JP2014113547A - Apparatus and method for treating waste water containing nitric acid and nitrous acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for treating waste water containing nitric acid and nitrous acid, in each of which the nitric acid concentration and nitrous acid concentration of the waste water can be measured quickly.SOLUTION: The apparatus for treating waste water containing nitric acid and nitrous acid includes: a hydrogen donor pump 26 for adding a hydrogen donor to the waste water containing nitric acid and nitrous acid; a denitrification tank 14 in which the hydrogen donor-added waste water is subjected to anaerobic biological treatment; an ultraviolet absorbance method-applied sensor 20 for measuring the nitric acid concentration and nitrous acid concentration of the waste water; an ion electrode method-applied sensor 18 for measuring the nitric acid concentration of the waste water; and a control part 28 for controlling the amount of the hydrogen donor to be added to the waste water by using the hydrogen donor pump 26 on the basis of the nitric acid concentration and nitrous acid concentration of the waste water, which are obtained by using the nitric acid concentration and nitrous acid concentration measured by the ultraviolet absorbance method-applied sensor 20 and the nitric acid concentration measured by the ion electrode method-applied sensor 18.

Description

  The present invention relates to a treatment apparatus and a treatment method for waste water containing nitric acid and nitrous acid.

  Nitrogen components such as ammonia nitrogen, nitrate nitrogen, nitrite nitrogen and the like contained in water cause eutrophication of environmental water, and a standard is set for the concentration in wastewater. In general, ammonia nitrogen in waste water is decomposed into nitrogen gas by a two-stage biological treatment of nitrification and denitrification. Nitrification is a reaction by an aerobic nitrifying bacterium, whereas denitrification is a reaction by an anaerobic denitrifying bacterium, so two types of reaction tanks, an aerobic tank and an anaerobic tank, are used to advance both reactions. is necessary. The denitrifying bacteria used in the conventional method are heterotrophic bacteria, and an organic substance or the like as a hydrogen donor must be added to the denitrifying tank in order to maintain the activity. At this time, since the amount of organic substances required for reduction differs between nitrous acid and nitric acid, controlling the injection amount accurately by measuring each of them is effective in optimizing the amount of chemicals used and also stabilizes the quality of the treated water. Connected.

  However, in the conventional on-line analysis method, the ion electrode method can measure nitric acid but cannot measure nitrous acid. In the UV absorbance method using a UV sensor, it is measured as NOx containing nitric acid and nitrous acid. Therefore, there was no method for measuring nitric acid and nitrous acid simultaneously online.

As a measuring method of nitrous acid, for example, in the section of 43.1.1 naphthylethylenediamine spectrophotometry of Japanese Industrial Standard JIS K0102 43.1 (nitrite ion NO ²⁻ ), sulfanilamide (4-aminobenzene) is used as a sample. A method is disclosed in which the amount of nitrite ions is estimated by diazotizing a sample with nitrite ions and measuring the absorbance of the resulting red azo compound. Further, in the section of JIS K0102 43.1.2 ion chromatographic method, a method for measuring nitrite ions by ion chromatographic method is also disclosed (for example, see Non-Patent Document 1).

  In Patent Document 1, in a method for measuring the concentration of nitrate ion and nitrite ion in seawater, an ultraviolet absorption spectrum is measured by an absorptiometry in a wavelength range of 215 to 240 nm to measure nitrate ion and nitrite ion. A method is disclosed.

  Patent Document 2 discloses a method for calculating the concentration of nitrous acid in a liquid from an ultraviolet absorbance spectrum measured for at least one of wavelengths of 336 nm, 347 nm, 359 nm, 372 nm, and 386 nm.

JP 2008-145297 A JP 2011-257341 A JP 2006-151779 A JP-A-7-256290

Japanese Industrial Standard JIS K0102 43.1 (Nitrite ion NO2-)

  However, the ion chromatographic method of Non-Patent Document 1 is considered to be unsuitable for quickly measuring the concentration of nitrous acid in a liquid because preparation and measurement are very laborious. The same applies to the naphthylethylenediamine absorptiometry.

  Moreover, in the measuring method by patent document 1, since it is measuring without knowing which peak of the wavelength of the absorbance spectrum resulting from nitrite ion out of the range of wavelengths 215 to 240 nm is derived from nitrite ion, There is no sufficient description about how nitrite ions can be measured.

Moreover, in the measuring method by patent document 2, since the peak height of the peak derived from nitrous acid changes with the nitric acid concentration contained in the liquid, the nitric acid concentration in the liquid is measured, and the ultraviolet absorbance spectrum of nitrous acid. By correcting the peak height at a wavelength of 386 nm, a more accurate nitrous acid concentration is obtained. However, it is necessary to correct the wastewater whose nitric acid concentration in the liquid fluctuates frequently, and it is considered that it is not suitable for quickly measuring the nitrite concentration in the wastewater.

  Then, the objective of this invention is providing the processing apparatus and the processing method of the waste_water | drain containing nitric acid and nitrous acid which can measure the nitric acid density | concentration and nitrous acid density | concentration in waste water rapidly.

