JPH06328066A - Water treatment - Google Patents

Abstract

PURPOSE:To provide a method for obtaining water which is free from a gasifiable dissolved substance. CONSTITUTION:Water containing a gasifiable dissolved substance is allowed to come into contact with a supplied carrier gas through a water impermeable membrane which permit gas permeation, while a decompressed state is maintained on the opposite side of the membrane. Thus, the gasifiable dissolved substance is selectively allowed to permeate as a gas through the membrane, and water free from the dissolved substance is obtained on the impermeable side of the membrane. At the same time, the gasifiable dissolved substance which is passed through a permeation process is removed and recovered.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water treatment method in which a vaporizable substance is dissolved.

[0002]

2. Description of the Related Art Recently, the pollution of the water environment by a vaporizable dissolved substance has become a problem. In particular, it has been clarified that a vaporizable substance such as a halogen compound is contained in water, and there is a concern that it may have an adverse effect on the human body and the environment, and its removal / recovery is needed.

In the water purification process in the water supply business,
Increasing amounts of humic acid and fulvic acid, which are natural corrosive substances, and organic substances brought by domestic wastewater have become a problem, and the pollution of organic substances such as rivers and lakes, which are the source of water, has come to exceed the environmental standard. As the pollution progresses, the amount of chlorine used for chlorine oxidative sterilization increases, and as a result, the chemical reaction causes
Vaporizable dissolved substances containing halogen compounds, especially trihalomethanes such as chloroform, bromodichloromethane, dibromochloromethane, bromoform, etc., are produced, and some of them have carcinogenicity, so these must be removed and recovered. I have to.

In recent years, many cases of unpleasant odor of tap water have occurred. As the unpleasant odor of tap water, chlorine derived from the chlorination process, cyanobacteria existing in the water source, diosmin by actinomycetes, 2-methylisoborneol, etc. have been confirmed. In order to remove these, usually, oxidative decomposition treatment with chlorine or ozone is required, and as a result, for example, but not limited to, trihalomethanes such as chloroform and volatile offensive odor components such as aldehydes such as acetaldehyde. A vaporizable dissolved substance containing is generated. Tap water, which has an unpleasant odor of vaporization, can be toxic and should be removed as it makes the drinker anxious. Meanwhile, in various industries, trichlorethylene,
Dissolvable substances that can be vaporized, such as tetrachloroethylene, are widely used as cleaning agents for metal machinery, cleaning solvents, hair treatment agents, and cleaning agents in the semiconductor manufacturing process.As a result, they are dissolved in wastewater. Pollution by vaporizable substances is becoming more serious. Nowadays, as environmental standards are being strengthened, removal and recovery of these substances are urgently needed.

However, with the recent increasing interest in the water environment, even though advanced treatment for removing the above substances is required, effective treatment has not been achieved due to operational management and environmental problems. Is the current situation.

[0006]

Although a method for removing vaporizable dissolved substances such as trihalomethane and vaporizable unpleasant odor components by an activated carbon adsorption method or an aeration method has been studied so far, the activated carbon adsorption method is Since the non-vaporizable substance is selectively adsorbed on the activated carbon together with the dissolved substance that can be vaporized,
Activated carbon needs to be frequently regenerated, which requires time and effort for operation management.Since the aeration method requires a large gas-liquid contact ratio, the equipment volume becomes large, and dissolved substances that are removed by aeration are released into the atmosphere. However, there was a problem that it was not a satisfactory processing method.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies conducted by the present inventor to solve the above-mentioned problems in the removal and recovery of vaporizable dissolved substances contained in water, a water-impermeable membrane that allows gas to permeate therethrough. Through one of them, contacting one of them with water containing a vaporizable dissolved substance while supplying a carrier gas, and maintaining the other under reduced pressure to selectively vaporize the vaporizable dissolved substance as a gas. By permeating the membrane through, it is possible to efficiently remove the above substances,
Further, the inventors of the present invention have found that the vaporized dissolved substance thus removed can be disposed of without being released to the outside by recovering the dissolved substance by various methods. In particular,
It has been found that when treating tap water, the above substances can be efficiently removed and recovered while maintaining the hardness and the residual chlorine concentration required for sterilization.

That is, according to the present invention, water containing a dissolved substance that can be vaporized while supplying a carrier gas is brought into contact with one side of the water-impermeable membrane that allows the gas to pass therethrough,
On the other hand, by maintaining a reduced pressure state, the vaporizable dissolved substance is vaporized and selectively permeated through the membrane as a gas, and water from which the vaporizable dissolved substance is removed is obtained on the impermeable side of the membrane, Provided is a water treatment method characterized by removing and recovering a permeated vaporizable dissolved substance.

In the present invention, the water to be treated is not particularly limited as long as it contains a dissolved substance that can be vaporized. For example, tap water, well water, ground water, river water, industrial water, agricultural water. , Industrial wastewater, agricultural wastewater, domestic wastewater, sewage, etc.

