JP7086793B2 - Water treatment method and water treatment system - Google Patents

Description

The present invention relates to a water treatment method and a water treatment system.

A method of desalting raw water such as groundwater and river water is known. The pH of the desalted water obtained by the desalination treatment is low, and corrosion of the pipes and equipment that supply the treated water has often become a problem. Therefore, demineralized water is usually subjected to post-treatment to suppress corrosiveness.

As such a post-treatment, a method of dissolving calcium carbonate in desalinated water is known. In Patent Document 1, a slurry of calcium carbonate is prepared using a feed solution (demineralized water) in which carbon dioxide is dissolved, and the obtained slurry and the feed solution are mixed to dissolve calcium carbonate in the feed water. The method is described.

Japanese Unexamined Patent Publication No. 2016-155128

However, the method described in Patent Document 1 requires two systems through which supply water flows, and has a problem that the configuration of the apparatus to be used is complicated.

The present invention has been made in view of the above circumstances, and provides a water treatment method and a water treatment system capable of easily suppressing corrosion of pipes and equipment.

The present invention has the following aspects.
[1] A desalting treatment step of desalting the supply water containing inorganic salts using a back-penetrating film to obtain desalted water, and adjusting the pH and free carbon dioxide concentration of the desalted water to obtain adjusted water. (1) A water treatment method comprising: an adjustment step, a contact treatment step of bringing the adjusted water into contact with carbonate particles to obtain treated water.
[2] The water treatment method according to [1], which comprises a second adjusting step of adjusting the pH and free carbon dioxide concentration of the raw water to obtain the supplied water prior to the desalting treatment step.
[3] The water treatment method according to [2], wherein in the second adjustment step, the raw water is aerated and decarboxylated under acidic conditions.
[4] The water treatment method according to any one of [1] to [3], which comprises a third adjustment step of adjusting the pH and free carbonic acid concentration of the treated water after the contact treatment step.
[5] The water treatment method according to [4], wherein in the third adjustment step, at least one selected from the group consisting of sulfuric acid, sulfate, sulfite and barous sulfate is mixed with the treated water.
[6] In any one of [1] to [5], in the first adjusting step, at least one selected from the group consisting of sulfuric acid, sulfate, sulfite and sulfite is mixed with the desalted water. The described water treatment method.
[7] The water treatment method according to any one of [1] to [6], wherein at least one selected from the group consisting of calcium carbonate and magnesium carbonate is used as the carbonate particles.
[8] The carbonate particles are composed of a plurality of particles, and the number of the particles having a particle size of 0.1 mm or more and 10 mm or less is 90% or more with respect to the total number of the carbonate particles [1] to [7]. ] The water treatment method according to any one of the following items.
[9] The water treatment method according to any one of [1] to [8], wherein the desalted water is brought into contact with the carbonate particles at a space velocity of 5 hr ^-1 or more and 30 hr ^-1 or less in the contact treatment step. ..
[10] The water treatment method according to any one of [1] to [9], wherein in the first adjusting step, carbon dioxide or a mixture of sodium hydrogen carbonate and sulfuric acid is added to the desalinated water.
[11] A desalting treatment unit having a reverse osmosis membrane, a contact treatment unit that brings the water obtained in the desalination treatment unit into contact with carbonate particles, and the desalination treatment unit and the contact treatment unit. A water treatment system having an adjusting unit, which is arranged between them and adjusts the pH and free carbonate concentration of the water.

According to one aspect of the present invention, there is provided a water treatment method and a water treatment system capable of easily suppressing corrosion of pipes and equipment.

FIG. 1 is a diagram showing a schematic configuration of the water treatment system 1 of the first embodiment. FIG. 2 is a graph showing the concentration distribution of total carbonic acid with respect to pH. In the figure, ◇ indicates carbon dioxide, □ indicates bicarbonate ion, and Δ indicates the concentration distribution of carbonate ion. FIG. 3 is a flowchart showing each step of the water treatment method of the first embodiment. FIG. 4 is a diagram showing a schematic configuration of the water treatment system 2 of the second embodiment. FIG. 5 is a flowchart showing each step of the water treatment method of the second embodiment.

<First Embodiment>
Hereinafter, the water treatment method and the water treatment system according to the first embodiment of the present invention will be described with reference to the drawings. In addition, in the drawings used in the following description, for the purpose of emphasizing the characteristic parts, the characteristic parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. do not have. In addition, for the same purpose, there are cases where non-characteristic parts are omitted.

In the water treatment method of the present embodiment, a desalting treatment step of desalting the feed water containing inorganic salts to obtain desalted water and adjusting the pH and free carbonic acid concentration of the desalted water are performed by using a back-penetration membrane. Prior to the first adjustment step of obtaining the adjusted water, the contact treatment step of contacting the adjusted water with the carbonate particles to obtain the treated water, and the desalting treatment step, the pH and free carbonic acid concentration of the raw water were adjusted. It has a second adjusting step of obtaining supply water, and a third adjusting step of adjusting the pH and free carbon dioxide concentration of the treated water after the contact treatment step.

As used herein, free carbonic acid refers to carbon dioxide dissolved in water.

In the following description, the water before each treatment in the water treatment system of the present embodiment is referred to as "raw water W1". Further, the water treated in the desalting treatment step is referred to as "supply water W2". Further, the water obtained in the desalination treatment step is referred to as "demineralized water W3". Further, the water treated in the contact treatment step is referred to as "adjusted water W4". Further, the water obtained in the contact treatment step is referred to as "treated water W5".

[Water treatment system]
Hereinafter, the water treatment system used in the water treatment method of the present embodiment will be described. FIG. 1 is a diagram showing a schematic configuration of the water treatment system 1 of the first embodiment.

As shown in FIG. 1, the water treatment system 1 of the present embodiment includes a contact treatment unit 10, a desalination treatment unit 20, a control unit 40, a storage tank 51, a first adjustment unit 160, and a second adjustment. It has a unit 60 and a third adjusting unit 340. In the present specification, the first adjustment unit 160 corresponds to the "adjustment unit" in the claims.

(2nd adjustment part)
The second adjusting unit 60 of the present embodiment adjusts the pH and free carbonic acid concentration of the raw water W1 supplied to the water treatment system 1 to obtain the supplied water W2. The second adjusting unit 60 of the present embodiment includes a pretreatment tank 61, a pH adjusting means 35, and an aeration device 36.

A fifth flow path 62 and a first flow path 22 are connected to the pretreatment tank 61 shown in FIG. 1.

