JPH11128982A - Treatment of selenium-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely remove both selenic acid ion and selenious acid ion by making the amt. of org. substances as a hydrogen donor to an optimum value when a selenium-contg. waste water contg. nitric acid nitrogen and/or nitrous acid nitrogen (NOx-N) is treated by anaerobic biologicaltreatment under a facultative anaerobic condition. SOLUTION: An anaerobic biotreatment is performed under a condition where at least 2-fold by wt.org. substances to the concn. of NOx-N in water to be treated exist as BOD when the concn. of NOx-N in the water to be treated is at least 5-fold by wt. of soluble selenium. For example, the concn. of NOx-N in raw water 2 is measured by a nitrogen concn. measuring means 9 and, based on this concn. of NOx-N, the amt. of addition of the org. substances to the raw water flowing in a raw water introducing pipe 8 from an org. substance addition mechanism 10 is controlled in such a way that the anaerobic biologicaltreatment is performed under a condition where at least 2-fold by wt.org. substances to the concn. of NOx-N in the raw water exist as BOD in a biologicaltreatment reaction tank 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a metal smelter
Regarding the method of treating wastewater containing selenium, such as glass factory wastewater, thermal power plant wastewater, mine wastewater, etc.
A selenium-containing wastewater containing nitrate nitrogen and / or nitrite nitrogen is subjected to biological treatment under anaerobic conditions under reduced anaerobic conditions, so that soluble selenium in the selenium-containing wastewater is reduced to single selenium to insolubilize and remove.

[0002]

2. Description of the Related Art In selenium-containing wastewater, selenium is usually selenate ion (SeO ₄ ^2- : hexavalent selenium) and / or
Alternatively, it is dissolved in the form of selenite ion (SeO ₃ ^2- : tetravalent selenium). In addition, these ions may be present alone in the wastewater, but usually, both of them are often present.

[0003] Conventionally, as a method for removing selenate ions and selenite ions (hereinafter sometimes referred to as soluble selenium) contained in selenium-containing wastewater, the following physicochemical treatment methods and the following biological methods are used. Chemical treatment methods are known. A method of adsorbing and removing soluble selenium contained in selenium-containing wastewater using an adsorbent made of resin or the like. A method of adding a metal salt such as a magnesium salt, a zinc salt, and a ferric salt to waste water containing selenium to separate and remove selenium as an insoluble selenium compound with the metal salt. Soluble selenium in selenium-containing wastewater as simple selenium (Se)
A method of adding a reducible ferrous salt to the solution to insolubilize the soluble selenium, and separating and removing the resulting insoluble material by precipitation or the like. After the soluble selenium contained in the selenium-containing wastewater is reduced to insoluble simple selenium by anaerobic biological treatment under aerobic anaerobic conditions, the simple selenium is adsorbed by microorganisms and separated with the microorganisms. A method of separating and removing itself by sedimentation or the like. In this method, it is considered that the selenite ion is once reduced to selenite ion and then reduced to simple selenium, and the selenite ion is directly reduced to simple selenium.

[0004]

However, the above-mentioned methods (1) to (4) have the following problems. That is, in the adsorption method, the quality of the treatment is easily affected by the coexisting substance, and the treatment of the soluble selenium contained in the waste liquid for regeneration of the adsorbent is problematic.

In the chemical treatment method, an insoluble selenium compound is relatively easily generated from tetravalent selenite ions, but an insoluble selenium compound is hardly generated from hexavalent selenite ions. Of selenate ion remained in the treated water, and as a result, it was difficult to remove the total selenium concentration to 0.1 mg Se / l or less, which is the wastewater standard value.

[0006] In the chemical treatment method, it is possible to remove both selenate ions and selenite ions, but this method requires a considerably large amount of ferrous salt, and after solid-liquid separation. Since a large amount of insoluble matter (sludge) is generated, it is disadvantageous in terms of running costs and waste disposal costs.

