can be reduced.

[0013] In one embodiment, the water treatment system 1 further includes a first heat exchanger 5. The first heat exchanger 5 causes heat exchange between liquefied oxygen and water serving as a heat medium, to vaporize the liquefied oxygen. The water serving as the heat medium for the first heat exchanger is not particularly limited as long as it can vaporize liquefied oxygen. Examples of the heat medium include treated water treated in a water treatment system; water collected from a water source such as a river or the sea, and preferably treated water treated in a water treatment system. In one embodiment, the water treatment system 1 further includes a heat medium supply line 6. The heat medium supply line 6 supplies the treated water treated in the water treatment system 1 to the first heat exchanger 5 as a heat medium. Therefore, the power for supplying the heat medium to the first heat exchanger can be reduced compared to the case where the heat medium is supplied from a water source (for example, a river or the sea) that is usually located at a position lower than the treated water. The temperature of the heat medium in the first heat exchanger is, for example, a temperature equivalent to that of environmental water when flowing into the first heat exchanger, and is, for example, 1°C to 10°C lower than that of the environmental water when flowing out of the first heat exchanger.

[0014] In one embodiment, the water treatment system 1 further comprises a power generation device 7. The power generation device 7 preferably includes a condenser 71. Cooling water is supplied to the condenser 71. The cooling water for the condenser is not particularly limited as long as it can cool the steam flowing into the condenser. Examples of the cooling water for the condenser include treated water treated in the water treatment system; water collected from a water source such as a river or the sea, preferably treated water treated in the water treatment system. Particularly preferred as treated water is treated water that has passed through the first heat exchanger. In one embodiment, the water treatment system 1 further comprises a cooling water supply line 8. The cooling water supply line 8 supplies treated water treated in the water treatment system (preferably treated water that has passed through the first heat exchanger 5) to the condenser 71 as cooling water for the condenser 71. Therefore, the power required to supply cooling water to the condenser can be reduced compared to when it is supplied from another water source (e.g., a river, the sea). Furthermore, when using river water as a cooling water source, the amount of water taken must be restricted to avoid a significant impact on the river's flow rate. Similarly, when using seawater as a cooling water source, there is the problem of the labor-intensive task of removing marine organisms that have proliferated along the water intake route. However, when using treated water from a water treatment system as a cooling water source, these problems can be avoided. Moreover, when the treated water cooled in the first heat exchanger is used as the cooling water for the condenser, a stable temperature difference can be maintained between the steam flowing into the condenser and the cooling water. As a result, the power generation capacity of the power generation device can be improved. In addition, since the treated water cooled in the first heat exchanger is heated in the condenser, the temperature of the treated water that has passed through the condenser can be brought closer to the temperature of environmental water such as river water. Therefore, even if the treated water that has passed through the condenser is discharged into rivers, the environmental impact can be reduced. The temperature of the cooling water in the condenser is, for example, 1°C to 10°C lower than the environmental water on the inflow side, and, for example, equivalent to the environmental water on the outflow side.

[0015] In one embodiment, the exhaust line 4 combines the carbon dioxide-containing gas with combustion air and supplies the resulting mixture to the combustor provided in the power generation device 7. The power generation device 7 is typically a gas turbine generator 7a, which includes a compressor, a combustor, and a turbine. The activated sludge accommodated in the reaction tank 2 may contain, in addition to aerobic microorganisms, nitrifying bacteria that oxidize ammoniacal nitrogen, and / or methanogens that convert carbon sources such as carbon dioxide into methane. Therefore, the carbon dioxide-containing gas exhausted from the reaction tank may contain, in addition to carbon dioxide, the residual oxygen described above, nitrous oxide by-produced in the reaction tank, methane by-produced in the reaction tank, or a combination thereof. When the exhaust line combines the carbon dioxide-containing gas with combustion air and supplies the mixture to the combustor, greenhouse gas components (for example, nitrous oxide and / or methane) contained in the carbon dioxide-containing gas can be removed by combustion or thermal decomposition together with fuel. Therefore, even if the exhaust gas from the power generation device is discharged to the atmosphere, the impact on the environment can be reduced.

