JP2021058828A - Selenium-containing water treatment method and selenium-containing water treatment device - Google Patents

Abstract

To provide a treatment method and a treatment device capable of efficiently reducing at least one of nitrate nitrogen, nitrite nitrogen, and selenate ion and selenite ion in the same reaction vessel while suppressing excessive addition of hydrogen donor in selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen.SOLUTION: A treatment device includes: a biological treatment tank 10; a nitrate nitrogen measuring device 20 as nitrate nitrogen measuring means for measuring a concentration of nitrate nitrogen in treated water or a reaction vessel; and a control device 14 as selenium concentration estimation means for estimating a selenium concentration in the treated water from the measured concentration of nitrate nitrogen. A selenium concentration in the treated water is estimated by measuring the concentration of nitrate nitrogen in the treated water or in the reaction vessel, and the amount of a hydrogen donor added to the selenium-containing water is adjusted based on the measured concentration of nitrate nitrogen.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and an apparatus for treating selenium-containing water, which removes at least one of selenium ion and selenite ion contained in selenium-containing water.

In selenium-containing water, selenium, typically selenate ion _(SeO ^{4 2-:} 6-valent selenium) or selenite ions: are dissolved in the form of _(SeO ^{3 2-} 4-valent selenium). In addition, these ions may exist alone in the selenium-containing water, but usually both of them coexist in many cases.

In addition to the conventional physicochemical treatment method, as a method for removing at least one of selenate ion and selenite ion contained in selenium-containing water (hereinafter, these may be referred to as "soluble selenium"). , Biological treatment methods have become known in recent years.

In the biological treatment method, among selenate ions and selenite ions, in the presence of selenate anaerobic conditions (conditions in which dissolved oxygen is substantially absent) and organic substances as hydrogen donors (for example, methanol). at least one bound oxygen (SeO ₄ ^2-of O, SeO ₃ ^2-of O) by microorganisms utilizing makes breathing, at least one of selenate ion and selenite ions to molecular selenium Reduce treatment. If the selenium-containing water contains organic matter, it can be utilized and the deficiency can be supplemented by external addition.

For example, Patent Document 1 describes a method in which a residence time is controlled to less than 12 hours so that selenium-containing water is brought into contact with biological sludge held in a porous fluid carrier under facultative anaerobic conditions and in the presence of organic matter. Is described, and when nitrate nitrogen or nitrite nitrogen is contained in the selenium-containing water, it is described that a denitrification tank is provided in front of the tank for performing the selenium treatment. However, in the method of Patent Document 1, the number of reaction tanks increases.

Further, in Patent Document 2, biological sludge containing denitrifying bacteria is utilized, and the redox potential (ORP) of the tank for selenium treatment is set to -50 mV or less, which is much stronger than denitrification. This describes a method for reducing selenate ion and selenate ion. As a method of lowering the redox potential to −50 mV or less, for example, it is said that by increasing the amount of the organic substance added, the redox potential is lowered and the anaerobic degree is increased. However, in the method of Patent Document 2, the amount of the organic substance added may be larger than the reaction equivalent.

In any of these methods, in the reduction treatment of selenium, oxygen (not molecular oxygen, but nitric acid, nitrite, carbohydrate, organic acid, sulfuric acid, etc.) contained in the form of oxygen that does not inhibit the reduction of the selenium compound becomes an oxidizing agent. It is said that only the mixture of (lubricated oxygen) can be tolerated.

Therefore, when nitrate nitrogen or nitrite nitrogen is contained in the selenium-containing water, the number of reaction tanks is increased, the amount of nitrate nitrogen or nitrite nitrogen mixed is limited, excessive addition of organic substances as hydrogen donors, etc. However, the applicability of the above method to selenium-containing water containing high concentrations of nitrate nitrogen and nitrite nitrogen has not been clarified. Furthermore, when the reduction treatment of selenium and the reduction treatment of nitric acid and nitrite are carried out in the same reaction tank, a hydrogen donor is required for both treatments, and if the hydrogen donor is insufficient, the treatment performance of both treatments deteriorates. Moreover, since selenium cannot be measured in real time, a method for detecting selenium is an issue.

