METHOD FOR REMOVING BIOFILM

Abstract

The present invention is a method for removing a biofilm formed in a water system comprising, exposing the biofilm to a liquid having a hydroxyl radical generation ability, obtained by a predetermined measurement method, of 0.15 or more.

Claims

1. A method for removing a biofilm formed in a water system comprising, exposing the biofilm to a liquid having a hydroxyl radical generation ability, obtained by the following method for measuring the amount of hydroxyl radicals, of 0.15 or more: [Method for measuring the amount of hydroxyl radicals] To a liquid subjected to the measurement of the amount of hydroxyl radicals, an iron oxide hydroxide and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) are added to have final concentrations of 50 μM and 5% (volume ratio), respectively, and signal strength values are measured 10 minutes later using an electron spin resonance (ESR) spectrometer; hydroxyl radicals generated by the reaction are captured by DMPO to form spin adducts; second and third signal strength values in a spectrum of the spin adducts are averaged and divided by a signal strength value of a Mn marker to relatively determine the amount of the hydroxyl radicals, a value of which is taken as the hydroxyl radical generation ability; the ESR is measured using an ESR spectrometer (ESR-X10SA) manufactured by KEYCOM Corporation and a flat quartz cell (RFIC-7) manufactured by Flash Point Co., Ltd. under the following conditions; and as an internal standard, Mn Marker for ESR System Model: MG01 manufactured by KEYCOM Corporation is used with the scale set to 13.5, Frequency: 9.50321 GHz Reson. MF: 330.3 mT Sweep width: 16 mT Mod. width: 0.5 mT ADC gain: 1 Amplitude gain: 10 Sweep time: 30 sec Time const: 300 ms Average: 1 MW power: 0 Moving average: 5 Multi accumu: 0.

2. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability of the liquid is 0.20 or more and 20 or less.

3. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability of the liquid is 0.3 or more and 15 or less.

4. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability of the liquid is 0.4 or more and 10 or less.

5. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability of the liquid is 0.8 or more and 7 or less.

6. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability of the liquid is 3.4 or more and 6 or less.

7. The method for removing a biofilm according to claim 1, wherein the hydroxyl radical generation ability is an ability to generate a hydroxyl radical through a Fenton-like reaction.

8. The method for removing a biofilm according to claim 1, wherein the liquid has a pH of 3.0 or more and 6.5 or less.

9. The method for removing a biofilm according to claim 1, wherein the liquid is a liquid composition comprising (a) a compound having a hydroxyl radical generation ability (hereinafter also referred to as component (a)), (b) a reducing agent (hereinafter also referred to as component (b)) and water.

10. The method for removing a biofilm according to claim 9, wherein the liquid further comprises (c) a monovalent or divalent organic acid or a salt thereof with a primary dissociation constant (hereinafter referred to as pKa1) of 1.2 or more and 4.6 or less (hereinafter also referred to as component (c)).

11. The method for removing a biofilm according to claim 10, wherein the component (c) is one or more organic acids or salts thereof selected from malonic acid, malic acid, 3-hydroxypropionic acid, succinic acid, lactic acid, tartaric acid, glycolic acid, maleic acid, fumaric acid, gluconic acid and salts thereof.

12. The method for removing a biofilm according to claim 9, wherein the component (a) is one or more compounds selected from hydrogen peroxide, percarbonate salts and organic peracids, and the component (b) is ascorbic acid or salts thereof.

13. The method for removing a biofilm according to claim 1, wherein the biofilm is exposed to the liquid for 5 minutes or more.

14. The method for removing a biofilm according to claim 1, wherein the biofilm is exposed to the liquid for 10 minutes or more and 48 hours or less.

15. The method for removing a biofilm according to claim 1, wherein the water system is a cooling system comprising a water-cooled cooling tower.

16. The method for removing a biofilm according to claim 1, wherein the water system comprises a water flow path and/or a water storage tank.

Description

EXAMPLES

Examination Examples 1 to 12

[0102] As liquids to be exposed to a biofilm formed in a water system, liquid compositions were prepared by using components shown in Table 1 and subjected to the following test. In addition, the hydroxyl radical generation ability of the liquid compositions in Table 1 was measured by the method described herein. The results are shown in Table 1. Note that after the pH of each composition in Table 1 was adjusted by using 10 mM acetate buffer, the concentration of each component was adjusted to a predetermined value. In addition, the balance of each composition in Table 1 is water.

[Biofilm Removal Test (Cooling Tower Model)]

(1) Production of Biofilm

[0103] For biofilm production, a water system model was used with an annular reactor (manufactured by Art Kagaku Co., Ltd.) having a culture vessel with a capacity of 100 mL. The culture vessel of the annular reactor was equipped with a cylindrical rotator rotating at a rate of 160 revolutions per minute, and a test piece (SUS304) was attached to this rotator in advance. Cooling water collected from a water-cooled cooling tower for cooling a reaction tank equipment in a chemical plant was supplied to the culture vessel of the annular reactor (maintained at 30° C.), and culture was carried out for 3 weeks to form a biofilm on the test piece.

(2) Biofilm Removal Test

[0104] The test piece on which the biofilm was formed was immersed in 5 mL of each liquid composition containing components in Table 1 at concentrations in Table 1 or a control (ultra-pure water) added into each well of a 6-well plate, and shake was carried out at 30° C. and 60 rpm for 16 hours. Each test piece was dyed with 0.1% crystal violet and thereafter cleaned with ultra-pure water, and the dye was extracted using 1 mL of ethanol to measure the absorbance (OD570). On the basis of the measured OD570, a biofilm removal rate was measured in accordance with the following formula. Note that a blank represents the OD570 of ethanol.

Biofilm removal rate (%)={(control OD570−blank OD570)−(OD570 of examination example−blank OD570)}×100/(control OD570−blank OD570)

[0105] Note that the larger a value of the biofilm removal rate in the present test is, the higher the effect is, and a difference of 5% in the biofilm removal rate in the present test can be recognized as a significant difference and a difference of 10% as a clearer difference.

TABLE-US-00001 TABLE 1 Examination example 1 2 3 4 5 6 7 8 9 10 11 12 Liquid Concen- (a) Hydrogen 100 100 100 100 100 100 100 100 100 100 1000 100 compo- tration peroxide sition (ppm) (b) Sodium 100 100 100 100 100 100 100 100 100 100 1000 100 ascorbate (c) Tartaric 100 acid Malic 100 acid Succinic 100 acid Maleic 100 acid Fumaric 100 acid Malonic 100 acid Glycolic 100 acid Lactic 100 acid 3- 100 hydroxy- propionic acid Citric acid 100 pH (20° C.) 4 4 4 4 4 4 4 4 4 4 4 4 Hydroxyl radical 3.70 0.31 0.97 5.16 3.87 0.21 3.20 1.15 0.49 0.13 1.5 0.18 generation ability Biofilm removal rate (%) 69.2 49.4 61.2 66.5 72.8 43.7 55.7 50.5 54.8 19.7 64.5 33.8

[0106] When external force is utilized to remove the biofilm, for example, in such a case that the biofilm is removed by cleaning by rubbing with a mop, a wiping cloth or the like, a biofilm removal rate of 33% or more in this evaluation is sufficient for the development of the effect. When external force is smaller, for example, in the case of removing the biofilm by flow, circulation or the like of the compositions in Table 1, a biofilm removal rate of 40% or more can be sufficient for the removal of the biofilm, and this rate is more preferable.