The fifth flow path 62 causes the raw water W1 to flow into the pretreatment tank 61. A measuring device 63 is provided in the fifth flow path 62.

The measuring device 63 measures the water quality of the raw water W1. Specifically, at least one selected from the group consisting of the ammonia concentration, the metal ion concentration, the pH, the free carbon dioxide concentration and the sulfate ion concentration contained in the raw water W1 is measured.

The measurement result of the measuring device 63 is output to the control unit 40.

The first flow path 22 causes the supply water W2 to flow into the desalting treatment section 20 in the subsequent stage.

The pH adjusting means 35 is a device capable of adding an acid or an alkali to the raw water W1. The drive of the pH adjusting means 35 is controlled by the control unit 40 described later.

Sulfuric acid is preferable as the acid added by the pH adjusting means 35. As the alkali added by the pH adjusting means 35, sodium hydroxide (NaOH) is preferable.

The aeration device 36 is provided inside the pretreatment tank 61. Further, a blower 37 is connected to the aeration device 36.

The aeration device 36 is a device capable of aerating the raw water W1. In the second adjusting unit 60 of the present embodiment, the pH adjusting means 35 and the aeration device 36 can be used in combination to aerate the raw water W1 under acidic conditions and perform decarboxylation treatment. In addition, in this specification, "aeration" means to supply air.

(Desalting treatment section)
In the desalting treatment unit 20 of the present embodiment, the supply water W2 containing inorganic salts is desalted (desalting treatment step).

The desalting treatment unit 20 of the present embodiment includes a reverse osmosis membrane module 21. The reverse osmosis membrane module 21 desalinates the supply water W2 containing inorganic salts by the reverse osmosis method.

Examples of the material of the reverse osmosis membrane used in the reverse osmosis membrane module 21 include polyamide, polysulfone, and cellulose acetate. Among them, as the material of the reverse osmosis membrane, a polyamide containing an aromatic polyamide or a crosslinked aromatic polyamide is preferable.

The reverse osmosis membrane module 21 shown in FIG. 1 is connected to the above-mentioned first flow path 22 and the second flow path 23.

The second flow path 23 allows the desalted water W3 obtained in the desalting treatment step to flow out from the reverse osmosis membrane module 21. A measuring device 24 is provided in the second flow path 23.

The measuring device 24 measures at least one selected from the group consisting of the pH of the demineralized water W3, the free carbon dioxide concentration and the sulfate ion concentration. The measuring device 24 preferably measures the pH of the demineralized water W3 and the concentration of free carbon dioxide, and more preferably measures the pH, the free carbon dioxide concentration and the sulfate ion concentration of the demineralized water W3.

The measurement result of the measuring device 24 is output to the control unit 40.

(1st adjustment part)
The first adjusting unit 160 of the present embodiment adjusts the pH and free carbonic acid concentration of the demineralized water W3 to obtain the adjusted water W4. The first adjusting unit 160 of the present embodiment includes an adjusting tank 16, a pH adjusting means 31, an aeration device 32, and a carbon dioxide supply means 38.

The adjustment tank 16 shown in FIG. 1 is connected to the above-mentioned second flow path 23 and the third flow path 12.

The third flow path 12 causes the adjusting water W4 to flow into the contact processing unit 10 in the subsequent stage. A measuring device 17 is provided in the third flow path 12.

The measuring device 17 measures at least one selected from the group consisting of the pH of the adjusted water W4, the free carbon dioxide concentration and the sulfate ion concentration. The measuring device 17 preferably measures the pH of the adjusted water W4 and the concentration of free carbon dioxide, and more preferably measures the pH, the free carbon dioxide concentration and the sulfate ion concentration of the adjusted water W4.

In order to efficiently proceed the reaction between the adjusted water W4 and the carbonate particles, it is preferable to control the concentration of free carbonic acid in the adjusted water W4 so as to satisfy a predetermined standard. In the present specification, the predetermined standard for the concentration of free carbonic acid in the prepared water W4 is, for example, 5 mg / L or more.

The measurement result of the measuring device 17 is output to the control unit 40.

The pH adjusting means 31 is a means capable of mixing an acid or an alkali with the desalinated water W3. As a method for mixing the acid or alkali in the pH adjusting means 31, it is preferable to add the acid or alkali to the desalinated water W3.

As the acid mixed by the pH adjusting means 31, at least one selected from the group consisting of sulfuric acid, sulfate, sulfite and sulfurous acid is preferable, and sulfuric acid is more preferable, because it easily meets the water quality standard. When sulfites or sulfites are used as the acid, sulfate ions are generated in the desalted water W3 by performing either or both of the aeration treatment and the addition of an oxidizing agent.

As the above-mentioned sulfate, at least one selected from the group consisting of sodium sulfate, magnesium sulfate and potassium sulfate is preferable.
Examples of the above-mentioned sulfite salt include sodium sulfite, magnesium sulfite, potassium sulfite and the like.
Examples of the above-mentioned sodium bisulfite include sodium bisulfite, magnesium sulfite, potassium metabisulfite and the like.
Examples of the above-mentioned oxidizing agent include sodium hypochlorite, ozone, hydrogen peroxide and the like.

As the alkali mixed by the pH adjusting means 31, sodium hydroxide (NaOH) is preferable because it easily meets the water quality standard.

The aeration device 32 is provided inside the adjusting tank 16. Further, a blower 33 is connected to the aeration device 32.

The aeration device 32 is a device capable of aerating the demineralized water W3. In the first adjusting unit 160 of the present embodiment, the pH adjusting means 31 and the aeration device 32 can be used in combination to aerate the demineralized water W3 under acidic conditions and perform decarboxylation treatment.

The carbon dioxide supply means 38 is a means capable of supplying carbon dioxide to the desalinated water W3.

In the carbon dioxide supply means 38, carbon dioxide may be supplied to the desalted water W3, or a mixture of sodium hydrogen carbonate and sulfuric acid may be supplied to generate carbon dioxide in the system to supply carbon dioxide. good.

(Contact processing unit)
In the contact treatment unit 10 of the present embodiment, the adjusted water W4 whose pH and free carbonic acid concentration of the demineralized water W3 are adjusted is brought into contact with the carbonate particles (contact treatment step).

The contact processing unit 10 shown in FIG. 1 includes a reaction tank 11.

