JP5670685B2 - Recovery method of dechlorination ability of activated carbon in the manufacturing process of drinking water - Google Patents

Description

  The present invention relates to a method for recovering the dechlorination ability of activated carbon used for dechlorination in a process for producing drinking water used in the production of soft drinks, tea, coffee, beer, and the like, and drinking water using the same. It relates to the manufacturing method.

In the past, tap water and well water have been used as raw water for beverages used in the production of soft drinks, tea, coffee, beer, etc., but in recent years, the purpose is to make product quality uniform and adjust mineral components. As a result, demineralized water is often used.
Examples of the desalting method for producing such desalted water include an ion exchange resin method and a reverse osmosis membrane method. However, the ion exchange resin method requires regular chemical regeneration and operation management. Due to the complexity, the reverse osmosis membrane method is increasingly employed.

  By the way, in drinking water production sites such as soft drinks, tea, coffee, and beer, it is necessary to store treated water that has been desalted. Is done.

Chlorine sterilization is an important technology that has supported the safety of waterworks in Japan, and has been particularly successful in eradicating waterborne infectious diseases. As sterilization / disinfection technology, technologies such as ozone and ultraviolet light are beginning to be used, but chlorine disinfection is still a technology that plays a main role in sterilization / disinfection. In drinking water manufacturing industries such as soft drinks, tea, coffee and beer, a chlorine agent is often added for the purpose of preventing bacterial growth in the water storage process.
However, since the residual chlorine has a unique chlorine odor and may alter the taste of the product, dechlorination treatment is performed to remove residual chlorine at the final stage of water use in the drinking water manufacturing industry. .

  As a dechlorination treatment method, there is a method of adding a reducing agent such as sodium sulfite or sodium bisulfite. However, since there is a problem such as excessive addition of a reducing agent, dechlorination treatment with activated carbon is generally adopted. It is.

With regard to the technology for dechlorination with activated carbon, for example, in Patent Document 1, drinking water containing chlorine ions is passed between a pair of platinum electrodes to which a DC voltage is applied to obtain alkaline water containing residual chlorine. After that, an invention of an apparatus for obtaining drinking water by flowing through a chlorine removal filter containing activated carbon has been disclosed.
Moreover, in patent document 2, a biological activated carbon tower is arrange | positioned as a pre-processing of a reverse osmosis membrane process, and the inflow water of this biological activated carbon is made into water temperature 10-35 degreeC, pH 4-8, and residual chlorine 0.5-5 mg / liter. A technique characterized by this is disclosed.

JP 2006-198555 A Japanese Patent Laid-Open No. 2002-336887

  As described above, as a method for producing drinking water used in the production of soft drinks, tea, coffee, beer, etc., a chlorine agent is added to the treated water obtained by desalinating the raw water to disinfect it. The sterilized water is passed through a dechlorination tank equipped with activated carbon to dechlorinate it to produce drinking water, but the reverse osmosis membrane treatment method is adopted as the desalination treatment method. As a result, it has been gradually found that the dechlorination ability of the activated carbon decreases with time and the residual chlorine concentration becomes high.

  Therefore, the object of the present invention is to provide a dechlorination treatment even when a reverse osmosis membrane treatment method is employed as a desalination treatment method in the production process of drinking water used in the production of soft drinks, tea, coffee, beer and the like. It is an object of the present invention to provide a method for recovering the dechlorination ability of activated carbon, which can effectively recover the dechlorination ability of the activated carbon used in the process.

  The present invention is a process for producing drinking water comprising a step of dechlorination by adding a chlorinating agent to treated water that has been subjected to reverse osmosis membrane treatment and then passing it through a dechlorination treatment tank equipped with activated carbon. A method for recovering the dechlorination capacity of activated carbon in a process for producing drinking water, wherein the dechlorination capacity of the activated carbon is recovered by washing the dechlorination tank with acid-added water to which an acid has been added. It is.

