JPWO2014080847A1 - Method and system for producing sterilizing water - Google Patents

Abstract

A sterilizing solution having a high sterilizing power is produced using sodium hypochlorite by a simple and safe method. For this purpose, sterilizing water is produced from diluted water, sodium hypochlorite and an acetic acid buffer having a pH of 4 to 6.5. In this case, the electric conductivity of the sterilizing water is measured, and the concentration of sodium hypochlorite related to the production of the sterilizing water is monitored based on the electric conductivity.

Description

  The present invention relates to a method and a system for producing sterilized water that enables safe and simple production of sterilized water containing hypochlorous acid as an active ingredient.

  Sodium hypochlorite is industrially manufactured as an alkaline aqueous solution by absorbing the chlorine gas generated at the anode into the sodium hydroxide aqueous solution generated at the cathode when producing sodium hydroxide by electrolysis of salt water. It is used as a bactericidal agent in various fields such as food processing, agriculture and fisheries, and medicine.

  On the other hand, when the pH of the sodium hypochlorite aqueous solution is adjusted from weakly acidic to a neutral region, the concentration of hypochlorous acid in the aqueous solution increases and the bactericidal power is enhanced. However, harmful chlorine gas is generated in an acidic pH range. Therefore, in order to produce sterilized water in which the sodium hypochlorite aqueous solution is adjusted to pH 3 to 6 while preventing such danger, the sodium hypochlorite aqueous solution and the acid are each sufficiently diluted with water. In order to monitor the concentration of dilute aqueous solution of sodium hypochlorite or dilute aqueous solution of acid and adjust the amount of these additives, it is proposed to mix (Patent Document 1). The electrical conductivity (d3) of the water used for dilution, the electrical conductivity (d1) of the diluted aqueous solution of sodium hypochlorite, and the electrical conductivity (d2) of the diluted aqueous solution of acid are measured, and (d1-d3) And (d2-d3) are proposed (Patent Document 2). According to this method, the concentration of the sodium hypochlorite diluted aqueous solution and the acid diluted aqueous solution can be monitored and the amount of addition can be adjusted without being affected by variations in the electrical conductivity of the diluted water.

  In addition, it is known that the pH of an aqueous solution to be electrolyzed is adjusted to pH 2 to 7 with a buffer solution of acetic acid and sodium acetate in an apparatus for cleaning a denture by producing an aqueous solution of hypochlorous acid by electrolyzing an aqueous NaCl solution. (Patent Document 3).

JP 10-182325 A JP2001-321778 JP2000-126210

  However, in the method of diluting and mixing the sodium hypochlorite aqueous solution and the acid with water (Patent Documents 1 and 2), the sodium hypochlorite aqueous solution and the acid stock solution before mixing are mixed due to an accident during transportation. If the undiluted solutions are mixed due to misoperation such as mixing up when diluting these undiluted solutions with water, toxic chlorine gas may be generated.

  Also, in order to monitor the concentration of dilute aqueous solution of sodium hypochlorite and dilute aqueous solution of acid and adjust the amount of these additives, we measured a total of three types of electrical conductivity: electrical conductivity of these and diluted water. And controlling these supply amounts (Patent Document 2) is complicated.

  Furthermore, the use of acetic acid as an acid is safer to the human body than when hydrochloric acid or the like is used. However, since the electrical conductivity of acetic acid is low, the aqueous solution of It is difficult to know exactly the concentration of acid in it. Since well water and seawater are also used for cleaning and sterilizing agricultural and marine products, this problem becomes prominent when the dilution water used for preparing the acetic acid aqueous solution is well water or seawater. Furthermore, when well water or seawater is used as dilution water, the pH deviates from the expected value due to the presence of coexisting ions, and it is difficult to reliably obtain sterilizing power.

  According to the method of generating hypochlorous acid aqueous solution by electrolyzing NaCl in pH buffer solution (Patent Document 3), the risk of generation of chlorine gas can be eliminated. Since equipment such as electrodes and power supply for electrolysis is required, the cost is lower than when sodium hypochlorite, which is available as a by-product when producing sodium hydroxide by electrolysis of salt water, is used at low cost. Become high. Also, with this method, it is difficult to produce a large amount of a hypochlorous acid aqueous solution having a high concentration of 200 ppm or more at a low cost.

