JPH1028981A - Chlorine disinfection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately control the amt. of residual combined chlorine by the efficient injection of a chemical. SOLUTION: Monochloramine and dichloramine are separately measured by an automatic effective chlorine and monochloramine measuring device 30, and ammoniacal nitrogen is measured by an automatic ammonium measuring device 32. The measured values are fed to a controller 20. The amt. of chlorine to be injected from a sodium hypochlorite storage tank 22 and the amt. of ammonia to be injected from an aq. ammonium sulfate soln. storage tank 26 are controlled by the controller 20 based on both the measured values so that the ratio of the monochloramine to ammoniacal nitrogen is controlled to 1:4 and dichloramine is substantially eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disinfection treatment system for water purification and the like for producing tap water and industrial water, and more particularly to a chlorination treatment using combined chlorine.

[0002]

2. Description of the Related Art Various methods have been proposed for killing Escherichia coli and general bacteria existing in water and suppressing their growth. Among them, chlorine disinfection utilizing the oxidizing power of chlorine is the most widely adopted method.

There are two types of chlorine disinfection: a method of disinfecting chlorine in the form of free chlorine and a method of disinfecting in the form of bound chlorine (chloramine) obtained by reacting with chlorine. The sum of free chlorine and bound chlorine is called available chlorine.
However, at present, disinfection in the form of free chlorine is generally employed. According to the method of disinfecting in the form of free chlorine, the chlorine concentration in the clean water, that is, the sterilizing power changes temporarily with respect to the injection amount of chlorine, which is advantageous for control, and the sterilization is also effective. Because he is powerful.

[0004] Here, in the disinfection method using free chlorine, there is a concern that trihalomethane, which is a carcinogenic substance, may be produced. That is, in a water purification plant that manufactures tap water (tap water), river water or dam lake water is usually used as raw water and purified. These raw waters contain various organic substances, and often contain a trihalomethane precursor such as humic acid. Therefore, in the water purification treatment, if the disinfection treatment is performed using free chlorine, trihalomethane may be generated.

[0005] On the other hand, if trihalomethane is produced during the water purification treatment, it can be removed. However, if a method is used in which free chlorine remains and water is supplied after the water purification treatment, the remaining trihalomethane precursor remaining in the water distribution pipe and the like may react with free chlorine to generate trihalomethane. In some cases, the concentration of trihalomethane at the outlet of the water faucet may be considerably increased.

[0006] On the other hand, the method of disinfection in the form of bound chlorine has a sterilizing power as low as several tenths as compared with free chlorine, but hardly produces trihalomethane. Therefore, a method has been proposed in which a predetermined amount of ammonia (usually an ammonium salt) is added to water after chlorination using ordinary free chlorine to convert free chlorine remaining in the water into bound chlorine. Thereby, it is possible to prevent the generation of trihalomethane in the water distribution pipe while maintaining the sterilizing power.

Here, it is generally known that a discontinuous point (breakpoint) exists in the reaction between ammonia and chlorine. This will be described on the assumption that the pH is around neutral. The ratio of chlorine to ammonia is 0
From the beginning, as shown in FIG. 2, as the proportion of chlorine increases at first, most of the chlorine becomes monochloramine and the effective chlorine amount increases. However, when the ratio reaches a certain ratio (chlorine: ammonia nitrogen = 1: 5), monochloramine starts to decrease while the ratio of dichloramine increases, and the available chlorine amount also starts to decrease. When the proportion of chlorine further increases, a point where available chlorine hardly exists, that is, a discontinuous point is reached. When the proportion of chlorine is increased beyond the discontinuous point, free chlorine and trichloramine increase, and available chlorine increases. As described above, the reaction between chlorine and ammonia up to the point where the discontinuous point is exceeded is complicated, and in some cases, available chlorine may be lost.

Therefore, when using bound chlorine, the amount of available chlorine is reduced with respect to the increase of chlorine in order to prevent a situation where available chlorine disappears even if the proportion of chlorine is slightly increased. It is preferable to control the ratio of chlorine and ammonia nitrogen to an increasing range, that is, a range in which available chlorine increases with an increase in the ratio of chlorine (for example, a range of chlorine addition rate of 0 to 5 in FIG. 2).

