JP2003088881A - Method and apparatus for treating sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for surely and stably removing the COD component of sewage by treating the sewage. SOLUTION: This sewage treating method comprises a step to prepare a bromine-based oxidizer by electrolyzing an aqueous solution of a bromine compound and a step to add the prepared bromine-based oxidizer to the dirty water having the COD component or the treated water of the sewage to remove the COD component. This sewage treating apparatus is provided with an electrolyzer for preparing the bromine-based oxidizer by electrolyzing the aqueous solution of the bromine compound and a bromine-based oxidizer adding unit for adding the bromine-based oxidizer prepared by the electrolyzer to the sewage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for removing COD components by treating sewage containing COD components or treated water thereof.

[0002]

2. Description of the Related Art In waste water such as sewage that is finally discharged into public water areas such as rivers and seas, it is necessary to remove COD components for environmental reasons. In the conventional sewage treatment method, the sewage is first subjected to biological treatment or coagulation-sedimentation treatment at low operating cost, and then COD components remaining in the obtained treated water are removed by activated carbon adsorption treatment or chemical oxidation treatment. Furthermore, recently, the COD total amount regulation has been established in closed sea areas such as Tokyo Bay,
To comply with this, low CO such as sewage treatment water
It is required to further remove the COD component from the waste water having D concentration to satisfy the regulation value.

Conventionally, as the oxidizing agent used for removing the COD component of wastewater, sodium hypochlorite, chlorine-based oxidizing agents such as chlorine, hydrogen peroxide and the like can be mentioned. These oxidizing agents are used alone, but for hydrogen peroxide, a chemical oxidation treatment in combination with a ferrous salt, so-called Fenton treatment, has been put to practical use.

[0004]

These conventional oxidizers do not completely disappear by reacting even when added to the object to be treated, but remain in the treated water, so that the residual oxidant is removed. Post-treatment must be done. In order to remove the residual oxidizing agent in the treated water, it is necessary to add a reducing agent to carry out reduction. Also, some of the chlorine-based oxidizers are powdery, but when using such powdery oxidizers, a device for dissolving the oxidizers is required and handling of the drug is a problem. there were. In addition, since the chlorine-based oxidizing agent first reacts with the ammoniacal nitrogen in the wastewater to produce chloramine, there is a problem that the effect of removing the COD component is reduced. Furthermore, when the treated water, which originally has a low COD concentration, is treated with an oxidant, C contained in the treated water is contained.
It is necessary to add an excess of oxidizing agent to the OD component,
As a result, a large amount of the oxidant remains in the treated water, which may adversely affect the environment at the discharge destination.

Therefore, it is an object of the present invention to provide a method and an apparatus capable of treating sewage containing a COD component to remove the COD component reliably and stably.

[0006]

In order to achieve the above object, the present invention prepares a bromine-based oxidizing agent by electrolyzing an aqueous solution of a bromine compound,
A method for treating sewage, which comprises removing COD components in addition to sewage containing D component or its treated water.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below, but the present invention is not limited thereto. COD (chemical oxygen demand) is the oxygen consumption by potassium permanganate (COD _Mn ) at 100 ° C. described by JIS-K0102 factory drainage test method, and oxygen by alkaline potassium permanganate. It is a value measured by either the amount of consumption (COD _OH ) or the amount of oxygen consumption by potassium dichromate (COD _Cr ).

The sewage that can be treated by the present invention includes various industrial effluents, human waste, landfill landfill leachate, dehydrated filtrate, liquid waste, and sewage discharged from general households and businesses, and sewage. Includes mixed sewage (rainwater sewage), rainwater, groundwater, etc. In addition, the treated water of the sewage refers to the above-described various sewage coagulation-sedimentation treated water, pressurized floating treatment water, activated carbon adsorption treated water, chemical oxidation treated water, various membrane separation treated water, and the like. Further, various industrial wastewater, human waste, septic tank sludge, and other liquid wastes can be treated by applying the present invention.

