JP7256058B2 - Method for suppressing or removing adherence or breeding of organisms to seawater cooling water system, and method for treating seawater cooling water system water - Google Patents

Description

The present invention relates to a method for treating aqueous water to which monochloramine has been added at a relatively low concentration for the purpose of suppressing or removing the adhesion and propagation of organisms that may cause various disorders to the water system.

In various water systems such as cooling water, various process water, food manufacturing water, pure water, boiler water raw water, etc., the purpose is to suppress or remove the adhesion or breeding of organisms that may cause various problems. Addition of monochloramine is performed as a method (Patent Document 1).

However, when aquatic water containing these monochloramines is discharged into rivers, lakes, marshes, or the sea after its use, aquatic organisms such as marine resources existing in the water area near the outlet may be adversely affected. Concerned.

For this reason, there is a need to suppress or eliminate the concern that aquatic organisms such as marine resources will be adversely affected even when discharged into rivers, lakes, marshes, or the sea.

Here, Patent Document 2 proposes a technique of adding a sulfite for dechloramination after adding monochloramine to raw water in the production of pure water. The present inventors also thought that sodium sulfite could be suitably used (Patent Document 3).

JP 2015-212248 A JP-A-02-052087 JP 2017-119245 A

Japan Fisheries Resources Conservation Association, "Fisheries Water Standards 7th Edition (2012 Edition)", January 2013

However, as a result of examination, it is assumed that when sulfite (including bisulfite) is added as a reducing agent to water containing low concentrations of monochloramine, the total amount of residual chlorine can be offset. It was found that the amount was insufficient and the addition of six times that amount was required.
The reason for this is that when sulfites are added to water containing a low concentration of monochloramine, most of these sulfites react with dissolved oxygen in the water, which is present in a large amount relative to the content of monochloramine, As a result, it was considered that it hardly contributes to offsetting all residual chlorine.

In this case, not only does the cost of the reducing agent required for offsetting the total residual chlorine increase, but the dissolved oxygen concentration is remarkably reduced due to the addition of a large amount of sulfite despite the total amount of the residual chlorine being offset. There is concern that aquatic organisms, including fisheries resources, may be adversely affected by this.

The present invention solves the above-mentioned problems that occur when using such sulfites, that is, even when discharged into rivers, lakes, marshes, or seas, combined residual chlorine and free residual chlorine, and further, To reduce the required amount of the reducing agent that offsets all residual chlorine while suppressing or eliminating the concern of adverse effects on aquatic organisms near the discharge port due to the decrease in dissolved oxygen concentration due to the reducing agent added to offset these. It is an object of the present invention to provide a method for treating water system water.

The method for suppressing or removing the adhesion and propagation of organisms to a seawater cooling water system of the present invention is such that the concentration of total residual chlorine is 0.01 mg in the seawater cooling water system water to which monochloramine is added, which is finally discharged into the sea . / L or more and 0.15 mg / L or less, and a first step of adding monochloramine to the seawater cooling water system water to which the monochloramine has been added before the monochloramine is discharged into the sea A second step of adding 1 to 1.5 times the amount of thiosulfate compound that is assumed to be able to offset the total amount of residual chlorine in the seawater cooling water system water to which It is characterized by having

Further, the method for suppressing or removing the adhesion or breeding of organisms to a seawater cooling water system of the present invention, in addition to the above configuration, includes the total residual chlorine concentration of the seawater cooling water system and/or the content of the thiosulfate compound The total residual chlorine concentration after addition may be measured, and the amount of the thiosulfate compound to be added may be controlled according to the total residual chlorine concentration.

In order to solve the above problems, the method for treating seawater cooling water system water of the present invention contains monochloramine at a concentration of 0.01 mg / L or more and 0.15 mg / L or less of total residual chlorine, and finally To the seawater cooling water system water discharged into the sea , 1 to 1.5 times the added amount of thiosulfate compounds that is assumed to be able to offset the total amount of all residual chlorine in the seawater cooling water system water. It is characterized by adding

Further, in the aqueous water treatment method of the present invention, in addition to the above configuration, the total residual chlorine concentration of the aqueous water and / or the total residual chlorine concentration after the addition of the thiosulfate compound is measured, The amount of the thiosulfate compound to be added may be controlled according to the total residual chlorine concentration.

