JP7560342B2 - Water treatment equipment - Google Patents

Description

The present invention relates to a water treatment device that reduces the chromaticity of the water being treated and then discharges it.

Conventionally, in addition to biological and physicochemical treatments, electrolysis has been known as a method for purifying wastewater containing organic matter such as human waste (see Patent Document 1, Patent Document 2, Patent Document 3, etc.). In the treatment of wastewater containing human waste, problems may occur such as urinary stones adhering to pipes and clogging the pipes, or the adhering urinary stones serving as a breeding ground for the proliferation of microorganisms, which then produce foul odors due to the decomposition of the urinary stones. It is believed that such urinary stones are formed when urea in the human waste is converted to ammonia by microorganisms, which increases the pH of the wastewater and causes calcium ions in the human waste to precipitate as calcium salts. In the electrolysis treatment of wastewater, hypochlorous acid is generated by electrolysis from chloride ions contained in the human waste and chloride ions derived from chlorides added to the wastewater. This sterilizes microorganisms in the wastewater, inhibits the generation of ammonia, prevents the generation of urinary stones, and suppresses the generation of foul odors. It is also known that the hypochlorous acid generated by electrolysis decomposes chromophores such as humic substances, which can reduce the chromaticity of the wastewater, and electrolysis is also used to reduce the chromaticity of the wastewater.

Japanese Patent Application Publication No. 8-294691 JP 2005-169320 A JP 2007-252965 A

When treated wastewater is reused as grey water, water quality standards are set for each application, and in addition to residual chlorine concentration, color is often set as one of the water quality standards. For this reason, it is common to measure the color of the treated wastewater using a color meter or the like, and to control the amount of current supplied to the electrodes used for electrolysis so that the color is reduced to a specified ratio.

However, the colorimeters used to measure color are expensive, which increases the cost of water treatment devices. In addition, colorimeters require regular cleaning, which increases the labor and costs required for maintenance.

The object of the present invention is to provide a water treatment device that eliminates the problems present in the prior art, enables reliable reduction of chromaticity to a specified ratio at low cost without using a colorimeter, and is easy to maintain.

In view of the above object, the present invention provides a water treatment device that reduces the chromaticity of water to be treated and discharges the water, comprising a mixing tank to which the water to be treated is supplied, an electrolytic tank having a capacity smaller than that of the mixing tank and provided with a first electrolysis section for electrolyzing the water to be treated, a circulation flow path that connects the mixing tank and the electrolytic tank and sends the water to be treated from the mixing tank to the electrolytic tank and returns the water to be treated in the electrolytic tank to the mixing tank, and at least one residual chlorine concentration meter that measures the free residual chlorine concentration of the water to be treated in the mixing tank and an ORP meter that measures the oxidation-reduction potential of the water to be treated in the mixing tank. The water treatment device includes at least one of a chromaticity determination unit and a chromaticity determination unit that determines whether the chromaticity of the water to be treated in the mixing tank has been reduced to a predetermined ratio or more, and an electrolysis control unit that controls the electrolysis capacity of the water treatment device based on the determination result of the chromaticity determination unit, and the chromaticity determination unit determines whether the chromaticity of the water to be treated has been reduced to the predetermined ratio or more based on at least one of the measurement values of the residual chlorine concentration meter and the measurement values of the ORP meter and a predetermined threshold value for at least one of the free residual chlorine concentration and the oxidation-reduction potential.

In the water treatment device, the water to be treated is supplied to the mixing tank, and the water to be treated is sent from the mixing tank through a circulation flow path and electrolyzed in an electrolytic tank having a smaller volume than the mixing tank to be decolorized, and the water to be treated is returned from the electrolytic tank to the mixing tank. In this way, the water to be treated in the electrolytic tank that performs electrolysis is circulated between the mixing tank and the water to be treated, so that even if the raw material ions (i.e., chloride ions, etc.) electrolyzed in the electrolysis unit are consumed as the electrolysis progresses, new ions are supplied, thereby improving the electrolysis efficiency. In addition, the chromaticity judgment unit judges whether the chromaticity of the water to be treated in the mixing tank, which is different from the electrolytic tank, has been reduced by a predetermined ratio or more based on at least one of the measured values of a residual chlorine concentration meter that measures the free residual chlorine concentration of the water to be treated in the mixing tank and an ORP meter that measures the oxidation-reduction potential of the water to be treated in the mixing tank, and the electrolysis control unit controls the operation of the electrolytic unit installed in the electrolytic tank based on the judgment result of the chromaticity judgment unit. Therefore, it is possible to reduce the chromaticity of the water to be treated in the mixing tank to a predetermined ratio or more and discharge it downstream without using a chromaticity meter.

In one embodiment of the water treatment device, the electrolysis control unit controls the operation of the first electrolysis unit to stop electrolysis of the water to be treated in the electrolysis cell when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter becomes equal to or greater than a first threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential, and to start electrolysis of the water to be treated in the electrolysis cell when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter becomes equal to or less than a second threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential.

The water treatment device may be equipped with both the residual chlorine concentration meter and the ORP meter, and the electrolysis control unit may control the operation of the first electrolysis unit to stop electrolysis of the water to be treated in the electrolysis cell when both the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter are equal to or greater than a first threshold value that is predetermined for the free residual chlorine concentration and the oxidation-reduction potential, and to start electrolysis of the water to be treated in the electrolysis cell when one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter is equal to or less than a second threshold value that is predetermined for the free residual chlorine concentration and the oxidation-reduction potential.

In the above water treatment device, in addition to or instead of the operation of the first electrolysis unit, the electrolysis control unit may control the circulation flow rate of the water to be treated so as to reduce the flow rate of the water to be treated in the circulation flow path when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter is equal to or greater than a predetermined first threshold, and to increase the flow rate of the water to be treated in the circulation flow path when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter is equal to or less than a predetermined second threshold.

In one embodiment of the water treatment device, the mixing tank may further be provided with a second electrolysis unit.

In this case, in addition to or instead of the operation of the first electrolysis unit, the electrolysis control unit may control the operation of the second electrolysis unit to stop the electrolysis of the water to be treated in the mixing tank when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter becomes equal to or greater than a first threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential, and to start the electrolysis of the water to be treated in the mixing tank when at least one of the measurement values of the residual chlorine concentration meter and the ORP meter becomes equal to or less than a second threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential.

In the water treatment device, for example, the threshold value is set to a conversion value that corresponds to a state in which the chromaticity of the water to be treated in the mixing tank is reduced by 40% or more compared to the chromaticity of the water to be treated before it is supplied to the mixing tank.

It is preferable that the water treatment device further includes a pretreatment device that performs biological or physicochemical treatment on the water to be treated before supplying it to the mixing tank.

In addition, in the water treatment device, it is preferable that the water to be treated is either kitchen wastewater, miscellaneous wastewater, or water containing chloride ions.

Furthermore, it is preferable that the outlet of a supply pipe that supplies the water to be treated from the upstream side of the water treatment device to the mixing tank and the outlet of a circulation flow path that circulates the water to be treated from the electrolytic tank to the mixing tank are open on the upper side of the mixing tank, and the inlet of a discharge pipe that discharges the water to be treated from the mixing tank to the downstream side of the water treatment device and the inlet of a circulation flow path that circulates the water to be treated from the mixing tank to the electrolytic tank are open on the lower side of the mixing tank at a position lower than the outlet of the supply pipe and the outlet of the circulation flow path. It is also preferable that the water treatment device further includes a flow rate adjustment device for adjusting the flow rate of the water to be treated supplied to the water treatment device.

