JP7850003B2 - Method for removing biofilms - Google Patents

Description

This invention relates to a biofilm remover used as an additive in industrial water systems such as those used in manufacturing and service industries, and to a method for removing biofilms.

In industrial water systems, such as those used for air conditioning and refrigeration, or in various manufacturing industries and plants including the paper and pulp sector, biofilms formed by bacteria, filamentous fungi, and algae accumulate on piping and equipment over time. This biofilm buildup can cause various problems, including reduced thermal efficiency, pipe blockage and reduced flow rate, and corrosion of metal components.

To prevent or mitigate damage caused by such biofilms, the use of chemicals has traditionally been common. Examples of chemicals used for biofilm control include biofilm removers that peel or wash away attached biofilms, and slime control agents and disinfectants (hereinafter referred to as "slime control agents, etc.") that prevent biofilm adhesion.

Among these agents, slime control agents reduce the slime adhesion potential by maintaining a low concentration of microorganisms in the water. Generally, slime control agents kill bacteria or suppress bacterial growth by inhibiting enzymatic reactions or denaturing cell membranes.

On the other hand, biofilm removers primarily work by reducing the viscosity of extracellular adhesive substances (generally polysaccharides), thereby dispersing bacterial aggregates and detaching the biofilm from the surface. Therefore, a drug effective as a slime control agent may not be effective as a biofilm remover, and vice versa.

Examples of biofilm release agents include organic fungicides such as isothiazolinone-based compounds proposed in Patent Document 1, chlorinated sulfamic acid compounds proposed in Patent Document 2, pyridine compounds proposed in Patent Documents 3 and 4, pyridinium compounds and phthalaldehyde combinations proposed in Patent Document 5, and polyoxyethylene compounds and isothiazolinone compounds combinations proposed in Patent Document 6. However, improvements in the release power and corrosion protection properties of these biofilm release agents are needed.

Furthermore, methods using strong chlorine-based chemicals or oxidizing agents such as hydrogen peroxide to quickly remove biofilms are often employed. However, in this case, the chemicals themselves are highly toxic and dangerous, requiring careful handling, and neutralization treatment is necessary afterward. Therefore, using these chemicals complicates the work and raises concerns about corrosion of metals such as pipes and equipment.

Japanese Patent Application Publication No. 5-157719 Japanese Patent Publication No. 2003-267811 Japanese Patent Publication No. 2005-325036 Japanese Patent Publication No. 2006-21105 Japanese Patent Publication No. 2009-215271 Japanese Patent Publication No. 2012-214388

The present invention aims to solve the above problems. Specifically, the present invention aims to provide a biofilm remover and a biofilm removal method for use in industrial water systems already covered with biofilm, wherein metal corrosion in the water system is suppressed, and the biofilm can be effectively removed at lower concentrations.

The inventors of this invention conducted extensive research to solve the above-mentioned problems and, as a result, discovered that by using orthophthalaldehyde and an organobromine compound in combination, biofilms can be effectively removed at lower concentrations, leading to the development of this invention.

In other words, the biofilm remover of the present invention is a biofilm remover for removing biofilms when added to aqueous water in which biofilms are attached, and contains (A) orthophthalaldehyde and (B) an organic bromine compound.

The (B) organobromine compound is preferably 2,2-dibromo-2-nitroethanol.

Furthermore, the mass ratio (A:B) of (A) orthophthalaldehyde to (B) the organic bromine compound is preferably within the range of 10:0.5 to 0.5:10.

On the other hand, one aspect of the biofilm removal method of the present invention involves adding (A) orthophthalaldehyde and (B) an organic bromine compound to aqueous water in which a biofilm is attached.

Furthermore, another aspect of the biofilm removal method of the present invention involves adding the biofilm removal agent of the present invention to an aqueous system in which a biofilm is attached.

In this case, it is preferable to add the biofilm release agent to the aqueous system water such that the total concentration of (A) orthophthalaldehyde and (B) the organic bromine compound (A + B) in the aqueous system water is within the range of 1 mg/L to 500 mg/L.