The method for suppressing or removing the adhesion and propagation of organisms to a seawater cooling water system of the present invention is such that the concentration of total residual chlorine is 0.01 mg in the seawater cooling water system water to which monochloramine is added, which is finally discharged into the sea . / L or more and 0.15 mg / L or less, and a first step of adding monochloramine to the seawater cooling water system water to which the monochloramine has been added before the monochloramine is discharged into the sea A second step of adding 1 to 1.5 times the amount of thiosulfate compound that is assumed to be able to offset the total amount of residual chlorine in the seawater cooling water system water to which Due to the equipped structure, when discharged into the sea , combined residual chlorine, free residual chlorine, and furthermore, a reduction in dissolved oxygen concentration due to the reducing agent added to offset them adversely affects aquatic organisms near the discharge port. It is possible to reduce the required amount of the reducing agent to offset all residual chlorine while significantly suppressing or eliminating the concerns. Furthermore, the adverse effects of combined residual chlorine and free residual chlorine can be suppressed or eliminated.

In addition to the above configuration, the total residual chlorine concentration of the seawater cooling water system and / or the total residual chlorine concentration after the addition of the thiosulfate compound is measured, and the thiosulfate compound is added according to this concentration. It can be configured to control the amount.

The seawater cooling water system water treatment method of the present invention contains monochloramine at a concentration of 0.01 mg / L or more and 0.15 mg / L or less of total residual chlorine, and is finally discharged into the sea . Discharged into the sea by adding a thiosulfate compound to water in an amount of 1 to 1.5 times the amount assumed to be able to offset the total amount of residual chlorine in the seawater cooling water system. In this case, it is possible to remarkably suppress or eliminate the concern that aquatic organisms near the discharge port may be adversely affected by a decrease in dissolved oxygen concentration due to combined residual chlorine, free residual chlorine, and a reducing agent added to offset them. , it is possible to reduce the amount of reducing agent required to offset the total residual chlorine. Furthermore, the adverse effects of combined residual chlorine and free residual chlorine can be suppressed or eliminated.

In addition to the above configuration, the total residual chlorine concentration of the water system and / or the total residual chlorine concentration after the addition of the thiosulfate compound is measured, and the amount of the thiosulfate compound added is adjusted according to this concentration. It can be configured to control.

1 is a model diagram showing a monochloramine generator used in Examples. FIG.

The aqueous water treatment method of the present invention is carried out on aqueous water containing monochloramine at a low concentration.

Here, monochloramine is added for the purpose of suppressing or removing organisms that may cause various disorders from adhering to water systems or breeding.

However, when monochloramine is added to aqueous water for the above purpose, the effect of addition can be sufficiently obtained and it is not excessively added. ) or more and 0.15 mg/L or less.

When monochloramine is contained in aqueous water at such a low concentration, for water systems containing organic matter such as cooling water systems, a relatively high concentration, for example 500 mg, is obtained due to the reaction between the hypochlorous acid compound and the ammonium salt compound. It is preferable to prepare a high-concentration monochloramine solution so that the concentration range is from 10000 mg/L to 10000 mg/L, and then add monochloramine to the aqueous water.
In the case of water-based water containing organic matter, even if the hypochlorous acid compound and the ammonium salt compound are directly added separately to a low concentration of, for example, several mg/L or less, the reaction rate of monochloramine production is slow. Since these organic substances rapidly react with low-concentration hypochlorous acid compounds to decompose the hypochlorous acid compounds, the added hypochlorous acid compounds cannot contribute to the production of monochloramine.

A relatively high concentration monochloramine solution can be prepared continuously, for example, as follows. That is, the free residual chlorine concentration in the water flowing through the liquid feeding path such as the pipe whose downstream end is connected to the water system to be added is, for example, 500 mg / L or more and 10000 mg / L or less. The hypochlorous acid compound is added, and the molar ratio of the free residual chlorine concentration and the ammonium ion concentration in the water is 1:1 to 1:1.5 downstream of the addition point of the hypochlorous acid compound in the liquid feeding path. By adding the ammonium salt compound so that the range of (including the boundary value), the hypochlorous acid compound and the ammonium salt compound are reacted to prepare a monochloramine solution.