《Reaction tank》
The reaction tank 11 is filled with carbonate particles. As the carbonate particles to be used, at least one selected from the group consisting of calcium carbonate and magnesium carbonate is preferable. The above-mentioned third flow path 12 and the fourth flow path 13 are connected to the reaction tank 11 shown in FIG. 1.

The fourth flow path 13 causes the treated water W5 obtained in the contact treatment step to flow out of the reaction tank 11.

The end of the fourth flow path 13 is connected to the upper part of the reaction tank 11. Further, the end of the third flow path 12 is connected to the lower part of the reaction tank 11. In the water treatment system 1 shown in FIG. 1, the adjusted water W4 flows upward in the reaction tank 11.

The carbonate particles filled in the reaction vessel 11 of the present embodiment are composed of a plurality of particles, and the number of particles having a particle size of 0.1 mm or more and 10 mm or less is 90% or more of the total number of carbonate particles. Is preferable. When the particle size of 90% or more of the total number of carbonate particles is 0.1 mm or more, when the adjusting water W4 is flowed upward in the reaction tank 11, the reaction tank 11 has a particle size of 0.1 mm or more. It is possible to suppress the outflow of the slurry of carbonate particles from the upper part. Further, when the particle size of 90% or more of the total number of carbonate particles is 10 mm or less, the contact area between the adjusting water W4 and the carbonate particles is sufficiently large, and the adjusting water W4 and the carbonate particles are used. Reaction can proceed efficiently.

In the carbonate particles of the present embodiment, it is more preferable that the number of particles having a particle size of 0.5 mm or more is 90% or more with respect to the total number of carbonate particles. This makes it possible to more effectively suppress the outflow of the slurry of carbonate particles from the upper part of the reaction tank 11 when the adjusted water W4 is flowed into the inside of the reaction tank 11 in an upward flow.

In the carbonate particles of the present embodiment, it is more preferable that the number of particles having a particle size of 1.2 mm or less is 90% or more with respect to the total number of carbonate particles. As a result, the contact area between the adjusting water W4 and the carbonate particles is sufficiently large, and the reaction between the adjusting water W4 and the carbonate particles can proceed more efficiently.

In the contact treatment unit 10 of the present embodiment, the reaction proceeds from the surface of the carbonate particles with which the adjusting water W4 comes into contact. Therefore, the particle size of the carbonate particles becomes smaller with time during the treatment. In the water treatment system 1 of the present embodiment, the carbonate particles are replenished so that the particle size of 90% or more of the total number of carbonate particles used is 0.1 mm or more and 10 mm or less. do.

In the present embodiment, the particle size distribution of the carbonate particles is measured by a sonic vibration sieving measuring instrument.

In the contact treatment unit 10 of the present embodiment, the equilibrium reaction represented by the following formula (1) proceeds between the prepared water W4 and the carbonate particles.

（式（１）中、ＭはＣａまたはＭｇである。）

(In formula (1), M is Ca or Mg.)

In the contact treatment unit 10 of the present embodiment, in order to dissolve the carbonate in the prepared water W4, it is necessary to increase the amount of free carbon dioxide (CO ₂ ) and proceed with the rightward reaction of the above formula (1). .. However, it is known that bicarbonate ion (HCO _3- ⁾ , which is an anion on the right side in the above formula (1), changes to free ^{carbonic acid and carbonate ion (CO 3-2-} ₎ depending on pH.

FIG. 2 is a graph showing the concentration distribution of total carbonic acid with respect to pH. The horizontal axis of the graph shown in FIG. 2 is pH. The vertical axis of the graph is the concentration distribution of bicarbonate ion, free carbonic acid and carbonate ion when the concentration of total carbonic acid is 100%. In addition, total carbonic acid means the sum of bicarbonate ion, free carbonic acid and carbonate ion.

As shown in FIG. 2, the graph showing the concentration of bicarbonate ion is convex upward, and when the pH is around 8.5, the concentration of bicarbonate ion shows the maximum value. On the acidic side of the pH around 8.5, the concentration of bicarbonate ion decreases and the concentration of free carbonic acid increases. On the other hand, on the alkaline side of the pH around 8.5, the concentration of bicarbonate ion decreases and the concentration of carbonate ion increases.

The pH of the adjusted water W4 is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 5.5 or higher. As a result, the concentration of free carbonic acid in the adjusted water W4 does not become too high, and the reaction time between the adjusted water W4 and the carbonate particles (the time for flowing the adjusted water W4 into the reaction tank 11) can be shortened. The pH of the adjusted water W4 is preferably less than 7.0, more preferably 6.5 or less. The above upper limit value and lower limit value can be arbitrarily combined. As a result, the concentration of carbonate ions contained in the adjusted water W4 does not become too high, and the concentration of carbonate ions in the obtained treated water W5 tends to satisfy the water quality standard.

When the pH of the adjusted water W4 is less than 4.0, the concentration of free carbonic acid in the adjusted water W4 becomes high, and when the reaction between the adjusted water W4 and the carbonate particles is to be completed, the adjusted water W4 is placed in the reaction tank 11. It is necessary to lengthen the time to flow.

On the other hand, when the pH of the adjusted water W4 is 7.0 or more, the concentration of carbonate ions contained in the adjusted water W4 becomes high, and the concentration of carbonate ions in the obtained treated water W5 may exceed the water quality standard.

The pH of the demineralized water W3 is adjusted in the adjusting tank 16 of the first adjusting unit 160. The detailed adjustment method of the pH of the demineralized water W3 will be described later.

The concentration of free carbonic acid in the adjusted water W4 is preferably 5 mg / L or more, more preferably 10 mg / L or more. As a result, the reaction between the adjusted water W4 and the carbonate particles can be efficiently promoted.

The concentration of free carbonic acid in the adjusted water W4 is preferably 25 mg / L or less, more preferably 20 mg / L or less, and even more preferably 15 mg / L or less. As a result, the time for flowing the adjusting water W4 into the reaction tank 11 is shortened.

When the concentration of free carbonic acid in the adjusted water W4 is more than 25 mg / L, the treatment time of the adjusted water W4 becomes long. Further, when the reaction between the adjusted water W4 and the carbonate particles is not completed, the free carbonic acid is not consumed, and the concentration of free carbonic acid in the obtained treated water W5 may exceed the water quality standard.

In the water treatment system 1 of the present embodiment, when the concentration of total carbonic acid in the adjusted water W4 is constant, the concentration of free carbonic acid is determined by the pH of the adjusted water W4. Further, the pH of the adjusted water W4 is controlled by the concentration of bicarbonate ion in the demineralized water W3 and the amount of acid or alkali mixed when adjusting the pH of the demineralized water W3.