  The apparatus for treating wastewater containing nitric acid and nitrous acid according to the present invention comprises a hydrogen donor addition means for adding a hydrogen donor to wastewater containing nitric acid and nitrous acid, and anaerobically the wastewater to which the hydrogen donor has been added. Measured by a denitrification tank for biological treatment, an ultraviolet absorbance method sensor for measuring the nitric acid and nitrous acid concentrations in the waste water, an ion electrode method sensor for measuring the nitric acid concentration in the waste water, and the ultraviolet absorbance method sensor Based on the concentration of nitric acid and nitrous acid in the wastewater determined by the concentration of nitric acid and nitrous acid, and the concentration of nitric acid measured by the ion electrode method sensor, the wastewater is added by the hydrogen donor addition means. And a control unit for controlling the amount of the hydrogen donor added therein.

  Further, in the apparatus for treating waste water containing nitric acid and nitrous acid, the amount of hydrogen donor added is a hydrogen donor necessary for reducing nitrous acid having a concentration obtained by multiplying the determined nitrous acid concentration by 1.1. The amount is preferably the sum of the amount of hydrogen donor required for the reduction of nitric acid with the determined nitric acid concentration.

  Further, in the wastewater treatment apparatus containing nitric acid and nitrous acid, the amount of the hydrogen donor added is obtained by multiplying the amount of hydrogen donor required for the reduction of nitrous acid having the determined nitrous acid concentration by 1.1. The amount is preferably the sum of the amount of hydrogen donor required for the reduction of nitric acid with the determined nitric acid concentration.

  The method for treating wastewater containing nitric acid and nitrous acid according to the present invention includes a hydrogen donor addition step of adding a hydrogen donor to wastewater containing nitric acid and nitrous acid, and the concentration of nitric acid and nitrous acid in the wastewater. A first measurement step for measuring by an ultraviolet absorbance method, a second measurement step for measuring the concentration of nitric acid in the waste water by an ion electrode method, and a deaeration for biologically treating the waste water to which the hydrogen donor has been added anaerobically. In the drainage determined by the concentration of nitric acid and nitrous acid measured by the ultraviolet absorbance method and the concentration of nitric acid measured by the ion electrode method. The amount of the hydrogen donor added to the waste water is controlled based on the concentration of nitric acid and the concentration of nitrous acid.

  Further, in the method for treating waste water containing nitric acid and nitrous acid, the amount of the hydrogen donor added is a hydrogen donor necessary for the reduction of nitrous acid having a concentration obtained by multiplying the determined nitrous acid concentration by 1.1. The amount is preferably the sum of the amount of hydrogen donor required for the reduction of nitric acid with the determined nitric acid concentration.

  In the method for treating wastewater containing nitric acid and nitrous acid, the amount of the hydrogen donor added is obtained by multiplying the amount of hydrogen donor required for reduction of nitrous acid having the determined nitrous acid concentration by 1.1. The amount is preferably the sum of the amount of hydrogen donor required for the reduction of nitric acid with the determined nitric acid concentration.

  ADVANTAGE OF THE INVENTION According to this invention, the processing apparatus and processing method of the waste_water | drain containing nitric acid and nitrous acid which can measure the nitric acid density | concentration and nitrous acid density | concentration in waste water rapidly can be provided.

It is a schematic block diagram which shows an example of a structure of the waste water treatment apparatus which concerns on this embodiment. It is a schematic block diagram which shows another example of a structure of the waste water treatment apparatus which concerns on this embodiment. It is a schematic block diagram which shows another example of a structure of the waste water treatment apparatus which concerns on this embodiment. It is a diagram showing the relationship between total nitrite concentration and nitric acid concentration of the standard (NO x _-N) and UV spectrophotometry expression measurements of nitrate sensors. It is a figure which shows the relationship between the nitrous acid density | concentration of a standard solution, and the value which deducted the measured value of the ion electrode method sensor from the measured value of the ultraviolet light absorbance method sensor. It is a schematic diagram which shows the structure of the waste water treatment equipment used in Example 2. It is a figure which shows the relationship between the ratio of the nitrous acid concentration (nitrite nitrogen concentration) with respect to the total nitrogen concentration in a 2nd nitrification tank, and the addition amount of the hydrogen donor (methanol) added to the denitrification tank.

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

  FIG. 1 is a schematic configuration diagram illustrating an example of a configuration of a wastewater treatment apparatus according to the present embodiment. The waste water treatment apparatus 1 shown in FIG. 1 includes waste water inflow lines 10a and 10b, a waste water storage tank 12, a denitrification tank 14, a treated water discharge line 16, an ion electrode method sensor 18, an ultraviolet absorbance method sensor 20, A hydrogen donor storage tank 22, a hydrogen donor addition line 24, a hydrogen donor pump 26 as a hydrogen donor addition means, and a control unit 28 are provided.