JP 2015-024360 Japanese Unexamined Patent Publication No. 8-323391

An object of the present invention is to efficiently add nitrate nitrogen and nitrite in the same reaction vessel while suppressing excessive addition of a hydrogen donor in selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen. It is an object of the present invention to provide a treatment method and a treatment apparatus capable of reducing at least one of nitrogen, selenate ion and nitrite ion.

The present invention relates to selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen in the same reaction vessel in the presence of a hydrogen donor to the nitrate nitrogen and the nitrite nitrogen. In the biological reaction step in which at least one of them is reduced to nitrogen gas and at least one of selenate ion and selenite ion is reduced to molecular selenium, the concentration of nitrate nitrogen in the treated water or the reaction vessel is adjusted. This is a method for treating selenium-containing water, in which the selenium concentration in the treated water is estimated by measurement.

In the method for treating selenium-containing water, it is preferable to adjust the amount of the hydrogen donor added to the selenium-containing water based on the measured concentration of nitrate nitrogen.

In the method for treating selenium-containing water, the Se concentration in the selenium-containing water is preferably 2 mg / L or less, and the nitrate nitrogen concentration is preferably 150 mg / L or less.

In the method for treating selenium-containing water, it is preferable to add the hydrogen donor to the selenium-containing water so that the concentration of nitrate nitrogen in the treated water or the reaction vessel is 4 mg / L or less.

In the biological reaction step in the method for treating selenium-containing water, the biological sludge held on the porous fluidized carrier is brought into contact with the selenium-containing water, and the fluidized carrier is a hydrophilic polyvinyl alcohol carrier. preferable.

The present invention relates to selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen in the same reaction vessel in the presence of a hydrogen donor to the nitrate nitrogen and the nitrite nitrogen. Biological reaction means for reducing at least one of them to nitrogen gas and at least one of selenate ion and selenite ion to molecular selenium, and the concentration of nitrate nitrogen in the treated water or the reaction vessel. It is a selenium-containing water treatment apparatus including a nitrite nitrogen measuring means for measuring and a selenium concentration estimating means for estimating the selenium concentration in the treated water from the measured concentration of nitrite nitrogen.

It is preferable that the selenium-containing water treatment apparatus further includes a hydrogen donor addition amount adjusting means for adjusting the addition amount of the hydrogen donor to the selenium-containing water based on the measured concentration of nitrate nitrogen.

In the selenium-containing water treatment apparatus, the Se concentration in the selenium-containing water is preferably 2 mg / L or less, and the nitrate nitrogen concentration is preferably 150 mg / L or less.

In the selenium-containing water treatment apparatus, the hydrogen donor addition amount adjusting means supplies hydrogen to the selenium-containing water so that the concentration of nitrate nitrogen in the treated water or the reaction vessel is 4 mg / L or less. It is preferable to adjust to add the body.

In the selenium-containing water treatment apparatus, the biological reaction means brings the biological sludge held on the porous fluid carrier into contact with the selenium-containing water, and the fluid carrier is a hydrophilic polyvinyl alcohol carrier. Is preferable.

In the present invention, in selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen, nitrate nitrogen and nitrite nitrogen can be efficiently added in the same reaction vessel while suppressing excessive addition of hydrogen donors. And at least one of selenate ion and selenate ion can be reduced.

It is a schematic block diagram which shows an example of the selenium-containing water treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows another example of the selenium-containing water treatment apparatus which concerns on embodiment of this invention. 3 is a graph showing the relationship between the treated water nitrate ion concentration (mg-N / L) and the selenate ion concentration (mg-Se / L) in Examples 1 to 3 and Comparative Example 1.

Embodiments of the present invention will be described below. The present embodiment is an example of carrying out the present invention, and the present invention is not limited to the present embodiment.

An outline of an example of a selenium-containing water treatment apparatus according to an embodiment of the present invention is shown in FIG. 1, and its configuration will be described. Further, FIG. 2 shows another example of the selenium-containing water treatment apparatus according to the present embodiment. FIG. 2 shows an example of a processing device using a carrier.

The selenium-containing water treatment apparatus 1 shown in FIG. 1 is nitrated in the same reaction tank in the presence of a hydrogen donor with respect to selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen. Treatment with a biological treatment tank 10 as a biological reaction means for reducing at least one of nitrogen and nitrite nitrogen to nitrogen gas and at least one of selenate ion and selenite ion to molecular selenium. As a nitrite nitrogen measuring means for measuring the concentration of nitrite nitrogen in water or in a reaction vessel, as a nitrite nitrogen measuring device 20, and as a selenium concentration estimating means for estimating the selenium concentration in treated water from the measured concentration of nitrite nitrogen. , The control device 14.