In the biological treatment method, both selenate ions and selenite ions can be reduced to simple selenium and removed. In this case, in the biological treatment method, anaerobic biological treatment is performed in the presence of an organic substance as a hydrogen donor. Further, in the actual apparatus for carrying out this method, the organic matter is removed from the water to be treated or the biological treatment reaction tank so that the organic matter necessary for reducing all the soluble selenium contained in the treated water is present. It must be added to the tank water.

On the other hand, in some selenium-containing wastewater, soluble selenium and nitrate nitrogen (NO ₃ ⁻ ) and / or nitrite nitrogen (NO ₂ ⁻ ) coexist (hereinafter referred to as “selenium-containing waste water”). Nitrate nitrogen and / or nitrite nitrogen may be abbreviated as NO _x -N). In anaerobic biological treatment of selenium-containing wastewater containing such NO _x -N is, since the reduction (denitrification) of NO _x -N together with a reducing biological solubility selenium, organic matter is consumed for denitrification You. In addition, NO _x -N tends to be preferentially reduced over soluble selenium,
O _x -N and solubility theory or more organic material needed to reduce all of the selenium is required.

[0009] However, conventionally, in the case of processing by anaerobic biological treatment selenium-containing wastewater containing NO _x -N, for organic matter of optimal conditions as a hydrogen donor, sufficient study has not been made. Therefore, regarding the amount of the organic substance to be added to the water to be treated or the water in the biological treatment reaction tank in the actual apparatus for performing the biological treatment, the optimal addition amount and the optimal control method were not known. Therefore, N
In anaerobic biological treatment of selenium-containing wastewater containing O _x -N is
There was a shortage of organic matter for the reduction of soluble selenium, and soluble selenium remained in the treated water.

The present invention has been made in view of the above circumstances, and makes the amount of organic matter as a hydrogen donor an optimum value when selenium-containing wastewater containing NO _x -N is treated by anaerobic biological treatment. Accordingly, it is an object of the present invention to provide a method for treating selenium-containing wastewater in which both selenite ions and selenite ions can be reliably removed.

[0011]

Means for Solving the Problems The present inventors, in order to achieve the above object, firstly, organic amount required to reduce all soluble selenium in selenium-containing wastewater containing no NO _x -N Was examined, and as a result, the organic matter
When the anaerobic biological treatment is performed under the condition that the concentration of the soluble selenium in the water to be treated is 6 to 9 times by weight as the (biochemical oxygen demand), a large amount of organic matter does not remain in the treated water, It has been found that both selenite ions and selenite ions can be reliably removed.

Further, the present inventor studied the amount of organic substances necessary for reducing all of the soluble selenium in the selenium-containing wastewater containing NO _x -N, and as a result, the NO _x- When the N concentration is 5 times or more the soluble selenium concentration in the water to be treated, the anaerobic biological treatment is performed under the condition that the organic substance is present as the BOD at 2 times or more the NO _x -N concentration in the water to be treated. It has been found that by doing so, both selenite ions and selenite ions can be reliably removed. This will be described in detail below.

[0013] In other words, when considered in the NO _x -N alone,
Organic amount required for the reduction of NO _x -N is a 2 to 2.5 times by weight of NO _x -N concentration as BOD. When selenium alone is considered, the amount of organic substances required for the reduction of soluble selenium is BO
D is 6 to 9 times the weight of the soluble selenium concentration. Therefore, the concentration [N] (mgN / l) BOD value of the amount of organic matter required for the reduction of NO _x -N of [N-BOD] (mg
O / l) and the BOD value of the organic matter necessary for the reduction of soluble selenium at the concentration [Se] (mgSe / l) [Se-
BOD] (mgO / l) is represented by the following formula (1),
It is represented by (2). Further, BOD value of the amount of organic matter required for the reduction of NO _x -N and solubility selenium in selenium-containing wastewater containing _{NO x -N [T-BOD]} (mgO / l) is
It is represented by the following equation (3). [N-BOD] = [N] × 2 to 2.5 (1) [Se-BOD] = [Se] × 6 to 9 (2) [T-BOD] = [N-BOD] + [Se -BOD] ... (3)

Considering the case where the ratio between the NO _x -N concentration and the soluble selenium concentration in the selenium-containing wastewater is different, first, both [N] and [Se] are 1 mg / sec.
l When the time of (1 times by weight of NO _x -N concentration is soluble selenium concentration) of the equation (1) ~ (3), [N-BOD] = 2~2.5mgO / l [Se-BOD ] = 6 to 9 mgO / l [T-BOD] = 8 to 11.5 mgO / l, the range of [T-BOD] is considerably different from the range of [N-BOD].

