JP3105024B2 - How to control microbes in water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for electrochemically controlling microorganisms in water.

[0002]

2. Description of the Related Art In an oligotrophic environment such as distilled water, seawater, or tap water, microorganisms grow at the interface between a liquid layer and a solid layer. This is because microorganisms use the organic matter as a nutrient because the dilute organic matter present in the water is adsorbed and concentrated at such an interface. The microorganisms proliferating on the solid surface diffuse again into water to cause water pollution or the like, or secrete a slime-like substance while adsorbed on the solid surface to pollute the surface. In particular, a large number of microorganisms are present in seawater, causing problems such as showing pathogenicity and attaching to marine structures. In addition, since marine structures are constantly in contact with enormous amounts of seawater, the propagation of various marine organisms starting from the attachment of microorganisms is a problem on the surface. The mechanism by which these problems occur is as follows. First, adherent Gram-negative bacteria adsorb to the surface and secrete large amounts of slime-like substances. Subsequently, other microorganisms gather in the slime layer and multiply to form a microorganism coating.
In addition, large organisms gradually grow on this microbial layer, and eventually the large organisms cover the surface.

[0003] Conventionally, such microorganisms adhere to and proliferate on the surface of the underwater structure, for example, by injecting a bactericide such as chlorine gas or hypochlorous acid, or coating the surface with an organotin compound or the like. In recent years, a method of processing using a chemical substance has been performed. However, in these methods, the used chemicals diffuse and remain in the water,
There was a problem of residual toxicity.

[0004]

SUMMARY OF THE INVENTION The present inventor has made intensive studies to develop means which can effectively prevent such biological contamination without using chemical substances which cause residual toxicity. As a result, it has been found that the microorganisms adsorbed on the surface of the underwater structure in the initial stage are successively electrochemically sterilized and then detached from the surface, whereby the adhesion and growth of the microorganisms can be controlled. The present invention is based on such findings.

[0005]

Accordingly, the present invention provides a method of (1) applying +0 to +1.5 Vvs.
Applying a positive potential of SCE to adsorb and sterilize microorganisms in water on the surface of the conductive substrate; (2)
The conductive substrate may have -0 to -0.4 Vvs. And removing a sterilized microorganism adsorbed on the surface of the conductive substrate by applying a negative potential of SCE .

The conductive substrate used in the method of the present invention may be entirely made of a conductive material, but it is sufficient that at least its surface (or a part of the surface immersed in water) is conductive. The shape of the conductive substrate is not particularly limited, but is preferably a substrate having a large surface area, capable of efficiently adsorbing microorganisms in water, making direct contact, and applying a potential. Preferred embodiments of the conductive substrate used in the method of the present invention include, for example, a sheet-like substrate immersed in a microorganism-containing liquid to be treated or a substrate in which the underwater surface of an underwater structure or ship is composed of the above-described conductive substrate. be able to.

[0007] The material of the conductive substrate is not particularly limited, either, but it has good plasticity and moldability capable of forming a conductive surface layer on a wide surface of a sheet-like substrate, an underwater structure, a ship or the like. Preferably, for example, a conductive substrate formed by mixing a conductive material (eg, graphite, carbon, platinum, or a conductive substance) with a binder polymer and molding as it is, or an underwater structure using a conductive material-containing coating composition A conductive film formed on the object surface is preferred. Examples of the binder polymer include a silicone resin, a vinyl acetate resin, a mixture of a vinyl chloride resin and a polyurethane resin, a styrene-butadiene rubber, a urethane resin, a chloroprene rubber, and an epoxy resin. Among them, the silicone resin is preferable. A conductive polymer (for example, polyaniline) can be added together with the binder polymer to lower the resistance value.

When a positive potential is applied to a conductive substrate in water containing microorganisms, the microorganisms in water can be adsorbed on the substrate surface. Further, the positive potential applied to the substrate has an action of electrochemically sterilizing microorganisms adsorbed and in contact with the substrate surface. That is, the microorganisms are adsorbed on the substrate surface by the positive potential and are sterilized on the surface. The applied positive potential is between +0 and +1.5 V vs. SCE, preferably +0.5 to +1.5 V vs. SCE. When the applied potential is +0 V vs. If it is below SCE, the microorganisms cannot be adsorbed on the substrate and sterilized, and +1.5 V vs. Exceeding the SCE is undesirable because water and dissolved salts are electrolyzed to generate toxic gases, and metals are deposited on the surface of the conductive substrate.

