JP2000042373A - Sterilization method in reverse osmosis membrane separation process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly generate a halogenated organic material in water to be treated and to make the ability of trihalomethane generation in permeated water of a reverse osmosis membrane small by adding free chlorine just before the reverse osmosis membrane in a membrane separation process using the reverse osmosis membrane by using free chlorine as a sterilizing agent for the water to be treated. SOLUTION: Relating to a desalination equipment as an experimental plant of reverse osmosis, suspension particles are removed by adding a flocculant into the water to be treated sucked up by an intake pump 1 by a fixed delivery pump 2 and passing the water through a sand filtration bed 3. After that, the water to be treated reserved in a treating water tank 4 is send by a sending pump 5 and is adjusted in pH by adding sulfuric acid using a fixed delivery pump 6. And the water is passed through a cartridge filter 7, sterilized by adding chlorine by a fixed delivery pump 6, increased in the pressure by a pressure pump 9 and fed to the reverse osmosis membrane module 10. At this time, the ejecting point of free chlorine is suitably just before the high pressure pump 9 or just before the cartridge filter 7 and the contact time is preferably <180 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for separating water to be treated to which free chlorine has been added as a disinfectant using a reverse osmosis membrane module. The present invention relates to a sterilization method for reducing by-products.

[0002]

2. Description of the Related Art Reverse osmosis is used in a wide range of fields such as desalination of seawater and brackish water, production of pure water and ultrapure water for the semiconductor and pharmaceutical industries, and municipal wastewater treatment. The reverse osmosis method is advantageous in terms of energy saving as compared with the evaporation method and the electrodialysis method, and has achieved great results so far.

In order to operate such a reverse osmosis membrane module stably for a long period of time, sterilization of water to be treated is indispensable. If sterilization is insufficient, the membrane may be eroded by microorganisms,
There are problems that the amount of production water decreases due to microorganisms and organic substances attached to the membrane surface, and the pressure loss of the reverse osmosis membrane module increases.

As a disinfectant, so-called free chlorine such as chlorine gas, sodium hypochlorite, calcium hypochlorite, and electrolytic chlorine is generally used.

[0005]

However, when these fungicides are used, there is a problem in that halogenated organic substances such as trihalomethane are formed. The halogenated organic substances generated in the sterilization process of the water to be treated cannot be completely removed by the reverse osmosis membrane module, and are not preferable because they are contained in the permeated water.
Also, if concentrated water containing a large amount of halogenated organic substances is discharged as it is, it is expected that it will have a bad influence on the environment.

The present inventors have conducted intensive studies on a sterilization process in which halogenated organic substances are less likely to be generated in the water to be treated in the reverse osmosis membrane separation process. As a result, the above object was achieved by adding free chlorine immediately before the reverse osmosis membrane. We have found what we can achieve and arrived at the present invention.

[0007]

The present invention is characterized in that in a membrane separation process using a reverse osmosis membrane using free chlorine as a disinfectant for water to be treated, free chlorine is added immediately before the reverse osmosis membrane. This is a sterilization method in the reverse osmosis membrane separation process.

Usually, in the reverse osmosis seawater desalination process, a bactericide is added to the intake section of the water to be treated. The amount of free chlorine varies greatly depending on the properties of the water to be treated,
Usually about 0.5 to 1.5 mg / l is required. It is preferable to adjust the addition amount so that the concentration in the feed water of the reverse osmosis membrane module becomes 0.1 to 1.0 mg / l.

In the present invention, the amount of free chlorine added is preferably adjusted so that the concentration in the feed water of the reverse osmosis membrane module becomes 0.1 to 1.0 mg / l. If lower than 0.1mg / l,
The membrane is contaminated by microorganisms, which is not preferable. In addition, 1.0mg /
Above l, oxidation degradation of the film may occur.

As a method of injecting a disinfectant, a continuous injecting method in which the disinfectant is continuously infused so as to have a constant concentration, and an intermittent injecting method in which a disinfectant is injected only for a certain period of time described in Japanese Patent Application Laid-Open No. H7-171565, for example Any of the above can be implemented.