[0016] Examples of sewage treated in such a water treatment system 1 include sewage and night soil sewage. Sewage is sewage collected through sewers. Sewage includes, for example, night soil drainage from flush toilets, domestic wastewater, rainwater, industrial wastewater, or a combination thereof. Night soil sewage is sewage collected separately from sewage. The night soil sewage includes, for example, night soil stored in the pit of a vault toilet, septic tank sludge generated in a septic tank, or a combination thereof. Hereinafter, as an embodiment of the water treatment system, a sewage treatment system 1a that biologically treats sewage will be described in detail.

[0017] B. Details of Water Treatment System (Sewage Treatment System) B-1. Grit Chamber, Primary Sedimentation Tank, Reaction Tank, and Final Sedimentation Tank The sewage treatment system 1a comprises a grit chamber 11, a primary sedimentation tank 12, the reaction tank 2 described above, and a final sedimentation tank 13. Typically, sewage from the sewer system is supplied to the grit chamber 11. In the grit chamber 11, for example, relatively large solids and / or sand contained in the sewage are removed from the sewage. The primary sedimentation tank 12 is supplied with sewage that has passed through the grit chamber 11. In the primary sedimentation tank 12, for example, relatively small solids contained in the sewage settle by gravity.

[0018] In this embodiment, the reaction tank 2 is supplied with sewage that has passed through the primary sedimentation tank 12. The biological oxygen demand (BOD) of the sewage supplied to the reaction tank is, for example, 100 mg / L to 300 mg / L. The BOD can be measured, for example, by the method specified in JIS K0102. The ammonia nitrogen concentration of the sewage supplied to the reaction tank is, for example, 5 mg / L to 100 mg / L. The amount of sewage supplied to the reaction tank is, for example, 10,000 m³. 3 / day more than 2 million m 3 It is less than / day. Reaction tank 2 contains activated sludge as described above, and in addition to sewage from the primary sedimentation tank 12, oxygen-containing gas is supplied from the oxygen supply line 3. As a result, the aerobic microorganisms contained in the activated sludge consume the supplied oxygen to decompose and remove organic matter in the sewage. This yields treated water from biologically treated sewage.

[0019] The final sedimentation tank 13 is supplied with treated water that has been biologically treated in the reaction tank 2. The treated water flowing from the reaction tank 2 into the final sedimentation tank 13 may contain activated sludge. In the final sedimentation tank 13, the activated sludge mixed in with the treated water settles by gravity and is separated from the treated water. The BOD of the treated water that has passed through the final sedimentation tank is, for example, 10 mg / L or less. The ammonia nitrogen concentration of the treated water that has passed through the final sedimentation tank is, for example, 20 mg / L or less.

[0020] Furthermore, the sewage treatment system 1a may include an anaerobic treatment tank between the primary sedimentation tank 12 and the reaction tank 2, and / or between the reaction tank 2 and the final sedimentation tank 13. The anaerobic treatment tank typically contains activated sludge containing anaerobic microorganisms. In the anaerobic treatment tank, under anaerobic conditions, anaerobic microorganisms consume nitrate nitrogen contained in the wastewater and discharge nitrogen gas. Therefore, if the sewage treatment system includes an anaerobic treatment tank, it is possible to reduce the nitrate nitrogen concentration in the treated water.

[0021] B-2. Oxygen supply unit In one embodiment, the sewage treatment system 1a includes an oxygen supply unit U1 for supplying oxygen-containing gas obtained by vaporizing liquefied oxygen to the reaction tank 2 in a supply amount corresponding to the oxygen concentration. The oxygen supply unit U1 includes, for example, a liquefied oxygen supply line 14, the first heat exchanger 5 described above, the oxygen supply line 3 described above, the exhaust line 4 described above, a pump 19, the measuring instrument 20 described above, and a control unit 18.

[0022] The liquefied oxygen supply line 14 is a pipe capable of supplying liquefied oxygen to the first heat exchanger 5. The downstream end of the liquefied oxygen supply line 14 in the direction of liquefied oxygen supply is connected to the inlet of the first flow path provided by the first heat exchanger 5. The upstream end of the liquefied oxygen supply line 14 in the direction of liquefied oxygen supply is connected to a liquefied oxygen tank for storing liquefied oxygen (not shown in the figure). The liquefied oxygen is prepared from air, for example, by a deep cooling separation method.

