Sterilization method and sterilization apparatus

Abstract

Provided is a sterilization method that is capable of expanding an application range of an object to be sterilized by a peroxynitric acid solution. The sterilization method is a method for sterilizing an object of interest by supplying a liquid containing peroxynitric acid and a diluting liquid to the object and continuing to supply at least the liquid containing the peroxynitric acid to the object for a half-time of the peroxynitric acid or longer in a state where the liquid is mixed with the diluting liquid.

Description

Sterilization method and sterilization apparatus

[0001] The present disclosure relates to a sterilization method and a sterilization apparatus.

[0002] Sterilization technology is one of the basic technologies that support modern life. In this specification, "sterilization" means reducing the number of viable bacteria. Further, the targets of sterilization treatment include a wide variety of items such as medical instruments, living bodies, seeds, agricultural products, food containers, and foods.

[0003] As a background art, a sterilization method using a pernitric acid solution by the inventors of the present application is exemplified (see, for example, Patent Document 1). In this sterilization method, the pernitric acid solution is applied to the sterilization target.

[0004] Japanese Patent No. 6087029

[0005] In Patent Document 1 above, the pH of the pernitric acid solution was set to an acidic condition of 4.8 or less. However, a pernitric acid solution with a pH of 4.8 or less may have an adverse effect on specific sterilization targets. For example, it is known that when meat is exposed to a solution with a pH of 5 or less, the meat turns white, and when seeds are exposed to an acidic solution, the germination rate deteriorates. In addition, a wound site in a state where healthy skin tissue is damaged is highly irritating to an acidic solution. Therefore, the sterilization method disclosed in Patent Document 1 has a problem that it is difficult to apply to specific sterilization targets.

[0006] One aspect of the present disclosure has been made in view of the above problems, and its object is to expand the application range of sterilization targets by a pernitric acid solution.

[0007] In order to solve the above problems, a sterilization method according to one aspect of the present disclosure supplies a liquid containing pernitric acid and a diluting liquid to an object, and at least the liquid containing pernitric acid is continuously supplied to the object for a period equal to or longer than the half-life of pernitric acid in a state where it is mixed with the diluting liquid to sterilize the object.

[0008] To solve the above problems, a sterilization method according to one aspect of the present disclosure involves mixing a liquid containing pernitrate and a diluent immediately before supplying it to the object, and sterilizing the object by continuously supplying the mixed solution of the pernitrate-containing liquid and the diluent to the object.

[0009] To solve the above problems, a sterilization method according to one aspect of the present disclosure involves simultaneously mixing a liquid containing pernitrate with a diluent, supplying the mixed liquid to an object, and refreshing the mixed liquid in the object.

[0010] To solve the above problems, a sterilization apparatus according to one aspect of the present disclosure comprises: pumps for dispensing a liquid containing pernitrate and a diluent, respectively; a mixer for mixing the liquid containing pernitrate and the diluent; and a nozzle for continuously supplying the mixture of the liquid containing pernitrate and the diluent to an object for a period of time equal to or longer than the half-life of the pernitrate in the mixture.

[0011] To solve the above problems, a sterilization apparatus according to one aspect of the present disclosure comprises a pump that delivers a liquid containing pernitrate and a diluent, respectively, and a first nozzle and a second nozzle that simultaneously supply the liquid containing pernitrate and the diluent to the target object for a period of time equal to or greater than the half-life of the pernitrate in the state in which it is mixed with the diluent.

[0012] According to one aspect of this disclosure, the scope of application for sterilization targets using pernitrate solutions can be expanded.

[0013] This is a table showing the half-life (seconds) of pernitrate solution with respect to temperature and pH. This is a block diagram showing the schematic configuration of the sterilization device according to Embodiment 1. This is a flowchart showing an example of the processing flow of the sterilization device according to Embodiment 1. This is a block diagram showing the schematic configuration of the sterilization device according to Embodiment 2. This is a flowchart showing an example of the processing flow of the sterilization device according to Embodiment 2. This is a block diagram showing the schematic configuration of the sterilization device according to Embodiment 3. This is a flowchart showing an example of the processing flow of the sterilization device according to Embodiment 3. These are graphs showing the changes in the number of viable cells for Examples and Comparative Examples 1 to 3. This is a graph showing the changes in the number of viable cells of Escherichia coli (E. coli). This is a graph showing the changes in the number of viable cells of Bacillus subtilis (B. subtilis).

[0014] (Regarding the features of one aspect of this disclosure) Prior to describing the sterilization method using a pernitrate solution according to this embodiment, the properties of pernitrate (also referred to as PNA (Peroxynitric acid) as needed), which is known as one of the reactive oxygen species, will be described below.

