JPH0592181A - Apparatus and method for removing water-isoluble volatile organic compound in water - Google Patents

Abstract

PURPOSE:To reduce the height of an aeration tower while keeping the quality of treated water and to enhance the treatment efficiency of exhaust gas. CONSTITUTION:A multi-tower system wherein at least two low aeration towers 1, 2 are provided is employed and the volume ratio of blown air to raw water containing a water-insoluble volatile org. compound [gas/liquid ratio (G/L)] within the first stage aeration tower 1 is made low and the concn. of the org. compound of the exhaust gas discharged from the aeration tower 1 is enhanced to enhance the treatment efficiency in an exhaust gas treatment apparatus 108 (e.g., activated carbon adsorbing tower). A gas/liquid ratio is enhanced in the second stage aeration tower 2 and the org. compound remaining in the treated water discharged from the aeration tower 1 is sufficiently removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for removing various water-insoluble volatile organic compounds such as trichlorethylene, tetrachloroethylene and 1,1,1-trichloroethane contained in groundwater and various wastewaters.

[0002]

2. Description of the Related Art In recent years, groundwater has been insufficiently handled and treated due to insufficient handling of harmful organic compounds such as trichlorethylene used for washing machines and various parts in the precision and electronics industries and tetrachlorethylene used for large amounts in dry cleaning. There are a wide range of cases in which the environment such as air and air is polluted to a high concentration.

Organochlorine compounds such as trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, etc. are nonflammable and have a large specific gravity, so when they enter groundwater, they tend to remain underground even though they are volatile. It has been clarified that decomposition by microorganisms in soil transforms to organochlorine compounds such as dichloroethylene, which is more toxic, and these compounds pose a problem because they are suspected to be carcinogenic.

Further, well water as a source of tap water and cleaning wastewater discharged from various factories also contain various toxic organic compounds, and environmental pollution is becoming serious.

The Ministry of Health and Welfare established in February 1984 that 3
Provisional standards have been established for certain organochlorine compounds (trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane), and since October 1, 1989, the Environmental Agency has decided to use diorganochlorine compounds of trichlorethylene and tetrachloroethylene as harmful under the Water Pollution Control Act. Since it was designated as a substance, it became necessary to take measures to reduce such harmful substances.

On the other hand, as exhaust gas, the above-mentioned three kinds of organic chlorine compounds are defined to be 50 ppm or less according to the working environment standard of the Occupational Health Law because of the possibility of carcinogenicity and liver dysfunction.

Further, a chlorofluorocarbon solvent (for example, fluorocarbon 11)
When various organic solvents such as 1 and Freon 114) are volatilized, they are attracting much attention because they may cause ozone layer depletion and global warming.

In the case of an organic chlorine compound solvent having a low boiling point and a high vapor pressure such as trichlorethylene, conventionally, the principle of aeration removal was mainly applied to raw water containing it in drinking water (tap water) facilities and waste water treatment facilities. It is processed by a gas-liquid contact type organic chlorine compound removing device.

That is, as shown in FIG. 2, a filler 102 such as Raschig rings or terraret packing is provided on the eye plate 112.
Raw water flows in from above the aeration tower 101 filled with the water through a distributor (sprinkler) 104,
1. Air is blown from below 1 through a blower (blower) 107 to bring the organic chlorine compound contained in the raw water into gas phase by bringing it into gas-liquid contact in the filler 102 portion, and the organic chlorine compound is removed from the air. Along with it, it is discharged into the atmosphere through an exhaust port 105 provided in the upper part of the aeration tower 101,
The treated water from which the organic chlorine compound has been removed is taken out from the outlet 103 provided in the lower part of the aeration tower 101. An air filter 106 that removes fine particles in the air sucked by the blower 107 is attached to the blower 107. A liquid disperser 111 is provided near the middle point of the layer of the packing material 102 of the aeration tower 101. This is because the raw water flowing along the inner wall of the aeration tower 101 has poor contact with air. Since the degree of removal of the organic chlorine compound from this is poor, the raw water once collected at this position acts to collect toward the center of the layer of the filler 102.