According to the present invention, in the water treatment device, the water to be treated in the electrolytic tank where electrolysis is performed is circulated between the electrolytic tank and the mixing tank, so that even if the raw material ions (i.e., chloride ions, etc.) electrolyzed in the electrolysis unit are consumed as the electrolysis proceeds, new ions are easily supplied, and the electrolysis efficiency can be improved. In addition, the color determination unit determines whether the water to be treated in the mixing tank, which is different from the electrolytic tank, has become equal to or lower than a predetermined color based on at least one of the measurements of a residual chlorine concentration meter that measures the free residual chlorine concentration of the water to be treated in the mixing tank and an ORP meter that measures the oxidation-reduction potential of the water to be treated in the mixing tank, and the electrolysis control unit controls the operation of the electrolysis unit installed in the electrolytic tank based on the judgment result of the color determination unit. Therefore, it is possible to reduce the color of the water to be treated in the mixing tank to a predetermined color and discharge it downstream at low cost without using a color meter. Furthermore, since a color meter is not used, maintenance is also easy.

1 is a block diagram showing an overall configuration of a first embodiment of a water treatment device according to the present invention; 1 is a graph showing the correlation between oxidation-reduction potential and chromaticity. 1 is a graph showing the correlation between the free residual chlorine concentration of the water to be treated in the mixing tank and the chromaticity reduction rate of the water to be treated in the mixing tank. 1 is a graph showing the correlation between the ORP of the water to be treated in the mixing tank and the chromaticity reduction rate of the water to be treated in the mixing tank. 4 is a flowchart of a first electrolysis capacity control method in the water treatment device shown in FIG. 1 . 4 is a flowchart of a second electrolysis capacity control method in the water treatment device shown in FIG. 1 . 4 is a flowchart of a third electrolysis capacity control method in the water treatment device shown in FIG. 1 . FIG. 4 is a block diagram showing the overall configuration of a second embodiment of a water treatment device according to the present invention. FIG. 11 is a block diagram showing the overall configuration of a third embodiment of a water treatment device according to the present invention. FIG. 1 is a schematic flow diagram illustrating a wastewater treatment method using a water treatment device according to the present invention.

Below, we will explain several embodiments of the water treatment device according to the present invention with reference to the drawings, but it goes without saying that the present invention is not limited to these embodiments.

First, the overall configuration of the water treatment device 11 according to the first embodiment of the present invention will be described with reference to FIG.

The water treatment device 11 includes a mixing tank 13, an electrolytic tank 15 having a smaller volume than the mixing tank 13, a first electrolytic section 17 provided in the electrolytic tank 15, a circulation flow path 19, a residual chlorine concentration meter 21, an ORP meter 23, a control device 25, and a raw water supply line 27 and a treated water discharge line 29 connected to the mixing tank 13. Raw water is supplied as the water to be treated from the upstream side via the raw water supply line 27, and the water to be treated is subjected to a decolorization process, and the treated water whose chromaticity has been reduced to a predetermined ratio or more is discharged downstream via the treated water discharge line 29.

Raw water as the water to be treated is supplied to the mixing tank 13 via the raw water supply line 27. As the raw water, tap water, seawater, industrial water, ozone-treated water, well water, kitchen wastewater or miscellaneous wastewater obtained as a result of using these water, etc. are used, but it is preferable that the wastewater contains chloride ions and is made of tap water or the like. If the wastewater contains chloride ions, decolorization can be performed without adding salt water or hydrochloric acid because of the chloride ions required for electrolysis. However, it is also possible to treat raw water that does not contain chloride ions. In this case, salt water or hydrochloric acid may be added to the raw water before supplying it to the water treatment device 11. It is preferable that a flow rate adjustment device 31 is provided on the raw water supply line 27 to adjust the supply flow rate of raw water (i.e., water to be treated) from the upstream side of the water treatment device 11 to the mixing tank 13. Furthermore, a color meter 33 for measuring the color of the raw water may be provided on the raw water supply line 27. It is preferable to use an ORP meter as the color meter 33, but a measuring device capable of measuring or estimating color, such as a color meter, may also be used. In addition, it is preferable that the raw water supply line 27 opens at the top of the mixing tank 13. On the other hand, it is preferable that the treated water discharge line 29 opens at the top of the side wall of the mixing tank 13 located on the opposite side to the open end of the raw water supply line 27, and is discharged from the mixing tank 13 to the downstream side of the water treatment device 11 by overflow.

When wastewater such as kitchen wastewater or miscellaneous wastewater is used as raw water, one or both of biological and physicochemical treatments are applied to the raw water before it is supplied to the water treatment device 11, as described below. As biological treatments, activated sludge treatment, biofilm filtration treatment, biofilm treatment, anaerobic biological treatment, etc. can be used, but it is preferable to use the membrane separation activated sludge method. In the membrane separation activated sludge method, wastewater such as kitchen wastewater or miscellaneous wastewater is subjected to activated sludge treatment, and then membrane filtration using a microfiltration membrane (MF membrane) and separation treatment is performed. In addition, as physicochemical treatments, coagulation sedimentation treatment, pressure flotation treatment, etc. can be used. In this way, the raw water that has been subjected to one or both of biological and physicochemical treatments is supplied to the mixing tank 13 of the water treatment device 11 as the water to be treated.

The electrolytic cell 15 is provided separately from the mixing cell 13 and has a smaller volume than the mixing cell 13. The mixing cell 13 and the electrolytic cell 15 are connected by a circulation flow path 19 including a first circulation flow path 19a and a second circulation flow path 19b, and the water to be treated is circulated between the mixing cell 13 and the electrolytic cell 15. In detail, the water to be treated in the mixing cell 13 is sent to the electrolytic cell 15 via the first circulation flow path 19a, and the water to be treated in the electrolytic cell 15 is returned to the mixing cell 13 via the second circulation flow path 19b. A circulation pump 35 is provided on the first circulation flow path 19a, and the water to be treated in the mixing cell 13 is sent to the electrolytic cell 15 by the circulation pump 35. In addition, a circulation flow meter 37 is provided on the first circulation flow path 19a to measure the flow rate of the water to be treated flowing through the first circulation flow path 19a. In this embodiment, the electrolytic cell 15 is installed at a higher position than the mixing cell 13, and one end of the first circulation flow path 19a is connected to the bottom side of the mixing cell 13 opposite to the open end of the raw water supply line 27 connected to the mixing cell 13, and the other end is connected to the side wall of the electrolytic cell 15, preferably to its upper side, so that the water to be treated at the bottom of the mixing cell 13 flows into the electrolytic cell 15 by the circulation pump 35. In addition, one end of the second circulation flow path 19b is connected to the upper part of the side wall of the electrolytic cell 15, and the other end is connected to the upper part of the mixing cell 13, so that the water to be treated that overflows in the electrolytic cell 15 flows into the mixing cell 13. In this way, a circulation flow path 19 is formed in which the water to be treated in the mixing cell 13 passes through the electrolytic cell 15 and flows into the mixing cell 13.

The electrolytic cell 15 is provided with a first electrolytic section 17 for electrolyzing the water to be treated in the electrolytic cell 15. The water to be treated, which contains chloride ions, is electrolyzed to decolorize the water to be treated, thereby reducing the chromaticity of the water to be treated. It is believed that decolorization can be achieved by electrolysis of the water to be treated because hypochlorous acid is generated by electrolysis, which decomposes chromophores such as humic substances contained in the water to be treated. The first electrolytic section 17 is immersed in the water to be treated in the electrolytic cell 15 and is composed of a pair of electrodes (e.g., platinum-coated titanium electrodes) composed of an anode and a cathode. However, the first electrolytic section 17 is not limited to electrodes as long as it can generate hypochlorous acid by electrolyzing the water to be treated. The water to be treated, the chromaticity of which has been reduced by the decolorization process, is returned to the mixing tank 13 by overflow from the electrolytic cell 15 through the second circulation flow path 19b.