  A drainage inflow line 10 a is connected to the drainage storage tank 12. One end of the drainage inflow line 10 b is connected to the drainage storage tank 12, and the other end is connected to the denitrification tank 14. A treated water discharge line 16 is connected to the denitrification tank 14. One end of the hydrogen donor addition line 24 is connected to the hydrogen donor storage tank 22, and the other end is connected to the denitrification tank 14 via a hydrogen donor pump 26. In the drainage storage tank 12, an ion electrode method sensor 18 and an ultraviolet absorbance method sensor 20 are installed. Both sensors and the control unit 28, and the control unit 28 and the hydrogen donor pump 26 are electrically connected to each other. Although details will be described later, the detection values detected by both sensors are transmitted to the control unit 28, and the control unit 28 adjusts the output of the hydrogen donor pump 26 and the like based on the detection values to add the hydrogen donor. Control the amount.

  It is desirable to install a stirring device 30 as stirring means inside the denitrification tank 14. By installing the stirring device 30, the contact efficiency between the microorganisms in the denitrification tank 14 and the wastewater can be increased. The stirring device 30 shown in FIG. 1 includes a motor, a shaft, and a stirring blade, and the shaft is rotated by the driving of the motor, and the stirring blade rotates as the shaft rotates. In addition, the stirring apparatus 30 shown in FIG. 1 is an example, Comprising: It does not restrict | limit to this structure. Moreover, you may install a baffle plate in the tank in the denitrification tank 14 at the point which improves stirring efficiency.

  Next, the operation of the waste water treatment apparatus 1 shown in FIG. 1 will be described.

  Waste water containing nitric acid and nitrous acid passes through the waste water inflow line 10 a and is stored in the waste water storage tank 12. In the waste water storage tank 12, the concentration of nitric acid and nitrous acid (NOx concentration) in the waste water is detected by the ultraviolet absorbance method sensor 20, and the concentration of nitric acid in the waste water is detected by the ion electrode method sensor 18. In the present specification, the nitric acid concentration is a nitrate nitrogen concentration, and the nitrite concentration is a nitrite nitrogen concentration. The detected density value is transmitted to the control unit 28. Thereafter, the wastewater in the wastewater storage tank 12 is supplied to the denitrification tank 14 through the wastewater inflow line 10b. A hydrogen donor is supplied from the hydrogen donor storage tank 22 to the denitrification tank 14 through the hydrogen donor addition line 24 by the hydrogen donor pump 26. As will be described later, the amount of hydrogen donor added is controlled by the control unit 28 based on the nitric acid concentration and the nitrous acid concentration. In the denitrification tank 14, in an anaerobic state where a hydrogen donor is present, nitric acid and nitrous acid in the wastewater are reduced to nitrogen gas by the action of the denitrifying bacteria. When nitric acid and nitrous acid are reduced by the denitrification reaction in the denitrification tank 14, the pH rises. Therefore, it is preferable to add a pH adjuster to the denitrification tank 14 so that the denitrifying bacteria have a high activity of pH 6-8. The treated water denitrified in the denitrification tank 14 is discharged out of the system through the treated water discharge line 16.

  Below, the addition amount of the hydrogen donor supplied in the denitrification tank 14 is demonstrated.

  Examples of the hydrogen donor used in the present embodiment include methanol, ethanol, isopropyl alcohol, acetic acid, hydrogen gas, acetone, glucose, and the like. However, the hydrogen donor is not limited thereto, and is conventionally known as a hydrogen donor. Can be used.

For example, when methanol is used as a hydrogen donor and nitric acid and nitrous acid are reduced by methanol (hydrogen donor), the following reaction formulas (1) and (2) are expressed.
^{_{6NO 3 - + 5CH 3 OH →}} 3N 2 + 5CO 2 + 7H 2 O + 6OH - (1)
2NO ₂ ⁻ + CH ₃ OH → N ₂ + CO ₂ + H ₂ O + 2OH ⁻ (2)

  From the above reaction formulas (1) and (2), the amount of methanol added is 1.9 times the weight of nitrogen contained in nitric acid (weight ratio) and 1.17 times the weight of nitrogen contained in nitrous acid (weight ratio). It becomes. As can be seen from this, the amount of hydrogen donor required to reduce nitrous acid may be less than the amount of hydrogen donor required to reduce nitric acid. Therefore, measuring the concentration of nitric acid and nitrous acid in the wastewater to determine the amount of hydrogen donor required for the reduction of nitric acid and nitrous acid is effective in optimizing the amount of chemicals used and stabilizing the quality of the treated water. Is also connected.