Next, when [N] is 10 mg / l and [Se] is 1 mg / l (NO _x -N concentration is 10 times by weight of soluble selenium concentration), [N-BOD] = 20 Since ２５25 mgO / l [Se-BOD] = 6 to 9 mgO / l [T-BOD] = 26 to 34 mgO / l, the range of [T-BOD] is very close to the range of [N-BOD].

Further, [N] is 100 mg / l, [S]
When [e] is 1 mg / l (NO _x -N concentration is 100 times the soluble selenium concentration), [N-BOD] = 200 to 250 mg O / l [Se-BOD] = 6 to 9 mg O / l Since [T-BOD] = 206 to 259 mgO / l, the range of [T-BOD] almost overlaps with the range of [N-BOD]. That is, as [N] becomes larger than [Se], [N-BOD] and [T-BO]
D].

It can be seen from the above that [NO _x -N concentration /
When the value of [soluble selenium concentration] is small, NO _x -N
From the concentration and the soluble selenium concentration, NO _x was calculated according to equation (3).
It is necessary to calculate the amount of organic substances necessary for the reduction of -N and soluble selenium. However, when the value of [NO _x -N concentration / soluble selenium concentration] increases, the value obtained by equation (1) and the equation (1) Since the values obtained by 3) are close to or overlap with each other, it is possible to calculate the amount of organic substances necessary for the reduction of NO _x -N and soluble selenium from equation (1) only from the NO _x -N concentration. It means that the BOD value of the organic substance amount is always at least 2 times the weight of the NO _x -N concentration.

[0018] The present inventors have, NO _x -N concentration in the water to be treated is 5 times the weight or more soluble selenium concentrations that include the results, the NO _x -N performing various experiments based on the consideration as described above When the anaerobic biological treatment is performed under the condition that the organic substance is present as BOD at least 2 times the NO _x -N concentration in the water to be treated,
In the case of the water to be treated that can reliably remove both selenate ions and selenite ions, and therefore, in the case of the water to be treated that satisfies the above-mentioned conditions, the water to be treated or the biological treatment reactor is based on the NO _x -N concentration in the water to be treated. It has been found that the amount of organic matter added to the water in the tank can be controlled, and the present invention has been accomplished.

Accordingly, the present invention provides a method for producing nitrate nitrogen and / or
Alternatively, when the selenium-containing wastewater containing nitrite nitrogen is subjected to biological treatment under aerobic anaerobic conditions and the soluble selenium in the selenium-containing wastewater is reduced to elemental selenium and removed, nitrate nitrogen and nitrous acid in the water to be treated are removed. When the total concentration of nitrate nitrogen is at least 5 times the soluble selenium concentration in the water to be treated, the organic matter is at least 2 times the weight of the total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated as BOD. The present invention provides a method for treating selenium-containing wastewater (first invention), wherein the anaerobic biological treatment is performed under existing conditions.

Further, the present invention provides a method for reducing the amount of soluble selenium in selenium-containing wastewater to elemental selenium by subjecting selenium-containing wastewater containing nitrate nitrogen and / or nitrite nitrogen to biological treatment under anaerobic conditions. The total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated is at least 5 times the weight of the soluble selenium in the water to be treated. A method for treating selenium-containing wastewater (second invention), characterized in that the amount of organic matter added to the water to be treated or the water in the biological treatment reaction tank is controlled based on the total concentration of nitrogen.

Hereinafter, the present invention will be described in more detail. In the first and second inventions, anaerobic biological treatment of the water to be treated that satisfies predetermined conditions is performed. The condition is that the water to be treated contains soluble selenium and NO _x -N, and the NO _x -N concentration is at least 5 times, preferably at least 10 times the weight of the soluble selenium concentration.

