JP6968682B2 - Manufacturing method of permeated water, water treatment device and operation method of the water treatment device - Google Patents

Description

The present invention relates to a water treatment method for treating groundwater using a reverse osmosis membrane.

Reverse osmosis membranes are known as water treatment membranes that consume less energy, are used in various fields, and are also used to treat wastewater, seawater, groundwater, and the like.
Further, conventionally, a water treatment system for removing dissolved iron, dissolved manganese, carbonate, and ammoniacal nitrogen contained in groundwater has been known.
For example, Patent Document 1 describes a reduction treatment device that adjusts groundwater to a reduced state by chemical means or physical means, and treatment of groundwater adjusted to a reduced state with a nanofiltration membrane or a reverse osmosis membrane to produce permeated water. A water treatment system including a membrane separation device is disclosed.

Japanese Unexamined Patent Publication No. 2011-189242

When a reverse osmosis membrane is used, it is recommended that the total amount of impurities and the like in the water to be treated be a certain amount or less for the water to be treated to be introduced into the reverse osmosis membrane. Therefore, the water to be treated to be introduced into the reverse osmosis membrane is usually pretreated in advance. In Patent Document 1, before introducing water to be treated into the reverse osmosis membrane, pretreatment such as sand separator, cation exchanger, ultraviolet irradiation, and filter filtration is performed.

When the present inventors examined the introduction of groundwater directly into a reverse osmosis membrane without performing the pretreatment as performed in the above patent document when treating the groundwater, carbon dioxide gas, ammonia gas, It was found that the removal of iron oxide and manganese oxide components was insufficient, and the following problems occurred.
First, when the groundwater is adjusted to pH 7.0 or less by chemical means and used as the water to be treated by the reverse osmosis membrane, the free carbon dioxide in the water to be treated increases, and when this is treated by the reverse osmosis membrane, carbon dioxide gas is produced. Permeated water containing a large amount of water is produced. Permeated water containing a large amount of carbon dioxide is highly corrosive and damages the equipment after the reverse osmosis membrane.
Second, when the ground water is adjusted to a reduced state by physical means and used as the water to be treated by the reverse osmosis membrane, the dissolved oxygen in the water to be treated is removed and the free carbon dioxide is also removed, but the decarbonation Due to the effect, the pH of the water to be treated shifts to the alkaline side, and as the pH becomes higher than 7.0, the proportion of ammonia gas in the water to be treated becomes higher than the proportion of ammonium ions, and when this is treated with a reverse osmosis membrane, Permeated water containing a large amount of ammonia gas is produced. Permeated water containing a large amount of ammonia gas causes an increase in the injection amount of sodium hypochlorite added for use as drinking water.
Third, when the water to be treated is treated with a reverse osmosis membrane and carbon dioxide gas permeates to the permeated water side, the pH of the concentrated water shifts to the alkaline side and becomes higher than pH 7.0, the dissolved iron and Dissolved manganese components are oxidized and precipitated, leading to membrane fouling on the reverse osmosis membrane.
The present invention solves the above problems in a method for producing permeated water in which groundwater is introduced into a reverse osmosis membrane without performing pretreatment.