  As a result of intensive studies on the measurement method of nitrous acid concentration that could not be measured and monitored in real time, the present inventors subtracted the measurement value of the ion electrode method sensor 18 from the measurement value of the ultraviolet absorbance method sensor 20. It was found that this value is highly correlated with the concentration of nitrous acid in wastewater. In the present embodiment, the ultraviolet light absorbance method sensor 20 measures the nitric acid and nitrous acid concentrations in the waste water as the nitric acid concentration, and the ion electrode method sensor 18 measures the nitric acid concentration in the waste water. From the nitric acid and nitrous acid concentrations in the wastewater measured by the sensor 20 and the nitric acid concentration in the wastewater measured by the ion electrode method sensor 18, the nitric acid concentration and nitrous acid concentration in the wastewater are obtained. And the addition amount of a hydrogen donor is controlled based on those density | concentrations. More specifically, for example, the nitric acid and nitrous acid concentration values in the wastewater measured by the ultraviolet absorbance method sensor 20 are transmitted to the control unit 28, and the nitric acid concentration in the wastewater measured by the ion electrode method sensor 18 is used. The value is transmitted to the control unit 28. Then, in the control unit 28, by subtracting the nitric acid concentration value in the wastewater measured by the ion electrode method sensor 18 from the nitric acid and nitrous acid concentration values in the wastewater measured by the measured ultraviolet absorbance method sensor 20, Nitrous acid concentration in waste water is required. In the control unit, for example, 1.9 times the amount of nitrogen contained in the nitric acid having the nitric acid concentration in the wastewater measured by the ion electrode sensor 18 and the nitrous acid having the nitrite concentration in the drainage obtained as described above. The discharge amount (output) of the hydrogen donor pump 26 is adjusted so that, for example, 1.17 times the amount of nitrogen contained is added. In the present embodiment, a pump is used as an example of the hydrogen donor addition means, but the present invention is not limited to this, and may be, for example, a solenoid valve. That is, the control unit may adjust the degree of opening and closing of the electromagnetic valve based on the nitric acid and nitrous acid concentrations obtained as described above, and may control the addition amount of the hydrogen donor.

  When only the UV absorbance sensor 20 is used, all the nitric acid and nitrous acid in the waste water are regarded as nitric acid, so an excessive amount of hydrogen donor is added, and the organic carbon concentration in the treated water increases. Although the chemical addition cost also increases, according to the present embodiment, the increase in the organic carbon concentration in the treated water and the chemical addition cost can be suppressed as compared with the case where only the ultraviolet absorbance sensor 20 is used. In addition, when only the ion electrode method sensor 18 is used, nitrous acid in the wastewater is not detected, the amount of hydrogen donor added is insufficient and sufficient treatment is not performed, and the total nitrogen concentration in the treated water increases. However, according to the present embodiment, since the concentration of nitrous acid can also be obtained, a necessary hydrogen donor addition amount can be supplied as compared with the case where only the ion electrode type sensor 18 is used. The increase in the total nitrogen concentration in the treated water can be suppressed.

  In the present embodiment, the concentration of nitrous acid and the concentration of nitric acid in the wastewater can be quickly measured by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18, respectively. As a result, even if concentration fluctuations occur in the nitric acid and nitrous acid in the wastewater supplied to the denitrification tank 14, the concentration of nitrous acid and nitric acid in the wastewater measured in real time by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18 Based on the concentration, it becomes possible to control the addition amount of the hydrogen donor, and it is possible to suppress an increase in organic carbon concentration in the treated water, an increase in chemical addition cost, an increase in the total nitrogen concentration in the treated water, and the like. .

  The amount of hydrogen donor added depends on the amount of hydrogen donor required for the reduction of nitrous acid at the nitrous acid concentration determined by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18, and the nitric acid concentration determined by the ion electrode method sensor 18. This is the sum of the amount of hydrogen donor required for the reduction of nitric acid. For example, in the case of methanol, the amount of hydrogen donor necessary for the reduction of nitrous acid is 1.17 times the amount of nitrogen contained in nitrous acid having a nitrous acid concentration determined by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18. Is preferably calculated on the basis of 1 and more preferably 1.17 to 2.1 times the amount of hydrogen donor. The concentration of nitrous acid determined by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18 is such that the measurement sensitivity to nitrite ions is inferior to the measurement sensitivity to nitrate ions in the ultraviolet absorbance method. May be 10% lower. Therefore, the amount of hydrogen donor required for the reduction of nitrous acid is the amount of hydrogen donor required for the reduction of nitrous acid at a concentration obtained by multiplying the nitrite concentration determined above by 1.1, or the above The amount is preferably an amount obtained by multiplying the amount of hydrogen donor necessary for reduction of nitrous acid having the obtained nitrous acid concentration by 1.1 times. On the other hand, the amount of hydrogen donor necessary for the reduction of nitric acid can be calculated based on, for example, 1.9 times the amount of nitrogen contained in nitric acid having a nitric acid concentration determined by the ion electrode sensor 18 in the case of methanol. Preferably, the hydrogen donor is 2.0 to 3.2 times the amount. That is, regardless of the type of hydrogen donor, the amount of hydrogen donor required for the reduction of nitrous acid is about two thirds of the amount of hydrogen donor required for the reduction of nitric acid.

  Hereinafter, the principle of the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18 will be described.

  The principle of the ultraviolet absorbance type sensor 20 is as follows. The UV light pulse-output from the UV light source incorporated in the sensor passes through the measurement liquid in the slit at the tip of the sensor and is received by the light receiving unit on the opposite side. Nitric acid and nitrous acid in the measurement liquid in the slit absorb a specific range of UV light, and the amount of absorption is proportional to the concentration of nitric acid and nitrous acid. Examples of the ultraviolet absorbance method sensor 20 include Nitra Vis700 IQ manufactured by WTW. The principle of the ion electrode sensor 18 is as follows. When the nitrate ion exchange thin film in the sensor comes into contact with a solution containing nitric acid, an electrode potential difference is generated according to the ion concentration in the solution. This potential is measured, and the ion concentration is calculated from a calibration curve prepared in advance. Examples of the ion electrode sensor 18 include VARiON 700 IQ manufactured by WTW.