In the present invention, the vaporizable dissolved substance is
For example, a halogen compound and a vaporizable unpleasant odor component may be mentioned. As the halogen compound, chloroform, bromodichloromethane, dibromochloromethane, bromoform,
Methylene chloride, carbon tetrachloride, trichloroethane, trichloroethylene, tetrachloroethylene, methylene bromide,
Examples thereof include methyl fluoride and methylene fluoride.

Examples of the vaporizing unpleasant odor component include the above-mentioned halogen compounds dissolved in water and aldehydes such as formaldehyde, acetaldehyde and propylaldehyde.

In the present invention, water containing the above substances is brought into contact with one of the water-impermeable membranes, the other (permeation side) is kept under reduced pressure, and the carrier gas is supplied to the impermeable side of the membrane. Thus, each substance is selectively permeated.

In the present invention, the method of keeping the permeate side in a reduced pressure state is not particularly limited, but the permeate side can be kept at a vacuum degree of about 5 to 150 Torr by using, for example, a vacuum pump. The carrier gas is not particularly limited, but for example, air or an inert gas such as nitrogen or helium can be used.

In the present invention, when the carrier gas is supplied while the pressure on the permeate side is reduced as described above,
In addition to the components to be removed, water vapor may permeate as a permeation component, which may increase the load on the vacuum pump and increase operating costs. Such a case can be dealt with by operating so as not to raise the degree of vacuum above the saturated steam at the operating temperature.

The supply of the carrier gas to the impermeable side in the present invention is not particularly limited, but the supply amount of the carrier gas at the impermeable side of the membrane is 20 times the outflow water amount of the impermeable side.
It is desirable to supply the carrier gas in an amount of at least 40%, preferably 40% to 10 times. If the supply of the carrier gas is too small and is less than 20%, the effect of enhancing the removability of the permeation component may be reduced.

The water-impermeable membrane used in the present invention is not particularly limited in its structure. For example, a homogeneous membrane composed of a non-porous active thin film, a dense layer or an active dense layer and a porous layer integrally supporting the same. An asymmetric membrane composed of and a composite membrane in which a non-porous active thin film is formed on the asymmetric membrane,
Preferred is a composite film in which a non-porous active thin film is partially impregnated and formed in a dense layer of an asymmetric film. Here, the activity means that it has a property of separating a vaporizable dissolved substance from water.

The nitrogen gas permeation rate of the water-impermeable membrane at 30 ° C. is 7 × 10 ^-4 to 2 × 10 ² Nm ³ / m ² .h.atm,
Preferably, it is 3 × 10 ^{−3 to} 5 × 10 ⁰ Nm ³ / m ² · h · atm. Nitrogen gas permeation rate is 7 × 10 ^-4 Nm ³ / m ² · h · at
If it is smaller than m, the permeation rate of the vaporizable dissolved substance may be reduced, while 2 × 10 ² Nm ³ / m ² · h · atm
If it is larger than this, water impermeability may not be maintained, which is not preferable.

Specific examples of the above-mentioned homogeneous film and non-porous active thin film include silicone and poly (4-methylpentene-).
1), natural rubber, poly (2,6-dimethylphenylene oxide), Teflon, neoprene, polyethylene, polystyrene, polypropylene, polytrimethylsilylpropyne and the like.

The asymmetric membrane used in the present invention is not particularly limited, and examples thereof include aromatic polysulfone type, aromatic polyamide type and aromatic polyimide type.
In particular, aromatic polysulfones are preferably used because they have durability in water such as chlorine resistance, pH resistance, and heat resistance.

The shape of the water-impermeable membrane is not particularly limited, but may be hollow fiber or flat membrane, and may be formed on a reinforcing material such as nonwoven fabric. The shape of such a water-impermeable membrane and the module containing the membrane are not particularly limited, but a so-called spiral type membrane module formed by winding a sheet-like membrane can be used, for example.

Since the phenomenon of removing the vaporizable dissolved substance in the present invention is based on the selective permeation of the vaporizable dissolved substance through the membrane, it is desirable that the permeation of the vaporizable dissolved substance through the membrane is prevented as much as possible. . For this reason, when the above spiral type membrane module is used, the permeation side flow path gap (permeation side intermembrane gap) is preferably 0.3 to 2.5 mm, particularly preferably 0.5 to 2 mm. It is 0.0 mm. If the thickness is less than 0.3 mm, the pressure loss in the permeation-side flow path gap becomes too large, so that permeation of vaporized dissolved substances through the membrane is suppressed, and the removal rate of these substances may be deteriorated. If the thickness is more than 2.5 mm, the volumetric efficiency of the membrane module with respect to the removal rate of each substance may deteriorate.

In the present invention, the method of recovering the vaporizable dissolved substance that has permeated as described above is not particularly limited, but it is preferable to use, for example, an activated carbon adsorption method, a solvent absorption method, a cooling condensation method or the like.

The activated carbon adsorption method may be a small one usually used for deodorization and the like, and in order to improve adsorption efficiency,
A honeycomb structure, a fibrous shape, a granular shape, a fine powder shape, or the like can be appropriately selected. Further, since the permeation component contains more water vapor than usual, it is preferable to perform a drying step as a pretreatment.