The dechlorination reaction with activated carbon is considered to be a catalytic reaction due to active sites in the activated carbon, and the inhibition factors include, for example, reduction of active sites due to oxidation, iron compounds, manganese compounds, calcium compounds and organic substances on the active site surface. It is conceivable to coat the surface of the activated carbon or to poison the catalyst due to the accumulation of oxides, etc. When the reverse osmosis membrane treatment is performed, the present inventors remove all iron compounds, manganese compounds, calcium compounds, organic substances, and the like. Therefore, the dechlorination reaction inhibition with respect to the reverse osmosis membrane treated water is caused by ClO ^{− on the} active site surface. Adsorption causes C ^* O to accumulate and stabilize, and hydroxide ions (OH ⁻ ) adsorb to the active site surface to accumulate and stabilize C ^* OH, thereby reducing the active site C ^* of activated carbon. It was estimated that going on was a factor. Then, it is considered that the active site C ^* of the activated carbon can be recovered if oxides or OH ⁻ that may be adsorbed on the active site surface of the activated carbon can be removed, and the desorption is performed with acid-added water to which an acid has been added. By removing the oxides and OH ⁻ by washing the chlorination tank, the dechlorination ability of the activated carbon could be recovered.

  According to the present invention, even if a reverse osmosis membrane treatment method is adopted as a desalting treatment method in the production process of drinking water for producing drinking water used in the production of soft drinks, tea, coffee, beer, etc., Since the dechlorination ability can be prevented from decreasing with time, delicious drinking water that does not bother with the chlorine odor can be stably produced. In addition, in the water treatment by the reverse osmosis membrane treatment method, the water recovery rate due to the soluble silicic acid is not reduced, the disinfection effect of the water storage step due to the low residual chlorine concentration is obtained, and the activated carbon is removed. It is possible to provide a method and apparatus for producing drinking water that does not cause a decrease in chlorine capacity.

It is process drawing which shows an example (backflow washing | cleaning) of embodiment of this invention. It is process drawing which showed the modification (backwashing) of FIG. It is process drawing which shows the other example (forward flow cleaning) of embodiment of this invention. It is process drawing which showed the modification (forward flow cleaning) of FIG.

  Next, as an example of an embodiment of the present invention, a preferred example of a method for producing drinking water using the activated carbon dechlorination ability recovery method proposed by the present invention will be described. However, the scope of the present invention is not limited to the embodiment described below.

<Production method>
A method for producing drinking water according to an example of an embodiment of the present invention (hereinafter referred to as “the present production method”) includes a desalting step of treating raw water with a reverse osmosis membrane, and a chlorine agent in the treated water subjected to the reverse osmosis membrane treatment. In a method for producing drinking water comprising a disinfection step to be added and a dechlorination step in which the disinfecting water obtained in the disinfection step is passed through a dechlorination tank equipped with activated carbon. It is the manufacturing method of the drinking water characterized by recovering the dechlorination capability of activated carbon by wash | cleaning the said dechlorination processing tank with the added acid addition water (refer FIGS. 1-4).
However, the order of each process can be changed as appropriate, and other processes can be added. For example, a storage process in which the disinfecting water obtained in the disinfection process is stored for a predetermined time can be inserted before the dechlorination process.

( Desalting step)
In this step, the reverse osmosis membrane treatment is a treatment operation in which the feed water is membrane-separated into membrane permeate and concentrated water under high pressure, and a currently known method and apparatus for reverse osmosis membrane treatment can be appropriately employed. Good.

When reverse osmosis membrane treatment is adopted as the desalting treatment method, precipitation of soluble silicic acid in the concentrated water is the largest inhibitory factor in improving the treated water recovery rate.
Therefore, in order to increase the solubility of the soluble silicic acid, it is preferable to increase the water recovery rate by increasing the pH of the water supplied to the desalting step. At this time, if the pH of the water supplied to the desalting step is set to 9.0 or higher, the effect of increasing the solubility of the soluble silicic acid can be obtained. However, since the disinfection effect of chlorine is lowered in the subsequent process, it is necessary to increase the chlorine concentration. From this point of view, it is preferable to adjust the pH of water supplied to the desalting step to 9.0 to 10.5, particularly 9.5 to 10.5.
At this time, examples of the alkali agent used for pH adjustment include hydroxides such as sodium hydroxide and potassium hydroxide, carbonates such as sodium bicarbonate, and the like. It is not limited to these. Sodium hydroxide is particularly preferred.

Specifically, as shown in FIGS. 1 to 4, an alkali adjustment process using an apparatus composed of an alkaline agent storage tank 4, a chemical injection pump 5, a control meter 6, and a pH meter 7 is arranged before the desalting step. , in a state in which by adding an alkali to the raw water 16 containing soluble silicate to adjust the pH to 9.0 to 10.5 to increase the solubility of the soluble silicate, as desalting Engineering by reverse osmosis membrane treatment apparatus 1 The dissolved salt may be removed by supplying to the solution. However, it is not limited to such specific means.

