JPH07241551A - Treatment of water containing trihalomethane - Google Patents

Abstract

PURPOSE:To obtain treated water of stable quality by efficiently removing trihalomethanes from water containing the trihalomethanes and residual chlorine by bringing water containing the trihalomethanes and residual chlorine into contact with gas to diffuse and remove the trihalomethanes and subjecting treated water to activated carbon treatment. CONSTITUTION:Water containing trihalomethanes is allowed to flow in an aeration tower 1 by a raw water pump or water head and the aeration tower 1 is packed with a packing material over the almost total height thereof in order to increase the contact area of water within air. The exhaust gas from the aeration tower 1 is sent to an exhaust gas treatment tower 2 packed with activated carbon and the trihalomethanes contained in the exhaust gas are adsorbed and separated. The water treated within the aeration tower 1 is allowed to flow in an activated carbon packed tower 3 by a pump or water head. The trihalomethanes and residual chlorine contained in water to be treated are almost perfectly adsorbed and removed by activated carbon within the activated carbon packed tower 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating water. More specifically, the present invention economically obtains treated water with a high removal rate of trihalomethane by volatilizing treatment of water containing trihalomethane and residual chlorine with a gas such as air, nitrogen or oxygen, and then treating with activated carbon. The present invention relates to a water treatment method that can be performed.

[0002]

2. Description of the Related Art In drinking water such as tap water, trihalomethane is produced by a reaction between chlorine and the like, which is injected and added as a bactericide in the purification step, and organic substances existing in the raw water. The demand for safe and delicious water is increasing, and at the water treatment plants and water supply destinations, the number of treatments using powdered activated carbon or granular activated carbon or a combination of ozone and activated carbon is increasing as advanced treatment. Activated carbon has a good adsorption and removal property for off-flavors such as musty odor and pesticides, etc., but since the amount of trihalomethane adsorbed is small, it is necessary to frequently regenerate or replace activated carbon by treating water containing trihalomethane with activated carbon. There was a problem that had to be done. A method in which water containing trihalomethane is aerated using a gas-liquid contacting device and the trihalomethane is forcibly transferred from water to the aerated gas and removed is disclosed in Japanese Patent Laid-Open Publication No. Sho 5-5
It is proposed in Japanese Patent Application Laid-Open No. 9-10382 and Japanese Patent Application Laid-Open No. 4-222685. However, in the aeration method, even if trihalomethane is removed using a large amount of gas, if the treated water is left standing or chlorine is added, trihalomethane is generated again over time until the water is used, and stable There was a problem that it was difficult to obtain treated water of the specified water quality.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made for the purpose of providing an economical treatment method for efficiently removing trihalomethane from water containing trihalomethane and residual chlorine to obtain treated water of stable water quality. It is a thing.

[0004]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that if the water containing trihalomethane is aerated, and then the treated water is treated with activated carbon, Find that they can achieve their goals,
The present invention has been completed based on this finding. That is, the present invention is a method for treating water containing trihalomethane, which comprises contacting water containing trihalomethane and residual chlorine with a gas to diffuse and remove most of the trihalomethane, and then treating the treated water with activated carbon. Is provided. The water supply system is a system for supplying drinking water, and it is necessary that it does not adversely affect the human body even if it is consumed, and strict standards are set for bacteria, harmful substances, and offensive taste. At present, tap water is purified to a substantially safe state by sedimentation and filtration, but in many cases, chlorine sterilization is performed for complete safety. The amount of chlorine added for sterilization is usually about 1 to 2 ppm with respect to water. Chlorine is very effective against pathogenic bacteria in water, but it reacts with organic compounds present in trace amounts in water to produce trihalomethane such as chloroform, and it is strongly suspected that these trihalomethanes have carcinogenicity, It's a big problem. In addition, a chlorine-based agent such as sodium hypochlorite is often used together with an ozone-based agent for sterilizing the water for the pool, and there is a concern that trihalomethane may be produced here as well.

The main cause of trihalomethane production is artificially added chlorine or chlorine-based chemicals, but other than that, bromine, iodine, etc. artificially added or existing in nature are involved. Thus, trihalomethanes such as chloroform, dichlorobromomethane, dibromochloromethane, bromoform and chlorodiiodomethane may be produced. The mechanism by which halogens such as chlorine react with organic compounds to form trihalomethanes has not yet been completely clarified, but it is considered that trihalomethanes are converted to trihalomethanes via halides having a relatively small number of carbon atoms.
According to the method of the present invention, trihalomethane-containing water is contacted with aerated air to volatilize and remove trihalomethane, and then the solution is passed through a granular activated carbon packed column to prevent re-reaction of chlorine and the trihalomethane precursor to prevent treated water. The amount of trihalomethane adsorbed on activated carbon is smaller when the concentration of trihalomethane is lower, but the treatment multiple of water containing trihalomethane per volume of activated carbon is large, and the replacement frequency of activated carbon is low and stable. It is possible to obtain treated water of the specified water quality. Examples of raw water that can be treated by the method of the present invention include tap water containing a chlorine-based bactericide, ground water containing a chlorine-based bactericide, industrial water, and the like. ~ 15
It often contains 0 ppb.