In the first invention, the anaerobic biological treatment is performed under the condition that a predetermined amount of organic matter is present. Examples of the organic substance include alcohols such as methanol, organic acids such as acetic acid, and saccharides such as glucose. Organic matter conditions, NO _x -N in the water to be treated organic matter as BOD
2 times or more by weight of the concentration, preferably 2 to 5 times by weight, that is, the value A obtained by the following formula is 2 or more,
It is preferably 2 to 5. A = b / c b: BOD value of organic substance (mgO
/ L) c: NO _x -N concentration in the water to be treated (mgN / l) If the value A is less than 2, it is difficult to remove both selenite ions and selenite ions reliably, and
If it is larger, a large amount of organic substances may remain in the treated water. A more preferred range of the value A is 2-3.

In this case, when the amount of organic substances originally meeting the above conditions is contained in the water to be treated, it is not necessary to add the organic substances to the water to be treated or the water in the biological treatment reaction tank. However, when the amount of organic matter that meets the above conditions is not contained in the water to be treated, the organic matter is added to the water to be treated or the water in the biological treatment reaction tank as in the second invention.
As a result, it is possible to constantly perform good operation in the actual device. In this case, examples of the organic substance to be added include the aforementioned alcohols such as methanol, organic acids such as acetic acid, and saccharides such as glucose. Further, wastewater containing organic matter may be added. However, particularly preferred as an organic substance to be added is methanol in terms of cost and the like.

[0024] In the second invention, as can be seen from the above description, organic matter in the water to be treated as BOD NO _x -
2 times by weight or more of N concentration, preferably 2 to 5 times by weight,
More preferably, the amount of the organic substance added to the water to be treated or the water in the biological treatment reaction tank is preferably controlled so that the anaerobic biological treatment is performed under the condition of 2 to 3 times by weight.

In the second aspect of the invention, the amount of the organic substance added is controlled based on the NO _x -N concentration in the water to be treated. That is, in the second invention, it is possible to easily control the amount of added organic substance only by detecting the NO _x -N concentration in the water to be treated. Examples of the method for detecting the NO _x -N concentration in the water to be treated include an electrode method, a colorimetric method, and ion chromatography.

The type of biological treatment that can be used in the present invention is not limited. For example, a fixed-bed biological treatment, a fluidized-bed biological treatment, a floating biological treatment, a sludge blanket biological treatment, or the like is employed. can do. It is also possible to perform multistage processing by combining two or more methods of the same type or different types. In addition, when the floating type biological treatment method is adopted, it is general to set up a sedimentation tank at the latter stage of the biological treatment reaction tank and to extract sludge therefrom. It may be performed from the inside of the reaction tank by air backwashing, water backwashing or the like. Further, if necessary, an aerobic biological treatment reaction tank may be provided at the final position of the biological treatment, and organic substances remaining in the treatment water of the anaerobic biological treatment reaction tank may be removed by oxidation of organic substances.

[0027]

FIG. 1 is a flow chart showing an example of a wastewater treatment apparatus used for carrying out the method of the present invention. In the figure, 2 is a raw water tank, 4 is a raw water circulation pipe connected to the raw water tank 2, 6 is a floating biological treatment reactor for performing anaerobic biological treatment, and 8 is raw water from the raw water tank 2 to the biological treatment reactor 6. Raw water introduction pipe to be introduced,
9 is a nitrogen measuring means for measuring NO _x -N concentration in raw water,
Reference numeral 10 denotes an organic substance addition mechanism for adding organic substances to raw water flowing through the raw water introduction pipe 8, reference numeral 12 denotes a stirring device for the biological treatment reaction tank 6,
4 is a sedimentation tank, 16 is a treated water transfer pipe for transferring biologically treated water from the biological treatment reaction tank 6 to the sedimentation tank 14, 18 is a purified water discharge pipe for discharging supernatant water from the sedimentation tank 14, and 20 is a sedimentation tank 14. A sludge return pipe for returning a part of the settled sludge 22 to the biological treatment reaction tank 6, and an excess sludge discharge pipe 24 for discharging the remaining sludge 22.