The concentration of free carbonic acid in the demineralized water W3 is adjusted in the adjusting tank 16 of the first adjusting unit 160. The detailed adjustment method of the concentration of free carbonic acid in the demineralized water W3 will be described later.

In the contact treatment unit 10 of the present embodiment, it is preferable to bring the adjusted water W4 into contact with the carbonate particles at a space velocity of 5 hr ^-1 or more and 30 hr ^-1 or less. The space velocity of the adjusting water W4 in the present embodiment is obtained by dividing the volume of the adjusting water W4 to be treated per unit time by the volume of the carbonate particles filled in the reaction tank 11.

When the space velocity of the adjusted water W4 is 5 hr ^-1 or more, the reaction between the adjusted water W4 and the carbonate particles can be efficiently promoted.

Further, when the space velocity of the adjusted water W4 is 30 hr ^-1 or less, the fluctuation of the water quality inside the reaction tank 11 becomes small between the operation and the stop of the water treatment system 1. As a result, it is easy to control the equilibrium reaction represented by the above formula (1). Further, when the adjusted water W4 is flowed into the reaction tank 11 in an upward flow, it is possible to suppress the outflow of the slurry of carbonate particles from the upper part of the reaction tank 11.

Returning to FIG. 1, a pump 14 and a measuring device 15 are provided in the fourth flow path 13.

In the water treatment system 1 of the present embodiment, the space velocity of the adjusted water W4 may be adjusted to a range of 5 hr ^-1 or more and 30 hr ^-1 or less by the output of the pump 14.

The measuring device 15 measures at least one selected from the group consisting of the pH, free carbon dioxide concentration and sulfate ion concentration of the treated water W5 flowing through the fourth flow path 13.

(3rd adjustment part)
The third adjusting unit 340 of the present embodiment adjusts the pH and free carbonic acid concentration of the treated water W5. The third adjusting unit 340 of the present embodiment includes a sulfate ion mixing means 34. The sulfate ion mixing means 34 of the present embodiment is a means capable of mixing at least one selected from the group consisting of sulfuric acid, sulfate, sulfite and heavy sulfite with the treated water W5. Among them, the sulfate ion mixing means 34 preferably mixes a sulfate with the treated water W5. The compound added by the sulfate ion mixing means 34 is the same as that of the pH adjusting means 31. The type of the compound to be mixed (added) by the pH adjusting means 31 and the sulfate ion mixing means 34 may be the same or different. As a method for mixing the acid or alkali in the sulfate ion mixing means 34, it is preferable to add the acid or alkali to the treated water W5.

As the sulfate salt added by the sulfate ion mixing means 34, at least one selected from the group consisting of sodium sulfate, magnesium sulfate and potassium sulfate is preferable because the effect of the treated water W5 on the pH is small.

(Control unit)
The control unit 40 of the present embodiment acquires at least one type of data selected from the group consisting of the pH of the desalted water W3, the free carbon dioxide concentration and the sulfate ion concentration from the measuring device 24, and the pH of the adjusted water W4 from the measuring device 17. , At least one selected from the group consisting of free carbon dioxide concentration and sulfate ion concentration.

The control unit 40 determines whether or not the adjusted water W4 satisfies the following (a) and the following (b) based on at least one data selected from the group consisting of the pH, free carbonic acid concentration and sulfate ion concentration of the adjusted water W4. Is determined. Then, the control unit 40 supplies the pH adjusting means 31, the aeration device 32, and carbon dioxide, if necessary, based on at least one data selected from the group consisting of the pH of the desalinated water W3, the free carbonic acid concentration, and the sulfate ion concentration. The drive of the means 38 is controlled. In the water treatment system 1 of the present embodiment, the following (a) and (b) are given as examples as the determination criteria of the adjusted water W4, but the present invention is not limited thereto. The determination criteria for the adjusting water W4 can be appropriately set according to the target treated water W5. In the following description, it is assumed that the determination criteria of the adjusting water W4 are the following (a) and (b).
(A) pH is 4.0 or more and less than 7.0 (b) Free carbonic acid concentration is more than 0 mg / L and 25 mg / L or less.

Further, the control unit 40 of the present embodiment acquires at least one type of data selected from the group consisting of pH, free carbon dioxide concentration and sulfate ion concentration in the treated water W5 from the measuring device 15.

The control unit 40 determines whether or not the treated water W5 satisfies the concentration range suitable for the target application based on at least one data selected from the group consisting of pH, free carbonic acid concentration and sulfate ion concentration in the treated water W5. judge. Then, the control unit 40 controls the drive of the sulfate ion mixing means 34 based on at least one data selected from the group consisting of pH, free carbon dioxide concentration and sulfate ion concentration in the treated water W5, if necessary.

Further, the control unit 40 of the present embodiment acquires at least one kind of data selected from the group consisting of the ammonia concentration, the metal ion concentration, the pH, the free carbon dioxide concentration and the sulfate ion concentration in the raw water W1 from the measuring device 63.

The control unit 40 determines whether or not the raw water W1 satisfies a desired concentration range based on at least one type of data selected from the group consisting of pH, free carbonic acid concentration and sulfate ion concentration in the raw water W1. Then, the control unit 40 controls the driving of the pH adjusting means 35 and the aeration device 36 based on at least one data selected from the group consisting of the pH, the free carbonic acid concentration and the sulfate ion concentration in the raw water W1, if necessary. ..

(Reservoir)
The storage tank 51 of the present embodiment stores the treated water W5. The treated water W5 stored in the storage tank 51 is used, for example, for drinking water.

The storage tank 51 of the present embodiment includes an aeration device 52. The aeration device 52 is provided inside the storage tank 51. Further, a blower 53 is connected to the aeration device 52.

The aeration device 52 is a device capable of aerating the treated water W5.

The fourth flow path 13 described above is connected to the storage tank 51 shown in FIG.

[Water treatment method]
When the groundwater is made into a drink by using a reverse osmosis membrane, it is preferable to adjust the water quality of the target water (treated water) as follows.
The free carbonic acid concentration of the treated water is preferably less than 5 mg / L, more preferably less than 3 mg / L.
The pH value of the treated water is preferably 6.0 or more, preferably 8.6 or less, and more preferably 8.2 or less.
The corrosiveness (Langeria index: LSI) of the treated water is preferably −1.3 or higher, more preferably −1.2 or higher, and even more preferably -1 or higher.
The free carbonic acid concentration (as carbon dioxide) of the treated water is preferably less than 5, more preferably less than 3.
Hereinafter, a water treatment method using the above-mentioned water treatment system 1 will be described with reference to FIG. FIG. 3 is a flowchart showing each step of the water treatment method of the first embodiment. The treated water W5 obtained by the water treatment method of the present embodiment is used as drinking water.

