JPH10225694A - Method of highly purifying organic matter containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower TOC of organic matter containing water to substantially highly purify the water. SOLUTION: Waste water is fed to an ejector 2 from a pipe 5, and also gaseous ozone is sucked from a pipe 7, and furthermore, the waste water is adjusted to within a range of pH 9.5-10.5 by a chemical such as sodium hydroxide from a chemical injection device 1 and is sent to an ozone reaction tank 3 to oxidize organic matter by ozone and is sent to a biological treatment tank 4 to treat it by a microorganism bed formed in a packed tank 42 therein, and TOC is lowered to purify the water. By making pH within the above range, ozone effectively acts on organic matter having low biological decomposability to accelerate its decomposition, and biological treatment effect is heightened and a TOC lowering rate is enlarged to highly purify water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying various kinds of wastewater containing organic substances, and more particularly to purification of water mainly containing water and organic substances having low decomposability by microorganisms after ordinary biological treatment. Used effectively for

[0002]

2. Description of the Related Art Conventionally, various methods employing biological treatment using microorganisms have been employed for purifying wastewater containing high concentrations of organic substances. However, in such biological treatments, organic substances of a type that cannot be treated by microorganisms or require a particularly long treatment time are discharged without treatment. On the other hand, the index of the water purification capacity of the biological treatment device is B
It is not impossible to purify wastewater to lower the BOD to about 1 ppm by using OD and maintaining operating conditions under which the function of the apparatus is sufficiently exhibited.

[0003] However, even with such treated water, the BOD value does not include organic dirt components which are difficult to treat by microorganisms. In most cases, 10
About 50 ppm of dirt remains. If such water is discharged into rivers or the sea, it causes environmental deterioration. In addition, since the water is too dirty, its use for reuse is extremely limited.

As a method for purifying water after biological treatment to a higher degree, there is, for example, an activated carbon adsorption method. However, since the adsorption capacity of activated carbon is limited, frequent replacement of activated carbon and treatment of activated carbon after use are expensive. Costly. Further, systems in which ozone, ultraviolet rays, and other oxidizing agents are combined have been proposed, but all have a problem that the operation cost is high and the practicability is low.

[0005] As a treatment method combining biological treatment and ozone treatment, raw water is treated by an ozone reaction tower and put into a biological treatment tower, and most of the water passing therethrough is returned to the ozone reaction tower while a part of the water is returned. As a method for extracting water as treated water, a method of adjusting the pH of an ozone reaction tower to 7 to 9 has been proposed (see Japanese Patent Application Laid-Open No. 5-277475).
However, in this method, in the embodiment, the ozone injection rate calculated from the ozone gas concentration, the ozone gas flow rate, and the liquid flow rate is 160 mg / liter (ppm), and a large amount of ozone is consumed. Therefore, in this method, there is a problem that the size of the ozone generator is increased, the power consumption is increased, and the equipment cost and the operating cost are increased as described above.

[0006] This method is characterized by continuous processing by return, and setting the pH value to 7 to 9 merely limits ordinary operations.
That is, when the wastewater is particularly acidic or alkaline, for example, when the wastewater has a pH of 5 or 10, a chemical is added to adjust the pH to 7 to 9, which is a usual wastewater treatment method. It is well known that in ozone treatment, the pH is preferably made alkaline in order to generate OH radicals having strong oxidizing power by ozone. On the other hand, when the carbon dioxide gas is dissolved in the waste water and the pH is high, OH radicals are consumed by CO ₃ ions, so that it is common knowledge that the pH is 9 or less.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a practical method for highly purifying organic substance-containing water with low facility and operation costs.

[0008]

In order to solve the above-mentioned problems, the present invention provides a method for highly purifying organic-containing water, which comprises subjecting the organic-containing water to an ozone oxidation treatment at a pH in the range of 9.5 to 10.5, followed by a biological treatment. Processing.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an apparatus capable of carrying out the method for highly purifying organic-containing water of the present invention. This device is
A chemical liquid injector 1, an ejector 2, an ozone reaction tank 3, and a biological treatment tank 4, which are disposed in the order of the flow direction of the wastewater that is organic substance-containing water. It is composed of an inlet pipe 7, connecting pipes 8, 9, a drain outlet pipe 10, an ozone gas discharge pipe 11, an air supply pipe 12, and the like.

The liquid injector 1 is provided with a metering pump 1a capable of supplying a pH adjusting agent such as caustic soda or caustic stored therein. The drainage inlet pipe 5 is connected to a drainage tank or a drainage line (not shown). Although not shown, the ozone gas inlet pipe 7 is connected to, for example, an electrolytic ozone generator that generates high-concentration ozone gas using a solid polymer film. However, another ozone gas generator using silent discharge or the like may be used. The ejector 2 sucks ozone gas using the drainage as driving water. The ozone reactor 3 is 1
It is desirable that the ozone gas be capable of discharging a surplus of ozone gas with a capacity that allows a residence time of at least one minute.

