JP2021084075A - Adsorption treatment device for scale causing substances and reverse osmosis membrane device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reverse osmosis membrane device which does not need to be operated in a highly alkaline environment in order to obtain highly concentrated water and realizes a high operating rate and cost reduction.
SOLUTION: The reverse osmosis membrane device of the embodiment includes a reverse osmosis membrane module having a reverse osmosis membrane and an adsorption treatment device provided in front of the reverse osmosis membrane module and supplying water to be treated to the reverse osmosis membrane module. Have. The adsorption treatment apparatus has a column and an adsorbent in the form of fibers on which tannins are fixed, which is provided in the column.
[Selection diagram] Fig. 1

Description

Embodiments of the present invention relate to an adsorption treatment device for scale-causing substances and a reverse osmosis membrane device.

In recent years, laws and regulations have been strengthened to realize a healthy water cycle. ZLD (Zero Liquid Discharge) recycles and uses water in the factory from the viewpoint of reducing the risk of water pollution, regenerating and reusing wastewater, and further reduces the amount of wastewater discharged from the factory to zero. It is a concept to protect the water environment by doing so.

In order to reduce the wastewater to zero, it is finally necessary to separate it into solids and deionized water by the evaporation method. The evaporation method is a method in which wastewater is heated to generate water vapor, and the water vapor is cooled to obtain deionized water to separate it into solid content and deionized water. This method has the advantage that deionized water with extremely high purity can be obtained because the two-stage flash evaporation method, the multi-stage flash evaporation method, etc. have been put into practical use, but energy is required because a heat source is required. It has the disadvantage of being inefficient. Therefore, from the viewpoint of reducing energy consumption, it is required to reduce the amount of wastewater treated by the evaporation method as much as possible by increasing the concentration of wastewater as much as possible.

For these reasons, a reverse osmosis (RO) membrane (hereinafter referred to as "RO membrane") is used as a separation membrane for separating solid-containing concentrated wastewater and fresh water before the evaporation method. Has been done. In the desalination / concentration system to which the RO membrane is applied, the water to be treated is pressurized and introduced into the RO membrane, and the deionized water, which is the water that has permeated the RO membrane, and the concentrated wastewater that does not permeate the RO membrane. It consists of the basic process of getting and.

The RO membrane has a removing effect on almost all of ionic substances, fine particles, organic substances, some dissolved gases, etc., and unless clogging or trouble occurs, it is not necessary to carry out discontinuous steps such as regeneration. It is widely used because it has advantages such as goodness.

However, RO membranes can become clogged due to silica, hardness scales and biofouling. When the RO film is clogged, it is necessary to stop the entire water treatment system in order to clean the RO film, so that the operating rate of the water treatment system decreases. In addition, wastewater that has not been concentrated to the expected concentration will be evaporated, which will increase the thermal energy required for evaporation, which will lead to an increase in the overall treatment cost.

As a method of increasing the concentration rate of wastewater using an RO membrane, the hardness component in the water to be treated is removed with a water softener such as an ion exchange resin, and after decarboxylation treatment with a decarboxylation tower, the pH of the water to be treated is set to high pH. A method for separating RO membranes is known. In this method, the hardness scale, which is one of the causes of clogging of the RO membrane, is removed by a water softener, and the carbonate ion component is removed by a decarbonation column, thereby suppressing the hardness scale. Further, by setting the pH (pH ≧ 10) at which at least most of the silica is present in the form of ions in the water to be treated from which the hardness component and the carbonate ion component have been removed, and operating the RO membrane separation device, RO by silica is used. It suppresses clogging of the membrane. It also has the effect of suppressing biofouling by raising the pH of the water to be treated.

However, when the RO membrane operation is performed with the water to be treated at a high pH, the higher the pH, the higher the membrane deterioration rate, and the membrane separation performance deteriorates over time. On the other hand, when the pH is lowered, silica having low solubility is likely to be precipitated, clogging of the RO film due to the silica scale occurs, and the system operating rate is reduced.

As a method for removing silica, a method for precipitating and removing silica by adding a magnesium salt and an iron salt in a specified concentration range to silica-containing water is described. However, this method requires the addition of a new magnesium salt, which increases the chemical cost.

