JP6621672B2 - Wastewater treatment method, wastewater treatment equipment - Google Patents

Description

  The present invention relates to a wastewater treatment method and a wastewater treatment apparatus for treating wastewater containing 1,4-dioxane.

1,4-dioxane (1,4-dioxane: C ₄ H ₈ O ₂ ) has been conventionally used as a reactant or stabilizer added to an organic solvent because it dissolves in water or a solvent at room temperature. In addition, 1,4-dioxane is known to be produced as a by-product in the production process of surfactants and PET resins. Specifically, 1,4-dioxane in the surfactant is used in the production of alkyl ether sulfate (AES), which is the main cleaning base used in shampoos and skin cleansing agents. It is produced as a reaction byproduct upon sulfation of ethoxylate (AE).

  1,4-Dioxane is considered to have a carcinogenic risk to humans as an effect on health. At least animal experiments have shown that it has carcinogenicity, and the International Agency for Research on Cancer (IARC) recognizes that it may be carcinogenic to humans. In view of such health risks, in Japan, wastewater standards with a regulatory value of 1,4-dioxane of 0.5 mg / L were enforced in May 2012.

  Conventionally, as a method for decomposing 1,4-dioxane, for example, a method for decomposing 1,4-dioxane biologically using a microorganism called 1,4-dioxane-decomposing bacteria (see Patent Document 1) In addition, a method of decomposing 1,4-dioxane using an accelerated oxidation method or a Fenton oxidation method (see Patent Document 2) is known. However, 1,4-dioxane is a water-soluble hardly decomposable substance, and when dissolved in waste water or the like, the above-described conventional method for biologically decomposing 1,4-dioxane, the accelerated oxidation method or Fenton The above-mentioned conventional method for decomposing 1,4-dioxane using an oxidation method cannot sufficiently decompose 1,4-dioxane contained in wastewater.

JP 2012-161737 A JP 2005-058854 A

  By the way, it is known that 1,4-dioxane is decomposed relatively quickly by the oxidation catalyst in a state where it exists as a gas in the atmosphere. Therefore, in order to remove 1,4-dioxane from wastewater, first, it is necessary to vaporize 1,4-dioxane from the wastewater and separate it as steam. Conventionally, a method is known in which wastewater stored in a treatment tank is heated to 100 ° C. or more to evaporate 1,4-dioxane (boiling point: 101.1 ° C.) together with water. However, as the water and 1,4-dioxane evaporate, the wastewater becomes higher in concentration due to other impurities, and the boiling point of the wastewater becomes higher. When heated at a temperature higher than that, other impurities are vaporized and released into the atmosphere. Problem arises. Moreover, in low-temperature heating, 1,4-dioxane cannot be vaporized from the concentrated wastewater, and there arises a problem that the content of 1,4-dioxane in the wastewater cannot be reduced to the regulation value or less.

  This invention is made | formed in view of the said situation, The objective is to provide the wastewater treatment method and wastewater treatment apparatus which can isolate | separate 1,4-dioxane from wastewater efficiently and reliably. is there.

  A wastewater treatment method according to an embodiment of the present invention is a method for treating wastewater containing 1,4-dioxane. The wastewater treatment method includes a primary concentration step of concentrating the wastewater by heating the wastewater stored in a storage tank to generate steam from the wastewater and discharging the steam, and the storage after the primary concentration step. A secondary concentration step of concentrating the wastewater by adding water to the wastewater remaining in the tank and diluting it, heating the diluted wastewater again to generate steam from the wastewater, and discharging the steam; including. In the secondary concentration step, the wastewater is diluted and concentrated until the concentration of 1,4-dioxane in the wastewater remaining in the storage tank after concentration is equal to or lower than a predetermined concentration value.

  The secondary concentration step includes a control step for controlling hydration during dilution of the wastewater and heating during concentration. When the waste water level in the storage tank decreases to a predetermined lower limit water level, the control step stops heating the waste water and stores the waste water until the waste water level reaches a predetermined upper limit water level. Water is supplied to the tank, and then the wastewater is heated until the level of the wastewater reaches the lower limit water level.

  In the secondary concentration step, 1 in the waste water remaining in the storage tank after the concentration is repeated by repeating the preset number of times corresponding to the concentration value in the control step. The concentration of 1,4-dioxane is made not more than the above concentration value.

  The wastewater treatment method of the present invention further includes an oxidative decomposition step of oxidizing and decomposing 1,4-dioxane contained in the steam discharged in the primary concentration step and the secondary concentration step with a catalyst.

  In the primary concentration step and the secondary concentration step, the waste water is heated at a temperature at which the heat of oxidation accompanying the oxidative decomposition becomes a steam generation amount that is equal to or lower than the heat resistant temperature of the catalyst.

  The concentration value is 0.5 mg / L.

  A wastewater treatment apparatus according to another embodiment of the present invention is a wastewater treatment apparatus that treats wastewater containing 1,4-dioxane. The wastewater treatment apparatus discharges the steam generated from the wastewater to the outside from the storage tank by storing the wastewater, a heating unit for heating the wastewater in the storage tank, and heating by the heating unit. A discharge unit, a water supply unit that supplies water to the storage tank, and a control unit that controls heating by the heating unit and water supply by the water supply unit. The control unit heats the waste water and supplies water to the storage tank until the concentration of 1,4-dioxane in the waste water remaining in the storage tank concentrated by the discharge of the steam is equal to or lower than a predetermined concentration value. The heating unit and the water supply unit are controlled so as to be repeatedly supplied.

  When the water level of the waste water in the storage tank decreases to a predetermined lower limit water level, the control unit stops heating by the heating unit and starts water supply by the water supply unit. In addition, when the water level of the waste water reaches a predetermined upper limit water level, the control unit stops water supply by the water supply unit and starts heating by the heating unit until the water level of the waste water reaches the lower limit water level. The waste water is heated.

