JPH06226253A - Treatment of feed water by memberane module - Google Patents

Abstract

PURPOSE:To prevent the sticking of a microorganisms slime to a membrane and to stably maintain the permeation performance of the membrane by decreasing the hardness component of a feed water to less than a specified level and treating the feed water with a synthetic high polymer system composite membrane module under the presence of a dissolved oxidizing agent. CONSTITUTION:In the case of treating the feed water containing abundantly the hardness component, a liq. feed pump 5 is driven to pass the feed water in a feed water tank through a water softener 3, and the hardness component such as calcium or magnecium is decreased down to <=10ppm, and once, the feed water is stored in an intermediate tank 4. Then, the storage liq. in the intermediate tank 4 is fed to the synthetic high polymer system composite membrane module 2 consisting of the laminated body of the active skin layer having selective separating function and a porous supporting membrane by a liq. feed pump 6 while injecting the oxidizing agent such as sodium hypochlorite or hydrogen peroxide soln. from an oxidizing agent injector 7, and the feed water is filtrated by a cross-flow system, and a permeated water is taken out by a take out pipe 23 while returning the part of an nonpermeated feed water to the intermediate tank 4 by a return pipe 81.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating raw water containing a large amount of hardness components with a synthetic polymer composite membrane module in the presence of an oxidizing agent as a bactericide or disinfectant. It is about.

[0002]

2. Description of the Related Art In a synthetic polymer composite membrane module, a composite membrane in which an active skin layer as a selective separation functional membrane is provided on a porous support membrane is used. When treating raw water with a membrane module, in order to prevent microorganisms such as bacteria and algae, the raw water may be treated after adding an oxidizing agent such as sodium hypochlorite to the raw water.

Conventionally, depending on the type of membrane, the residual chlorine residual amount has an upper limit, and in order to keep the chlorine concentration at the inlet of the membrane module using such a membrane within the specified value, sodium hypochlorite is used. Method of intermittent injection, method of continuously injecting sodium hypochlorite and neutralizing by injecting a reducing agent immediately before the membrane module, method of continuously injecting sodium hypochlorite of the membrane module Immediately before, a method of adsorbing and removing sodium hypochlorite with activated carbon or the like has been proposed.

[0004]

However, in the first method, the amount of the oxidizing agent is insufficient, and it is difficult to expect reliable disinfection / sterilization. In the second and third methods, the inside of the membrane module contains the oxidizing agent. Therefore, the generation of microorganisms in the membrane module is unavoidable.

In order to eliminate such irrationality, the applicant of the present invention has conducted extensive studies and experimentally confirmed that the deterioration of the composite film due to the above-mentioned oxidizing agent is accelerated by the catalytic action of heavy metals such as iron and manganese. The raw water is supplied to the synthetic polymer composite membrane module through a pretreatment membrane module such as an ultrafiltration membrane module or a microfiltration membrane module, and this pretreatment membrane module is supplied. It was previously proposed to add an oxidant between the resin and the synthetic polymer composite membrane module (Japanese Patent Application No. 2-36629).

According to this raw water treatment method, heavy metals such as iron can be removed by the membrane module for pretreatment, and even if the composite membrane comes into contact with the oxidizer at the limit necessary for sterilization, the composite metal is produced by the catalytic action of the heavy metals. Since deterioration promotion of the membrane can be suppressed, the deterioration of the performance of the composite membrane due to the oxidizing agent can be suppressed to a small degree, and the residual chlorine allowable amount for the synthetic polymer composite membrane module can be made larger than that of the conventional one. The growth of microorganisms in the membrane can be well prevented, and the adhesion of algae or the like to the surface of the composite membrane can be eliminated. Therefore, the permeation performance of the composite membrane module can be maintained sufficiently stable.

[0007]

However, as a result of further studies and experiments conducted by the present inventors, the content of a certain value or more depending on the hardness components such as calcium and magnesium contained in the raw water. Under the circumstances, it was found that the performance deterioration of the composite film was promoted by the oxidizing agent.

It has been well known that hardness components such as calcium produce a precipitating substance such as calcium carbonate or calcium sulfate to deteriorate the performance of the composite membrane.