  In the method of mixing the dilute aqueous solution of sodium hypochlorite and the dilute aqueous solution of the acid described above (Patent Document 2), a pH adjuster is used instead of the dilute aqueous solution of acid, and the electrical conductivity of water used for dilution is It is also conceivable to measure each of the electric conductivity of the diluted sodium hypochlorite aqueous solution and the electric conductivity of the pH adjuster. However, it is still cumbersome to measure the electrical conductivity of three kinds of dilution water, dilute sodium hypochlorite aqueous solution and pH adjuster used for the production of sterilizing water, and to monitor the usage amount of these. .

  In contrast to the conventional techniques as described above, an object of the present invention is to enable a simple and safe method to produce a bactericidal solution having a high bactericidal power using sodium hypochlorite.

  In order to solve the above-mentioned problems, the present invention produces sterilized water from diluted water, sodium hypochlorite and an acetic acid buffer solution having a pH of 4 to 6.5, measures the electrical conductivity of the sterilized water, Provided is a method for producing sterilizing water that monitors the concentration of sodium hypochlorite related to the production of sterilizing water based on conductivity.

  In addition, the present invention provides a mixing part for producing sterilizing water composed of a mixture of diluted water, sodium hypochlorite and an acetic acid buffer having a pH of 4 to 6.5, and the electric conductivity of the sterilizing water produced in the mixing part. And a sterilizing water production system comprising a monitoring means for monitoring the concentration of sodium hypochlorite related to the production of sterilizing water based on an output signal from the electric conductivity measuring means .

  According to the present invention, without adding acid to the sodium hypochlorite aqueous solution, the concentration of hypochlorous acid in the sodium hypochlorite aqueous solution is increased by adding an acetic acid buffer, thereby enhancing the bactericidal power. can do. In this case, even if sodium hypochlorite is mixed with an acetic acid buffer without being sufficiently diluted with diluting water due to an accident or an erroneous operation, there is no possibility that the pH is lowered in an acidic region where chlorine gas is generated. Therefore, the safety in the manufacture of sterilizing water is ensured.

  In addition, when manufacturing sterilizing water, there is no risk of pH drop in the acidic region where chlorine gas is generated, so that a commercially available sodium hypochlorite aqueous solution can be mixed with an acetate buffer without diluting with water in advance. Can do.

  Furthermore, the concentration monitoring of the sterilizing water is sufficient if the electrical conductivity of the sterilizing water is measured. Therefore, compared to the previous method of measuring hypochlorous acid concentration in sodium hypochlorite aqueous solution using a polarograph or pH meter, the concentration monitoring and concentration adjustment of sterilizing water is extremely simple, inexpensive and safe. Can be done.

FIG. 1 is a schematic configuration diagram of a sterilizing water production system according to an embodiment of the present invention. FIG. 2 is a relationship diagram of hypochlorous acid content and pH in a sodium hypochlorite aqueous solution. FIG. 3 is a cross-sectional view of an example of a mixing tube. 4 is a graph showing the relationship between the pH of the sodium hypochlorite aqueous solution and the electrical conductivity in each operation of Example 1. FIG. FIG. 5 is a graph showing the relationship between the pH of the aqueous sodium hypochlorite solution and the electrical conductivity in each operation of Comparative Example 1.

  Hereinafter, the present invention will be described in detail. In addition, in each figure, the same code | symbol represents the same or equivalent component.

  FIG. 1 is a schematic configuration diagram of an embodiment of a sterilizing water manufacturing system for implementing the sterilizing water manufacturing method of the present invention. The sterilizing water production system 100 monitors the concentration of sterilizing water composed of a mixture of dilution water, sodium hypochlorite and an acetic acid buffer solution having a pH of 4 to 6.5 based on the measurement of electric conductivity of the sterilizing water. More specifically, dilution water, a sodium hypochlorite aqueous solution, and an acetic acid buffer solution are supplied to the mixing unit 6, and sterilizing water is produced in the mixing unit 6.

  In the present system 100, a dilution water supply passage for supplying dilution water to the mixing unit 6 is provided with a dilution water supply port 1, a dilution water opening / closing valve 2 supplied from the supply port 1, and a flow rate of the dilution water at a constant flow rate. A constant flow valve 3 for adjustment and an electric conductivity measuring means (D1) 4 for measuring the electric conductivity of dilution water are provided. Here, tap water, reverse osmosis water, well water or the like can be used as the dilution water, and a tap faucet or the like is connected to the supply port 1, for example. As the electrical conductivity measuring means (D1) 4, a flow-type electrical conductivity sensor can be preferably used.

