JP2019107592A - Method for producing permeation water, water treatment device and method for operating the water treatment device - Google Patents

Abstract

To provide a method for producing permeation water that directly introduces underground water into a reverse osmosis membrane without performing any pretreatment.SOLUTION: The present invention provides a method for producing permeation water by supplying underground water directly into a reverse osmosis membrane, and treating the water so that the concentration water of the reverse osmosis membrane is 7.0 or less in pH.SELECTED DRAWING: Figure 1

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 with low energy consumption, are used in various fields, and are also used in the treatment of drainage, seawater, groundwater and the like.
Also, conventionally, there has been known a water treatment system for removing dissolved iron, dissolved manganese, carbonate, and ammonia nitrogen contained in groundwater.
For example, in Patent Document 1, a reduction treatment apparatus for adjusting ground water to a reduced state by a chemical means or a physical means, and groundwater adjusted to a reduced state is treated with a nanofiltration membrane or a reverse osmosis membrane to produce permeated water. A water treatment system is disclosed, comprising a membrane separation device.

JP, 2011-189242, A

  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 introduced into the reverse osmosis membrane. Therefore, it is normal to pre-treat the water to be treated introduced into the reverse osmosis membrane. In patent document 1, before introduce | transducing a to-be-processed water to a reverse osmosis membrane, pretreatments, such as a sand separator, a cation exchanger, ultraviolet irradiation, and filter filtration, are performed.

When treating the groundwater, the present inventors examined introducing the groundwater directly to the reverse osmosis membrane without performing the pretreatment as described in the above-mentioned patent documents, carbon dioxide gas, ammonia gas, It was found that the removal of iron oxide and manganese oxide components is insufficient and the following problems occur.
First, when ground water is adjusted to pH 7.0 or less by chemical means to be treated water of reverse osmosis membrane, when free carbonic acid in the treated water increases, and this is treated with reverse osmosis membrane, carbon dioxide gas Permeate containing a large amount of water is produced. The permeated water containing a large amount of carbon dioxide gas is highly corrosive and damages the devices after the reverse osmosis membrane.
Second, when the ground water is adjusted to a reduced state by physical means and treated as reverse osmosis membrane treated water, dissolved oxygen in the treated water is removed and free carbon dioxide is also removed. As the pH of the water to be treated shifts to the alkali side due to the effect and becomes higher than pH 7.0, the proportion of ammonia gas in the water to be treated becomes higher than the proportion of ammonium ions, and this is treated with a reverse osmosis membrane, A permeate containing a large amount of ammonia gas is produced. The permeate containing a large amount of ammonia gas causes an increase in the injection amount of sodium hypochlorite added to use it as drinking water.
Thirdly, when the water to be treated is treated with the reverse osmosis membrane and carbon dioxide gas permeates to the permeate side, the pH of the concentrated water shifts to the alkali side and becomes higher than pH 7.0, the dissolved iron and The dissolved manganese component oxidizes and precipitates, causing membrane fouling to the reverse osmosis membrane.
The present invention solves the above-mentioned problems in a method of producing permeated water in which groundwater is introduced into a reverse osmosis membrane without performing pretreatment.

In order to solve the above problems in the case of introducing groundwater directly to the reverse osmosis membrane, the present inventors
We further investigated the removal of carbon dioxide gas, ammonia gas, iron oxide and manganese oxide components, and found that the problem can be solved by conducting water treatment so that the pH value of the concentrated water of the reverse osmosis membrane is 7.0 or less. The
The present invention includes the following.
[1] A method for producing permeated water, which is obtained by directly supplying groundwater to a reverse osmosis membrane, and treating the water so that the pH of concentrated water of the reverse osmosis membrane becomes 7.0 or less.
[2] The method for producing permeated water according to [1], wherein the pH of the concentrated water is 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 by degassing membrane.
[5] A water treatment apparatus for treating ground water directly with a reverse osmosis membrane, which comprises an acid addition means for adding an acid component to ground water, a reverse osmosis membrane, and a drainage means capable of draining at least a part of ground water And a water treatment device.
[6] The water treatment apparatus according to [5], wherein at least a part of the pipe for transferring groundwater is a vinyl chloride pipe.
[7] The operating method of the water treatment apparatus according to [5] or [6], wherein when the water treatment apparatus is temporarily stopped and then reactivated, it is retained in the pipe for transferring the ground water to the reverse osmosis membrane A method of operating a water treatment system, operating to drain stagnant 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 matter concentration of 10 ppm or more A method for producing permeated water, which is supplied to a membrane and subjected to water treatment such that the pH of concentrated water of the reverse osmosis membrane is 7.0 or less.