  FIG. 2 is a schematic configuration diagram illustrating another example of the configuration of the waste water treatment apparatus according to the present embodiment. In the waste water treatment apparatus 2 shown in FIG. 2, the same components as those in the waste water treatment apparatus 1 shown in FIG. The waste water treatment apparatus 2 shown in FIG. 2 includes a nitrification tank 32 in place of the waste water storage tank 12 provided in the preceding stage of the denitrification tank 14. In the nitrification tank 32, an ultraviolet absorbance method sensor 20 and an ion electrode method sensor 18 are installed. The nitrification tank 32 is provided with an aeration apparatus 34 for supplying oxygen to the tank and stirring it. A drainage inflow line 10 a is connected to the nitrification tank 32. One end of the drainage inflow line 10 b is connected to the nitrification tank 32, and the other end is connected to the denitrification tank 14. In the wastewater treatment apparatus 2 shown in FIG. 2, a configuration in which the denitrification tank 14 is installed at the subsequent stage of the nitrification tank 32 will be described as an example. The structure installed in the front | former stage may be sufficient.

  Below, operation | movement of the waste water treatment apparatus 2 of this embodiment is demonstrated.

  The wastewater to be treated in this embodiment is, for example, wastewater containing ammonia, organic nitrogen, and the like, and examples include industrial wastewater such as domestic wastewater, food factory wastewater, power plant wastewater, and electronic industrial wastewater. . Waste water containing ammonia, organic nitrogen and the like is supplied to the nitrification tank 32 from the waste water inflow line 10a. In the nitrification tank 32, ammonium and organic nitrogen in the wastewater are nitrified into nitric acid and nitrous acid mainly by nitrifying bacteria while being aerated by the aeration apparatus 34, that is, under aerobic conditions. In addition, nitrifying bacteria include, for example, ammonia-oxidizing bacteria that are auxotrophic bacteria that nitrify ammonium ions contained in wastewater to nitrite, nitrite-oxidizing bacteria that are auxotrophic bacteria that nitrify ammonium ions to nitric acid, etc. Consists of

  In the nitrification tank 32, when ammonia and organic nitrogen are nitrified to nitric acid as described above, the pH is lowered. Therefore, it is preferable to add an alkaline agent to the nitrification tank 32 so that the pH of the bacteria is high and is 6-8. Examples of the alkaline agent to be used include sodium hydroxide and potassium hydroxide, but are not particularly limited.

  Further, in the nitrification tank 32, the concentration of nitric acid and nitrous acid (NOx concentration) in the wastewater is detected by the ultraviolet absorbance method sensor 20, and the concentration of nitric acid in the wastewater is detected by the ion electrode method sensor 18. The detected density value is transmitted to the control unit 28. The primary treated water treated in the nitrification tank 32 is supplied to the denitrification tank 14 through the drainage inflow line 10b. A hydrogen donor pump 26 supplies a hydrogen donor from the hydrogen donor storage tank 22 to the denitrification tank 14 through a hydrogen donor pipe. As described above, the addition amount of the hydrogen donor is controlled by the control unit 28 based on the nitric acid concentration and the nitrous acid concentration. In the denitrification tank 14, in an anaerobic state where a hydrogen donor is present, nitric acid and nitrous acid in the wastewater are reduced to nitrogen gas by the action of the denitrifying bacteria. The treated water denitrified in the denitrification tank 14 is discharged out of the system through the treated water discharge line 16.

  According to this embodiment, the nitric acid and nitrous acid concentrations in the waste water (primary treated water) in the nitrification tank 32 are quickly measured by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18, that is, in the denitrification tank 14. The concentration of nitrous acid and nitric acid immediately before entering can be measured quickly. As a result, even if concentration fluctuations occur in the nitric acid and nitrous acid in the wastewater supplied to the denitrification tank 14, the concentration in the wastewater (primary treated water) measured in real time by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18 is increased. Based on the nitrous acid concentration and nitric acid concentration, it becomes possible to control the amount of hydrogen donor added, increasing the organic carbon concentration in the treated water, increasing the cost of adding chemicals, increasing the total nitrogen concentration in the treated water, etc. Can be suppressed.

  FIG. 3 is a schematic configuration diagram illustrating another example of the configuration of the waste water treatment apparatus according to the present embodiment. In the waste water treatment apparatus 3 shown in FIG. 3, the same code | symbol is attached | subjected about the structure similar to the waste water treatment apparatus 1 shown in FIG. 1, and the description is abbreviate | omitted. The waste water treatment apparatus 3 shown in FIG. 3 further includes an oxidation tank 36 provided at the subsequent stage of the denitrification tank 14. The oxidation tank 36 is provided with an aeration device 38 for supplying oxygen to the tank and stirring it. One end of the drainage inflow line 10 c is connected to the denitrification tank 14, and the other end is connected to the oxidation tank 36. Further, the treated water discharge line 16 is connected to the oxidation tank 36.

  Below, operation | movement of the waste water treatment equipment 3 of this embodiment is demonstrated.

