JPWO2008105242A1 - Disinfection method using expansion of dissolved gas - Google Patents

Abstract

With a simple and inexpensive device, without using chemicals such as chlorine, the liquid to be sterilized is ejected from the nozzle 3 by applying pressure to the sealed container 1 and the liquid collides against the wall of the container 1 to generate a liquid film. To dissolve the gas to a high concentration. After the liquid in which the gas has been dissolved at a high concentration is taken into the body to maintain its form in the microorganism in the liquid, the gas dissolved in the liquid in the body of the microorganism is foamed by reducing the pressure such as releasing the pressure. Swell and sterilize by rupturing the microorganisms in the liquid.

Description

  The present invention relates to a method and apparatus for sterilizing microorganisms present in liquids without using chemicals or physical separation membranes in water and sewage, rivers, lakes and the like, or in the liquid food industry and the food and beverage industry.

  Conventionally, sterilization and disinfection of tap water and liquid have been sterilized by sterilization and membrane treatment such as chlorination and ozone treatment, and heat sterilization treatment and high-pressure sterilization treatment have been performed in the field of liquid food, or A sterilization method using supercritical carbon dioxide is known.

  In sterilization by membrane treatment, in order to remove microorganisms such as viruses, it is necessary to use multiple membranes with small pore diameters, and costs such as maintenance costs and facility costs are incurred. However, there was a problem that the cost became high.

  Chlorination is the most commonly used method for disinfecting tap water, but some people dislike it when it increases the amount of chlorine and the odor of the salt becomes unsuitable for drinks, and high concentrations of chlorine pollute the environment. There is also a danger that trihalomethane or the like having a carcinogenicity generated by the reaction of chlorine and an organic substance pollutes the environment, or chlorine gas leaks due to mishandling. Recently, microorganisms that do not work with chlorine have appeared.

  Therefore, a method using ozone, bromine, chlorinated cyanuric acid or the like instead of chlorine has been proposed. However, these methods are more than twice as expensive as the chlorine method and are not economical. A further problem is the effect of the production of substances that adversely affect the human body due to the reaction between the chemicals used for sterilization and the organic substances in the liquid.

  Considering these points comprehensively, in the present situation where a wide variety of microorganisms and various substances are present in water, sterilization by chemical reaction is problematic, and introduction and maintenance are very expensive.

  Therefore, in the field of liquid food, a heat sterilizer is used as a typical sterilizer. In addition, although an ultra-high pressure processing apparatus is used, in the high-pressure processing apparatus, the liquid must be pressurized in order to kill microorganisms and maintained at a high pressure of 20 MPa or more. It is required and dangerous because of the high pressure, and the maintenance is expensive, and the high-pressure device itself is very expensive.

  Moreover, as disclosed in Patent Document 1 and Patent Document 2, a sterilization method using supercritical carbon dioxide has been proposed. The sterilization method using supercritical carbon dioxide is to mix and dissolve liquefied carbon dioxide gas in the sample to be sterilized, and maintain the supercritical state at a predetermined temperature and pressure while feeding the sample in which liquefied carbon dioxide gas is dissolved. The sample is sterilized, and then the sample is discharged under normal pressure. In this method, the use of liquefied carbon dioxide gas, an apparatus for forming a supercritical state, and the like are required, and there is a problem that the running cost is relatively high.

As described above, the development of an effective sterilization method against microorganisms with low cost equipment and low running cost is expected as a sterilization method for tap water, liquid food, or sewage such as sewage, rivers and lakes. It was.
JP 2000-83634 A Japanese Patent Laid-Open No. 7-170965 JP 2003-340251 A

  Accordingly, the present invention provides a sterilization method that does not use chemicals, has a low sterilization effect with a simple facility, has the same sterilization effect as chlorine sterilization, and can be easily applied to existing facilities. With the goal.

  In the sterilization method of the present invention, a pressurized gas is dissolved in a liquid containing microorganisms, the dissolved gas is taken into the body of the microorganism, and the dissolved gas is expanded and expanded in the body of the microorganism by rapidly reducing the pressure. Sterilizes microorganisms.

  In a preferred embodiment of the present invention, the pressure of the pressurized gas is about 0.15 MPa to 1 MPa, and the pressure is not so high. This decompression means is generally achieved by opening to atmospheric pressure. The pressure release means preferably flushes the liquid dissolving the gas under pressure to atmospheric pressure.

  In the present invention, means for dissolving the pressurized gas in the liquid in which microorganisms are present is not limited in any way, but means for supplying a liquid containing microorganisms to a container in which pressurized gas is present, such as a pressurized absorption tower, A container having a structure such as an irrigation tower, a packed tower, a thin film absorption tower, or the like, as shown in FIG. 2, a wall surface in a state where liquid is accumulated in the bottom of the container, particularly a collision plate provided in the bottom liquid reservoir (also a wall surface) A method of jetting the liquid to make it collide and bubbling the liquid is suitably employed.

  In addition, a method of supplying pressurized gas as bubbles from the bottom of a container in which a liquid containing microorganisms is present is also suitably employed. In this case as well, it is preferable to take measures to increase the absorption efficiency, such as filling the container with a filling such as Raschig Ring or providing a shelf.