The injection point is suitable immediately before the high-pressure pump or immediately before the cartridge filter, and the contact time is preferably less than 180 seconds.

The water to be treated is separated into concentrated water and permeated water by a reverse osmosis membrane, but free chlorine is not removed by the membrane but is contained in the permeated water. However, trihalomethane is not generated because the precursor of the trihalomethane is removed in the reverse osmosis membrane module and hardly contained in the permeated water.

[0013] Free chlorine is a strong oxidizing agent. Therefore, when supplying the water to be treated sterilized with free chlorine to the reverse osmosis membrane module, it is necessary to use a reverse osmosis membrane having oxidation resistance. From such a viewpoint, the reverse osmosis membrane module used in the present invention includes an oxidizing agent-resistant, chlorine-resistant cellulose triacetate membrane, and a substantial one as disclosed in JP-A-62-244404. A polyamide film having excellent chlorine resistance is preferred.

The form of the reverse osmosis membrane module is not particularly limited, and the present invention can be applied to any type of reverse osmosis membrane module such as a hollow fiber type, a spiral type, and a tubular type.

[0015]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

As an experimental plant for the reverse osmosis method, a desalination apparatus as shown in FIG. 1 was used. Description will be made below using the numbers in the figure. A coagulant is added to the water to be treated pumped up by the water intake pump (1) by the metering pump (2), and the water is passed through the sand filtration tank (3). Here, suspended particles are removed. Thereafter, the water to be treated once stored in the treated water tank (4) is fed by a pump (5), and sulfuric acid is added using a metering pump (6) to adjust the pH.

Then, after passing through a cartridge filter (7), chlorine (sodium hypochlorite) is added and sterilized by a metering pump (8), the pressure is increased by a high-pressure pump (9), and the reverse osmosis membrane module ( 10).

The analysis of free chlorine was carried out by the DPD method described in the method for testing clean water (Japan Water Works Association, 1993).

The analysis of trihalomethane and trihalomethane-producing ability was carried out by a headspace-gas chromatograph-mass spectrometry method described in a method for testing water supply (Japan Water Works Association, 1993 edition).

The measurement of the number of general bacteria was performed according to the method described in ASTM.

Embodiment 1 A case where seawater is used as the water to be treated is shown. As a reverse osmosis membrane module, Toyobo Horosep HR8355
Using one FI (cellulose triacetate membrane), pressure 55k
The operation was performed under the conditions of g / cm ² and a recovery rate of 30%. The reverse osmosis membrane module has a performance of salt removal of 99.4% and water permeability of 1
It was 1.5 m ³ / day (converted to 25 ° C.). The chlorine addition concentration was 0.2 mg / l, and stable operation was performed for 7 days. The chlorine concentration of the feed water of the reverse osmosis membrane module is 0.13 mg / l, pH 6.5
The water temperature was 13.0 ° C. When the concentration of trihalomethane in the feed water and permeate of the reverse osmosis membrane module was analyzed, it was 1 μg.
/ L or less. Trihalomethane generating ability of permeate is 4
μg / l. Table 1 shows measured values of chlorine and the number of common bacteria in the chlorine addition point, feed water, permeated water and concentrated water. Table 2 shows the analysis values of trihalomethane and trihalomethane generation ability at each point.

[0022]

[Table 1]

[0023]

[Table 2]

Comparative Example 1 The same apparatus as in Example 1 was used, and the concentration of addition was changed.
The chlorine addition concentration was 0.05 mg / l, and stable operation was performed for 7 days. The chlorine concentration of the feed water of the reverse osmosis membrane module is 0.01 g /
l, pH 6.5, water temperature 14.2 ° C. The analysis of the feed water and permeate trihalomethane concentration of the reverse osmosis membrane module was 1 μg / l or less. The trihalomethane generating ability of the permeated water was 6 μg / l. Table 3 shows the measured values of chlorine and the number of common bacteria in the chlorine addition point, feed water, permeate water and concentrated water. Table 4 shows the analysis values of trihalomethane and trihalomethane generation ability at each point.