  Waste water containing nitric acid and nitrous acid is supplied to the waste water storage tank 12 from the waste water inflow line 10a. In the drainage storage tank 12, the concentration of nitric acid and nitrous acid (NOx concentration) in the wastewater is detected by the ultraviolet absorbance method sensor 20, and the concentration of nitric acid in the wastewater is detected by the ion electrode method sensor 18. The detected density value is transmitted to the control unit 28. And the waste_water | drain in the waste_water | drain storage tank 12 passes along the waste_water | drain inflow line 10b, and is supplied to the denitrification tank 14. FIG. A hydrogen donor pump 26 supplies a hydrogen donor from the hydrogen donor storage tank 22 to the denitrification tank 14 through a hydrogen donor pipe. As described above, the addition amount of the hydrogen donor is controlled by the control unit 28 based on the nitric acid concentration and the nitrous acid concentration. In the denitrification tank 14, in an anaerobic state where a hydrogen donor is present, nitric acid and nitrous acid in the wastewater are reduced to nitrogen gas by the action of the denitrifying bacteria. Waste water (primary treated water) denitrified in the denitrification tank 14 is supplied to the oxidation tank 36 from the drain inflow line 10c. In the oxidation tank 36, organic carbon (hydrogen donor) remaining mainly in the primary treated water is oxidized while being aerated by the aeration apparatus 38. The treated water oxidized in the oxidation tank 36 is discharged out of the system from the treated water discharge line 16. Although it is not necessary to control the pH in the oxidation tank 36, when the wastewater concentration is high, the inorganic carbon produced by the denitrification treatment also becomes a high concentration, so that the inorganic carbon is converted into carbon dioxide by oxidation treatment (aeration). By being released, the pH may increase. When the pH of the treated water does not satisfy the drainage standard or the environmental standard, it is preferable to add an acid such as hydrochloric acid to the oxidation tank 36 and adjust the treated water so that it becomes the reference value of the treated water.

  According to the present embodiment, the concentration of nitric acid and nitrous acid in the waste water is quickly measured by the ultraviolet absorbance method sensor 20 and the ion electrode method sensor 18, that is, the concentration of nitrous acid and nitric acid immediately before flowing into the denitrification tank 14 is determined. It can be measured quickly. As a result, the hydrogen donor necessary for the reduction of nitrous acid and nitric acid can be appropriately controlled, and for example, an increase in the organic carbon concentration in the primary treated water can be suppressed. Therefore, an increase in the load of organic carbon (hydrogen donor) to be treated in the oxidation tank 36 can be suppressed, and the volume of the oxidation tank 36 can be reduced.

  Hereinafter, other conditions in the nitrification / denitrification reaction will be described.

  In the wastewater treatment of this embodiment, if the temperature of the wastewater is low, the treatment speed in the nitrification / denitrification process decreases, so if necessary, install heating equipment in the nitrification tank and denitrification tank. Each treatment may be performed by heating the waste water. The temperature of the nitrification reaction and denitrification reaction is preferably in the range of 10 to 40 ° C.

  When SS components, hydrogen peroxide, and fluorine ions are mixed in the wastewater, hydrogen peroxide and fluorine ions have an inhibitory effect on living organisms. Therefore, remove them before performing the nitrification reaction or denitrification reaction. It is preferable to keep it. As a method for treating these inhibitory substances, existing techniques can be used, and in the treatment of hydrogen peroxide, a method of adding an enzyme, a method of injecting a reducing agent, a method of contacting with activated carbon and the like can be mentioned. It is done. In addition, SS components and the like can be treated by coagulation precipitation, and in the treatment of fluorine ions, there are a method of adding calcium and removing it as calcium fluoride, a method of treating with an ion exchange resin, and the like.

  If fluorine ions are previously removed using Ca or the like before performing the nitrification step and the denitrification step, Ca may be contained in the wastewater to be treated in the present embodiment. There is a possibility that calcium carbonate reacts to precipitate calcium carbonate. In that case, precipitation of calcium carbonate can be prevented by determining the pH of the denitrification step with reference to the Langeria index. These are coping methods that cannot be applied with USB, which cannot stir the inside of the tank. In the present embodiment, even if the Ca ion concentration in the waste water is 200 mg / L or more, precipitation of calcium carbonate can be suppressed by adjusting the pH.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail more concretely, this invention is not limited to a following example.

<Example 1>
Sodium nitrate and sodium nitrite are dissolved in pure water, and standard solutions shown in Table 1 are prepared. Using an ultraviolet absorbance method sensor (Nitra Vis700 IQ manufactured by WTW) and an ion electrode method sensor (VARiON700 IQ manufactured by WTW). The concentration of the standard solution was measured. Table 1 shows the nitric acid concentration, nitrous acid concentration in the standard solution, the sum of both concentrations (NO _x -N), the measurement value A (concentration value) by the ultraviolet absorbance method sensor, and the measurement value B (concentration) by the ion electrode method sensor. value), and measurements A- summarizing measurement B (= _NO 2 -N).

FIG. 4 is a graph showing the relationship between the total nitrite concentration and the nitric acid concentration (NO _x -N) of the standard solution and the measured value of the ultraviolet absorbance method nitric acid sensor. As can be seen from Table 1 and FIG. 4, the total of the nitrous acid concentration and the nitric acid concentration (NO _x -N) of the standard solution and the measured value of the UV absorbance sensor almost coincided.