[0023] Any suitable liquid-liquid type heat exchanger can be used as the first heat exchanger 5. Typically, the first heat exchanger 5 comprises a first channel through which liquefied oxygen passes and a second channel through which water, as a heat transfer medium, passes. When liquefied oxygen passes through the first channel and the heat transfer medium passes through the second channel, thermal energy is exchanged between the heat transfer medium and the liquefied oxygen, causing the liquefied oxygen to be heated and vaporized.

[0024] The oxygen supply line 3 is a pipe capable of supplying oxygen-containing gas, obtained by vaporizing liquefied oxygen, to the reaction vessel 2. The upstream end of the oxygen supply line 3 in the direction of oxygen-containing gas supply is connected to the outlet of the first flow path provided by the first heat exchanger 5. In the illustrated example, the downstream end of the oxygen supply line 3 in the direction of oxygen-containing gas supply is located at the bottom of the internal space of the reaction vessel 2 and is connected to a diffuser plate that generates fine bubbles, thus communicating with the internal space of the reaction vessel 2. As a result, the oxygen-containing gas that has passed through the oxygen supply line 3 is blown into the activated sludge and / or sewage contained in the reaction vessel 2.

[0025] The exhaust line 4 is a pipe capable of exhausting the carbon dioxide-containing gas described above from the reaction vessel 2. In the illustrated example, the upstream end of the exhaust line 4 in the direction of exhausting the carbon dioxide-containing gas is connected to the upper wall of the reaction vessel 2 so as to communicate with the internal space of the reaction vessel 2. In this embodiment, the downstream end of the exhaust line 4 in the direction of exhausting the carbon dioxide-containing gas is connected to the combustion air supply line 15, which will be described later.

[0026] Pump 19 can adjust the flow rate of liquefied oxygen through the liquefied oxygen supply line 14. In the illustrated example, pump 19 is located in the liquefied oxygen supply line 14 between the liquefied oxygen tank and the first heat exchanger 5. Any suitable liquid transfer pump can be used as pump 19.

[0027] In the illustrated example, the measuring instrument 20 is installed in the exhaust line 4, between the reaction vessel 2 and the combustion air supply line 15. Any suitable carbon dioxide concentration meter or oxygen concentration meter can be used as the measuring instrument 20.

[0028] The control unit 18 can control the amount of oxygen-containing gas supplied to the reaction vessel. The control unit 18 includes, for example, a central processing unit (CPU), ROM, and RAM. In the illustrated example, the control unit 18 is electrically connected to the pump 19 and the measuring instrument 20. When the control unit 18 receives a measurement result (carbon dioxide concentration or oxygen concentration in the carbon dioxide-containing gas) from the measuring instrument 20, it calculates an appropriate amount of liquefied oxygen to be supplied to the first heat exchanger 5 based on the measurement result and the oxygen concentration in the oxygen-containing gas. Next, the control unit 18 adjusts the output of the pump 19 so that the amount of liquefied oxygen supplied to the first heat exchanger 5 becomes the calculated value. Specifically, the amount of liquefied oxygen supplied to the first heat exchanger 5 is appropriately adjusted within the range of 1 ton / day to 300 ton / day. This adjusts the amount of oxygen-containing gas supplied to the reaction vessel 2. In other words, the control unit 18 can adjust the amount of oxygen-containing gas supplied to the reaction vessel 2 according to the oxygen concentration of the oxygen-containing gas stored in advance and the carbon dioxide concentration or oxygen concentration of the carbon dioxide-containing gas passing through the exhaust line 4. The illustrated example of the sewage treatment system 1a includes one liquefied oxygen supply line 14, one first heat exchanger 5, one oxygen supply line 3, and one pump 19, but the configuration of the sewage treatment system is not limited to this. For example, the sewage treatment system may include multiple liquefied oxygen supply lines, heat exchangers, oxygen supply lines, and pumps so that the total supply of liquefied oxygen falls within the above range.

[0029] B-3. ​​Power Generation Unit In one embodiment, the sewage treatment system 1a includes a power generation unit U2 equipped with a gas turbine generator 7a, which passes treated water sequentially through a first heat exchanger 5 and a condenser 71. The power generation unit U2 includes the heat transfer medium supply line 6, the cooling water supply line 8, the gas turbine generator 7a, a discharge line 17, a fuel supply line 22, a combustion air supply line 15, and an atmospheric discharge line 16.