The step of adsorbing and sterilizing microorganisms, which comprises applying a positive potential to the conductive substrate, varies depending on the concentration and type of microorganisms present in the water, the flow rate or the temperature, but is not more than 6 hours, preferably 5 to 30 minutes. It is preferred to do so. If the potential application time is longer than 6 hours, other microorganisms will be adsorbed on the microorganisms sterilized on the substrate. Since the microorganisms adsorbed later are not in direct contact with the conductive substrate, they are not subjected to the electrochemical sterilization action due to the positive potential. Therefore, living microorganisms are successively adsorbed on the substrate surface,
Even if a step of removing microorganisms to which a negative potential is applied is performed, surface microorganisms cannot be removed, and the substrate is contaminated.

Subsequently, when a negative potential is applied to the conductive substrate, microorganisms adsorbed on the substrate surface can be eliminated. The negative potential to be applied is −0 to −0.4 V vs. S
CE, preferably -0.1 to -0.2 V vs. SCE. When the applied potential is −0 V vs. Above SCE, the microorganisms cannot be detached from the substrate, and -0.4 V vs. SCE.
If it is lower than SCE, the pH increases, which is not preferable. The step of removing microorganisms by applying a negative potential varies depending on the amount and type of microorganisms adhering to the surface, but is preferably performed for 30 seconds to 30 minutes, preferably for 1 minute to 5 minutes. . If the time is shorter than 30 seconds, the disinfected microorganisms will not be sufficiently detached, and if the next step of adsorption and disinfection of microorganisms applying a positive potential is performed, other microorganisms will be adsorbed on the disinfected microorganisms. If the time is longer than 30 minutes, the liquid to be treated cannot be effectively sterilized.

In the method of the present invention, it is preferable to repeat the above-mentioned adsorption and sterilization step of microorganisms and desorption step. When performing a process of repeating the cycle consisting of the adsorption sterilization step and the desorption step for the microorganism-containing water in the closed container, the microorganisms contained therein are successively adsorbed on the substrate surface and sterilized. Is eventually eliminated, so that virtually all microorganisms can be finally killed. Also,
When the method of the present invention is used in an open system such as a structure in seawater, the above-described cycle can be repeatedly performed to permanently prevent the structure surface from being contaminated.

In the method of the present invention, the potential applied to the conductive substrate is controlled by using the conductive substrate as a working electrode and using an appropriate counter electrode, reference electrode and potentiostat for the working electrode of the conductive substrate. It is necessary. The counter electrode, reference electrode and potentiostat that can be used are not particularly limited as long as a predetermined potential can be applied to the surface of the conductive substrate.

The water which can be treated by the method of the present invention is not particularly limited as long as it contains microorganisms. Examples of the water include seawater, river water, lake water, tap water and drinking water. is there. The target microorganism is not particularly limited as long as it is a microorganism existing in the water, and includes bacteria, filamentous fungi, yeast, deformed fungi, algae, protozoa, and the like.

[0014]

EXAMPLES The present invention will be described below in more detail with reference to examples, but these examples do not limit the scope of the present invention.

In the following examples, the apparatus shown in FIG. 1 was used as a sterilization apparatus. In this apparatus, a conductive resin plate electrode 3 formed on a glass substrate 2 is disposed in a sterilization tank 1, and the plate electrode 3 is in communication with a potentiostat 4. The potentiostat 4 is in communication with the reference electrode 6 and the counter electrode 7 arranged in the control tank 5, respectively. The sterilization tank 1 and the control tank 5 are connected by a salt bridge 8, and a stirrer 9 and a stirring rod 10 are arranged at the bottom of the sterilization tank 1. As the conductive resin plate electrode 3, a material obtained by adding 50% by weight of graphite (Fluka) to a silicone resin is formed on a glass substrate 2 in a plate shape (26 mm × 26 mm ×
The counter electrode 7 was made of platinum, and the reference electrode 6 was made of a saturated sweet potato electrode (SCE).
In addition, by this apparatus, the water 11 to be treated in the sterilization tank 1 is treated.
The microorganisms 12 contained in are sterilized.

Example 1 Effect of Applied Potential on Seawater Using the apparatus shown in FIG. 1, the effect of applied potential on seawater was examined. 50ml of seawater (pH 8.0) collected from Miura Beach
Was placed in the sterilization tank 1 and a positive potential was applied to the plate electrode 3 for 30 minutes at room temperature while stirring at 350 rpm, and changes in current density, residual chlorine concentration and pH were measured. As apparent from FIG. 2 showing the measurement results, 1.6 V vs. 1.6 V. SC
At the potential below E, no residual chlorine (▲ in FIG. 2) was measured. Furthermore, from -0.4 V to +1.5 V vs. No pH change (■ in FIG. 2) was observed in the SCE range. Therefore, from -0.4 V to +1.5 V vs. Sterilization by chlorine or pH change does not occur in the SCE range.