The method of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flow sheet showing an example of an apparatus for carrying out the present invention. In the method of the present invention, water containing trihalomethane flows into the air aeration tower 1 by a raw water pump or a head pressure (head). In order to increase the contact area between water and air in the air aeration tower, 5 to 50 mm spherical, cylindrical, crushed, or amorphous packing material made of plastic, metal, or earthenware is used in the tower. It is filled almost all the height. The liquid level in the tower may be in a state where the packing material is submerged, but it is more convenient that the liquid level is lower than the packing material in terms of volatilization efficiency. Further, it is possible to use an empty tower without using a packing material, but in that case, it is desirable that the water depth is deep. In the method of the present invention, air is blown from the lower part of the air aeration tower,
Countercurrent contact with water is preferred. It is necessary that the air used does not contain trihalomethane, but it is desirable to filter it in advance with a filter so that the water to be treated is not contaminated with bacteria or foreign substances. Instead of air, nitrogen gas or oxygen gas that does not contain trihalomethane can be used. The pressure in the air aeration tower may be normal pressure or reduced pressure. In the method of the present invention, the amount of air (G) is preferably 0.1 to 10 in weight ratio (L / G) to the flow rate of raw water (L), and more preferably 0.5 to 5.0. More preferable. L
When the value of / G exceeds 5 and the amount of air is small, the concentration of trihalomethane remaining in water is high and the life of activated carbon is shortened. When the value of L / G is less than 0.5, the amount of air is large, Although the removal rate of trihalomethane increases, the amount of exhaust gas to be treated increases and the treatment cost of exhaust gas increases, which is not preferable.

In the method of the present invention, the method of feeding air into the air aeration tower can be arbitrarily selected from known methods, but the method of atomizing by blowing with an air diffuser can increase the contact area of air and treated water. Is preferred. The exhaust gas discharged from the air aeration tower is sent to the exhaust gas processing tower 2. It is preferable to fill the exhaust treatment tower with activated carbon and to adsorb and separate the trihalomethane contained in the exhaust gas. Alternatively, the exhaust treatment tower may be filled with a suitable catalyst and the trihalomethane may be detoxified by an oxidation or reduction treatment.
The exhaust gas from which the contained trihalomethane has been removed can be circulated and sent to the air aeration tower. It is preferable to circulate and use the exhaust gas in this way, because the amount of air filtered by the filter can be reduced and the load on the filter can be reduced. In the method of the present invention, in the air aeration tower, trihalomethane in the water to be treated is volatilized and removed by contact with air, and usually 80 to 95% or more of trihalomethane is removed. In the method of the present invention, the water treated in the air aeration tower flows into the activated carbon packed tower 3 by a pump or a head. The activated carbon packed column may be a fixed bed with a downward flow or a fluidized bed with an upward flow, but a multi-stage fluidized bed having a high utilization rate of the saturated adsorption amount of trihalomethane is preferable. The activated carbon packed in the activated carbon packed column is repeatedly used after washing the suspended matter that has been captured by backwashing at all times. Bacteria and the like that grow and accumulate in the activated carbon packed tower can be sterilized and washed by passing hot water or steam. In the method of the present invention, in the activated carbon packed tower, the trihalomethane and residual chlorine remaining in the water to be treated are almost completely adsorbed and removed by the activated carbon. According to the method of the present invention, all trihalomethanes including a trihalomethane precursor are removed, so that trihalomethane is not regenerated and treated water having excellent stability can be obtained.

