JPH0736907B2 - Groundwater purification method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing and purifying volatile toxic substances, especially groundwater containing organic chlorine compounds such as chloroform, trichloroethylene, dichloroethane and tetrachloroethylene.

[0002]

2. Description of the Related Art In recent years, as groundwater pollution, along with heavy metals and inorganic eutrophic salts, pollution by organic chlorine solvents and pesticides discharged from factories has become a serious social problem. In particular, chloroform, trichloroethylene, dichloroethane, and tetrachloroethylene are particularly contaminated, and groundwater surveys in Japan have increased the number of contaminated wells exceeding the provisional standard value by WHO, and various countermeasures are being considered.

Up to now, as a method for removing pollutants in groundwater, a method of oxidative decomposition with ozone or ozone and hydrogen peroxide (J. AWWA., 1988, 57th).
(See page 63), packed tower aeration method, granular activated carbon filtration method, etc., but treating the large amount of groundwater is very expensive, and the latter simply pollutes other media. However, there is a drawback in that it is not a fundamental solution because it is incomplete from the perspective of comprehensive environmental purification simply by switching to.

A method has also been proposed in which volatile organic compounds are removed from drinking water by circulating the air outside the membrane while allowing the drinking water to pass inside the hollow fiber membrane (J. AWWA., 1989, 78th-8th
(Page 1), this is a method of treating water pumped from underground, and it is not possible to treat groundwater directly.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, groundwater, that is, water remaining underground is treated in situ by a simple device to efficiently remove volatile harmful substances contained therein. The purpose is to provide a method for doing so.

[0006]

Means for Solving the Problems As a result of various studies on purification of contaminated groundwater, the present inventors have found that a membrane using a separation membrane obtained by treating the surface of a plastic substrate membrane with fluorocarbon gas plasma We found that the process can efficiently remove volatile harmful substances from groundwater,
The present invention has been completed based on this finding.

That is, according to the present invention, the treated surface of the separation membrane obtained by treating one surface of the plastic substrate membrane with the fluorocarbon gas plasma is brought into contact with ground water, and the other surface is scavenged with air to remove volatile harmful substances. The present invention provides a method for purifying groundwater, which is characterized in that a substance is transferred into the air.

Next, the structure of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a vertical cross-sectional view of a tubular separation membrane used in the method of the present invention, in which a polymerized membrane 2 produced by plasma polymerization of fluorocarbon is laminated on the outer surface of a tubular plastic substrate membrane 1.

When the outer side of the tubular separation membrane having such a structure is brought into contact with groundwater and air is continuously scavenged by flowing air inside, volatile harmful substances in groundwater are transferred into the air and removed from the groundwater. To be done.

Since the tubular plastic substrate membrane 1 constituting this tubular separation membrane is permanently arranged in the underground water layer, it is made of a material having water resistance, corrosion resistance and mechanical strength. Needs to be done. Examples of such a material include polyamide-based and polyimide-based polymer materials, and silicone rubber is particularly suitable.

The plasma-polymerized layer formed on the surface of the tubular plastic substrate film needs to be highly hydrophobic, and in the present invention, a plasma-polymerized fluorocarbon is used. Examples of this fluorocarbon include compounds consisting only of carbon and fluorine such as tetrafluoromethane, tetrafluoroethylene, perfluoropropylene, perfluoropropane, and perfluorobenzene. As the plasma-polymerized layer thus formed, one having a fluorine / carbon atomic ratio of 1.2 or more is particularly advantageous.

A particularly suitable tubular separation membrane for use in the method of the present invention is a silicone rubber tube having a diameter of 0.2 to 1.0 mm, on which a plasma polymerized layer having a thickness of about 0.05 to 10 μm is laminated. It is a thing.

The plasma polymerized layer can be formed on the surface of the tubular plastic substrate membrane by using a fluorocarbon monomer gas according to a commonly used plasma polymerization method. The excitation power at this time is 10 to 5
0 W, the pressure is 1 to 100 Pa, and the film growth rate is 1 to 10 nm / min.

[0014]

FIG. 2 is a simplified illustration of an overall system for operating the method of the present invention for extended periods.

This system is composed of a separation membrane module A which is buried underground and is brought into contact with groundwater, and a control box B which is installed on the ground.

The separation membrane module A has a tubular membrane 3
An air supply pipe 5 for supplying air thereto, an exhaust pipe 6 for discharging air therefrom, and an outer cylinder 7 for accommodating these parts and connecting with a control box. The tubular membrane 3 described above is wrapped around a support frame for stabilization.

The separation membrane module A is covered with a protective outer cylinder 4 in order to prevent damage when the separation membrane module A is buried underground.
Removed by withdrawal or other means. The separation membrane module A is usually formed with a diameter of several cm.

On the other hand, the control box B includes an air feed pump 8 for supplying the air taken in through the intake port 9 to the separation membrane module A, an electromagnetic flow control valve 10 for adjusting the amount of the air, and a separation membrane. Decomposing device 11 for decomposing volatile harmful substances discharged from module A along with air, neutralizing tank 12 for neutralizing decomposing gas from this decomposing device 11, neutralizing and detoxifying An exhaust port 13 for discharging the generated gas to the outside is provided.