However, when treating raw water having relatively large fluctuations in water quality, such as river water, the amount of free chlorine remaining after disinfection with free chlorine fluctuates greatly. Therefore, the amount of available chlorine in water distribution cannot be maintained at a predetermined value only by the addition of ammonia, and in some cases, the addition of chlorine is required. That is, water distribution (treated water in the water distribution tank)
The amount of available chlorine is detected and the amount of added chlorine is controlled based on the detected value. Specifically, if the detected amount of available chlorine is smaller than a predetermined value, the amount of added chlorine is increased.

However, as described above, the discontinuous point may be approached by increasing the amount of chlorine added, and the effective chlorine amount may decrease. Therefore, in a normal case, the amount of available chlorine in the treated water is controlled to a predetermined value by controlling both the amounts of addition of ammonia and chlorine. That is, if the amount of addition of both ammonia and chlorine is increased or decreased, the available chlorine is also increased or decreased with this increase or decrease. Therefore, the same control as the normal control can be performed without considering the discontinuous point.

[0011]

However, as described above,
In the method of increasing and decreasing both ammonia and chlorine together, a chlorine agent (for example, sodium hypochlorite, chlorine gas, calcium hypochlorite, etc.) and an ammonia agent (ammonium sulfate, etc.) are supplied in excess. It can be uneconomical.

In other words, when the effective chlorine amount tends to decrease as the chlorine ratio increases (in FIG. 2, the chlorine addition ratio is in the range of 5 to 10), the chlorine addition amount is simply reduced. Thus, the amount of available chlorine can be increased. In such a case, it is inefficient to increase the amounts of both chlorine and ammonia added.

The present invention has been made in view of the above problems, and has as its object to provide a chlorine disinfection treatment system capable of securing a reliable effective chlorine amount by efficiently adding a chemical.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a chlorine disinfection treatment system for chlorinating water, comprising chlorine adding means for adding a chlorine agent to the water to be treated, and adding an ammonia agent to the water to be treated. Ammonia adding means, chloramine measuring means for measuring bound chlorine in treated water to which chlorine and ammonia are added separately into monochloramine and dichloramine, and ammonia adding means and chlorine based on the measurement values obtained by the chloramine measuring means. Control means for controlling the amount of addition in the addition means.

As described above, the chloramine measuring means separately measures both monochloramine and dichloramine. When chlorine is gradually added to water in which ammonia exists,
At first, monochloramine is generated and the available chlorine amount increases. However, when the ratio of ammonia nitrogen to chlorine exceeds 5: 1, dichloramine starts to be generated and the available chlorine amount starts to decrease.

In the present invention, since both monochloramine and dichloramine are measured, the composition of bound chlorine can be known. Therefore, the ratio of chlorine to ammonia can be controlled to a position where available chlorine increases with an increase in chlorine, that is, a position where mainly monochloramine is generated and dichloramine is not substantially present. Therefore, the necessary effective chlorine amount can be ensured by always using chlorine and ammonia as optimal addition amounts.

Further, the present invention further comprises ammonia measuring means for measuring the ammonia concentration of the treated water, and the control means uses the measured value of the ammonia measuring means to measure the ammonia concentration in the ammonia adding means and the chlorine adding means. The amount is controlled.

As described above, by measuring the ammonia, more appropriate control of the amounts of the chlorine agent and the ammonia agent can be performed.

Further, the present invention is characterized in that it further comprises a pH adjusting means for adjusting the pH of the treated water. pH
By adjusting the ratio, the ratio of monochloramine to dichloramine can always be maintained at a predetermined ratio, and more accurate control of the amounts of the chlorine agent and the ammonia agent can be performed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. FIG. 1 shows a configuration of an example of the embodiment.

First, the inflow water such as river water is coagulated and settled in a pond 10.
Flows into. In this coagulation sedimentation basin 10,
Coagulation sedimentation treatment with an aluminum coagulant or the like is performed. Then, the coagulated sedimentation treatment water is supplied to the rapid filtration pond 12, where it undergoes rapid filtration treatment.