[0025]

[Table 3]

[0026]

[Table 4]

Comparative Example 2 In Example 1, the chlorine addition point was changed to the conventional seawater intake section, the addition concentration was 0.7 mg / l, and stable operation was performed for 7 days. Chlorine concentration of supply water of reverse osmosis membrane module is 0.13mg
/ l, pH 6.5, water temperature 12.9 ° C. Analysis of the feed water and permeate trihalomethane concentrations of the reverse osmosis membrane module was 27,24 μg / l, respectively. The trihalomethane generating ability of the permeated water was 53 μg / l. Chlorine addition point,
Table 5 shows the measured values of chlorine and the number of general bacteria in feed water, permeate water, and concentrated water. Table 6 shows the analysis values of trihalomethane and trihalomethane generation ability at each point.

[0028]

[Table 5]

[0029]

[Table 6]

Example 2 A case where brackish water is used as the water to be treated is shown. As a reverse osmosis membrane module, Toyobo Horosep HA835
Use one 5FI (cellulose triacetate membrane) at a pressure of 30
The operation was performed under the conditions of kg / cm ² and a recovery rate of 75%. The reverse osmosis membrane module has a salt removal rate of 92.0% and a water permeability of 6
It was 0 m ³ / day (converted to 25 ° C.). 0.2 chlorine concentration
The concentration was set to 5 mg / l, and stable operation was performed for 7 days. The chlorine concentration of the water supplied to the reverse osmosis membrane module was 0.10 mg / l, the pH was 6.6, and the water temperature was 18.0 ° C. The analysis of the feed water and permeate trihalomethane concentration of the reverse osmosis membrane module was 1 μg / l or less. The trihalomethane generating ability of the permeated water is 4 μg /
l. Table 7 shows the measured values of chlorine and the number of common bacteria in the chlorine addition point, the feed water, the permeated water, and the concentrated water.
Table 8 shows the analysis values of trihalomethane and trihalomethane generation ability at each point.

[0031]

[Table 7]

[0032]

[Table 8]

[0033]

According to the method of the present invention, the amount of halogenated organic substances such as trihalomethane in the sterilization process of the water to be treated is very small, and the ability of the reverse osmosis membrane to produce trihalomethane in the permeated water can be reduced as compared with the conventional method. It is possible.

[Brief description of the drawings]

FIG. 1 is an external view of a reverse osmosis method desalination apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intake pump 2 Metering pump for adding coagulant 3 Sand filtration tank 4 Treated water tank 5 Water pump 6 Metering pump for adding sulfuric acid 7 Cartridge filter 8 Metering pump for adding chlorine 9 High pressure pump 10 Reverse osmosis membrane module 11 Permeate outlet 12 Concentration Water outlet

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/50 531 C02F 1/50 531M 540 540A 540B 550 550C 560 560E F term (Reference) 4D006 GA03 HA01 HA21 HA61 HA61 KA03 KA33 KA64 KB14 KB15 KB30 KD06 KD08 KD11 KD23 KE30R MC18X MC54 PB02 PB03 PB05 PB08 PB24 PC02 PC42 PC51

Claims (4)

[Claims] In a membrane separation process using a reverse osmosis membrane using free chlorine as a germicide for water to be treated, the water to be treated is contacted with free chlorine immediately before the reverse osmosis membrane. Sterilization method in the separation process. 2. The residual chlorine concentration of the water to be treated is 0.1
The sterilization method in the membrane separation process according to claim 1, wherein the sterilizing agent is brought into contact with the water to be treated continuously or intermittently in the range of 1.0 to 1.0 mg / l. 3. The method according to claim 1, wherein the reverse osmosis membrane is made of cellulose triacetate. 4. The method for sterilizing in a membrane separation process according to claim 1, wherein the reverse osmosis membrane is made of a polyamide having chlorine resistance.