In summary, the water treatment system can reduce costs by reducing the thermal energy required for evaporation of wastewater. For this purpose, it is essential to increase the concentration of wastewater, and RO membrane separation is usually performed. In RO membrane separation, the precipitation of silica causes clogging of the separation membrane, which causes a problem of lowering the operating rate. Although the precipitation of silica is suppressed in a highly alkaline environment, on the contrary, in a highly alkaline environment, the film deterioration rate increases and the membrane separation performance deteriorates, which may be a factor of lowering the operating rate.

In consideration of the above circumstances, a reverse osmosis membrane device that does not need to be operated in a highly alkaline environment and realizes a high operating rate and cost reduction is desired in order to obtain highly concentrated wastewater.

Further, the problem caused by the generation of silica scale is not limited to the reverse osmosis membrane device, but typically occurs in a boiler or the like. Therefore, a treatment device for removing scale-causing substances, particularly silica, from the water to be treated is desired.

Japanese Unexamined Patent Publication No. 2000-254690

The problem to be solved by the present invention is an adsorption treatment device for scale-causing substances, which does not need to be operated in a highly alkaline environment in order to obtain highly concentrated wastewater, and realizes a high operating rate and cost reduction. It is to provide a reverse osmosis membrane apparatus.

The scale-causing substance adsorption treatment apparatus of the embodiment includes a column and an adsorbent in the form of fibers on which tannins are fixed, which are provided in the column.

The reverse osmosis membrane device of another embodiment includes a reverse osmosis membrane module having a reverse osmosis membrane and an adsorption treatment device provided in front of the reverse osmosis membrane module and supplying water to be treated to the reverse osmosis membrane module. Have. The adsorption treatment device has a column and an adsorbent in the form of fibers on which tannins are fixed, which is provided in the column.

FIG. 1 is a block diagram of a reverse osmosis membrane device according to an embodiment. FIG. 2 is a block diagram of a reverse osmosis membrane device according to another embodiment.

In the scale-causing substance adsorption treatment device or reverse osmosis membrane device of the embodiment, an example of a fiber to which tannin is fixed is a fiber treated with tannic acid and tartrate. Examples of fibers include cellulose and include cotton or paper.

Other examples of tannin-fixed fibers in the scale-causing substance adsorption treatment device or reverse osmosis membrane device of the embodiment include tea leaves.

The reverse osmosis membrane device of the embodiment may have a water softener and a decarboxylation tower in addition to the adsorption treatment device in front of the reverse osmosis membrane module. Further, the reverse osmosis membrane module may include a low pressure reverse osmosis membrane module and a high pressure reverse osmosis membrane module, or may include a low pressure reverse osmosis membrane module, a high pressure reverse osmosis membrane module and an ultrahigh pressure reverse osmosis membrane module. Good.

Hereinafter, embodiments will be described in more detail.

Embodiment 1
-Production of adsorbent 1A: Tannin-fixed gauze First treatment: 10.6 g of cotton cloth (gauze) as a fiber was immersed in 500 mL of water. The fiber / water weight ratio is about 1/50. 15 g of tannic acid was dissolved in this water (concentration 3%), and the mixture was heated at 70 ° C. for 2 hours. After this treatment, the cotton cloth was washed with water.

Second treatment: The cotton cloth after the first treatment was immersed in 500 mL of water. 10 g of liquor stone was dissolved in this water (concentration 2%) and heated at 40 ° C. for 20 minutes. After this treatment, the cotton cloth was washed with water.

In this way, an adsorbent in the form of cotton cloth (gauze) to which tannin was fixed was obtained.

1B: Cotton wool with tannins fixed The same treatment as in Embodiment 1 except that cotton wool was used instead of cotton cloth (gauze) was carried out to obtain an adsorbent in the form of cotton wool with tannins fixed.

1C: Filter paper with tannins fixed The same treatment as in Embodiment 1 was carried out except that a filter paper was used instead of cotton cloth (gauze) as fibers to obtain an adsorbent in the form of a filter paper with tannins fixed.

1D: Kakishibu dyed cloth A commercially available Kakishibu dyed cloth was prepared and used as an adsorbent in the form of a cloth to which Kakishibu, which is a kind of tannin, was fixed.