Here, in this embodiment, the intermediate chlorination treatment is performed on the coagulated sedimentation treatment water by free chlorine treatment. For this purpose, sodium hypochlorite from the first sodium hypochlorite storage tank 14 is added to the coagulated sedimentation treatment water by the first sodium hypochlorite injection pump 16 and supplied to the rapid filtration pond 12. I do. Therefore, in the rapid filtration pond 12,
Disinfection with chlorine is performed. At this time, the amount of sodium hypochlorite added is the same as in the normal treatment, the free chlorine treatment of adding chlorine beyond the discontinuous point, that is, a predetermined amount of free chlorine in the outlet water of the rapid filtration pond 12. It is treated so as to leave no ammonia nitrogen.

Here, the amount of sodium hypochlorite added in the intermediate chlorination is controlled appropriately using a chlorine demand meter or the like. Furthermore, the rapid filtration pond 12
Is provided with an automatic free chlorine measuring device 18 for measuring the free chlorine concentration. This automatic chlorine detector 18
Is supplied to a control device 20. The control device 20 controls the first sodium hypochlorite injection pump 16 so that the amount of sodium hypochlorite added becomes an appropriate amount. doing.

However, even with such control, the concentration of free chlorine at the outlet of the rapid filtration pond 12 varies considerably due to factors such as fluctuations in raw water quality and time delays in control. Therefore, a second sodium hypochlorite storage tank 22 and a second sodium hypochlorite injection pump 24 are provided,
When the free chlorine concentration is lower than a predetermined value, the insufficient chlorine is added to the treated water of the rapid filtration pond 12. That is, the control device 20 controls the second sodium hypochlorite injection pump 24 in accordance with the measurement value of the automatic free chlorine measuring device 18 to supply a shortage of free chlorine to the outlet water of the rapid filtration tank 12. I do.

Further, in this embodiment, the 2% ammonium sulfate solution from the ammonium sulfate aqueous solution storage tank 26 is added to the outlet water of the rapid filtration pond 12 by the ammonium sulfate aqueous solution injection pump 28, and the free chlorine contained therein is combined with the bound chlorine. And

The amount of ammonium sulfate added is also adjusted by controlling the ammonium sulfate aqueous solution injection pump 28 by the controller 20. Here, the addition of ammonium sulfate is performed so that the ratio of chlorine to ammonia nitrogen is 1: 4, for example, in order to generate monochloramine but not dichloramine.

That is, the free chlorine concentration at the outlet of the rapid filtration pond 12 is measured by the automatic free chlorine measuring device 18,
If it is less than the target value, a shortage of sodium hypochlorite is added from the second sodium hypochlorite storage tank 22, and ammonium sulfate is added from the ammonium sulfate aqueous solution storage tank 26 by an almost constant amount of the ammonium sulfate aqueous solution injection pump 28. On the other hand, when the free chlorine is larger than the target value, only ammonium sulfate is added in proportion to the free chlorine so that the ratio of chlorine to ammonia becomes 1: 4.

However, these operations merely adjust the outputs of the second sodium hypochlorite injection pump 24 and the ammonium sulfate aqueous solution injection pump 28 automatically, and change the effective concentration of the injected chemical and the water quality. Since the fluctuation is not corrected, the concentration of the actually generated bound chlorine does not always match the target value. Therefore, in the present embodiment, the actual available chlorine amount and the monochloramine amount are measured by the automatic available chlorine / monochloramine measuring device 30, and the ammonia nitrogen concentration is measured by the automatic ammonia measuring device 32.
Measure with. This measurement is performed at intervals of 2 to 10 minutes, and the measured value is supplied to the control device 20. The control device 20 determines the excess or deficiency of sodium hypochlorite and ammonium sulfate based on each measurement value, and a second sodium hypochlorite injection pump 24 for sodium hypochlorite injection, and a second sodium hypochlorite injection pump for ammonium sulfate injection. The output of the ammonium sulfate aqueous solution injection pump 28 is adjusted.

At this time, the pH of the outlet water of the rapid filtration pond 12 is measured by a pH meter 34. The measured value is supplied to the control device 20. The control device 20
Sulfuric acid is injected from the sulfuric acid storage tank 36 with the sulfuric acid injection pump 38 or the sodium hydroxide aqueous solution injection pump 42 is injected from the sodium hydroxide aqueous solution storage tank 40 so that the pH of the outlet water becomes 7.5 ± 0.5. Control injection of sodium hydroxide solution. Thereby, the pH in the process for producing bound chlorine can be kept within a predetermined range. In addition, the treated water is distributed via the water purification pond 44.