  FIG. 5 is a diagram showing the relationship between the concentration of nitrous acid in the standard solution and the value obtained by subtracting the measurement value of the ion electrode method sensor from the measurement value of the ultraviolet absorbance method sensor. The value obtained by subtracting the measurement value of the ion electrode method sensor from the measurement value of the ultraviolet absorbance method sensor tended to be about 10% lower than the nitrous acid concentration of the standard solution. The proportionality coefficient was almost constant.

<Example 2>
FIG. 6 is a schematic diagram illustrating a configuration of the waste water treatment apparatus used in the second embodiment. 6 includes a first nitrification tank 40, a second nitrification tank 42, a denitrification tank 44, an oxidation tank 46, a precipitation tank 48, and drainage inflow lines 50a, 50b, 50c, 50d, 50e, treated water discharge line 52, sludge return line 54, ion electrode method sensor 56, ultraviolet absorbance method sensor 58, hydrogen donor storage tank 60, hydrogen donor addition line 62, and hydrogen donor pump. 64 and a control unit 66. A drainage inflow line 50 a is connected to the first nitrification tank 40. One end of the drainage inflow line 50 b is connected to the first nitrification tank 40, the other end is connected to the second nitrification tank 42, one end of the drainage inflow line 50 c is connected to the second nitrification tank 42, and the other end is denitrification tank 44. One end of the drainage inflow line 50d is connected to the denitrification tank 44, the other end is connected to the oxidation tank 46, one end of the drainage inflow line 50e is connected to the oxidation tank 46, and the other end is connected to the precipitation tank 48. One end of the sludge return line 54 is connected to the bottom of the sedimentation tank 48, and the other end is connected to the drainage inflow line 50a. In addition, a treated water discharge line 52 is connected to the settling tank 48. One end of the hydrogen donor addition line 62 is connected to the hydrogen donor storage tank 60, and the other end is connected to the denitrification tank 44. Aeration devices 68 and 70 are installed in the first nitrification tank 40 and the second nitrification tank 42, and an ion electrode method sensor 56 and an ultraviolet absorbance method sensor 58 are installed in the second nitrification tank 42. . The ion electrode method sensor 56 and the ultraviolet absorbance method sensor 58 and the control unit 66 are electrically connected, and the measured values of both sensors are transmitted to the control unit 66. The controller 66 and the hydrogen donor pump 64 are electrically connected, and the output of the hydrogen donor pump 64 is adjusted based on the measured values (nitric acid and nitrous acid concentration values) measured by both sensors. The amount of hydrogen donor added is controlled.

The composition of drainage and the dimensions of each tank are as follows.
First nitrification tank: dimension 382 mmφ × 528 mm height, capacity 25 L (water surface height approximately 225 mm), treatment method is floating activated sludge method Second nitrification tank: dimension 140 mm × 140 mm × 550 mm height, capacity 5.1 L (water surface) The height is about 320 mm), and the treatment method is the floating activated sludge method. Water temperature in the first and second nitrification tanks: 20 ° C
DO concentration in the first and second nitrification tanks: 5 mg / L
Denitrification tank: dimension 382 mmφ × 528 mm height, capacity 22 L (water surface height approximately 190 mm), treatment method is heterotrophic denitrification treatment Oxidation tank: dimension 200 mm × 200 mm × 250 mm height, capacity 4.5 L (water surface height approximately 113 mm) )
Sedimentation tank: dimension φ100mm × 200mm height, capacity 15L

  In Example 2, waste water is supplied from the waste water inflow line 50a to the first nitrification tank 40 and subjected to nitrification treatment. The nitrified primary waste water is supplied from the drain inflow line 50b to the second nitrification tank 42 and nitrified. In the second nitrification tank 42, the concentration of nitric acid and nitrous acid is measured by the ultraviolet absorbance method sensor 58, the concentration of nitric acid is measured by the ion electrode method sensor 56, and the measured values are transmitted to the controller 66. The secondary waste water nitrified in the second nitrification tank 42 is supplied to the denitrification tank 44 from the drain inflow line 50c. Further, the control unit 66 obtains the nitric acid concentration and the nitrous acid concentration based on the measured values, 1.17 times the amount of nitrogen contained in the nitrous acid having the obtained nitrous acid concentration, and the obtained nitric acid. The hydrogen donor pump is supplied so that the hydrogen donor is supplied into the denitrification tank 44 by adding the hydrogen donor amount of 1.9 times the amount of nitrogen contained in the nitric acid in the concentration to the added amount of the hydrogen donor amount. 64 outputs are controlled. The tertiary drainage denitrified in the denitrification tank 44 is supplied from the drain inflow line 50d to the oxidation tank 46, and after the oxidation treatment, the oxidized fourth drainage is supplied from the drain inflow line 50e to the settling tank 48, The sludge in the fourth drain is separated from the drain. The sludge collected from the treated water discharge line 52 using the supernatant water of the settling tank 48 as treated water and accumulated at the bottom of the settling tank 48 is supplied from the sludge return line 54 to the first nitrification tank 40 via the drainage inflow line 50a. Is done.