The treated water from which the COD component has been removed, which has been treated according to the present invention, may be discharged as it is, or may be used as recycled water in the manufacturing process or the like. The present invention is characterized in that an aqueous solution of a bromine compound is electrolyzed by an electrolytic device to prepare a bromine-based oxidant. The main component of the bromine-based oxidizing agent prepared by this method is a bromine compound, but it contains an oxidizing substance related to halogen generated during electrolysis due to impurities in the bromine compound as a raw material or impurities from dissolved water. You can leave. Examples of the halogen compound other than bromine, which may be contained in the oxidizing agent according to the present invention, include hypochlorous acid, hypochlorite, hypochlorite ion, hypoiodic acid, hypoiodite, hypochlorite. Examples thereof include iodate ion. In addition, a chlorine-based oxidizing agent of the present invention may be used for the chlorine-based oxidizing agent such as hypochlorous acid, hypochlorite ion, or hypochlorite, which is obtained by electrolyzing a chlorine compound such as sodium chloride or seawater. It can also be included in the agent. These chlorine-based oxidants are inferior to the bromine-based oxidant according to the present invention in terms of reactivity, but by using the chlorine-based oxidant together, the oxidative effect of the bromine-based oxidant according to the present invention can be obtained. It can be increased. Note that chlorine, hypochlorous acid, hypochlorite, and the like are generated from the chlorine compound by electrolysis, but these chlorine-based oxides do not adversely affect the effect of the oxidizing agent according to the present invention.

The electrolysis conditions for preparing the bromine-based oxidant according to the present invention are preferably a voltage of 5 to 20 V, a current density of 1 to 5 A / dm ² , and an electrode interval of 5 to 20 mm. Examples of the electrode material that can be used for electrolysis include carbon and platinum. Further, in the present invention, the electrolysis conditions can be arbitrarily changed depending on the electrolysis temperature, the concentration of the electrolytic solution, the size of the electrolyzer, and the like. By changing the electrolysis conditions in this way, the concentration of the brominated oxidant prepared can be controlled. Therefore, in the present invention, the addition ratio of the bromine-based oxidizer to the wastewater is extremely easily and simply changed by appropriately changing the operating conditions of the electrolyzer, that is, the voltage and current density and the electrolyte concentration of the electrolyzer. -It can be adjusted quickly, and it is possible to immediately respond to changes in the water quality of treated wastewater and changes in the amount of water.

In the present invention, as the bromine compound which can be subjected to electrolysis for the preparation of the bromine-based oxidizing agent, sodium bromide, potassium bromide, magnesium bromide, ammonium bromide, hydrogen bromide water, etc. Water-soluble bromine compounds can be used. Also, a waste liquid containing a bromine compound can be used as a bromine compound for the preparation of the bromine-based oxidizing agent in the present invention.

In the present invention, the electrolytic solution to be electrolyzed for the preparation of the bromine-based oxidizing agent may contain a bromine compound as a main component and a chlorine compound, sodium chloride or the like. Chlorine compounds produce chlorine, hypochlorous acid, and hypochlorite salts by electrolysis, but the chlorine-based compounds thus produced also have an adverse effect on the effect of the bromine-based oxidizing agent according to the present invention. Not something to give. this is,
This is because the bromine-based oxidizing agent according to the present invention is also produced by the reaction of unreacted bromine compound with chlorine, hypochlorous acid, or hypochlorite. In this case, there is no limitation on the mixing ratio of the bromine compound and the chlorine compound in the electrolytic solution.

In the present invention, the concentration of the bromine compound in the aqueous bromine compound solution that is subjected to electrolysis to prepare the bromine-based oxidizing agent is preferably about 1 to 20% by weight in terms of bromine equivalent. When the bromine conversion concentration in the aqueous solution is 1% by weight or less, the electrolytic treatment efficiency decreases, the concentration of the obtained bromine-based oxidizing agent decreases, and the necessary addition amount of the oxidizing agent increases in the decomposition treatment of the COD component. Conversely, the bromine equivalent concentration is 2
If it is 0% by weight or more, scale trouble may occur inside the electrolysis apparatus.

The pH of the aqueous bromine compound solution to be electrolyzed is preferably 8 or less, and if necessary, it is preferable to adjust the pH with a mineral acid such as sulfuric acid. In the present invention, the bromine-based oxidizing agent obtained by electrolysis of an aqueous solution of a bromine compound contains hypobromite, hypobromite ion, and hypobromite as oxidizing active ingredients.

The addition rate of the bromine-based oxidizing agent thus prepared is preferably 1 to 100 mg / L in terms of chlorine with respect to the amount of wastewater to be treated or treated wastewater. If the addition rate is 1 mg / L or less, the effect of removing COD components is low and 100%
If it is more than mg / L, the chemical cost becomes a problem, and the possibility that the bromine-based oxidizing agent remains in the treated water increases, and it is necessary to add a reducing agent to reduce and remove the residual oxidizing agent.