  On the other hand, an acetic acid buffer storage tank 7 and a pump P1 are provided to supply the acetic acid buffer to the mixing unit 6, and sodium hypochlorite is used to supply the sodium hypochlorite aqueous solution to the mixing unit 6. An aqueous solution storage tank 8 and a pump P2 are provided, and dilution water and a mixed solution thereof, that is, a sterilizing solution can be discharged from the outlet 15.

  Here, the content (%) of hypochlorous acid in the sodium hypochlorite aqueous solution, the generation of chlorine gas, and the pH are in the relationship shown in FIG. Therefore, in the present invention, the pH of the acetic acid buffer in the storage tank 7 is 4 or more, preferably, in order to prevent generation of chlorine gas from the mixture of the dilution water, the acetic acid buffer, and the sodium hypochlorite aqueous solution. 4.5 or more. Moreover, from the point which raises the content rate of hypochlorous acid in the sodium hypochlorite aqueous solution, and strengthens bactericidal power, the pH of an acetic acid buffer solution shall be 6.5 or less, Preferably it is 6.0 or less, More preferably, it is 5 .5 or less.

  The acetate buffer is prepared from acetic acid at a concentration of 0.3 mol / L or more, more preferably 5 to 7 mol / L, and sodium acetate or sodium hydroxide, preferably an electrical conductivity of 10 ms / cm or more, more preferably. Is an acetic acid-sodium acetate buffer solution of 30 to 80 ms / cm, more preferably 50 to 70 ms / cm, and the electric conductivity of the acetic acid buffer solution is substantially the same as the electric conductivity of the sodium hypochlorite aqueous solution in the storage tank 8. More specifically, it is preferable to adjust the difference between the electrical conductivities of both to within about 10 ms / cm. Thereby, in manufacturing sterilization water, the consumption per unit time of the acetic acid buffer solution in the storage tank 7 and the consumption per unit time of the sodium hypochlorite aqueous solution in the storage tank 8 can be made equal. Therefore, the replenishment timings of these liquid agents are the same, the liquid agent management becomes easy, and the labor required for replenishment of the liquid agents can be reduced.

  On the other hand, as the sodium hypochlorite aqueous solution in the storage tank 8, for example, a commercially available sodium hypochlorite aqueous solution having a concentration of 5 to 12% by mass and a pH of 12 to 13 can be used. In particular, it is preferable from the viewpoint of cost to use a 12 mass% sodium hypochlorite aqueous solution that can be obtained at a low cost as a by-product in producing sodium hydroxide by electrolysis of brine.

  In addition, the supply amount to each mixing part 6 of dilution water, sodium hypochlorite aqueous solution, and a pH adjuster is the sodium hypochlorite which concerns on manufacture of sterilization water according to the use and intended purpose of the said sterilization water. (That is, the concentration of hypochlorous acid residue present in the sterilized water regardless of dissociation or non-dissociation) is set and determined according to the set concentration. For example, in the case of sterilizing water used for sterilizing applications such as medical devices and foods, the concentration of sodium hypochlorite involved in the manufacture of sterilizing water is preferably 5 ppm or more.

  As the mixing unit 6, an arbitrary mixer having a stirring ability by a stirring bar, a baffle plate, a flow hole that causes turbulent flow, or the like can be used. In particular, it is preferable to provide a closed type mixing part in the piping line from the dilution water supply port 1 to the sterilizing water outlet 15. As shown in FIG. 3, the outer container 21 and the inner cylinder are provided as the closed type mixing part. The mixing tube 20 provided with the flow hole 23 which causes a turbulent flow in the inner cylinder 22 with the double container structure of 22 is preferable. By making the mixing unit 6 closed, for example, when a tap water faucet is connected to the dilution water supply port 1, the water pressure applied to the dilution water supply port 1 is changed to the sterilization water at the sterilization water outlet 15. It can be used for the discharge pressure. Moreover, by using the mixing tube 20 shown in FIG. 3 for the mixing unit 6, a uniform mixed solution of dilution water, acetate buffer solution and sodium hypochlorite aqueous solution can be obtained with a simple structure.

  Between the outlet 15 for discharging the sterilized water prepared by the mixing unit 6 and the mixing unit 6, an electrical conductivity measuring means (D 2) 9 for measuring the electrical conductivity of the sterilized water, and a flow path of the sterilized water There is provided a valve 14 for opening and closing.