The waste water in Example 2 was a synthetic waste water prepared by adding ammonium chloride and adjusting the NH ₄ —N concentration to 200 mg / L.

  FIG. 7 is a diagram showing the relationship between the ratio of nitrite concentration (nitrite nitrogen concentration) to the total nitrogen concentration in the second nitrification tank and the amount of hydrogen donor (methanol) added to the denitrification tank. As shown in FIG. 7, as the nitrous acid concentration increased with respect to the total nitrogen concentration (TN), the amount of hydrogen donor supplied to the denitrification tank decreased. For example, as shown in Patent Document 4, it is known that the amount of methanol required for denitrification of nitrate nitrogen needs to be 2.8 times the amount of nitrogen contained in nitric acid. . However, as shown in FIG. 7, when 70% of the nitrous acid concentration (nitrate nitrogen concentration) is included with respect to the total nitrogen concentration, 1.5 times the total nitrogen amount contained in nitric acid and nitrous acid. It can be seen that the amount of the hydrogen donor may be added, and the amount of hydrogen donor may be less than that conventionally known. That is, in Example 2 where the concentration of nitrous acid and the concentration of nitric acid were respectively determined, and the amount of hydrogen donor required to reduce the determined concentrations of nitric acid and nitrous acid was determined, the amount of hydrogen donor added was appropriately set. Can be controlled.

  1-4 Wastewater treatment equipment, 10a-10c, 50a-50e Wastewater inflow line, 12 Wastewater storage tank, 14,44 Denitrification tank, 16,52 Treated water discharge line, 18,56 Ion electrode type sensor, 20,58 UV absorbance Legal sensor, 22, 60 Hydrogen donor storage tank, 24, 62 Hydrogen donor addition line, 26, 64 Hydrogen donor pump, 28, 66 Control unit, 30 Stirrer, 32 Nitrification tank, 34, 38, 68, 70 Aeration apparatus, 36, 46 Oxidation tank, 40 First nitrification tank, 42 Second nitrification tank, 48 Sedimentation tank, 54 Sludge return line.

Claims (6)

Hydrogen donor addition means for adding a hydrogen donor to waste water containing nitric acid and nitrous acid;
A denitrification tank for anaerobically biotreating the wastewater to which the hydrogen donor is added;
An ultraviolet absorbance method sensor for measuring the nitric acid and nitrous acid concentrations in the waste water;
An ion electrode type sensor for measuring the concentration of nitric acid in the waste water;
Based on the concentration of nitric acid and nitrous acid measured by the ultraviolet absorbance method sensor and the concentration of nitric acid and nitrous acid in the waste water determined by the concentration of nitric acid measured by the ion electrode method sensor, the hydrogen A wastewater treatment apparatus containing nitric acid and nitrous acid, comprising: a control unit that controls an addition amount of the hydrogen donor added to the wastewater by a donor addition means.   The amount of hydrogen donor added is the amount of hydrogen donor necessary for the reduction of nitrous acid having a concentration obtained by multiplying the determined nitrous acid concentration by 1.1 and the reduction of nitric acid having the determined nitric acid concentration. The apparatus for treating waste water containing nitric acid and nitrous acid according to claim 1, which is a sum of the amount of hydrogen donor.   The amount of hydrogen donor added is the amount obtained by multiplying the amount of hydrogen donor required for the reduction of nitrous acid with the determined nitrite concentration by 1.1 and the reduction of nitric acid with the determined nitric acid concentration. The apparatus for treating waste water containing nitric acid and nitrous acid according to claim 1, which is a sum of the amount of hydrogen donor. A hydrogen donor addition step of adding a hydrogen donor to waste water containing nitric acid and nitrous acid;
A first measurement step of measuring the concentration of nitric acid and nitrous acid in the waste water by an ultraviolet absorbance method;
A second measurement step of measuring the nitric acid concentration in the waste water by an ion electrode method,
A denitrification step for anaerobically biotreating the wastewater to which the hydrogen donor has been added,
In the hydrogen donor addition step, the concentration of nitric acid and nitrous acid in the wastewater determined by the nitric acid and nitrous acid concentrations measured by the ultraviolet absorbance method and the nitric acid concentration measured by the ion electrode method A method for treating wastewater containing nitric acid and nitrous acid, wherein the amount of the hydrogen donor added to the wastewater is controlled based on the above.   The amount of hydrogen donor added is the amount of hydrogen donor necessary for the reduction of nitrous acid having a concentration obtained by multiplying the determined nitrous acid concentration by 1.1 and the reduction of nitric acid having the determined nitric acid concentration. 5. The method for treating waste water containing nitric acid and nitrous acid according to claim 4, wherein the amount is a sum of the amount of hydrogen donor.   The amount of hydrogen donor added is the amount obtained by multiplying the amount of hydrogen donor required for the reduction of nitrous acid with the determined nitrite concentration by 1.1 and the reduction of nitric acid with the determined nitric acid concentration. 5. The method for treating waste water containing nitric acid and nitrous acid according to claim 4, wherein the amount is a sum of the amount of hydrogen donor.

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