First, raw water W1 such as groundwater or river water is supplied to the water treatment system 1 (step S1).

Next, at least one selected from the group consisting of the ammonia concentration, the metal ion concentration, the pH, the free carbon dioxide concentration and the sulfate ion concentration of the raw water W1 is measured by the measuring device 63 (step S2). The data obtained in step S2 is output to the control unit 40.

Next, based on the result obtained in step S2, whether or not the concentration of free carbonic acid in the raw water W1 is 25 mg / L or less and the pH is 4.0 or more and less than 7.0 in the control unit 40 (determination A1). ) Judgment (step S3). The desired concentration range of free carbonic acid in the raw water W1 is determined according to the target water quality of the treated water W5 and the treatment performance of the subsequent stage.

Next, in step S3, when the control unit 40 determines that the concentration of free carbonic acid in the raw water W1 is lower than the desired concentration range (step S3: NO), the control unit 40 drives the pH adjusting means 35. Specifically, in the pretreatment tank 61, an acid is added to the raw water W1 by the pH adjusting means 35 to set the pH of the supplied water W2 to the acidic side (step S32).

As shown in FIG. 2, by setting the pH of the raw water W1 to the acidic side, the concentration of bicarbonate ion decreases and the concentration of free carbonic acid increases. Since free carbonic acid easily permeates the reverse osmosis membrane of the reverse osmosis membrane module 21, the concentration of free carbonic acid in the desalted water W3 can be increased by performing the next step S4 under acidic conditions.

Further, when sulfuric acid is used in step S32, the sulfate ion, which is a divalent ion, is easily captured by the reverse osmosis membrane of the reverse osmosis membrane module 21, and therefore the sulfate ion is contained in the desalted water W3 obtained in the next step S4. Is hard to remain. Therefore, according to the water treatment method of the present embodiment, it is easy to satisfy the water quality standard of sulfate ion in the treated water W5.

Here, the concentration of bicarbonate ion can be calculated from the concentration of free carbonic acid by using the graph of FIG. As one aspect, in step S3, the control unit 40 determines whether or not the concentration of bicarbonate ion in the raw water W1 satisfies a desired concentration range. When the control unit 40 determines that the concentration of bicarbonate ion in the raw water W1 is higher than the desired concentration range or the pH is high (step S3: NO), the control unit 40 determines the pH adjusting means 35 and the aeration device 36. To drive. Specifically, in the pretreatment tank 61, the raw water W1 is aerated and decarboxylated under acidic conditions by using the pH adjusting means 35 and the aeration device 36 (step S33). By decarboxylating the raw water W1, the concentration of total carbonic acid in the raw water W1 can be lowered. As a result, the concentration of bicarbonate ion in the raw water W1 can be lowered. The desired concentration range of bicarbonate ion in the raw water W1 is determined according to the target water quality of the treated water W5 and the treatment performance of the subsequent stage.

Next, the supply water W2 supplied to the reverse osmosis membrane module 21 of the reverse osmosis treatment unit 20 is desalted using the reverse osmosis membrane (step S4). After step S4, the obtained desalinated water W3 flows through the second flow path 23.

Next, at least one selected from the group consisting of the pH, free carbonic acid concentration and sulfate ion concentration of the desalted water W3 is measured by the measuring device 24, and from the group consisting of the pH, free carbonic acid concentration and sulfate ion concentration of the adjusted water W4. At least one selected is measured by the measuring device 17 (step S5). The data obtained in step S5 is output to the control unit 40.

Next, among the results obtained in step S5, based on the result of the pH of the adjusting water W4, the control unit 40 determines whether or not the adjusting water W4 satisfies the above (a) (determination A2) (determination A2). Step S6).

In step S6, when the control unit 40 determines that the adjusting water W4 does not satisfy the above (a) (step S6: NO), the pH adjusting means 31 is driven. Specifically, an acid or an alkali is mixed with the demineralized water W3 in the adjusting tank 16 by using the pH adjusting means 31 so that the pH of the adjusting water W4 is 4.0 or more and less than 7.0 (step S61). ). In step S61, the pH adjusting means 31 may be controlled based on at least one data selected from the group consisting of the pH of the desalinated water W3, the free carbonic acid concentration and the sulfate ion concentration, if necessary.

On the other hand, when the control unit 40 determines in step S6 that the adjusting water W4 satisfies the above (a) (step S6: YES), among the results obtained in step S5, the free carbonic acid in the adjusting water W4 Based on the result of the concentration of (step S7), it is determined whether or not the adjusted water W4 satisfies the above (b) (determination A3).

In step S7, when the control unit 40 determines that the adjusting water W4 does not satisfy the above (b) (step S7: NO), the concentration of free carbonic acid in the adjusting water W4 exceeds 25 mg / L or 5 mg. It is determined whether it is less than / L (determination A31) (step S71).

In step S71, when the control unit 40 determines that the concentration of free carbonic acid in the adjusting water W4 exceeds 25 mg / L (step S71: YES), the pH adjusting means 31 and the aeration device 32 are driven. Specifically, the demineralized water W3 is aerated in the adjusting tank 16 under acidic conditions by using the pH adjusting means 31 and the aeration device 32 so that the concentration of free carbonic acid in the adjusted water W4 is 25 mg / L or less. , Decarbonation treatment (step S72). In step S72, the pH adjusting means 31 and the aeration device 32 may be controlled, if necessary, based on at least one data selected from the group consisting of the pH of the desalinated water W3, the free carbon dioxide concentration and the sulfate ion concentration. ..

As shown in FIG. 2, by setting the pH of the desalinated water W3 to the acidic side, the concentration of bicarbonate ion decreases and the concentration of free carbonic acid increases. By aerating the desalted water W3 having the pH on the acidic side, free carbon dioxide is released into the air as carbon dioxide, and the concentration of free carbonic acid in the adjusted water W4 is reduced. Therefore, aeration of the demineralized water W3 under acidic conditions reduces the concentration of total carbonic acid in the adjusted water W4.