In the selenium-containing water treatment device 1 of FIG. 1, a treated water pipe 22 is connected to the inlet of the biological treatment tank 10, and a treated water pipe 24 is connected to the outlet. In the biological treatment tank 10, a stirring device 18 is installed as a stirring means having a rotation driving means such as a motor and a stirring blade. Further, in the biological treatment tank 10, a nitrate nitrogen measuring device 20 is installed as a nitrate nitrogen measuring means, and a hydrogen donor storage tank 12 is connected as a hydrogen donor supplying means by a hydrogen donor pipe 26 via a pump 16. ing. The nitrate nitrogen measuring device 20 may be installed in the treated water pipe 24. The control device 14 may be connected to the nitrate nitrogen measuring device 20 and the pump 16 by an electrical connection means or the like.

The selenium-containing water treatment device 3 shown in FIG. 2 includes a biological treatment tank 10 filled with a porous carrier 30. A screen 28 is installed near the outlet inside the biological treatment tank 10 as an outflow suppressing means for suppressing the outflow of the carrier 30 from the outlet to the treated water pipe 24.

The method for treating selenium-containing water and the operations of the selenium-containing water treatment devices 1 and 3 according to the present embodiment will be described.

In the selenium-containing water treatment apparatus 1, selenium to be treated is water containing at least one of nitrate nitrogen and nitrite nitrogen and at least one of selenate ion and selenite ion (soluble selenium). The contained water is stored in the water tank to be treated as needed, and then supplied to the biological treatment tank 10 through the water pipe 22 to be treated. In the biological treatment tank 10, at least one of nitrate nitrogen and nitrite nitrogen is nitrogen gas due to biological sludge such as selenate-reducing bacteria in the presence of a hydrogen donor while the contents are being stirred by the stirring device 18. In addition, soluble selenium is reduced to insoluble molecular selenium (biological reaction step). When a predetermined amount of hydrogen donor is not contained in the selenium-containing water, the hydrogen donor is supplied from the hydrogen donor storage tank 12 to the biological treatment tank 10 through the hydrogen donor pipe 26 by the pump 16 (hydrogen donor supply). Process). The biologically treated biologically treated water is discharged as treated water through the treated water pipe 24. Here, the concentration of nitrate nitrogen in the treated water or the biological treatment tank 10 is measured by the nitrate nitrogen measuring device 20 (nitrate nitrogen measuring step), and selenium in the treated water is measured based on the measured concentration of nitrate nitrogen. The concentration is estimated (selenium concentration estimation step). The amount of the hydrogen donor added by the pump 16 may be adjusted based on the measured concentration of nitrate nitrogen (hydrogen donor addition amount adjusting step). Even if the control device 14 estimates the selenium concentration in the treated water based on the measured concentration of nitrate nitrogen and adjusts the amount of hydrogen donor added by the pump 16 based on the measured concentration of nitrate nitrogen. Good.

In the selenium-containing water treatment apparatus 3, selenium to be treated is water containing at least one of nitrate nitrogen and nitrite nitrogen and at least one of selenate ion and selenite ion (soluble selenium). The contained water is stored in the water tank to be treated as needed, and then supplied to the biological treatment tank 10 such as a fluidized bed type filled with the porous carrier 30 through the water pipe 22 to be treated. In the biological treatment tank 10, while the contents are being stirred by the stirring device 18, nitrate nitrogen and nitrate nitrogen and biological sludge such as selenate-reducing bacteria adhered to and retained on the porous carrier 30 in the presence of a hydrogen donor. At least one of the nitrite nitrogen is reduced to nitrogen gas and soluble selenium is reduced to insoluble molecular selenium (biological reaction step). When a predetermined amount of hydrogen donor is not contained in the selenium-containing water, the hydrogen donor is supplied from the hydrogen donor storage tank 12 to the biological treatment tank 10 through the hydrogen donor pipe 26 by the pump 16 (hydrogen donor supply). Process). The biologically treated biologically treated water is discharged as treated water through the treated water pipe 24. Here, the concentration of nitrate nitrogen in the treated water or the biological treatment tank 10 is measured by the nitrate nitrogen measuring device 20 (nitrate nitrogen measuring step), and selenium in the treated water is measured based on the measured concentration of nitrate nitrogen. The concentration is estimated (selenium concentration estimation step). The amount of the hydrogen donor added by the pump 16 may be adjusted based on the measured concentration of nitrate nitrogen (hydrogen donor addition amount adjusting step). Even if the control device 14 estimates the selenium concentration in the treated water based on the measured concentration of nitrate nitrogen and adjusts the amount of hydrogen donor added by the pump 16 based on the measured concentration of nitrate nitrogen. Good.