The present inventors have solved the above-mentioned problems in the case of directly introducing groundwater into a reverse osmosis membrane.
Further studies on the removal of carbon dioxide gas, ammonia gas, iron oxide and manganese oxide components, and found that the problem can be solved by performing water treatment so that the pH value of the concentrated water in the reverse osmosis membrane is 7.0 or less. rice field.
The present invention includes:
[1] A method for producing permeated water, which is obtained by directly supplying groundwater to a reverse osmosis membrane and treating it with water so that the pH of the concentrated water in the reverse osmosis membrane is 7.0 or less.
[2] The method for producing permeated water according to [1], wherein the pH of the concentrated water is set to 7.0 or less by adding an acid component to groundwater.
[3] The method for producing permeated water according to [1] or [2], further comprising a decarboxylation treatment step.
[4] The method for producing permeated water according to [3], wherein the decarboxylation treatment step is decarboxylation by aeration and / or decarboxylation by a decarboxylation membrane.
[5] A water treatment device for directly treating groundwater with a reverse osmosis membrane, which includes an acid addition means for adding an acid component to the groundwater, a reverse osmosis membrane, and a drainage means capable of draining at least a part of the groundwater. , A water treatment device.
[6] The water treatment device according to [5], wherein at least a part of the pipe for transferring groundwater is a vinyl chloride pipe.
[7] According to the method of operating the water treatment device according to [5] or [6], when the water treatment device is temporarily stopped and then restarted, it stays in the pipe for transferring the groundwater to the reverse osmosis membrane. An operation method of a water treatment device that operates so as to drain accumulated water.
[8] Reverse osmosis of treated water having an FI value of 3 or more, an iron ion concentration of 0.01 ppm or more, a manganese ion concentration of 0.01 ppm or more, an ammoniacal nitrogen concentration of 0.5 ppm or more, and an organic substance concentration of 10 ppm or more. A method for producing permeated water, which is supplied to a membrane and treated with water so that the pH of the concentrated water in the reverse osmosis membrane is 7.0 or less.

According to the present invention, since the permeation of carbon dioxide gas into the permeated water is suppressed, the corrosion of the device and the like after the reverse osmosis membrane can be suppressed. Further, since the permeation of ammonia gas into the permeated water is suppressed, the amount of sodium hypochlorite used in the post-treatment can be reduced, and the quality of the permeated water can be maintained. Furthermore, since the oxidative precipitation of dissolved iron and dissolved manganese components from concentrated water is suppressed, membrane fouling to the reverse osmosis membrane can be suppressed. In addition, when the water treatment equipment is temporarily stopped and then restarted, the operation is performed so as to drain the accumulated water accumulated in the equipment, in order to suppress the oxidative precipitation of dissolved iron and dissolved manganese components, so that the reverse osmosis membrane can be used. Membrane fouling can be suppressed. By suppressing membrane fouling to the reverse osmosis membrane, the device can be operated for a long period of time. In addition to these, when groundwater is directly introduced into the reverse osmosis membrane, a pretreatment device is not required, so that the water treatment device can be simplified.

It is a processing flow diagram which shows one Embodiment of this invention. It is a graph which shows the result of Experiment 1. It is a graph which shows the result of Experiment 2.

Hereinafter, embodiments of the present invention will be described in detail. The description of the constituent elements described below is an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents as long as the gist thereof is not exceeded.

FIG. 1 is a processing flow diagram showing an embodiment of the present invention. In one form of the water treatment apparatus 100 to which the treatment flow is applied, the acid addition means 1, the spray nozzle 2, the raw water tank 3, the aeration blower 4, the circulation pump 5A, the supply pump 5B, the pH meter 6, the switching valve 7, and the reverse osmosis Includes osmosis membrane 8 and degassing membrane 9. Means and measuring instruments other than these may be included. Other means include a hypochlorous acid addition device for removing and / or sterilizing ammonia required when permeated water is used as tap water.

In the water treatment apparatus 100, the pumped groundwater 10 can be directly supplied to the reverse osmosis membrane 8.
Groundwater is water that exists in the ground and fills the gaps in the stratum, and although the water quality differs slightly depending on the region, it is not particularly limited depending on the region or country.