According to the present invention, it is possible to provide a biofilm remover that suppresses the corrosion of metal materials used in industrial water systems where biofilms are already attached, and exhibits excellent biofilm removal effects with a small amount added to the water system.

Furthermore, according to the biofilm removal method of the present invention, by using (A) orthophthalaldehyde and (B) an organic bromine compound, or the biofilm removal agent of the present invention, corrosion of metal materials used in industrial water systems already covered with biofilm can be suppressed, and an excellent biofilm removal effect can be obtained with a small amount of additive to the water system.

The present invention will be described in detail below, divided into two parts: the biofilm release agent and the biofilm release method.

[Biofilm remover]
The biofilm remover of the present invention is a biofilm remover that is added to aqueous water in which biofilm is attached to remove the biofilm, and contains (A) orthophthalaldehyde and (B) an organic bromine compound as essential components. In addition, the biofilm remover of the present invention may contain conventionally known metal corrosion inhibitors, scale inhibitors, and various other additives as optional components.

The biofilm release agent of the present invention is prepared by dissolving or dispersing these components in water.
The following provides a detailed explanation of each of these components.

<Essential ingredients>
(A) Orthophthalaldehyde The orthophthalaldehyde used in this invention is also called _{phthalaldehyde} and is represented by the chemical formula _C6H4 (CHO) ₂ . More specifically, it is an aromatic compound in which two aldehyde groups are attached to the ortho position of a benzene ring.

Orthophthalaldehyde is readily available on the market as a disinfectant for medical devices and other equipment. Specific examples of orthophthalaldehyde products include "Disopa®" (manufactured by Johnson & Johnson).

(B) Organobromine compounds The organobromine compounds used in the present invention are not particularly limited, and any organic compound having a carbon-bromine bond can be used. Preferred organobromine compounds in the present invention include, for example, bromonitro alcohol compounds such as 2-bromo-2-nitropropane-1,3-diol and 2,2-dibromo-2-nitroethanol and their esters; bromoamide compounds such as N-bromoacetamide and 2,2-dibromo-3-nitrilopropionamide; bromoacetic acid ester compounds such as 1,2-bis(bromoacetoxy)ethane, 1,2-bis(bromoacetoxy)propane and 1,4-bis(bromoacetoxy)-2-butene; bromosulfone compounds such as hexabromodimethylsulfone; bromonitro compounds such as bromonitrostyrene; and the like.

Among the organic bromine compounds used in this invention, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-nitroethanol, and 2,2-dibromo-3-nitrilopropionamide are more preferred, and 2,2-dibromo-2-nitroethanol is particularly preferred.

<Optional ingredients>
• Metal Corrosion Inhibitors The biofilm release agent of the present invention may contain metal corrosion inhibitors as optional components to further suppress the corrosion of metals such as pipes and equipment. Azole compounds are preferred as metal corrosion inhibitors that can be used with the biofilm release agent of the present invention. Examples of azole compounds that can be used as metal corrosion inhibitors include monocyclic azole compounds such as imidazole, pyrazole, oxazole, thiazole, triazole, and tetrazole; and condensed polycyclic azole compounds such as benzimidazole, benzoxazole, benzoisoxazole, benzothiazole, mercaptobenzimidazole, mercaptomethylbenzimidazole, mercaptobenzothiazole, benzotriazole, tolyltriazole, indazole, purine, imidazothiazole, and pyrazoloxazole. Furthermore, among azole compounds, salts of such compounds can be mentioned.

In the biofilm release agent of the present invention, benzotriazole or toltriazole are particularly preferred as azole compounds for use as metal corrosion inhibitors, due to their high effectiveness in suppressing the decomposition of oxidative substances that contribute to the progression of metal corrosion.

