JP2001334255A - Method for controlling concentration of chemical for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling the concentration of a chemical for water treatment which measures the concentration of the chemical added into water easily, promptly, and accurately. SOLUTION: A known amount of coloring matter which is water soluble, light resistant, and oxidation resistant is dispersed as a tracer by a dispersant with a known amount of the chemical for water treatment in water such as cooling water in an open system. The concentration of the coloring matter in the water is detected optically by measuring the absorption of the coloring matter preferably at two or more wavelengths including at least one wavelength of absorption, preferably by absorptiometry. By determining the concentration of the chemical in the water from the detected concentration of the coloring matter proportional to the known amount of the chemical, the concentration of the chemical added into the water is controlled properly. As the coloring matter as a tracer, WA Color Blue A-01 (using C. I Pigment Blue 15, dispersed by a water soluble resin) (R) of Dainichi Seika Ind. Company can be used especially preferably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the concentration of water treatment chemicals (water treatment chemicals, water-based chemicals) in circulating water such as a cooling water system. The present invention relates to a method for stably and efficiently controlling the concentration of a chemical for water treatment by adding a dye as a tracer, and desirably detecting and quantifying the dye by spectrophotometry.

[0002]

2. Description of the Related Art Circulating water systems that are frequently used include boiler water systems and open and closed cooling water systems. Various water treatment chemicals (chemicals) are used in the water treatment of these circulating water systems in order to prevent water, such as corrosion, scale, and slime. Generally, water treatment chemicals used in circulating water systems such as cooling water systems include anticorrosives, dispersants, scale inhibitors, bactericides, slime control agents (biofouling inhibitors), and the like.

In order to carry out appropriate water treatment based on the effects of these various chemicals and to maintain the effects of these chemicals, the concentration of these chemicals at any position, time, etc. must be accurately grasped. It is necessary to perform appropriate concentration management.

However, it is impossible or difficult to measure the concentration of water in some types of drugs. Also,
Even if the concentration of the drug in water can be measured by colorimetry, turbidimetry, or other quantitative methods, the operation is complicated or takes a long time, which is not practical for plant operation management. There are cases. Therefore, as a concentration control method in the case of using a chemical whose concentration cannot be measured or used as a water treatment chemical, a substance whose concentration can be easily measured is used as a tracer. According to the method using the tracer, it is possible to quickly measure the concentration of a drug whose concentration itself cannot be measured or a drug that is difficult to measure in water. Heretofore, conventional methods for measuring the concentration of a chemical for water treatment using a tracer include a bromine tracer method, a lithium tracer method, a fluorescent tracer method, and a dye tracer method. Among them, the dye tracer method includes a method disclosed in JP-B-8-14536 using a water-soluble and photodegradable dye such as fluorescein as the dye tracer, and a water-soluble and light-fast dye tracer. A certain dye, brilliant blue FCF (CI Acid
Blue 9) and the like, which are disclosed in JP-A-2000-61448.

[0005] It is generally desired that these substances used as tracers satisfy a number of conditions as described below. (1) Does it exist in industrial water, etc.
Alternatively, its abundance is negligibly small, (2) it is chemically stable, (3) it is not easily decomposed by the action of microorganisms, and (4) it is substantially from the viewpoint of preventing pollution. Harmless, (5) reacting with dissolved salts in service water such as target industrial water, do not produce insoluble substances or scale, and (6) have no corrosiveness to metallic materials such as water-based piping materials. (7) Quantitative analysis can be performed without being disturbed by dissolved salts, and (8) Analysis can be performed accurately and quickly.

[0006]

Among the conventional tracer methods for measuring the concentration of water treatment chemicals, the bromine tracer method, lithium tracer method, fluorescent tracer method and the like are difficult to measure on site, Time is long,
Because a large-scale device is required for measurement,
There is a disadvantage that it takes a long time from the sampling of the sample water until the measurement result is obtained.

[0007] On the other hand, the dye tracer method is a concentration measuring method having an advantage that it can be measured immediately and easily on site, so that the concentration of a water treatment chemical can be easily controlled by using this method.