  The gas used in the present invention is not particularly limited, but from the viewpoint of cost, it is better to use air, and considering sterilization efficiency, oxygen (especially against anaerobic bacteria) is effective, Carbon dioxide having a high solubility in an aqueous medium and a large change in solubility due to a pressure difference is preferable because of high sterilization efficiency.

  According to the present invention, it is only necessary to dissolve a gas in a liquid, a toxic substance such as chlorine is not used, and a bactericidal effect can be obtained by using a gas that is harmless to the human body. The energy consumption is small. In addition, because it is sufficient to pressurize well water such as a simple water supply that pumps well water, a gas dissolving device can be easily added to the existing equipment and operated without any major construction work. Is possible.

  In addition, since it is possible to reduce the effective volume of the gas dissolving device, the present invention can be applied not only to water and sewage facilities but also to water faucets in each household. Since it is not necessary to use or the amount of use can be reduced, it becomes possible to supply delicious water simultaneously with sterilization.

  The present invention applies a relatively small pressure, generally 0.15 MPa (megapascal: 1 atm≈0.1 MPa) to 1 MPa, preferably about 0.2 to 0.6 MPa, so that a larger amount under normal pressure. Is dissolved in a liquid such as water, and the dissolved liquid is rapidly returned to atmospheric pressure (0.1 MPa) to foam the gas. Therefore, it is extremely high as conventionally used for high-pressure sterilization. Since no pressure is required, the equipment cost is not expensive.

FIG. 1 is a conceptual diagram illustrating the sterilization method of the present invention. FIG. 2 is a cross-sectional view of an example of a gas dissolver. FIG. 3 is a conceptual diagram of the experimental apparatus. FIG. 4 is a graph showing the bactericidal effect in the experiment. FIG. 5 is a conceptual diagram of the one-pass sterilization apparatus of the present invention.

Explanation of symbols

1 Gas dissolving device 2 Pressure vessel 3 Nozzle

  In the present invention, a gas is dissolved under pressure in a liquid in which microorganisms are present, particularly an aqueous medium, the dissolved gas is taken into the body of the microorganism, and then sterilized by rapidly reducing the pressure.

  The gas generally dissolves in proportion to the partial pressure of the gas present on the liquid, almost according to Henry's law. The amount is considered to be almost determined by Henry's constant and partial pressure near normal pressure.

  Table 1 shows Henry's constants of carbon dioxide, air and oxygen at 20 ° C and 25 ° C.

  Moreover, Table 2 and Table 3 show the gas solubility at the time of 0.35 MPa and 0.1 MPa of carbon dioxide gas, air and oxygen with respect to water at 20 ° C. and 25 ° C. as an example.

  These are estimated values, and Henry's law does not always apply to real gases, but they are only a guide.

  As understood from Tables 2 and 3, when the pressure is reduced from 0.35 MPa to 0.1 MPa (about atmospheric pressure) at 20 ° C. to 25 ° C., about 71 to 72 for carbon dioxide, air and oxygen. % Of dissolved gas is released.

  When such a dissolved gas release occurs suddenly in the microorganism, the microorganism cannot cope with the change, and it is as if a human suffered from a submerged disease, or is sterilized by rupture of the microorganism. It is.

  This is schematically shown in FIG. That is, FIG. 1 (1) on the left side of FIG. 1 shows a state where a liquid (water) in which a large amount of gas is dissolved by pressurization is taken into the microorganism.

  Moreover, the figure (2) on the right side of FIG. 1 shows a state in which the microorganisms are ruptured because the pressure is released and the dissolved gas is foamed from the liquid to become gaseous and the volume is increased.

  In order to dissolve a gas in a liquid, a structure generally used for an absorption tower, that is, a method in which a liquid is dropped from the upper part using an irrigation tower, a packed tower, etc. A method of injecting gas into the plate tower from the bottom, a method of injecting and dissolving liquid from the top of the pressure tank into the gas, a method of mixing and dissolving liquid and gas in the pressure tank, etc. Is adopted.

  As the gas dissolver used in the method of the present invention, for example, the one disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 2003-340251) is optimal because it consumes less energy for gas dissolution. .

  In FIG. 2, the conceptual diagram of the preferable gas dissolving apparatus 1 is shown. The liquid to be processed stored in the tank 5 is pressurized by the pump P, and is ejected by increasing the flow velocity from the nozzle 3 in the sealed container 2, and the jet stream ejected from the nozzle 3 is made to collide with the wall 21 of the sealed container 2. A very thin film (hereinafter, liquid film) of the liquid to be processed is formed in the vicinity of the wall 21. The periphery of the liquid film is filled with gas, the contact area between the gas in the sealed container 2 and the liquid to be processed increases, and the liquid level gradually rises in the sealed container 2 so that the volume of the gas phase is increased. The gas is compressed (pressurized) and a large amount of gas in the sealed container 2 is dissolved in the liquid to be treated.