In the water treatment device 11, an electrolytic cell 15 is provided in addition to the mixing cell 13, and the water to be treated is electrolyzed in the electrolytic cell 15. This shortens the hydraulic residence time of the electrolytic cell 15, which performs electrolysis even with a small circulation flow rate, and increases the efficiency of replenishing chloride ions, which are the raw material for generating hypochlorous acid. As a result, the electrolysis efficiency can be improved, and power saving effects can also be achieved.

In the mixing tank 13, a residual chlorine concentration meter 21 for measuring the free residual chlorine concentration of the water to be treated in the mixing tank 13 and an ORP meter 23 for measuring the oxidation-reduction potential (hereinafter referred to as ORP) of the water to be treated in the mixing tank 13 are provided. In the illustrated embodiment, a water sampling pump 39 is provided between the mixing tank 13 and the circulation pump 35 on the first circulation flow path 19a connected to the bottom side of the side wall of the mixing tank 13, and the free residual chlorine concentration of the water to be treated in the mixing tank 13 is measured by transferring the water to the residual chlorine concentration meter 21. However, the installation location of the water sampling pump 39 is not limited to the embodiment, and a pipe with the water sampling pump 39 may be connected to another location of the mixing tank 13 to transfer the water to be treated in the mixing tank 13 from the water sampling pump 39 to the residual chlorine concentration meter 21. The water to be treated transferred to the residual chlorine concentration meter 21 is returned to the mixing tank 13 after the free residual chlorine concentration is measured.

In this embodiment, in addition to the first electrolysis unit 17, a second electrolysis unit 41 is also provided in the mixing tank 13 for electrolyzing the water to be treated in the mixing tank 13. By electrolyzing the water to be treated containing chloride ions, the water to be treated in the mixing tank 13 can be decolorized and the chromaticity of the water to be treated can be reduced. In this way, if the second electrolysis unit 41 is provided in addition to the first electrolysis unit 17, the electrolysis capacity of the water to be treated can be increased, and by switching between starting and stopping electrolysis by the second electrolysis unit 41 while keeping the first electrolysis unit 17 on (electrolysis has started), it is possible to change the electrolysis capacity while maintaining a constant electrolysis capacity.

The free residual chlorine concentration and ORP of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 and the ORP meter 23 are sent to the control device 25, which controls the electrolysis capacity of the water treatment device 11, i.e., the decolorization capacity (color reduction capacity), based on the sent free residual chlorine concentration and ORP. The following three methods can be adopted to control the electrolysis capacity of the water treatment device 11. In the first control method, the electrolysis capacity of the water treatment device 11 is changed by switching between starting or continuing and stopping the power supply to the electrodes of the first electrolysis unit 17 (i.e., switching between starting or continuing and stopping electrolysis by the first electrolysis unit 17), thereby controlling the electrolysis capacity of the water treatment device 11. In the second control method, the electrolysis of the second electrolysis unit 41 is started or continued and stopped by switching between starting or continuing and stopping the supply of power to the electrodes of the first electrolysis unit 17 independently of the first electrolysis unit 17, and the electrolysis capacity of the entire water treatment device 11 is controlled by adding or not adding the electrolysis capacity of the second electrolysis unit 41 to the electrolysis capacity of the first electrolysis unit 17. In the third control method, the electrolysis capacity of the first electrolysis unit 17 is changed by changing the residence time of the water to be treated in the electrolysis tank 15, i.e., the circulating flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15, thereby controlling the electrolysis capacity of the water treatment device 11. By increasing the circulating flow rate, the amount of chloride ions consumed in the generation of hypochlorous acid by electrolysis is increased, and the decrease in electrolysis efficiency can be suppressed. As a result, the electrolysis capacity of the first electrolysis unit 17 can be changed to adjust the electrolysis capacity of the water treatment device 11. The circulating flow rate is adjusted by controlling the operation of the circulating pump 35 using, for example, feedback control based on the circulating flow rate measured by the circulating flow meter 37. Similarly, in addition to or instead of adjusting the electrolysis capacity of the first electrolysis unit 17 by changing the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15, it is also possible to adjust the electrolysis capacity of the second electrolysis unit 41 by changing the flow rate of the raw water supplied to the mixing tank 13 and the flow rate of the treated water discharged from the mixing tank 13 using the flow rate control device 31. The control device 25 can also control the electrolysis capacity of the water treatment device 11 by combining the three control methods described above.

The control device 25 includes a chromaticity judgment unit 25a and an electrolysis control unit 25b. The chromaticity judgment unit 25a judges whether the chromaticity of the water to be treated in the mixing tank 13 has been reduced to a predetermined ratio or more based on at least one of the measured values of the residual chlorine concentration meter 21 and the measured values of the ORP meter 23 and predetermined threshold values for the free residual chlorine concentration and the ORP. The electrolysis control unit 25b adjusts the electrolysis capacity of the water treatment device 11 by the first electrolysis unit 17 and the second electrolysis unit 41, i.e., the decolorization treatment capacity, based on the judgment result of the chromaticity judgment unit 25a. The three methods described above can be adopted as a method for controlling the electrolysis capacity of the water treatment device 11. Of course, as described above, the electrolysis capacity of the water treatment device 11 may be controlled by combining the three control methods described above.

In this type of water treatment device 11, instead of an expensive colorimeter, a residual chlorine concentration meter 21 or an ORP meter 23 is used to estimate the color of the water being treated in the mixing tank 13, and the water being treated whose color has been reduced from the color of the raw water to a predetermined color reduction rate or more can be discharged downstream without using a colorimeter. In addition, since an expensive colorimeter is not used, the increase in cost of the water treatment device 11 is suppressed compared to when a colorimeter is used, and maintenance of the colorimeter is also unnecessary, making maintenance of the water treatment device 11 easier.

Next, a method for estimating the reduction rate of color from the free residual chlorine concentration and ORP will be described with reference to Figures 2 to 4. Figure 2 is a graph showing the correlation between oxidation-reduction potential (ORP) and color. Also, Figure 3 is a graph showing the correlation between the free residual chlorine concentration of the water to be treated in the mixing tank 13 and the reduction rate of the color of the water to be treated in the mixing tank 13 relative to the color of the raw water, and Figure 4 is a graph showing the correlation between the ORP of the water to be treated in the mixing tank 13 and the reduction rate of the color of the water to be treated in the mixing tank 13 relative to the color of the raw water. The graphs in Figures 2 to 4 were obtained by experiments under the following conditions.