  The wastewater treatment apparatus of the present invention further includes an oxidative decomposition unit that oxidatively decomposes 1,4-dioxane contained in the steam discharged from the storage tank using a catalyst.

  The heating unit heats the wastewater at a temperature such that the heat of oxidation accompanying the oxidative decomposition becomes a steam generation amount that is equal to or lower than the heat resistant temperature of the catalyst.

  The concentration value is 0.5 mg / L.

  According to the present invention, it is possible to efficiently and reliably separate 1,4-dioxane from wastewater.

FIG. 1 is a perspective view showing a wastewater treatment apparatus 10 according to an embodiment of the present invention. FIG. 2 is a system diagram showing the configuration of the wastewater treatment apparatus 10. FIG. 3 is a block diagram showing a control system configuration of the wastewater treatment apparatus 10. FIG. 4 is a flowchart showing an example of a procedure of waste water concentration and decomposition processing in the waste water treatment apparatus 10. FIG. 5 is a flowchart illustrating an example of a procedure of waste water concentration and decomposition processing in the waste water treatment apparatus 10.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, embodiment described below is only an example which actualized this invention, and does not limit the technical scope of this invention.

[Waste water treatment apparatus 10]
FIG. 1 is a perspective view showing the external appearance of the wastewater treatment apparatus 10. FIG. 2 is a system diagram showing the configuration of the wastewater treatment apparatus 10. FIG. 3 is a block diagram showing a control system configuration of the wastewater treatment apparatus 10. The wastewater treatment apparatus 10 according to this embodiment is an apparatus capable of treating wastewater containing 1,4-dioxane. The wastewater treatment apparatus 10 is installed and used in a surfactant or PET resin manufacturing factory or a sewage treatment factory, for example.

  As shown in FIG. 1 and FIG. 2, the wastewater treatment apparatus 10 roughly includes a wastewater concentration apparatus 11 and a decomposition treatment apparatus 12, and steam is discharged from the wastewater concentration apparatus 11 to the decomposition treatment apparatus 12. The waste water concentrating device 11 and the decomposition treatment device 12 are connected by a connecting duct 14 so that the contained gas can be fed.

[Waste water concentrator 11]
The waste water concentrator 11 includes a treatment tank 21 (an example of a storage tank of the present invention), a heat exchanger 22 (an example of a heating unit of the present invention), a steam supply unit 23, an air supply blower 24, and a bubbling pipe 25. An air supply unit 26, an antifoaming agent supply unit 27, a water supply unit 28, a discharge pump 29, and a control panel 30.

  The treatment tank 21 is for storing wastewater to be treated, and is formed in a substantially rectangular parallelepiped shape. A predetermined amount of waste water is stored inside the treatment tank 21. In the present embodiment, the processing layer 21 has a height size of 1400 mm and a volume of 2100 liters. Moreover, the waste water stored in the processing tank 21 contains at least 1,4-dioxane and water. The content of water in the wastewater is approximately 80% to 99%, and therefore the viscosity of the wastewater is relatively low. The waste water may contain impurities other than 1,4-dioxane and water.

  In the present embodiment, waste water to be treated is stored in a waste water tank 81 installed separately. The waste water tank 81 is installed at a position higher than the processing tank 21 and is connected to the bottom of the processing tank 21 by a pipe 81A. The pipe 81A is provided with an electric valve 81B that is opened and closed by electric drive. When the electric valve 81B is controlled and opened by the control unit 100 of the control panel 30, waste water is supplied from the waste water tank 81 to the treatment tank 21, and when closed, the supply of waste water is stopped.

  A plurality of frame legs 16 are provided at the bottom of the treatment tank 21, and the frame legs 16 are attached to a base frame 15 that is a frame for the waste water concentration apparatus 11. Thereby, the processing tank 21 is provided at a position spaced apart from the base frame 15 by a predetermined height by the frame leg 16.

  The wastewater stored in the treatment tank 21 is, for example, sewage (so-called industrial wastewater) that is used for industrial production in a factory or the like and is discarded after use. If such wastewater is discharged as it is into the river or the sea, it will contaminate the natural environment. Therefore, the wastewater must be purified to such an extent that it can be discharged into the natural environment before being discharged into the river or the sea. Especially, industrial wastewater from factories for producing surfactants and PET resins contains 1,4-dioxane. Therefore, when such wastewater is discharged into water areas (public water areas) including rivers and seas. Needs to be subjected to a predetermined decomposition treatment so as to clear the waste water standard (0.5 mg / L) defined by the Water Pollution Control Law.

  The heat exchanger 22 heats the waste water stored in the processing tank 21 and is provided inside the processing tank 21. The heat exchanger 22 is, for example, a radiator having a pipe that circulates and circulates a liquid or gaseous heat medium. The heat exchanger 22 is provided below the intermediate position in the height direction inside the processing tank 21, and the entire heat exchanger 22 is disposed in the waste water in a state where the waste water is stored in the processing tank 21. When high-temperature steam is supplied to the heat exchanger 22 from a steam supply unit 23 described later, heat exchange is performed between the waste water and the high-temperature steam in the heat exchanger 22 to heat the waste water. By heating the wastewater, water and 1,4-dioxane contained in the wastewater become steam.

  The steam supply unit 23 is for supplying high-temperature steam (saturated steam) to the heat exchanger 22 in the processing tank 21, and is provided in the vicinity of the processing tank 21. A steam supply port 21 </ b> A communicating with the heat exchanger 22 is provided on the side wall of the processing tank 21. The steam supply unit 23 includes a steam source 23A that supplies high-pressure (for example, 0.4 MPa) steam, and supplies high-temperature steam from the steam source 23A to the steam supply port 21A through the pipe 23B. In the present embodiment, approximately 120 ° C. high temperature steam is supplied to the steam supply port 21A. The pipe 23B is provided with an electric valve 23C for adjusting the steam amount. The electric valve 23C is, for example, an electric ball valve. The opening / closing angle of the motor-operated valve 23C is controlled by the control unit 100 provided in the control panel 30, and the amount of steam flowing through the pipe 23B is adjusted. A steam discharge port 21 </ b> B communicating with the heat exchanger 22 is provided at the bottom of the treatment tank 21, and a steam trap 83 for discharging drain water generated in the heat exchanger 22 is provided in the steam discharge port. 21B.