Since the organic chlorine compound is a volatile substance in the conventional device shown in FIG. 2, the organic chlorine compound contained in water is transferred to the gas phase by utilizing Henry's law. By treating with, the organic chlorine compounds in the treated water are reduced to a level where they are hardly detected.

However, in the conventional apparatus shown in FIG. 2, since the exhaust gas containing the organic chlorine compound is discharged into the atmosphere through the exhaust port 105, there is a problem of secondary pollution of the atmosphere.

Therefore, recently, an apparatus as shown in FIG. 3 has been adopted to prevent the above-mentioned secondary pollution of the atmosphere.

That is, the exhaust port 105 at the upper part of the aeration tower 101.
The activated carbon adsorption tower 108 filled with activated carbon such as granular activated carbon or fibrous activated carbon is connected by the exhaust gas pipe 109, and the exhaust gas discharged from the exhaust port 105 is passed through the activated carbon adsorption tower 108, whereby the organic matter in the exhaust gas It adsorbs chlorine compounds with activated carbon. According to the conventional apparatus shown in FIG. 3, since the exhaust gas discharged from the discharge pipe 110 contains almost no organic chlorine compound, the above-mentioned problem of secondary air pollution disappears.

The removal performance of the organic chlorine compounds such as trichlorethylene in the aeration tower 101 is as follows: the water flow rate in the aeration tower 101, the type of the filler 102, the height of the layer of the filler 102, the sprinkler 104 and the screen 112. Structure, liquid disperser 11
1 and the ratio of blown air to the raw water to be passed (usually called gas-liquid ratio “G / L”, expressed as volume ratio), etc., but if the mechanical and physical conditions are the same. If so, the two layers that have the greatest influence are the layer height (Zm) of the filler 102 and the gas-liquid ratio (G / L).

Therefore, when the content of the organic chlorine compound such as trichlorethylene in the raw water is large or there is a demand for lowering the concentration of the organic compound in the treated water, the height of the packing material layer, and thus the aeration tower. Either increase the height or increase the amount of air blown in, or take measures against both of these.

Increasing the height of the aeration tower means an increase in the basic construction of the aeration tower, which not only causes an increase in construction cost but also causes inconveniences in the inspection and maintenance of the equipment, resulting in indirect costs. Will increase.

When the amount of air to be blown in is increased, the concentration of the organic chlorine compound in the treated water in the apparatus of FIG.
From the standpoint of treating exhaust gas containing organic chlorine compounds, the large amount of blown air means that the concentration of organic chlorine compounds in the exhaust gas becomes low, and when adsorption treatment with activated carbon etc. The amount of organic chlorine compounds adsorbed per unit weight decreases, and the treatment efficiency decreases. This is because, generally, there is a relationship that the adsorption amount of the organic chlorine compound per unit weight of activated carbon increases in a logarithmic relationship with the decrease in the concentration of the organic chlorine compound in the exhaust gas.

Further, when the amount of blown air is large, the speed at which the exhaust gas passes through the activated carbon layer becomes high, so that the contact time becomes short (that is, the residence time becomes short), and the exhaust gas treatment efficiency decreases. Become. To prevent this, there is no choice but to increase the size of the activated carbon layer, which is naturally costly.

The present invention is intended to solve the above-mentioned problems of the prior art, and treats exhaust gas without raising the aeration tower and maintaining the removal rate of water-insoluble volatile organic compounds in raw water. It is intended to provide a device for removing a water-insoluble volatile organic compound in water and a method for removing the organic compound, which does not cause a reduction in efficiency.

[0020]

According to the present invention, a plurality of aeration towers for gas-liquid separating the liquid organic compound by aerating water containing a water-insoluble volatile organic compound,
And an exhaust gas treatment device communicating with at least the first-stage aeration tower of the plurality of aeration towers, the water containing the organic compound is sequentially serially connected from the first-stage aeration tower to the second-stage and subsequent aeration towers. An apparatus for removing water-insoluble volatile organic compounds in water is provided, which is characterized in that it is configured to process through.