  The formed liquid film returns to a liquid at the bottom of the hermetic container 2 and the gas is dissolved at a high concentration. The extraction of the liquid to be processed from the sealed container 2 is adjusted by the opening degree of the valve 22. The operation index when the gas is dissolved in the liquid to be processed is the pressure in the sealed container 2, and the operating conditions are the discharge pressure of the pump P and the internal pressure of the container by the valve 22 for discharging the processing liquid from the sealed container 2. Is controlled. The discharge pressure of the pump and the pressure in the sealed container 2 are measured by pressure gauges 41 and 42, respectively.

  Of course, it can be controlled by the supply gas pressure. In practice, these elements are appropriately combined for operation. The liquid to be processed taken out from the sealed container 2 by the valve 22 is flushed under atmospheric pressure, the dissolved gas is precipitated and foamed and expanded, and microorganisms in the liquid to be processed are killed.

  When the gas in the sealed container 2 is carbon dioxide, a sufficient sterilizing effect can be obtained even when pressurized with tap water pressure of 0.2 to 0.3 MPa, so sterilization without newly installing a drive source. It can be applied to a 24-hour bath and a domestic water purifier.

  Further, FIG. 3 shows an example of an apparatus for repeating the foaming / expansion of the dissolved gas to sterilize it more completely. The liquid reservoir 5 containing microorganisms is open to the atmosphere, and treated water containing microorganisms such as turbid water is placed therein. This is pressurized by the pump P and sent to the sealed container 2, and the gas in the sealed container 2 is pressurized and dissolved in the liquid introduced into the sealed container 2 in the same manner as in FIG. Is sterilized by reducing the pressure by abruptly discharging the liquid from the water to the liquid reservoir 5 under atmospheric pressure. If sufficient sterilization cannot be obtained by one-pass flushing to atmospheric pressure, sterilization can be achieved to a higher degree by circulating the treatment liquid several times.

  Experiments on sterilization treatment were performed on the muddy water collected from the sludge storage tank and aeration tank of the sewage treatment plant using the experimental apparatus shown in FIG. The gas dissolving apparatus 2 is the same as that shown in FIG.

  The treated water of the sample containing microorganisms is ejected from the nozzle 3 into the sealed container 2 by the pressure pump P, and air is used as the gas dissolved in the sample containing microorganisms, and the pressure in the sealed container 2 is adjusted by the pressure regulating valve 22. did. The discharge pressure of the pump was 0.3 MPa, the internal pressure of the sealed container 2 was 0.26 MPa, the differential pressure was 0.04 MPa, and repeated operation for 20 minutes was performed. In the meantime, the treated water containing microorganisms was circulated 4 to 6 times.

  Samples used in the experiment were water temperature of 10 ° C and 25 ° C, pH (potential Hydrogen: hydrogen ion index) 7 and 9.5, turbidity 20NTU (Nephelometric Turbidity Unit) and 2000NTU. These are combined and shown in Table 3.

  The change in the number of coliform groups (CFU: Colony Forming Unit) in this experiment is shown in FIG. In 10 minutes after the start of operation, the number of coliforms was reduced to half, and in 20 minutes after the start of operation, the number of coliforms was reduced to about 20% of the initial value, confirming the bactericidal effect.

  Moreover, although the influence which temperature and turbidity have on the bactericidal effect was small, it was confirmed that the sterilizing effect is significantly higher at pH 9.5 than 7.0.

  The gas used was carbon dioxide gas, and the sterilization effect by one pass in which flushing to atmospheric pressure was performed only once was measured using the apparatus shown in FIG. The discharge pressure of the pump P was 0.3 MPa, the gas phase inside the sealed container was full-pressure carbon dioxide, and the differential pressure from the internal pressure was 0.04 MPa (internal pressure 0.26 MPa).

  In the case of turbidity of 20 NTU and 800 NTU, high bactericidal rates were obtained in which the number of coliforms decreased by 95% and 87%, respectively.

Claims (6)

  Dissolved gas that sterilizes microorganisms by dissolving pressurized gas in a liquid containing microorganisms, taking the dissolved gas into the body of the microorganism, and rapidly decompressing the dissolved gas to foam and expand the dissolved gas in the body of the microorganism Sterilization method using the expansion of.   The sterilization method according to claim 1, wherein the pressure of the pressurized gas is 0.15 MPa to 1 MPa, and the rapid pressure reduction is a pressure reduction to atmospheric pressure.   The sterilization method according to claim 2, wherein a liquid containing the microorganism is supplied into the pressurized gas, and the gas is dissolved in the liquid.   3. The sterilization method according to claim 2, wherein the pressurized gas is supplied into a liquid containing the microorganism to dissolve the gas in the liquid.   The liquid containing the microorganisms is jetted into a sealed container in which the pressurized gas exists, and the pressurized gas is dissolved in the liquid by colliding the liquid containing the microorganisms with the wall surface of the sealed container. The sterilization method according to claim 3.   The sterilization method according to any one of claims 1 to 5, wherein the liquid containing the microorganisms is water, and the gas to be dissolved is one or more of air, oxygen, and carbon dioxide.

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