  The steam source 23A is, for example, a steam boiler that generates steam. In the present embodiment, the steam source 23A is an existing steam boiler or the like installed for other uses in a factory, and high-pressure steam branched from the steam supply path of the existing steam boiler and flowing into the pipe 23B is generated. It is supplied to the steam supply port 21A.

  The air supply blower 24 is an electrically driven blower. The air supply blower 24 discharges the steam generated from the waste water in the treatment tank 21 by heating by the heat exchanger 22 from the treatment tank 21 to the outside. The air supply blower 24 constitutes a discharge portion of the present invention together with an exhaust blower 45 described later. As shown in FIG. 1, the air supply blower 24 is attached to the upper surface of the processing tank 21. A pipe 24A is connected from the air supply blower 24 to the upper surface of the processing tank 21, and air is sent from the air supply blower 24 to the air layer inside the processing tank 21 through the pipe 24A. In this embodiment, since the connection duct 14 is connected to the upper surface of the processing tank 21, the air sent into the air layer of the processing tank 21 enters the connection duct 14 together with the vapor existing in the air layer, and is processed. It is discharged outside the tank 21. Note that the steam that has entered the connection duct 14 is sent to the decomposition processing apparatus 12 through the connection duct 14.

  In addition, in this embodiment, although the structure which implement | achieves the exhaust part of this invention with the air supply blower 24 and the exhaust blower 45 is illustrated, the exhaust part of this invention is not restricted to this structure. For example, any one of the air supply blower 24 and the exhaust blower 45 may be provided as the exhaust part.

  The bubbling pipe 25 generates bubbles in the waste water of the treatment tank 21 and causes an upward flow in the liquid. The bubbling tube 25 is installed on the bottom surface of the processing tank 21, and specifically, is disposed below the heat exchanger 22 in the processing tank 21. The bubbling tube 25 has a plurality of nozzle holes through which bubbles are sent out. An air supply unit 26 is provided outside the processing tank 21, and the air supply unit 26 and the bubbling pipe 25 are connected by a pipe 26A.

  The air supply unit 26 supplies air to the bubbling pipe 25 through the pipe 26A. The air supply unit 26 has an air tank 26B that stores compressed air of a predetermined pressure, and a pipe is provided between the air tank 26B and the bubbling pipe 25 so that the air in the air tank 26B can be supplied to the bubbling pipe 25. 26A is connected. The pipe 26A is provided with an electric valve 26C for adjusting the amount of air supplied. The electric valve 26C is, for example, an electric ball valve. The opening / closing angle of the motor-operated valve 26C is controlled by the control unit 100 of the control panel 30 to adjust the flow rate of the air supply amount flowing through the pipe 26A. When air is supplied to the bubbling tube 25, bubbles are generated from the nozzle holes of the bubbling tube 25. Generating bubbles in this way is called bubbling. Bubbles generated by the bubbling rise through the periphery of the heat exchanger 22. At this time, an upward flow is generated around the heat exchanger 22, and a downward flow is generated around the inner wall surface of the treatment tank 21. That is, the waste water in the treatment tank 21 is in a circulating flow state due to the upward flow and the downward flow. As a result, heat transfer from the heat exchanger 22 to the waste water is promoted, and heat is efficiently and uniformly transferred to the entire waste water in the treatment tank 21.

  The defoamer supply unit 27 includes a storage box 27A that stores the defoamer, a pipe 27B that connects the storage box 27A and the processing tank 21, and an electric valve 27C that is provided in the pipe 27B. When it is determined by the bubble detection sensor 33 described later that bubbles have occurred in the processing tank 21, the motor operated valve 27C is opened, and the antifoaming agent is introduced into the processing tank 21 from the storage box 27A through the pipe 27B. . As the antifoaming agent, for example, a silicone-based antifoaming agent or an organic defoaming agent can be applied.

  The water supply unit 28 supplies water such as industrial water to the treatment tank 21 and is provided in the vicinity of the treatment tank 21. A water supply port 21 </ b> C communicating with the inside of the processing tank 21 is provided on the side wall of the processing tank 21. The water supply unit 28 has a water supply pipe 28 </ b> A extending from the industrial water supply, and the water supply pipe 28 </ b> A is connected to the water supply port 21 </ b> C of the treatment tank 21. The water supply unit 28 supplies water from the industrial water supply to the water supply port 21C through the water supply pipe 28A. The water supplied to the water supply port 21 </ b> C is stored in the treatment tank 21. The water supply pipe 28A is provided with an electric valve 28B for adjusting the amount of water supplied. The electric valve 28B is, for example, an electric ball valve. The opening / closing angle of the motor-operated valve 28B is controlled by the control unit 100 of the control panel 30, and the amount of water flowing through the water supply pipe 28A is adjusted.

  The discharge pump 29 is provided below the processing tank 21. Specifically, the discharge pump 29 is fixed to the upper surface of the base frame 15 below the processing tank 21. The discharge pump 29 is a pump for discharging waste water stored in the treatment tank 21 to the outside as necessary. Therefore, a drain pipe 84 extending from the bottom of the processing tank 21 is connected to the suction port of the discharge pump 29. In the present embodiment, the discharge pump 29 discharges waste water to an external tank 82 (see FIG. 2) that is installed separately. Therefore, a drain pipe 85 that leads to the external tank 82 is connected to the discharge port of the discharge pump 29. The discharge pump 29 is driven and controlled by the control unit 100 of the control panel 30.