However, the promotion of the deterioration of the performance of the composite film by the oxidizing agent in the presence of the hardness component such as calcium is caused by the coordination of the hardness component with the amide bond of the synthetic polymer forming the active skin layer. It is presumed that the hydrogen bond related to the amide bond is cleaved, so that the decomposition of the amide bond due to the generally known oxidation proceeds at an accelerated rate. Even under a certain several tens of ppm (FIG. 4 shows the relationship between pH and calcium hardness where scale generation is a problem, and under neutral conditions, a calcium hardness of 700 ppm is the boundary value for problem occurrence. ), Accelerated deterioration (accelerated deterioration) of the composite film due to the hardness component is observed, and in order to effectively prevent the accelerated deterioration of performance, the experimental results show that
The hardness component must be 10 ppm or less.

Therefore, the hardness component content of raw water, especially groundwater, is much larger than that of the above-mentioned heavy metals such as iron and manganese, and the ultra-membrane module for removing the above-mentioned heavy metals in the raw water. It is extremely difficult to suppress the hardness component such as calcium to 10 ppm or less by the pretreatment with a vacuum filter or a microfiltration module.

The object of the present invention is to treat raw water with a membrane module in the presence of an oxidizing agent such as sodium hypochlorite so that the membrane is contacted with the oxidizing agent in the presence of a hardness component. However, based on the findings from the experimental results that the deterioration of the composite film can be sufficiently reduced by limiting the content of the hardness component to 10 ppm or less, the raw water can be treated while suppressing the film deterioration due to the oxidant to a small extent. It is to propose a method for treating raw water by a polymer composite membrane module.

[0012]

The method of treating raw water by the membrane module of the present invention reduces the hardness component of the raw water to 10 ppm or less, preferably 5 ppm or less, and the raw water is prepared in the presence of an oxidizing agent in a high synthetic amount. It is characterized in that it is treated with a molecular composite membrane module, and the hardness component can be reduced by using a water softener, a cellulose acetate membrane module or 1500 pp.
Use a synthetic polymer membrane module having a permeated water amount of 0.10 m ³ / m ² · d · (kgf / cm ² ) or more at a pressure of 15 kgf / cm ² for an aqueous solution of mNaCl, and a combination thereof. You can

If the concentration of the oxidant in the stock solution chamber of the synthetic polymer composite membrane module is too high, the oxidative deterioration of the synthetic polymer compound becomes severe, while if it is too low, the growth of microorganisms is prevented. For example, when using sodium hypochlorite, the chlorine concentration in the stock solution chamber of the synthetic polymer composite membrane module is usually adjusted to 0.1 ppm to 1.0 ppm.

[0014]

[Function] Although the composite film of the synthetic polymer composite module is contacted with the oxidizing agent in the presence of the hardness component, the hardness component is 10 ppm.
Since it is suppressed below, the deterioration of the permeation performance of the composite membrane can be suppressed to a slight extent. In addition, raw water is treated with the same module in a dissolved amount of an oxidizing agent, which is the limit necessary for sterilization, and the propagation of microorganisms on the composite membrane surface is sufficiently prevented.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a raw water treatment apparatus used in the present invention. In FIG. 1, reference numeral 1 is a raw water tank, and the raw water contains hardness components such as calcium and magnesium. Reference numeral 2 denotes a synthetic polymer composite membrane module, and the composite membrane is composed of a laminate of an active skin layer having a selective separation function and a porous support membrane made of a material different from the active skin layer.

The material for the active skin layer comprises a monomeric aliphatic or aromatic polyamine reactant having an amine functional group and a monomeric aliphatic or aromatic amine reaction comprising a polyfunctional acyl halide. It is preferable to use a crosslinked polyamide-based polymer obtained by interfacial polycondensation with a body, but in addition to this, carboxylic acid, sulfonic acid,
A polymer containing a polymer having a group such as phosphoric acid or sulfuric acid as a main component can be used. The module type may be any of spiral type, hollow fiber membrane type, tuber type, and plate type. Reference numeral 21 is a raw water side of the synthetic polymer composite membrane module, 22 is a permeate side, 23 is a permeate take-out pipe, and 24 is a pressure regulating valve.

Reference numeral 3 is a water softener that reduces the hardness component from the raw water to 10 ppm or less, preferably 5 ppm or less, and is installed upstream of the synthetic polymer composite membrane module 2. 4 is an intermediate tank. 5 and 6 are liquid feed pumps. 7
Is an injector for an oxidizing agent such as sodium hypochlorite and hydrogen peroxide, and can be installed at an appropriate position between the water softener 3 and the synthetic polymer composite membrane module 2. For this oxidizer injector 7, for example, a metering pump can be used. Reference numeral 81 is a return pipe for returning a part of the non-permeated raw water to the intermediate tank 4, 82 is a non-permeated raw water discharge pipe, and 9 is an oxidant detection sensor.