In the biological treatment tank 10, as shown in FIG. 2, the carrier 30 is charged into the biological treatment tank 10 and held on the carrier 30 on which the microorganisms flow, so that the contact efficiency between the water to be treated and the microorganisms becomes high. In addition to enabling high-load operation, sludge management becomes easier.

In the examples of the selenium-containing water treatment devices 1 and 3, the control device 14 is based on the selenium concentration estimation means for estimating the selenium concentration in the treated water from the measured concentration of nitrate nitrogen and the measured concentration of nitrate nitrogen. It functions as a hydrogen donor addition amount adjusting means for adjusting the addition amount of the hydrogen donor to the selenium-containing water.

According to the present embodiment, the present inventors efficiently nitrate in a selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen in the same reaction vessel while suppressing excessive addition of a hydrogen donor. It has been found that at least one of nitrogen, nitrite nitrogen, and selenate ion and selenite ion can be reduced. It was clarified that the excess or deficiency of the hydrogen donor could be judged from the residual concentration of nitrate nitrogen in the treated water, and that the residual concentration of nitrate nitrogen in the treated water was related to the treatment performance of selenium.

In the method for treating selenium-containing water according to the present embodiment, the soluble selenium in the selenium-containing water is reduced and rendered harmless by bringing the selenium-containing water into contact with biological sludge. At this time, ^{it is estimated that Se 6+} is reduced to at least one of Se ⁰ and Se ^{2- via Se 4+.}

In the above reaction, biological sludge is made into an electron acceptor by using bound oxygen contained in the form of selenate ion or selenate ion instead of molecular oxygen, and selenate ion or selenate ion is reduced. A hydrogen donor such as an organic substance is used as the substrate, and if it is contained in selenium-containing water, it can be used as it is, but if it is not contained in a predetermined amount, a hydrogen donor such as an organic substance such as methanol is separately added. May be good.

The selenium-containing water to be processed, at least one of a nitrate nitrogen and nitrite nitrogen, selenium ion _(SeO ^{4 2-:} 6-valent selenium) and selenite ion _(SeO ^{3 2-:} 4-valent Selenium) is a wastewater or other water containing at least one (soluble selenium). The selenium-containing water may contain a simple substance of selenium in addition to the soluble selenium.

Examples of selenium-containing water include metal smelting industrial wastewater, glass industrial wastewater, thermal power plant wastewater, mine wastewater, chemical industrial wastewater, and wastewater from coal, oil or combustion exhaust gas treatment processes. The selenium-containing water treatment method and treatment apparatus according to the present embodiment are particularly preferably applied to coal-fired power plant desulfurization wastewater. In addition to selenium compounds and sulfates, these selenium-containing waters may contain organic substances, nitrogen compounds and the like.

The concentration of selenium ion in the selenium-containing water is not particularly limited, but is, for example, in the range of 0.1 to 10 mg-Se / L, and the concentration of selenite ion is, for example, 0.1 to 10 mg-Se. It is in the range of / L, but is not limited to these ranges. In particular, it is preferably applied when treating selenium-containing water containing soluble selenium as total selenium at a concentration of, for example, 2 mg-Se / L or less, preferably 0.1 to 2 mg-Se / L.

The concentration of nitrite nitrogen and the concentration of nitrate nitrogen contained in the selenium-containing water are not particularly limited, but for example, the concentration of nitrate nitrogen is 150 mg-N / L or less, preferably in the range of 30 to 150 mg-N / L. More preferably, it is preferably applied when treating selenium-containing water contained in the range of 60 to 150 mg-N / L.