Example 2 Preparation of Plate Electrode Vibrio alginolytics (Vibrio alg)
inolyticus: ATCC 17749), marine broth (Marine b
roth) 1 at 25 ° C in 2216 (DIFCO Laboratory)
The cells were cultured aerobically for 0 hours. The cells after culturing are collected by centrifugation (1
(0 min; 2000 g), and then washed well with sterilized seawater. Subsequently, using a hemacytometer, 10 ⁵ cells
Sample water of s / ml was prepared. The plate electrode 3 is immersed in 150 ml of the sample water, and left for 90 minutes with gentle stirring at 350 rpm without applying a potential.
The cells were sufficiently adsorbed on the surface of. The plate electrode 3 was washed with sterilized seawater to remove cells that had not been adsorbed on the surface, thereby preparing a plate electrode 3 to which cells were attached.

Example 3 Desorption by Applying Negative Potential The above-mentioned cell-adhering plate electrode 3 (cell adhering amount: 8.0 ×) was placed in a sterilization tank 1 containing 150 ml of sterilized seawater (pH 8.0). 10 ⁴ CFU / cm ² ) and insert 350r
-0.4 Vvs. SCE ~
+ 0.4Vvs. SCE potential was applied. After applying a potential for 10 minutes, the plate electrode 3 was taken out of the sterilization tank 1. Microorganisms (microorganisms detached from the plate electrode 3 during potential application) in the residual seawater in the sterilization tank 1 were collected by pipetting, and the number of viable microbes was measured by the colony counting method. This measurement result is shown in FIG. 3 as the number of viable cells detached from the electrode unit area. + 0.4-0V
vs. In the range of SCE, about 5.0 × 10 ⁴ CFU / cm ² of cells were recovered from the residual seawater in the sterilization tank 1.
−0.4 to 0 V vs. In the range of SCE, the number of cells recovered increases as the potential is lowered, and -0.2 Vv
s. In SCE, 6.3 × 10 ⁴ CFU / cm ² cells and -0.4 V vs. 7.2 × 10 ⁴ CFU in SCE
/ Cm ² cells were recovered.

Example 4: Sterilization by application of positive potential The above-mentioned cell-adhered plate electrode 3 (cell-adhered amount: 5.6 × 10 5) was placed in a sterilization tank 1 containing 150 ml of sterilized seawater (pH 8.0). ³ CFU / cm ² ) and 350r
pm with gentle stirring at 0 V. SCE- + 1.
5Vvs. An SCE potential was applied for 10 minutes. After the application of the positive potential, −0.4 V vs. The SCE potential is applied for 2 minutes to detach the cells from the plate electrode 3, the plate electrode 3 is taken out of the sterilization tank 1, and the cells present in the residual seawater in the sterilization tank 1 (during the potential application). Plate electrode 3
Was removed by pipetting, and the number of viable cells was measured by a colony counting method. The measurement results are shown in FIG. 4 as the number of viable cells detached from the electrode unit area. The number of viable cells recovered decreased as the applied potential was increased. That is, 0Vvs. In SCE, about 1.8 × 10 ³ CFU / cm ² of cells were recovered.
1.0Vvs. About 1.3 × 10 ³ CFU / cm for SCE
² cells and +1.5 V vs. About 0.2 for SCE
× 10 ³ CFU / cm ² cells were recovered.

Example 5: Influence of positive potential application time In a sterilization tank 1 containing 150 ml of sterilized seawater (pH 8.0), a cell adhesion plate electrode 3 (cell adhesion amount:
5.6 × 10 ³ CFU / cm ² ) and 350 rpm
+1.5 V vs. with gentle stirring. After applying the SCE potential for 1 minute, 5 minutes, 10 minutes and 30 minutes,
Each of -0.4 V vs. The cells are detached from the plate electrode 3 by applying a potential of SCE for 2 minutes.
Is removed from the sterilization tank 1 and the cells present in the residual seawater in the sterilization tank 1 (cells detached from the plate electrode 3 during potential application) are collected by pipetting, and the viable cells are collected by the colony counting method. The number was measured. The measurement results are shown in FIG. 5 as the number of viable cells detached from the electrode unit area. After 1 minute, it decreased to about 2.3 × 10 ³ CFU / cm ² and after 5 minutes to about 1.0 × 10 ³ CFU / cm ² .