On the other hand, when the control unit 40 determines in step S71 that the concentration of free carbonic acid in the adjusted water W4 is less than 5 mg / L (step S71: NO), the carbon dioxide supply means 38 is driven. Specifically, carbon dioxide is supplied to the demineralized water W3 in the adjusting tank 16 by using the carbon dioxide supplying means 38 so that the concentration of free carbonic acid in the adjusted water W4 is 5 mg / L or more (step S73). .. In step S73, the carbon dioxide supply means 38 may be controlled based on at least one data selected from the group consisting of the pH of the desalinated water W3, the free carbonic acid concentration and the sulfate ion concentration, if necessary.

When returning to step S7 and determining that the control unit 40 satisfies the above (b) (step S7: YES), the adjusting water W4 is brought into contact with the above-mentioned carbonate particles in the reaction tank 11 (step S8). ..
The speed SV for contacting the carbonate particles is preferably 40 (1 / hr) or less, more preferably 30 (1 / hr) or less, and further preferably 20 (1 / hr) or less. .. If the SV is too high, the contact time between the adjusted water W4 and the carbonate particles is short, so that the equilibrium reaction (formula (1)) between the adjusted water W4 and the carbonate particles is insufficient, and the treated water is released. High carbonic acid concentration and high corrosiveness.
Further, the SV is preferably 3 (1 / hr) or more, more preferably 5 (1 / hr) or more, and further preferably 10 (1 / hr) or more. If the SV is too low, the contact time between the adjusted water W4 and the carbonate particles is long, so that the bicarbonate (HCO _3- ) produced by the equilibrium reaction (formula (1)) ^between the adjusted water W4 and the carbonate particles ) Is high, and the corrosiveness is also high.

Since the SV and the pH and the concentration of free carbonic acid affect the effect of the contact treatment, the free carbonic acid concentration (however, as calcium carbonate) and the pH of the prepared water W4 may be adjusted as follows.
When SV is less than 10 (1 / hr): The concentration of free carbonic acid is more than 5 mg / L and 25 mg / L or less, and the pH is 4.0 or more and less than 7.0.
When SV is 10 or more and less than 30 (1 / hr): The concentration of free carbonic acid is more than 5 mg / L and less than 20 mg / L, and the pH is 5.5 or more and 7.0 or less.
When the SV is 30 or more and 40 (1 / hr) or less: The concentration of free carbonic acid is more than 5 mg / L and 15 mg / L or less, and the pH is 6.0 or more and less than 7.5.

Next, using the measuring device 15, at least one selected from the group consisting of the pH, free carbon dioxide concentration and sulfate ion concentration of the treated water W5 obtained in step S8 is measured (step S9).

Next, the control unit 40 determines whether or not the concentration of sulfate ion in the treated water W5 is equal to or higher than the lower limit of the concentration of sulfate ion suitable for drinking water based on the result of the measurement by the measuring device 15 (determination A4). ) Judgment (step S10).

In step S10, when the control unit 40 determines that the concentration of sulfate ion in the treated water W5 does not satisfy the lower limit of the concentration of sulfate ion suitable for drinking water (step S10: NO), the treated water W5 is described above. At least one selected from the group consisting of sulfuric acid, sulfate, sulfate and persulfate is added (step S101). This makes it possible to increase the concentration of sulfate ions and obtain treated water W5 suitable for drinking water.

On the other hand, when the control unit 40 determines in step S10 that the concentration of sulfate ion in the treated water W5 is equal to or higher than the lower limit of the concentration of sulfate ion suitable for drinking water (step S10: YES), it is obtained in step S8. The treated water W5 is stored in the storage tank 51.

When it is determined in steps 4 and 5 that the adjusting water W4 satisfies the above (a) and (b) (step S6: YES, step S7: YES), the desalinated water obtained in step S5. W3 can be used as it is as the adjusting water W4 in step S8.

In the water treatment method of the present embodiment, instead of step S33, an alkali may be added to the raw water W1 by the pH adjusting means 35 to set the pH of the supplied water W2 to the alkaline side (step S31).

As shown in FIG. 2, by setting the pH of the supply water W2 to the alkaline side, the concentration of carbonate ions increases. Since carbonate ions, which are divalent ions, are easily captured by the reverse osmosis membrane of the reverse osmosis membrane module 21, the concentration of carbonate ions in the demineralized water W3 can be reduced by performing step S4 under alkaline conditions. can. Therefore, by performing step S4 under alkaline conditions, the concentration of total carbonic acid is reduced.

As described above, the pH of the prepared water W4 is controlled by the concentration of bicarbonate ion in the desalinated water W3 and the amount of acid (eg, sulfuric acid) or alkali mixed in the pH adjustment of the desalinated water W3. To. As one aspect, if the concentration of bicarbonate ion in the desalinated water W3 is too high, the amount of sulfuric acid mixed to adjust the pH of the desalinated water W3 to the acidic side increases, and the concentration of the sulfate ion in the adjusted water W4 increases. It may exceed 30 mg / L.

However, if the concentration of sulfate ions in the adjusted water W4 exceeds 30 mg / L, a large amount of sulfate ions may remain in the treated water W5, and the treated water W5 may not meet the water quality standard. Therefore, in the water treatment system 1 of the present embodiment, the concentration of sulfate ions in the prepared water W4 is preferably 30 mg / L or less.

On the other hand, in the water treatment method of the present embodiment, when the concentration of sulfate ion in the prepared water W4 exceeds 30 mg / L, the raw water W1 is decarboxylated (step S33) to obtain the decarboxylated water W3. Reduce the concentration of total carbonate. As a result, in the water treatment method of the present embodiment, the concentration of bicarbonate ion can be lowered. As a result, the concentration of sulfate ions in the treated water W5 can be controlled to be below the water quality standard.

As another aspect, as described above, in order to efficiently proceed the reaction between the adjusted water W4 and the carbonate particles, the concentration of free carbonic acid in the adjusted water W4 is controlled to be 5 mg / L or more. Is preferable. In step S71, when the control unit 40 determines that the concentration of free carbonic acid in the adjusted water W4 is less than 5 mg / L (step S71: NO), the control unit 40 returns between steps S1 and S4, and the control unit 40 adjusts the pH. Drive the means 35. Specifically, in the pretreatment tank 61, an acid is added to the raw water W1 by the pH adjusting means 35 to set the pH of the supplied water W2 to the acidic side (step S32). By performing step S4 on the supply water W2, the concentration of free carbonic acid in the desalinated water W3 can be increased.