In order to treat the raw water using the apparatus shown in FIG. 1 according to the present invention, the liquid feed pump 5 is driven to pass the raw water in the raw water tank 1 through the water softener 3 to obtain calcium, magnesium, etc. in the raw water. Hardness component of 10ppm or less, preferably,
It is reduced to 5 ppm or less and is temporarily stored in the intermediate tank 4, and the liquid stored in the intermediate tank 4 is pumped while injecting an oxidizing agent such as sodium hypochlorite from the oxidizing agent injector 7 6
Is supplied to the synthetic polymer composite membrane module 2 by means of the cross flow method, and a part of the non-permeated raw water is returned to the intermediate tank 4 by the return pipe 81, while the permeated water is taken out from the permeated water. Take out from 23.

During the treatment of this raw water, the oxidant detection sensor-9
The oxidizer injector 7 is controlled to maintain the oxidizer concentration on the raw water side 21 of the synthetic polymer composite membrane module 2 at an appropriate concentration required for sterilization. For example, sodium hypochlorite
In the case of using the da, the chlorine concentration on the raw water side 21 of the synthetic polymer composite membrane module 2 is adjusted within the range of 0.1 ppm to 1.0 ppm.

Instead of the water softener 3, as shown in FIG.
The membrane module 30 may be used in a cross flow system so that a part of the non-permeated water is returned to the raw water tank 1. Figure 2
In the figure, reference numerals 31, 32 and 33 denote the raw water side, the permeate side and the pressure regulating valve of the membrane module 30, respectively.

When the apparatus shown in FIG. 2 is used, the operating pressure of the pump 5 needs to be higher than that of the apparatus shown in FIG. 1 in order to apply a predetermined transmembrane pressure difference to the membrane module 30. However, it does not require the regeneration treatment required in a water softener, is easy to maintain and handle, and can also remove heavy metals such as iron and manganese that act as catalysts for deterioration reactions by oxidants, thus removing heavy metals. There are advantages such as being advantageous for raw water containing a large amount.

When a cellulose acetate-based membrane module is used as the membrane module 30, the membrane is excellent in oxidation resistance as shown by the dotted line in FIG. Three
Oxidizer can be injected upstream of (7 'is oxidizer injector),
Sterilization of the entire system is possible.

When a synthetic polymer membrane module is used for the membrane module 30, the permeated water content is 0.10 m ³ / m ² · d. (kgf / c
It is desirable to use m ²⁾ or more.

When the membrane module 30 is used to reduce the hardness component, the membrane module 30 and the synthetic polymer composite membrane module 2 can be directly connected as shown in FIG. Also in this case, when a cellulose acetate-based membrane module is used for the membrane module 30, as shown by the dotted line in FIG. 3 (7 'is an oxidizer injector), the upstream side of the module It is possible to inject the oxidizer with.

2 and 3, the same reference numerals as those in FIG. 1 indicate the same components as those in FIG.

When the raw water is treated according to the present invention, the amount of the oxidizing agent required for sterilization can be brought into contact with the membrane to sufficiently disinfect and sterilize the membrane. It is possible to well prevent the occurrence of the above, and it is possible to sufficiently prevent the variation of the permeation characteristics due to the adhesion of microbial slime on the membrane surface.

Further, even though the membrane of the synthetic polymer composite membrane module comes into contact with the oxidizer, the contact is performed with a very small amount such as 10 ppm or less of the hardness component of calcium, magnesium, etc. Accelerated deterioration, which cannot be avoided under the coexistence with the hardness component, can be well avoided, and the deterioration of the permeation performance of the synthetic polymer composite membrane can be suppressed to a slight extent.

Therefore, it is possible to well prevent the deterioration of the permeated water quality and the increase of the low water quality permeated water amount. This is also clear from the comparison between the following examples and comparative examples.

Example 1 In FIG. 1, the raw water had an electric conductivity of 230 μS / cm, PH6.
5, well water having FI (fouling index) 4 and hardness of 50 ppm was used. The synthetic polymer composite membrane module 2 has an aroma of 0.15 wt% salt rejection of 99.5% and permeated water of 7.0 m ³ / day at an operating pressure of 15 kgf / cm ² and a temperature of 25 ° C. Nitto Denko Co., Ltd.'s spiral module using a group polyamide polyamide composite membrane is used for the water softener 3, Organ-2's SAT-2.
56A is used, and the pressure regulating valve 24 is adjusted so that the synthetic polymer composite membrane module 2 has a transmembrane pressure difference of 10 kgf / cm ² ,
It was operated at a total recovery rate of 50%. Sodium hypochlorite was used as the oxidant, and the injection amount of sodium hypochlorite was controlled so that the concentration of free chlorine detected by the detection sensor 9 was maintained at 0.3 ppm.