As the water flowing through the liquid-feeding path to be used, in addition to clear water such as tap water and industrial water, water containing organic matter to which monochloramine is added can be used alone or in combination with clear water.
By significantly increasing the amount of hypochlorous acid compound added compared to the amount of organic matter that reacts with the hypochlorous acid compound in the water, monochloramine can be produced even if water containing organic matter is used. It is possible to suppress the reduction of hypochlorous acid compounds to the extent that it adversely affects production. However, if the organic substances in the water react with the hypochlorous acid compound, trihalomethanes may be produced. Therefore, it is preferable to use fresh water in order to prevent the production of trihalomethanes.
Even if a monochloramine solution obtained by reacting a hypochlorous acid compound and an ammonium salt compound is added to aqueous water containing organic matter, the monochloramine reacts with the organic matter in the water to produce trihalomethane. never.

The hypochlorous acid compound to be used includes, but is not limited to, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, or a combination thereof. Any compound that generates chlorate may be used.
Among these, when using a commercially available 5 to 12% by mass sodium hypochlorite aqueous solution, it is easy to inject with a pump, and furthermore, a moderate amount of free alkali coexists in the commercially available sodium hypochlorite aqueous solution. This is preferable because the production reaction of monochloramine proceeds rapidly.

When preparing the monochloramine solution, the hypochlorous acid compound is preferably added so that the concentration of free residual chlorine in water is 500 mg/L or more and 10000 mg/L or less. If the concentration of the hypochlorous acid compound added is too low, it becomes difficult to generate monochloramine.
In addition, since the concentration of monochloramine produced is also low, in order to make the concentration of monochloramine added to the water system to be added to the desired total residual chlorine concentration range of 0.01 mg / L or more and 0.15 mg / L or less, A large amount of monochloramine solution must be added to the target water system. As a result, there arises a problem that the monochloramine generating apparatus is enlarged.
Further, if the concentration of the monochloramine solution is too high at the time of addition, even if the molar ratio of ammonium ion to free residual chlorine is 1 or more, by-products such as dichloramine and trichloramine are produced in addition to monochloramine, which is preferable. do not have.
The dichloramine and trichloramine produced in this way are unstable, and they react in a complex manner with monochloramine to proceed with the decomposition reaction of ammonia nitrogen, thereby lowering the concentration of monochloramine.
In addition, this reaction is a reaction accompanied by a decrease in pH, and when the pH of the solution becomes acidic, chlorine gas is generated from hypochlorite ions, which is extremely dangerous. A more preferable concentration range is 1000 mg/L or more and 5000 mg/L or less.

Ammonium salt compounds used to prepare the monochloramine solution include ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate, ammonium phosphate, ammonium sulfate, ammonium borate, and the like, and combinations thereof, but relatively high concentrations of Ammonium chloride and ammonium sulfate are preferred because they can be aqueous monochloramine solutions and are easier to pump.

When the ammonium salt compound is added so that the ammonium ion concentration (molarity) is 1 or more when the free residual chlorine concentration (molarity) in water is 1, monochloramine can be efficiently produced, which is preferable.

As will be described later, when the water in which all the residual chlorine in water containing monochloramine at a low concentration is offset by a thiosulfate compound is discharged into rivers, lakes, marshes, or seas with marine resources. If the above molar ratio exceeds 1.5, the concentration of ammonium nitrogen in the water area near the outlet may exceed the standard for marine water (Non-Patent Document 1), which is not preferable.

Moreover, it is preferable to add the ammonium salt compound downstream of the point where the hypochlorous acid compound is added. When the ammonium salt compound is added upstream of the hypochlorous acid compound addition point, before the hypochlorous acid compound near the hypochlorous acid compound addition point and water are completely mixed, the ammonium ion The molar ratio of hypochlorite ions (=free residual chlorine) partially becomes 1 or more. As a result, dichloramine and trichloramine, which are by-products, are produced in addition to monochloramine at a molar ratio of 1 or more.