  The control panel 30 controls the heating of the wastewater by the heat exchanger 22 and the amount of water supplied to the treatment tank 21 by the water supply unit 28. As shown in FIGS. 1 and 2, the control panel 30 includes a self-supporting box-shaped cabinet 30A installed on the base frame 15, and further includes a control unit 100 such as a sequencer, An operation unit 105, a liquid crystal monitor 106, a meter display unit 107, a heater control unit 108, and the like are mounted. An openable / closable door 30B is provided at the upper front of the cabinet 30A. When the door 30B is opened, an operation unit 105, a liquid crystal monitor 106, a meter display unit 107 for displaying a pressure value, and the like appear. .

  The control unit 100 is a computer having a CPU 101, a ROM 102, a RAM 103, an EEPROM 104, and the like, and comprehensively controls the wastewater treatment apparatus 10. A control program is stored in the ROM 102, and the CPU 101 reads out and executes the control program, whereby a concentration and decomposition process described later is executed. The concentration and decomposition process will be described later.

  An operation unit 105, a liquid crystal monitor 106, a meter display unit 107, and a heater control unit 108 are connected to the control unit 100, and are configured to be able to mutually communicate signals and data.

  The heater control unit 108 controls heating of a heater 42 described later provided in the decomposition processing apparatus 12. In the present embodiment, the heater control unit 108 performs PID control of the heater 42 so that the inlet temperature of the oxidation catalyst 43 of the decomposition treatment apparatus 12 becomes 350 ° C.

  The processing tank 21 is provided with a temperature sensor 32, a foam detection sensor 33, and a liquid level sensor 34.

  The temperature sensor 32 detects the temperature of the wastewater stored in the treatment tank 21 and is composed of, for example, a resistance temperature detector, a thermocouple, or a thermistor. The temperature sensor 32 sends a sensor signal corresponding to the temperature to be detected to the control unit 100 of the control panel 30. The control unit 100 calculates the temperature of the detection target based on the sensor signal and displays the temperature information on the liquid crystal monitor 106. Further, the control unit 100 controls the motor operated valve 23C of the steam supply unit 23 so that the detected temperature becomes a preset temperature. Information on the set temperature is stored in the EEPROM 104. In this embodiment, the set temperature is set to 105 ° C. The control unit 100 feedback-controls the motor operated valve 23C based on the detected temperature of the waste water. Specifically, when the detected temperature is lower than the set temperature, the control unit 100 controls the motor operated valve 23C to increase the steam amount. Further, when the detected temperature exceeds the set temperature, the motor valve 23C is controlled to reduce the steam amount.

  The bubble detection sensor 33 detects whether or not bubbles are generated on the liquid level of the wastewater stored in the treatment tank 21. For example, the light-emitting element provided on one side wall of the treatment tank 21 and its And a light receiving element provided on the other side wall facing the side wall. The upper limit water level of the wastewater to be stored is set in the processing tank 21, and in this embodiment, the water level is set to a level equivalent to about 64% with respect to the volume of the processing tank 21 (2100 liters). Specifically, a position of 900 mm from the bottom surface of the processing tank 21 is set as the upper limit water level. The light emitting element and the light receiving element are provided at a position slightly above the upper limit water level, specifically at a position 150 mm higher than the upper limit position.

  The light emitting element is, for example, a light emitting diode. The light receiving element is, for example, a phototransistor. Light is emitted from the light emitting element to the light receiving element, and a voltage signal corresponding to the emitted light is sent to the control unit 100. When bubbles are generated on the liquid surface of the waste water, the light is blocked and the voltage level of the voltage signal is lowered. The control unit 100 determines that bubbles are generated on the liquid surface when the voltage level is less than the threshold value. In the present embodiment, when the generated bubbles are separated from the liquid surface and sent to the decomposition processing device 12 through the connection duct 14, the decomposition processing device 12 may stop or break down. Therefore, when it determines with the bubble having arisen, the control part 100 controls the motor operated valve 27C, and supplies an antifoamer from the antifoamer supply part 27 to the processing tank 21. FIG.

  The liquid level sensor 34 detects the position of the liquid level of the waste water stored in the treatment tank 21. For example, a float switch type or a capacitance type is conceivable. The liquid level sensor 34 detects whether or not the liquid level of the waste water has reached the upper limit water level or the lower limit water level determined in the treatment tank 21. In the present embodiment, the lower limit water level is set to a water level corresponding to about 57% with respect to the volume of the treatment tank 21 (2100 liters). Specifically, a position of 800 mm from the bottom surface of the processing tank 21 is set as the lower limit water level. The liquid level sensor 34 sends a sensor signal corresponding to the water level of the waste water to the control unit 100, and the control unit 100 has a level value corresponding to the upper limit water level or the lower limit water level. Whether or not the liquid level has reached the upper limit water level or the lower limit water level.

  A temperature sensor 35 is provided in the connection duct 14. The temperature sensor 35 is provided in the vicinity of a connection portion between the connection duct 14 and the upper surface of the processing tank 21. The temperature sensor 35 detects the temperature of the gas immediately after entering the connection duct 14 from the processing tank 21, and is composed of, for example, a resistance temperature detector. The temperature sensor 35 sends a sensor signal corresponding to the temperature to be detected to the control unit 100. The control unit 100 calculates the temperature of the detection target based on the sensor signal and displays the temperature information on the liquid crystal monitor 106.

[Decomposition processing device 12]
The decomposition processing apparatus 12 includes a housing 41, a heater 42, an oxidation catalyst 43, an exhaust duct 44, an exhaust blower 45, a temperature sensor 46, and a temperature sensor 47.