In the experiment, in the water treatment device 11 shown in FIG. 1, the volume of the mixing tank 13 was 1 m ³ , and the volume of the electrolytic tank 15 was 0.3 m ³ . The electrodes used as both the cathode and the anode of the first electrolysis unit 17 were platinum-coated titanium electrodes with an electrode area of 1600 to 6000 cm ² . The current supplied to these electrodes was changed in the range of 21.7 to 43.2 A and the current density in the range of 0.69 to 2.1 A/dm ² . The raw water used in the experiment had a chromaticity of 14 to 23 degrees, a raw water supply flow rate in the range of 30 to 100 L/min, and a circulation flow rate in the range of 30 to 100 L/min. A chromaticity meter was arranged next to the ORP meter as the chromaticity meter 33 on the raw water supply line 27, and a chromaticity meter was also installed at the position of the ORP meter 23 to measure the chromaticity of the raw water and the chromaticity of the water to be treated in the mixing tank 13. The experiment was conducted without using the second electrolysis unit 41. Under these different conditions, the ORP and color of the raw water, which change over time, and the free residual chlorine concentration, ORP, and color of the water to be treated in the mixing tank 13 were measured. In Fig. 2, the obtained measurement results are plotted on the same graph, with the ORP measured by the ORP meter as the color meter 33 and the ORP meter 23 in the mixing tank 13 as the X-axis (horizontal axis) and the color measured by the color meter attached to each ORP meter at the same time as the ORP measurement, as the Y-axis (vertical axis). In addition, in Figure 3, the free residual chlorine concentration of the water to be treated in the mixing tank 13 is plotted on the X-axis, and the chromaticity reduction rate obtained by dividing the difference in chromaticity between the raw water flowing in from the raw water supply line 27 and the chromaticity of the water to be treated in the mixing tank 13, measured at the same time as the measurement of the free residual chlorine concentration of the water to be treated in the mixing tank 13, by the chromaticity of the raw water, is plotted on the Y-axis on the same graph. In Figure 4, the ORP of the water to be treated in the mixing tank 13, measured by the ORP meter 23, is plotted on the X-axis, and the chromaticity reduction rate obtained by dividing the difference in chromaticity between the raw water flowing in from the raw water supply line 27 and the chromaticity of the water to be treated in the mixing tank 13, measured at the same time as the measurement of the ORP of the water to be treated in the mixing tank 13, by the chromaticity of the raw water, is plotted on the Y-axis on the same graph.

The measurement methods for each parameter are as follows.
(1) Residual Chlorine Concentration The residual chlorine concentration was measured by the DPD method using a residual chlorine concentration meter (manufactured by Hanna Japan: HI96734B).
(2) ORP
The ORP measurement was carried out by a platinum electrode method using a personal pH/ORP meter (manufactured by Yokogawa Electric Corporation: PH72).
(3) Chromaticity Chromaticity was measured by a transmitted light measurement method (light source wavelength 390 nm) using a digital turbidity meter (Kyoritsu Chemical Co., Ltd.: DTC-4DG).
(4) Current Current was measured using a clamp meter (Kyoritsu Electric Instruments Co., Ltd.: R2300).
(6) Flow rate (raw water supply flow rate and circulation flow rate)
The raw water supply flow rate was measured by ultrasonic method using a clamp-on type flow meter (Keyence: FD-Q50C). The circulation flow rate was measured by ultrasonic method using a clamp-on type flow meter (Keyence: FD-R50).

Referring to FIG. 2, the measurement points were approximated by a regression equation of y = -0.0162x + 19.585, with a correlation coefficient of R, and a coefficient of determination of ^R2 = 0.8134. It can be seen that there is a strong correlation between ORP and chromaticity, and that chromaticity can be estimated by measuring ORP.

Also, referring to FIG. 3, there is a correlation between the free residual chlorine concentration of the water to be treated in the mixing tank 13 and the chromaticity reduction rate, and similarly, referring to FIG. 4, there is a correlation between the ORP of the water to be treated in the mixing tank 13 and the chromaticity reduction rate. Therefore, by using the free residual chlorine concentration and ORP of the water to be treated in the mixing tank 13, it is possible to estimate the reduction rate of the chromaticity of the water to be treated in the mixing tank 13 relative to the chromaticity of the raw water. Furthermore, it can be seen that the ORP cannot be detected with good sensitivity unless the chromaticity reduction rate becomes large to a certain extent, while it is sensitive to a chromaticity reduction rate of a certain extent or more, and the free chlorine concentration is sensitive when the chromaticity reduction rate is small, but when the chromaticity reduction rate becomes large, its sensitivity becomes poor and the change becomes small. Therefore, by using both the free residual chlorine concentration and the ORP, it is possible to compensate for the shortcomings of each and to detect the change in the chromaticity reduction rate with good sensitivity and little error in both the area where the chromaticity reduction rate is small and the area where the chromaticity reduction rate is large. In particular, when controlling the electrolysis unit to start operating when the chromaticity reduction rate is small and to stop operating the electrolysis unit when the chromaticity reduction rate becomes large, it is preferable to control using both the residual chlorine concentration and the ORP.

With reference to FIG. 3, it can be seen that if the free residual chlorine concentration of the water to be treated in the mixing tank 13 is 1.6 mg/L or more, the chromaticity reduction rate of the water to be treated in the mixing tank 13 is 40% or more. Therefore, for example, if the electrolytic capacity of the first electrolytic unit 17 or the second electrolytic unit 41 is controlled so that the free residual chlorine concentration of the water to be treated in the mixing tank 13 is 1.6 mg/L or more, it is possible to achieve a chromaticity reduction rate of 40% or more for the water to be treated in the mixing tank 13. Also, with reference to FIG. 4, it can be seen that if the ORP of the water to be treated in the mixing tank 13 is 700 mV or more, the chromaticity reduction rate of the water to be treated in the mixing tank 13 is 40% or more. Therefore, for example, if the electrolytic capacity of the first electrolytic unit 17 or the second electrolytic unit 41 is controlled so that the ORP of the water to be treated in the mixing tank 13 is 700 mV or more, it is possible to achieve a chromaticity reduction rate of 40% or more for the water to be treated in the mixing tank 13. Furthermore, by controlling the electrolysis capacity of the first electrolysis unit 17 and the second electrolysis unit 41 based on a combination of the ORP of the water to be treated in the mixing tank 13 and the free residual chlorine concentration of the water to be treated in the mixing tank 13, the chromaticity reduction rate of the water to be treated in the mixing tank 13 can be more reliably achieved by 40% or more, compared to control based on only one of the ORP of the water to be treated in the mixing tank 13 and the free residual chlorine concentration of the water to be treated in the mixing tank 13.

In addition, if the chromaticity of the raw water is measured by the chromaticity meter 33, the chromaticity of the water to be treated in the mixing tank 13 can be estimated from the free residual chlorine concentration of the water to be treated in the mixing tank 13 and the chromaticity reduction rate estimated from the ORP, and it is also possible to confirm that the chromaticity of the water to be treated has decreased to a predetermined level or lower. In particular, by taking advantage of the ability to estimate chromaticity from ORP and measuring the chromaticity of the raw water using an ORP meter as the chromaticity meter 33, it becomes possible to confirm that the chromaticity of the water to be treated has decreased to a predetermined level or lower without using a chromaticity meter. Furthermore, since an expensive chromaticity meter is not used, the increase in cost of the water treatment device 11 is suppressed and maintenance of the water treatment device 11 is also made easier.

Next, with reference to Figures 5 to 7, three control methods that form the basis of the electrolysis capacity of the water treatment device 11 according to the first embodiment shown in Figure 1 will be described in detail.

Figure 5 shows a first control method in which the electrolysis capacity of the water treatment device 11 is controlled by changing the electrolysis capacity of the first electrolysis unit 17 by switching between starting or continuing and stopping the supply of power to the electrodes of the first electrolysis unit 17. In the control device 25 (specifically, the chromaticity determination unit 25a), a lower threshold value Tcl of the free residual chlorine concentration and a lower threshold value Tol of the ORP suitable for achieving a desired chromaticity reduction rate are preset based on the correlation between the free residual chlorine concentration and the ORP and the chromaticity reduction rate as shown in Figures 3 and 4 obtained by prior experiments, etc. For example, if a chromaticity reduction rate of 40% or more is to be achieved, Tcl may be set to 1.6 mg/L and Tol to 700 mV from Figures 3 and 4. In addition, upper threshold values Tcu and Tou are preset with a predetermined width from the lower threshold values Tcl and Tol. For example, Tcu is set to 1.7 mg/L and Tou to 750 mV.

