JP2011212573A - Method and apparatus for sterilizing liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adequately sterilize a liquid with ultraviolet rays even if the liquid has low ultraviolet transmittance.SOLUTION: In an apparatus 3 for sterilizing a liquid, which includes an ultraviolet irradiator 11 for radiating ultraviolet rays and irradiates the liquid with the ultraviolet rays to sterilize it, a slit nozzle 13 is provided as a thickness limiting part for limiting the thickness of the liquid in the place irradiated with the ultraviolet rays to a predetermined thickness.

Description

  The present invention relates to a technique for sterilizing a liquid with ultraviolet rays, and particularly to an ultraviolet sterilization technique suitable for use in sterilizing drinking water.

  Conventionally, as a method for sterilizing drinking water, a method is known in which drinking water is passed through a flow path tube made of an ultraviolet transmitting material, and the flow path pipe is irradiated with ultraviolet rays from the outside to be sterilized (for example, Patent Document 1). reference).

JP 2002-262837 A

However, in the case of drinking water having a high ultraviolet light absorbance and a low ultraviolet light transmittance, the ultraviolet light does not reach the deep part of the flow path tube and the sterilization treatment becomes insufficient. For this reason, ultraviolet sterilization technology cannot be used for sterilization of drinking water having poor ultraviolet transmittance, and heat sterilization during the manufacturing process is generally used. However, in the heat sterilization, there is a problem that discoloration or alteration occurs in the drinking water and the flavor of the drinking water is impaired.
This invention is made | formed in view of the situation mentioned above, and it aims at providing the liquid sterilization method and liquid sterilizer which can fully sterilize even if it is a liquid with a high light absorbency.

  In order to achieve the above object, the present invention is characterized in that, in a liquid sterilization method for sterilizing a liquid by irradiating the liquid with ultraviolet rays, the thickness of the liquid at the portion irradiated with the ultraviolet rays is limited to a predetermined thickness. .

  In the liquid sterilization method, the present invention corrects the ultraviolet irradiation amount necessary for obtaining a desired sterilization ability based on the difference between the inactivation rate constant and the reaction rate constant due to the difference in the absorbance of the liquid. The liquid is sterilized by irradiating with an ultraviolet ray having a corrected ultraviolet ray dose.

  In the liquid sterilization method, the present invention limits the thickness of the portion where the thickness is limited to a thickness in which the decrease in the survival rate of the microorganism to be sterilized is not saturated with respect to the increase in the ultraviolet irradiation amount and the ultraviolet irradiation time. It is characterized by that.

  The present invention also includes an ultraviolet irradiator that irradiates ultraviolet rays, and in a liquid sterilization apparatus that sterilizes the liquid by irradiating the ultraviolet rays, a thickness that limits the thickness of the liquid at a location irradiated with the ultraviolet rays to a predetermined thickness A limiting unit is provided.

  According to the present invention, the portion where the thickness of the liquid is limited to a predetermined thickness is sterilized by irradiating with ultraviolet rays, so that a high ultraviolet illuminance is achieved in the deep part of the liquid and not only the liquid surface but also the deep part is sufficiently sterilized with ultraviolet rays. Can do.