[0015] Pernitrate in pernitrate solution (HOONO ２ ) generates HOO• through radical dissociation. This HOO• becomes the actual bactericidal factor. Here, HOO• and O ２ － - This means that it is in acid dissociation equilibrium with a dissociation constant pKa of 4.8. By lowering the pH of the pernitrate solution to 4.8 or below, ２ － The acid dissociation equilibrium between • and HOO• shifts towards HOO•, and therefore, the concentration of electrically neutral HOO•, which has high permeability into cells, increases, and the bactericidal power of the pernitrate solution increases.

[0016] Furthermore, pernitrate in pernitrate solution is chemically unstable and has a short half-life. Therefore, sterilization using pernitrate solution is highly safe because no pernitrate remains after the sterilization treatment. Figure 1 is a table showing the half-life (seconds) of pernitrate as a function of temperature and pH of pernitrate solution. As shown in Figure 1, it can be seen that the half-life becomes significantly shorter as the temperature and pH of the pernitrate solution increase. In other words, increasing the pH or temperature of the pernitrate solution causes the pernitrate to become inactive in a short time.

[0017] Pernitrate can be obtained by methods such as mixing nitrite and hydrogen peroxide, but the reaction pathway requires conditions of at least pH < 2, preferably pH ≈ 0. Therefore, the stock pernitrate solution obtained by chemical synthesis generally has a pH of around 0. At such an extremely low pH, as shown in Figure 1, the half-life is long even at room temperature, but the low pH often damages the object to be sterilized. Therefore, pernitrate solutions obtained by chemical synthesis are often adjusted to a pH suitable for sterilization (pH > 3, etc.) by mixing with a buffer solution before use. For example, at pH 3.5 and 20°C, the half-life is 204 seconds (about a few minutes). If the pH is > 4.8, the sterilizing power of the pernitrate solution weakens, and the half-life of pernitrate becomes significantly shorter. Beyond the half-life, the concentration of pernitrate decreases rapidly. Even if the object to be sterilized is immersed in such a pernitrate solution for a long time, effective sterilization cannot be achieved.

[0018] Therefore, conventional sterilization methods required maintaining an acidic pH of 4.8 or lower for the pernitrate solution to be effective. Consequently, it was difficult to apply conventional sterilization methods to objects that would be adversely affected by such acidic conditions.

[0019] Therefore, the present inventors have found that a sterilization method that supplies a pernitrate solution to a target object before the pernitrate is deactivated can perform sterilization more effectively than conventional methods, even when the pH of the pernitrate solution is 4.8 or higher. Specifically, this sterilization method involves supplying a liquid containing pernitrate (hereinafter simply referred to as pernitrate solution) and a diluent to a target object, and continuing to supply the pernitrate solution to the target object for at least the half-life of pernitrate in the state mixed with the diluent, thereby sterilizing the target object. Instead of preparing a weakly acidic (e.g., pH > 4.8) pernitrate solution in advance, by supplying a strongly acidic (e.g., pH ≤ 4.8) pernitrate solution to the target object together with the diluent, it is possible to make the pernitrate solution supplied to the target object weakly acidic while performing sterilization before the pernitrate is deactivated. Furthermore, by continuing to supply the pernitrate solution to the target object for at least the half-life of pernitrate, effective sterilization can be performed.

[0020] The inventors have discovered that effective sterilization can also be performed by the following sterilization method. This sterilization method involves mixing a pernitrate solution and a diluent immediately before supplying it to the target object, and then continuously supplying the mixed solution to the target object to sterilize it. Mixing the pernitrate solution and the diluent increases the pH of the pernitrate solution, and by performing this mixing immediately before supplying it to the target object, sterilization can be performed before the pernitrate becomes inactive.

[0021] The inventors have discovered that effective sterilization can also be performed by the following sterilization method. This sterilization method involves performing three steps in parallel: mixing a pernitrate solution with a diluent, supplying the mixed solution to the target object, and refreshing the mixed solution on the target object. In particular, the refreshing step allows for a continuous supply of freshly mixed pernitrate solution to the target object. That is, by continuously irradiating the target object with a weakly acidic pernitrate solution, sustained sterilization can be achieved even for treatment times exceeding the half-life.

[0022] The following describes specific embodiments for implementing this sterilization method.

[0023] [Embodiment 1] (Configuration of sterilization device 100) Figure 2 is a block diagram showing the schematic configuration of the sterilization device 100 according to Embodiment 1. As shown in Figure 2, the sterilization device 100 comprises a first container 11, a second container 12, a first pump 13, a second pump 14, a mixer 15, and a nozzle 16. The sterilization device 100 is a device for carrying out the sterilization method described above.