According to the first embodiment, a water treatment method and a water treatment system capable of easily suppressing corrosion of pipes and equipment are provided. Further, according to the first embodiment, it is easy to satisfy the water quality standard of sulfate ion in the treated water W5.

<Second Embodiment>
Hereinafter, the water treatment method and the water treatment system according to the second embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a diagram showing a schematic configuration of the water treatment system 2 of the second embodiment. As shown in FIG. 4, the water treatment system 2 of the present embodiment includes a contact treatment unit 10, a desalination treatment unit 20, a control unit 40, a storage tank 51, a first adjustment unit 160, and a third adjustment. It has a unit 340 and.

That is, the water treatment system 2 of the second embodiment does not include the second adjusting unit 60. That is, in the present embodiment, it is assumed that the raw water W1 supplied in step S1 is used as it is as the supply water W2 in the next step S4.

Hereinafter, a water treatment method using the above-mentioned water treatment system 2 will be described with reference to FIG. FIG. 5 is a flowchart showing each step of the water treatment method of the second embodiment. The treated water W5 obtained by the water treatment method of the present embodiment is used as drinking water.

First, raw water W1 such as groundwater or river water is supplied to the water treatment system 1 (step S1).

Next, the supply water W2 (raw water W1) supplied to the reverse osmosis membrane module 21 of the reverse osmosis treatment unit 20 is desalted using the reverse osmosis membrane (step S4). After step S4, the obtained desalinated water W3 flows through the second flow path 23.

Next, at least one selected from the group consisting of the pH, free carbonic acid concentration and sulfate ion concentration of the desalted water W3 is measured by the measuring device 24, and from the group consisting of the pH, free carbonic acid concentration and sulfate ion concentration of the adjusted water W4. At least one selected is measured by the measuring device 17 (step S5). The data obtained in step S5 is output to the control unit 40.

Next, among the results obtained in step S5, based on the result of the pH of the adjusting water W4, the control unit 40 determines whether or not the adjusting water W4 satisfies the above (a) (determination A2) (determination A2). Step S6).

In step S6, when the control unit 40 determines that the adjusting water W4 does not satisfy the above (a) (step S6: NO), the pH adjusting means 31 is driven. Specifically, an acid or an alkali is mixed with the demineralized water W3 in the adjusting tank 16 by using a pH adjusting means so that the pH of the adjusting water W4 is 4.0 or more and less than 7.0 (step S61). ..

On the other hand, when the control unit 40 determines in step S6 that the adjusting water W4 satisfies the above (a) (step S6: YES), among the results obtained in step S5, the free carbonic acid in the adjusting water W4 Based on the result of the concentration of (step S7), it is determined whether or not the adjusted water W4 satisfies the above (b) (determination A3).

In step S7, when the control unit 40 determines that the adjusting water W4 does not satisfy the above (b) (step S7: NO), the concentration of free carbonic acid in the adjusting water W4 exceeds 25 mg / L or 5 mg. Whether it is less than / L or not (determination A31) is determined (step S71).

In step S71, when the control unit 40 determines that the concentration of free carbonic acid in the adjusting water W4 exceeds 25 mg / L (step S71: YES), the pH adjusting means 31 and the aeration device 32 are driven. Specifically, the demineralized water W3 is aerated in the adjusting tank 16 under acidic conditions by using the pH adjusting means 31 and the aeration device 32 so that the concentration of free carbonic acid in the adjusted water W4 is 25 mg / L or less. , Decarbonation treatment (step S72).

On the other hand, when the control unit 40 determines in step S71 that the concentration of free carbonic acid in the adjusted water W4 is less than 5 mg / L (step S71: NO), the carbon dioxide supply means 38 is driven. Specifically, carbon dioxide is supplied to the demineralized water W3 in the adjusting tank 16 by using the carbon dioxide supplying means 38 so that the concentration of free carbonic acid in the adjusted water W4 is 5 mg / L or more (step S73). ..

When returning to step S7 and determining that the control unit 40 satisfies the above (b) (step S7: YES), the adjusting water W4 is brought into contact with the above-mentioned carbonate particles in the reaction tank 11 (step S8). ..

Next, using the measuring device 15, the concentration of sulfate ions in the treated water W5 obtained in step S8 is measured (step S9).

Next, the control unit 40 determines whether or not the concentration of sulfate ion in the treated water W5 is equal to or higher than the lower limit of the concentration of sulfate ion suitable for drinking water based on the result of the measurement by the measuring device 15 (determination A3). ) Judgment (step S10).

In step S10, when the control unit 40 determines that the concentration of sulfate ion in the treated water W5 does not satisfy the lower limit of the concentration of sulfate ion suitable for drinking water (step S10: NO), the treated water W5 is described above. At least one selected from the group consisting of sulfuric acid, sulfate, sulfate and persulfate is mixed (step S101). This makes it possible to increase the concentration of sulfate ions and obtain treated water W5 suitable for drinking water.

On the other hand, when the control unit 40 determines in step S10 that the concentration of sulfate ion in the treated water W5 is equal to or higher than the lower limit of the concentration of sulfate ion suitable for drinking water (step S10: YES), it is obtained in step S8. The treated water W5 is stored in the storage tank 51.

According to the second embodiment, there is provided a water treatment method and a water treatment system capable of easily suppressing corrosion of pipes and equipment. Further, when it is known in advance that the raw water W1 can be used as the supply water W2 as it is, the apparatus configuration can be simplified by applying the water treatment system of the second embodiment.

Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the present embodiment are examples, and additions, omissions, substitutions, and the like of the configurations are added, omitted, replaced, and the like without departing from the spirit of the present invention. It can be changed. Further, the present invention is not limited to the embodiments.

For example, in the water treatment system of the above embodiment, the end of the fourth flow path 13 is connected to the lower part of the reaction tank 11, and the end of the third flow path 12 is connected to the upper part of the reaction tank 11. May be good. In this case, the adjusting water W4 flows downward in the reaction tank 11.

Further, for example, in the water treatment system of the above embodiment, either or both of the adjusting tank 16 and the pretreatment tank 61 may be omitted. When the adjusting tank 16 is omitted, the pH and free carbonic acid concentration of the desalinated water W3 are adjusted between the reaction tank 11 and the reverse osmosis membrane module 21. When the pretreatment tank 61 is omitted, the pH and free carbonic acid concentration of the raw water W1 are adjusted by the reverse osmosis membrane module 21.