Scale inhibitors Examples of scale inhibitors that can be used as optional components in the biofilm release agent of the present invention include phosphonic acids such as 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylenephosphonic acid and their water-soluble salts; polymers such as acrylic acid, maleic acid, methacrylic acid, sulfonic acid, itaconic acid, or isobutylene polymers and copolymers thereof; phosphinocarboxylic acids such as hypophosphorous adducts of acrylic acid polymers; and the like.

Among these, it is preferable to incorporate at least one scale inhibitor selected from the group consisting of 2-phosphonobutane-1,2,4-tricarboxylic acid or its water-soluble salt; a terpolymer of maleic acid, alkyl acrylate, and vinyl acetate; a hypophosphite adduct of polyacrylic acid; and a hypophosphite adduct of a copolymer of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid, because this hardly causes any decomposition of oxidizing substances by the incorporated scale inhibitor.

• Other various additives In addition to the essential and optional components mentioned above, various other additives may be added to the biofilm release agent of the present invention as optional components. Examples of other additives that can be added include colorants, dispersants, fragrances, fluorescent substances (such as 1,3,6,8-pyrenetetrasulfonate sodium salt (PTSA), uranine, etc.).

<Water>
There are no particular restrictions on the water that can be used in the biofilm release agent of the present invention, and general industrial water, well water, city water, tap water, river water, deionized water, RO water, pure water, etc. can be used as appropriate. It is preferable that the water used is sterilized or disinfected before being used to prepare the biofilm release agent. Here, "sterilization" does not mean completely killing all organisms, but rather significantly reducing the probability of microorganisms existing (the same applies in the following description).

<Ingredient proportions>
(Essential ingredient)
The mass ratio (A:B) of (A) orthophthalaldehyde to (B) organic bromine compound is preferably 10:0.5 to 0.5 to 10, and more preferably 10:1 to 1:10. Too much (A) orthophthalaldehyde is undesirable not only because it is cost-intensive, but also because it raises concerns about environmental impact, such as an increase in chemical oxygen demand (COD). On the other hand, too little (A) orthophthalaldehyde is undesirable because it makes it difficult to obtain a sufficient biofilm peeling effect.

The aqueous solution concentration of (A) orthophthalaldehyde and (B) organic bromine compounds in the biofilm release agent should preferably be within a range that allows for an appropriate concentration (addition concentration) in the aqueous system when the biofilm release agent is added to the aqueous system in the "biofilm release method" described later, while also maintaining the stability of the solution. Specifically, the aqueous solution concentration of the total (A+B) is preferably within the range of 1 mg/L to 500 mg/L.

(optional ingredient)
In biofilm removers, there are no particular restrictions on the concentration of optional components such as metal corrosion inhibitors, scale inhibitors, and other various additives, as long as they do not impair the function of the biofilm remover.

Of course, it is desirable that the concentration of the metal corrosion inhibitor in the biofilm release agent be at or above the amount that provides the desired effect. Similarly, it is desirable that the concentration of the scale inhibitor in the biofilm release agent be at or above the amount that provides the desired effect.

[Method for removing biofilm]
The present invention provides a method for removing biofilms, which involves adding (A) orthophthalaldehyde and (B) an organic bromine compound to an aqueous system containing a biofilm. While (A) orthophthalaldehyde and (B) the organic bromine compound may be added separately, they may also be added by adding the biofilm remover of the present invention.

The following description will primarily focus on the method of adding the biofilm release agent of the present invention, but this description also applies directly to the method of adding (A) orthophthalaldehyde and (B) an organic bromine compound separately.

When adding the biofilm release agent to the aqueous system, it is preferable that the total concentration of (A) orthophthalaldehyde and (B) organic bromine compounds (A + B) in the aqueous system be within the range of 0.5 mg/L to 800 mg/L, more preferably within the range of 1 mg/L to 500 mg/L, and even more preferably within the range of 1 mg/L to 300 mg/L.

If the combined concentration of (A) orthophthalaldehyde and (B) organic bromine compounds (A + B) is too low, the biofilm removal effect may be insufficient. On the other hand, even if the combined concentration of (A + B) is excessive, there are no particular performance issues, but further improvement in the biofilm removal effect cannot be achieved.