However, in circulating water such as boiler water and cooling water (especially in open-system cooling water), the dyes emit light,
Discoloration and discoloration under the influence of heat, pH, and the like often occur. For example, the above-mentioned Tokuhei 8-1453
No. 6, fluorescein proposed as a dye tracer in the conventional dye tracer method is, for example,
In an open cooling water system, it is easily discolored by the influence of light, etc.
There is a disadvantage that the concentration is reduced irrespective of the concentration of the chemical for water treatment and cannot be converted to the concentration of the chemical for water treatment.

Further, there is also a disadvantage that many of the pigments discolor or fade in the presence of an oxidizing agent. As water for circulating water systems such as boiler water systems and cooling water systems, especially as makeup water,
Depending on the site, an oxidizing agent such as sodium hypochlorite is added to industrial water or well water as a disinfectant or a slime controlling agent, or tap water containing sodium hypochlorite is used. Therefore, in this case, Japanese Patent Application Laid-Open No. 2000-61
The brilliant blue FCF disclosed in Japanese Patent No. 448 is easily discolored by an oxidizing agent such as sodium hypochlorite. Irrespective of this, there is a disadvantage that the concentration cannot be converted to the concentration of the chemical for water treatment.

[0010] The present invention solves the above-mentioned problems of the prior art, and makes it possible to easily and quickly and more accurately dispose of water treatment chemicals, for which it is impossible or difficult to accurately measure the concentration by the conventional dye tracer method, by the dye tracer method. An object of the present invention is to provide a method for controlling the concentration of a chemical for water treatment that can be measured well.

[0011]

According to the method for controlling the concentration of a chemical for water treatment of the present invention which has been made to achieve the above object, a dye having light fastness and oxidation fastness as a tracer is dispersed in water with a dispersant. It is characterized by being used. The term "dye" as used in the present invention refers to a pigment, and the present invention has been completed based on the discovery that, if it is dispersed in water using an appropriate pigment dispersant, it can be used as a dye tracer. Things. That is, the present invention disperses a light-resistant and oxidation-resistant dye as a tracer together with a water treatment chemical in water with a dispersant, and optically detects the concentration of the dye in water to be added to water. It is another object of the present invention to provide a method for controlling the concentration of a water treatment chemical, wherein the concentration of the water treatment chemical is controlled.

Hereinafter, the present invention will be described in detail. According to the present invention, a known amount of a dye having light resistance and oxidation resistance together with a known amount of a water treatment chemical is dispersed in a water in a circulating water system such as a cooling water system with a dispersant, and the By optically detecting the concentration of the dye, the concentration of the water treatment chemical present in the water can be quantified and detected from the detection concentration of the dye substantially proportional to the known amount of the water treatment chemical, The concentration of the water treatment chemical can be controlled.

That is, since the dyes used in the present invention are not usually present in service waters such as industrial waters and have light fastness and oxidation fastness which can serve as indicators of chemical stability, they are easily discolored. It is chemically stable, is not affected by microorganisms, is substantially harmless at its use concentration, and does not cause scale hindrance due to its chemical properties.

Optically detecting the dye concentration in the water of the circulating water system can be carried out by measuring at one wavelength where the dye is absorbed. However, the circulating water such as boiler water or cooling water containing a water treatment chemical other than the tracer can be used. Since the substance itself is colored to a greater or lesser degree due to the influence of dirt such as sludge, the measurement must be performed in consideration of the interference. As described in JP-A-2000-61448, the interference by dirt or particles such as sludge in the water of the circulating water system is not caused by absorption of a specific wavelength, but is caused by light scattering. Therefore, it is preferable to perform the measurement at two or more wavelengths including at least one wavelength at which the dye absorbs. The measurement at two or more wavelengths enables simple and efficient dye concentration detection. The optical detection of the dye concentration is preferably performed by an absorption spectrophotometric method from the viewpoint of easy operation. One of the features of the present invention is that if an absorption spectrophotometry method involving the measurement of absorbance at two or more wavelengths is used as an efficient absorption photometry method, it can be effectively used for controlling the concentration of a water treatment chemical. .

Generally, in measuring the concentration of a solution in which a dye is dispersed, the dye concentration is measured by measuring the absorbance at a specific absorption wavelength having a large absorbance (preferably near the maximum absorption wavelength of the dye). However, the absorbance varies due to various factors. For example, the apparent absorbance increases due to absorption by a solution not containing only the dye (hereinafter, abbreviated as “blank solution”), light scattering due to suspension of the solution due to suspended substances, contamination of the absorbance measurement cell, and the like. For the purpose of correcting these, it is required to measure a blank solution at the same time as the solution in which the dye is dispersed, to use a clean absorbance measurement cell, and the like.