If the order of addition of the hypochlorous acid compound and the ammonium salt compound and their concentrations and molar ratios are appropriate, the above side reactions do not occur and only monochloramine can be produced. The reaction proceeds most easily in weakly alkaline conditions of pH 8-9.
Therefore, it is preferable to use an aqueous sodium hypochlorite solution containing free alkali as the hypochlorous acid compound, because the pH of the water after addition of the hypochlorous acid compound naturally becomes weakly alkaline.

Incidentally, it is preferable to install a stirring means such as a line mixer downstream of the addition point of the hypochlorous acid compound and the addition point of the ammonium salt compound, since monochloramine is efficiently generated.
In particular, when a line mixer is installed between the point where the hypochlorous acid compound is added and the point where the ammonium salt compound is added, the concentration of hypochlorite ions in the water becomes uniform, and the molar ratio of hypochlorite ions and ammonium ions increases. This is preferable because partial reversal of the ratio can be prevented. Moreover, a mixing tank may be provided in the middle of the liquid feeding path, and stirring may be performed in this mixing tank.

By producing the monochloramine solution by the above method, almost all of the free residual chlorine derived from the initially added hypochlorous acid compound contributes to the production of monochloramine. Therefore, the total residual chlorine concentration in the produced monochloramine solution becomes an arbitrary concentration of 500 mg/L or more and 10000 mg/L or less, which is almost the same as the free residual chlorine concentration in water when the hypochlorous acid compound is added.

A monochloramine solution with an arbitrary concentration of 500 mg / L or more and 10000 mg / L or less prepared by the above method is added to the aqueous water to be added as a total residual chlorine concentration of 0.01 mg / L or more and 0.15 mg / L or less. It is preferred to add in concentration.
If the concentration of monochloramine added is less than 0.01 mg/L, the effect of adding monochloramine, such as the suppression or removal of the adhesion of organisms that may cause various disorders to the water system, or the breeding, is not sufficient. I can't do it. On the other hand, when the additive concentration exceeds 0.15 mg / L, the increase in the effect corresponding to the increase in the additive concentration is not obtained, and furthermore, the concentration of ammonium nitrogen in the water area near the outlet exceeds the above marine water standard There is a risk of exceeding

In the aqueous water treatment method of the present invention, when the monochloramine in the aqueous water becomes unnecessary, a thiosulfate compound is added to offset the residual monochloramine. For example, in a seawater cooling water system, monochloramine is added for the purpose of adhering organisms to the water system, and when the cooling water is finally discharged into the sea, monochloramine remaining in the cooling water is removed by thiosulfuric acid at the upstream of the discharge port. Offset by addition of salt compounds.

Sodium salts, potassium salts, barium salts, magnesium salts, ammonium salts and the like are known as thiosulfate compounds. Among these, water-soluble and reducing compounds are used alone or in combination of two or more.
Among these, sodium thiosulfate, which is easily available, is preferably used. The thiosulfate compound is usually added as an aqueous solution of fresh water such as tap water or industrial water, but water to which monochloramine is added partially or wholly may be used.

It is preferable that the amount of the thiosulfate compound to be added is capable of canceling out the total amount of residual chlorine in the aqueous water containing monochloramine, since this makes it possible to suppress or prevent the occurrence of various problems caused by residual chlorine.

When an aqueous solution of a thiosulfate compound is used, if the concentration is 0.1% by mass or more and 30% by mass or less, the addition can be easily controlled and the addition device including the chemical tank can be made compact. It is preferable because it can be done.

In the present invention, it is essential to add a thiosulfate compound as described above, and at this time, for example, monochloramine and sodium thiosulfate react in a molar ratio of 4:1 as shown in formula (I) below. .

<Chemical 1>
_{4NH2Cl + Na2S2O3.5H2O → 2NaHSO4 + 4NH4Cl}
…… (I)

In the present invention, the total amount of residual chlorine in the aqueous water to be added is assumed to be due to monochloramine, and an amount assumed to be able to offset the entire amount, that is, a thiosulfate compound with a molar number of 1/4 of the molar number of this monochloramine It is preferable to add the thiosulfate compound in a mass of 1 or more and 1.5 or less when the mass of is 1.