  The housing | casing 41 is formed in the cylinder shape of the cross-sectional square extended in a perpendicular direction. The casing 41 is provided on a stand 48 different from the base frame 15. An exhaust duct 44 is attached to the upper portion of the housing 41. A connecting duct 14 is connected to the lower part of the housing 41. The steam sent from the connection duct 14 is guided upward through the inside of the housing 41 and flows into the exhaust duct 44. That is, in the housing 41, an air flow is generated from the lower part to the upper part.

  The heater 42 heats the gas (steam and air) inside the housing 41. The heater 42 is, for example, a halogen heater. As long as the heater 42 heats the gas in the casing 41, any heating method of resistance heating method, infrared heating method, microwave heating method, dielectric heating method, induction heating method may be used. . The heater 42 is heated and controlled by the control unit 100.

  The oxidation catalyst 43 is provided above the heater 42 inside the housing 41. The oxidation catalyst 43 is a metal catalyst mainly composed of platinum, and is a so-called metal honeycomb catalyst having a honeycomb structure. When the gas containing the vapor sent from the connection duct 14 passes through the inside of the honeycomb structure, 1,4-dioxane contained in the gas and the oxidation catalyst 43 undergo an oxidation reaction, and 1,4-dioxane is converted into It is completely decomposed. Specifically, 1,4-dioxane is decomposed to produce water vapor (water) and carbon dioxide. Further, when the gas contains VOC gas, the VOC gas and the oxidation catalyst 43 undergo an oxidation reaction, and the VOC gas is completely decomposed. The decomposition processing apparatus 12 provided with the oxidation catalyst 43 is an example of the oxidative decomposition unit of the present invention.

  The temperature sensor 46 detects a temperature (catalyst inlet temperature) below the oxidation catalyst 43 inside the housing 41. The temperature sensor 47 detects the temperature above the oxidation catalyst 43 (catalyst outlet temperature) inside the housing 41. The temperature sensors 46 and 47 send a sensor signal corresponding to the temperature to be detected to the control unit 100. The control unit 100 calculates the temperature of the detection target based on the sensor signal and displays the temperature information on the liquid crystal monitor 106. Further, the heater control unit 108 controls the heating of the heater 42 so that the temperature detected by the temperature sensor 46 becomes a predetermined target temperature (for example, 350 ° C.). Information on the target temperature is stored in the EEPROM 104.

  The exhaust blower 45 is an electrically driven blower. The exhaust blower 45 is attached to the gantry 48. The exhaust blower 45 generates negative pressure inside the casing 41 by blowing air in the exhaust duct 44 in the discharge direction. Due to this negative pressure, steam generated from the waste water in the treatment tank 21 is sucked (intake) from the treatment tank 21 into the casing 41 through the connection duct 14. That is, the exhaust blower 45 plays a role of discharging steam generated from the waste water in the treatment tank 21 from the treatment tank 21 to the outside.

[Concentration decomposition process]
Next, an exemplary procedure of the concentration / decomposition process executed by the control unit 100 will be described with reference to the flowcharts of FIGS. 5 and 6. Here, the said concentration decomposition process is a process which decomposes | disassembles 1, 4- dioxane and VOC gas which are contained in the vapor | steam which vaporizes and concentrates the waste water in the processing tank 21 in the waste water concentration apparatus 11. FIG. By performing the concentration and decomposition treatment, the wastewater treatment method of the present invention is realized. In the figure, S11, S12,... Represent processing procedure (step) numbers. Processing in each step is performed by the control unit 100, more specifically, by the CPU 101 executing a control program in the ROM 102. Here, in this embodiment, the waste water treatment method of this invention is implement | achieved when the control part 100 performs a concentration decomposition process. In the following description, it is assumed that waste water is not stored in the treatment tank 21.

  First, in step S11, the control unit 100 controls the motor operated valve 81B to operate the motor operated valve 81B from the open position to the closed position. Accordingly, waste water is supplied from the waste water tank 81 to the treatment tank 21 by the head pressure (water head pressure) of the waste water tank 81.

  In step S <b> 12, the control unit 100 determines whether waste water has been supplied up to the upper limit water level in the treatment tank 21. This determination process is performed based on a sensor signal from the liquid level sensor 34. When determining that the liquid level of the waste water has reached the upper limit water level (YES in S12), the control unit 100 returns the motor operated valve 81B from the open position to the closed position, and stops the supply of waste water from the waste water tank 81 ( S13). In step S12, the supply of the waste water is continued until it is determined that the liquid level of the waste water has reached the upper limit water level.

  When the supply of the waste water is stopped, in the next step S14, the primary heating evaporation process is executed. The primary heating steam treatment is a treatment for concentrating the waste water by heating the waste water stored in the treatment tank 21 to generate steam from the waste water and discharging the steam. The step of performing the primary heating evaporation process is the primary concentration step of the present invention. The primary heating evaporation process in step S14 includes a steam supply process (S141) for supplying high-temperature steam from the steam supply unit 23 to the heat exchanger 22, a bubbling process (S142) for performing the bubbling, and air in the air layer of the processing tank 21. It includes an air supply process (S143) to be sent, an intake process (S144) by the exhaust blower 45, and a heating process (S145) by the heater 42.

  In step S141 (steam supply process), the control unit 100 controls the electric valve 23C of the steam supply unit 23 to operate the electric valve 23C from the closed position to the open position. Thereby, high temperature steam is supplied to the heat exchanger 22, and the waste water in the processing tank 21 is heated. Here, when the temperature of the wastewater is adjusted by increasing or decreasing the supply amount of the high-temperature steam, the opening / closing angle of the motor-operated valve 23C is controlled. In the present embodiment, the control unit 100 controls the open / close angle of the motor operated valve 23 </ b> C so that the temperature of the wastewater in the treatment tank 21 is 105 ° C. When stopping the supply of high-pressure steam, the motor operated valve 23C is operated from the open position to the closed position.