[0030] In the illustrated example, the heat transfer medium supply line 6 is a pipe capable of supplying treated water that has passed through the final sedimentation tank 13 as a heat transfer medium to the first heat exchanger 5. The upstream end of the heat transfer medium supply line 6 in the direction of heat transfer medium supply is connected to the final sedimentation tank 13. The downstream end of the heat transfer medium supply line 6 in the direction of heat transfer medium supply is connected to the inlet of the second flow path of the first heat exchanger 5. A pump and / or valve may be provided in the heat transfer medium supply line as needed.

[0031] In the illustrated example, the cooling water supply line 8 is a pipe capable of supplying treated water that has passed through the first heat exchanger 5 to the condenser 71 as cooling water. The upstream end of the cooling water supply line 8 in the cooling water supply direction is connected to the outlet of the second flow path provided by the first heat exchanger 5. The downstream end of the cooling water supply line 8 in the cooling water supply direction is connected to the inlet side of the condenser 71.

[0032] The discharge line 17 is a pipe for discharging treated water that has passed through the condenser 71. In the illustrated example, the upstream end of the discharge line 17 in the direction of treated water passage is connected to the outlet side of the condenser 71. The downstream end of the discharge line 17 in the direction of treated water passage is connected to a disinfection facility as needed. As a result, the treated water that has passed through the final sedimentation tank 13 passes through the first heat exchanger 5 and the condenser 71 in sequence, is disinfected at a disinfection facility as needed, and then discharged into rivers, etc.

[0033] As described above, the gas turbine generator 7a is equipped with a compressor, a combustor, and a turbine, and is capable of generating electricity by the rotation of the turbine. Although not shown in the figures, the gas turbine generator 7a may be electrically connected to an energy storage facility. In this case, the energy storage facility can store the electricity generated by the gas turbine generator 7a.

[0034] The fuel supply line 22 is a pipe capable of supplying fuel to the combustor of the gas turbine generator 7a. The downstream end of the fuel supply line 22 in the fuel supply direction is typically connected to the combustor. Although not shown in the figure, the upstream end of the fuel supply line 22 in the fuel supply direction is connected to a fuel tank that stores fuel. Examples of fuels include ammonia, preferably liquid ammonia, and more preferably green ammonia in liquid form (ammonia produced using raw materials produced in a way that does not emit carbon dioxide, and produced in a way that does not emit carbon dioxide).

[0035] The combustion air supply line 15 is a pipe capable of supplying combustion air to the compressor of the gas turbine generator 7a. The downstream end of the combustion air supply line 15 in the direction of combustion air supply is typically connected to the intake port of the compressor.

[0036] In this embodiment, the downstream end of the exhaust line 4 is connected to the portion of the combustion air supply line 15 that is connected to the compressor. Therefore, the exhaust line 4 can combine the carbon dioxide-containing gas from the reaction vessel 2 with the combustion air passing through the combustion air supply line 15. The compressor of the gas turbine generator 7a takes in a mixture of carbon dioxide-containing gas and combustion air (intake step) and then compresses the mixture (compression step). The combustor injects fuel supplied from the fuel supply line 22 into the mixture compressed by the compressor and burns it (combustion step). If the fuel is liquid ammonia, the ammonia may be vaporized first or decomposed into hydrogen and nitrogen before combustion. The gas turbine generator 7a exhausts the combustion gas produced by the combustion of the fuel (exhaust step). The gas turbine generator 7a generates electricity by continuously rotating the turbine.

[0037] The atmospheric discharge line 16 is a pipe for releasing combustion gases exhausted from the gas turbine generator 7a into the atmosphere. In the illustrated example, the upstream end of the atmospheric discharge line 16 in the direction of combustion gas passage is connected to the gas turbine generator 7a. The downstream end of the atmospheric discharge line 16 in the direction of combustion gas passage is open to the atmosphere. The combustion gases passing through the atmospheric discharge line 16 contain virtually no greenhouse gas components (specifically nitrous oxide and / or methane). The percentage of greenhouse gas components in the combustion gases released into the atmosphere is, for example, 1 volume% or less, preferably 0 volume%, when green ammonia is used as fuel. Therefore, even if combustion gases are released into the atmosphere from the gas turbine generator 7a, the environmental impact can be reduced.