In this invention, a water system with biofilm adhesion refers to an industrial water system in which biofilm adhesion has been confirmed through methods such as a decrease in the heat exchange efficiency of equipment within the water system, a decrease in the water permeability of piping, changes in the feel and appearance of equipment and piping, evaluation of increased hydrophilicity of equipment surfaces, ATP (adenosine triphosphate) analysis, or staining methods.

In the biofilm removal method of the present invention, methods for adding the biofilm removal agent to the water system include, but are not particularly limited, adding it directly, continuously and/or intermittently, into the waterway in the water system; adding it directly, continuously and/or intermittently, to stagnant areas of the water system; adding it continuously and/or intermittently to a channel branched off from the waterway in the water system; or collecting the water system water from the waterway in the water system, adding it in batches to a pit where the water is stored, distributing it, and then returning it to the waterway.

Alternatively, the biofilm may be removed by directly supplying the biofilm remover of the present invention to the area where the biofilm is attached, using methods such as spraying, pouring, injecting, coating, or immersion.

Although preferred embodiments of the biofilm release agent and biofilm release method of the present invention have been described above, the biofilm release agent and biofilm release method of the present invention are not limited to the configurations of the embodiments described above.
Furthermore, those skilled in the art may appropriately modify the biofilm remover and biofilm removal method of the present invention in accordance with conventionally known knowledge. Such modifications, as long as they still possess the configuration of the present invention, are of course included within the scope of the present invention.

The biofilm release agent and biofilm release method of the present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

<Test Example 1>
The following chemicals (1) to (6) were prepared as test chemicals.
[Test chemicals]
(1) Orthophthalaldehyde (OPA) ... (A) Orthophthalaldehyde (2) 2,2-dibromo-2-nitroethanol (DBNE) ... (B) Organobromine compound (3) 2-bromo-2-nitropropane-1,3-diol (Bronopol) ... (B) Organobromine compound (4) 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) ... for comparison (5) 1,4-bis(3,3'-(1-decylpyridinium)methyloxy)butanedibromide (BDPMOB) ... for comparison (6) Poly[oxyethylene (dimethyliminio)ethylene (dimethyliminio)ethylene]dichloride (POD) ... for comparison

[Preparation of biofilm release agent]
Using test chemicals (1) to (6), the test chemicals shown in Table 1 below were diluted with sterilized Tsukuba water to the proportions shown in the same table to prepare the biofilm release agents for Examples 1 to 6 and Comparative Examples 1 to 8, respectively. Comparative Example 1 is a blank test specimen (i.e., water itself) without any added biofilm release agent components, but for convenience it is referred to as a "biofilm release agent".

[Test Method]
1) P. aeruginosa, pre-cultured on MHB (Müller-Hinton agar), was inoculated into fresh MHB at an ATP concentration of approximately 10 nM.
2) Dispense 1) into a 24-well microplate, dispensing 1 mL per well, and incubate at 30°C for 48 hours.
3) After standing, the culture medium was discarded, and 1.2 mL of PBS (phosphate-buffered saline) was dispensed per well for washing. This washing was performed three times.
4) The biofilm release agents of Examples 1-6 and Comparative Examples 1-8 were each dispensed at a rate of 1.2 mL per well into the 24-well microplate obtained in 3), and left to stand at room temperature for 3 hours.
5) After standing for 3 hours, discard the biofilm remover and wash with PBS in the same manner as in 3) (repeated 3 times).

[evaluation]
(ATP concentration and removal rate)
5) For the 24-well microplate obtained in step 2), the walls and bottoms of the wells were wiped with a sterile cotton swab, and the ATP concentration was measured after suspending the samples in 1 mL of sterile water.