In the method of the present invention, since a dye having an absorption at a wavelength at which the absorption by the blank solution is negligible is used, the light scattering effect due to the suspension of the solution due to suspended substances and the like and the cell for measuring the absorbance are used. It is only necessary to consider only the dirt. Furthermore, the interference by dirt or particles such as sludge in the water of the circulating water system is not detected as absorption at a specific wavelength, but is detected as an increase in apparent absorbance without large wavelength dependence in the present invention. Therefore, the absorbance at the absorption wavelength of the dye (hereinafter, abbreviated as “measurement wavelength”) is measured, and the wavelength at which the absorption by the dye is relatively small, almost absent, or substantially absent (hereinafter, “reference wavelength”) Abbreviation) is also measured and subtracted from the absorbance at the measurement wavelength of the dye, whereby the change in apparent absorbance due to light scattering can be canceled out and corrected. In addition, fluctuations due to contamination of the absorbance measurement cell and the like can be similarly canceled out and corrected. Further, more accurate measurement can be performed by setting a plurality of measurement wavelengths and / or reference wavelengths as necessary.

That is, if the method of the present invention is carried out by an absorptiometric method involving absorbance measurements at two or more wavelengths, there is no need to perform a blank measurement, and by monitoring the absorbance at the reference wavelength, the contamination of the absorbance measurement cell can be improved. Since the degree can also be monitored, the implementation of optical detection is simpler and more accurate.

The measurement wavelength in the optical detection of the dye concentration is preferably 400 nm to 800 nm, more preferably 550 nm to 800 nm. That is, JP 2
As described in JP-A-000-61448, water of a circulating water system such as a general cooling water system (including various water treatment agents such as an anticorrosive, a dispersant, a scale inhibitor, a bactericide, and a slime-controlling agent). As a result of conducting extensive research on these waters, preferably, the sample water after filtration has a low absorbance with respect to visible light of 400 nm to 800 nm, especially at a wavelength of 550 nm to 800 nm. It is known that there is hardly any absorption, or even if there is, little fluctuation with time. Further, the interference by dirt or particles such as sludge in the water of the circulating water system does not absorb a specific wavelength as described above, but is caused by light scattering, and a large wavelength in the above wavelength region. We also know that there are no dependencies. Therefore, if a dye having an absorption wavelength within the above wavelength range (preferably near the maximum absorption wavelength) is used as a tracer, there is almost no interference with coloring due to contamination of circulating water such as cooling water, etc.
This is convenient because the dye concentration can be easily measured by an absorption photometric method.

Among many dyes, those which are not affected as much as possible by light, heat, pH, oxidizing agent and the like in various circulating water systems such as a cooling water system are preferable as dye tracers, In open circulating water systems such as cooling water systems, those that are not affected by light as much as possible, and especially in circulating water systems where oxidizing agents such as sodium hypochlorite are introduced, Those that do not have to be dye tracers. In view of these points, in the present invention, a pigment is used as a dye having light resistance and oxidation resistance.
The pigment used in the present invention, which is dispersed in water in the form of fine particles, is affected by light or an oxidizing agent from the surface of the fine particles. It is generally expected that the composition will have excellent oxidation resistance. Regarding the light resistance and oxidation resistance of the dye, the residence time in a circulating water system of actual circulating water containing various water treatment chemicals together with the dye (for example, usually 1 to 3 days in a cooling water system)
When the dye is circulated in the circulating water system for one week in consideration of the above, the decrease in the optically detected density of the dye is preferably about 30% or less, more preferably about 10% or less.
However, the standards of light resistance and oxidation resistance vary greatly depending on the type of water treatment chemicals contained in the circulating water and various conditions of the circulating water system. Depends.

In addition, it is desirable that the functional group of the dye be as simple as possible. In other words, as long as the pigment is dispersed in water with the dispersant, the smaller the number of functional groups, the more the adsorption reaction or chemical reaction of the pigment to a pipe or the like that can occur in the circulating water system can be suppressed. In addition, it is desired that the dye does not harm the environment as much as possible after being released into the environment after use. This is related to the concentration used and the like.