It is a figure which shows typically the structure of a liquid sterilization system. It is a top view of an ultraviolet irradiation device. It is a figure which shows the result of having investigated the mode of attenuation | damping when irradiating a 1 cm-thick liquid sample with an ultraviolet-ray about four types of liquid samples from which the ultraviolet-ray light absorbency differs. It is a figure which shows the result of having experimented by changing illumination intensity ratio _IE , and the relationship between the survival rate S of E. coli phage MS2 after irradiating ultraviolet light to the liquid sample which mixed E. coli phage MS2, and ultraviolet irradiation amount H. a) ~ (C) is the absorbance a of the liquid sample, respectively, 1.0 cm ^-1, 2.0 cm ^-1, which shows the case of 3.0 cm ^-1. It is a figure which shows the result of having experimented by changing illuminance ratio _IE about the relationship between the survival rate S of Escherichia coli phage MS2, and ultraviolet irradiation time t (sec: second), (A)-(C) are liquid The cases where the absorbance A of the sample is 1.0 cm ⁻¹ , 2.0 cm ⁻¹ , and 3.0 cm ⁻¹ are shown. It is a figure which shows the relationship between the ultraviolet irradiation amount H (mJ / cm < ² >) and the survival rate S for every illumination intensity ratio _IE . It is a figure which shows the relationship between the reaction rate constant Dt calculated | required from the experimental result of FIGS. It is a figure which shows the relationship between reaction rate constant Dt / inactivation rate constant Di, and illuminance ratio _IE for every light absorbency A. It is a figure which shows the relationship between the inclination coefficient Z and the light absorbency A. FIG. It is a figure which shows typically the thickness of the drinking water made into a film | membrane form with the slit nozzle. It is a figure which shows the modification of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram schematically showing a configuration of a liquid sterilization system 1 according to the present embodiment.
The liquid sterilization system 1 is a system that sufficiently sterilizes drinking water having a high ultraviolet absorbance, and includes a liquid sterilizer 3, an introduction pump 5, and a discharge pump 7, as shown in FIG. The introduction pump 5 is a pump that introduces the sterilization target drinking water stored in the tank 9 into the liquid sterilization apparatus 3, and the discharge pump 7 is a pump that discharges the drinking water after ultraviolet sterilization from the liquid sterilization apparatus 3. .

  The liquid sterilizer 3 includes a pair of ultraviolet irradiators 11 disposed facing each other across a flow path R of drinking water introduced by an introduction pump 5 and a pair of ultraviolet irradiators provided in the flow path R. 11 and a receiving tank 15 for receiving drinking water that has been sterilized with ultraviolet rays through the ultraviolet irradiator 11. Drinking water stored in the receiving tank 15 is led out from the liquid sterilizer 3 by the discharge pump 7.

The ultraviolet irradiator 11 includes an ultraviolet lamp 17 and a reflection plate 19. The ultraviolet lamp 17 is a straight tube lamp that irradiates light with a wavelength of 254 nm, and is provided horizontally in a posture extending in the depth direction of the ultraviolet irradiator 11 as shown in FIG.
The slit nozzle 13 functions as a thickness limiting portion that limits the thickness of the portion irradiated with ultraviolet rays by spraying drinking water in the form of a film. The slit nozzle 13 extends over a predetermined slit length in the depth direction of the liquid sterilizer 3, and a plurality of inlets 21 serving as drinking water inlets are provided on the upper surface at a constant pitch. 5 is connected. A slit 23 (see FIG. 1) having a predetermined slit width is provided as a nozzle portion at the lower end of the slit nozzle 13, and the drinking water introduced from the inlet 21 has a film thickness corresponding to the slit width of the slit 23. The liquid film is ejected as a liquid film having a length corresponding to the slit length.

  In this way, since drinking water is formed into a film and passed between the ultraviolet irradiators 11, the amount of treatment to be sterilized with ultraviolet rays per unit time is reduced as it is, but a liquid film over a predetermined slit length is generated, and the liquid Since the ultraviolet lamp 17 is extended along the film, this compensates for a reduction in the processing amount and does not hinder productivity.

Next, liquid sterilization by ultraviolet irradiation will be described.
In liquid sterilization by ultraviolet irradiation, since very small microorganisms are targeted, it can be assumed that light that the liquid has not absorbed, that is, light that has passed through the liquid has been irradiated to the microorganism. In general, opaque liquids such as milk and fruit juice and drinking water in which liquids absorb ultraviolet rays such as liquor do not transmit ultraviolet rays, so sterilization and disinfection by ultraviolet irradiation are very inefficient.