When the treatment by the water treatment device 11 is started, first, the control device 25 (specifically, the electrolysis control unit 25b) starts the supply of power to the first electrolysis unit 17, starts the supply of raw water to the mixing tank 13, and operates the circulation pump 35 to start the circulation of the water to be treated in the mixing tank 13 to the electrolysis tank 15 and then from the electrolysis tank 15 back to the mixing tank 13 (step S101). As a result, the water to be treated in the electrolysis tank 15, whose chromaticity has been reduced by electrolysis by the first electrolysis unit 17, is sent to the mixing tank 13, the chromaticity of the water to be treated in the mixing tank 13 decreases, and the chromaticity reduction rate begins to increase. At this time, the second electrolysis unit 41 may be operated at the same time, or may be left in a stopped state. When circulation of the water to be treated between the mixing tank 13 and the electrolytic tank 15 and electrolysis by the first electrolytic unit 17 in the electrolytic tank 15 are started, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S102), and the electrolysis control unit 25b continues electrolysis of the water to be treated in the electrolytic tank 15 by the first electrolytic unit 17 until the chromaticity judgment unit 25a judges that the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu and the measured ORP is equal to or greater than the upper threshold value Tou (step S103). When only the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu or when only the measured ORP is equal to or greater than the upper threshold value Tou, electrolysis by the first electrolytic unit 17 is continued. On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S102). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or greater than the upper threshold value Tcu and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or greater than the upper threshold value Tou, and the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 has reached a predetermined value, the electrolysis control unit 25b stops the supply of power to the first electrolysis unit 17 and stops the electrolysis of the water to be treated in the electrolysis tank 15 by the first electrolysis unit 17 (step S104).

When the water treatment device 11 is operating, raw water is supplied to the mixing tank 13 regardless of the operating state of the first electrolysis unit 17. Therefore, if electrolysis by the first electrolysis unit 17 is stopped, the chromaticity of the water to be treated in the mixing tank 13 increases over time, i.e., the chromaticity reduction rate decreases, and the free residual chlorine concentration and ORP of the water to be treated in the mixing tank 13 decrease. As a result, the chromaticity reduction rate of the water to be treated in the mixing tank 13 may fall below a predetermined value.

Therefore, when electrolysis by the first electrolysis unit 17 is stopped, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S105). If the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or greater than the lower threshold value Tcl and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is equal to or greater than the lower threshold value Tol, the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 is maintained at a chromaticity reduction rate equal to or greater than a predetermined lower limit, and the electrolysis control unit 25b continues to stop the supply of power to the first electrolysis unit 17 and continues to stop the electrolysis of the water to be treated in the electrolysis tank 15 by the first electrolysis unit 17 (step S106). Unless a command to stop the operation of the water treatment device 11 is issued in step S107, steps S105 to S107 are repeated until the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl, or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tol.

On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S105). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tol, the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 has become equal to or lower than a predetermined lower limit value, and the electrolysis control unit 25b starts supplying power to the first electrolysis unit 17 to start electrolysis of the water to be treated in the electrolysis tank 15 by the first electrolysis unit 17 (step S108). When electrolysis by the first electrolysis unit 17 is started, the water to be treated, whose chromaticity has been reduced by electrolysis, is sent to the mixing tank 13, so that the chromaticity of the water to be treated in the mixing tank 13 is reduced again, and the chromaticity reduction rate can be increased. As a result, it becomes possible to maintain the chromaticity reduction rate of the water to be treated discharged from the water treatment device 11 at a predetermined value or higher. Steps S102 to S109 are then repeated unless a command to stop the operation of the water treatment device 11 is issued in step S109.

By controlling in this manner, it is possible to avoid excessive electrolysis and reduce power consumption, while maintaining a predetermined pigment reduction rate in the treated water discharged from the water treatment device 11.

When a command to stop the operation of the water treatment device 11 is received in step S107 or step S109, the control unit 25 (more specifically, the electrolysis control unit 25b) stops the supply of power to the first electrolysis unit 17 to stop the electrolysis of the water to be treated in the electrolytic cell 15 by the first electrolysis unit 17, stops the supply of raw water to the mixing cell 13, and further stops the operation of the circulation pump 35 to stop the circulation of the water to be treated between the mixing cell 13 and the electrolytic cell 15 (step S110).

Figure 6 shows a second control method in which the electrolysis capacity of the second electrolysis unit 41 is controlled by switching between starting or continuing and stopping the supply of power to the electrodes of the first electrolysis unit 17 independently of the first electrolysis unit 17, and the electrolysis capacity of the entire water treatment device 11 is controlled by adding or not adding the electrolysis capacity of the second electrolysis unit 41 to the electrolysis capacity of the first electrolysis unit 17. As in the first control method, the control unit 25 (specifically, the chromaticity determination unit 25a) is preset with a lower threshold value Tcl of the free residual chlorine concentration and a lower threshold value Tol of the ORP suitable for achieving a desired chromaticity reduction rate based on the correlation between the free residual chlorine concentration and the ORP and the chromaticity reduction rate as shown in Figures 3 and 4 obtained by prior experiments. In addition, the upper threshold values Tcu and Tou are preset with a predetermined width from the lower threshold values Tcl and Tol.

When treatment by the water treatment device 11 is started, first, the control device 25 (specifically, the electrolysis control unit 25b) starts supplying power to the first electrolysis unit 17, starts supplying raw water to the mixing tank 13, and operates the circulation pump 35 to start circulating the water to be treated in the mixing tank 13 to the electrolysis tank 15 and then from the electrolysis tank 15 back to the mixing tank 13 (step S201). As a result, the water to be treated in the electrolysis tank 15, whose chromaticity has been reduced by electrolysis by the first electrolysis unit 17, is sent to the mixing tank 13, the chromaticity of the water to be treated in the mixing tank 13 decreases, and the chromaticity reduction rate begins to increase. When circulation of the water to be treated between the mixing tank 13 and the electrolytic tank 15 and electrolysis by the first electrolysis unit 17 in the electrolytic tank 15 are started, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S202). Until the chromaticity judgment unit 25a judges that the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu and the measured ORP is equal to or greater than the upper threshold value Tou, the electrolysis control unit 25b starts or continues electrolysis of the water to be treated in the mixing tank 13 by the second electrolysis unit 41 in addition to electrolysis of the water to be treated in the electrolytic tank 15 by the first electrolysis unit 17 (step S203). When only the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu or when only the measured ORP is equal to or greater than the upper threshold value Tou, electrolysis by the second electrolysis unit 41 is continued. On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S202). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or higher than the upper threshold value Tcu and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or higher than the upper threshold value Tou, and the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 has reached a predetermined value, the electrolysis control unit 25b stops the power supply to the second electrolysis unit 41 and stops the electrolysis of the water to be treated in the mixing tank 13 by the second electrolysis unit 41 (step S204). At this time, the electrolysis of the water to be treated in the electrolysis tank 15 by the first electrolysis unit 17 is continued.