The biological treatment tank 4 includes, for example, a cylindrical tower 41,
It is composed of a filling layer 42, an air lift tube 43, a perforated plate 44 for supporting the filling layer, and the like. In the filling layer 42, a porous ceramic sintered body having a diameter of about 8 mm to 12 mm is filled. This sintered body has high strength and is chemically stable and has a very large contact area with water, so that it is suitable for a carrier of microorganisms. However, other suitable materials and shapes can be used.

With the above apparatus, the method for highly purifying organic-containing water of the present invention is carried out as follows. First,
The wastewater is oxidized with ozone in a pH range of 9.5 to 10.5. Therefore, ozone gas is sucked by the ejector 2 and dissolved in the drainage, and the metering pump of the chemical liquid injector 1 is controlled so that the pH of the drainage is in the range of 9.5 to 10.5. 1a is adjusted to supply a chemical solution. The ozone injection rate is set at about 40% of the TOC of the wastewater. The reaction time in the ozone reactor 3 is about several minutes.

Next, the wastewater oxidized with ozone is introduced into the biological treatment tank 4 and treated therein. When the biological treatment tank 4 is new, a small amount of a sintered body in which microorganisms have already been propagated is charged into the packed bed 42, and a medium component used for culturing microorganisms is appropriately charged, and the wastewater is discharged to a depth of 2 to 2. Circulate for 4 weeks. In this way, a microbial membrane is sufficiently developed on the surface of another new sintered body, and the microbial membrane is previously made ready for microbial treatment. Then, as shown in FIG. 1, the drainage is collected in the tank, air is blown from the air supply pipe 12 into the air lift pipe 43 to supply oxygen into the drainage, and the drainage as indicated by an arrow in the filling layer 42. A circulation flow is formed. This process is performed until the TOC decreases by a certain amount, for example, about 25%, or until the biological treatment reaction stops progressing and the rate of decrease in TOC with respect to time decreases.
Effluent after treatment is discarded, reused, or recirculated.

According to the above-mentioned waste water treatment, as will be apparent from the embodiments described later, the T o
The reduction rate of OC can be increased. Then, by reducing the TOC in this way, it is possible to substantially remove water stains. In addition, by repeating the batch processing and the continuous processing a plurality of times, it becomes possible to purify the wastewater to a maximum degree. It is presumed that these effects are based on the following effects of the method of the present invention.

Organic substances which are hardly decomposed by microorganisms have 10 carbon atoms.
Although they are relatively high-molecular substances of about 50, they are partially converted into carboxylic acid groups by ozone oxidation.
In this case, the pH is higher than the normal value of about 7 to 9.
By setting the ratio to 5 to 10.5, it is presumed that the carboxylic acid groups generated at various places are dissociated and ionized. As a result, an electric repulsion is generated between each of the organic substances, and the organic substances reach an extended configuration in the aqueous solvent. Therefore, when ozone is injected, the probability of contact between ozone and an organic substance increases, so that ozone oxidation is promoted, and the amount of carboxylic acid groups generated increases relative to the amount of ozone.

On the other hand, in the metabolism of microorganisms during biological treatment of organic matter, for example, when the organic matter is glucose, the organic acid is converted into organic acid once, such as carbon dioxide and water via pyruvic acid. It is considered important in decomposing. Therefore, if a large amount of carboxylic acid is formed by ozone, the decomposition of organic substances by microorganisms is promoted. As a result, even if the amount of ozone to be injected is reduced, the organic matter is effectively removed, and the TOC can be reduced and the wastewater can be highly purified.

In addition, when a large amount of dissolved ozone remains in the biological treatment after the ozone treatment, the microbial membrane developed on the ceramic sintered body is destroyed, the treatment capacity is greatly reduced, and the TOC is increased. Results. In this case, according to the present invention, the ozone is effectively consumed for the generation of the carboxylic acid group as described above, and thus the residual dissolved ozone is reduced. Also, by increasing the pH to 9.5 to 10.5, hydroxyl ions act as a catalyst, and ozone is rapidly increased at a rate 3 to 5 times faster than the conventional case of pH 7 to 9. Can self-decompose. As a result, the biological treatment tank can be maintained in a good state with a large treatment effect, and the treatment time with ozone can be shortened.

Examples and Comparative Examples: In Examples and Comparative Examples, the apparatus as shown in FIG.
Experiments on the treatment of various types of organic-containing water were conducted. In the experimental apparatus, the height of the packed layer 43 of the porous ceramic sintered body was set to 64 cm by using the tower 41 of the biological treatment apparatus 4 having a diameter of 10 cm. The ozone-treated wastewater was collected in a biological treatment device and subjected to batch treatment therein. In addition, it is easy to perform continuous processing by changing the dimensions of the filling tank.

The following Tables 1 and 2 show the measurement results of Examples and Comparative Examples, respectively.