More specifically, when the absorbance of drinking water that is compatible with ultraviolet treatment is A (cm ⁻¹ ), the incident light illuminance I ₀ (mW / cm ² ), which is the ultraviolet illuminance at the time of incidence, is a point at a distance d (cm). Then, it attenuates to the ultraviolet illuminance I _d (mW / cm ² ). This attenuation amount can be expressed by the following equation (1) according to the Lambert Beer rule.
I _d = I ₀ × 10 ^−Ad (1)

FIG. 3 is a diagram showing the results of examining four types of liquid samples having different absorbances A of ultraviolet rays when the liquid sample having a thickness of 1 cm is irradiated with ultraviolet rays.
This figure shows a phenomenon in which ultraviolet rays attenuate as the distance d from the liquid surface, which is the ultraviolet irradiation surface, increases. In particular, when the absorbance A is as small as A = 0.01 cm ⁻¹ , the ultraviolet illuminance is large even at the farthest point (distance d = 1 cm) of the liquid sample, and is almost the same as the illuminance upon incidence. On the other hand, when the absorbance A is as large as A = 1 cm ⁻¹ , the ultraviolet illuminance attenuates to about half of the incident light at a distance d = 0.3 cm from the ultraviolet irradiation surface. This also shows that sterilization and disinfection by ultraviolet irradiation are not suitable for a liquid having a large absorbance A.
In contrast, in the present embodiment, as described above, drinking water having a high absorbance A is formed by limiting the thickness of the portion irradiated with ultraviolet rays by spraying drinking water in the form of a film by the slit nozzle 13. Even in this case, high UV illuminance can be achieved at the farthest point, and UV sterilization and disinfection can be performed.

FIG. 4 shows the relationship between the survival rate S of Escherichia coli phage MS2 and the amount of ultraviolet irradiation H (mJ / cm ² ) from the surface of the liquid sample when the liquid sample mixed with E. coli phage MS2 is irradiated with ultraviolet rays. It is a figure which shows the result of having experimented by varying distance d (namely, thickness) to a far point, and FIG. 4 (A)-FIG.4 (C) are the light absorbency A of a liquid sample, respectively 1.0 cm < ^-1 >. , 2.0 cm ⁻¹ , 3.0 cm ⁻¹ .
FIG. 5 shows the relationship between the survival rate S of Escherichia coli phage MS2 and the ultraviolet irradiation time t (sec: second) by experimenting with different distances d from the liquid surface to the farthest point of the liquid sample. a diagram, FIG. 5 (a) ~ FIG 5 (C) is the absorbance a of the liquid sample, respectively, 1.0 cm ^-1, 2.0 cm ^-1, which shows the case of 3.0 cm ^-1.

In the following description, the incident light illuminance I ₀ (mW / cm ² ), which is the ultraviolet illuminance on the liquid surface of the liquid sample, and the emitted light illuminance, which is the ultraviolet illuminance at the measurement point of the water depth (distance) d from the liquid sample surface. The ratio of I _d (mW / cm ² ) will be referred to as the illuminance ratio I _E. This incident light illuminance I ₀ is obtained by measuring the ultraviolet intensity of the sample surface with a chemical dosimeter (potassium iodide solution). The ultraviolet irradiation amount H is obtained from the product of the average ultraviolet intensity in the sample obtained by correcting the incident light illuminance I ₀ with the absorbance A and the distance d and the ultraviolet irradiation time t.

When the incident light illuminance I ₀ is constant, the illuminance ratio I _E increases as the thickness increases and the distance d increases so that the amount of ultraviolet light absorbed by the liquid sample increases and the emitted light illuminance I _d decreases. It becomes small according to. In other words, when the illuminance ratio I _E decreases, since it reduces the emission light intensity I _d, bactericidal activity at this point is reduced. Therefore, as shown in FIGS. 4 and 5, the survival rate S increases as the illuminance ratio _IE decreases in common for all liquid samples having different absorbances A.

Further, when the illuminance ratio I _E is constant, the output light intensity I _d to become larger in accordance with the incident light intensity I _0, ultraviolet irradiation amount H of the incident light intensity I ₀ is large enough sterilizing effect is enhanced. Moreover, if the ultraviolet irradiation amount H is constant, the sterilization ability is enhanced as the ultraviolet irradiation time t becomes longer. Therefore, as shown in FIGS. 4 and 5, the survival rate S decreases as the ultraviolet ray irradiation amount H increases or the ultraviolet ray irradiation time t increases in common for all liquid samples having different absorbances A.
However, as shown in FIGS. 4 and 5, when the illuminance ratio _IE is 20% or less, unlike the above-described tendency, even if the ultraviolet irradiation amount H is increased or the ultraviolet irradiation time t is increased. In all absorbances A, the survival rate S varies, and a tendency to saturate at a relatively high order (approximately 10 ⁻² ) is observed.