When the water treatment device 11 is operating, raw water is supplied to the mixing tank 13 regardless of the operating state of the second electrolysis unit 41. Therefore, when electrolysis by the second electrolysis unit 41 is stopped, even if electrolysis by the first electrolysis unit 17 continues, the electrolysis capacity of the entire water treatment device 11 decreases by the amount of electrolysis of the water to be treated by the second electrolysis unit 41. As time passes, the chromaticity of the water to be treated in the mixing tank 13 increases, i.e., the chromaticity reduction rate decreases, and the free residual chlorine concentration and ORP of the water to be treated in the mixing tank 13 decrease. As a result, the chromaticity reduction rate of the water to be treated in the mixing tank 13 may fall below a predetermined value.

Therefore, when electrolysis by the second electrolysis unit 41 is stopped, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S205). If the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or greater than the lower threshold value Tcl and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is equal to or greater than the lower threshold value Tol, the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 is maintained at a chromaticity reduction rate equal to or greater than a predetermined lower limit, and the electrolysis control unit 25b continues to stop the supply of power to the second electrolysis unit 41 and continues to stop the electrolysis of the water to be treated in the electrolysis tank 15 by the second electrolysis unit 41 (step S206). Unless a command to stop the operation of the water treatment device 11 is issued in step S207, steps S205 to S207 are repeated until the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl, or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tol.

On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S205). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tou, the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 has become equal to or lower than a predetermined lower limit value, and the electrolysis control unit 25b starts supplying power to the second electrolysis unit 41 to start electrolysis of the water to be treated in the mixing tank 13 by the second electrolysis unit 41 (step S208). When electrolysis by the second electrolysis unit 41 is started, the treated water whose chromaticity has been reduced by electrolysis by the first electrolysis unit 17 is supplied from the electrolytic cell 15 to the mixing tank 13. In addition, the chromaticity of the treated water in the mixing tank 13 can be reduced by electrolysis by the second electrolysis unit 41, so that the chromaticity of the water to be treated in the mixing tank 13 is reduced again, and the chromaticity reduction rate can be increased. As a result, it is possible to maintain the chromaticity reduction rate of the water to be treated discharged from the water treatment device 11 at a predetermined value or higher. Steps S202 to S209 are then repeated unless a command to stop the operation of the water treatment device 11 is issued in step S209.

By using the above-described control, it is possible to avoid excessive electrolysis and reduce power consumption, as in the first control method, while maintaining a predetermined pigment reduction rate in the treated water discharged from the water treatment device 11.

When a command to stop the operation of the water treatment device 11 is received in step S207 or step S209, the control unit 25 (more specifically, the electrolysis control unit 25b) stops the power supply to the first electrolysis unit 17 and the second electrolysis unit 41 to stop the electrolysis of the water to be treated in the electrolytic cell 15 by the first electrolysis unit 17 and the electrolysis of the water to be treated in the mixing cell 13 by the second electrolysis unit 41, stops the supply of raw water to the mixing cell 13, and further stops the circulation pump 35 to stop the circulation of the water to be treated between the mixing cell 13 and the electrolytic cell 15 (step S210).

Figure 7 shows a third control method, in which the residence time of the water to be treated in the electrolytic cell 15, i.e., the circulating flow rate, is changed to change the electrolytic capacity of the first electrolytic unit 17 and control the electrolytic capacity of the water treatment device 11. Increasing the circulating flow rate increases the amount of chloride ions consumed in the production of hypochlorous acid by electrolysis, thereby suppressing the decrease in electrolytic efficiency. As a result, the electrolytic capacity of the first electrolytic unit 17 can be changed to adjust the electrolytic capacity of the water treatment device 11. As with the first and second control methods, the control device 25 (specifically, the chromaticity determination unit 25a) is preset with a lower threshold Tcl of the free residual chlorine concentration and a lower threshold Tol of the ORP suitable for achieving a desired chromaticity reduction rate based on the correlation between the free residual chlorine concentration and the ORP and the chromaticity reduction rate as shown in Figures 3 and 4 obtained by prior experiments. In addition, the upper thresholds Tcu and Tou are preset with a predetermined width from the lower thresholds Tcl and Tol.

When the treatment by the water treatment device 11 is started, the control device 25 (specifically, the electrolysis control unit 25b) first starts the supply of power to the first electrolysis unit 17, starts the supply of raw water to the mixing tank 13, and operates the circulation pump 35 to start the circulation of the water to be treated in the mixing tank 13 to the electrolysis tank 15 and then from the electrolysis tank 15 back to the mixing tank 13 at a predetermined initial flow rate (step S301). As a result, the water to be treated in the electrolysis tank 15, whose chromaticity has been reduced by electrolysis by the first electrolysis unit 17, is sent to the mixing tank 13, the chromaticity of the water to be treated in the mixing tank 13 decreases, and the chromaticity reduction rate begins to increase. At this time, the second electrolysis unit 41 may be operated at the same time, or may be kept stopped. When circulation of the water to be treated between the mixing tank 13 and the electrolytic tank 15 and electrolysis by the first electrolysis unit 17 in the electrolytic tank 15 are started, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S302). Until the color determination unit 25a determines that the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu and that the measured ORP is equal to or greater than the upper threshold value Tou, the electrolysis control unit 25b controls the operation of the circulation pump 35 based on the measurement results of the circulation flow meter 37 while keeping the amount of power supplied to the first electrolysis unit 17 constant, to increase the circulation flow rate between the mixing tank 13 and the electrolytic tank 15 (step S303). When only the measured free residual chlorine concentration is equal to or greater than the upper threshold value Tcu or when only the measured ORP is equal to or greater than the upper threshold value Tou, the electrolysis control unit 25b controls the circulation pump 35 to increase the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic tank 15. Such an increase in the circulation flow rate of the water to be treated causes more water to be treated containing chloride ions to be sent from the mixing tank 13 to the electrolytic tank 15, replenishing the chloride ions consumed in the electrolysis by the first electrolysis unit 17. Therefore, even if the amount of power supplied to the first electrolysis unit 17 is kept constant, the efficiency of electrolysis by the first electrolysis unit 17 can be improved and the rate of increase in the chromaticity reduction rate can be increased. On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the upper threshold value Tcu, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the upper threshold value Tou (step S302). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or higher than the upper threshold value Tcu and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or higher than the upper threshold value Tou, and the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 has reached a predetermined value, the electrolysis control unit 25b controls the operation of the circulation pump 35 to reduce the circulating flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15 while keeping the amount of power supplied to the first electrolysis unit 17 constant (step S304). This reduction in the circulation flow rate of the water to be treated reduces the amount of chloride ions consumed by electrolysis in the first electrolysis unit 17 that are replenished to the electrolysis cell 15. This reduces the efficiency of electrolysis in the first electrolysis unit 17 and prevents excessive color reduction even when the amount of power supplied to the first electrolysis unit 17 is kept constant, and also reduces power consumption in the circulation pump 35.

When the water treatment device 11 is operating, raw water is supplied to the mixing tank 13 regardless of the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic tank 15. Therefore, if the electrolysis capacity of the first electrolysis unit 17 is reduced by decreasing the circulation flow rate, the chromaticity of the water to be treated in the mixing tank 13 increases over time, i.e., the chromaticity reduction rate decreases, and the free residual chlorine concentration and ORP of the water to be treated in the mixing tank 13 decrease. As a result, the chromaticity reduction rate of the water to be treated in the mixing tank 13 may fall below a predetermined value.