The solvent absorption method is a method of absorbing and separating and recovering a vaporizable dissolved substance in a solvent having a high solubility. For example, alcohols such as ethyl alcohol, isopropyl alcohol, butyl alcohol, acetone, methyl ethyl ketone, etc. Ketones, butyl acetate, butyl propionate, butyl butyrate, and other esters, hexane, pentane, petroleum benzine, kerosene, heavy oil, light oil, hydrocarbons such as toluene, machine oil, paraffin oil, and vegetable oil are used. In this case, in order to improve the recovery efficiency of the vaporizable dissolved substance, a solvent having a low vapor pressure and a high boiling point is excellent, and particularly kerosene, heavy oil, light oil, machine oil, paraffin oil, vegetable oil and the like are preferably used. To be These liquids can also be treated by incineration with the absorbed and recovered vaporizable dissolved substances.
Also in this case, it is preferable to perform a drying step as a pretreatment.

The cooling condensation method is a method of condensing and recovering with a condenser using water cooling, alcohols, dry ice, liquid nitrogen, etc. Although the recovering method is simpler than the above method, there are cases where the recovery rate is inferior. is there.

[0026]

According to the treatment method of the present invention, the membrane permeation rate of a vaporizable dissolved substance can be increased, and the membrane permeation of water vapor can be suppressed. Therefore, the operation management can be simplified as compared with the conventional method. Moreover, there is an advantage that it does not cause environmental pollution. Especially when treating tap water, the above substances can be efficiently removed while maintaining the hardness and the residual chlorine concentration required for sterilization. The residual chlorine concentration required for sterilization in tap water varies depending on the degree of pollution of the water source such as rivers and lakes, but is regulated to be 0.1 ppm or more by the Waterworks Law Enforcement Regulations.

[0027]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 Polydimethylsiloxane was formed on the porous polysulfone membrane formed on the nonwoven fabric to a thickness of 1.5 μm to obtain a composite membrane. The nitrogen gas permeation rate at 30 ° C. of this composite film was 0.6 Nm ³ / m ² · h · atm. This membrane (membrane area: 2.0 m ² ) was molded into a spiral type membrane module having an outer diameter of 2 inches, a length of 1 m and a permeation side flow path gap of 0.6 mm.

One of such membrane modules has a hardness of 40 pp
m, residual chlorine 1.02ppm, halogen compounds shown in Table 1 and vaporized unpleasant odor components dissolved at 20 ℃ tap water, 120L / min flow the other, vacuum degree 40 vacuum
As a result of supplying air as a carrier gas so that the amount of outflow gas on the impermeable side of the membrane was 70% of the amount of outflow water on the impermeable side of the membrane in the membrane module, the hardness and residual chlorine concentration were , 39 ppm and 0.9 respectively
It became 0 ppm. 100% of the obtained permeated gas was put into a kerosene absorption tank with a filling amount of 500 mL installed in the post process of a vacuum pump.
After passing the time, no halogen compound or vaporizable unpleasant odor component was detected in the outlet gas. Table 1 shows the measurement results of the halogen compound and the halogen compound recovery amount of the membrane module supply solution and the treatment solution at this time.

[0029]

[Table 1]

Examples 2 to 3 In the method of Example 1, the amount of feed gas on the non-permeate side in the membrane module is 45, 60 of the amount of water discharged on the non-permeate side of the membrane, respectively.
The concentrations of chloroform in the membrane module supply liquid and the treatment liquid when the carrier air was supplied were measured so that the concentration became%, and the results are shown in Table 2.

Comparative Example As a comparative example, Table 2 also shows the result when the same operation as in Example 1 was performed except that the carrier air was not supplied.

[0032]

[Table 2]

From these results, it is understood that according to the method of the present invention, water free of halogen compounds and vaporizable unpleasant odor components can be efficiently obtained while maintaining hardness and residual chlorine concentration.

Claims (5)

[Claims] 1. A water-impermeable membrane that allows gas to permeate therethrough, and one of them is brought into contact with water containing a dissolved substance that can be vaporized while supplying a carrier gas, and the other is brought into a depressurized state. By keeping it, the vaporizable dissolved substance is selectively permeated through the membrane as a gas, and the water from which the vaporizable dissolved substance is removed is obtained on the impermeable side of the membrane, and the permeated vaporizable dissolved substance is removed. And a water treatment method characterized by recovering. 2. The water treatment method according to claim 1, wherein the vaporizable dissolved substance is a halogen compound and a vaporizable unpleasant odor component. 3. The tap water treatment method according to claim 2, wherein tap water from which halogen compounds and vaporized unpleasant odor components are removed is obtained while maintaining hardness and residual chlorine concentration necessary for sterilization. 4. The carrier gas is supplied to the impermeable side of the membrane so that the supply amount of the carrier gas is 20% or more of the outflow water amount on the impermeable side of the membrane. The water treatment method according to claim 1, which is characterized in that. 5. The water treatment method according to claim 1, wherein the carrier gas is air or an inert gas.