The "removal rate (%)" was defined as the ratio of the ATP concentration of the other comparative examples and examples (test specimens using each biofilm remover) to the ATP concentration of Comparative Example 1 (a blank test specimen). The "removal rate" in subsequent test examples was determined similarly.
The measurement results for ATP concentration and the calculation results for removal rates are summarized in Table 1, which was previously presented.

As shown in Table 1, in Examples 1 to 6, where the biofilm remover of the present invention was used in combination with (A) orthophthalaldehyde and (B) an organic bromine compound, the biofilm removal rate was high even at low concentrations, clearly demonstrating the effectiveness of the biofilm remover of the present invention.

<Test Example 2>
The following chemicals (1), (2), (5), (7), and (8) were prepared as test chemicals.
[Test chemicals]
(1) Orthophthalaldehyde OPA... (A) Orthophthalaldehyde (2) 2,2-dibromo-2-nitroethanol (DBNE)... (B) Organobromine compound (5) 1,4-bis(3,3'-(1-decylpyridinium)methyloxy)butanedibromide (BDPMOB)... For comparison (7) Glutaraldehyde... For comparison (8) Hydrogen peroxide... For comparison

[Preparation of biofilm release agent]
Using test chemicals (1), (2), (5), (7), and (8), the test chemicals shown in Table 2 below were diluted with sterilized Tsukuba water to the proportions shown in the same table to prepare the biofilm release agents for Examples 7 to 9 and Comparative Examples 1, 9 to 13.

[Test Method]
In the [Test Method] of Test Example 1, test specimens were obtained using each biofilm remover in the same manner as the [Test Method], except that the incubation time in 2) was changed from 48 hours to 24 hours.

[evaluation]
In the same manner as in the evaluation of Test Example 1 (ATP concentration and removal rate), the "ATP concentration" and "removal rate (%)" were determined for each test specimen.
The measurement results for ATP concentration and the calculation results for removal rates are summarized in Table 2, which was previously presented.

As shown in Table 2, in Examples 7-9, where the biofilm remover of the present invention was used in combination with (A) orthophthalaldehyde and (B) an organic bromine compound, the ATP concentration was low even at low concentrations, clearly demonstrating the effectiveness of the biofilm remover of the present invention. In the case of Comparative Example 9 using glutaraldehyde and Comparative Example 13 using hydrogen peroxide, high concentrations of 2000 mg/L or more and 10000 mg/L or more, respectively, were required to achieve a removal rate close to 100%.

<Test Example 3>
The following chemicals (1) to (3) and (7) were prepared as test chemicals.
[Test chemicals]
(1) Orthophthalaldehyde (OPA) ... (A) Orthophthalaldehyde (2) 2,2-dibromo-2-nitroethanol (DBNE) ... (B) Organobromine compound (3) 2-bromo-2-nitropropane-1,3-diol (Bronopol) ... (B) Organobromine compound (7) Glutaraldehyde ... For comparison

[Preparation of biofilm release agent]
Using test chemicals (1) to (3) and (7), the test chemicals shown in Table 3 below were diluted with sterilized Tsukuba water to the proportions shown in the same table to prepare the biofilm release agents for Examples 2, 4, 10 to 12 and Comparative Examples 1, 14 to 17.

[Test Method]
Ten polyvinyl chloride test pieces (25 mm x 75 mm x 1 mm) were immersed in the water from an actual operating cooling tower system and left for 14 days to allow a biofilm to adhere to the surface.

500 mL each of the biofilm release agents from Examples 2, 4, 10-12 and Comparative Examples 1, 14-17 were placed in glass containers. The test pieces with the biofilm attached were immersed in these containers so that the plane with the largest surface area was perpendicular to the surface. The containers were then left at room temperature for 5 hours while stirring at 60 rpm (revolutions/minute).

[evaluation]
After standing for 5 hours, each test specimen was removed, the attached material was wiped off with a sterile cotton swab, and the specimens were resuspended in 10 mL of sterile deionized water. The ATP concentration was then measured. In this case, a lower ATP concentration indicates a smaller amount of attached microorganisms.
The measurement results for ATP concentration and the calculation results for removal rates are summarized in Table 3, which was previously presented.