Here, generation of bound chlorine will be described. In order to secure the necessary available chlorine amount and make monochloramine the main disinfectant, it is necessary to control the chlorine amount and the ammonia amount and their ratio. In the case of pH 7.5, monochloramine, dichloramine, and residual ammonia nitrogen concentration are as follows:
The relationship is as shown in FIG. Therefore, by measuring these, it is possible to determine whether the chlorine concentration should be reduced, the ammonia should be increased, the chlorine and ammonia should be increased, or the chlorine and ammonia should be reduced to obtain an arbitrary effective chlorine concentration.

Therefore, the control device 20 controls the second sodium hypochlorite injection pump 24 and the ammonium sulfate aqueous solution injection pump 28 so that the combined chlorine (monochloramine) becomes the target value and that dichloramine does not exist. To This makes it possible to control the effective chlorine amount in FIG. 2 to a position where the amount of available chlorine is uphill (the region on the left side of the straight line 1 in FIG. 2), and it is possible to make the added amounts of the chlorine agent and the ammonia agent appropriate.

For example, in the case of a point, it is only necessary to reduce the chlorine while leaving the ammonia as it is, in the case of a point it is sufficient to increase the ammonia while keeping the chlorine as it is, and in the case of the point, the chlorine and ammonia are increased at a constant ratio to increase the point. In the case of, the ratio may be constant and both may be reduced.

In this embodiment, monochloramine and dichloramine are separately measured by the automatic effective chlorine / monochloramine measuring device 30. This analysis is performed by an amperometric titration method using phenyl arsen oxide (hereinafter, PAO) as a reagent.

Although this analysis method is generally known, this titration is performed by an automatic titrator. The measuring method at this time is as follows.

(I) The pH of the measurement sample water is adjusted to 7.

(Ii) Amperometric titration using PAO to determine the free chlorine concentration. This titration neutralizes free chlorine.

(Iii) Potassium iodide is added to the same sample water, and current titration is again performed using PAO to determine the monochloramine concentration. Monochloramine is neutralized by this titration.

(Iv) Adjust the pH to 4 with the same sample water,
Further, potassium iodide is added, and amperometric titration is performed using PAO, and the dichloramine concentration is measured.

The automatic effective chlorine / monochloramine measuring instrument 30 automatically performs these series of analysis operations,
The concentrations of free chlorine, monochloramine and dichloramine are separately output and supplied to the control device 20.

[0040]

【Example】

(Example 1) For example, it is assumed that the target value of the residual chlorine at the outlet of the quick filtration pond 12 is 2 mg / l, and the free residual chlorine concentration measured by the automatic free chlorine measuring device 18 is 1.0 mg / l. . In this case, the second sodium hypochlorite injection pump 24 injects so as to add 1.0 mg / l of available chlorine in calculation. The target amount of ammonium sulfate was 0.5 mg /
1 (2 ÷ 4).

10 to 30 minutes after the injection of ammonium sulfate, the ammonia nitrogen concentration of the treated water is measured by an automatic ammonia measuring device 32, and the effective chlorine concentration and monochloramine concentration are measured by the automatic effective chlorine / monochloramine measuring device 30.
And supplies those values to the control device 20. The control device 20 accurately grasps the position in FIG. 2 based on the measurement values supplied from the automatic ammonia measuring device 32 and the automatic effective chlorine / monochloramine measuring device 30 so that the position is the target position. The second sodium hypochlorite injection pump 24 and the ammonium sulfate aqueous solution injection pump 28 are adjusted.

Effective chlorine-monochloramine concentration = dichloramine concentration. Therefore, for example, the effective chlorine concentration is lower than the target value of 2 mg / l, and dichloramine exists,
In the case where the ammonia nitrogen concentration is 0.2 mg / l or less, that is, in the case as shown in FIG. 2, the chlorine concentration is higher than the ammonia nitrogen concentration. For this reason, the injection amount of sodium hypochlorite by the second sodium hypochlorite injection pump 24 is reduced. Thereby, the effective chlorine concentration can be increased to the target value, and dichloramine can be prevented from being present.