  According to the present invention, since the permeation of carbon dioxide gas to the permeated water is suppressed, the corrosion of the devices after the reverse osmosis membrane can be suppressed. In addition, since the permeation of ammonia gas to 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 oxidation precipitation of the dissolved iron and the dissolved manganese component from the concentrated water is suppressed, the membrane fouling to the reverse osmosis membrane can be suppressed. In addition, when the water treatment apparatus is restarted after being temporarily stopped, operation to drain the stagnant water retained in the apparatus also suppresses oxidation and precipitation of the dissolved iron and the dissolved manganese components, so that the reverse osmosis membrane Membrane fouling can be suppressed. By suppressing membrane fouling to the reverse osmosis membrane, the device can be operated for a long time. In addition to these, when introducing groundwater directly to the reverse osmosis membrane, the water treatment system can be simplified because the pretreatment system is not required.

FIG. 5 is a process flow diagram illustrating an embodiment of the present invention. 7 is a graph showing the results of Experiment 1. 7 is a graph showing the results of Experiment 2.

  Hereinafter, embodiments of the present invention will be described in detail. The description of the configuration requirements 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 of the invention is not exceeded.

FIG. 1 is a process flow diagram illustrating 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 A permeable membrane 8 and a degassing membrane 9 are included. Other means or measuring instruments may be included. Another means is, for example, a hypochlorous acid addition device for ammonia removal and / or sterilization which is necessary when using permeated water as tap water.

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

The groundwater 10 contains various substances. The method for producing permeated water, the water treatment apparatus and the operation method of the water treatment apparatus of the present embodiment can be suitably used for underground water containing dissolved iron, dissolved manganese, carbonate, ammonia nitrogen and organic matter.
When the dissolved iron is contained, the concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and still more preferably 10 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.01 ppm or more, may be 0.1 ppm or more, and may be 1 ppm or more.
When dissolved iron is contained in the said range, removal of the dissolved iron component by the reverse osmosis membrane 8 contained in this embodiment is performed suitably.
When the dissolved manganese is contained, its concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and still more preferably 10 ppm or less. The lower limit is not particularly limited, and may be, for example, 0.01 ppm or more, may be 0.1 ppm or more, and may be 1 ppm or more.
When the dissolved manganese is contained in the above range, removal of the dissolved manganese component by the reverse osmosis membrane 8 included in the present embodiment is suitably performed.
When the carbonate is contained, its concentration is preferably 500 ppm or less, more preferably 200 ppm or less, and still more 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, removal of free carbonic acid is suitably performed by the decarboxylation step included in the present embodiment.
When the ammonia nitrogen is contained, the concentration is preferably 50 ppm or less, more preferably 20 ppm or less, and still 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 the ammoniacal nitrogen is contained in the above range, removal of ammonia gas is suitably performed by the reverse osmosis membrane 8 included in the present embodiment.
When the organic substance is contained, the concentration is preferably 200 ppm or less, more preferably 100 ppm or less, and still more 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 matter is contained in the above range, removal of the organic matter is suitably performed by the reverse osmosis membrane 8 included in the present embodiment.
In addition, the groundwater may contain various minerals derived from minerals and the like, such as calcium ion, sodium ion, potassium ion, magnesium ion, chloride ion, sulfate ion, silica and the like.
The ground water preferably has an FI value of 6.5 or less, more preferably 6 or less, preferably 0 or more, and still more preferably 3 or more. In addition, FI value is a value of the index which quantifies the trace amount suspended substance in the feed water to a module in a reverse osmosis method.

