JP4069167B2 - Method and apparatus for suppressing microbial growth of stored water - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method and an apparatus capable of suppressing the growth of microorganisms when storing water, particularly purified water.
[0002]
[Prior art]
Vending machine storage tanks, emergency drinking water storage devices, cooling tower cooling water circulation devices, and the like are equipped with devices that suppress the growth of microorganisms in the water. Among such microbial growth suppression devices, one of the sterilization and sterilization devices that do not use chemicals recently attracting attention is a device that sterilizes and sterilizes using electrolysis. Such equipment targets water containing chlorine ions, such as tap water, and generates and generates active chlorine species (referred to as effective chlorine) such as hypochlorous acid by electrolyzing water containing chlorine ions. It uses the effective bactericidal and sterilization and growth suppression effect.
[0003]
The tap water to be stored contains chlorine ions derived from water sources in addition to chlorination (existing as hypochlorous acid by reacting with water) for sterilization treatment or bacterial growth control in the water distribution, Even when very clean groundwater is used as a water source, it contains a minimum of 2 mg / l and an average of 4 mg / l, and when the middle river basin is used as a water source, it contains a maximum of 45 mg / l and an average of 20 to 25 mg / l of chlorine ions. When water containing such chlorine ions is electrolyzed, chlorine is generated on the anode surface, and the generated chlorine reacts with water to produce hypochlorous acid, which is sterilized or sterilized by the hypochlorous acid. It is said that.
[0004]
On the other hand, it has recently been purified by reverse osmosis membrane filtration or distillation to avoid the generation of carcinogenic organochlorine compounds such as trihalomethanes, which are caused by the presence of chlorine and combined with organic substances due to the smell of chlorine and chlorine ions. There is an increasing demand for water that does not contain effective chlorine or chloride ions, or that does not exceed the detection limit (hereinafter referred to as purified water).
[0005]
In the case of such purified water, effective chlorine is not generated even when electrolyzed, and sterilization and sterilization with effective chlorine cannot be expected. Adding chlorine ion raw materials such as salt to purified water to generate effective chlorine Not only has a chemical and biological effect, but also changes to pH as a result of electrolysis, impairing the essence of purified water. Therefore, the use of electrolysis for microbial control of purified water has not been considered an effective means.
[0006]
Therefore, methods such as ultraviolet irradiation or ozone injection are used to suppress the increase in microorganisms in purified water. In the case of ultraviolet irradiation, in water, the microorganism is inhibited by the decomposition of water by the irradiated ultraviolet rays to generate OH radicals. In addition, ozone injection suppresses an increase in microorganisms due to the strong oxidizing action of ozone.
[0007]
[Problems to be solved by the invention]
However, in the case of irradiation with ultraviolet rays, since ultraviolet rays are scattered and absorbed in water, only the surface layer portion to which the ultraviolet rays reach has an effect, and cannot sufficiently cope with microorganism control at a location away from the surface layer. In addition, since the useful life of an ultraviolet lamp is only a few hundred hours, it is necessary to perform frequent maintenance such as checking the lamp state and replacing the lamp. Furthermore, when an ultraviolet lamp is installed in water, it is costly to take measures against deterioration of the watertight packing. When irradiating from the surface of the water, it is necessary to sufficiently take measures against leakage of ozone generated by ultraviolet rays to ensure safety.
[0008]
In addition, in the case of ozone injection, ozone has a strong oxidizing power and is a dangerous gas that erodes the human mucous membrane violently. Therefore, the material selection and management of the ozone flow path from the ozone generator to the nozzle for blowing into the stored water, Safety measures such as a device to eliminate excess ozone released from the atmosphere are required, humidity control of the raw air to stabilize ozone generation, and prevention of purified water contamination by floating dust contained in the raw air Filter management and the like, and manufacturing and maintenance costs are high. Therefore, there is little merit in practical use unless it is a facility for refining and storing water on a large scale.
[0009]
As described above, the means for inhibiting microbial growth of water that does not contain chlorine and chlorine ions is expensive to manufacture and maintain in order to maintain the effect and ensure safety.
[0010]
The present invention has been made in view of the above-described points, and an object of the present invention is to provide a method and an apparatus capable of efficiently suppressing microbial growth of water containing no chlorine or chlorine ions at low cost.