If the amount of the thiosulfate compound added is less than the above range, there is a greater concern that residual monochloramine will have an adverse effect on aquatic organisms when the water after offsetting treatment is discharged into rivers, lakes, marshes, or the sea. On the other hand, if the amount is too large, the amount of the thiosulfate compound to be used is increased, which may lead to an increase in the treatment cost and a decrease in the dissolved oxygen concentration in the effluent. Therefore, there is a growing concern about adverse effects on aquatic organisms in water areas near the outlet.
Therefore, the amount of the thiosulfate compound to be added is more preferably 1.05 or more when the amount of the thiosulfate compound assumed to be able to offset the total amount of residual chlorine in the water system to be added is 1.05 or more. 3 or less.

When adding a thiosulfate compound, the total residual chlorine concentration in the water to which the thiosulfate compound is added and/or after the addition of the thiosulfate compound is measured with a residual chlorine meter or the like, and the amount added is controlled. , it is possible to optimize the amount of addition. This control makes it possible to more reliably suppress or prevent the occurrence of adverse effects of residual chlorine on aquatic organisms, and to prevent excessive addition that causes an increase in cost and a decrease in dissolved oxygen.

Here, the reaction formula with monochloramine when sodium hydrogen sulfite (sodium bisulfite) is used instead of a thiosulfate compound as a reducing agent is shown in formula (II).

<Chemical 2>
_NH2Cl + _NaHSO3 + _H2O -> _NaHSO4 + _NH4Cl
…… (II)

In this way, when monochloramine and sodium hydrogen sulfite react, even if the counteracting reaction of monochloramine by sodium hydrogen sulfite proceeds 100%, hydrogen sulfite is added to monochloramine at a molar ratio of 1:1. You need sodium.
And, although it is presumed to be due to the dissolved oxygen in the water to be treated, the required amount is actually even greater, and the reduction is 6 times the addition amount assumed to be able to offset the total amount of all residual chlorine in the water system. You will need a drug.

In addition, when the width of the water channel where the thiosulfate compound is added is wide, the addition of the thiosulfate compound to the water channel may be performed at multiple points in the width direction of the water channel. It is preferable because the canceling effect of
In addition, if a mixing means such as a line mixer, a baffle plate that partially blocks the flow of the water system, or a mixing tank equipped with a stirrer is installed downstream of the addition point of the thiosulfate compound in the water flow direction, the residual chlorine will be offset. It is preferable because it becomes possible to ensure the

In the present invention, the addition of monochloramine and the thiosulfate compound may be carried out continuously, or may be carried out intermittently depending on the purpose of addition of monochloramine.

Although the present invention has been described above with reference to preferred embodiments, the method for treating aqueous water of the present invention is not limited to the configurations of the above embodiments.

Those skilled in the art can appropriately modify the aqueous water treatment method of the present invention according to conventionally known knowledge. Even with such modification, as long as it has the configuration of the aqueous water treatment method of the present invention, it is of course included in the scope of the present invention.

<<Example 1>>
One week after preparation, monochloramine was added as a chlorinating agent to pure water that was considered to contain dissolved oxygen at a saturated or near-saturated level, and test water with a total residual chlorine concentration of 0.1 mg/L ( 15.0°C) was prepared.

1 L of this test water is collected in a 1 L beaker and stirred at 300 revolutions per minute. amount of 0.1 mol/L sodium thiosulfate aqueous solution was added. Table 1 shows the history of the total residual chlorine concentration of the test water.

It can be seen from Table 1 that when sodium thiosulfate is used, it is possible to offset the total amount of residual chlorine by monochloramine with the assumed required amount of sodium thiosulfate aqueous solution.

<<Comparative example 1>>
As in Example 1, except that instead of the sodium thiosulfate aqueous solution, a 0.1 mol/L sodium hydrogensulfite aqueous solution is used, and it is assumed that the total amount of monochloramine in the test water reacts with sodium hydrogensulfate according to the reaction formula (II). The required amount was added when the test water was added, and the total residual chlorine concentration of the test water was measured.
As a result, the total residual chlorine concentration in the test water was 0.08 mg / L, and the offset by sodium hydrogen sulfite was insufficient, so the same amount of hydrogen sulfite was added until the total residual chlorine in the test water was not detected. The addition of aqueous sodium solution and measurement of total residual chlorine concentration were repeated. Table 2 shows the history of the total residual chlorine concentration of the test water at this time.