Example 6: Adsorption / sterilization / desorption treatment of bacterial cells and comparative example Sterilization containing 50 ml of seawater (pH 8.0) adjusted to 1.0 × 10 ³ cells / ml using a hemacytometer. The plate electrode 3 to which no cells were attached was inserted into the treatment tank 1, and (1) +1.0 V vs. 1.0 V with gentle stirring at 350 rpm. An adsorption / sterilization step of applying a positive potential of SCE for 10 minutes, and (2) -0.2 V vs. SCE. A treatment cycle consisting of a detachment step of applying a negative potential of SCE for 2 minutes was repeatedly performed, and the number of viable cells in 1 ml was counted by a colony counting method. In FIG. 6 showing the results, the case where the above-mentioned treatment cycle was repeatedly carried out is indicated by Δ, and the case where no potential is applied (control) is indicated by ●
Plotted. In the control, 1.1 × 10 ³ after 1 hour
cells / ml, 1.2 × 10 ³ cells / ml after 6 hours, 1
At 0 hours, the cells increased to 5.0 × 10 ³ cells / ml and at 12 hours to 9.3 × 10 ³ cells / ml. On the other hand, when the above-described treatment cycle in which the positive potential and the negative potential were alternately applied was performed, no viable bacteria were observed after 6 hours, indicating that the electrochemical sterilization was performed efficiently.

As a comparative example, +1.0 Vvs. S
CE positive potential or -0.2 V vs. The same treatment was performed by continuously applying the negative potential of SCE. In FIG. 7 showing the results, +1.0 Vvs. When the positive potential of SCE is continuously applied (after 1 hour, 1.3 × 10 ³ cells / ml, 6
6. 2.0 × 10 ³ cells / ml after 10 hours 7.
0 × 10 ³ cells / ml, and 12.4 × 1 in 12 hours
(Cells increase to 0 ³ cells / ml)
s. When the negative potential of SCE is continuously applied (1.4 × 10 ³ cells / ml after 1 hour, 1.6 × 1 after 6 hours)
0 ³ cells / ml, 5.6 × 10 ³ cells / after 10 hours
ml, and the cells increased to 11.8 × 10 ³ cells / ml in 12 hours), and plotted with ■, and when no potential was applied (control), plotted with ●.

Reference Example: Examination of conductive plate electrode material Silicone resin, ethylene vinyl acetate copolymer resin, a mixture of vinyl chloride and polyurethane resin, styrene butadiene rubber, urethane resin, chloroprene rubber, and epoxy resin were each made of graphite ( Fluka)
9 wt%, 64 wt%, 59 wt%, 63 wt%, 70 wt%
By weight, 60% by weight, and 46% by weight were mixed and formed into a plate shape on a glass substrate, and the carbon fiber was used as a lead wire to form an electrode. When a resistance value between two points between the electrode surface and the lead wire was measured, a low resistance value of about 20 to 50Ω was shown. In addition, when cyclic voltammetry measurement of ferricyanide was performed, when a silicone resin and chloroprene rubber were used, the oxidation-reduction peak was confirmed.

Next, the resistance value of the plate electrode using a silicone resin as a binder polymer with respect to the graphite content was measured.
As the weight increases to 5%, 42% and 50% by weight, the resistance values become 160Ω, 42Ω and 11%, respectively.
It turned out that it decreases with Ω. The content rate is 50
It showed a substantially constant resistance value of about 11 Ω at weight% or more. Further, when a conductive polymer polyaniline (prepared by stirring purified aniline in 1N-HCl with ammonium persulfate as an oxidizing agent at ─5 ° C. overnight) was added thereto, the resistance value was further decreased. all right.

[0025]

According to the method of the present invention, unlike the conventional method using a chemical substance causing residual toxicity, microorganisms in water can be sterilized by a clean electrochemical method which does not cause water pollution. In addition, biological pollution can be effectively prevented under mild conditions different from the very severe conventional electrode sterilization method using a high voltage.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing an effect when a potential is applied to seawater.

FIG. 3 is a graph showing the effects of positive and negative potentials on microorganisms.

FIG. 4 is a graph showing the effect of positive potential on microorganisms.

FIG. 5 is a graph showing an effect when a positive potential is applied for a long time.

FIG. 6 is a graph showing an effect when a process of alternately applying a positive potential and a negative potential is performed.

FIG. 7 is a graph showing an effect when a process of continuously applying a constant positive potential or a negative potential is performed.

[Explanation of Signs] 1 sterilization tank 2 glass substrate 3 conductive resin plate electrode 4 potentiostat 5 control tank 6 counter electrode 7 reference electrode 8 salt bridge 9 stirrer 10 stirrer rod 11 water to be treated 12 microorganism

──────────────────────────────────────────────────続 き Continued on the front page (56) References JP-A-3-106492 (JP, A) JP-A-3-224686 (JP, A) Matsunaga, S., “Electrostatic control of microorganisms”, Chemical engineering, Chemical Industry Co., Ltd., December 1, 1990, Vol. 35, No. 12, p. 35-40 (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 1/46-1/48

Claims (1)

(57) [Claims] Claims: 1. In water, a conductive substrate has +0 to +
1.5Vvs. By applying the positive potential of SCE ,
Adsorbing and sterilizing microorganisms in water on the surface of the conductive substrate ; SC
Removing the sterilized microorganism adsorbed on the surface of the conductive substrate by applying a negative potential of E to the underwater microorganism.