In the present invention, when the bromine-based oxidizer prepared by electrolyzing an aqueous solution of a bromine compound is mixed with sewage or treated water thereof, the prepared liquid bromine-based oxidizer is
Mixing and stirring can be carried out by the flow of waste water or its treated water. It is also possible to dilute the bromine-based oxidizer with a part of the treated water, industrial water, and sewage, and then add this to the sewage.

In a preferred embodiment of the present invention, it is preferable that an aqueous solution of a bromine compound is electrolyzed at an on-site (situ) of sewage treatment to prepare a bromine-based oxidizing agent, which is used immediately. Brominated oxidizer prepared by electrolysis is
Since the oxidation effect is highest in the initial stage of formation, it is preferable to prepare it at the place of use. In the method according to a preferred embodiment of the present invention, the brominated oxidant prepared by electrolysis is
In general, it is preferable to add the sewage or its treated water within 120 minutes, more preferably within 30 minutes, and further preferably within 5 minutes after preparation.

As described above, according to the present invention, a bromine-based oxidizing agent prepared by electrolysis of a bromine compound is used as CO
The COD component in the wastewater can be decomposed by adding it to the wastewater containing the D component or its treated water.

Further, the sewage water to which the bromine-based oxidant has been added according to the present invention or the treated water thereof can be further contacted with activated carbon to further purify the sewage water. That is, another embodiment of the present invention relates to a method for treating sewage, which comprises adding a bromine-based oxidizing agent prepared by electrolysis of a bromine compound to sewage or its treated water and then contacting it with activated carbon. In such a treatment method, the main function of activated carbon is not removal of COD components by adsorption, but C
The purpose is to accelerate the reaction between the OD component and the brominated oxidant and to remove the residual oxidant by adsorption.

The activated carbon used in the method according to another aspect of the present invention may be in the form of powder, particles or crushed form. Preferably, the activated carbon tower filled with activated carbon having a particle size of 0.1 to 10 mm is brought into contact with sewage containing a brominated oxidant. The water flow rate at the time of water flow to the activated carbon tower is preferably ¹ to 40 h ^-1 as a space velocity SV. Water flow rate is 1h
^If it is less than ^-1 , the required activated carbon tower becomes too large, and if it exceeds 40 h ^-1 , the contact time becomes short, so that the COD component removing effect and the residual oxidant removing effect decrease.

The present invention further provides an apparatus for carrying out the method for treating sewage or treated water thereof as described above. That is, another aspect of the present invention is to add an electrolyzer for electrolyzing an aqueous solution of a bromine compound to prepare a bromine-based oxidizer, and to add the bromine-based oxidizer prepared in the electrolyzer to sewage. And a bromine-based oxidizer addition device for the treatment of sewage.

FIG. 1 shows the concept of the sewage treatment apparatus according to the present invention. The sewage treatment apparatus according to the present invention is an electrolyzer for receiving an aqueous solution of a bromine compound and subjecting it to electrolysis, and a bromine-based oxidant addition apparatus for adding a bromine-based oxidant prepared by the electrolyzer into wastewater. And. The bromine-based oxidizer and wastewater are mixed in a mixing tank, and the bromine-based oxidizer and CO
The reaction with the D component is carried out. Also, as shown in FIG.
If necessary, an activated carbon tower can be installed in the latter stage of the mixing tank.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 In the sewage treatment apparatus shown in FIG. 1, a vessel having a capacity of about 0.5 m ³ was used as a mixing tank, and an activated carbon tower was not arranged,
A small-scale sewage secondary treated water sample was treated. Table 1 shows the properties of the small-scale sewage secondary treated water sample to be treated.

[0025]

[Table 1]

As the bromine-based oxidizer, commercially available sodium hypochlorite, an aqueous solution of sodium hypochlorite containing 10% by weight of available chlorine, is added with sodium bromide in the same amount as sodium hypochlorite and reacted. The prepared hypobromous acid (prepared hypobromous acid) and the bromine-based oxidizing agent (electrolytic bromine-based oxidizing agent) prepared by electrolysis according to the present invention were used. As the electrolytic bromine-based oxidizing agent, an aqueous solution of 10% by weight of sodium bromide was used as an electrolytic solution, and the electrolytic temperature was 25 ° C, the voltage was 10 V, and the current density was 2 A.
/ dm ² , and the distance between the carbon electrodes was set to 5 mm, and the electrolysis reaction was performed.