From Table 2, it can be seen that 6 times the amount of the sodium bisulfite aqueous solution originally assumed is required to offset the total amount of residual chlorine.

<Example 2 and Comparative Example 2>
The test was conducted in the same manner as in Example 1 and Comparative Example 1, except that instead of pure water, seawater sampled at the inlet of the seawater cooling water system of a factory located on the coast of Tokyo Bay was used.

As a result, when sodium thiosulfate was used, the total amount of residual chlorine in the test water could be offset by the addition amount assumed to be able to offset the total amount of residual chlorine, but when using the sodium sulfite aqueous solution required 6 times the amount of aqueous sodium sulfite solution expected to offset the total amount of residual chlorine in the test water.

<Example 3>
The test was conducted in the seawater cooling water system of a factory located on the Tokyo Bay.
Monochloramine was produced using a monochloramine production apparatus A modeled in FIG.

In the monochloramine generator A, a pump 11 pumps industrial water at a flow rate of 0.3 L per hour from a water tank 10 storing a constant amount of industrial water through ball tap LS control.
In the liquid feeding route, a 12% by mass sodium hypochlorite aqueous solution in the tank 12 is added by the pump 13 at an addition amount of 2.5 g per hour, stirred by the line mixer 14, and then further downstream A 15 mass % ammonium chloride aqueous solution in tank 15 was added by pump 16 at an addition rate of 1.8 g per hour to produce monochloramine.
At this time, the molar ratio of free residual chlorine concentration and ammonium ion concentration mixed in the liquid feeding path was 1:1.2, and the concentration of the produced monochloramine aqueous solution was 1000 mg/L as the total residual chlorine concentration. .

The monochloramine solution thus produced was added to seawater flowing through the seawater cooling water system so that the total residual chlorine concentration was 0.1 mg/L.

In the upstream of this seawater cooling water system near the discharge port to the sea, install the first chlorine concentration meter, the chemical injection pump, the baffle plate for stirring, and the second chlorine concentration meter in the order of the flow direction of the seawater cooling water. , 30 masses, which is 1.2 times the required amount assumed to be able to offset the total residual chlorine concentration detected by the first chlorine concentration meter by reacting with sodium thiosulfate according to the reaction formula (I) % sodium thiosulfate aqueous solution. No residual chlorine was detected by the second chlorine concentration meter.

In addition, it was possible to prevent the attachment of barnacles, hydroids, sea squirts, shellfish such as mussels, and marine organisms such as slime derived from microorganisms to the cooling water system throughout the year. .

A Monochloramine generator LS Ball tap 10 Water tank 11 Pump 12 Tank 13 Pump 14 Line mixer 15 Tank 16 Pump

Claims (4)

First , monochloramine is added so that the concentration of total residual chlorine is 0.01 mg / L or more and 0.15 mg / L or less to the seawater cooling water system water to which monochloramine is added, which is finally discharged to the sea . It is assumed that the seawater cooling water system water to which the monochloramine has been added can offset the total amount of all residual chlorine in the seawater cooling water system water to which the monochloramine has been added before being discharged into the sea. and a second step of adding a thiosulfate compound in an amount of 1 to 1.5 times the amount added, in this order . Or how to remove it. The total residual chlorine concentration of the seawater cooling water system and/or the total residual chlorine concentration after the addition of the thiosulfate compound is measured, and the amount of the thiosulfate compound added is controlled according to the total residual chlorine concentration. 2. The method for suppressing or removing organisms from adhering to or breeding in a seawater cooling water system according to claim 1, characterized by: For seawater cooling water system water containing monochloramine at a concentration of 0.01 mg / L or more and 0.15 mg / L or less total residual chlorine and finally discharged to the sea , in the seawater cooling water system water A method for treating seawater cooling system water, characterized by adding a thiosulfate compound in an amount of 1 to 1.5 times the amount assumed to be able to offset the total amount of residual chlorine. The total residual chlorine concentration of the seawater cooling water system and/or the total residual chlorine concentration after the addition of the thiosulfate compound is measured, and the amount of the thiosulfate compound added is controlled according to the total residual chlorine concentration. The method for treating seawater cooling water system water according to claim 3, characterized in that:

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