That is, in the liquid sterilizer 3, when the illuminance ratio _IE is 20% or less, sufficient sterilization ability cannot be obtained by controlling the ultraviolet irradiation amount H and the ultraviolet irradiation time t of the ultraviolet irradiator 11.
Therefore, in the present embodiment, the thickness (distance d) of the liquid sample is limited to a thickness at which the illuminance ratio _IE is 20% or more, whereby the survival rate of microorganisms depends on the ultraviolet irradiation amount H and the ultraviolet irradiation time t. S is reduced and efficient sterilization is realized.

FIG. 6 is a diagram showing the relationship between the ultraviolet irradiation amount H (mJ / cm ² ) and the survival rate S for each illuminance ratio _IE . The data in the figure was measured under experimental conditions in which the absorbance A was increased to ¹ to 3 cm ⁻¹ while decreasing the water depth (distance d).
In the graph of the figure, the relationship between the ultraviolet irradiation amount H and the survival rate S was linearly approximated, and the reaction rate constant D _t (mJ / cm ² ) with respect to the ultraviolet irradiation amount H was determined from the slope. This reaction rate constant D _t indicates the amount of ultraviolet irradiation H required to inactivate E. coli phage MS2 by 90% under the experimental conditions of FIG. 6. In FIG. 6, “reaction rate constant D _t = ln ( 10) / tilt ". In the linear approximation in FIG. 6, data corresponding to tailing is excluded.

The survival rate S can be expressed by the average ultraviolet intensity in the sample in consideration of light attenuation with respect to the water depth (distance d) direction. The reason is that when the water depth (distance d) and the absorbance A are sufficiently small at I _d = I ₀ × 10 ^−Ad , that is, when the absorbance A is about 10 ⁻³ (cm ⁻¹ ), the absorbance is small. This is because the influence of A is considered negligible.
Ultraviolet irradiation dose H required for 90% inactivation of E. coli phage MS2 in an experiment using a sample having a small water depth (distance d) and a small absorbance A, for example, absorbance A = 10 ⁻³ (cm ⁻¹ ) as a reference sample The inactivation rate constant D _i is determined in advance, and the average ultraviolet ray amount is calculated again from the survival rate S using the inactivation rate constant D _i . The average ultraviolet ray amount thus calculated is defined as a converted equivalent ultraviolet ray amount RED (mJ / cm ² ). This equivalent equivalent ultraviolet ray amount RED is the ultraviolet ray irradiation amount H absorbed by the microorganism.
Then, in FIGS.
Survival rate S = exp (−average amount of ultraviolet light / reaction rate constant D _t ) (2)
ln (survival rate S) = − (average amount of ultraviolet rays / reaction rate constant D _t ) (3)
−ln (survival rate S) × inactivation rate constant D _i
= Reduced equivalent ultraviolet ray RED
= Reaction rate constant D _t × −ln (survival rate S) (4)
Is obtained.

FIG. 7 is a graph showing the relationship between the reaction rate constant Dt and the absorbance A obtained from the experimental results of FIGS.
Originally, light attenuates in the depth direction in accordance with the Lambert Beer rule. Therefore, if the illuminance ratio _IE is the same, the equivalent (ultracalculated) equivalent equivalent ultraviolet ray amount RED is obtained. Therefore, as shown in the relationship of the above equation (4), the inactivation rate constant D _i of the reference sample and the reaction rate constant D _t for the sample having a relatively large absorbance A are theoretically the same.
However, in practice, as shown in FIG. 7, the absorbance A is a tendency that the reaction rate constant D _t decreases observed with increasing large, the knowledge of difference occurs, and between the inactivation rate constant D _i The inventors obtained.