(Example 2) For example, the target value of the residual chlorine at the outlet of the rapid filtration tank 12 is 2 mg / l, and the concentration of the residual free chlorine measured by the automatic free chlorine measuring device 18 is 2.5 mg / l.
In the case of 1, the output of the first sodium hypochlorite injection pump 16 is reduced to 80% assuming that the output up to that time is 100%. Ammonium sulfate is the target value of 0.5 mg / l by the ammonium sulfate aqueous solution injection pump 28.
It is infused to a further increase to 0.63 mg / l (2.5 / 4). At this time, the output of the second sodium hypochlorite injection pump 24 becomes 0%.

10 to 30 minutes after the injection of ammonium sulfate, the ammonia nitrogen concentration of the water to be treated is measured by the automatic ammonia analyzer 32, and the effective chlorine concentration and monochloramine concentration are measured by the automatic chlorine / monochloramine analyzer 30. And supplies these values to the control device 20. The control device 20 calculates the supplied measurement values and adjusts the outputs of the second sodium hypochlorite injection pump 24 and the ammonium sulfate aqueous solution injection pump 28.

The effective chlorine-monochloramine concentration is equal to the dichloramine concentration. For example, when the effective chlorine concentration is higher than the target, no dichloramine is present, and the ammonia nitrogen concentration is 0.5 mg / l or more, that is, FIG. In such a case, both the ammonia nitrogen concentration and the chlorine concentration are high,
The output of the second sodium hypochlorite injection pump 24 is 0
% Of the second sodium hypochlorite injection pump 24 until the residual free chlorine concentration at the outlet of the rapid filtration pond 12 controlled by the first sodium hypochlorite injection pump 16 becomes lower than the target value. No feedback control is performed.

However, basically, such a case hardly occurs because the operation is performed such that the concentration of free residual chlorine at the outlet of the rapid filtration pond 12 becomes lower than the target value. In other words, the output of the second sodium hypochlorite injection pump 24 and the output of the ammonium sulfate aqueous solution injection pump 28, which normally supplements the free chlorine that is insufficient at the outlet of the rapid filtration pond 12, are connected to the automatic ammonia meter 32 and the automatic available chlorine / monochloramine. The value obtained from the measuring device 30 is calculated and fed back for correction.

As described above, according to the present invention, by measuring monochloramine, dichloramine, pH and ammonia nitrogen concentration, it becomes clear where the discontinuous point is located. Accordingly, it is possible to determine whether to reduce the chlorine, increase the ammonia, or increase the chlorine and the ammonia in order to make the monochloramine at an arbitrary concentration. Therefore, stable control can be performed by automatic operation.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an embodiment.

FIG. 2 is an explanatory diagram showing an example of a change in an injection ratio of chlorine and ammonia nitrogen, a form of generated chlorine, and an example of the ratio.

[Explanation of symbols]

10 coagulation sedimentation basin, 12 rapid filtration pond, 14,22 sodium hypochlorite storage tank, 16,24 sodium hypochlorite injection pump, 18 automatic free chlorine measuring instrument, 20
Control device, 26 ammonium sulfate aqueous solution storage tank, 28
Ammonium sulfate aqueous solution injection pump, 30 Automatic effective chlorine / monochloramine measuring device, 32 Automatic ammonia measuring device, 34 pH measuring device, 36 Sulfuric acid storage tank, 38 Sulfuric acid injection pump, 40 Sodium hydroxide aqueous solution storage tank, 42
Sodium hydroxide aqueous solution injection pump.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C02F 1/50 540 C02F 1/50 540B 550 550L

Claims (3)

[Claims] 1. A chlorine disinfection treatment system for chlorinating water, comprising: chlorine adding means for adding a chlorine agent to the water to be treated; ammonia adding means for adding an ammonia agent to the water to be treated; Chloramine measuring means for separately measuring bound chlorine in monochloramine and dichloramine in treated water to which is added, and controlling the amount of addition in the ammonia adding means and the chlorine adding means based on the measurement value obtained by the chloramine measuring means. A chlorine disinfection treatment system, comprising: a control unit. 2. The system according to claim 1, further comprising ammonia measuring means for measuring the ammonia concentration of the treated water, wherein said controlling means also uses an ammonia adding means using a measured value of the ammonia measuring means. A chlorine disinfection treatment system characterized by controlling the amount of chlorination in the chlorination means. 3. The chlorination system according to claim 1, further comprising a pH adjusting means for adjusting the pH of the treated water.