  In step S142 (bubbling process), the control unit 100 controls the electric valve 26C of the air supply unit 26 to operate the electric valve 26C from the closed position to the open position. As a result, air is supplied to the bubbling tube 25, and bubbles are generated from the bubbling tube 25.

  In step S143 (air supply process), the control unit 100 drives the air supply blower 24 to send air into the air layer of the processing tank 21. Thereby, the gas in the air layer flows into the connection duct 14 together with the air sent into the air layer, and flows into the housing 41 through the connection duct 14.

  In step S144 (intake processing), the control unit 100 drives the exhaust blower 45 to send air into the exhaust duct 44. As a result, air flows into the housing 41 from the connecting duct 14 due to the negative pressure of the exhaust duct 44.

  In step S145 (heating process), the control unit 100 causes the heater control unit 108 to perform heating by the heater. That is, the heater control unit 108 heats the heater 42 by PID control so that the inlet temperature of the oxidation catalyst 43 becomes the target temperature (350 ° C.). By this heating, the gas containing the vapor that has entered the casing 41 is heated to 350 ° C., and the oxidation reaction by the oxidation catalyst 43 is promoted.

  When the waste water is heated by performing the primary heating evaporation process in step S14, the water contained in the waste water flows into the connection duct 14 as steam. Further, 1,4-dioxane having a boiling point almost the same as that of water also flows into the connecting duct 14 as vapor. Further, when VOC is included in the wastewater, the VOC is converted into steam (VOC gas) and flows into the connecting duct 14. Thereafter, it flows into the housing 41. The gas flowing into the housing 41 is heated to 350 ° C. by the heater 42 and decomposed into water vapor and carbon dioxide by the oxidation reaction with the oxidation catalyst 43 when passing through the oxidation catalyst 43. Thus, the process of supplying the gas to the oxidation catalyst 43 and oxidizing and decomposing 1,4-dioxane or VOC gas contained in the gas is the oxidative decomposition process of the present invention.

  The heat generated by the oxidation reaction in the oxidation catalyst 43 raises the temperature around the oxidation catalyst 43 to about 400 ° C. to 450 ° C. That is, the temperature of the gas that has passed through the oxidation catalyst 43 rises by 50 ° C. to 100 ° C. from the catalyst inlet temperature (eg, 350 ° C.). In this state, gas is discharged from the exhaust duct 44 to the outside. The gas is not discharged at a high temperature of 400 ° C. to 450 ° C., but is cooled while being diluted by the air blown into the exhaust duct 44 by the exhaust blower 45 and then discharged to the atmosphere.

  By performing the primary heating evaporation treatment, the amount of waste water stored in the treatment tank 21 is gradually reduced. In the next step S15, the control unit 100 determines whether or not the waste water in the treatment tank 21 has decreased to the lower limit water level. This determination process is performed based on a sensor signal from the liquid level sensor 34. When it is determined that the liquid level of the waste water has decreased to the lower limit water level (YES in S15), the control unit 100 stops the steam supply process (S141) and the bubbling process (S142).

  In the next step S <b> 16, the control unit 100 counts up the number of times of performing the primary heating evaporation process and stores it in the RAM 103.

  In the next step S17, the control unit 100 determines whether or not the counted number of processes is a preset number of times. In the present embodiment, the set number of times is set to 100 times. In addition, the setting value of this setting frequency | count is arbitrary and is determined according to the content rate of the water in wastewater, the volume of the processing tank 21, the setting temperature (for example, 105 degreeC in this embodiment) of the wastewater heated. When it is determined in step S17 that the number of processes is less than the set number, the control unit 100 repeats the processes of steps S11 to S16. In the present embodiment, as described above, the upper limit water level is a position 900 mm from the bottom surface, the lower limit water level is set to a position 800 mm from the bottom surface, and the capacity from the upper limit water level to the lower limit water level is about 150. Liters. Therefore, the processing of each procedure of steps S11 to S16 is repeatedly performed each time the water and 1,4-dioxane contained in the wastewater in the processing tank 21 are evaporated and reduced by 150 liters. On the other hand, when it is determined in step S17 that the number of processes is the set number, the control unit 100 executes the processes after step S18 in FIG.

  When the processes of steps S11 to S17 are repeatedly performed, the waste water below the lower limit water level remaining in the treatment tank 21 becomes waste water in which impurities that have not been removed as steam are concentrated. Hereinafter, the wastewater thus concentrated is referred to as concentrated wastewater. Since the concentrated wastewater has a low water content, the boiling point of the concentrated wastewater is higher than the boiling point of water and may be higher than the set temperature (105 ° C.). In this case, the concentrated wastewater contains 1,4-dioxane that could not be evaporated. In order to prevent 1,4-dioxane from being contained in such concentrated wastewater, it is conceivable to increase the temperature of the wastewater by changing the set temperature to a higher value. However, when the temperature of the waste water is increased, bubbles are likely to be generated on the liquid surface. Further, when the temperature of the waste water is increased, mist of the waste water is easily generated in the air layer of the treatment tank 21. If bubbles or mist separated from the liquid level flows into the casing 41 through the connection duct 14, the amount of the substance that undergoes an oxidation reaction increases compared to the case where steam flows into the casing 41. As a result, the amount of heat generated increases, and the outlet temperature of the oxidation catalyst 43 may exceed the heat resistance temperature of the oxidation catalyst 43. In this case, there arises a problem that the oxidation catalyst 43 deteriorates or the decomposition processing device 12 fails.

  With respect to such a problem, in this embodiment, in order to completely remove 1,4-dioxane from the concentrated wastewater, the set temperature of the wastewater to be heated is maintained at 105 ° C. Is performed.

  In step S18, the control unit 100 controls the motor operated valve 28B to operate the motor operated valve 28B from the open position to the closed position. Thereby, water, such as industrial water, is supplied (water supply) to the processing tank 21 through the water supply pipe 28A. By this water supply operation, the concentrated waste water remaining in the treatment tank 21 is diluted with water.