After operating for 1 year under these conditions, the average conductivity of the permeated water remained at the initial value (9.8 μS / cm),
It was 10.5 μS / cm, and the amount of permeated water was only 5% of the initial value. The average hardness of the synthetic polymer composite membrane module 2 on the raw water side was about 0.7 ppm.

Example 2 In FIG. 2, an operating pressure of 30 kgf / cm was applied to the membrane module 30.
^{2. Using} a acetate cellulose spiral module manufactured by Nitto Denko Corporation having a rejection rate of 0.2 wt% magnesium sulfate at a temperature of 25 ° C. of 99.5%, and adjusting the pressure regulating valve 33. The same procedure as in Example 1 was carried out except that the membrane module 30 was operated at a transmembrane pressure difference of 15 kgf / cm ² and a total recovery rate of 50%.

After operating for 1 year under these conditions, the average conductivity of the permeated water remained at the initial value (5.1 μS / cm),
It was 5.5 μS / cm, and the amount of permeated water was only 5% of the initial value. The average hardness of the synthetic polymer composite membrane module 2 on the raw water side was about 0.8 ppm.

Example 3 In FIG. 2, the membrane module 30 has an operating pressure of 20 kgf / cm.
² , 0.2 wt% magnesium sulphate rejection at a temperature of 25 ℃ is 99.0%, and the amount of permeated water is 0.13 m ³ / m ² · d · (kgf
/ cm ² ), a synthetic polymer spiral module manufactured by Nitto Denko Co., Ltd. is used, the pressure regulating valve 33 is adjusted, and the membrane module 30 is subjected to a transmembrane pressure difference of 10 kgf / cm ² and a total recovery. The same as Example 1 except that the operation was performed at a rate of 50%.

After operating for 1 year under these conditions, the average conductivity of the permeated water remained at the initial value (7.4 μS / cm),
It was 8.3 μS / cm, and the amount of permeated water was only 5% of the initial value. The average hardness of the synthetic polymer composite membrane module 2 on the raw water side was about 1.2 ppm.

Comparative Example In contrast to Example 1, the use of a water softener was omitted, and the raw water was treated under the same conditions as in Example 1 except that the conductivity increased to about 3 times the initial value after 6 months of operation. However, the amount of permeated water increased twice.

[0036]

The method for treating raw water with the membrane module of the present invention has the constitution as described above, and when treating raw water with the synthetic polymer composite membrane module, the membrane module
Since the raw water side of the rubber can be sterilized, it is possible to prevent microbial slime from adhering to the film, and to prevent accelerated deterioration of the polymer film due to the coexistence of hardness components under this amount of oxidizer, the amount of hardness component is adjusted. Since the amount is reduced, the deterioration can be suppressed to a slight extent, and thus the permeation performance of the membrane can be stably maintained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a raw water treatment device used in the present invention.

FIG. 2 is an explanatory diagram showing another example of the raw water treatment apparatus used in the present invention.

FIG. 3 is an explanatory view showing another example of the raw water treatment apparatus used in the present invention.

FIG. 4 is a chart showing the relationship between calcium hardness and pH with respect to scale generation in raw water.

[Explanation of symbols]

 1 Raw Water Tank 2 Synthetic Polymer Composite Membrane Module 3 Water Softener 30 Membrane Module 4 Intermediate Tank 5 Liquid Delivery Pump 6 Liquid Delivery Pump 7 Oxidant Injector 9 Oxidant Detection Sensor-

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoshiyasu Kamiyama 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (4)

[Claims] 1. The hardness component of raw water is reduced to 10 ppm or less,
The raw water is mixed with an oxidant in a synthetic polymer composite membrane module.
A method for treating raw water with a membrane module, which comprises treating the raw water with a membrane module. 2. The method for treating raw water with a membrane module according to claim 1, wherein a water softener is used to reduce the hardness component. 3. The method for treating raw water with a membrane module according to claim 1, wherein a cellulose acetate-based membrane module is used to reduce the hardness component. 4. 1500 ppm NaCl for reducing the hardness component
The amount of permeated water at a pressure of 15 kgf / cm ² against an aqueous solution is 0.1
The method for treating raw water with a membrane module according to claim 1, wherein a synthetic polymer membrane module having a density of 0 m ³ / m ² · d · (kgf / cm ² ) or more is used.