  Here, as the electrical conductivity measuring means (D2) 9, the same electrical conductivity measuring means (D1) 4 provided in the flow path of the dilution water can be used. By means 4 and 9, the concentration of sodium hypochlorite related to the production of sterilizing water is monitored. That is, the sodium hypochlorite used for the production of sterilizing water is almost completely dissociated in the sterilizing water at a weakly acidic to neutral pH by the pH adjuster. The electrical conductivity of the sterilizing water increases according to the amount of sodium hypochlorite used in the production of and the amount of acetate buffer used. On the other hand, the electrical conductivity of the sterilizing water also changes depending on the electrical conductivity of the dilution water. Therefore, the sensor signal of the electrical conductivity of the diluted water measured by the electrical conductivity measuring means 4 is converted into a DC signal by the sensor signal converter 5 and supplied to the signal processing unit 11, and the electrical conductivity measuring means. The sensor signal of the electric conductivity of the sterilizing water measured in 9 is also converted into a DC signal by the sensor signal converter 10 and supplied to the signal processing unit 11, and the sensor signal detected by the electric conductivity measuring means 9 of the sterilizing water is detected. Then, the electric conductivity obtained by subtracting the influence of the sensor signal detected by the electric conductivity measuring means 4 of the diluted water is calculated by the signal processing unit 11, and the output signal is output from the output unit 12 to the monitor display, printer, alarm. Output to an output device.

  Here, an operational amplifier IC or the like can be used as the sensor signal converters 5 and 10, and the signal processing unit 11 can be configured by an analog computing unit or a digital computing unit.

  By obtaining the relationship between the electrical conductivity of the sterilizing water and the pH of the sterilizing water in advance, the pH of the sterilizing water is known from the electrical conductivity output from the signal processing unit 11, and then contained in the sterilizing water. It is possible to know the concentration of chlorous acid or the concentration of sodium hypochlorite related to the production of sterilizing water. When the electrical conductivity output from the signal processing unit 11 is different from the predetermined electrical conductivity, either the supply of the acetate buffer solution or the supply of the aqueous sodium hypochlorite solution to the mixing unit 6 is performed. Since it means that one or both are abnormal, it is possible to take measures such as issuing an alarm or stopping the system by outputting a signal notifying the abnormality.

  In the sterilizing water production system of the present invention, an acid having a pH lower than 4 is not added to the sodium hypochlorite aqueous solution in the mixing unit 6, so an acid is added to the sodium hypochlorite aqueous solution. There is no need to prevent the generation of chlorine gas. Therefore, it is not necessary to monitor the mixing ratio of the sodium hypochlorite and the acid supplied to the mixing unit 6, and from the measurement of the electric conductivity of the sterilizing water produced in the mixing unit 6, the set concentration of hypochlorous acid is set in the sterilizing water. What is necessary is just to monitor whether chloric acid is contained or whether the sodium hypochlorite of the predetermined density | concentration which concerns on manufacture of sterilization water is contained.

  In addition, as a method of measuring the hypochlorous acid content in sterilized water, there is a method using a polarograph, but a hypochlorous acid concentration detection sensor using a polarograph is relatively expensive, and in order to maintain detection accuracy In addition, maintenance work such as electrode maintenance is costly.

  The conventional method of adding acid to sodium hypochlorite while monitoring the pH of the sodium hypochlorite aqueous solution using a pH meter is based on the risk of damage to the glass electrode of the pH meter. However, according to the present invention, sterilized water with enhanced sterilizing power of an aqueous sodium hypochlorite solution can be obtained inexpensively, simply and safely. Can be obtained.

  The present invention can take various aspects. For example, when producing sterilizing water for food using reverse osmotic pressure water or the like as dilution water, the electrical conductivity is low. May be omitted, and the concentration of sodium hypochlorite related to the production of sterilizing water may be monitored based only on the measurement of the electrical conductivity of the sterilizing water.

  Hereinafter, the present invention will be specifically described based on examples.

[Example 1]
First, an acetic acid-sodium acetate buffer solution having a pH of 4.85 and an electric conductivity of 59.9 ms / cm (25 ° C.) from 400 g of 5 mol / L acetic acid aqueous solution (30% by mass acetic acid aqueous solution) and 200 g of sodium acetate (trihydrate). Was prepared.