Taking the above into consideration, in the present invention, for example, a copper phthalocyanine pigment (CI Pigment B)
lue 15) and monochloro copper phthalocyanine pigments (CI P
igment Blue 15: 1) and various dyes such as chlorinated copper phthalocyanine pigments such as polychloro copper phthalocyanine pigments, and these can be used alone or in combination. Polychloro copper phthalocyanine pigments are particularly excellent in terms of oxidation resistance. As the dispersant, any dispersant may be used as long as the dye that can be used in the present invention can be stably dispersed in the aqueous water of the object.For example, a water-soluble dispersant such as a nonionic dispersant or a water-soluble acrylic resin may be used. A resin-based dispersant or the like can be used, but is not limited thereto. A dispersion compound containing the pigment and the dispersant as described above is commercially available, and such a dispersion compound is preferably used in the present invention. Examples of such commercially available dispersion compounds include, for example, WA Color Blue A-
Water-based pigments such as 01 (using CI Pigment Blue 15: 1 and dispersed in a water-soluble resin), EP 520 Blue 2B (CI Pigment Blue
Blue 15 used, dispersed with nonionic surfactant), EP 510
Processed pigments for water-based paints such as Green B (using CI Pigment Green 7 and dispersed with a nonionic surfactant), AF Blue E-2B
(Using CI Pigment Blue 15 and dispersed in water-soluble acrylic resin), AF Green E-1 (using CI Pigment Green 7
Processed pigments for aqueous paints such as water-soluble acrylic resin) can be suitably used, and these can be used alone or in combination. However, it is preferable to use them alone in terms of simplicity. Among these aqueous processed pigments, WA Color Blue A-01 is particularly preferable because it has little discoloration in circulating water and can be optically detected at an extremely low concentration.
In the present specification, for the sake of simplicity of description, these "aqueous processed pigments" are also referred to as "dyes" hereinafter.

The dye used in the present invention is particularly excellent in oxidation resistance, so that it can be advantageously used as a dye tracer in a circulating water system into which an oxidizing agent is introduced. For example, a circulating water system using tap water that normally contains sodium hypochlorite, industrial water or well water to which an oxidizing agent such as sodium hypochlorite, sodium hypobromite, hydrogen peroxide, or ozone is added. The dyes described above can be used particularly advantageously as dye tracers in water such as circulating water systems using The oxidizing agent as described above is often used as a disinfectant or a slime controlling agent in a piping system by being added to makeup water in a circulating water system such as a cooling water system.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION WA Color Blue A-01 is a dye having a maximum absorption wavelength of 610 nm, which has light resistance, heat resistance,
Since it is a stable dye excellent in reduction resistance, oxidation resistance, acid resistance and alkali resistance, it is particularly preferable as a dye tracer. The present invention will be described in more detail by taking this as an example, but it goes without saying that the present invention is not limited to this.

WA Color Blue A-01 is added as a dye tracer in proportion to the amount of water treatment chemical added. As the addition method, a dye tracer and a water treatment chemical are separately added to water at a fixed ratio, or a dye tracer is previously blended into a water treatment chemical at a fixed ratio, and the water treatment chemical and the dye tracer are added. Is simultaneously added to water.

The concentration of WA Color Blue A-01 in circulating water such as cooling water is 1 to 10 mg / L (liter, the same applies hereinafter).
It works well as a dye tracer with a trace amount. Moreover, in such a concentration range, the calibration curve of the absorbance with respect to the dye concentration shows linearity.

As a method of calculating the concentration of the chemical for water treatment, the ratio between the amount of the chemical for water treatment and the amount of the dye tracer added to the water system is grasped in advance as a known coefficient (chemical concentration conversion coefficient by the dye). If this is done, for example, the concentration of the dye tracer in the water is optically detected using an absorptiometer or the like at an appropriate collection position and time, and the value is multiplied by a coefficient to obtain a chemical for water treatment. The concentration can be calculated. According to the calculated value, the necessary amount of the water treatment chemical and the dye tracer added to the water can be calculated.