FIG. 8 is a diagram showing the relationship between the reaction rate constant D _t / inactivation rate constant D _i (hereinafter referred to as “ultraviolet ray irradiation amount ratio”) and the illuminance ratio _IE for each absorbance A. Note that 21.4 (mJ / cm ² ) is used as the experimental value of the inactivation rate constant Di of the reference sample.
According to FIG. 8, by approximation,
UV irradiation dose ratio = reaction rate constant D _t / inactivation rate constant D _i
= Z × I _E +1 (where Z is a function with absorbance A as a variable) (5)
Therefore, if the absorbance A is close to zero, that is, if the transmittance of the sample is very high, the ratio of the ultraviolet irradiation amount H gradually approaches 1.

When an approximate expression with the absorbance A as a variable is obtained for Z (slope coefficient), it is approximated by a quadratic equation as shown in FIG. (However, the intercept is zero.)
Z = 1.39 * 10 < ^-1 > * A < ² > + 2.26 * 10 < ^-1 > * A (6)

From the above, assuming that the required (irradiated) ultraviolet ray irradiation amount H is B (mJ / cm ² ), at least in the case of absorbance A ≦ 3 cm ⁻¹ , which is the experimental condition of this time, the actual irradiation is performed. The ultraviolet ray irradiation amount H is attenuated by the attenuation factor K with respect to the required ultraviolet ray irradiation amount B.
UV irradiation amount actually irradiated H = B × K (7)
The attenuation rate K is the same as the above-mentioned UV irradiation dose ratio and is expressed by a function of absorbance A.
Attenuation rate K = Z × I _E +1 (8)
Z = 1.39 * 10 < ^-1 > * A < ² > + 2.26 * 10 < ^-1 > * A (9)
It is.

Therefore, when the drinking water having an absorbance A of A = 2.5 cm ⁻¹ is sterilized at an illuminance ratio I _E = I _d / I ₀ = 0.4 (= 40%), the water depth (distance d) is: According to the formula (1), it is limited to d = 0.159 cm. Z = 1.43 is obtained according to equation (9), attenuation factor K = 1.57 is obtained according to equation (8), and if the amount of ultraviolet light irradiation B desired to be irradiated on the target is 40 mJ / cm ² , actual irradiation is required. The correction value of the necessary UV irradiation amount H is obtained as 62.9 mJ / cm ² according to the equation (7).

  Thus, according to this embodiment, since it is provided with the slit nozzle 13 as a thickness limiting portion that limits the thickness (distance d) of drinking water at a location irradiated with ultraviolet rays to a predetermined thickness, the deep portion of drinking water In this case, a high ultraviolet illuminance can be achieved, and not only the liquid surface but also the deep part can be sufficiently sterilized with ultraviolet rays. Thereby, since it is not necessary to sterilize drinking water by heat processing, flavor is not impaired by sterilization, and alteration by sterilization can be suppressed.

Further, according to the present embodiment, the ultraviolet irradiation amount B necessary for obtaining a desired sterilizing ability is set such that the difference between the inactivation rate constant D _i and the reaction rate constant D _t caused by the absorbance A of the drinking water to be sterilized. (Ie, based on the attenuation rate K in the above equation (7)), the ultraviolet irradiation amount B necessary to obtain a desired sterilizing ability is corrected, and the corrected ultraviolet irradiation amount H is converted into the drinking water. It was set as the structure which irradiates and sterilizes the location which restricted thickness.
Thereby, it can irradiate with sufficient ultraviolet irradiation amount B required in order to obtain desired sterilization ability to each drinking water from which the light absorbency A differs, and can fully sterilize.

Furthermore, according to this embodiment, since the thickness of the ultraviolet irradiation portion is limited so that the illuminance ratio _IE is 20% or more, the sterilization ability is not saturated with respect to the increase in the ultraviolet irradiation amount H, and the efficiency is high. Sterilization can be realized.
In addition, after the thickness is defined so that the sterilization ability is not saturated with respect to the increase in the ultraviolet irradiation amount H, the ultraviolet irradiation amount B necessary for obtaining the desired sterilizing ability is corrected based on the attenuation rate K. By irradiating, the desired sterilizing ability can be reliably obtained with the corrected ultraviolet ray irradiation amount H without causing saturation in the sterilizing ability.