  400 mL of tap water (temperature: 25 ° C.) as dilution water was placed in a beaker, and while stirring with a magnetic stirrer, a pH meter sensor and an electrical conductivity meter were inserted, and the pH and electrical conductivity of tap water were measured.

  To this was added 0.5 mL of a 6% by mass aqueous sodium hypochlorite solution, and the pH and electrical conductivity were measured after mixing.

  Next, 0.5 mL of the above-mentioned acetic acid-sodium acetate buffer was added, and pH and electrical conductivity were measured after mixing.

  Further, 0.5 mL of 6 mass% sodium hypochlorite aqueous solution, 0.5 mL of acetic acid-sodium acetate buffer solution, and 0.5 mL of 6 mass% sodium hypochlorite aqueous solution were sequentially added. Conductivity was measured.

The above results are shown in Table 1 and FIG.
In addition, HM-21P (manufactured by Toa DK Corporation) was used as a pH meter, and CM-11P (manufactured by Toa Denpa Inc.) was used as an electric conductivity meter.

  From Table 1 and FIG. 4, when acetic acid-sodium acetate buffer solution and sodium hypochlorite aqueous solution are alternately added to tap water, the pH becomes constant at about 5 due to the buffering action of acetic acid-sodium acetate. I understand. Therefore, when producing sterilized water by mixing sodium hypochlorite and acetic acid-sodium acetate buffer, the obtained sterilized water has a high hypochlorous acid concentration (see FIG. 2) and a strong sterilizing power. Moreover, since it does not become the acidic region below pH3 which generate | occur | produces chlorine gas during manufacture, it turns out that it is safe.

  In addition, when the acetic acid-sodium acetate buffer solution and the sodium hypochlorite aqueous solution are alternately added to the tap water, it can be seen that the electrical conductivity increases according to the amount of addition. In this case, in the operations up to operation 5 in Table 1, when 1.0 mL each of an aqueous sodium hypochlorite solution and an acetic acid-sodium acetate buffer solution is added to 400 mL of tap water, the electric conductivity is about 1530 μs / cm. is there. Therefore, for example, in the sterilizing water production system shown in FIG. 1, tap water is supplied at a flow rate of 400 mL per minute with the constant flow valve 3, and a sodium hypochlorite aqueous solution and an acetic acid-sodium acetate buffer solution are supplied every minute. When it is set to be added to the mixing unit 6 at a flow rate of 1.0 mL, when these are added to the mixing unit 6 in a set amount, the electric conductivity of the sterilizing water obtained from the outlet 15 is about 1530 μs / cm. In this case, the hypochlorous acid concentration is 0.06 / 402 = 149 ppm. On the other hand, when the electrical conductivity of the sterilizing water obtained from the outlet 15 is lower than this, the supply amount of the acetic acid buffer solution or the sodium hypochlorite aqueous solution or both to the mixing unit 6 is more than the set amount. If the electrical conductivity of the sterilizing water is higher than this, the supply amount of the acetate buffer solution or the sodium hypochlorite aqueous solution or both to the mixing part must be larger than the set amount. I understand.

[Comparative Example 1]
Without using an acetic acid-sodium acetate buffer, 0.5 mL of a 6% by mass sodium hypochlorite aqueous solution (30% by mass acetic acid aqueous solution) and 0.5 mL of a 5 mol / L acetic acid aqueous solution are alternately used for 400 ml of tap water. The pH and electrical conductivity were measured after each addition.
The results are shown in Table 2 and FIG.

  From Table 2 and FIG. 5, it can be seen that even when an acetic acid aqueous solution is added in operation 3, the electrical conductivity hardly changes before and after the addition. Therefore, even if it measures the electrical conductivity of sterilization water, it turns out that the addition amount of the acetic acid aqueous solution used for the manufacture cannot be monitored.