In the method of the present invention, an absorption spectrophotometer for measuring two or more wavelengths is used, and as a tracer for the absorption spectrophotometry.
When using WA Color Blue A-01, for example, WA Color
One wavelength (measurement wavelength) around 610 nm, which is the maximum absorption wavelength of Blue A-01, and no absorption of WA ColorBlue A-01,
Moreover, the absorbance is measured at two wavelengths around 670 nm as a wavelength (reference wavelength) substantially free from the influence of absorption due to water contamination, and the difference is measured by the WA Color Blue A-01 tracer.
The concentration of the dye for water treatment can be controlled by determining the dye concentration as the absorbance of the dye.

[0028]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. In the following examples, the concentration measurement of WA Color Blue A-01 was performed by an absorption spectrophotometric method of measuring two wavelengths at a measurement wavelength of 610 nm and a reference wavelength of 670 nm, and the concentration measurement of brilliant blue FCF was performed at a measurement wavelength of 628 nm and a reference wavelength of 730 nm. The two-wavelength measurement was carried out by the absorption spectrophotometry.

Example 1 WA Color Blue A-01 was used as a dye. In order to confirm the stability of the dye, light, heat, pH, and oxidizing agent were used in each aqueous dispersion of WA Color Blue A-01. The effect of "free chlorine (sodium hypochlorite)" was examined by a beaker test.

[Effect of Light] A sample dispersion and a sample solution prepared by diluting with a pure water such that the concentrations of WA Color Blue A-01 and fluorescein for comparison become 4 mg / L each were placed in a place exposed to sunlight. The photostability was tested on standing. The experimental method was carried out by measuring the concentration of each dye over time and comparing the detection concentration percentage (%) when the detection concentration of each dye measured immediately after preparation of the sample solution was 100%. Was. The experiment period was one week in consideration of the residence time of the cooling water system and the like. The concentration of fluorescein was measured by an absorption spectrophotometer, and the measurement wavelength was 490 nm.

As a result of the test, as shown in Table 1, the fluorescein fades rapidly with time due to sunlight, whereas the stability of WA Color Blue A-01 is maintained without fading. It was confirmed that.

[0032]

[Table 1]

[Effect of Heat] A sample dispersion prepared by diluting with pure water so that the concentration of WA Color Blue A-01 was 4 mg / L was divided into three parts, and the water temperature was reduced to 0 ° C., 25 ° C., and 50 ° C. The sample dispersion was maintained and tested for thermal stability. The experimental method was performed by measuring the dye concentration over time and comparing the detection concentration percentage (%) with the detection concentration measured immediately after preparation of the sample dispersion as 100%. The experiment period was one week in consideration of the residence time of the cooling water system and the like.

As a result of the test, as shown in Table 2, WA Color
It was confirmed that Blue A-01 was hardly affected by heat in the range of 0 ° C to 50 ° C.

[0035]

[Table 2]

[Effect of pH] The concentration of WA Color Blue A-01 was 4 mg / L and the pH was 4, 7, and 11,
The stability of a sample dispersion prepared by adding pure water and an acid (hydrochloric acid) or pure water and an alkali (sodium hydroxide) to the dye was tested. The experimental method was performed by measuring the dye concentration over time and comparing the detection concentration percentage (%) with the detection concentration measured immediately after preparation of the sample dispersion as 100%. The experimental period was one week, taking into account the residence time of the cooling water system.

As a result of the test, as shown in Table 3, WA Color
It was confirmed that Blue A-01 was hardly affected in the above pH range (pH 4 to 11).

[0038]

[Table 3]

[Effect of Free Chlorine] The concentration of WA Color Blue A-01 was 4 mg / L, and the concentration of free chlorine was 0.1 and 0.1.
3. The stability of a sample dispersion prepared by adding pure water and sodium hypochlorite (oxidizing agent) to a concentration of 0.5 mg / L was tested. The experimental method measures the dye concentration over time,
The detection concentration percentage (%) was compared with the detection concentration measured immediately after preparation of the sample dispersion as 100%. The experimental period was one week, taking into account the residence time of the cooling water system.

As a result, as shown in Table 4, WA Color B
lue A-01 is in the above free chlorine concentration range (0.1-0.5
mg / L) was found to be hardly affected.

[0041]

[Table 4]

Example 2 In order to confirm that the dye according to the invention can be used as a dye tracer, a test was carried out in an open circulating cooling water system.