[0024] The first container 11 is a container for storing the pernitrate solution. The pernitrate solution is a liquid containing pernitrate. The second container 12 is a container for storing the buffer solution. The buffer solution is an example of the dilution liquid described above and is a liquid used to adjust the pH of the pernitrate solution. The buffer solution has a higher pH than the pernitrate solution stored in the first container 11. Hereinafter, the pernitrate solution before dilution with the buffer solution will be referred to as the strongly acidic PNA solution, and the pernitrate solution after dilution with the buffer solution will be referred to as the weakly acidic PNA solution, as necessary. The buffer solution may be any buffer solution such as acetic acid, citric acid, carbonic acid, phosphoric acid, boric acid, Tris, and Good's buffers in general (HEPES, PIPES, TES, Trisine, Glycineamide, etc.).

[0025] The first pump 13 and the second pump 14 are pumps that send the pernitrate solution stored in the first container 11 and the buffer solution stored in the second container 12 to the mixer 15, which will be described later. If it is necessary to maintain a constant mixing ratio of the pernitrate solution and the buffer solution in the mixer 15, the first pump 13 and the second pump 14 are pumps whose pumping operations are synchronized with each other in order to suppress the effects of pulsation. In the example shown in Figure 2, the sterilization device 100 includes a pump device 17 configured to synchronize the rotational movements of two tube pumps (the first pump 13 and the second pump 14).

[0026] Mixer 15 is a device for mixing the pernitrate solution and buffer solution delivered by the pump device 17. Mixer 15 mixes the pernitrate solution and buffer solution instantaneously (for example, within 1 second) inside. Mixer 15 can be any device that can instantaneously mix the pernitrate solution and buffer solution, such as a static mixer or a microreactor. Mixer 15 mixes the pernitrate solution and buffer solution to produce a weakly acidic PNA solution (mixture). The pH of the weakly acidic PNA solution is, for example, pH > 4.8.

[0027] The nozzle 16 discharges the weakly acidic PNA solution generated by the mixer 15 toward the object to be sterilized OB. The nozzle 16 continuously supplies the weakly acidic PNA solution, which is continuously sent from the pump device 17 through the mixer 15, to the object to be sterilized OB. The nozzle 16 is configured integrally with, for example, the static mixer, which is the mixer 15.

[0028] A few seconds after being supplied to the object to be sterilized OB, the deactivated weakly acidic PNA solution is removed from the object to be sterilized OB. For example, if the object to be sterilized OB is held in a container, the weakly acidic PNA solution is poured into the container and then drained. If the object to be sterilized OB is supported in the air or placed on a stand, the weakly acidic PNA solution is poured over the object to be sterilized OB. Specifically, the weakly acidic PNA solution is poured onto the object to be sterilized OB from the nozzle 16 and then flows down from the object to be sterilized OB.

[0029] (Example of operation of sterilization device 100) Figure 3 is a flowchart showing an example of the processing flow of the sterilization device 100. Referring to Figure 3, the method of sterilizing the object OB by the sterilization device 100 will be described below.

[0030] As shown in Figure 3, first, the sterilization device 100 performs processes S1 and S2 in parallel. In S1, the first pump 13 sends a strongly acidic PNA solution to the mixer 15. In S2, the second pump 14 sends a buffer solution to the mixer 15. As described above, the delivery operations of the first pump 13 and the second pump 14 are synchronized.

[0031] Next, the pernitrate solution and the buffer solution are mixed in the mixer 15 (S3). This generates a weakly acidic PNA solution (mixture). Immediately afterward, the weakly acidic PNA solution is discharged from the nozzle 16 towards the object to be sterilized OB (S4). The weakly acidic PNA solution is then supplied to the object to be sterilized OB (S5). The weakly acidic PNA solution supplied to the object to be sterilized OB is removed from the object to be sterilized OB after a few seconds (S6).

[0032] The sterilization device 100 is configured to supply the weakly acidic PNA solution to the object to be sterilized OB within a period of four times the half-life of pernitric acid in the weakly acidic PNA solution, after mixing the pernitric acid solution and the buffer solution. This ensures that the remaining pernitric acid at the time of supply is at least 1 / 16 of the amount before mixing, thereby achieving sufficient sterilization. Preferably, the elapsed time from mixing the pernitric acid solution and the buffer solution to supplying the weakly acidic PNA solution to the object to be sterilized OB should be within three times the half-life. This ensures that the remaining pernitric acid at the time of supply is at least 1 / 8 of the amount before mixing. More preferably, the elapsed time should be within the half-life. This ensures that the remaining pernitric acid at the time of supply is at least 1 / 2 of the amount before mixing.