  Also, since reverse osmosis membranes generally have low oxidation resistance against residual chlorine, etc., reducing agents such as sodium sulfite and sodium bisulfite are added at the pretreatment stage of reverse osmosis membrane treatment, and residual chlorine is removed by activated carbon treatment. You may make it.

(Disinfection process)
In this step, it is preferable to add a chlorine agent to the treated water treated with the reverse osmosis membrane and adjust the chlorine concentration in water to 0.1 to 10.0 mg / liter.
If the chlorine concentration in water, that is, the amount of residual chlorine is 0.1 mg / liter or more, bacterial growth can be prevented in a water storage step such as a water storage tank or piping in a subsequent process. On the other hand, even if the amount of residual chlorine is more than 10.0 mg / liter, it does not lead to an improvement in the effect of preventing the growth of bacteria, and the treatment life of activated carbon or the like in the subsequent dechlorination treatment step is reduced.
From this point of view, the addition amount of the chlorinating agent is preferably an amount for adjusting the chlorine concentration in water to 0.1 to 10.0 mg / liter, among which 1.0 mg / liter or more, or 5.0 mg / liter. More preferably, it is not more than 1 liter, and particularly preferably not more than 3.0 mg / liter.

  The chlorine agent to be used is not particularly limited, for example, hypochlorite, chlorine gas, etc., but sodium hypochlorite is preferable.

Specifically, as shown in FIGS. 1 to 4, a disinfection process using a device composed of a chlorine storage tank 8, a chemical injection pump 9, a control meter 10, and a residual chlorine meter 11 is arranged next to the desalting step. It is preferable to add a chlorinating agent so as to prevent bacterial growth in the water storage step using the water storage tank 2 and piping. However, it is not limited to such specific means.

(Storage process)
The disinfecting water obtained in the disinfecting process is rarely used immediately for beverage production, and is usually used after being stored for an appropriate time in a storage tank or the like.
Therefore, also in this manufacturing method, you may make it use for a dechlorination process, after once having stored the disinfecting water obtained at the disinfection process (storage process).
The temperature for storage is preferably 30 ° C. or less, particularly 15 to 25 ° C., and the storage time is preferably 30 minutes to 24 hours, particularly preferably 1 hour or more or 2 hours or less.

(Dechlorination process)
In the dechlorination step, chlorine concentration can be lowered by passing disinfecting water containing chlorine through a dechlorination treatment tank equipped with activated carbon. Specifically, the residual chlorine concentration is 0.05 mg / liter or less. , Preferably 0.01 mg / liter or less, particularly preferably 0.005 mg / liter or less.

  The apparatus used for the dechlorination treatment can be of any configuration as long as it is an apparatus having a layer filled with activated carbon. For example, a configuration including an activated carbon layer filled with granular activated carbon, activated carbon fiber, and an activated carbon molded body, a configuration including a cartridge filter filled with them, or another configuration may be used.

  As will be described later, the dechlorination treatment tank used in this production method desirably maintains the residual chlorine half-layer thickness at 20 cm or less at a water flow pH. It is desirable to recover the dechlorination ability by washing the dechlorination tank with acid-added water described later so that the residual chlorine half-layer thickness at water pH is 20 cm or less.

(Cleaning process)
In this production method, it is important to recover the dechlorination ability of the activated carbon by washing the dechlorination tank using acid-added water prepared by adding acid.

In this case, examples of the acid to be added include sulfuric acid, hydrochloric acid, and carbonic acid. Among these, carbonic acid is particularly preferable from the viewpoint of not increasing the salt concentration.
When carbonic acid is added, carbonated water in which carbon dioxide gas is blown may be added, or carbon dioxide gas may be blown directly.

  The amount of acid added is preferably adjusted so that the pH of the water after the addition is less than 9. Among these, it is preferable to adjust the pH to 5.8 or more, or 8.6 or less, and particularly preferably to pH 7.0 or more, or 8.6 or less.

As the cleaning method, either back-flow cleaning or forward-flow cleaning may be employed, but from the viewpoint of removing pulverized coal, it is preferable to employ back-flow cleaning.
When the dechlorination tank is washed, the amount of acid-added water can be adjusted as appropriate according to the activated carbon layer expansion rate at the time of washing. As a guideline, the linear velocity LV (Linear Velocity) The amount of water flow per unit [m ³ / m ² / hour]) may be washed by passing water at ^{30 to} 60 m / hour.