[0011]
[Means for Solving the Problems]
In order to achieve this object, the method for inhibiting microbial growth of stored water according to the present invention irradiates ultrasonic waves in the stored water and generates hydroxyl radicals (HO.) To suppress the growth of microorganisms such as bacteria. A method for inhibiting microbial growth, characterized in that the ultrasonic frequency is selected in the range of 1650 kHz ± 100 kHz . Further, the microbial growth suppression device for stored water of the present invention is a microbial growth suppression device for stored water that suppresses the growth of microorganisms such as bacteria by irradiating ultrasonic waves into the stored water, and the frequency of the ultrasonic waves is 1650 kHz ± It is characterized by being selected in the range of 100 kHz .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 is a cross-sectional view showing an example of a purified water storage apparatus embodying the present invention. In the figure, reference numeral 1 denotes a water storage tank, and purified water is supplied into the water storage tank from a water injection port 2 provided at the upper portion, stored, and then taken out from a water intake port 3 provided at the bottom as necessary. . Purified water produced by passing tap water through the activated carbon filter 4 and the reverse osmosis membrane filter 5 is supplied to the water injection port 2. A solenoid valve 6 and a water pressure sensor 7 are installed in the flow path between the tap water channel and the activated carbon filter 4, and the flow path between the activated carbon filter 4 and the reverse osmosis membrane filter 5 is installed in the flow path. A booster pump 8 is provided for applying pressure to pass through the filter.
[0013]
On the other hand, a water discharge pump 9, a hydrogen peroxide decomposition device 10, and a check valve 11 are installed in the discharge flow path connected to the water intake 3.
[0014]
An upper limit water level sensor 12U that detects an upper limit set water level U and a lower limit water level sensor 12L that detects a lower limit set water level L are installed on the inner side surface of the water tank 1. Furthermore, ultrasonic oscillators 13a and 13b are attached to the inner side surface of the water tank 1 at positions below the lower limit set water level L so as to face each other, and a position between the upper limit set water level U and the lower limit set water level L. The ultrasonic oscillators 14a and 14b are attached to face each other.
[0015]
In addition, a heater 15 is installed at the inner bottom of the water storage tank 1, and a temperature sensor 16 for detecting the water temperature is installed at a position below the lower limit set water level L on the side surface. Reference numeral 17 denotes an overflow discharge port, and the stored water overflowed from the discharge port 17 is discharged to the outside through the check valve 18. Reference numeral 19 denotes a controller which supplies high-frequency power to the ultrasonic oscillators 13a, 13b, 14a and 14b, supplies heating power to the heater 15 based on a detection signal from the temperature sensor 16, and outputs from the two water level sensors 12U and 12L. The booster pump 8 is controlled based on the detection signal. Reference numeral 20 denotes a vent provided at the top of the water tank 1.
[0016]
In such a configuration, the purified water purified through the activated carbon filter and the reverse osmosis membrane filter is supplied to the water tank 1, and the upper limit water level sensor 12U detects that the upper limit set water level U has been reached. Then, the controller 19 stops the pump 8 and the supply is stopped. When the water level drops from the lower limit set water level L due to water intake or evaporation, the controller 19 supplies the water again.
The vent 20 is provided above the upper limit set water level U of the water tank 1 and serves as an air inlet / outlet due to fluctuations in the water level caused by the supply and intake of purified water. Dust and microorganisms in the atmosphere are passed through the vent inside the water tank. In order to prevent intrusion, a two-layer structure comprising a filter having a pore diameter of 1 μm or less and a prefilter for capturing relatively large particles for preventing clogging thereof is desirable. When this device is used in an environment where dust, fiber dust, oil droplets or the like are likely to be generated, the prefilter is an effective countermeasure against clogging. It is desirable that these filters have a structure that can be replaced as necessary.
[0017]
Then, when high frequency power is input from the controller 19 to the ultrasonic oscillation elements 13a, 13b, 14a, and 14b provided in the water storage tank 1, ultrasonic waves are irradiated to the stored water. When ultrasonic waves are irradiated, micro bubbles are generated in the stored water by cavitation.
[0018]
According to the inventors' experiment, it has been found that when purified water is irradiated with ultrasonic waves, hydroxyl radicals are selectively generated from water in which oxygen is dissolved. In the absence of oxygen, both hydroxyl radicals and hydrogen atoms were generated. This is presumed to be caused by the ultrasonic decomposition of water to generate hydroxyl radicals and hydrogen atoms (finally hydrogen peroxide reacts with hydrogen gas or oxygen). It has been discovered that the generation of hydroxyl radicals when oxygen is generated is not derived from hydrogen peroxide, and a new method for the generation of hydroxyl radicals has been established. Normally, hydrogen peroxide reacts in the presence of metal ions to generate hydroxy radicals.