The sewage sample is added to the mixing tank of the treatment device at 0.5 to 0.5%.
It was continuously supplied at 5 m ³ / hour, and the above-mentioned various oxidizing agents were added to the mixing tank in the proportions shown in Table 2. The chemical concentration of each oxidant added was 8% in terms of chlorine. The electrolytic bromine-based oxidizer is
Addition to the mixing tank within 2 minutes after preparation by electrolysis. The COD concentration (COD _Mn ) of the outlet water of the mixing tank and the concentration of the residual oxidant were measured. The oxidant addition rate and the residual oxidant concentration are chlorine conversion values obtained by the iodometric titration method described in JIS-K0102. The results are shown in Table 2.

[0028]

[Table 2]

From the results shown in Table 2, when the bromine-based oxidizing agent prepared by electrolytic treatment of the bromine compound according to the present invention was used, it was compared with commercially available sodium hypochlorite and prepared hypobromous acid prepared by chemical reaction. It can be seen that the COD component removal efficiency is high.

Example 2 In the sewage treatment apparatus shown in FIG. 1, an sewage treatment test was conducted in the same manner as in Example 1 except that an activated carbon tower filled with 0.5 m ³ of activated carbon having a particle size of about 1 mm was arranged. Dirty water sample to the mixing tank
It was supplied at a flow rate of 10 m ³ / hour, and then water was passed upward from the mixing tank at the same flow rate to the activated carbon tower at SV = 2 to 20 h ⁻¹ .
The COD concentration and the residual oxidant concentration of the outlet water of the activated carbon tower were measured. The results are shown in Table 3.

[0031]

[Table 3]

From the results shown in Table 3, when a bromine-based oxidizing agent prepared by electrolytic treatment of a bromine compound according to the present invention was used and further activated carbon tower treatment was carried out, it was prepared by commercially available sodium hypochlorite or a chemical reaction. It can be seen that the COD component can be effectively removed and the residual oxidant of the treated water can be reduced as compared with the prepared hypobromite.

[0033]

According to the method of the present invention, the following effects can be obtained. (1) The COD component of sewage or its treated water can be efficiently removed, and the treatment performance of the COD component can be stabilized.

(2) By preparing an oxidizer by electrolyzing it at the site of wastewater treatment, it is possible to avoid a large amount of storage of dangerous chemicals, and the operation management is easy. (3) The raw material of the bromine-based oxidizing agent according to the present invention is, for example, sodium bromide, which is stable and does not change its properties even after long-term storage. Therefore, the bromine-based oxidizing agent according to the present invention,
Since stable raw materials can be used to produce and use only the required amount by electrolysis when needed, it can be used with conventional oxidizers that deteriorate during storage such as sodium hypochlorite. In comparison, stable sewage treatment is possible.

(4) The amount of residual oxidant in the treated water is small, the environment at the discharge destination can be preserved, and there is no trouble such as corrosion at the time of reuse. (5) The bromine-based oxidant addition rate can be easily adjusted by changing the operating conditions of the electrolyzer, and can respond to fluctuations in the water quality and quantity of the wastewater to be treated.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a configuration of a sewage treatment apparatus according to one aspect of the present invention.

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Claims (5)

[Claims] 1. An aqueous solution of a bromine compound is electrolyzed to prepare a bromine-based oxidant, and the prepared bromine-based oxidant is treated with COD.
A method for treating sewage, which comprises removing COD components in addition to sewage containing components or treated water thereof. 2. The method for treating sewage according to claim 1, wherein the bromine compound is selected from sodium bromide, potassium bromide, magnesium bromide, ammonium bromide, and hydrogen bromide water. 3. The treatment of sewage according to claim 1 or 2, wherein the electrolysis of the aqueous bromine compound solution is carried out at the sewage treatment site to rapidly add the prepared brominated oxidant to the sewage. Method. 4. The method for treating sewage according to any one of claims 1 to 3, wherein the bromine-based oxidizing agent is added to sewage or its treated water and then contacted with activated carbon. 5. An electrolyzer for preparing a bromine-based oxidizer by electrolyzing an aqueous solution of a bromine compound, and a bromine-based oxidizer for adding the bromine-based oxidizer prepared in the electrolyzer to wastewater. A treatment device for sewage, comprising an agent addition device.