[0033] Here, operations S1 to S6 are performed in parallel and continuously. That is, the sterilization device 100 continuously sends the pernitrate solution and buffer solution to the mixer 15 by the pump device 17, and continues to supply the mixed weakly acidic PNA solution to the object to be sterilized OB. In detail, the sterilization device 100 continues to supply the weakly acidic PNA solution to the object to be sterilized OB for at least half the lifespan of the pernitrate in the weakly acidic PNA solution. This makes it possible to sustain the sterilizing effect of the weakly acidic PNA solution for at least half the lifespan of the pernitrate. This cannot be achieved with a sterilization method that ends after supplying the weakly acidic PNA solution to the object to be sterilized OB only once.

[0034] Furthermore, in parallel with the supply of the weakly acidic PNA solution (pernitrate solution and buffer solution) to the object to be sterilized OB (S5), the weakly acidic PNA solution supplied to the object to be sterilized OB is removed from the object to be sterilized OB (S6). This ensures that the pernitrate solution, immediately after mixing, is continuously supplied to the object to be sterilized OB. In other words, the weakly acidic PNA solution in contact with the object to be sterilized OB is renewed over time.

[0035] (Effects) The half-life of conventional disinfectants (e.g., hypochlorous acid) is more than one year. Therefore, a solution with the pH adjusted in advance can be stored and used at any time. In other words, it is not necessary to prepare the solution immediately before supplying it to the object to be disinfected (OB). In contrast, the half-life of pernitric acid is remarkably short, and it is not possible to store pernitric acid in liquid form (i.e., at room temperature). Especially at high pH or high temperature, the half-life is short, so unlike conventional disinfectants, it is necessary to mix it with a buffer solution immediately before supplying it to the object to be disinfected (OB), and it is necessary to continue supplying it to the object to be disinfected (OB) for more than the half-life for effective disinfection.

[0036] With the above configuration, instead of preparing a weakly acidic PNA solution in advance, the pernitrate solution and buffer solution can be mixed immediately before supplying it to the object to be sterilized OB to generate a weakly acidic PNA solution. Therefore, the pernitrate solution, whose half-life is shortened by making it weakly acidic, can be quickly supplied to the object to be sterilized OB. Consequently, sterilization can be performed using the weakly acidic PNA solution before the pernitrate becomes inactive.

[0037] Furthermore, with the above configuration, the weakly acidic PNA solution can be continuously supplied to the object to be sterilized OB for at least the half-life of pernitric acid in the weakly acidic PNA solution. Therefore, in sterilization treatment using a weakly acidic PNA solution, the bactericidal effect of the weakly acidic PNA solution can be sustained for at least the half-life of pernitric acid. Consequently, even when using a weakly acidic PNA solution with a short half-life, effective sterilization treatment can be performed.

[0038] This shows that effective sterilization treatment is possible even when the pH of the pernitric acid solution is 4.8 or higher (weakly acidic). That is, it shows that the sterilization method according to the present embodiment can be applied to objects that are difficult to apply with conventional sterilization methods and are adversely affected by acidic conditions. For example, since meat turns white when exposed to a solution with a pH of 5 or lower, pernitric acid sterilization of meat was considered difficult. However, with the sterilization method according to the present embodiment, since sterilization treatment using a weakly acidic PNA solution is possible, meat can be a sterilization target. In addition, it can also be applied to seed sterilization and wound disinfection where sterilization treatment with a solution close to neutral pH is desired. Furthermore, by increasing the pH and making the half-life shorter, the biosafety can also be improved.

[0039] (Modification) The diluting liquid may be a heated liquid having a higher temperature than the strongly acidic PNA solution. By using the heated liquid as the diluting liquid, the temperature of the generated weakly acidic PNA solution can be increased, and the reactivity of the radicals can be improved. That is, rapid sterilization becomes possible. For example, warm water (water having a higher temperature than the strongly acidic PNA solution) may be used as the diluting liquid.

[0040] Also, the diluting liquid may be a dilute basic solution (for example, NaOH, KOH, or Ca(OH) ２ etc.).

[0041] Also, the sterilization device 100 may further mix dilution water in addition to the pernitric acid solution and the buffer solution. In this case, the pump device 17 further includes a pump that sends the dilution water to the mixer 15.

[0042] [Embodiment 2] Another embodiment of the present disclosure will be described below. For the sake of convenience of explanation, members having the same functions as the members described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

[0043] (Configuration of the sterilization device 100A) FIG. 4 is a block diagram showing a schematic configuration of the sterilization device 100A according to the second embodiment. As shown in FIG. 4, the sterilization device 100A includes a first container 11, a second container 12, a first pump 13, a second pump 14, a first nozzle 15A, and a second nozzle 16A. The sterilization device 100A is a device for implementing the above-described sterilization method.

