JPH09314182A - Treatment process for selenium containing drain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the good removing efficiency even when a hexavalent selenium compound is contained in drain and treat simply selenium containing drain by adding reducing bacteria in the selenium containing drain and reducing, adding a flocculant and/or a chelate agent into the drain and sedimentation separating a selenium content. SOLUTION: Selenium containing drain is introduced into a reduction tank 12, and the drain reduced in the reduction tank 12 is introduced into a flocculation reaction tank 14, and also introduced into a sedimentation separation tank 16 to flocculation separate a selenium compound. Thus even when a sexivalent selenium compound is contained, the removing efficiency is demonstrated in a good manner. The reason why the efficient removal of selenium can be carried out as above-mentioned is that the reduction of hexavalent selenium into tetravalent selenium becomes easier, which is considered to be difficult heretofore. A conventional flocculation separation tank can be utilized simply for the removing process.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating selenium-containing wastewater containing at least a hexavalent selenium compound.

[0002]

BACKGROUND ART Industrially, selenium is a useful element having a wide range of uses such as rectifiers, solar cells, photoconductors for copying machines, red pigments, catalysts, and glass colorants because of its unique electrical characteristics. is there.

On the other hand, regarding health effects, selenium is considered to be an essential element as a nutrient, and it has been suggested that it has a protective action against certain cancers. But,
Ingestion of excessive selenium for a long time causes dermatitis, central nervous system and gastrointestinal disorders. In addition, selenium has been suspected of being carcinogenic. ("Inorganic treatment technology for US provisional first-class drinking water regulation-selenium removal-", 28th
See page, Journal name: “Water” May 1981, Author: Yoshio Adachi, Publisher: Monthly “Water” publisher) Therefore, even in Japan, following the American Public Health Association standards, 1994 February A part of the Enforcement Ordinance of the Water Pollution Control Law was revised in March, and selenium (allowable limit 0.1 mg / L) was added to the new item as a wastewater standard substance.

Therefore, there is a need for a simple method for removing selenium compounds from industrial wastewater.

In water, selenium is selenous acid (SeO ₃
^2- ) (Tetravalent selenium compound) or Selenate (SeO
₄ ^2- ) (hexavalent selenium compound) exists in only two forms, and both are acidic. Both forms of selenium are stable and are unlikely to undergo redox. The difference of this existence form is
It is believed that the selenium mineral dissolves in water at a pH and in a redox atmosphere. It is estimated that the form of existence in industrial wastewater varies depending on the source.

[0006] As a simple method for treating selenium-containing wastewater, there is, for example, a method for removing selenium by a flocculation method using a flocculant containing ferric sulfate (Publication No. 31 above).
(See page 1st tier). Although a method using an ion exchange resin can be considered, the ion exchange resin is generally expensive,
Moreover, it is not suitable for mass processing.

[0007]

However, in the above-mentioned conventional coagulation treatment method, the removal rate is as high as 80% for tetravalent selenium compounds, but the removal rate is 10% for hexavalent selenium compounds. % (See the above-mentioned publication page 31 column 1).

Therefore, it is conceivable to add a reducing agent to the selenium-containing wastewater to reduce the hexavalent selenium compound.

However, the present inventors have found that the removal efficiency is not good even if the reduction / aggregation treatment is performed with a general-purpose reducing agent such as ferrous sulfate, ferrous chloride, sodium bisulfite and sodium sulfite. .

In view of the above, it is an object of the present invention to provide a method for treating selenium-containing wastewater which has a good removal efficiency even if it contains a hexavalent selenium compound and is simple in removal method.

[0011]

The method for treating selenium-containing wastewater according to the present invention solves the above problems by the following constitution.

[0012] A method for treating selenium-containing wastewater containing at least a hexavalent selenium compound, which comprises a reducing treatment step performed by adding reducing bacteria to the selenium-containing wastewater, and a coagulant and / or a chelating agent in the wastewater. And an aggregating treatment step of adding and precipitating and separating the selenium component.

[0013]

[Detailed Description of Means] Next, each component of the above means will be described in detail.

(1) Specific examples of the reducing bacteria used in the present invention include Nitrobacter and the like.

The amount of the reducing bacteria added varies depending on the strength and type of the reducing bacteria. For example, in the case of Nitrobacter, it is 40 to 160 L (preferably 60 to 100 L) per 1 m ^{3 of} waste water.

If the amount added is less than 40 L / m ³ , the amount of reducing bacteria is too small to reduce hexavalent selenium sufficiently, and if it exceeds 160 L / m ³ , the reduction action is further increased. It is useless because we cannot expect much.

The flocculant used in the present invention includes aluminum sulfate, polyaluminum chloride, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, magnesium sulfate, magnesium chloride, sodium hydrogen sulfite. , Sodium sulfite, and the like, and one or more of them can be selected from these. Those containing ferric chloride are particularly desirable.

Examples of the chelating agent used in the present invention include polymeric heavy metal scavengers having a chelate forming group such as —NH—CS ₂ Na and —SNa.
Specifically, "Epofloc L-1" (made by Miyoshi Yushi)
And the like.

When a mixture of a coagulant and a chelating agent is used, the mixing ratio of coagulant / chelating agent is 5 / 2-
5/1 (desirably 3/1 to 4/1).