Using this apparatus, raw water, that is, NO _x -N
Hints and if NO _x -N concentration is performing 5 times by weight or more is processed in selenium-containing wastewater soluble selenium concentration, introducing raw water from the raw water tank 2 in the biological treatment reactor 6, in the biological treatment reactor 6 It performs anaerobic biological treatment. In this apparatus, the NO _x -N concentration in the raw water is measured by the nitrogen measuring means 9, and based on the NO _x -N concentration, the organic matter is converted into BOD in the raw water in the biological treatment reaction tank 6 based on the NO _x -N concentration.
O as anaerobic biological treatment under the conditions present more than 2 times by weight of the _x -N concentration is carried out to control the amount of organic matter to the raw water flowing through the raw water inlet pipe 8 from organic adding mechanism 10. As a result, both selenite ions and selenite ions in the treated water can be reliably removed. The precipitated selenium precipitates together with the sludge 22 in the sedimentation tank 14, and the supernatant water from which selenium has been removed is discharged from the purified water discharge pipe 18. This elemental selenium may be separated and collected from sludge at an appropriate place as needed. The supernatant water discharged from the purified water discharge pipe 18 is filtered using a membrane filter using a membrane such as an ultrafiltration membrane (UF membrane) or a microfiltration membrane (MF membrane) or a sand filter. Alternatively, a configuration may be adopted in which simple selenium remaining in a trace amount in the supernatant water is removed.

[0029]

EXAMPLES The following experiments were conducted to confirm the effects of the present invention. [Experiment 1] Anaerobic biological treatment was performed by continuously flowing synthetic wastewater in which the following components were dissolved in tap water at the following concentrations into an upward sludge blanket type biological treatment reaction tank. Methanol as hydrogen donor started at 50 mg / l (about 40 mg O / l as BOD) and was gradually increased. In the following composition, ammonium chloride and potassium dihydrogen phosphate are microbial nutrients. Sodium selenate 10 mg Se / l Sodium nitrate 10 mg N / l Ammonium chloride 1 mg N / l Potassium dihydrogen phosphate 0.2 mg P / l Methanol 50 mg CH ₃ OH / l (B
Starting from about 40 mg O / l as OD) and gradually increasing

About one month after the start of water passage at a methanol concentration of 50 mg / l, the treatment reached a steady state, but selenite ions were almost completely removed, but one selenite ion was contained in the treated water.
２2 mg Se / l remained. This is probably because selenite ions generated by reduction of selenite ions remained. Thereafter, when gradually increasing the methanol concentration in the synthesis waste water, in 80mgO / l methanol concentration as BOD (8 times by weight of NO _x -N concentration in the raw water as BOD), selenate ions, selenite ions Was 0.1 mgSe / l or less, and this favorable state was always maintained at a methanol concentration higher than 0.1 mgSe / l.

According to the above formulas (1) to (3), [N-BOD] = 20 to 25 mgO / l [Se-BOD] = 60 to 90 mgO / l [T-BOD] = 80 to 115 mgO / l . Therefore, by this experiment, NO _x −
When the N concentration was 1 time by weight of the soluble selenium concentration, the value obtained by equation (3) was the necessary amount of organic matter, and it was found that the amount of organic matter could not be controlled by the value obtained by equation (1).

[Experiment 2] An experiment similar to Experiment 1 was performed except that the concentration of sodium nitrate in the synthetic wastewater was set to 100 mgN / l. As a result, the methanol concentration became 250 mg O / l as BOD (2.5% of the NO _x -N concentration in the raw water).
When the amount of methanol exceeded 0.1% by weight, the selenate ion and selenite ion both became 0.1 mg Se / l or less, and this favorable state was always maintained at a methanol concentration higher than 0.1 mg Se / l.