[0044] In the second embodiment, the first pump 13 sends the strongly acidic PNA solution stored in the first container 11 to the first nozzle 15A. Further, the second pump 14 sends the buffer solution stored in the second container 12 to the second nozzle 16A.

[0045] The first nozzle 15A discharges the strongly acidic PNA solution toward the object to be sterilized OB. The second nozzle 16A discharges the buffer solution toward the object to be sterilized OB. The first nozzle 15A and the second nozzle 16A simultaneously supply the strongly acidic PNA solution and the buffer solution to the object to be sterilized OB, respectively. Specifically, the first nozzle 15A and the second nozzle 16A supply the strongly acidic PNA solution and the buffer solution to the object to be sterilized OB in a shower or mist form, respectively. The first nozzle 15A and the second nozzle 16A are, for example, ultrasonic nebulizers that discharge the solution in a mist form. Thereby, the strongly acidic PNA solution and the buffer solution are mixed in the air or on the surface of the object to be sterilized OB. That is, in the sterilization method according to the second embodiment, in terms of mixing the strongly acidic PNA solution and the buffer solution in the air or on the surface of the object to be sterilized OB, it is different from the sterilization method according to the first embodiment in which the strongly acidic PNA solution and the buffer solution are mixed by the mixer 15.

[0046] (Example of operation of the sterilization device 100A) FIG. 5 is a flowchart showing an example of the process flow of the sterilization device 100A. Referring to FIG. 5, the sterilization method of the object to be sterilized OB by the sterilization device 100A will be described below.

[0047] As shown in FIG. 5, first, the sterilization device 100A performs the processes of S11 and S12 in parallel. In S11, the strongly acidic PNA solution is sent to the first nozzle 15A by the first pump 13. In S12, the buffer solution is sent to the second nozzle 16A by the second pump 14.

[0048] After S11 and S12, the sterilization device 100A performs the processes of S13 and S14 in parallel. In S13, a strongly acidic PNA solution is discharged from the first nozzle 15A toward the object to be sterilized OB. In S14, a buffer solution is discharged from the second nozzle 16A toward the object to be sterilized OB. In S13 and S14, the strongly acidic PNA solution and the buffer solution are discharged in a shower-like or mist-like manner, respectively. The discharged strongly acidic PNA solution and buffer solution are mixed in the air or on the surface of the object to be sterilized OB (S15). This generates a weakly acidic PNA solution (mixture). Subsequently, the weakly acidic PNA solution is quickly supplied to the object to be sterilized OB (S16). The weakly acidic PNA solution supplied to the object to be sterilized OB is removed from the object to be sterilized OB after a few seconds (S17). Specifically, if the object to be sterilized OB is supported in the air, the weakly acidic PNA solution drips from the object to be sterilized OB. Alternatively, if the object to be sterilized (OB) is placed on a stand, the weakly acidic PNA solution will flow down from the object to be sterilized (OB).

[0049] Similar to Embodiment 1, the operations of S11 to S17 are performed in parallel (dynamically). Specifically, the sterilization device 100A continues to supply the strongly acidic PNA solution and the buffer solution to the object to be sterilized OB simultaneously for at least the half-life of pernitric acid in the state in which the strongly acidic PNA solution and the buffer solution are mixed. Also, S17 is performed in parallel with S16.

[0050] (Effects) With the above configuration, similar to Embodiment 1, a weakly acidic PNA solution can be produced by mixing the pernitrate solution and the buffer solution immediately before supplying it to the object to be sterilized OB. Therefore, sterilization can be performed using the weakly acidic PNA solution before the pernitrate is deactivated.

[0051] Furthermore, since the pernitrate solution and buffer solution are mixed in the air or on the surface of the object to be sterilized OB, the time elapsed from mixing the pernitrate solution and buffer solution to supplying the weakly acidic PNA solution to the object to be sterilized OB can be further shortened compared to Embodiment 1. Therefore, a weakly acidic PNA solution with a shorter half-life (i.e., higher pH and temperature) can be used.

[0052] [Embodiment 3] Another embodiment of the present disclosure is described below. For the sake of convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0053] (Configuration of sterilization device 100B) Figure 6 is a block diagram showing the schematic configuration of the sterilization device 100B according to Embodiment 3. As shown in Figure 6, the sterilization device 100B comprises a first container 11, a first pump 13, and a nozzle 16. The sterilization device 100B is a device for carrying out the sterilization method described above.

[0054] In Embodiment 3, after supplying the buffer solution to the object to be sterilized OB, the supply of the strongly acidic PNA solution to the object to be sterilized OB is started. Specifically, the buffer solution is applied to the object to be sterilized OB in advance, or the object to be sterilized OB is immersed in the buffer solution. The strongly acidic PNA solution is then supplied to the object to be sterilized OB in this manner.