Therefore, in a state in which the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic tank 15 is reduced, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S305). If the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or higher than the lower threshold value Tcl and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is equal to or higher than the lower threshold value Tol, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or higher than the lower threshold value Tcl and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is equal to or higher than the lower threshold value Tol (step S306), the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or higher than the lower threshold value Tcl and the ORP of the water to be treated in the mixing tank 13 is equal to or higher than the lower threshold value Tol (step S307), and the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is equal to or higher than the lower threshold value Tcl. If the ORP of the water to be treated in the mixing tank 13 is equal to or higher than the lower threshold value Tol, the chromaticity determination unit 25a determines that the chromaticity reduction rate of the water to be treated in the mixing tank 13 is maintained at or above the lower limit value, and the electrolysis control unit 25b controls the circulation pump 35 to reduce the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic cell 15, thereby reducing the efficiency of electrolysis of the water to be treated in the electrolytic cell 15 by the first electrolysis unit 17 and reducing the electrolysis capacity (step S306). Unless a command to stop the operation of the water treatment device 11 is issued in step S307, steps S305 to S307 are repeated until the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tol.

On the other hand, the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 is compared with the lower threshold value Tcl, and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 is compared with the lower threshold value Tol (step S305). When the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl or the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23 becomes equal to or lower than the lower threshold value Tol, the color determination unit 25a determines that the color reduction rate of the water to be treated in the mixing tank 13 has become equal to or lower than a predetermined lower limit value, and the electrolysis control unit 25b controls the circulation pump 35 to increase the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic cell 15, thereby increasing the efficiency of electrolysis of the water to be treated in the electrolytic cell 15 by the first electrolysis unit 17 and improving the electrolysis capacity (step S308). When the electrolysis capacity of the first electrolysis unit 17 is improved by increasing the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolytic tank 15, the treated water whose chromaticity reduction rate has been increased by electrolysis in the first electrolytic tank 17 is supplied from the electrolytic tank 15 to the mixing tank 13, and the chromaticity of the treated water in the mixing tank 13 can be reduced, so that the chromaticity reduction rate of the water to be treated in the mixing tank 13 can be increased. As a result, it is possible to maintain the chromaticity reduction rate of the water to be treated discharged from the water treatment device 11 at a predetermined value or higher. Steps S302 to S309 are then repeated unless a command to stop the operation of the water treatment device 11 is issued in step S309.

By using the above-described control, as in the first and second control methods, it is possible to avoid excessive electrolysis and reduce power consumption while maintaining a predetermined pigment reduction rate in the treated water discharged from the water treatment device 11.

When a command to stop the operation of the water treatment device 11 is received in step S307 or step S309, the control unit 25 (more specifically, the electrolysis control unit 25b) stops the supply of power to the first electrolysis unit 17 to stop the electrolysis of the water to be treated in the electrolysis tank 15 by the first electrolysis unit 17, stops the supply of raw water to the mixing tank 13, and stops the circulation pump 35 to stop the circulation of the water to be treated between the mixing tank 13 and the electrolysis tank 15 (step S310).

Although the above-mentioned three control methods are described as separate methods, these control methods do not need to be performed selectively and may be performed in combination. For example, the first control method and the second control method may be performed simultaneously, and the circulation flow rate may be controlled based on the free chlorine concentration and ORP of the water to be treated in the mixing tank 13, while switching between starting or continuing and stopping the power supply to the first electrolysis unit 17. Of course, the three control methods may be performed simultaneously, and the circulation flow rate may be controlled based on the free chlorine concentration and ORP of the water to be treated in the mixing tank 13, while switching between starting or continuing and stopping the power supply to the first electrolysis unit 17 and the second electrolysis unit 41.

In the above three control methods, the chromaticity determination unit 25a determines that the chromaticity of the water to be treated in the mixing tank 13 is equal to or greater than the predetermined reduction rate when the free residual chlorine concentration is equal to or greater than the upper threshold value Tcu and the ORP is equal to or greater than the upper threshold value Tou. However, the chromaticity determination unit 25a may determine that the chromaticity of the water to be treated in the mixing tank 13 is equal to or greater than the predetermined reduction rate when the free residual chlorine concentration is equal to or greater than the upper threshold value Tcu or the ORP is equal to or greater than the upper threshold value Tou. Similarly, the chromaticity determination unit 25a may determine that the chromaticity of the water to be treated in the mixing tank 13 is equal to or less than the lower threshold value Tcl and the ORP is equal to or less than the lower threshold value To.

Next, we will explain another embodiment of the water treatment device according to the present invention.

Figure 8 shows in block diagram form the overall configuration of a water treatment device 11' according to a second embodiment of the present invention. The water treatment device 11' according to the second embodiment differs from the water treatment device 11 according to the first embodiment in that the water treatment device 11' does not have a second electrolysis unit 41, but is the same in other respects. The configuration and operation of each component of the water treatment device 11' is the same as the corresponding component of the water treatment device 11, so a description thereof will be omitted here.

Since the water treatment device 11' of the second embodiment does not include the second electrolysis unit 41, the second control method (i.e., the electrolysis capacity control method by switching between starting or continuing and stopping electrolysis by the second electrolysis unit 41) of the electrolysis capacity control methods in the water treatment device 11 of the first embodiment cannot be used. However, the water treatment device 11' is similar to the state in which the second electrolysis unit 41 is stopped in the water treatment device 11, and the water treatment device 11' can also perform the first control method (i.e., the electrolysis capacity control method by switching between starting or continuing and stopping electrolysis by the first electrolysis unit 17) and the third control method (i.e., the electrolysis capacity control method by increasing or decreasing the circulating flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15). Also, as in the case of the water treatment device 11, the water treatment device 11' can also perform a combination of the first control method and the third control method simultaneously.

Furthermore, if the electrolysis capacity is not controlled by increasing or decreasing the circulation flow rate, it is possible to further omit the circulation flow meter 37 in the water treatment device 11'.

Figure 9 shows in block diagram form the overall configuration of a water treatment device 11" according to a third embodiment of the present invention. The water treatment device 11" according to the third embodiment differs from the water treatment device 11 according to the first embodiment in that the water treatment device 11" does not have an ORP meter 23, but is the same in other respects. The configuration and operation of each component of the water treatment device 11" is the same as the corresponding component of the water treatment device 11, so a description thereof will be omitted here.

The water treatment device 11" according to the third embodiment also controls the electrolysis capacity based on the measured chromaticity of the water to be treated in the mixing tank 13, similar to the water treatment device 11 according to the first embodiment. However, the water treatment device 11" according to the third embodiment does not have an ORP meter 23. Therefore, the water treatment device 11" differs from the water treatment device 11 in that the chromaticity determination unit 25a of the control device 25 determines the chromaticity reduction rate of the water to be treated in the mixing tank 13 based only on the free residual chlorine concentration measured by the residual chlorine concentration meter 21. However, apart from this point, the three control methods described above can be performed in the same way. Also, like the water treatment device 11, the water treatment device 11" can also combine and simultaneously perform the first to third control methods.

Therefore, in the case of the water treatment device 11", in the three control methods shown in Figures 5 to 7, the chromaticity determination unit 25a can estimate the chromaticity reduction rate of the water to be treated in the mixing tank 13 based only on the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21. That is, when the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or higher than the upper threshold value Tcu, the power supply to the first electrolysis unit 17 or the second electrolysis unit 41 can be stopped or the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15 can be reduced, and when the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 becomes equal to or lower than the lower threshold value Tcl, the power supply to the first electrolysis unit 17 or the second electrolysis unit 41 can be started or continued, or the circulation flow rate of the water to be treated between the mixing tank 13 and the electrolysis tank 15 can be increased.