According to the above formulas (1) to (3), [N-BOD] = 200 to 250 mgO / l [Se-BOD] = 60 to 90 mgO / l [T-BOD] = 260 to 340 mgO / l The theoretical [T-BOD] value obtained from the equation (3) is 260 mgO / l or more, but actually 250 mgO / l.
At / l, the treatment was good. Therefore, according to this experiment, the NO _x -N concentration in the raw water was 10% of the soluble selenium concentration.
When the weight is multiplied, the range of [T-BOD] is [N-BOD].
D], it was found that the amount of organic matter can be controlled by the value obtained by equation (1).

[Experiment 3] The same experiment as in Experiment 1 was performed except that the concentration of sodium nitrate in the synthetic wastewater was 1000 mgN / l. As a result, the methanol concentration was 2000 mg O / l as BOD (2 times the NO _x -N concentration in the raw water).
When the amount of methanol exceeded 0.1% by weight, the selenate ion and selenite ion both became 0.1 mg Se / l or less, and this favorable state was always maintained at a methanol concentration higher than 0.1 mg Se / l.

According to the above formulas (1) to (3), [N-BOD] = 2000 to 2500 mgO / l [Se-BOD] = 60 to 90 mgO / l [T-BOD] = 2060 to 2590 mgO / l . Therefore, by this experiment, NO _x −
When the N concentration is 100 times the weight of the soluble selenium concentration,
Since the range of [T-BOD] and the range of [N-BOD] overlap, it was found that the amount of organic matter can be controlled by the value obtained by the equation (1).

From the above experiments 1 to 3, it was found that N in raw water
When the concentration of O _x -N is 10 times or more the concentration of soluble selenium, the amount of organic matter is determined by the value obtained by the formula (1) [N-BOD] = [N] × 2 to 2.5 (1) Although it has been clarified that control is possible, in the present invention, the amount of the organic substance may be set to an amount exceeding 2.5 times by weight the NO _x -N concentration in the raw water. For example, when the NO _x -N concentration in the raw water of 5 times the weight of soluble selenium concentration, organic matter content may be about 3 to 4 times by weight of NO _x -N concentration in the raw water.

[0037]

As described above, according to the first invention, the case where selenium-containing wastewater containing nitrate nitrogen and / or nitrite nitrogen is treated by anaerobic biological treatment under aerobic anaerobic conditions In addition, by setting the amount of the organic substance as the hydrogen donor to an optimum value, it is possible to reliably remove both selenite ions and selenite ions. Also,
According to the second invention, the amount of organic matter added to the water to be treated or the water in the biological treatment reaction tank is easily controlled based on the concentration of nitrate nitrogen and / or nitrite nitrogen in the water to be treated. be able to.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a wastewater treatment apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

 2 Raw water tank 6 Floating biological treatment reaction tank 8 Raw water introduction pipe 9 Nitrogen measuring means 10 Organic substance addition mechanism

Claims (3)

[Claims] 1. The method according to claim 1, wherein the selenium-containing wastewater containing nitrate nitrogen and / or nitrite nitrogen is subjected to biological treatment under a permeating anaerobic condition to reduce soluble selenium in the selenium-containing wastewater to single selenium and to remove the same. The total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated is 5% of the concentration of soluble selenium in the water to be treated.
The anaerobic biological treatment is carried out under the condition that the organic substance is present as BOD at a weight concentration of 2 times or more the total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated when the amount is at least twice the weight. How to treat wastewater containing selenium. 2. The method according to claim 1, wherein the selenium-containing wastewater containing nitrate nitrogen and / or nitrite nitrogen is subjected to biological treatment under anaerobic conditions under reduced anaerobic conditions to reduce soluble selenium in the selenium-containing wastewater to elemental selenium. The total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated is 5% of the concentration of soluble selenium in the water to be treated.
When the weight is more than twice the weight, the amount of organic substances added to the water to be treated or the water in the biological treatment reaction tank is controlled based on the total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated. Of selenium-containing wastewater. 3. A method for treating anaerobic organisms such that an anaerobic biological treatment is carried out under conditions in which organic substances are present as BOD in an amount of at least 2 times the total concentration of nitrate nitrogen and nitrite nitrogen in the water to be treated. 3. The method for treating selenium-containing wastewater according to claim 2, wherein the amount of the organic substance added to the water in the treatment reaction tank is controlled.