[Chlorine gas generation test]
In producing sterilizing water by diluting and mixing the sodium hypochlorite aqueous solution as the stock solution and the acid aqueous solution as the stock solution, respectively, when the stock solutions are mixed carelessly, or the dilution rate is the original In order to investigate the danger of chlorine gas being generated when it is different from the setting, dilute each of the sodium hypochlorite aqueous solution (stock solution) and the acid aqueous solution (stock solution) to give the solutions with the prescribed concentrations shown in Table 3, As shown in Table 3, 10 to 50 mL was poured into a plastic bottle with a lid (capacity 500 mL), mixed by shaking with the lid closed. Within 2 minutes, the gas at the top of the PET bottle was inhaled, and the chlorine gas concentration in the gas was measured with a detector tube type gas measuring device (test chamber temperature 14.7 ° C.) (JIS K 0804). In this case, the detector tube 8H (25 to 1000 ppm) or detector tube 8LL (0.025 to 2 ppm) manufactured by Gastec Co., Ltd. was used as the detector tube depending on the chlorine gas concentration of the air in the PET bottle.

Similarly, the chlorine gas concentration of the air in the PET bottle when the sodium hypochlorite aqueous solution and the acetic acid-sodium acetate buffer were mixed in the PET bottle was measured.
These results are shown in Table 3.

  From Table 3, when diluting and mixing the sodium hypochlorite aqueous solution (stock solution) and the acid aqueous solution (stock solution), the stock solution is of course mixed inadvertently. Chlorine gas is generated even when diluted 100 times, so a system that produces sterilized water by diluting and mixing sodium hypochlorite aqueous solution (stock solution) and acid aqueous solution (stock solution) is put into actual operation. In contrast to this, there is a risk of a large amount of chlorine gas being generated. In contrast, according to the method of the present invention for producing sterilized water by mixing sodium hypochlorite and an acetic acid buffer, the generation of chlorine gas It turns out that there is no danger and is safe.

  The method for producing sterilized water and the method for producing sterilized water of the present invention are useful as a bactericidal agent used in various fields such as food processing, agricultural and marine industries, and medicine.

DESCRIPTION OF SYMBOLS 1 Supply port of dilution water 2 Valve 3 Constant flow valve 4 Electrical conductivity measurement means 5 Sensor signal converter 6 Mixing part 7 Acetic acid buffer solution storage tank 8 Sodium hypochlorite aqueous solution storage tank 9 Electrical conductivity measurement means 10 Sensor signal converter 11 Signal processing part 12 Output part 14 Valve 15 Outlet 20 Mixing tube 21 Outer container 22 Inner cylinder 23 Flow hole P1, P2 Pump 100 Sterilization water production system

Claims (10)

  The sterilizing water is produced from the diluted water, sodium hypochlorite and an acetic acid buffer solution having a pH of 4 to 6.5, and the electric conductivity of the sterilizing water is measured. A method for producing sterilizing water that monitors the concentration of sodium chlorite.   The method for producing sterilized water according to claim 1, wherein the sterilized water is produced by adding an aqueous sodium hypochlorite solution and an acetic acid buffer solution having a pH of 4 to 6.5 to the dilution water in a closed-type mixing part of the piping line.   The method for producing sterilizing water according to claim 2, wherein the electric conductivity of the sodium hypochlorite aqueous solution and the electric conductivity of the acetate buffer are substantially the same.   The electrical conductivity of the dilution water is measured, and the concentration of sodium hypochlorite related to the production of the sterilizing water is monitored based on the electrical conductivity of the dilution water and the electrical conductivity of the sterilizing water. The manufacturing method of disinfection water as described in any one of.   The method for producing sterilized water according to any one of claims 1 to 4, wherein the pH of the acetate buffer is 4.5 or more.   The method for producing sterilized water according to claim 5, wherein the acetate buffer is prepared from acetic acid having a concentration of 0.3 mol / L or more and sodium acetate or sodium hydroxide, and has an electric conductivity of 10 ms / cm or more.   The method for producing sterilized water according to any one of claims 1 to 6, wherein the concentration of sodium hypochlorite involved in the production of sterilized water is 5 ppm or more.   Electricity which measures the electric conductivity which measures the electric conductivity of the mixing part by which the sterilization water which consists of a mixture of dilution water, sodium hypochlorite, and the acetic acid buffer solution of pH 4-6.5 is manufactured, and the mixing part A sterilizing water production system comprising monitoring means for monitoring the concentration of sodium hypochlorite related to the production of sterilizing water based on output signals from the measuring means and electrical conductivity measuring means.   The system for producing sterilizing water according to claim 8, wherein dilution water, sodium hypochlorite aqueous solution and acetic acid buffer are mixed in a closed type mixing section of the piping line.   The sterilizing water production system according to claim 9, wherein a constant flow valve is provided in a dilution water supply path for supplying dilution water to the mixing unit.