-Adsorption experiment An adsorption experiment was conducted by the following method.
First, a solution used for the adsorption experiment was prepared. A commercially available water glass [sodium silicate solution] (Kanto Chemical Co., Inc.) was prepared to prepare an aqueous solution containing silica. Sodium silicate is represented by the _{composition formula Na 2} SiO _3. The prepared water glass contains 35-38% as _{SiO 2 and 17-19% as Na 2} O, and 52-57% of both sodium silicate in total. The sodium silicate concentration in the aqueous solution used as the water to be treated is set to, for example, about 0.1 g / L. A concentration of about 0.1 g / L corresponds to a silica concentration in groundwater or river water that is expected to be treated. In order to prepare the water to be treated having a sodium silicate concentration of about 0.1 g / L, the concentration of the water glass may be in the range of 0.175 to 0.192 g / L. For example, when the concentration of water glass is 0.188 g / L shown in Table 1 below, the sodium silicate concentration in the aqueous solution is 0.098 to 0.107 g / L. Other aqueous solutions having sodium silicate concentration were also prepared based on the same calculation as above.

Specifically, an adsorption experiment was conducted using the following method.
In the adsorption experiment below, a conductivity meter manufactured by HORIBA, Ltd. or CD-4318SD manufactured by FUSO Corporation was used.

(X) Tannin-fixed gauze or tannin-fixed cotton wool was filled in the funnel, or one or three layers of tannin-fixed filter paper were set on the funnel, and the sodium silicate aqueous solution was filtered. All were performed by one-pass filtration without circulating the sodium silicate aqueous solution. The conductivity of the sodium silicate aqueous solution before and after filtration was measured with a conductivity meter, and the removal rate of sodium silicate was calculated. In the table below, this experimental method is referred to as "filtration".

(Y) Tannin-fixed gauze, tannin-fixed cotton wool or tannin-fixed filter paper was placed in a beaker, and an aqueous solution of sodium silicate was poured and stirred for a predetermined time to adsorb sodium silicate on these adsorbents. The conductivity of the sodium silicate aqueous solution before and after adsorption was measured with a conductivity meter, and the removal rate of sodium silicate was calculated. In the table below, this experimental method is referred to as "stirring in the beaker".

Table 1 below summarizes the details of these experiments. Experiment No. in Table 1 Indicates the combination of the adsorbent and the adsorption method and assigns a number 1 to the first experiment. If two experiments are performed in which these two conditions are the same but the other conditions are different, the second experiment is performed. Is numbered 2.

For comparison, refer to the adsorption of silica by an ion exchange resin. Japanese Patent Application Laid-Open No. 2002-361247 states that "when the amount of silica adsorbed on the strong basic anion exchange resin _{is larger than 2.5 g-SiO 2} / L-SA, the silica adsorbed on the strong basic anion exchange resin by regeneration is sufficient. It cannot be removed, and silica leaks into the treated water when water flow is resumed. ”(Paragraph 0025). It is known that 1 L of the strong basic anion exchange resin weighs 700 to 800 g.

Although the water-soluble polymer can be used for adsorbing scale in the same manner as the ion exchange resin, it cannot be used for removing the scale of the water to be treated because it is water-soluble and easily dissolves in the water to be treated. .. Examples of the water-soluble polymer include polyvinylpyrrolidone, ethylene glycol, and sodium polyvinyl acetate.

In Table 1, for example, Experiment No. In 1CX-2, a sodium silicate aqueous solution of about 1 g / L can be obtained by adding 10 g of a sodium silicate aqueous solution having a concentration of about 0.1 g / L to three layers of tannin-fixed filter paper. .. Therefore, the weight of the filter paper required for adsorbing 2.5 g / L of sodium silicate is about 5.6 g, which is 2.5 times that of 2.25 g, which is equivalent to about 9 sheets of filter paper.

Therefore, as compared with the prior art which requires 1 L of anion exchange resin for adsorbing 2.5 g / L of sodium silicate, this embodiment requires only about 5.6 g of filter paper, and thus has much better performance.

When the fibers were treated with quince, which is the raw material of tannic acid, even if the treated fibers were washed with water, the outflow of the components of the quintuplets was not interrupted, so the adsorption experiment could not be performed. It was.

-Reproducibility experiment Each experiment No. after hydrochloric acid treatment regeneration. 1CX-2 3-layer tannin-fixed filter paper, and Experiment No. after adsorption 3 times or more. Using 1AX-1 tannin-fixed gauze again, a reproduction experiment of filtration was performed under the same conditions as above. Table 2 below summarizes the details of these experiments. Experiment No. in Table 2 Is an R indicating a reproduction experiment.