In the present embodiment, groundwater is directly supplied to the reverse osmosis membrane. The term "directly" as used herein means that the reverse osmosis membrane is used to treat the groundwater without performing the pretreatment for introducing the underground water into the reverse osmosis membrane, for example, for removing metals, removing organic substances, and sterilization. It means to introduce.
When a reverse osmosis membrane is used, it is recommended to introduce the water to be treated introduced into the reverse osmosis membrane into the reverse osmosis membrane after setting the total amount of impurities and the like in the water to be treated to a certain amount or less. This is because the reverse osmosis membrane is clogged and reduced in permeability by being introduced into the reverse osmosis membrane while the total amount of impurities and the like is not reduced, and the reverse osmosis is achieved by increasing the pressure difference to maintain the permeability. This is because there is a risk that the membrane may be broken. However, the present inventors reached the conclusion that the pH of the concentrated water of the reverse osmosis membrane can be controlled to a certain value or less, and groundwater can be continuously supplied directly to the reverse osmosis membrane and treated.

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

  The underground water 10 may be added with an acid component by the acid addition 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 carbonic acid to permeated water in the reverse osmosis membrane 8 described later, and the permeation suppression of ammonia gas, and the membrane fouling suppression of iron oxide and manganese oxide to the reverse osmosis membrane. From the viewpoint, it is preferable that the ground water 10 be provided at a front stage supplied to the reverse osmosis membrane 8 and that the ground water 10 be provided at a front stage and / or a rear stage where the spray nozzle 2 sprays the raw water tank 3.

  The acid component to be added by the acid addition means 1 is not particularly limited as long as it lowers the pH of the ground water 10 and the concentrated water 12. For example, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid and carbonic acid, and organic acids are exemplified. Although inorganic acids are preferred, sulfuric acid is more preferred. Since the amount of acid added is appropriately set by the pH value of the groundwater 10 and the concentrated water 12, the acid is added while confirming the value of pH indicated by the pH meter 6, and the pH of the groundwater 10 and the concentrated water 12 is 7 It is preferable to set it to .0 or less, more preferably to 6.5 or less, further preferably to 6.0 or less, and most preferably to 5.5 or less.

When the pH of the ground water 10 and the concentrated water 12 is 7.0 or less, the following effects can be obtained on the dissolved iron, dissolved manganese, carbonate and ammonia nitrogen in the ground water 10 and the concentrated water 12.
The dissolved iron and the dissolved manganese are suppressed from being oxidized and precipitated as iron oxide and manganese oxide, respectively, and the membrane fouling to the reverse osmosis membrane 8 is suppressed. In the carbonate, the ratio of free carbonic acid among the free carbonic acid, the bicarbonate ion and the carbonate ion is high, and the free carbonic acid is efficiently removed by the decarboxylation step described later. Furthermore, the ammoniacal nitrogen is in a state in which the ratio of ammonium ions is high among the ammonium ions and the ammonia gas, and the permeation of ammonium ions to the permeated water 11 obtained through the reverse osmosis membrane 8 is suppressed.

The method of producing the permeated water 11 in the present embodiment may further include a decarboxylation step.
The decarboxylation means in the decarboxylation step is not particularly limited as long as free carbon dioxide in the ground water 10, the permeate water 11 and the concentrated water 12 can be removed, for example, decarboxylation by aeration, decarboxylation by reduced pressure, degassing The decarboxylation by a membrane, or the combination of these decarboxylation means etc. is mentioned.

The decarboxylation step of the present embodiment may be decarboxylation by aeration and / or decarboxylation by a degassed membrane.
Decarboxylation by aeration is performed by blowing 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 ground water 10, and examples thereof include inert gas such as nitrogen gas and air. Moreover, it is preferable to perform decarboxylation by aeration in the front | former stage of the reverse osmosis membrane 8, and it is preferable to be performed in the back | latter stage to which the acid component was added to the ground water 10. FIG.
On the other hand, the decarbonation by the degassing membrane is performed by the degassing membrane 9 installed in the pipe for transferring the ground water 10 and / or the permeated water 12. The degassing membrane 9 is not particularly limited as long as free carbon dioxide can be removed from the ground water 10 and the permeate water 12. Typically, a hollow fiber membrane is used, but is not limited thereto. In addition, decarboxylation by the degassing membrane may be performed at the former stage of the reverse osmosis membrane 8 or may be performed at the latter stage of the reverse osmosis membrane 8, and performed at both of the former stage and the latter stage of the reverse osmosis membrane 8. It is also preferable to be performed in the latter stage where the acid component is added to the groundwater 10.