The operating conditions of the open circulating cooling water system are as follows. Water quality: Toda industrial water Water holding volume: 2 tons Circulating water volume: 1 ton / min Cooling water inlet water temperature of heat exchanger: 15 ° C Cooling water outlet water temperature of heat exchanger: 25 ° C. Evaporated water amount and splash water equivalent to Toda It was replenished with industrial water, but sodium hypochlorite was added to the make-up water at a free chlorine concentration of 0.5 mg / L, and the water treatment chemical to which the dye was added was opened and circulated before being introduced into the open circulating cooling water system. The cooling water system was operated for 24 hours or more, and the circulating water system was filled with Toda industrial water mixed with sodium hypochlorite.

A water treatment chemical prepared by mixing a certain amount of bromide ions in a cooling water system, and each pigment of WA ColorBlue A-01 and Brilliant Blue FCF having a concentration of 4 mg.
/ L, 0.05 mg / L, and circulated cooling water. Then, the bromide ion concentration and the dye concentration were measured with time, and the detection concentration percentages (%) when the detection concentrations of both were measured immediately after the addition were each 100%. The bromide ion concentration was determined by an ion chromatography method. Tables 5 and 6 show the composition of each water treatment chemical. In Tables 5 and 6, Caisson WT is an isothiazolone fungicide manufactured by Rohm and Haas, Accumer 2000 is a sulfonated acrylate copolymer manufactured by Rohm and Haas, and Diquest 2010 is Monsanto Japan ( Co., Ltd.).

[0045]

[Table 5]

[0046]

[Table 6]

As a result, as shown in Table 7, the behavior of the bromide ion concentration and the WA Color Blue A-01 concentration and the behavior of the bromide ion concentration and the brilliant blue FCF concentration were compared. It was found that the use of WA Color Blue A-01 as a dye tracer substance gave a better agreement when was present in an open circulating cooling water system. From these results, it was confirmed that when an oxidizing agent such as sodium hypochlorite is present in the open circulation cooling water system, the dye used in the method of the present invention is more effective as a dye tracer.

[0048]

[Table 7]

[0049]

According to the present invention, in a method for controlling the concentration of chemicals for water treatment in a circulating water system such as a cooling water system using a dye tracer, it is difficult to measure the concentration accurately by the conventional dye tracer method. Even in water systems affected by oxidizing agents such as sodium oxyacid, the concentration of water treatment chemicals added to water systems can be measured easily, quickly and accurately, and appropriate concentration management of water treatment chemicals added to water systems Can be performed. The circulating water system has been mainly described with reference to an open cooling water system (water cooling tower) as a typical example, but the method of the present invention is also applicable to a closed cooling water system, a boiler, an evaporative condenser, and the like. Of course, it can be used.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Horiike 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation F-term (reference) 2G020 AA03 AA04 BA02 BA14 CA02 CB07 CD05 CD13 CD38 2G059 AA01 BB04 BB20 CC20 DD03 DD05 DD20 EE01 EE12 FF13 HH02 HH06 PP10

Claims (5)

[Claims] 1. A light-fast and oxidation-resistant dye is dispersed in water with a dispersant as a tracer together with a water treatment chemical, and the dye is added to water by optically detecting the concentration of the dye in water. A method for controlling the concentration of a water treatment chemical, wherein the concentration of the water treatment chemical is controlled. 2. The water treatment chemical according to claim 1, wherein the optical detection of the concentration of the dye is performed by measurement at two or more wavelengths including at least one wavelength at which the dye absorbs. Concentration control method. 3. The method for controlling the concentration of a chemical for water treatment according to claim 1, wherein the optical detection of the concentration of the dye is performed by an absorptiometry. 4. The wavelength for measurement in the optical detection of the concentration of the dye is 400 nm to 800 nm, preferably 550 n.
4. The structure according to claim 1, wherein the wavelength is from m to 800 nm.
The method for controlling the concentration of a chemical for water treatment according to any one of the above. 5. The pigment according to claim 1, wherein the pigment contains at least one pigment selected from the group consisting of copper phthalocyanine pigments, monochloro copper phthalocyanine pigments, and polychloro copper phthalocyanine pigments. The method for controlling the concentration of the chemical for water treatment described above.