As a specific example of backflow cleaning, as shown in FIGS. 1 and 2, in a normal state, that is, in a state where cleaning is not performed, the switching valve 21 and the switching valve 19 are opened, and the switching valve 22 and the switching valve 20 are closed. Then, water is passed through the dechlorination process by the dechlorination apparatus 3 to perform the dechlorination process.
When the dechlorination apparatus 3 is cleaned, the switching valve 21 and the switching valve 19 are closed, the switching valve 22 and the switching valve 20 are opened, and the dechlorination apparatus 3 is provided between the switching valve 22 and the dechlorination apparatus 3. An acid adjustment facility, that is, an acid agent storage tank 12, a chemical injection pump 13, a controller 14 and a pH meter 15, an acid adjustment facility or a carbon dioxide gas storage tank 23, an electromagnetic flow meter 24, a controller 14 and a pH meter 15. The acid-added water is prepared by the acid adjusting equipment , the backwashing of the dechlorination apparatus 3 is performed, and the active point of the dechlorination apparatus filler is regenerated.
However, it is not limited to such specific means.

On the other hand, as a specific example of the forward flow cleaning, as shown in FIGS. 3 and 4, in the normal state, that is, in the state where cleaning is not performed, the switching valve 19 is opened and the switching valve 20 is closed, so that the dechlorination apparatus 3 Water is passed through the dechlorination process by, so that dechlorination is performed.
When the dechlorination apparatus 3 is washed, the switching valve 19 is closed and the switching valve 20 is opened, so that an acid adjustment facility provided between the water storage tank 2 and the dechlorination apparatus 3, that is, an acid agent storage tank. 12, pH 8.6 by an acid adjustment facility or a carbon dioxide gas storage tank 23, an electromagnetic flow meter 24, a control meter 14, and a pH meter 15 composed of a chemical injection pump 13, a control meter 14 and a pH meter 15. The following acid-added water is prepared, and the dechlorination apparatus 3 is washed in the forward direction to regenerate the active sites of the dechlorination apparatus filler.
However, it is not limited to such specific means.

The frequency of the cleaning treatment is preferably performed at least once a week, preferably at least once a day.
Moreover, as a washing | cleaning time of 1 time, it is preferable to carry out backwashing or forward-flow washing | cleaning continuously 10 minutes-8 hours, especially 20 minutes-1 hour.

<Evaluation of the present invention>
As an index of the dechlorination ability of activated carbon, the chlorine half-layer thickness (German national standard DIN 19603 (1963)) is known. This index is defined as the number of centimeters of the activated carbon layer thickness required to reduce the residual chlorine concentration of the influent water by half (see the following formula (v)).

Gg = 0.301 × t ÷ log (u / ν) (v)
Gg: Residual chlorine half layer thickness of granular activated carbon (cm)
t: Activated carbon layer thickness (cm)
u: Residual chlorine concentration in raw water (mg / liter)
v: Residual chlorine concentration in treated water after 29 minutes of water flow (mg / liter)
(Test conditions): pH: 7.0, u: 2.5 mg / liter, water flow LV: 36 m / hour

  In the calculation by the inventors, when calculated from the theoretical formula of the dechlorination reaction, the activated carbon packed layer thickness of the dechlorination treatment apparatus is 1000 mm, the water flow LV is 20 m / hour, and the residual chlorine in the treated water is less than 0.05 mg / liter. When the inflow water residual chlorine concentration is 10 mg / liter, the required half-layer thickness of the activated carbon is 20 cm. Therefore, in the present invention, the residual chlorine half-layer thickness at the water flow pH of the dechlorination tank equipped with the activated carbon is set. If it was possible to recover to 20 cm or less, it was determined that the method for producing drinking water as in the present invention exhibited a sufficient dechlorination ability.

  In addition, although the test method of German national standard DIN19603 is based on pH 7.0, in actual dechlorination processing, it is necessary to evaluate by the chlorine half layer thickness in actual water flow pH. Therefore, in the present invention, the chlorine half-layer thicknesses are all evaluated as the chlorine half-layer thicknesses at the respective water flow pHs.

<Explanation of terms>
In the present invention, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It means “smaller”.
Further, in the present invention, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and “Y or less” (Y is an arbitrary number). ) Includes the meaning of “preferably smaller than Y” unless otherwise specified.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not restrict | limited by the following Example.