High reproducibility was obtained in all of the adsorption experiments in Table 2, and it can be seen that the life of the adsorbent is long.

Embodiment 2
-Preparation of adsorbent 2A: black tea husk and 2B: green tea husk were prepared as adsorbents.

Here, the tea leaves will be described. Tea husks are tea leaves after tea has been added, that is, after being soaked in a solvent such as water or hot water. If the tea leaves have been brewed more than once, they are considered as tea leaves.

As the black tea husks and green tea husks used this time, the tea husks used after adding tea twice and further washing with water were used.

Table 3 summarizes the tannin content in black tea and green tea and the tannin content in black tea leachate and green tea leachate.

It is known that polyphenols containing tannins remain in the tea leaves, and since the tea leaves, that is, the leaf components, contain fiber cellulose, the tea leaves are adsorbed in the form of tannins adhering to the fibers. It can be used as an agent.

-Adsorption experiment An adsorption experiment was conducted by the following method.
First, an aqueous solution having a desired sodium silicate concentration was prepared in the same manner as in the first embodiment.

Specifically, an adsorption experiment was conducted using the following method.
(X) A tea bag containing black tea husks or green tea husks was filled in a funnel, and an aqueous sodium silicate solution was filtered. All were performed by one-pass filtration without circulating the sodium silicate aqueous solution. The conductivity of the sodium silicate aqueous solution before and after filtration was measured with a conductivity meter, and the removal rate of sodium silicate was calculated. In the table below, this experimental method is referred to as "filtration".

(Y) A tea bag containing black tea husks or green tea husks was placed in a beaker, and sodium silicate was adsorbed on these adsorbents by pouring an aqueous solution of sodium silicate and stirring for a predetermined time. The conductivity of the sodium silicate aqueous solution before and after adsorption was measured with a conductivity meter, and the removal rate of sodium silicate was calculated. In the table below, this experimental method is referred to as "stirring in the beaker".

Table 4 below summarizes the details of these experiments. Experiment No. in Table 4 Indicates the combination of the adsorbent and the adsorbing method, and numbered 1 in the first experiment.

-Reproducibility experiment No. of experiment after one adsorption. A tea bag containing 2AX-1 black tea leaves was used again, and a reproduction experiment of filtration was performed under the same conditions as above. Table 4 below summarizes the details of this experiment. Experiment No. in Table 4 Is an R indicating a reproduction experiment.

Also in Table 4, a high removal rate is obtained.

In the present embodiment, tea husks are used, but tea leaves that are not tea husks and have never been filled with tea also have the form of fibers to which tannins are fixed, and therefore can also be used. Since tea leaves that have never been filled with tea contain more components such as catechin than tea husks, it is conceivable that they will dissolve in the water to be treated. Therefore, it is preferable to use tea leaves.

As shown in the first and second embodiments, the adsorbent having the form of a fiber to which tannin is fixed can be used as an adsorbent for adsorbing a scale-causing substance. Such an adsorbent for adsorbing scale-causing substances is not limited to application to reverse osmosis membrane devices. For example, it can be used to remove scale adhering to the piping of a geothermal power plant. It is known that the hot water used in geothermal power plants contains a large amount of silica. Therefore, silica adheres to the piping and the turbine as it is. In order to prevent this adhesion, the maintenance work of the geothermal power plant can be simplified by appropriately equipping the device provided with the geothermal power plant with an adsorbent for adsorbing the scale-causing substance. It can also be used in nuclear power plants. By equipping nuclear power plants with scales, or equipment used to remove scales, such as pure water production equipment, condensate desalination equipment, and filtration desalination equipment, an adsorbent for adsorbing scale-causing substances Maintenance work for nuclear power plants can be easily performed.

Embodiment 3
FIG. 1 shows a block diagram of the reverse osmosis membrane device 1 according to the present embodiment.

In FIG. 1, raw water (groundwater, river water, etc.) containing scale-causing substances such as silica, which is the water to be treated, includes a water softener 11, a silica adsorption tower 12 as an adsorption treatment device, a decarbonization tower 13, and a low-pressure pump. Water is supplied to the low pressure reverse osmosis (RO) membrane module 15 via 14.

The water softener 11 has a function of reducing the burden of removing silica in the subsequent stage by removing minerals other than silica. Specifically, in the water softener 11, cations such as calcium ions and magnesium ions contained in the raw water are replaced with sodium ions by an ion exchange resin.