The coagulant and / or chelating agent is added in an amount of 50 to 800 with respect to the total amount of selenium contained in the wastewater.
Double the amount (preferably 200 to 600 times the amount).

When the amount added is less than 50 times, the selenium cannot be sufficiently aggregated / precipitated, and when it exceeds 800 times, the selenium is excessively added and further aggregation and precipitation of the selenium compound is expected. It is useless because it cannot be done.

(2) The method for treating selenium-containing wastewater of the present invention is specifically carried out as follows (see FIG. 1).

First, selenium-containing wastewater is introduced into the reduction tank 12, and the wastewater that has undergone the reduction treatment in the reduction tank 12 is introduced into the coagulation reaction tank 14 and further into the precipitation separation tank 16 to remove the selenium compound. Perform aggregation and separation processing.

The reduction tank 12 is divided into three chambers, a nitrification chamber 18, a denitrification chamber 20, and an oxidation chamber 22, and it is presumed that the hexavalent selenium compound is mainly reduced in the denitrification chamber 20. It

[0025]

The method for treating selenium-containing wastewater of the present invention comprises:
As described above, a method for treating selenium-containing wastewater containing at least a hexavalent selenium compound, the reduction treatment step being carried out by adding reducing bacteria to the selenium-containing wastewater, and a coagulant and / or a chelating agent in the wastewater. And a coagulation treatment step in which the selenium component is coagulated and separated, and a constitution characterized by including the following effects.

The selenium-containing wastewater treatment method of the present invention has good removal efficiency even when it contains a hexavalent selenium compound, and the removal method is the same as that of the conventional coagulation / separation tank, as supported by the examples described later. Can be used and is simple. The reason why efficient removal of selenium is possible is that reduction of hexavalent selenium to tetravalent selenium, which has been difficult in the past, is facilitated by reducing bacteria.

[0027]

EXAMPLE An example (actual machine test shown in FIG. 1) carried out to confirm the effect of the present invention will be described below.

<Example 1> In FIG. 1, selenium-containing wastewater containing 0.19 mg / L of selenium in the reducing tank 12
(Nitrobacter addition amount: 80 L / m ³ ) and after reduction treatment (treatment time: 2 hours), the waste water was treated with the flocculation reaction tank 14 (flocculant addition amount: aluminum sulfate / ferric chloride (mixing ratio). 2/1) mixture (100 mg / L) and subjected to a flocculation reaction treatment (treatment time: about 10 minutes), and further introduced into a precipitation separation tank 16 to perform a precipitation separation treatment (treatment time: about 1 minute).
Time).

At this time, the total amount of selenium and the amount of hexavalent selenium and tetravalent selenium in the wastewater at the inlet and outlet of the reduction tank and the outlet of the precipitation separation tank were measured. From Table 1 showing the results, although the content ratio of hexavalent selenium in the waste water is high (hexavalent selenium / tetravalent selenium = 2/15) in this example, the selenium removal efficiency is high as a whole. It turns out that it is as high as about 80%.

[0030]

[Table 1]

<Example 2> In Example 1, the selenium-containing wastewater having a total selenium content of 0.23 mg / L was used, and 80 L / m ^{3 of} nitrobacter was added to the coagulation reaction tank. Waste water treatment was performed in the same manner except that diiron (coagulant) 60 mg / L and chelating agent: "Epofloc L-1" 20 mg / L were added.

The results measured in the same manner as in Example 1 are shown in Table 2.
Although the content of hexavalent selenium in the wastewater is high (hexavalent selenium / tetravalent selenium = 9/1) in this example, the selenium removal efficiency is as high as about 75% as a whole. I understand.

[0033]

[Table 2]

[Brief description of drawings]

FIG. 1 Sewage treatment equipment containing selenium used in the present invention

[Explanation of symbols]

 12 reduction tank 14 aggregation reaction tank 16 precipitation separation tank 18 nitrification chamber 20 denitrification chamber 22 oxidation chamber

Claims (6)

[Claims] 1. A method for treating selenium-containing wastewater containing at least a hexavalent selenium compound, wherein a reduction treatment step is performed by adding bacteria having a reducing action (hereinafter referred to as “reducing bacteria”) to the selenium-containing wastewater. A coagulation treatment step of coagulating and separating a selenium component by adding a coagulant and / or a chelating agent to the wastewater, and a method for treating selenium-containing wastewater. 2. The method for treating selenium-containing wastewater according to claim 1, wherein the reducing bacterium is Nitrobacter. 3. The method for treating selenium-containing wastewater according to claim 2, wherein the amount of nitrobacter added to the wastewater is 40 to 160 L / m ³ . 4. The selenium according to claim 3, wherein the coagulant contains ferric chloride, and the amount of the ferric chloride added as a coagulant is 40 to 150 mg / L. Treatment method of contained wastewater. 5. The method for treating selenium-containing wastewater according to claim 1, wherein the coagulant contains ferric chloride. 6. The selenium according to claim 2, wherein the coagulant contains ferric chloride, and the amount of the ferric chloride added as a coagulant is 40 to 150 mg / L. Treatment method of contained wastewater.