Groundwater 10 contains various substances. The method for producing permeated water, the method for operating the water treatment device and the water treatment device according to the present embodiment can be suitably used for groundwater containing dissolved iron, dissolved manganese, carbonate, ammoniacal nitrogen and organic substances.
When the dissolved iron is contained, its concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and further preferably 10 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.01 ppm or more, 0.1 ppm or more, or 1 ppm or more.
When the dissolved iron is contained in the above range, the dissolved iron component is preferably removed by the reverse osmosis membrane 8 contained in the present embodiment.
When the dissolved manganese is contained, its concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and further preferably 10 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.01 ppm or more, 0.1 ppm or more, or 1 ppm or more.
When the dissolved manganese is contained in the above range, the dissolved manganese component is preferably removed by the reverse osmosis membrane 8 contained in the present embodiment.
When a carbonate is contained, its concentration is preferably 500 ppm or less, more preferably 200 ppm or less, and further preferably 100 ppm or less. The lower limit is not particularly limited, and may be, for example, 1 ppm or more, 10 ppm or more, or 50 ppm or more.
When the carbonate is contained in the above range, the free carbonic acid is preferably removed by the decarboxylation treatment step contained in the present embodiment.
When it contains ammoniacal nitrogen, its concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and even more preferably 10 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.5 ppm or more, 1 ppm or more, or 2 ppm or more.
When ammoniacal nitrogen is contained in the above range, the ammonia gas is preferably removed by the reverse osmosis membrane 8 contained in the present embodiment.
When an organic substance is contained, its concentration is preferably 200 ppm or less, more preferably 100 ppm or less, and further preferably 50 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.3 ppm or more, 1 ppm or more, 3 ppm or more, or 10 ppm or more.
When the organic substance is contained in the above range, the organic substance is preferably removed by the reverse osmosis membrane 8 contained in the present embodiment.
In addition, the groundwater may contain various minerals derived from minerals and the like, for example, calcium ion, sodium ion, potassium ion, magnesium ion, chloride ion, sulfate ion, silica and the like.
Further, the groundwater has a FI value of 6.5 or less, more preferably 6 or less, more preferably 0 or more, still more preferably 3 or more. The FI value is an index value for quantifying a trace amount of suspended solids in the water supplied to the module in the reverse osmosis method.

In this embodiment, groundwater is directly supplied to the reverse osmosis membrane. The term "directly" as used herein means that the groundwater is transferred to the reverse osmosis membrane without any pretreatment that is usually performed when the groundwater is introduced into the reverse osmosis membrane, for example, treatments that are performed for the purpose of removing metals, removing organic substances, sterilizing, and the like. Means to introduce.
When a reverse osmosis membrane is used, it is recommended that the water to be treated to be introduced into the reverse osmosis membrane be introduced into the reverse osmosis membrane after the total amount of impurities and the like in the water to be treated is set to a certain amount or less. This is because the reverse osmosis membrane is introduced into the reverse osmosis membrane without reducing the total amount of impurities, etc., so that the reverse osmosis membrane is clogged and the permeability is reduced. This is because there is a risk that the membrane will be damaged. However, the present inventors have come to the conclusion that the pH of the concentrated water of the reverse osmosis membrane can be controlled to a certain value or less, and the groundwater can be continuously supplied directly to the reverse osmosis membrane for treatment.

The method for producing permeated water in the present embodiment is obtained by directly supplying groundwater 10 to the reverse osmosis membrane 8 and treating the concentrated water 12 of the reverse osmosis membrane with water so that the pH is 7.0 or less. 11 is the manufacturing method.
The reverse osmosis membrane 8 is not particularly limited, and a commercially available one can be used. Further, a nanofiltration membrane (also referred to as an NF membrane) having a slightly larger pore diameter than a membrane usually called a reverse osmosis membrane is also included in the reverse osmosis membrane in the present embodiment.

The groundwater 10 may be added with an acid component by the acid adding means 1 so that the pH of the concentrated water 12 of the reverse osmosis membrane is 7.0 or less. The acid addition means 1 suppresses the permeation of free carbon dioxide into the permeated water in the reverse osmosis membrane 8 described later, suppresses the permeation of ammonia gas, and suppresses the membrane fouling of iron oxide and manganese oxide into the reverse osmosis membrane. From the viewpoint, it is preferable that the ground water 10 is provided in the pre-stage where the reverse osmosis membrane 8 is supplied, and it is preferable that the ground water 10 is provided in the pre-stage and / or the post-stage in which the raw water tank 3 is spray-sprayed by the spray nozzle 2.

The acid component added by the acid adding means 1 is not particularly limited as long as it lowers the pH of the ground water 10 and the concentrated water 12, but examples thereof include inorganic acids such as sulfuric acid, hydrochloric acid, nitrate and carbon dioxide, and organic acids. However, inorganic acids are preferred, and sulfuric acid is more preferred. Since the amount of acid added is appropriately set according to the pH values of the groundwater 10 and the concentrated water 12, the acid is added while checking the pH value shown in the pH meter 6, and the pH of the groundwater 10 and the concentrated water 12 is changed to 7. It is preferably 0.0 or less, more preferably 6.5 or less, further preferably 6.0 or less, and most preferably 5.5 or less.