As the energy required to operate the control box B, commercial power may be used, but as shown in the figure, the self-supplied energy obtained by combining the solar cell panel 14 and the power distribution control mechanism 15 is used. Is preferably used.

By using such a system, the separation membrane module A is buried underground, and this is linked with the control box B installed on the ground so that the solar cell can be autonomously operated by using it as an energy source for a long period of time. Continuous purification of contaminated groundwater can be carried out.

In practical use, a large number of separation membrane modules A are arranged around the pollution source to prevent the pollution from spreading to the surroundings and purify the groundwater in the contaminated area.

The pollutants such as the organic chlorine-based solvent separated and concentrated underground are accompanied by the air flow supplied by the air feed pump 8, and the noble metal-based catalyst or the noble metal-based catalyst installed in the control box B on the ground. It is introduced into a decomposition device 11 filled with a catalyst made of a metal such as iron, manganese, or cobalt or an oxide thereof, and decomposed. Decomposition products such as hydrogen chloride produced by this decomposition are sent to the neutralization tank 12, where they are neutralized with an alkali, rendered harmless, and then exhausted.

In order to operate the catalyst of this decomposition apparatus sufficiently efficiently, it is advantageous that the concentration of pollutants recovered via the exhaust pipe is as high as possible, and the existing membranes do not have sufficient separation performance. A silicone rubber film or the like is known as a film for separating a hydrophobic liquid component such as an organic solvent. However, in order to further improve the separation performance, the surface is covered with a layer of a plasma polymerization film having higher hydrophobicity. Specifically, it is covered with a polymerized film of a perfluorocarbon-based monomer composed of only carbon and fluorine such as ethylene tetrafluoride, perfluoropropylene, perfluoropropane, perfluorobenzene, and tetrafluoromethane. The hydrophobicity of polymerized films can be easily compared by the ratio of elemental fluorine contained, and it has been found that a film having a fluorine / carbon ratio of 1.2 or more is highly efficient.

The improvement of the efficiency of the separation membrane is due to the action of the plasma-polymerized membrane formed on the surface of the substrate membrane. In principle, the same effect can be obtained even if the porous substrate membrane is covered with a similar polymerized membrane. However, a material that permeates the membrane and comes into contact with a concentrated solvent to dissolve it cannot be used as the substrate membrane.

The maximum pressure applied to the membrane from the surrounding soil is 2k
Since it is estimated to be about g / cm 2, the base membrane is a hollow fiber membrane of a normal size (outer diameter 200 to 400 μm, inner diameter 100
˜200 μm), and since it is necessary to stably support the polymerized membrane while maintaining a high permeation rate, in the case of a porous base membrane, the pore diameter distribution should be 0. It may be in the range of 1 to 0.45 μm.

Since it is not possible to control the conditions on the groundwater side (in particular, the flow velocity is several centimeters to several meters / day), the separation membrane module, the decomposition device, the energy, etc. can be controlled by controlling the air flow for recovery on the permeate side. It is necessary to be able to set the conditions for efficient operation. in this case,
The retention time of gas in the separation membrane module A is optimized to increase the concentration at the inlet of the decomposition device as much as possible (for example, in the case of silicone rubber, several percent of the untreated membrane is a tetrafluoroethylene plasma polymerized membrane with a maximum of 20 to 30). It is important to increase to%). Here, it is preferable that the decomposition temperature in the decomposition apparatus is as high as possible and is usually set to 100 ° C. or higher so that 100% decomposition can be achieved as fast as possible.

The optimum residence time of gas in the separation membrane module is not uniform in a separation membrane module (surface area of about 0.1 m 2 / module) in which a large number of tubular membranes are bundled, and is not uniform because it is experimental. In search of
The condition can be realized by controlling the valve with the built-in microcomputer. In addition, the control box may be combined with a plurality of membrane modules to configure the system for centralized management. In this case, it is desirable to allocate the control time to realize the optimum condition stored for each module.

[0028]

EFFECTS OF THE INVENTION According to the present invention, it is possible to remove volatile harmful substances in groundwater with high efficiency by using a device which has a simple structure and can be easily installed in the ground. When combined with a self-generated energy source, there is an advantage that the facility can be constructed in any place and with a small dedicated area. Moreover, since the removed harmful substances are detoxified and then discharged into the atmosphere, there is no risk of secondary pollution.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a tubular separation membrane used in the present invention.

FIG. 2 is an explanatory diagram of an integrated system for carrying out the method of the present invention.

[Explanation of symbols]

 1 Tubular Plastic Substrate Membrane 2 Plasma Polymerization Membrane 3 Tubular Membrane 8 Air Inlet Pump 11 Decomposing Device 12 Neutralization Tank

Claims (2)

[Claims] 1. A ground water is brought into contact with the treated surface of a separation membrane obtained by treating one surface of a plastic substrate membrane with a fluorocarbon gas plasma, and the other surface is scavenged with air to remove volatile harmful substances in the air. A method for purifying groundwater, characterized in that 2. A separation membrane module composed of a tubular plastic membrane whose surface is treated with fluorocarbon gas plasma is brought into contact with underground water in the ground, and air is flown inside the tubular plastic membrane to remove volatile harmful substances in the groundwater. A method for purifying groundwater, characterized in that the air is passed through a decomposing device to decompose the volatile harmful substances to render them harmless.