[0019]
However, when hydrogen peroxide is dissolved in water at a high concentration (10 mole / l), a large amount of hydroxyl radical radicals are generated, and sterilization of microorganisms naturally causes biological injury. Therefore, it is desirable to generate an appropriate concentration of hydroxyl radicals to oxidize and decompose microorganisms and pollutants in water. In the case of the apparatus of the present invention, the amount of oxygen dissolved in water (about 0.25 mMol / l) is the upper limit for the generation of hydroxyl radicals. It has been confirmed that the bactericidal action of microorganisms can be used without causing biological damage. In addition, an appropriate amount of bubbles are generated in the purified water irradiated with ultrasonic waves, and movement of water is caused by the movement of the bubbles. As a result, in the ultrasonic device, a circulating flow due to bubbles is generated in the storage water container, and at the same time, the generated hydroxyl radicals are diffused. An efficient circulation flow can be generated without using a water flow generator such as a pump.
[0020]
Some ultrasonic oscillators have a frequency of several tens of kHz to several MHz and a maximum output of 1000 W. An apparatus that efficiently generates hydroxyl radicals at a low output is desirable. In an experiment using ultrasonic generators of 28 kHz (100 W), 48 kHz (100 w), 100 kHz (100 W), 950 kHz (300 W), 1650 kHz (30 W), 2000 kHz (30 W), and 2500 kHz (30 W), the frequency is 1650 kHz. Thus, when a device with an output of 30 W was used, the production of hydroxyl radicals 10-20 times that of other frequency ultrasonic devices was observed. This was about five times as efficient as a 950 kHz (300 W) device.
[0021]
In summary of the measurement results, the use of ultrasonic waves in the frequency range of 950 kHz to 2000 kHz has resulted in the generation of hydroxyl radicals with higher efficiency than other frequency ranges. Use frequencies in this range. Is preferred. Among them, in the frequency range of ± 100 kHz centered on 1650 kHz, as described above, the generation of hydroxyl radicals could be observed with about five times the efficiency of 950 kHz (300 W). More preferably, the frequency of
[0022]
Whatever the ultrasonic oscillator is used, the output is selected so as to generate a hydroxyl radical of 0.01 mMol / l or more sufficient to inhibit the growth of microorganisms in the stored water not containing chlorine or chlorine ions. Thus, the growth of microorganisms can be suppressed.
[0023]
According to the experiments of the present inventors, the ultrasonic generator of 1650 kHz-30 W can generate ³ × 10 ⁻³ M / sec hydroxyl radical, and 10 ⁶ spores can be obtained by ultrasonic irradiation within 60 seconds. and it is the sterilization of 10 ⁶ of Euglena garacilis (unicellular eukaryotes).
[0024]
When water was continuously irradiated with ultrasonic waves, a temperature increase of 20 ° C./30 minutes was observed. By providing a timer mechanism, the time for irradiating ultrasonic waves depending on the state of the stored water and the time for stopping the irradiation By setting the ratio, the amount of hydroxyl radicals generated in the stored water can be controlled within a predetermined concentration range.
[0025]
For the purpose of this apparatus, the surface of the ultrasonic element should be made of a material that is not affected by hydroxyl radicals generated by ultrasonic irradiation.
The amount of hydroxyl radicals generated by ultrasonic irradiation is determined by the number of irradiation devices (ultrasound oscillators) and input power, and the sterilization efficiency associated with irradiation is also proportional to the amount of hydroxyl radicals.
The ultrasonic irradiation time for generating and retaining hydroxyl radicals at a concentration necessary for inhibiting the growth of microorganisms depends on conditions such as the degree of contamination by the microorganisms and organic matter in the stored water and the structure of the water storage device. the number of initial bacteria 10 ² units or less of water level, water channel that connects the like filtration device, the connection portion of the reservoir and the lid, in a structure in which dust, microbial entry from the vent or the like, wetted parts clean condition When water storage is started, it is possible to control microorganisms in the water by irradiating ultrasonic waves at a rate of about 1 hour per 50 hours of water storage amount. On the other hand, if there is a lot of microorganisms or organic matter in the supplied water, or the structure is such that microorganisms and dust can easily enter the water storage container, or if the inner wall of the water storage tank is dirty when starting water storage, In order to control proliferation by decreasing, it may be necessary to irradiate several times more than the above.