[0055] The sterilization device 100B differs from Embodiment 1 in that it does not include a second container 12 for storing buffer solution, a second pump 14 for dispensing buffer solution, and a mixer 15 for mixing the strongly acidic PNA solution and the buffer solution. Specifically, the first pump 13 dispenses the strongly acidic PNA solution stored in the first container 11 to the nozzle 16. The nozzle 16 discharges the strongly acidic PNA solution toward the object to be sterilized OB, which has been supplied with buffer solution in advance. As a result, the strongly acidic PNA solution and the buffer solution are mixed on the surface of the object to be sterilized OB. In other words, the sterilization method according to Embodiment 3 differs from the sterilization methods according to Embodiments 1 and 2, which supply buffer solution to the object to be sterilized OB together with the pernitrate solution, in that the buffer solution is supplied to the object to be sterilized OB in advance.

[0056] (Example of operation of sterilization device 100B) Figure 7 is a flowchart showing an example of the processing flow of sterilization device 100B. Referring to Figure 7, the method of sterilizing the object OB by sterilization device 100B will be described below.

[0057] As shown in Figure 7, first, buffer solution is supplied to the object to be sterilized OB in advance (S21). Specifically, buffer solution is applied to the object to be sterilized OB in advance, or the object to be sterilized OB is immersed in buffer solution. Next, the first pump 13 delivers a strongly acidic PNA solution to the nozzle 16 (S22). Next, the strongly acidic PNA solution is discharged from the nozzle 16 toward the object to be sterilized OB to which the buffer solution has been supplied in advance (S23). The strongly acidic PNA solution discharged from the nozzle 16 is mixed with the buffer solution to produce a weakly acidic PNA solution (mixture) (S24). Subsequently, this weakly acidic PNA solution is quickly supplied to the object to be sterilized OB (S25).

[0058] The operations in S22 to S25 are performed in parallel (dynamically). Specifically, the sterilization device 100B continues to supply the strongly acidic PNA solution to the object to be sterilized OB for at least the half-life of pernitric acid in the state in which the strongly acidic PNA solution and the buffer solution are mixed.

[0059] (Effects) With the above configuration, a weakly acidic PNA solution can be generated on the surface of the object to be sterilized OB. Therefore, sterilization can be performed using the weakly acidic PNA solution before the pernitrate is deactivated. In addition, since the buffer solution is supplied to the object to be sterilized OB in advance, the configuration for continuously supplying the buffer solution to the object to be sterilized OB can be omitted.

[0060] [Evaluation of sterilization effect] The number of viable bacteria to be sterilized was measured when sterilization treatment was carried out using PNA solutions produced by the methods described in Examples and Comparative Examples 1 to 3. Figure 8 is a graph showing the change in the number of viable bacteria in Examples and Comparative Examples 1 to 3. In the graph of Figure 8, the vertical axis is the logarithmically transformed value of the number of viable bacteria [Log(CFU / sample)], and the horizontal axis is the treatment time [seconds].

[0061] The final pH of the weakly acidic PNA solution used for sterilization was 6.0, the concentration was 0.9 mM, and the temperature was 18.5°C. In this case, the half-life of pernitric acid in the weakly acidic PNA solution was approximately 4.2 seconds. The target of sterilization was a carrier (SUS disk) coated with bacterial spores extracted from a biological indicator (HMV-091, manufactured by Mesalabs).

[0062] In the examples, a weakly acidic PNA solution was provided to the object to be sterilized using the sterilization method shown in Embodiment 1. Specifically, a strongly acidic PNA solution and a buffer solution were pumped using a tube pump, then mixed with a static mixer, and the mixture was continuously supplied to the object to be sterilized in the container. In Comparative Example 1, the object to be sterilized was immersed in the buffer solution in the container, and then the strongly acidic PNA solution was added to the container and mixed. In Comparative Example 2, the buffer solution and the strongly acidic PNA solution were added to the container and mixed, and then the object to be sterilized was added and mixed immediately afterward. In Comparative Example 3, a fixed amount of the mixture produced by the method shown in Embodiment 1 was added to the object to be sterilized in the container all at once (only once).

[0063] As can be seen from Figure 8, in Comparative Examples 1 to 3, since only a fixed amount of weakly acidic PNA solution is supplied to the target for sterilization, the sterilization effect is obtained for a maximum of about four times the half-life of the weakly acidic PNA solution (about ten seconds). In fact, in Comparative Examples 1 to 3, the number of viable bacteria hardly decreased even after the half-life had elapsed. In contrast, the Example employs a sterilization method that continuously supplies weakly acidic PNA solution, so a continuous sterilization effect can be achieved regardless of the half-life. In fact, in the Example, the number of viable bacteria decreased with the treatment time, and the number of viable bacteria decreased to below the detection limit.