As the hydrogen donor, organic substances contained in the water to be treated can be used, but if there is a shortage, the hydrogen donor may be supplied from the outside. When the nitrite nitrogen concentration and the nitrate nitrogen concentration are relatively high, the hydrogen donor is often insufficient, so the hydrogen donor may be supplied from the outside.

Examples of the hydrogen donor supplied from the outside include alcohols such as methanol, ethanol and isopropyl alcohol, organic acids such as acetic acid, and organic substances such as hydrogen gas, acetone, glucose, ethylmethyl ketone and tetramethylammonium hydroxide (TMAH). However, the present invention is not limited to this, and all conventionally known hydrogen donors can be used. Methanol is preferable from the viewpoint of odor, handling, price and the like.

When the hydrogen donor is not contained in the selenium-containing water, the amount of the hydrogen donor added may be, for example, about 2.5 to 4 times the amount of nitrate nitrogen in the case of methanol, and is finally added. The amount of hydrogen donor added varies depending on the nitrate nitrogen in the treated water and the selenium concentration estimated from it.

It is preferable to adjust the amount of the hydrogen donor added to the selenium-containing water based on the measured concentration of nitrate nitrogen. For example, when the nitrate nitrogen rises, the amount of hydrogen donor added may be increased to decrease the selenium treatment concentration. For example, the hydrogen donor may be added to the selenium-containing water so that the concentration of nitrate nitrogen in the treated water or the biological treatment tank 10 is 4 mg / L or less. It is also possible to estimate the amount of hydrogen donor added to the selenium-containing water based on the concentration of nitrate nitrogen in the selenium-containing water, which is the water to be treated (raw water). However, the present inventors have found that the control of nitrate nitrogen in the reaction tank (biological treatment tank 10) is important. It is considered that this is because the hydrogen donor is not used for denitrification and selenium treatment and the amount of mere decomposition of organic matter (hydrogen donor) changes due to changes in the residence time and temperature in the reaction vessel. Therefore, it was considered more accurate and preferable to detect an increase in nitrate nitrogen concentration, that is, a shortage of hydrogen donors, by monitoring the nitrate nitrogen concentration in the reaction vessel. And it is important for selenium treatment to suppress the shortage of this hydrogen donor.

As the nitrate nitrogen measuring device 20, a nitrate ion electrode may be used, or the nitrate concentration may be estimated from the total nitrogen (TN) measured using a total nitrogen concentration (TN) meter. As the nitrate nitrogen measuring device 20, it is particularly preferable to use a nitrate ion electrode. Since the nitrate ion electrode can measure the concentration in real time, it can quickly respond to changes in water quality. That is, it is possible to indirectly monitor the selenium concentration, which has been difficult in the past, and to manage the treated water of nitrogen and selenium at the same time.

When the biological treatment tank 10 is of the upward flow type, a circulation pipe for circulating a part of the treated water from the treated water pipe 24 to the water to be treated pipe 22 may be provided. As the means, a rotary driving means such as a motor and a stirring device having a stirring blade or the like may be provided. Considering that the pH can be easily controlled, the completely mixed type is preferable.

The water temperature of the biological treatment tank 10 is preferably maintained in the range of, for example, 15 to 40 ° C.

When the pH rises with the reduction reaction in the biological treatment tank 10, it is preferable to add an acid such as hydrochloric acid or sulfuric acid or an alkaline agent to maintain the pH at 6.0 to 8.5.

The residence time in the biological treatment tank 10 is, for example, in the range of 1 hour to 24 hours. If the residence time in the biological treatment tank 10 is less than 1 hour, the reduction reaction may not proceed, and if it exceeds 24 hours, it becomes excessive. The residence time in the biological treatment tank 10 is controlled by, for example, adjusting the internal volume of the biological treatment tank 10, the amount of water to be treated to the biological treatment tank 10, and the like.

The carrier 30 is not particularly limited as long as it is a carrier conventionally used under anaerobic conditions, and examples thereof include a porous plastic carrier, a sponge-like carrier, and a gel-like carrier. In particular, by using a gel-like carrier as the carrier 30, the floating of the carrier due to the gas generated during reduction is suppressed, and the fluidity of the carrier by stirring is high, so that the carrier is compared with the plastic carrier and the sponge-like carrier. , High load processing becomes possible.