[0026]
Hydrogen peroxide contained in the water taken out from the water storage tank 1 is decomposed by natural decomposition in the open air and catalytic action of a trace amount of metal ions (ppb level) contained in the water without taking any special measures. It decreases with time by releasing oxygen and returning to water. When storing the water used for eating and drinking, it is necessary that the extracted water is not detected by the inspection stipulated in the Food Sanitation Law when eating or drinking the extracted water. It is desirable to set it to (0.32 mg / l) or less.
[0027]
As an active means for reducing the hydrogen peroxide concentration of the water to be taken out, in this embodiment, a hydrogen peroxide decomposing apparatus made of a substance such as a ceramic containing a divalent or trivalent metal oxide is provided in the taking water channel. . When water taken out in this decomposition apparatus is brought into contact with a substance containing a divalent or trivalent metal oxide, the decomposition of hydrogen peroxide and the effect of killing microorganisms in the water by the action of hydroxyl radicals generated at that time are improved. be able to.
[0028]
In the case where the water level control by the water level detection sensor 12U for detecting the upper limit set water level U and the controller 19 is not sufficiently reliable, it is preferable to provide the overflow outlet 17 as in this embodiment, and also in the overflow drainage channel. It is desirable to provide a check valve to prevent bacteria, dust, insects and the like from entering the water tank 1 through the overflow outlet 17.
[0029]
In this embodiment, the water temperature can be controlled to a predetermined temperature by the heater 15 and the temperature sensor 16. Such temperature control plays an important role in carrying out the method of the present invention. That is, since the amount of hydroxyl radicals generated increases in proportion to the rise in water temperature, the sterilizing power increases as the water temperature rises even if the input power of ultrasonic waves is constant. Therefore, by setting the water temperature high, the input power of ultrasonic waves can be set low. However, when used for a water purifier, it is said that the water temperature is easy to drink around 18 degrees, and by making it constant temperature, it is possible to ensure homogeneous drinking water in a state that is easy to drink.
[0030]
In addition, when the apparatus is stopped for a long period of time, it can be efficiently sterilized by first irradiating with ultrasonic waves at a high temperature. Therefore, the apparatus may be operated after being lowered to a steady temperature.
[0031]
【The invention's effect】
As described above in detail, according to the present invention, by using ultrasonic waves, a method and an apparatus capable of efficiently suppressing microbial growth of water not containing chlorine or chlorine ions at low cost can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a purified water storage apparatus embodying the present invention.
[Explanation of symbols]
1: Water storage tank, 2: Water injection port, 3: Water intake port, 4: Activated carbon filter, 5: Reverse osmosis membrane filter, 8: Booster pump, 9: Water discharge pump, 10: Hydrogen peroxide decomposition device, 11: Reverse Stop valve, 12U, 12L: water level sensor, 13a, 13b, 14a, 14b: ultrasonic oscillator, 15: heater, 16: temperature sensor, 17: overflow outlet, 19: controller

Claims (5)

A method for suppressing the growth of microorganisms in stored water that suppresses the growth of microorganisms such as bacteria by irradiating ultrasonic waves into the stored water to generate hydroxyl radicals (HO.), And the frequency of the ultrasonic waves is in the range of 1650 kHz ± 100 kHz. A method for suppressing microbial growth of stored water, characterized by being selected . The method for suppressing microbial growth of stored water according to claim 1, wherein ultrasonic waves are intermittently irradiated. A device for suppressing the growth of microorganisms in stored water that suppresses the growth of microorganisms such as bacteria by irradiating ultrasonic waves into the stored water, wherein the frequency of the ultrasonic waves is selected in the range of 1650 kHz ± 100 kHz. Water microbial growth suppression device. The apparatus for suppressing microbial growth of stored water according to claim 3, further comprising temperature control means for controlling the temperature of the stored water. A member containing a divalent or trivalent metal oxide that decomposes hydrogen peroxide generated in the stored water in association with generation of hydroxyl radicals by ultrasonic irradiation of the stored water is stored in the stored water discharge channel of the water storage container. The apparatus for suppressing microbial growth of stored water according to claim 3 or 4, wherein the apparatus is installed so as to be in contact with water.

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