[0064] [Relationship between PNA solution temperature and bactericidal effect] The number of viable cells was measured when bactericidal treatment was performed on bacterial suspensions of E. coli (vegetative cells) and B. subtilis (spores) using weakly acidic PNA solutions at various temperatures. Figure 9 is a graph showing the change in the number of viable cells of E. coli. Figure 10 is a graph showing the change in the number of viable cells of B. subtilis. In the graphs of Figures 9 and 10, the vertical axis is the logarithmic value of the number of viable cells [Log(CFU / mL)], and the horizontal axis is the exposure time [seconds]. The exposure time is the time during which the acidic PNA solution was continuously supplied to E. coli and B. subtilis.

[0065] In this measurement, sterilization was performed using a bacterial suspension to evaluate the temperature dependence of sterilization. Sterilization experiments were conducted at a constant temperature by mixing a buffer solution and the bacterial suspension, adjusting the temperature beforehand, and then adding a small amount of stock PNA solution. Experiments were conducted with specified exposure times by adding a scavenger that rapidly eliminates the bactericidal activity of pernitrate at appropriate intervals. The pH of the acidic PNA solution was set to 3.5. The PNA concentrations supplied to E. coli and B. subtilis were ultimately 0.5 mM and 2.2 mM, respectively, resulting in acidic PNA solutions.

[0066] As shown in Figures 9 and 10, the reaction rate (bactericidal power) increased as the temperature rose, regardless of whether E. coli (vegetative cells) or B. subtilis (spores) was the target of sterilization. Therefore, it can be seen that more effective sterilization can be achieved by using a high-temperature, weakly acidic PNA solution. This indicates that the sterilization method of Embodiment 1, which can achieve a sustained bactericidal effect regardless of the half-life, can be more effective by using a high-temperature, weakly acidic PNA solution with a short half-life.

[0067] Furthermore, the data shown in Figures 9 and 10 closely match a pseudo-first-order reaction model based on the Arrhenius plot. Therefore, it was verified that sterilization treatment by chemical reaction of a weakly acidic PNA solution, i.e., sterilization treatment whose sterilizing power depends on temperature, was performed. [Summary]

[0068] A sterilization method according to Embodiment 1 of the present disclosure involves supplying a liquid containing pernitrate and a diluent to a target object, and sterilizing the target object by continuing to supply the liquid containing pernitrate to the target object for at least the half-life of the pernitrate in the state mixed with the diluent.

[0069] A sterilization method according to aspect 2 of the present disclosure involves mixing a liquid containing pernitrate and a diluent immediately before supplying it to the object, and sterilizing the object by continuously supplying the mixed solution of the pernitrate-containing liquid and the diluent to the object.

[0070] A sterilization method according to aspect 3 of this disclosure involves simultaneously mixing a liquid containing pernitrate with a diluent, supplying the mixed liquid to an object, and refreshing the mixed liquid in the object.

[0071] In the sterilization method according to aspect 4 of the present disclosure, in any of aspects 1 to 3 above, the liquid containing the pernitrate and the diluent liquid may be continuously supplied to the object for a period of time equal to or greater than the half-life of the pernitrate in the state in which it is mixed with the diluent liquid.

[0072] In the sterilization method according to aspect 5 of the present disclosure, the supply of the liquid containing pernitrate and the diluent to the target object and the removal of the liquid containing pernitrate and the diluent from the target object that have been supplied to the target object may be carried out in parallel, in aspect 4 above.

[0073] In the sterilization method according to embodiment 6 of the present disclosure, in any of embodiments 1 to 5 above, a mixture obtained by mixing the liquid containing the pernitrate and the diluent liquid may be continuously supplied to the object for a period of time equal to or longer than the half-life of the pernitrate in the mixture.

[0074] The sterilization method according to embodiment 7 of the present disclosure may be mixed in the air or on the surface of the object by supplying the liquid containing pernitrate and the diluent liquid to the object in any of embodiments 1 to 5 above in a shower-like or mist-like manner.

[0075] In the sterilization method according to embodiment 8 of the present disclosure, in any of embodiments 1 to 5 above, the supply of the liquid containing the pernitric acid to the object may be started after the dilution liquid has been supplied to the object.

[0076] In the sterilization method according to embodiment 9 of the present disclosure, in any of embodiments 1 to 8, the dilution liquid may be a buffer solution with a pH higher than that of the liquid containing pernitric acid.

[0077] In the sterilization method according to embodiment 10 of the present disclosure, in any of embodiments 1 to 8 above, the dilution liquid may be a heated liquid with a temperature higher than the liquid containing pernitric acid.