[0038] C. Variations of water treatment systems (sewage treatment systems) In the sewage treatment system 1a shown in Figure 1, the downstream end of the exhaust line 4 is connected to the combustion air supply line 15, but the configuration of the sewage treatment system 1a is not limited to this.

[0039] As shown in Figure 2, the sewage treatment system 1a may further include a greenhouse gas recovery device 9 that recovers carbon dioxide as an example of a greenhouse gas from carbon dioxide-containing gas. This allows for the smooth recovery of greenhouse gases. In this embodiment, the downstream end of the exhaust line 4 is connected to the greenhouse gas recovery device 9. The measuring instrument 20 is also provided in the exhaust line 4 between the reaction tank 2 and the greenhouse gas recovery device 9 that recovers carbon dioxide. In one embodiment, the sewage treatment system 1a further includes a recovered treatment gas supply line 21. The recovered treatment gas supply line 21 combines the recovered treatment gas that has passed through the greenhouse gas recovery device 9 that recovers carbon dioxide with combustion air and supplies it to the combustor. In the illustrated example, the upstream end of the recovered treatment gas supply line 21 in the direction of recovery treatment gas supply is connected to the greenhouse gas recovery device 9 that recovers carbon dioxide. The downstream end of the recovered treatment gas supply line 21 in the direction of recovery treatment gas supply is connected to the portion of the combustion air supply line 15 that is connected to the compressor. This allows the recovered treatment gas to be combined with the combustion air, and the mixed gas of recovered treatment gas and combustion air can be supplied to the combustor via a compressor. The recovered treatment gas contains residual oxygen, carbon dioxide, nitrous oxide, methane, or a combination thereof. The carbon dioxide content in the recovered treatment gas is typically 5% by volume or less.

[0040] As shown in Figure 3, the recovered treatment gas that has passed through the greenhouse gas recovery device 9 that recovers carbon dioxide may be returned to the reaction tank 2. In one embodiment, the sewage treatment system 1a includes a return line 10 for returning the recovered treatment gas to the reaction tank 2. The upstream end of the return line 10 in the direction of return of the recovered treatment gas is connected to the greenhouse gas recovery device 9 that recovers carbon dioxide. The downstream end of the return line 10 in the direction of return of the recovered treatment gas is connected to the portion of the oxygen supply line 3 between the first heat exchanger 5 and the reaction tank 2. This allows the recovered treatment gas to be mixed with the oxygen-containing gas, and the mixed gas of the recovered treatment gas and the oxygen-containing gas can be supplied to the reaction tank 2.

[0041] Furthermore, as shown in Figure 4, the water treatment system 1 (sewage treatment system 1a) that uses liquefied ammonium as fuel for the power generation device 7 (gas turbine generator 7a) may also be further equipped with a second heat exchanger 23. The second heat exchanger 23 vaporizes the liquefied ammonia by exchanging heat between the liquefied ammonia and the treated water treated by the water treatment system. In such a water treatment system 1, the ammonia vaporized in the second heat exchanger 23 is supplied to the combustor of the power generation device 7.

[0042] The second heat exchanger 23 is typically located in the fuel supply line 22 up to the power generator 7. Any suitable liquid-liquid heat exchanger can be used as the second heat exchanger 23. The second heat exchanger 23 typically comprises a first flow path connected to the fuel supply line 22 through which liquefied ammonia passes, and a second flow path through which treated water, which serves as a heat transfer medium, passes. When liquefied ammonia passes through the first flow path and the heat transfer medium passes through the second flow path, thermal energy is exchanged between the heat transfer medium and the liquefied ammonia, causing the liquefied ammonia to be heated and vaporized.

[0043] In one embodiment, the heat transfer medium supply line 6 branches into a first heat transfer medium supply line 61 and a second heat transfer medium supply line 62. The downstream end of the first heat transfer medium supply line 61 in the direction of heat transfer medium supply is connected to the inlet of the second flow path of the first heat exchanger 5. The downstream end of the second heat transfer medium supply line 62 in the direction of heat transfer medium supply is connected to the inlet of the second flow path of the second heat exchanger 23. This allows treated water to be supplied to both the first heat exchanger 5 and the second heat exchanger 23.

