JPH0824913B2 - Method and apparatus for reduction treatment of wastewater containing oxidant - 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 treating wastewater containing an oxidizing agent, and more particularly to a method and apparatus for treating wastewater containing an oxidizing agent with a reducing agent so that the agent can be efficiently controlled. .

[0002]

2. Description of the Prior Art Oxidizing agents such as chlorine and hydrogen peroxide are used as bleaching agent oxidizing agents and are discharged from various factories, business sites and the like. These oxidants are detected as COD,
There is concern that it may damage the organisms at the release destination. Therefore, it is necessary to remove the oxidizing agent in the wastewater, and it is usually reduced and removed by sulfite. The reduction treatment method using sulfite is a reliable treatment method with a high reaction rate. However, in the conventional method, the drug control is performed by ORP (oxidation-reduction potential), which requires not only an expensive ORP meter but also a small change in ORP when the oxidizer in the wastewater has a low concentration. Drug control by
In many cases it is practically impossible.

[0003]

The present invention is based on the above OR.
A method of treating wastewater containing an oxidant, which improves the drawbacks of chemical control by P, efficiently decomposes and removes the oxidant in wastewater, and can surely decompose and remove even a low-concentration oxidizer, and is inexpensive. An object is to provide a device.

[0004]

In order to solve the above-mentioned problems, in the present invention, instead of ORP, the dissolved oxygen concentration in wastewater (hereinafter referred to as DO) is measured with time, and the reducing agent is injected by the change. It controls. That is, the present invention provides a method for reducing treatment of wastewater containing an oxidizing agent, wherein dissolved oxygen is present in the wastewater at a concentration of 5 mg / l or more, the reducing agent is added to the wastewater, and dissolved oxygen in the wastewater is added. The change in the concentration is measured, and the addition of the reducing agent is stopped when the measured value of the dissolved oxygen concentration begins to decrease. Further, the present invention, in a reduction treatment apparatus for wastewater containing an oxidant, has DO adjustment means and a reaction treatment tank for adjusting DO in the wastewater to 5 mg / l or more, and the reaction treatment tank has DO. It has a measuring means and a reducing agent injecting means.

Oxidizing agents targeted by the present invention include hydrogen peroxide (hereinafter referred to as H ₂ O ₂ ), persulfate, perchlorate,
Examples include hypochlorite and chlorine (hereinafter referred to as residual chlorine). As the reducing agent used in the present invention, any known reducing agent can be applied, for example, ferrous salt, ascorbic acid,
Examples of the sulfite include bisulfite, and it is preferable to use bisulfite because it is inexpensive and does not significantly lower the pH of the treated water after the reduction treatment. The present invention uses 5 mg of DO in wastewater
The waste water having a DO of 5 mg / l or less is required to have a DO of 5 mg / l or more. Since the wastewater containing the reducing agent does not consume much DO, the DO can be easily increased to the saturated concentration.

As the DO supply means, any ordinary aeration apparatus can be applied, for example, an air diffusing tube, a perforated tube, an underwater aerator or a surface aeration apparatus can be applied, but a perforated tube system is preferable. In addition, if there is even a small amount of DO in the wastewater, D by natural aeration using the water level and head
It is possible to set O = 5 mg / l or more. In addition, for wastewater that originally contained 5 mg / l or more of DO, see D above.
No O enrichment step is required.

Next, an example of the present invention will be described with reference to FIG. 1, but the embodiment of the present invention is not limited to this. Wastewater 1
First, the state of DO is grasped by a DO meter (not shown) and, if necessary, it is introduced into a DO adjusting tank, for example, aeration tank 2, and the DO is diffused by permeation from a perforated pipe 3 arranged at the bottom of the aeration tank. It is adjusted to 5 mg / l or more, preferably near the saturated concentration in the waste liquid. When DO in the wastewater is 5 mg / l or more, the above steps may be omitted, and the aeration tank 2 is bypassed or air diffusion from the perforated pipe is stopped. Or always DO
If the waste water is 5 mg / l, it is not necessary to install the above equipment.

The waste liquid whose DO is adjusted to 5 mg / l or more is
Then, it is introduced into the reaction treatment tank 5. Here, the reducing agent is injected from the reducing agent storage tank 10 by the reducing agent injection pump 9 while the DO meter 8 measures the DO of the waste water. The oxidizing agent in the wastewater immediately reacts with the reducing agent and is removed. At this time, DO in the wastewater hardly changes. Thus, when the oxidizing agent in the waste water is consumed, the DO in the waste water is rapidly lowered by the excess reducing agent. A baffle plate 1 is provided near the exit of the reaction treatment tank 5.
2 is installed and the DO sensor 6 provided on the outflow side
Thus, at the time when this decrease in DO is detected, the oxidizing agent in the wastewater has been completely removed, so the reducing agent injection pump 9 is stopped according to the instruction from the DO meter 8. Since the excess reducing agent is also removed by DO in the waste water, it is possible to obtain treated water that does not have an oxidizing agent and a reducing agent originally contained therein.

As a result, the DO in the wastewater is usually reduced by the reduction tank 5.
It will be reduced by 2-3 mg / l. That is, for example, the waste water flowing into the reaction treatment tank 5 at DO = 8 mg / l is
When DO = 6 to 5 mg / l, the oxidizing agent in the water to be treated is completely removed and the treated water is discharged. As the DO meter 8 used in the present invention, one having a general indication adjusting function can be applied, and various arithmetic devices may be incorporated. Further, the apparatus of the present invention can be configured as a batch type or a continuous type, and the aeration step and the reduction treatment step can be performed in a single tank.