In the above-mentioned apparatus for removing water-insoluble volatile organic compounds, the exhaust gas treating apparatus is preferably an activated carbon adsorption tower, but it may be a catalytic combustion apparatus. In the latter case, the catalyst is generally used by supporting a precious metal such as platinum on a ceramic material.

In the present specification, the case of an activated carbon adsorption tower will be mainly described, but the case of a catalytic combustion device can be generally considered to be substantially the same. This is understandable, considering that in catalytic combustion, the organic compound is first adsorbed on the catalyst as in the case of activated carbon adsorption, and only the combustion chemical reaction occurs thereafter.

Further, it is an essential requirement that such an exhaust gas treatment device is provided in communication with the first-stage aeration tower, while it is not necessary to provide it in the second-stage and subsequent aeration towers. If the concentration of organic compounds in the exhaust gas discharged from the aeration tower of the second and subsequent stages is high, it may be provided if necessary.

Further, according to the present invention, in the apparatus for removing water-insoluble volatile organic compounds in water configured as described above, the ratio of aeration gas to water in the first-stage aeration tower is set to the second-stage aeration gas. A method of removing a water-insoluble volatile organic compound in water, characterized by treating the exhaust gas from the first-stage aeration tower with an exhaust gas treatment device, with the ratio of aeration gas to water being equal to or less than that in the subsequent aeration tower Is also provided.

The water-insoluble volatile organic compound which can be treated by the apparatus and method of the present invention is any kind of liquid organic substance as long as it is substantially water-insoluble and volatile so that it can be expelled from raw water by aeration treatment. Although it may be a compound, examples thereof include trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane,
Organochlorine compounds such as 1,1-dichloroethane, 1,2-cis-dichloroethylene, carbon tetrachloride and chloroform, CFC-based fluoroorganic compounds such as CFC 114 and CFC 111, and aromatic organic compounds such as benzene and toluene. Can be mentioned.

The number of aeration towers may be determined according to various conditions such as the concentration and type of the organic compound in the raw water to be treated, the concentration of the organic compound to be removed in the treated water, the height of the aeration tower, etc., but is not particularly limited. Since increasing the number leads to an increase in construction cost, it is most preferable to have two towers.

FIG. 1 shows an example of the device of the present invention. Figure 1
2 and FIG. 3 have the same functions and have the same functions.
This device consists of a first stage aeration tower 1 and a second stage aeration tower 2
This is an apparatus in which a tower is provided and one exhaust gas treatment device 108 is provided in communication with the first stage aeration tower. The height and the horizontal area of the first-stage aeration tower 1 and the second-stage aeration tower 2 may be determined according to various conditions, and may be the same or different, but it is preferable in terms of design cost. ..

The diameter and height of both aeration towers and the length and diameter of the exhaust gas treatment device in FIG. 1 are shown in FIGS. 2 and 3 in the drawings.
Although it is the same as that of the actual device, it is not necessarily the same in the case of an actual device, and is the same for the convenience of drawing. In particular, it should be considered that the height of both aeration towers in FIG. 1 is actually about half as compared with the case of the apparatuses in FIGS. 2 and 3 due to the two tower system.

In this apparatus, for example, in the first stage aeration tower 1, when the gas-liquid ratio is set to be 5 to 20 times the volumetric flow rate of air to the volumetric flow rate of raw water, the second stage aeration is performed. The gas-liquid ratio of the column 2 is preferably 20 to 80 times, and may be higher than 80 times in some cases, but is not limited thereto.

Further, the exhaust gas flowing out through the aeration tower contains water droplets, and the relative humidity is 100 even if water droplets are excluded.
%, Therefore, in order to eliminate the drawback that the utilization efficiency of activated carbon is not sufficient, between the aeration tower and the exhaust gas treatment device, a mist separator (not shown) for physically removing water droplets in the exhaust gas and the It is preferable to provide a heating device (not shown) for reducing the relative humidity of the exhaust gas, or a cooling / dehumidifying device or a combination of these devices after the mist separator (1990 utility model registration application No. 24890). ..