(Comparative Example 1)
Sodium hydroxide was added to tap water in Sodegaura City, Chiba Prefecture to adjust the pH value to 9.5 to 10.5. This water was desalted using a reverse osmosis membrane treatment device using NTR-759HR reverse osmosis membrane element manufactured by Nitto Denko, and free residual chlorine was 2.0 to 2.5 mg / liter in the obtained treated water. Then, a sodium hypochlorite solution was added and stored in a water storage tank having a residence time of 2 hours at 22 to 25 ° C. After that, the activated carbon Evadia LG-10SC made by Ebara Engineering Service Co., Ltd. (chlorine half-layer thickness (based on DIN 19603): 2.5 cm, average diameter of activated carbon: 1.0 mm, uniformity coefficient: 1.5) was removed. Chlorine treatment equipment, linear velocity LV (Linear Velocity: flow rate per cross-sectional area [m ³ / m ² / hour]) 20 m / hour, superficial velocity SV (Space Velocity: flow rate per packed volume [m ³ / m ³ / hour]) Water was passed at 20 hours ⁻¹ for dechlorination to obtain drinking water. In addition, the dechlorination apparatus performed the back-flow washing | cleaning with raw water flow once a week.
The residual chlorine in the dechlorinated water 6 months after the start of water flow was 0.15 mg / liter, and the chlorine half layer thickness of the filled activated carbon at pH 10.5 was 55.8 cm.

Example 1
As shown in FIG. 2, the dechlorination apparatus was back-washed for 30 minutes at a frequency of once a week using acid-added water adjusted to pH 6.5 by adding carbon dioxide to the raw water. Except that, drinking water was obtained in the same manner as in Comparative Example 1.
The residual chlorine in the dechlorinated water 6 months after the start of water passage was less than 0.05 mg / liter, and the chlorine half layer thickness of the filled activated carbon at pH 10.5 was 18.8 cm.

(Example 2)
As shown in FIG. 3, the dechlorination apparatus was washed forward with an acid-added water adjusted to pH 6.5 by adding sulfuric acid to the raw water flow for 1 hour at a frequency of once a week. Except that, drinking water was obtained in the same manner as in Comparative Example 1.
The residual chlorine in the dechlorinated water 6 months after the start of water flow was less than 0.05 mg / liter, and the chlorine half layer thickness of the filled activated carbon at pH 10.5 was 19.4 cm.

Example 3
As shown in FIG. 1, backwashing of the dechlorination apparatus was performed once a day for 20 minutes using acid-added water adjusted to pH 6.5 by adding hydrochloric acid to raw water flow. Except that, drinking water was obtained in the same manner as in Comparative Example 1.
The residual chlorine in dechlorinated water 6 months after the start of water flow was less than 0.05 mg / liter, and the chlorine half-layer thickness of the filled activated carbon at pH 10.5 was 15.8 cm.

(Comparative Example 2)
Sodium hydroxide was added to tap water in Sodegaura City, Chiba Prefecture to adjust the pH value to 10.0-10.5. Hypochlorous acid so that free residual chlorine becomes 2.0 to 2.5 mg / liter in treated water obtained by desalting this water with a reverse osmosis membrane treatment apparatus (manufactured by Ebara Engineering Service Co., Ltd.). After adding a sodium solution and storing in a water storage tank having a residence time of 2 hours at 22 to 25 ° C., a linear velocity LV (Linear Velocity) is passed through a cartridge filter type dechlorination treatment apparatus filled with commercially available activated carbon fibers. Water flow per cross-sectional area [m ³ / m ² / hour]) Water was passed at 100 m / hour for dechlorination to obtain drinking water. In addition, the dechlorination apparatus performed the back-flow washing | cleaning with raw water flow once a week.
The residual chlorine in the dechlorinated water 2 months after the start of water passage was 0.4 mg / liter.

Example 4
As shown in FIG. 2, the dechlorination apparatus was back-washed for 30 minutes at a frequency of once a week using acid-added water adjusted to pH 6.5 by adding carbon dioxide to the raw water. Otherwise, drinking water was obtained in the same manner as in Comparative Example 2.
The residual chlorine in the dechlorinated water 2 months after the start of water flow was less than 0.05 mg / liter.

(Example 5)
As shown in FIG. 3, the dechlorination apparatus was washed forward with an acid-added water adjusted to pH 6.5 by adding sulfuric acid to the raw water flow for 1 hour at a frequency of once a week. Otherwise, drinking water was obtained in the same manner as in Comparative Example 2.
The residual chlorine in the dechlorinated water 2 months after the start of water flow was less than 0.05 mg / liter.