[0010]

The function of the present invention is to use H ₂ O _{2 as} an oxidizing agent and N as a reducing agent.
Description will be made taking aHSO ₃ as an example. The redox reaction in wastewater is understood by the following equation. H ₂ O ₂ + NaHSO ₃ → NaHSO ₄ + H ₂ O (1) O + NaHSO ₃ → NaHSO ₄ (2) When the oxidizers H ₂ O ₂ and DO are mixed in the wastewater, the formula (1) takes precedence, and H ₂ O ₂ reacts with NaHSO ₃ .
This is due to the strength of the oxidizing power, and O as DO
This is because the oxidizing power of (oxygen) is much weaker than that of the oxidizing agent H ₂ O ₂ . Therefore, the reaction proceeds until H ₂ O ₂ in the waste water is completely removed by the strong reducing agent NaHSO ₃ .

When the reaction of the formula (1) is completed, the excessively added NaHSO ₃ reacts with DO as shown in the formula (2) and is removed from the waste water. Therefore, the DO in the wastewater is reduced. Therefore, the time point of DO reduction can be used as a guide for the completion of processing. In order for the above reaction to proceed, DO must be present in the wastewater, and in order to remove excess reducing agent and obtain safe discharge water, DO of the inflowing wastewater is 5 mg / l or more, It is preferable that the concentration is close to the saturated concentration in the wastewater.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 Using the experimental apparatus shown in FIG. 1, artificial wastewater containing 10 mg / l of residual chlorine was reduced with NaHSO ₃ . As a DO meter, UC-12 of Central Science Co., Ltd. was used. The result is shown in FIG. When the amount of NaHSO ₃ injected was gradually increased and 13 mg / l of NaHSO ₃ was injected, the DO that had been showing a constant value up to that point was rapidly increased from 9 mg / l to 6 mg / l.
At the same time, the residual chlorine in the wastewater was 0 mg / l
Became. By measuring the DO in the waste water, it can be seen that the reducing agent injection control can be easily performed.

Comparative Example 1 Using the experimental apparatus of FIG. 1 and using an ORP meter instead of the DO meter, the same artificial wastewater as in Example 1 was treated with NaHSO.
Reduction treatment was performed at ₃ . The result is shown in FIG. Excess Na
Even when HSO ₃ was injected, no significant change was seen in the ORP value, which revealed that it was difficult to control the injection of the reducing agent by ORP.

Example 2 An artificial wastewater containing 10 mg / l H ₂ O ₂ was tested with the same experimental equipment as in Example 1. This artificial wastewater is DO9.1mg / l,
The ORP + 270 mV and the liquid temperature were 23 ° C. The result is shown in FIG. When slowly injected NaHSO ₃ until 40 mg / l, abrupt D near NaHSO ₃ injection amount 35 mg / l
There was a decrease in O. H in wastewater at DO 5.8 mg / l
_{The 2} O ₂ concentration was less than 1 mg / l. Like the second embodiment, it is possible to easily control the injection of the reducing agent in the DO.

Comparative Example 2 The artificial wastewater of Example 2 was tested with the experimental apparatus of Comparative Example 1.
The result is shown in FIG. NaHSO ₃ 5 in this artificial wastewater
Even if 0mg / l is added excessively, the ORP of wastewater is +
It was 230 mV. At this point, the H ₂ O ₂ in the wastewater is 1
It was below mg / l. As in the first embodiment, it is difficult to control the injection by ORP.

[0016]

According to the present invention, the DO of the wastewater containing the oxidant is
Since the injection of the reducing agent is controlled by measuring with time, it is possible to reliably and safely reduce and remove the oxidizing agent in a short time with a simple device and operation.

[Brief description of drawings]

FIG. 1 is a process diagram showing an apparatus for treating wastewater containing an oxidant according to the present invention.

FIG. 2 is a graph showing the treatment results depending on the amount of NaHSO ₃ injection of residual chlorine waste water.

FIG. 3 is a graph showing the treatment results of H ₂ O ₂ -containing wastewater depending on the amount of NaHSO ₃ injected.

[Explanation of symbols]

1: Water to be treated, 2: Aeration tank, 3: Perforated pipe, 4: Air supply pipe, 5: Reaction treatment tank, 6: DO sensor, 7: Stirrer,
8: DO meter, 9: reducing agent injection pump, 10: reducing agent storage tank, 11: treated water, 12: baffle plate

Claims (2)

[Claims] 1. A method for reducing waste water containing an oxidizing agent, wherein dissolved oxygen is present in the waste water at a concentration of 5 mg / l or more, the reducing agent is added to the waste water, and the dissolved oxygen in the waste water is added. A method for reducing treatment of wastewater containing an oxidant, which comprises measuring the change in concentration and stopping the addition of the reducing agent when the measured value of the dissolved oxygen concentration starts to decrease. 2. A reduction treatment device for wastewater containing an oxidant, comprising DO adjusting means and a reaction treatment tank for adjusting the dissolved oxygen concentration (DO) in the wastewater to 5 mg / l or more, and the reaction treatment An apparatus for reducing oxidant-containing wastewater, characterized in that the tank has DO measuring means and reducing agent injection means.