[0031]

As described above, when the amount of air blown into the first stage aeration tower is suppressed to a small amount, the concentration of organic compounds in the exhaust gas can be increased. For example, when an activated carbon adsorption tower is used as an exhaust gas treatment device, the activated carbon unit The amount of adsorbed organic compound per weight increases, and the adsorption efficiency also increases with the increase of contact time. Therefore, breakthrough of activated carbon
The utilization efficiency of the activated carbon adsorption capacity up to is improved, and the reduction of the basic unit of activated carbon regeneration and replacement can be realized.

The concentration of organic compounds in the exhaust gas discharged from the second stage aeration tower is low, and the absolute amount of organic compounds in the exhaust gas can be suppressed to about 2-10% of that in the case of the first stage aeration tower. Generally, it can be discharged into the atmosphere as it is.

Further, since the amount of exhaust gas discharged from the first stage aeration tower can be reduced, the exhaust gas treatment equipment such as the activated carbon adsorption tower can be made compact.

On the other hand, since the raw water is treated in at least two stages, the concentration of organic compounds in the treated water can be generally lowered as compared with the conventional apparatus, so that environmental pollution can be reduced and human beings can be reduced. The living environment can be preserved.

Since the height of the aeration tower can be reduced, it is possible to reduce the cost of foundation work and to make it convenient for inspection and maintenance of the equipment.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail with reference to the accompanying drawings, but the present invention is not limited to the embodiments.

Example 1 FIG. 1 is a schematic explanatory view of an organic compound removing apparatus of the present invention, in the case of the simplest configuration including two aeration towers and one activated carbon adsorption tower as an exhaust gas treatment apparatus. The water is treated in two stages, and the exhaust gas treatment is performed only in the activated carbon adsorption tower 108 communicating with the first stage aeration tower.

In the apparatus shown in FIG. 1, both aeration towers have a diameter of 1.5 m and a packed bed height of 4.6 m. The amount of raw water treated per unit time is 100 m ³ / hr.

The activated carbon adsorption tower 108 is a prismatic (1.1 m × 1.1 m) tower having a cross-sectional area of 1.2 m ² and a wood-based granular activated carbon packed in a bed height of 2 m.

When the gas-liquid ratio in the first-stage aeration tower was set to 20 times and raw water with a trichlorethylene concentration of 5 mg / l was passed through the first-stage aeration tower, the trichlorethylene concentration of the primary treated water was 0.2 mg / l. (It can be calculated based on Henry's law using factors such as the overall mass transfer coefficient and contact area between the gas phase and the liquid phase, which have been obtained in advance by experiments. The same applies to the calculation of the height of the packed bed described later. For the specific calculation method, see, for example, "Water Supply Association Magazine, Vol. 53, No. 2, pp. 105-117".)

When the gas-liquid ratio in the second stage aeration tower is set to 60 times and this primary treated water is passed through the second stage aeration tower, the trichlorethylene concentration of the secondary treated water obtained is 0.005.
It becomes mg / l.

The concentration of trichlorethylene in the exhaust gas discharged from the first stage aeration tower is 43 ppm, and the concentration of trichlorethylene in the exhaust gas discharged from the second stage aeration tower is 0.
It becomes 584 ppm (ratio of both concentrations: about 73 times).

Since the concentration of trichlorethylene in the exhaust gas coming out of the first stage aeration tower is still quite high, it is passed through the activated carbon adsorption tower 108. The amount of exhaust gas passed through the activated carbon adsorption tower 108 is 2000 m ³ / hr.

Since the concentration of trichlorethylene in the exhaust gas coming out from the second stage aeration tower is as low as 1 ppm or less,
It is released into the atmosphere.