[0078] In the sterilization method according to embodiment 11 of the present disclosure, in any of embodiments 1 to 10, the pH of the liquid containing the pernitric acid in the state mixed with the diluent liquid may be pH > 4.8.

[0079] In the sterilization method according to embodiment 12 of this disclosure, in embodiment 2, after mixing the liquid containing the pernitrate with the diluent, the mixture may be supplied to the object within a period of four times the half-life of the pernitrate in the mixture.

[0080] A sterilization apparatus according to embodiment 13 of the present disclosure comprises: pumps for dispensing a liquid containing pernitrate and a diluent liquid, respectively; a mixer for mixing the liquid containing pernitrate and the diluent liquid; and a nozzle for continuously supplying the mixture obtained by mixing the liquid containing pernitrate and the diluent liquid to the target object for a period of time equal to or longer than the half-life of the pernitrate in the mixture.

[0081] A sterilization apparatus according to embodiment 14 of the present disclosure comprises a pump that dispenses a liquid containing pernitrate and a diluent, respectively, and a first nozzle and a second nozzle that simultaneously supply the liquid containing pernitrate and the diluent to an object for a period of time equal to or greater than the half-life of the pernitrate in the state in which it is mixed with the diluent.

[0082] With the above configuration, the range of targets for sterilization using pernitrate solution can be expanded. Such effects contribute, for example, to achieving United Nations Sustainable Development Goals (SDGs) Goal 2, "Zero Hunger," and Goal 3, "Good Health and Well-being."

[0083] [Additional Notes] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure.

[0084] 100, 100A, 100B Sterilization device 11 First container 12 Second container 13 First pump 14 Second pump 15 Mixer 16 Nozzle 17 Pumping device 15A First nozzle 16A Second nozzle

Claims

1. A sterilization method for sterilizing an object by supplying a liquid containing pernitric acid and a diluent to the object, and continuing to supply the liquid containing pernitric acid to the object for at least half the lifespan of the pernitric acid in the mixed state with the diluent.

2. A sterilization method in which a liquid containing pernitric acid and a diluent are mixed immediately before being supplied to the object, and the mixture of the pernitric acid-containing liquid and the diluent is continuously supplied to the object to sterilize it.

3. A sterilization method comprising simultaneously performing the following steps: mixing a liquid containing pernitric acid with a diluent; supplying the mixture obtained by mixing the liquid containing pernitric acid with the diluent to an object; and refreshing the mixture in the object.

4. The sterilization method according to claim 1, wherein the liquid containing the pernitric acid and the diluent liquid are continuously supplied to the object for a period of time equal to or greater than the half-life of the pernitric acid in the state in which it is mixed with the diluent liquid.

5. The sterilization method according to claim 4, wherein the supply of the liquid containing pernitric acid and the diluent liquid to the target object and the removal of the liquid containing pernitric acid and the diluent liquid supplied to the target object are carried out in parallel.

6. The sterilization method according to claim 1, wherein the mixture obtained by mixing the liquid containing pernitric acid with the diluent liquid is continuously supplied to the object for a period of time equal to or longer than the half-life of the pernitric acid in the mixture.

7. The sterilization method according to claim 1, wherein the liquid containing pernitric acid and the diluent liquid are supplied to the object in a shower-like or mist-like manner, thereby mixing the liquid containing pernitric acid and the diluent liquid in the air or on the surface of the object.

8. The sterilization method according to claim 1, wherein after supplying the dilution liquid to the object, the supply of the liquid containing the pernitric acid to the object is started.

9. The sterilization method according to any one of claims 1 to 8, wherein the dilution liquid is a buffer solution with a pH higher than that of the liquid containing pernitric acid.

10. The sterilization method according to any one of claims 1 to 8, wherein the dilution liquid is a heated liquid with a temperature higher than the liquid containing pernitric acid.

11. The sterilization method according to any one of claims 1 to 8, wherein the pH of the liquid containing pernitric acid when mixed with the diluent is pH > 4.

8.

12. The sterilization method according to claim 2, wherein after mixing the liquid containing pernitric acid with the diluent, the mixture is supplied to the object within a period of four times the half-life of the pernitric acid in the mixture.

13. A sterilization device comprising: pumps for dispensing a liquid containing pernitric acid and a diluent; a mixer for mixing the liquid containing pernitric acid and the diluent; and a nozzle for continuously supplying the mixture of the liquid containing pernitric acid and the diluent to an object for a period of time equal to or greater than the half-life of the pernitric acid in the mixture.

14. A sterilization device comprising: pumps for dispensing a liquid containing pernitric acid and a diluent, respectively; and a first nozzle and a second nozzle for simultaneously supplying the liquid containing pernitric acid and the diluent to an object for a period of time equal to or greater than the half-life of the pernitric acid in the mixed state with the diluent.

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