[0008]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, the residual chlorine concentration was measured according to the water purification test method DPD method, and the trihalomethane concentration was
Water purification test method It was measured according to the headspace-gas chromatographic method. Example 1 An air aeration tower having an inner diameter of 150 mm and a height of 2,500 mm was provided with a cylindrical ceramic packing material having an inner diameter of 10 mm and a length of 10 mm, and a space of 500 mm was provided in each of the upper and lower parts in the height direction of the tower to form a central space 1,
Tap water containing 0.5 mg / l of residual chlorine as water containing trihalomethane was charged into the part of 500 mm from the top of 250 liters per hour, and air was supplied from the bottom of the column so that L / G was 0.5. Blow 7m ³ every minute. At this time, the water surface was at a height of 300 mm in the air aeration tower. Next, the air aeration treated water that has been treated in the air aeration tower is filled with coal-based crushed activated carbon having a particle size of 20 to 40 mesh to a height of 1,000 mm, an inner diameter of 100 mm, and a height of 1,
Water was continuously passed through a 500 mm packed column of activated carbon at an upward flow rate of 80 liters per hour. Raw water, air aeration-treated water, and activated carbon-treated water were sampled every 100 hours or 200 hours of water passage, and the trihalomethane concentration (μg / liter) was measured for each sample, and the measurement results are shown in Table 1. .

[0009]

[Table 1]

Comparative Example 1 In parallel with Example 1, the same activated carbon packed column as in Example 1 was continuously fed with the same tap water as in Example 1 directly at a flow rate of 80 liters per hour without passing through the air aeration column. I passed water. The activated carbon-treated water was sampled every 100 hours or 200 hours of water passage, the trihalomethane concentration (μg / liter) was measured for the sample, and Table 1 shows the measurement results. The results of Example 1 and the results of Comparative Example 1 are compared. In Comparative Example 1, treated water of good water quality having a low trihalomethane concentration was obtained up to a water passage time of 200 hours, but the trihalomethane concentration was 12 μg / at a water passage time of 300 hours.
The trihalomethane concentration was 52 μg / liter at a water flow time of 400 hours, which was almost the same as the raw water, reaching a trihalomethane concentration of 52 μg / liter. On the other hand, in Example 1 in which the air aeration process was performed, the treated water of good water quality having a low trihalomethane concentration was obtained up to the water passing time of 600 hours, and the water passing time was 80 hours.
The trihalomethane concentration was 5 μg / liter at 0 hours, and the trihalomethane concentration was 11 μ at water flow time of 1,000 hours.
The concentration of trihalomethane reaches almost the same as that of the aerated and treated water of g / liter. That is, it is understood that the treatment capacity of the activated carbon packed tower is tripled or more by performing the treatment by the air aeration tower. Example 2 A sample of activated carbon-treated water having a water passage time of 200 hours in Example 1 was allowed to stand at 20 ° C. for 2 days, and then the trihalomethane concentration was measured to be 4 μg / liter or less, showing a large change in the trihalomethane concentration. I was not able to admit. Comparative Example 2 A sample of air-treated aerated water having a water passage time of 200 hours in Example 1 was allowed to stand at 20 ° C. for 2 days and then the trihalomethane concentration was measured to be 21 μg / liter, and the trihalomethane concentration was 6 μg / liter. Was increasing.

Example 3 Sodium hypochlorite was added to a sample of activated carbon-treated water at a water passage time of 200 hours in Example 1 so that the residual chlorine concentration was 5 mg / liter, and the mixture was kept at 20 ° C. for 2 days. When the trihalomethane concentration was measured after leaving it,
The concentration was 4 μg / liter, and the trihalomethane concentration was slightly increased. Comparative Example 3 Sodium hypochlorite was added to the sample of the air-aerated treated water of Example 1 having a water passage time of 200 hours so that the residual chlorine concentration was 5 mg / liter, and the mixture was allowed to stand at 20 ° C. for 2 days. When the concentration of trihalomethane was measured, it was 30μ
g / l and the trihalomethane concentration is 15 μg /
It was increasing by liter. Examples 2, 3 and Comparative Examples 2, 3
Comparing the results, the treated water that had been only subjected to air aeration treatment had an increased trihalomethane concentration when left to stand, and the tendency became more pronounced when chlorine was added. It can be seen that the treated water that has passed through the packed tower shows a slight increase in the trihalomethane concentration not only when it is left as it is but also when it is left with chlorine added.

[0012]

Industrial Applicability When water containing trihalomethane and residual chlorine is subjected to air aeration and then activated carbon treatment, activated carbon has a long life and is replaced less frequently. Further, the trihalomethane concentration of the treated water is stable and low, and the trihalomethane concentration does not increase much even when chlorine is added.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of an apparatus for carrying out the present invention.

[Explanation of symbols]

 1 Air aeration tower 2 Exhaust treatment tower 3 Activated carbon filling tower

Claims (1)

[Claims] 1. A water containing trihalomethane and residual chlorine, characterized in that water containing trihalomethane and residual chlorine is contacted with a gas to dissipate and remove most of the trihalomethane, and then the treated water is treated with activated carbon. Processing method.