On the other hand, consider the case where the apparatus of the one aeration tower system of FIG. 2 is used. Raw water treatment amount per unit time is 100m ³
/ hr and perform aeration treatment at a gas-liquid ratio of 60 times, and the trichlorethylene concentration of the treated water is the same as in the case of the device in FIG.
If the diameter of the aeration tower is 1.5 m, which is the same as that of the apparatus of FIG. 1, to obtain 5 mg / l, the packed bed height needs to be about 9 m. In this case, the amount of exhaust gas is 6000 m ³ / hr and the concentration of trichlorethylene in the exhaust gas coming out of the aeration tower is 15 ppm.
Becomes

Using the one aeration tower system shown in FIG. 2, the raw water treatment amount per unit time was similarly set to 100 m ³ / hr, and the aeration treatment was carried out at a gas-liquid ratio of 20 times to obtain the same concentration of trichlorethylene in the treated water. If the diameter of the aeration tower is 1.5m, the height of the packed bed is about 10.2.
m is required. The amount of exhaust gas in this case is 2000 m ³ / hr
However, the concentration of trichlorethylene in the exhaust gas coming out of the aeration tower is 45 ppm. The height of the packed bed is 1
If it is 0.2 m, the aeration tower structure will be about 13 m tall.

[0047]

As described above, by adopting at least two aeration tower systems, the height of the equipment can be lowered without deteriorating the quality of treated water, and the convenience of inspection and maintenance of the equipment can be achieved. It is only necessary to treat the exhaust gas with a high trichlorethylene concentration of a small air volume coming out from the stage aeration tower with the exhaust gas treatment apparatus, and the exhaust gas treatment apparatus can be made compact as compared with the case of treating a large air volume exhaust gas, In addition, the amount of activated carbon adsorbed per unit weight can be increased, and the adsorption time can be lengthened. Further, when the activated carbon is regenerated, it is possible to set a long regeneration interval, and it is possible to reduce the cost associated with the replacement and regeneration of the activated carbon.

The concentration of organic compounds in the exhaust gas discharged from the second stage aeration tower is usually low, and generally, it can be discharged to the atmosphere as it is. Therefore, the exhaust gas treatment communicating with the second stage aeration tower is performed. In many cases there is no need to install a tower.

Further, since the raw water is treated in at least two stages, generally, the concentration of the organic compound in the treated water can be easily lowered as compared with the conventional apparatus.
Environmental pollution can be reduced and the human living environment can be preserved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an insoluble volatile organic compound removing device of the present invention.

FIG. 2 is an explanatory diagram of a conventional organic chlorine compound removing apparatus.

FIG. 3 is an explanatory view of another conventional organic chlorine compound removing device.

[Explanation of symbols]

 101 Aeration Tower 102 Filler 103 Outlet 104 Distributor 105 Exhaust Port 106 Air Filter 107 Blower 108 Exhaust Gas Treatment Device 109 Exhaust Gas Pipe 110 Exhaust Gas Discharge Pipe 111 Liquid Disperser 112 Eye Plate

Claims (4)

[Claims] 1. A plurality of aeration towers for gas-liquid separating the organic compounds by aerating water containing a water-insoluble volatile organic compound, and at least a first-stage aeration tower of the plurality of aeration towers. An underwater characterized in that it includes an exhaust gas treatment device and is configured to process water containing the organic compound by sequentially passing it in series from the first-stage aeration tower to the second-stage and subsequent aeration towers. Equipment for removing water-insoluble volatile organic compounds. 2. The device for removing water-insoluble volatile organic compounds in water according to claim 1, wherein the exhaust gas treatment device is an activated carbon adsorption tower. 3. The apparatus for removing water-insoluble volatile organic compounds in water according to claim 1 or 2, wherein the ratio of aeration gas to water in the first-stage aeration tower is equal to that of water in the second and subsequent stages. A method for removing a water-insoluble volatile organic compound in water, characterized in that the exhaust gas from the first stage aeration tower is treated with the exhaust gas treatment device at a ratio equal to or less than the ratio of the gas for aeration. 4. The water-insoluble volatile organic compound is trichloroethylene, tetrachloroethylene, 1,1,1-
Trichloroethane, 1,1-dichloroethane, 1,2-
A method for removing a water-insoluble volatile organic compound in water, which is an organic chlorine compound such as cis-dichloroethylene, carbon tetrachloride and chloroform.