[Table 1]

[Table 2] As shown in the table, in the example and the comparative example, the ozone injection rate was set to be approximately the same as the TOC of the water to be treated, and the pHs after the biological treatment of the water to be treated were 9.4 to 9.6 and 5 respectively. .
The range is 4 to 8.7. In this experiment, the pH at the time of oxidizing ozone was not directly measured, but the pH in the biological treatment tank 4 was reduced by about 0.5.
Is 9.9 to 10.1, which is within the pH range of the present invention, and 5.9, which is outside the range, in the Examples and Comparative Examples, respectively.
９9.2. In addition, although this pH is a value adjusted by the chemical liquid injector 1 in the example, it is a value that is not particularly adjusted in the comparative example.

According to this example and the comparative example, the TOC reduction rate of the example and the comparative example was 1 in the beer factory wastewater, the PVA-added artificial wastewater, and the combined treated water, respectively.
8.8-37.3% and 3.3-6.3%, 32.1
And 9.7%, and 20.0-25.3% and 2.
8%. Therefore, the biodegradability of organic substances can be increased by 3 to 10 times by applying the present invention at an alkaline pH as described above, compared with the conventional neutral or weak alkaline treatment up to about pH 9. Can be greatly improved.

The method of the present invention is also effective for a chemical substance having almost no biodegradability such as PVA, and a TOC reduction rate about three times as large as that of the conventional method was obtained. Further, according to the treatment of the present invention, even if the TOC of the water to be treated is small, the large reduction rate can be maintained, so that water which has already been biologically treated by an ordinary method or an organic substance having low biodegradability is used. It is also effective for water containing a large amount of. As a result, it is possible to realize advanced purification of water, which is difficult with the conventional method.

In the examples and comparative examples, TO
The reason why C is slightly different is that the TOC cannot be made completely the same even if the same raw water is used as the sample water, due to the repetition of ozone oxidation and biological treatment and the difference in the number of days elapsed after the treatment.

The ozone injection rate of the embodiment is determined by
The amount is as small as 25% to 46% (about 38% on average) with respect to C. And the TOC reduction rate is 18.8%
高 い 37.3% (25.7% on average). In order to compare the ozone injection rate of the example of the present invention with that of the prior art example, it is assumed from the results of the example of the present invention that the TOC reduction rate is 25% when the ozone injection rate is 40%, and 65 ppm. If the raw water is treated to 17 ppm by multiple batch treatments, the process would follow roughly as follows:

Number of treatments Ozone injection amount ppm TOC ppm after treatment 126 49 2 20 38 3 15 29 4 12 22 5 9 17 Total ozone amount Total 82 ppm

Therefore, according to the method of the present invention, the ozone injection amount can be reduced by half as compared with the prior art method in which the amount of injected ozone is 160 ppm. As a result, even if an expensive ozone generator is reduced in size, power consumption is reduced, and an increase in the amount of chemicals due to an increase in pH is taken into consideration, equipment costs and operation costs can be significantly reduced. Note that the reason why the TOC 65 of the raw water is 17 after the treatment in the conventional technique is that the treated water of the biological treatment tower is continuously treated while being returned to the ozone treatment tower in a large amount.

[0026]

As described above, according to the present invention, water containing organic matter is subjected to ozone oxidation treatment in a range of pH 9.5 to 10.5, which is beyond the common knowledge of the prior art, and then biologically treated.
Ozone can be effectively contacted and reacted with organic substances that are relatively high in molecular weight and are not easily decomposed by microorganisms, and these can be oxidized with ozone to increase the amount of organic acids and promote the effect of decomposition and treatment by microorganisms. . As a result, the TOC can be significantly reduced for the amount of ozone to be injected, and water can be truly purified. Further, it is possible to reduce the power consumption by reducing the size of the ozone generator, reduce equipment costs and operating costs, and significantly reduce the cost of treating organic-containing water.

Further, by setting the pH value as described above, ozone is effectively consumed for the production of organic acid, the residual amount of dissolved ozone is reduced, and the hydroxide ion acts as a catalyst. Ozone is rapidly self-decomposed at a rate several times that of a normal pH value, so that there is no adverse effect on microorganisms due to residual ozone in the biological treatment tank, and this can be maintained in a good state with a large treatment effect. .

According to the present invention, since the organic matter which is hardly decomposable by microorganisms can be treated, even when the water to be treated is purified to some extent and the TOC becomes small, the rate of decrease can be maintained at a large value. . As a result, the organic substance-containing water can be purified to an extremely high level by a plurality of continuous or batch treatments.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an apparatus capable of carrying out the method for highly purifying organic-containing water of the present invention.

[Explanation of symbols]

 Reference Signs List 1 Chemical injection device (for pH adjustment) 2 Ejector (for ozone oxidation) 3 Ozone reaction tank (for ozone oxidation) 4 Biological treatment tank (for biological treatment)

Claims (1)

[Claims] 1. An organic substance-containing water having a pH of 9.5 to 10.5.
A method for highly purifying water containing organic substances, which comprises subjecting an organic matter-containing water to an ozone oxidation treatment in the range described above, followed by biological treatment.