The gel-like carrier is not particularly limited, and examples thereof include a water-absorbent polymer gel-like carrier containing polyvinyl alcohol, polyethylene glycol, polyurethane and the like.

Further, as a method of maintaining sludge on the carrier, there are a method of comprehensively immobilizing sludge inside the carrier, a method of putting the carrier and seed sludge into a biological treatment tank, and a method of forming a biological film on the carrier. A method of forming a biological film on the carrier is preferable in terms of increasing the contact efficiency with water and keeping the activity high. In particular, porous hydrophilic polyvinyl alcohol has a large amount of adhesion and good fluidity.

The shape of the carrier 30 is not particularly limited, but a spherical or cubic shape (cube shape), a rectangular parallelepiped shape, a cylindrical shape, or the like having a size of about 1 mm to 10 mm is preferable. In particular, a spherical or cylindrical gel-like carrier having a size of about 3 to 8 mm is preferable. In order to facilitate the formation of a fluid state inside the biological treatment tank 10, the specific gravity of the carrier 30 is preferably at least 1.0, and the true specific gravity is 1.1 or more, or the apparent specific gravity is 1.01 or more. ..

As a stirring method when the carrier method is used, a draft tube which is installed substantially vertically inside the biological treatment tank 10 and has an open top and bottom is installed, and a downward flow is formed inside the draft tube and an upward flow is formed outside the draft tube. A vertical stirrer or an underwater aerator may be used.

The amount of the carrier 30 charged into the biological treatment tank 10 is preferably in the range of 10 to 70% with respect to the volume of the biological treatment tank 10. If the input amount of the carrier 30 is less than 10% with respect to the volume of the biological treatment tank 10, the reaction rate may decrease, and if it exceeds 70%, the carrier 30 becomes difficult to flow, and clogging due to sludge during long-term operation, etc. In some cases, the water to be treated may short-pass and the quality of the treated water may deteriorate.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Examples 1 to 3 and Comparative Example 1>
A continuous water flow test of simulated wastewater was carried out using a treatment device by the carrier method as shown in FIG.

<Test conditions>
Biological treatment tank volume: 1.4L
Carrier for retaining microorganisms: Porous hydrophilic polyvinyl alcohol gel-like carrier Carrier filling rate: 20% (carrier bulk capacity / biological treatment tank capacity)
Test water: Sodium nitrate and sodium selenite were added to pure water, and other phosphoric acid and trace element solutions were added as simulated wastewater.
Hydrogen donor: Methanol is added to a predetermined concentration. Water temperature in the biological treatment tank: 30 ° C.
PH in the biological treatment tank: 7.6
Resident time of biological treatment tank: 2.4 hours

As a start-up, water was continuously passed for 40 days, microorganisms were attached to the carrier, and water was passed under the conditions of the water to be treated shown in Table 1. The nitrate ion and selenate ion of the treated water were measured by ion chromatography (Thermo Fisher Scientific Co., Ltd., DIONEX INTERION). The results are shown in Table 2.

In Comparative Example 1, the selenate ion concentration of the treated water was 0.18 mg-Se / L, which exceeded the uniform wastewater standard of 0.1 mg-Se / L, and the nitrate ion concentration at that time was 4.7 mg-N. It was / L.

When the methanol concentration was increased with respect to Comparative Example 1 (Example 1), the selenate ion concentration was 0.084 mg-Se / L, which was lower than the uniform wastewater standard of 0.1 mg-Se / L. The nitrate ion concentration at that time was 1.0 mg-N / L.

In Examples 2 and 3 in which the nitrate ion concentration of the water to be treated was increased to 100 mg-N / L and 150 mg-N / L, respectively, the nitrate ion concentration of the treated water was 1.7 mg-N / L and 2.0 mg, respectively. The water quality was −N / L, and the selenate ion concentration was stably below the uniform wastewater standard of 0.1 mg-Se / L.

FIG. 3 shows the relationship between the nitrate ion concentration (mg-N / L) and the selenate ion concentration (mg-Se / L) in the treated water. It remains, and by increasing the amount of methanol added as in Example 1 when the nitrate ion rises, it became possible to stably treat the selenate ion. Further, by adding methanol so that the nitrate ion concentration was low as in Examples 2 and 3, the selenate ion could be treated stably.