In the liquid sterilization apparatus 3 of the present embodiment, as shown in FIG. 1, the emitted light illuminance I _d when determining the illuminance ratio _IE is used to sterilize by irradiating ultraviolet rays from both sides of the film-like drinking water. As the value of, not the farthest point from the liquid surface but the value at the center point C in the thickness direction is used as shown in the schematic diagram of FIG. And this drinking water can fully be sterilized by irradiating the ultraviolet-ray of the ultraviolet irradiation amount H calculated | required as mentioned above from the both sides of the drinking water made into the film form.
Moreover, according to this embodiment, since ultraviolet rays are irradiated from both sides of the drinking water, sterilization unevenness can be reliably suppressed.

  The above-described embodiment is merely an aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

For example, in the above-described embodiment, the thickness of the drinking water at the location where the slit nozzle 13 irradiates ultraviolet rays is limited. However, as a means for limiting the thickness, any means can be used as long as the illuminance ratio _IE is 20% or more, and any means can be used, for example, a large number of thin tubes. May be arranged in parallel and irradiated with ultraviolet rays while passing drinking water through each tube.
Further, for example, as shown in FIG. 11, a cylindrical lamp sleeve 130 formed of an ultraviolet transmitting material containing a straight tube type ultraviolet lamp 117 is coaxially placed in a flow pipe 132 through which drinking water flows, and the lamp It is good also as a structure which restrict | limits the thickness of the drinking water of the location irradiated with the ultraviolet lamp 117 by distribute | circulating drinking water to the clearance gap between the sleeve 130 and the distribution pipe 132. FIG. According to such a configuration, by connecting a plurality of flow tubes 132 containing the lamp sleeves 130 in series, the ultraviolet irradiation time t to the drinking water can be extended, and the sterilizing ability can be easily increased.

Further, for example, in the above-described embodiment, the case of sterilizing by irradiating ultraviolet rays from both sides of the drinking water has been illustrated, but the present invention is not limited thereto, and the configuration may be such that the ultraviolet rays are irradiated from one side of the drinking water.
Moreover, although the case where ultraviolet-ray sterilization of the drinking water with a large light absorbency A was illustrated in embodiment mentioned above, it cannot be overemphasized that this invention can be used for the ultraviolet sterilization of not only a drinking water but arbitrary liquids.

DESCRIPTION OF SYMBOLS 1 Liquid sterilization system 3 Liquid sterilizer 11 Ultraviolet irradiation device 13 Slit nozzle (thickness restriction part)
17, 117 UV lamp 19 Reflector d Distance (thickness)
A absorbance S survival rate D _i inactivation rate constant D _t rate constant H UV irradiation amount K attenuation factor (= Dt / Di)
I _E Illuminance ratio I _d Output light illuminance I ₀ Incident light illuminance d Distance t UV irradiation time

Claims (4)

In a liquid sterilization method of sterilizing a liquid by irradiating with ultraviolet rays,
A liquid sterilization method, characterized in that the thickness of the liquid at the place irradiated with the ultraviolet rays is limited to a predetermined thickness.   The amount of UV irradiation necessary to obtain the desired sterilizing ability is corrected based on the difference between the inactivation rate constant and the reaction rate constant caused by the difference in absorbance of the liquid, and the corrected amount of UV irradiation is irradiated. The liquid sterilization method according to claim 1, wherein the liquid is sterilized.   3. The liquid sterilization method according to claim 2, wherein the thickness of the portion where the thickness is limited is limited to a thickness in which the decrease in the survival rate of the microorganisms to be sterilized is not saturated with respect to the increase in the amount of ultraviolet irradiation. . In a liquid sterilizer equipped with an ultraviolet irradiator that irradiates ultraviolet rays, and sterilizing the liquid by irradiating the ultraviolet rays,
A liquid sterilization apparatus comprising: a thickness limiting unit that limits the thickness of the liquid at a location irradiated with the ultraviolet rays to a predetermined thickness.

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