(Example 6)
As shown in FIG. 1, backwashing of the dechlorination apparatus was performed once a day for 20 minutes using acid-added water adjusted to pH 6.5 by adding hydrochloric acid to raw water flow. Otherwise, drinking water was obtained in the same manner as in Comparative Example 2.
The residual chlorine in the dechlorinated water 2 months after the start of water flow was less than 0.05 mg / liter.

(Discussion)
Comparing Comparative Example 1 with Examples 1 to 3 in which the reverse osmosis membrane treatment apparatus was washed with acid-added water in the same flow, the reverse osmosis membrane treatment apparatus was washed with acid-added water. The chlorine half-layer thickness of the treatment tank of the osmotic membrane treatment apparatus could be remarkably reduced, and the dechlorination ability could be recovered to 20 cm or less. It was the same even if the comparative example 2 and Examples 4-6 were compared.

The effect of adding any of carbon dioxide, sulfuric acid, and hydrochloric acid was recognized as the acid to be added, but carbon dioxide can be considered most preferable from the viewpoint of not increasing the residual salt concentration.
In addition, based on the test results other than the above, it is possible to obtain the minimum effect if the cleaning treatment of the reverse osmosis membrane treatment apparatus is performed at least once a week for 10 minutes. Can think.

1: Reverse osmosis membrane treatment device 2: Water storage tank 3: Dechlorination treatment device 4: Alkaline agent storage tank 5: Chemical injection pump 6: Control meter 7: pH meter 8: Chlorine agent storage tank 9: Chemical injection pump
10: Controller 11: Residual chlorine meter 12: Acid storage tank
13: Chemical injection pump 14: Control meter 15: pH meter
16: Raw water 17: Dechlorinated water 18: Wash drainage
19, 20, 21, 22: Switching valve 23: Carbon dioxide tank 24: Electromagnetic flow meter

Claims (10)

  In the manufacturing process of drinking water with a step of dechlorination by adding a chlorinating agent to the treated water treated with reverse osmosis membrane and then passing it through a dechlorination tank equipped with activated carbon, acid was added. A method for recovering the dechlorination capacity of activated carbon in a process for producing drinking water, wherein the dechlorination capacity of the activated carbon is recovered by washing the dechlorination tank with acid-added water.   2. The method for recovering the dechlorination ability of activated carbon according to claim 1, wherein the treatment for washing the dechlorination tank with acid-added water to which an acid has been added is performed at least once a week.   The method for recovering the dechlorination ability of activated carbon according to claim 1 or 2, wherein the acid to be added is sulfuric acid, hydrochloric acid or carbonic acid. Desalination process for treating raw water with reverse osmosis membrane, disinfection process for adding chlorine agent to treated water treated with reverse osmosis membrane, and disinfecting water obtained in the disinfection process is passed through a dechlorination tank equipped with activated carbon. A method for producing drinking water comprising a dechlorination step of dechlorinating by hydrating,
A method for producing drinking water, wherein the dechlorination ability of activated carbon is recovered by washing the dechlorination tank with acid-added water to which an acid has been added.   The method for producing drinking water according to claim 4, wherein the treatment for washing the dechlorination tank with acid-added water to which an acid has been added is performed at least once a week.   The method for producing drinking water according to claim 4 or 5, wherein the acid to be added is sulfuric acid, hydrochloric acid or carbonic acid.   Demineralization means for treating raw water with a reverse osmosis membrane, disinfection means for adding a chlorine agent to treated water treated with a reverse osmosis membrane, and disinfecting water obtained by the disinfection means passed through a dechlorination treatment tank equipped with activated carbon. An apparatus for producing drinking water, comprising: dechlorination means for dechlorination treatment by water; and means for recovering the dechlorination ability of activated carbon by washing the dechlorination tank with acid-added water. The method for recovering the dechlorination ability of activated carbon according to any one of claims 1 to 3, wherein the treated water is obtained by subjecting raw water having a pH adjusted to 9.0 or more to reverse osmosis membrane treatment. Raw water has pH adjusted to 9.0 or more, The manufacturing method of the water for drinks in any one of Claims 4-6. The apparatus for producing drinking water according to claim 7, wherein the raw water has a pH adjusted to 9.0 or more.

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