When the pH of the groundwater 10 and the concentrated water 12 becomes 7.0 or less, the following effects can be obtained on the dissolved iron, the dissolved manganese, the carbonate and the ammoniacal nitrogen in the groundwater 10 and the concentrated water 12.
Dissolved iron and dissolved manganese are suppressed from oxidative precipitation as iron oxide and manganese oxide, respectively, and membrane fouling to the reverse osmosis membrane 8 is suppressed. Further, the carbonate has a large proportion of free carbonic acid among the free carbonic acid, bicarbonate ion, and carbonate ion, and the free carbonic acid is efficiently removed by the decarbonation treatment step described later. Further, the ammoniacal nitrogen has a large proportion of ammonium ions in the ammonium ions and the ammonia gas, and the permeation of the ammonium ions into the permeated water 11 obtained by permeating through the reverse osmosis membrane 8 is suppressed.

The method for producing the permeated water 11 in the present embodiment may further include a decarboxylation treatment step.
The decarboxylation means in the decarboxylation treatment step is not particularly limited as long as it can remove free carbonic acid in the groundwater 10, the permeated water 11, and the concentrated water 12, and is, for example, decarboxylation by exposure, decarboxylation by decompression, and decarboxylation. Decarboxylation with a membrane or a combination of these decarboxylation means can be mentioned.

The decarboxylation treatment step of the present embodiment may be decarboxylation by aeration and / or decarboxylation by a decarboxylation membrane.
Decarboxylation by aeration is performed by blowing a gas into the groundwater 10 by the aeration blower 4. The gas to be blown is not particularly limited as long as it can remove free carbonic acid from the groundwater 10, and examples thereof include an inert gas such as nitrogen gas and air. Further, decarboxylation by aeration is preferably performed before the reverse osmosis membrane 8, and preferably after the acid component is added to the groundwater 10.
On the other hand, decarboxylation by the degassing membrane is performed by the degassing membrane 9 installed in the pipe for transferring the groundwater 10 and / or the permeated water 12. The degassing membrane 9 is not particularly limited as long as it can remove free carbonic acid from the groundwater 10 and the permeated water 12, and a hollow fiber membrane is typically used, but the degassing membrane 9 is not limited thereto. Further, decarbonization by the degassing membrane may be performed in the front stage of the reverse osmosis membrane 8, may be performed in the rear stage of the reverse osmosis membrane 8, and may be performed in both the front stage and the rear stage of the reverse osmosis membrane 8. It is also preferable that the procedure is carried out after the acid component is added to the ground water 10.

The groundwater 10 and / or the permeated water 12 obtained by permeating through the reverse osmosis membrane 8 supplied to the reverse osmosis membrane 8 is corroded because free carbonic acid is efficiently removed by the acid treatment and the decarbonation step. It is suppressed that the water becomes highly acidic.

The water treatment device 100 in the present embodiment may further have a drainage means capable of draining at least a part of the groundwater.
The drainage means is not particularly limited as long as it is installed in front of the reverse osmosis membrane 8, and examples thereof include a switching valve 7 installed in a pipe for transferring groundwater 10.
By installing the drainage means, when the water treatment device 100 is temporarily stopped and then restarted, even if the dissolved iron in the accumulated water accumulated in the pipe for transferring the groundwater 10 to the raw water tank 3 is oxidized and precipitated, it is retained. Since the operation method of draining water becomes possible, membrane fouling to the reverse osmosis membrane 8 can be suppressed.

At least a part of the pipe for transferring the groundwater 10 of the water treatment apparatus 100 in this embodiment may be a vinyl chloride pipe.
By making at least a part of the pipe for transferring the groundwater 10 a vinyl chloride pipe, it is possible to suppress the corrosion of the pipe due to the free carbonic acid of the groundwater 10.