  In step S <b> 12, the control unit 100 determines whether or not the diluted concentrated waste water (hereinafter, treated water) in the treatment tank 21 has been supplied up to the upper limit water level. When the control unit 100 determines that the liquid level of the water to be treated has reached the upper limit water level (YES in S19), the motorized valve 28B is returned from the open position to the closed position, and the supply of water from the water supply unit 28 is stopped. (S20). In step S20, the supply of water is continued until it is determined that the liquid level of the water to be treated has reached the upper limit water level.

  When the concentrated wastewater is diluted with water, the concentration of impurities (substances other than water) in the treated water after dilution is lowered, and the boiling point of the whole treated water is lowered below the set temperature. For this reason, even if to-be-processed water is heated in the state which maintained the said preset temperature, the water and 1, 4- dioxane which are contained in to-be-processed water evaporate.

  Thereafter, in step S21, the control unit 100 executes the secondary heating evaporation process having the same content as the primary heating evaporation process in step S14 described above. The secondary heating evaporation process is performed after adding the diluted water to the water to be treated remaining in the processing tank 21 after the primary heating evaporation process has been performed the set number of times (in this embodiment, for example, 100 times), and after the dilution. The water to be treated is heated again to generate steam from the water to be treated, and the steam is discharged to concentrate the water to be treated. The difference between the secondary heat evaporation process and the primary heat evaporation process is that the water to be treated is heated after adding water to dilute the water to be treated instead of adding waste water to the water to be treated. The step of performing the secondary heating evaporation process is the secondary concentration step of the present invention. By performing the secondary heating evaporation treatment, the water to be treated is heated, evaporated and decomposed, and 1,4-dioxane and VOC contained in the water to be treated are further removed. Further, by performing the secondary heating evaporation process, the amount of water to be treated in the treatment tank 21 is gradually reduced and concentrated again.

  In this embodiment, as will be described later, the concentration of 1,4-dioxane in the water to be treated remaining in the treatment tank 21 is less than or equal to a predetermined target concentration value by repeatedly performing the steps S18 to S24. The dilution, evaporation, decomposition and concentration of the water to be treated are repeated until the water reaches the end.

  Specifically, in step S22, the control unit 100 determines whether the water to be treated in the treatment tank 21 has decreased to the lower limit water level. This determination process is performed based on a sensor signal from the liquid level sensor 34. When determining that the liquid level of the water to be treated has decreased to the lower limit water level (YES in S22), the control unit 100 stops the steam supply process and the bubbling process in step S21.

  In the next step S <b> 23, the control unit 100 counts up the number of times of dilution of the concentrated wastewater by water supply and stores it in the RAM 103.

  In the next step S24, the control unit 100 determines whether or not the number of dilutions counted up is a preset number of times. In the present embodiment, the set number of times is set to five. In addition, the set value of this setting frequency | count is arbitrary, According to the content rate of the water in to-be-processed water, the volume of the processing tank 21, the set temperature (for example, 105 degreeC in this embodiment) of the to-be-treated water heated Determined. If it determines with the frequency | count of dilution being less than the said setting frequency in step S24, the control part 100 will repeat the process of each procedure of step S18-S24. Here, the process of each procedure of step S18-S24 is repeatedly performed whenever the water and 1, 4- dioxane contained in the waste water in the processing tank 21 evaporate, and 150 liters reduce. On the other hand, if it determines with the frequency | count of dilution being the said setting frequency in step S24, the control part 100 will progress to step S25.

  The set number of times (in this embodiment, for example, 5 times) is set to the number of times corresponding to the target concentration value that is predetermined as the concentration value of 1,4-dioxane in the water to be treated remaining in the treatment tank 21. Yes. Specifically, the set number of times is determined by performing the dilution process in steps S18 to S21 and the thermal decomposition process in steps S22 to S23, so that the concentrated surface after the liquid level becomes less than the lower limit water level. It is set to the number of times that it can be evaluated that 1,4-dioxane is not contained in the treated water, or even if it contains a concentration of 0.5 mg / L or less. As the set number of times, every time the processing from step S18 to step S24 is performed on the water to be processed, the water level remaining when the liquid level is determined to be lower than the lower limit water level in step S22. When the concentration of 1,4-dioxane is measured from water and the measured value becomes substantially zero, or the number of times of measurement when it becomes 0.5 mg / L or less can be used. Since the set number of times is set to such a number of times, 1,4-dioxane is completely contained in the water to be treated in the treatment tank 21 when it is determined in step S24 that the number of dilutions is the set number of times. It is not contained, or it is in a state where it is contained only below the drainage standard (0.5 mg / L) defined by the Water Pollution Control Law.

  In step 25, the control unit 100 drives the discharge pump 29 and opens a motorized valve (not shown) provided in the pipe 85 as necessary, and the processed object after concentration remaining in the processing tank 21. Water is discharged to the external tank 82. As a result, the water to be treated flows from the treatment tank 21 into the external tank 82 through the drain pipe 84 and the drain pipe 85 by the discharge pump 29.

  As described above, in the wastewater treatment apparatus 10 of the above-described embodiment, the primary heating evaporation treatment is performed a set number of times (100 times), and thereafter, 1 in the treated water remaining in the treatment tank 21 after concentration. The secondary heating evaporation process is performed a set number of times (5 times) until the concentration of 4-dioxane falls below the predetermined target concentration value. For this reason, it becomes possible to isolate | separate and decompose | disassemble 1, 4- dioxane efficiently and reliably from the wastewater which is a process target. In addition, since concentrated concentrated wastewater that does not exceed the wastewater standard (0.5 mg / L) defined by the Water Pollution Control Law is finally obtained, this concentrated wastewater is appropriately disposed of in accordance with the Industrial Waste Treatment Law. Processing can be performed.