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

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

At least a part of the pipe for transferring the underground water 10 of the water treatment apparatus 100 in the present embodiment may be a vinyl chloride pipe.
By making at least a part of the piping for transferring the ground water 10 a vinyl chloride pipe, it is possible to suppress the corrosion of the piping due to the free carbonation of the ground water 10.

The water treatment apparatus 100 in the present embodiment may have a circulation pump 5A for circulating the ground water 10. It is preferable that the circulation pump 5A be installed at the front stage of the reverse osmosis membrane 8 and be installed so as to be able to circulate the underground water 10 stored in the raw water tank 3.
The circulation pump 5A is not an essential component in the present embodiment, but the circulation pump 5 is operated when there is a large amount of free carbon dioxide in the ground water 10 supplied to the reverse osmosis membrane 8 and the decarboxylation is insufficient. It is preferable to have the operation method in which the acid treatment by the acid addition unit 1 and the decarboxylation treatment by the aeration blower 4 can be additionally performed in the ground water 10 by circulating the ground water 10 in the above.

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

Below, the experimental result which examined various conditions in providing a reverse osmosis membrane is shown.
<Experiment 1: Relationship between pH and alkalinity removal rate of groundwater before decarboxylation treatment>
In order to change the pH of the ground water before decarboxylation treatment and to consider the margin of the process as an experiment and to prevent OH ^- precipitation even if the pH fluctuates, aeration is performed until the pH of the ground water reaches 6.5. The result of having measured the removal rate of the alkalinity from groundwater was shown in FIG. The alkalinity is the amount of alkali component such as hydrogen carbonate, carbonate or hydroxide contained in water, which is expressed by the concentration of calcium carbonate (CaCO ₃ ) corresponding to it, like ground water. 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 pH of groundwater supplied to reverse osmosis membrane and concentration of ammonia nitrogen contained in permeate>
The pH of groundwater with an ammoniacal nitrogen concentration of 4.5 mg / L was changed, and the recovery rate was 70%. The result was supplied to the reverse osmosis membrane (Nippon Denko ESPA 2) and the concentration of ammoniacal nitrogen contained in the permeate was measured. Is shown in FIG.
As shown in FIG. 3, it can be understood that the concentration of ammonia nitrogen contained in the permeate increases as the pH of the groundwater increases. Therefore, when the pH of the groundwater is 7 or less, the blocking rate by the reverse osmosis membrane is increased, while the blocking rate by the reverse osmosis membrane is decreased as the pH of the groundwater is higher than 7.0.

100 water treatment apparatus 10 ground water 11 permeate 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 deaeration membrane

Claims (8)

  A method for producing permeated water, which is obtained by directly supplying underground water to a reverse osmosis membrane, and treating the water so that the pH of the concentrate of the reverse osmosis membrane becomes 7.0 or less.   The manufacturing method of the permeated water of Claim 1 which makes pH of the said concentrated water 7.0 or less by adding an acid component to underground water.   The manufacturing method of the permeated water of Claim 1 or 2 which further has a decarboxylation treatment process.   The method for producing permeated water according to claim 3, wherein the decarboxylation treatment step is decarboxylation by aeration and / or by degassing membrane.   A water treatment apparatus for treating ground water directly with a reverse osmosis membrane, comprising an acid addition means for adding an acid component to ground water, a reverse osmosis membrane, and a drainage means capable of draining at least a part of the ground water. , Water treatment equipment.   The water treatment apparatus according to claim 5, wherein in the water treatment apparatus, at least a part of a pipe for transferring ground water is a vinyl chloride pipe. A method of operating a water treatment apparatus according to claim 5 or 6, wherein
A method of operating a water treatment apparatus, which operates so as to drain water staying in a pipe for transferring ground water to a reverse osmosis membrane when the water treatment apparatus is temporarily stopped and then reactivated.   Supply to the reverse osmosis membrane water to be treated with FI value of 3 or more, iron ion concentration of 0.01 ppm or more, manganese ion concentration of 0.01 ppm or more, ammoniacal nitrogen concentration of 0.5 ppm or more and organic matter concentration of 10 ppm or more And a method of producing permeated water, wherein water treatment is performed so that the pH of the concentrated water of the reverse osmosis membrane is 7.0 or less.

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