In the third embodiment, only the residual chlorine concentration meter 21 is provided, but it is also possible to provide only an ORP meter 23 instead of the residual chlorine concentration meter 21, and estimate the chromaticity reduction rate of the water to be treated in the mixing tank 13 based on the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23. Also, if the electrolysis capacity is not controlled by increasing or decreasing the circulation flow rate, it is also possible to further omit the circulation flow meter 37 in the water treatment device 11".

It is also possible to further omit the second electrolysis unit 41 from the water treatment device 11" of the third embodiment. In this case, it goes without saying that it will be impossible to use the second control method (i.e., the method of controlling the electrolysis capacity by switching between starting and stopping electrolysis by the second electrolysis unit 41).

Next, with reference to FIG. 10, a wastewater treatment method using the water treatment device 11 according to the present invention will be described.

When wastewater treatment is performed using the water treatment device 11, a pretreatment device 53 is provided in front of the water treatment device 11. Wastewater is supplied to the pretreatment device 53, which performs one or both of biological and physicochemical treatment. This decomposes or removes organic matter in the wastewater and sterilizes it. The wastewater that has been pretreated in the pretreatment device 53 is then supplied to the water treatment device 11 as raw water, where it is subjected to a chromaticity reduction treatment and discharged. As biological treatment, activated sludge treatment, biofilm filtration treatment, biofilm treatment, anaerobic biological treatment, etc. can be used. As physicochemical treatment, coagulation sedimentation treatment, pressure flotation treatment, etc. can be used. The chromaticity of the discharged treated water is reduced to a predetermined chromaticity reduction rate. In addition, since the water treatment device 11 is provided with a residual chlorine concentration meter 21, it is also possible to make the treated water contain a predetermined residual chlorine concentration. Therefore, it can be used as grey water in buildings where regulations for chromaticity and residual chlorine concentration are set.

Although the water treatment device of the present invention has been described above with reference to the illustrated embodiment, the present invention is not limited to the illustrated embodiment. For example, a pH meter for measuring the pH of the water to be treated may be further provided in the mixing tank 13 of the illustrated water treatment device 11. When the water to be treated is used as so-called grey water, the pH of the water to be treated may also be regulated according to a standard, and since the ratio of hypochlorous acid contained in the water to be treated also affects the pH, it is possible to respond to meet the standard by controlling the electrolysis capacity based on the measurement value of the pH meter in addition to the measurement value of the residual chlorine concentration meter 21 and the ORP meter 23. In addition, in the water treatment device 11 of the first embodiment and the water treatment device 11' of the second embodiment, it has been described that the electrolysis capacity is controlled based on the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23. However, it is also possible to control the electrolysis capacity based on only one of the free residual chlorine concentration of the water to be treated in the mixing tank 13 measured by the residual chlorine concentration meter 21 and the ORP of the water to be treated in the mixing tank 13 measured by the ORP meter 23.

REFERENCE SIGNS LIST 11 Water treatment device 11' Water treatment device 11" Water treatment device 13 Mixing tank 15 Electrolytic tank 17 First electrolysis section 19 Circulation flow path 21 Residual chlorine concentration meter 23 ORP meter 25 Control device 25a Color determination section 25b Electrolysis control section 35 Circulation pump 37 Circulation flow meter 41 Second electrolysis section

Claims (11)

A water treatment device that reduces the chromaticity of water to be treated and discharges the water,
A mixing tank to which the water to be treated is supplied;
An electrolytic tank having a volume smaller than that of the mixing tank, the electrolytic tank being provided with a first electrolysis unit for electrolyzing the water to be treated;
a circulation flow path formed to connect the mixing tank and the electrolytic tank, to send the water to be treated from the mixing tank to the electrolytic tank, and to return the water to be treated in the electrolytic tank to the mixing tank;
At least one of a residual chlorine concentration meter for measuring a free residual chlorine concentration of the water to be treated in the mixing tank and an ORP meter for measuring an oxidation-reduction potential of the water to be treated in the mixing tank;
a color determination unit that determines whether the color of the water to be treated in the mixing tank has been reduced to a predetermined ratio or more;
an electrolysis control unit that controls an electrolysis capacity of the water treatment device based on a determination result of the chromaticity determination unit;
wherein the color determination unit determines whether the color of the treated water has been reduced to or above the predetermined ratio based on at least one of the measurement values of the residual chlorine concentration meter and the measurement value of the ORP meter and a predetermined threshold value for at least one of the free residual chlorine concentration and the oxidation-reduction potential. The water treatment device according to claim 1, wherein the electrolysis control unit controls the operation of the first electrolysis unit to stop electrolysis of the water to be treated in the electrolysis tank when at least one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter becomes equal to or greater than a first threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential, and to start electrolysis of the water to be treated in the electrolysis tank when at least one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter becomes equal to or less than a second threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential. The water treatment device according to claim 1, which is equipped with both the residual chlorine concentration meter and the ORP meter, and the electrolysis control unit controls the operation of the first electrolysis unit to stop electrolysis of the water to be treated in the electrolysis cell when both the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter are equal to or greater than a first threshold value that is predetermined for the free residual chlorine concentration and the oxidation-reduction potential, and to start electrolysis of the water to be treated in the electrolysis cell when one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter is equal to or less than a second threshold value that is predetermined for the free residual chlorine concentration and the oxidation-reduction potential. The water treatment device according to any one of claims 1 to 3, wherein the electrolysis control unit controls the circulation flow rate of the water to be treated so as to reduce the flow rate of the water to be treated in the circulation flow path when at least one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter is equal to or greater than a predetermined first threshold value, and to increase the flow rate of the water to be treated in the circulation flow path when at least one of the measurement value of the residual chlorine concentration meter and the measurement value of the ORP meter is equal to or less than a predetermined second threshold value. The water treatment device according to any one of claims 1 to 4, further comprising a second electrolysis unit in the mixing tank. The water treatment device according to claim 5, wherein the electrolysis control unit controls the operation of the second electrolysis unit to stop electrolysis of the water to be treated in the mixing tank when at least one of the measurement values of the residual chlorine concentration meter and the measurement value of the ORP meter becomes equal to or greater than a first threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential, and to start electrolysis of the water to be treated in the mixing tank when at least one of the measurement values of the residual chlorine concentration meter and the measurement value of the ORP meter becomes equal to or less than a second threshold value that is predetermined for at least one of the free residual chlorine concentration and the oxidation-reduction potential. The water treatment device according to any one of claims 1 to 6, wherein the threshold value is set to a conversion value corresponding to a state in which the chromaticity of the water to be treated in the mixing tank is reduced by 40% or more compared to the chromaticity of the water to be treated before being supplied to the mixing tank. The water treatment device according to any one of claims 1 to 7, further comprising a pretreatment device that performs biological or physicochemical treatment on the water to be treated before it is supplied to the mixing tank. The water treatment device according to any one of claims 1 to 8, wherein the water to be treated is kitchen wastewater, miscellaneous wastewater, or water containing chloride ions. The water treatment device according to any one of claims 1 to 9, wherein the outlet of a supply pipe that supplies the water to be treated from the upstream side of the water treatment device to the mixing tank and the outlet of a circulation flow path that circulates the water to be treated from the electrolytic tank to the mixing tank are open on the upper side of the mixing tank, and the inlet of a discharge pipe that discharges the water to be treated from the mixing tank to the downstream side of the water treatment device and the inlet of a circulation flow path that circulates the water to be treated from the mixing tank to the electrolytic tank are open on the lower side of the mixing tank at a position lower than the outlet of the supply pipe and the outlet of the circulation flow path. The water treatment device according to any one of claims 1 to 10, further comprising a flow rate control device for controlling the flow rate of the water to be treated supplied to the water treatment device.

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