[0044] In one embodiment, the treated water that has passed through the second heat exchanger 23 merges with the treated water that has passed through the first heat exchanger 5 and is supplied as cooling water to the condenser 71 of the power generation device 7. This increases the temperature difference between the steam flowing into the condenser and the cooling water. In the illustrated example, the water treatment system 1 further includes a connection line 24. The connection line 24 is a pipe that supplies the treated water that has passed through the second heat exchanger 23 to the cooling water supply line 8. The upstream end of the connection line 24 in the direction of cooling water supply is connected to the outlet of the second flow path of the second heat exchanger 23. The downstream end of the connection line 24 in the direction of cooling water supply is connected to the portion of the cooling water supply line 8 between the condenser 71 and the first heat exchanger 5. [Industrial applicability]

[0045] The water treatment system according to the embodiment of the present invention can be used in water treatment facilities that biologically treat wastewater, and is particularly suitable for use in sewage treatment facilities that biologically treat wastewater. [Explanation of Symbols]

[0046] 1. Water treatment system 2 Reaction vessels 3. Oxygen supply line 4 Exhaust lines 5 1st heat exchanger 6. Heat transfer medium supply line 7. Power generation equipment 71 Condenser 8. Cooling water supply line 9. Greenhouse gas recovery devices 10 Return Line 21. Recovery and processing gas supply line 23 Second heat exchanger

Claims

1. A reaction tank containing activated sludge with aerobic microorganisms and supplied with wastewater; The reaction vessel is provided with an oxygen supply line that supplies an oxygen-containing gas with a higher oxygen concentration than that of the atmosphere; The reactor is equipped with an exhaust line for exhausting carbon dioxide-containing gas from the reactor; The oxygen supply line supplies oxygen-containing gas obtained by vaporizing liquefied oxygen to the reaction vessel. The pressure of the oxygen-containing gas obtained by vaporizing the liquefied oxygen is higher than the water pressure at the bottom of the reaction vessel. A water treatment system that controls the amount of oxygen-containing gas supplied to the reaction vessel according to the oxygen concentration of the oxygen-containing gas.

2. The water treatment system according to claim 1, further comprising a measuring instrument provided in the exhaust line capable of measuring carbon dioxide concentration or oxygen concentration.

3. The water treatment system according to claim 1 or 2, further comprising a first heat exchanger that vaporizes liquefied oxygen by exchanging heat between liquefied oxygen and treated water treated in the water treatment system.

4. Power generation equipment including a condenser; A water treatment system according to claim 1 or 2, further comprising: a cooling water supply line for supplying treated water, which has been treated in the water treatment system, to the condenser as cooling water for the condenser;

5. The water treatment system according to claim 4, wherein ammonia is used as fuel for the power generation device.

6. As the ammonia mentioned above, liquefied ammonia is used. The water treatment system according to claim 5, further comprising a second heat exchanger that vaporizes ammonia by exchanging heat between the liquefied ammonia and treated water treated by the water treatment system.

7. Further equipped with a power generation device including a combustor, The exhaust line supplies the carbon dioxide-containing gas to the combustor after combining it with the combustion air. The water treatment system according to claim 1, wherein the carbon dioxide-containing gas includes residual oxygen remaining in the reaction vessel without being consumed by aerobic microorganisms, nitrous oxide produced as a by-product in the reaction vessel, methane produced as a by-product in the reaction vessel, or a combination thereof.

8. The water treatment system according to claim 1, further comprising a greenhouse gas recovery device for recovering greenhouse gases from the carbon dioxide-containing gas.

9. The water treatment system according to claim 8, further comprising a return line for returning the recovered treated gas that has passed through the greenhouse gas recovery device to the reaction tank.

10. Power generation equipment including a combustor; The system further comprises: a recovery gas supply line that combines the recovered gas that has passed through the greenhouse gas recovery device with combustion air and supplies it to the combustor; The water treatment system according to claim 8, wherein the recovered treatment gas includes residual oxygen remaining in the reaction tank without being consumed by aerobic microorganisms, carbon dioxide generated in the reaction tank, nitrous oxide produced as a by-product in the reaction tank, methane produced as a by-product in the reaction tank, or a combination thereof.

Images