That is, when the reduction treatment is performed in the same reaction vessel, if the nitrate nitrogen concentration (nitrate ion concentration) is monitored, it is estimated that the selenate ion concentration also increases when the nitrate ion concentration increases. By increasing the amount of methanol added as a hydrogen donor when nitrate ion rises, that is, when selenate ion rises, stable reduction treatment of nitrate ion and selenate ion becomes possible while suppressing excessive addition of methanol. It turned out to be.

As described above, in the selenium-containing water containing at least one of nitrate nitrogen and nitrite nitrogen by the method of the example, nitrate nitrogen is efficiently added in the same reaction tank while suppressing excessive addition of the hydrogen donor. , Nitrite nitrogen, and at least one of selenate ion and selenate ion could be reduced.

1,3 Treatment equipment, 10 Biological treatment tanks, 12 Hydrogen donor storage tanks, 14 Control equipment, 16 Pumps, 18 Stirrers, 20 Nitrate nitrogen measuring equipment, 22 Processed water pipes, 24 Treated water pipes, 26 Hydrogen donors Body plumbing, 28 screens, 30 carriers.

Claims (10)

For selenic acid-containing water containing at least one of nitrate nitrogen and nitrite nitrogen, at least one of the nitrate nitrogen and the nitrite nitrogen in the presence of a hydrogen donor in the same reaction vessel. In a biological reaction step in which at least one of selenate ion and selenite ion is reduced to molecular selenium in nitrogen gas.
A method for treating selenium-containing water, which comprises estimating the selenium concentration in the treated water by measuring the concentration of nitrate nitrogen in the treated water or the reaction vessel. The method for treating selenium-containing water according to claim 1.
A method for treating selenium-containing water, which comprises adjusting the amount of the hydrogen donor added to the selenium-containing water based on the measured concentration of nitrate nitrogen. The method for treating selenium-containing water according to claim 1 or 2.
A method for treating selenium-containing water, wherein the Se concentration in the selenium-containing water is 2 mg / L or less, and the nitrate nitrogen concentration is 150 mg / L or less. The method for treating selenium-containing water according to any one of claims 1 to 3.
A method for treating selenium-containing water, which comprises adding the hydrogen donor to the selenium-containing water so that the concentration of nitrate nitrogen in the treated water or the reaction vessel is 4 mg / L or less. The method for treating selenium-containing water according to any one of claims 1 to 4.
In the biological reaction step, the biological sludge held on the porous fluidized carrier is brought into contact with the selenium-containing water, and the fluidized carrier is a hydrophilic polyvinyl alcohol carrier. Processing method. For selenic acid-containing water containing at least one of nitrate nitrogen and nitrite nitrogen, at least one of the nitrate nitrogen and the nitrite nitrogen in the presence of a hydrogen donor in the same reaction vessel. To nitrogen gas, and at least one of selenate ion and selenite ion to molecular selenium.
Nitrate nitrogen measuring means for measuring the concentration of nitrate nitrogen in the treated water or the reaction vessel, and
A selenium concentration estimating means for estimating the selenium concentration in the treated water from the measured nitrate nitrogen concentration,
A selenium-containing water treatment apparatus comprising the above. The selenium-containing water treatment apparatus according to claim 6.
A selenium-containing water treatment apparatus further comprising a hydrogen donor addition amount adjusting means for adjusting the addition amount of the hydrogen donor to the selenium-containing water based on the measured concentration of nitrate nitrogen. The selenium-containing water treatment apparatus according to claim 6 or 7.
A selenium-containing water treatment apparatus, wherein the Se concentration in the selenium-containing water is 2 mg / L or less, and the nitrate nitrogen concentration is 150 mg / L or less. The selenium-containing water treatment apparatus according to any one of claims 6 to 8.
The hydrogen donor addition amount adjusting means is adjusted so that the hydrogen donor is added to the selenium-containing water so that the concentration of nitrate nitrogen in the treated water or the reaction vessel is 4 mg / L or less. A selenium-containing water treatment apparatus. The selenium-containing water treatment apparatus according to any one of claims 6 to 9.
The biological reaction means brings the biological sludge held on the porous fluid carrier into contact with the selenium-containing water, and the fluid carrier is a hydrophilic polyvinyl alcohol carrier. Containing water treatment equipment.

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