[Example]
Hereinafter, the Example which performed wastewater treatment on the following conditions using the wastewater treatment apparatus 10 which concerns on the above-mentioned embodiment is described. The treatment target is wastewater having a water content of 95 to 99% containing water, 1,4-dioxane, and a surfactant. Moreover, heating control was performed so that the temperature of the wastewater in the treatment tank 21 was 105 ° C. In this case, the average evaporation speed in the treatment tank 21 is 120 liters / h. The set temperature of the catalyst inlet temperature was 350 ° C. Further, the air blower 24 was adjusted so that the flow rate of the gas flowing from the waste water concentrating device 11 to the oxidation catalyst 43 of the decomposition treatment device 12 was 427 m ₃ / h. Under this condition, the waste water treatment apparatus 10 is used to perform the primary heat evaporation process 100 times on the waste water, and further, the secondary heat evaporation process is performed 5 times. It was confirmed that the concentration of 1,4-dioxane contained was 0.5 mg / L or less, which is the drainage standard. The content of 1,4-dioxane contained in the gas at the inlet of the oxidation catalyst 43 is 1.432 ppm, whereas the content of 1,4-dioxane contained in the exhaust at the outlet of the oxidation catalyst 43 is 5 It was also confirmed that it was 0.0 ppm or less.

  In the above-described embodiment, the wastewater treatment apparatus 10 including the wastewater concentration apparatus 11 and the decomposition treatment apparatus 12 is described as an example of the wastewater treatment apparatus of the present invention, but the present invention is not limited to this configuration. For example, the wastewater treatment apparatus of the present invention may be regarded as comprising only the wastewater concentration apparatus 11 described above.

  Moreover, although the above-mentioned embodiment demonstrated the example which processes the wastewater with low viscosity whose water content rate is about 80%-99%, the wastewater used as a process target has a water content rate of less than 80%. But you can. In this case, when the wastewater is heated, foaming may increase due to its viscosity, or in some cases, there is a risk of bumping. Therefore, the wastewater treatment apparatus 10 of the above-described embodiment can also treat by reducing the heating temperature for the wastewater. Is possible.

DESCRIPTION OF SYMBOLS 10: Waste water processing apparatus 11: Waste water concentration apparatus 12: Decomposition processing apparatus 21: Processing tank 22: Heat exchanger 23: Steam supply part 24: Air supply blower 25: Bubbling pipe 26: Air supply part 27: Defoamer supply part 28: Water supply section 29: Discharge pump 30: Control panel 42: Heater 43: Oxidation catalyst 44: Exhaust duct 45: Exhaust blower 46: Temperature sensor 47: Temperature sensor

Claims (9)

A wastewater treatment method for treating wastewater containing 1,4-dioxane,
A primary concentration step of concentrating the wastewater by heating the wastewater stored in a storage tank to generate steam from the wastewater, and discharging the steam;
After hydrating and diluting the wastewater remaining in the storage tank after the primary concentration step, the diluted wastewater is heated again to generate steam from the wastewater, and the wastewater is concentrated by discharging the steam. A secondary concentration step,
Waste water characterized in that the secondary concentration step dilutes and concentrates the waste water until the concentration of 1,4-dioxane in the waste water remaining in the storage tank after concentration is equal to or lower than a predetermined concentration value. Processing method. The secondary concentration step includes a control step for controlling hydration during dilution of the wastewater and heating during concentration.
The control step includes
When the water level of the waste water in the storage tank decreases to a predetermined lower limit water level, heating to the waste water is stopped, and water is supplied to the storage tank until the water level of the waste water reaches a predetermined upper limit water level. Then, the wastewater treatment method according to claim 1, wherein the wastewater is heated until the water level of the wastewater reaches the lower limit water level.   In the secondary concentration step, 1 in the waste water remaining in the storage tank after the concentration is repeated by repeating the preset number of times corresponding to the concentration value in the control step. The wastewater treatment method according to claim 2, wherein the concentration of 1,4-dioxane is set to the concentration value or less.   The wastewater treatment method according to any one of claims 1 to 3, further comprising an oxidative decomposition step of oxidizing and decomposing 1,4-dioxane contained in the steam discharged in the primary concentration step and the secondary concentration step with a catalyst. .   The wastewater treatment method according to any one of claims 1 to 4, wherein the concentration value is 0.5 mg / L. A wastewater treatment apparatus for treating wastewater containing 1,4-dioxane,
A storage tank for storing the waste water;
A heating unit for heating the wastewater in the storage tank;
A discharge unit that discharges the steam generated from the wastewater by heating by the heating unit to the outside from the storage tank;
A water supply unit for supplying water to the storage tank;
A control unit for controlling heating by the heating unit and supply of water by the water supply unit,
The control unit supplies water to the waste water remaining in the storage tank concentrated by discharging the steam by controlling the water supply unit , dilutes the waste water, and controls the heating unit after dilution. The waste water is heated to concentrate the waste water, and the concentration of 1,4-dioxane in the waste water remaining in the storage tank after the concentration is equal to or lower than a predetermined concentration value. A wastewater treatment apparatus that controls the water supply unit and the heating unit so as to repeatedly dilute the wastewater by supply and concentrate the wastewater by heating the wastewater. The controller is
When the water level of the wastewater in the storage tank decreases to a predetermined lower limit water level, the heating by the heating unit is stopped and water supply by the water supply unit is started,
When the water level of the waste water reaches a predetermined upper limit water level, the water supply by the water supply unit is stopped and heating by the heating unit is started to heat the waste water until the water level of the waste water reaches the lower limit water level. Item 7. A wastewater treatment apparatus according to item 6.   The wastewater treatment apparatus according to claim 6 or 7, further comprising an oxidative decomposition unit that oxidatively decomposes 1,4-dioxane contained in the steam discharged from the storage tank using a catalyst. The wastewater treatment apparatus according to any one of claims 6 to 8, wherein the concentration value is 0.5 mg / L.

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