As shown in Table 3, in Examples 2, 4, and 10-12, where the biofilm release agent of the present invention using (A) orthophthalaldehyde and (B) an organic bromine compound was used in combination, the ATP concentration was low, clearly demonstrating the effectiveness of the biofilm release agent of the present invention.

<Test Example 4>
The following chemicals (1), (2), (9), and (10) were prepared as test chemicals.
[Test chemicals]
(1) Orthophthalaldehyde (OPA) ... (A) Orthophthalaldehyde (2) 2,2-dibromo-2-nitroethanol (DBNE) ... (B) Organic bromine compound (9) Sodium hypochlorite (12% by mass aqueous solution of sodium hypochlorite) ... For comparison (10) Hydrogen peroxide solution (35% by mass aqueous solution of hydrogen peroxide) ... For comparison

[Preparation of biofilm release agent]
Using test chemicals (1), (2), (9), and (10), the test chemicals shown in Table 4 below were diluted with sterilized Tsukuba water to the proportions shown in the same table to prepare the biofilm release agents for Examples 7 and 8 and Comparative Examples 18 and 19, respectively.

* (9) The concentration of sodium hypochlorite was determined by diluting the sodium hypochlorite aqueous solution (9) as the test chemical so that the concentration of sodium hypochlorite in the aqueous solution was as described above.
* (10) Similarly, the concentration of hydrogen peroxide was determined by diluting the hydrogen peroxide solution (10) as the test chemical so that the concentration of hydrogen peroxide in the aqueous solution was the above concentration.

[evaluation]
Each of the biofilm release agents from Examples 7 and 8 and Comparative Examples 18 and 19 was placed in a glass container in a 1000 mL volume. Three polished copper test pieces (C1220P) measuring 20 mm × 60 mm × 2 mm were immersed in the container, and a corrosion test was conducted at 35°C for two days while stirring at 300 rpm (revolutions/minute). After the corrosion test, the corrosion loss of the copper plate was measured, and the corrosion rate (mg/ ^dm² /day (mdd)) was calculated.
The results of the corrosion test (corrosion rate) are summarized in Table 4, which was previously presented.

As shown in Table 4, in Examples 7 and 6, which used the biofilm remover of the present invention containing (A) orthophthalaldehyde and (B) an organic bromine compound in combination, corrosion was suppressed. In particular, in Examples 7 and 6, the corrosion rate was significantly slower than in Comparative Examples 18 and 19, which correspond to the sodium hypochlorite concentration and hydrogen peroxide concentration that yield the biofilm remover effect, clearly demonstrating the effectiveness of the present invention.

Claims (5)

A biofilm removal method for removing a biofilm by adding ( A) orthophthalaldehyde and (B) an organic bromine compound to water in an aqueous system in which a biofilm is attached,
The (B) organobromine compound has a carbon-bromine bond,
A method for removing a biofilm, comprising adding (A) orthophthalaldehyde and (B) an organic bromine compound to the aqueous water system such that the total concentration of (A + B) of (A) orthophthalaldehyde and (B) an organic bromine compound is within the range of 0.5 mg/L to 800 mg/ L . The method for peeling a biofilm according to claim 1, wherein the (B) organic bromine compound is 2,2-dibromo-2-nitroethanol. The method for peeling a biofilm according to claim 1 or claim 2, wherein the mass ratio (A:B) of (A) orthophthalaldehyde to (B) the organic bromine compound is in the range of 10:0.5 to 0.5:10. A method for removing a biofilm according to claim 1 or 2 , wherein a biofilm remover containing (A) orthophthalaldehyde and (B) an organic bromine compound is added to the aqueous water system. The method for removing a biofilm according to claim 4, wherein the mass ratio (A:B) of (A) orthophthalaldehyde to (B) an organic bromine compound in the biofilm remover is in the range of 10:0.5 to 0.5:10.