The water treatment device 100 in the present embodiment may have a circulation pump 5A for circulating the groundwater 10. The circulation pump 5A may be installed in front of the reverse osmosis membrane 8, and is preferably installed so that the groundwater 10 stored in the raw water tank 3 can be circulated.
Although the circulation pump 5A is not an essential configuration in the present embodiment, when the groundwater 10 supplied to the reverse osmosis membrane 8 has a large amount of free carbonic acid and the decarbonation is insufficient, the circulation pump 5 operates and the raw water tank 3 is operated. By circulating the groundwater 10 in the above, it is preferable to have the groundwater 10 because it enables an operation method in which the acid treatment by the acid addition means 1 and the decarbonation treatment by the aeration blower 4 are additionally performed.

The water treatment device 100 in the present embodiment may have a supply pump 5B for supplying the groundwater 10 to the reverse osmosis membrane. The supply pump 5B may be installed in front of the reverse osmosis membrane 8, and is preferably installed so that the groundwater 10 stored in the raw water tank 3 can be supplied to the reverse osmosis membrane 8.
Although the supply pump 5B is not an essential configuration in the present embodiment, it is preferable to have the supply pump 5B because it enables an operation method for keeping the flow rate and pressure of the groundwater 10 supplied to the reverse osmosis membrane 8 constant.

The following shows the experimental results that examined various conditions when the reverse osmosis membrane was provided.
<Experiment 1: Relationship between pH of groundwater before decarboxylation and removal rate of alkalinity>
In order to change the pH of the groundwater before decarbonation treatment and consider the process margin in the experiment and ^{set it so that OH-} precipitation does not occur even if the pH fluctuates, aeration is performed until the pH of the groundwater reaches 6.5. The result of measuring the removal rate of alkalinity from the groundwater by performing the decarbonation treatment by the above is shown in FIG. The alkalinity is the amount of alkali content such as bicarbonate, carbonate or hydroxide contained in water _{expressed by the corresponding concentration of calcium carbonate (CaCO 3} ), such as groundwater. In the case of natural water, it is known that carbonate or bicarbonate is the main component.
As shown in FIG. 2, it can be understood that the removal rate of alkalinity is 75% or more when the pH of the groundwater before the decarboxylation treatment is 5.5 or less. Therefore, it is preferable that the pH of the groundwater before the decarboxylation treatment is 5.5 or less and the decarboxylation treatment is performed until the pH of the groundwater reaches 7.0.

<Experiment 2: Relationship between the pH of groundwater supplied to the reverse osmosis membrane and the concentration of ammoniacal nitrogen contained in the permeated water>
Results of measuring the concentration of ammoniacal nitrogen contained in permeated water by changing the pH of groundwater with an ammoniacal nitrogen concentration of 4.5 mg / L and supplying it to a reverse osmosis membrane (ESPA2 manufactured by Nitto Denko) under the condition of a recovery rate of 70%. Is shown in FIG.
As shown in FIG. 3, it can be understood that the concentration of ammoniacal nitrogen contained in the permeated water increases as the pH of the groundwater increases. Therefore, for ammoniacal nitrogen, the inhibition rate by the reverse osmosis membrane increases when the pH of the groundwater is 7 or less, while the inhibition rate by the reverse osmosis membrane decreases as the pH of the groundwater becomes higher than 7.0.

100 Water treatment device 10 Groundwater 11 Permeated water 12 Concentrated water 13 Drainage 1 Acid addition means 2 Spray nozzle 3 Raw water tank 4 Aeration blower 5A Circulation pump 5B Supply pump 6 pH meter 7 Switching valve 8 Reverse osmosis membrane 9 Degassing membrane

Claims (1)

The FI value is 0 or more and 6.5 or less , the iron ion concentration is 0.01 ppm or more, the manganese ion concentration is 0.01 ppm or more, the ammoniacal nitrogen concentration is 0.5 ppm or more, and the organic substance concentration is 0.3 ppm or more and 200 ppm or less. A method for producing permeated water, in which treated water is supplied to a reverse osmosis membrane and water treatment is performed so that the pH of the concentrated water in the reverse osmosis membrane is 7.0 or less.

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