Further, either one or both of the second adjusting unit 60 and the third adjusting unit 340 may be omitted. That is, in the water treatment method of the above embodiment, either or both of the second adjustment step and the third adjustment step may be omitted.

Hereinafter, the contact treatment of the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example A1
Using the water treatment device 1 shown in FIG. 1, the contact speed when the prepared water W4 is in contact with the contact treatment unit is set to SV = 5 (1 / hr), and the free carbon dioxide concentration of the prepared water W4 is 14. The treatment was carried out by contacting the prepared water W4 with the contact treatment section at 70 mg / L (however, as calcium carbonate) and a pH of 6.50.
Table 1 shows the water quality of the treated water W5 obtained by the contact treatment of the prepared water W4.

Examples A2 to A6, Comparative Examples A1 to A2
The free carbonic acid concentration and pH of the prepared water W4 were adjusted as shown in Table 1, and the prepared water W4 was contact-treated in the same manner as in Example A1.
Table 1 shows the water quality of the treated water W5 obtained by the contact treatment of the prepared water W4.

Examples B1 to B7, Comparative Examples B1 to B2
Examples except that the contact speed when the prepared water W4 was in contact with the contact treatment portion was set to SV = 10 (1 / hr), and the free carbonic acid concentration and pH of the prepared water W4 were adjusted as shown in Table 2. The prepared water W4 was contact-treated in the same manner as in A1.
Table 2 shows the water quality of the treated water W5 obtained by the contact treatment of the prepared water W4.

Examples C1 and Comparative Examples C1 to C8
Examples except that the contact speed when the prepared water W4 was in contact with the contact treatment portion was set to SV = 30 (1 / hr), and the free carbonic acid concentration and pH of the prepared water W4 were adjusted as shown in Table 3. The prepared water W4 was contact-treated in the same manner as in A1.
Table 3 shows the water quality of the treated water W5 obtained by the contact treatment of the prepared water W4.

In the table, in "treated water (W5) water quality", each index means the following.

<pH>
The pH of the treated water W5 obtained by the contact treatment of the prepared water W4 was measured according to a conventional method.

<M-Alkali>
The alkalinity of the treated water W5 was measured by the following method.
The treated water W5 was titrated with a sulfuric acid solution of 0.01 mol / L until the pH reached 4.8, and M-alkali was calculated based on the following formula.
M-alkali (unit: mg / L, as CaCO ₃ ) =
A1 x (1000 / S) x V ... (2)
The symbols in the equation (2) have the following meanings.
A1: Titration (mL) of 0.01 mol / L sulfuric acid solution to the end point.
1000: Unit conversion factor (mL / L).
S: Sampling amount (mL).
V: Calcium carbonate equivalent amount (mg) of 1 mL of a sulfuric acid solution of 0.01 mol / L.
In the present invention, since the pH of the treated water W5 is adjusted to be less than 7.0, the M-alkalinity is equal to the bicarbonate concentration in this region.

<Free carbonic acid concentration>
The free carbonic acid concentration in the treated water W5 was measured as the amount of carbon dioxide according to a conventional method.

<Ca>
The concentration of calcium ions contained in the treated water W5 was measured according to an ion chromatograph cation simultaneous analysis method.

<Steamed residual value>
The amount of the evaporated dry solid residue remaining after heating the treated water W5 and evaporating the volatile components including water is expressed by the amount per 1 L of the treated water W5.

<Water temperature>
The water temperature at the time of measuring each index of the water quality of treated water W5 is shown.

1,2 ... Water treatment system, 10 ... Contact treatment unit, 11 ... Reaction tank, 15, 17, 24, 63 ... Measuring device, 16 ... Adjustment tank, 20 ... Desulfation treatment unit, 21 ... Reverse osmosis membrane module, 31 , 35 ... pH adjusting means, 32, 36 ... aeration device, 34 ... sulfate ion mixing means, 38 ... carbon dioxide supply means, 40 ... control unit, 51 ... storage tank, 61 ... pretreatment tank, W1 ... raw water, W2 ... Supply water, W3 ... Desalted water, W4 ... Adjusted water, W5 ... Treated water

Claims (9)

Using a reverse osmosis membrane, the supply water containing inorganic salts is desalted to obtain desalted water, and the desalting process.
The first adjusting step of adjusting the pH and free carbonic acid concentration of the demineralized water to obtain the adjusted water, and
A contact treatment step of bringing the adjusted water into contact with carbonate particles to obtain treated water,
Prior to the desalting treatment step, a second adjusting step of adjusting the pH and free carbonic acid concentration of the raw water to obtain the supply water is provided .
A water treatment method in which the raw water is aerated and decarboxylated under acidic conditions in the second adjustment step . The water treatment method according to claim 1, further comprising a third adjustment step of adjusting the pH and free carbonic acid concentration of the treated water after the contact treatment step. The water treatment method according to claim 2 , wherein in the third adjustment step, at least one selected from the group consisting of sulfuric acid, sulfate, sulfate and persulfate is mixed with the treated water. The water treatment method according to any one of claims 1 to 3 , wherein in the first adjustment step, at least one selected from the group consisting of sulfuric acid, sulfate, sulfite and sulfite is mixed with the desalted water. .. The water treatment method according to any one of claims 1 to 4 , wherein at least one selected from the group consisting of calcium carbonate and magnesium carbonate is used as the carbonate particles. One of claims 1 to 5 , wherein the carbonate particles are composed of a plurality of particles, and the number of the particles having a particle size of 0.1 mm or more and 10 mm or less is 90% or more with respect to the total number of the carbonate particles. The water treatment method described in the section. The water treatment method according to any one of claims 1 to 6 , wherein in the contact treatment step, the desalted water is brought into contact with the carbonate particles at a space velocity of 5 hr ^-1 or more and 30 hr ^-1 or less. The water treatment method according to any one of claims 1 to 7 , wherein in the first adjustment step, carbon dioxide or a mixture of sodium hydrogen carbonate and sulfuric acid is added to the desalinated water. A desalination treatment unit with a reverse osmosis membrane and
A contact treatment unit that brings the water obtained in the desalting treatment unit into contact with the carbonate particles, and the contact treatment unit.
A first adjusting unit, which is arranged between the desalting treatment unit and the contact processing unit and adjusts the pH and free carbonic acid concentration of the water,
It has a second adjusting section, which is arranged in front of the desalting treatment section and adjusts the pH and free carbonic acid concentration of the raw water .
The second adjusting unit is a water treatment system that aerates the raw water under acidic conditions and decarboxylates the water.

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