The silica adsorption tower 12 has a column and an adsorbent in the form of fibers on which tannins are fixed, which is provided in the column. The adsorbent may be filled in the column or indicated on a support member having an opening provided in the column. Decarboxylation also contributes to the removal of minerals.

The decarboxylation tower 13 has a function of releasing carbon dioxide in water into the atmosphere by blowing air.

The concentrated water in which the solute is concentrated without being permeated by the low-pressure reverse osmosis (RO) membrane module 15 is supplied to the high-pressure reverse osmosis (RO) membrane module 17 via the high-pressure pump 16. The concentrated water in which the solute is concentrated without being permeated by the high-pressure reverse osmosis (RO) membrane module 17 is supplied to the evaporator 20 and heated to generate water vapor, and the water vapor is cooled to obtain deionized water. Separates into solid content and deionized water.

The reverse osmosis membrane device 1 of the present embodiment has a high-performance silica adsorption tower 12 using an adsorbent in the form of fibers to which tannin is fixed, and does not need to be operated in a highly alkaline environment, so that the operation is high. Achieve rate and cost reduction.

Embodiment 4
FIG. 2 shows a block diagram of the reverse osmosis membrane device 2 according to the present embodiment.

Similar to the reverse osmosis membrane device 1 of FIG. 1, the reverse osmosis membrane device 2 of FIG. 2 includes a water softener 11, an adsorption tower 12, a decarbonization tower 13, a low pressure pump 14, a low pressure reverse osmosis (RO) membrane module 15, and a high pressure. It has a pump 16 and a high pressure reverse osmosis (RO) membrane module 17. The difference from the reverse osmosis membrane device 1 of FIG. 1 is that an ultrahigh pressure pump 18 and an ultrahigh pressure reverse osmosis (RO) membrane module 19 are provided between the high pressure reverse osmosis (RO) membrane module 17 and the evaporator 20. It is that you are. The reverse osmosis membrane device 2 of the present embodiment can also obtain the same effect as the reverse osmosis membrane device 1.

Further, the silica adsorption tower 12 according to the embodiment can be applied to, for example, a cooling water system of a nuclear power plant or a geothermal power plant, and can be effectively used to prevent adhesion of silica scale.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1,2 ... Reverse osmosis membrane device, 11 ... Water softener, 12 ... Silica adsorption tower, 13 ... Decarbonization tower, 14 ... Low pressure pump, 15 ... Low pressure reverse osmosis (RO) membrane module, 16 ... High pressure pump, 17 ... High pressure Reverse osmosis (RO) membrane module, 18 ... ultrahigh pressure pump, 19 ... ultrahigh pressure reverse osmosis (RO) membrane module, 20 ... evaporator.

Claims (11)

Column and
An adsorption treatment device for scale-causing substances provided in the column, which has an adsorbent in the form of fibers to which tannins are fixed. The device for adsorbing a scale-causing substance according to claim 1, wherein the fiber to which the tannin is fixed is a fiber treated with tannic acid and tartrate. The device for adsorbing a scale-causing substance according to claim 1 or 2, wherein the fiber is a cellulose fiber. The device for adsorbing a scale-causing substance according to any one of claims 1 to 3, wherein the fiber is cotton. The device for adsorbing a scale-causing substance according to any one of claims 1 to 3, wherein the fiber is paper. The device for adsorbing a scale-causing substance according to claim 1, wherein the fiber to which the tannin is adhered includes tea leaves. A reverse osmosis membrane module with a reverse osmosis membrane,
The adsorption treatment apparatus according to any one of claims 1 to 6, which is provided in front of the reverse osmosis membrane module and supplies water to be treated to the reverse osmosis membrane module.
A reverse osmosis membrane device having. The reverse osmosis membrane device according to claim 7, further comprising a water softener and a decarboxylation tower in addition to the adsorption treatment device in front of the reverse osmosis membrane module. The reverse osmosis membrane device according to claim 7, wherein the reverse osmosis membrane module includes a low pressure reverse osmosis membrane module and a high pressure reverse osmosis membrane module. The reverse osmosis membrane apparatus according to claim 7, wherein the reverse osmosis membrane module includes a low pressure reverse osmosis membrane module, a high pressure reverse osmosis membrane module, and an ultrahigh pressure reverse osmosis membrane module. An adsorbent for adsorbing scale-causing substances that has the form of fibers with tannins fixed.

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