JP5586972B2 - Nitrite nitrogen measuring method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for measuring nitrite nitrogen in a solution by flow injection analysis using an electrochemical measurement method as a detection system using a flow cell.

  The total water quality regulation system is inland in upstream prefectures, etc. that flow into the water area in order to secure environmental standards for wide-area closed water areas such as Tokyo Bay, which are highly polluted due to industrial concentration and population growth. It was established for the purpose of uniformly and effectively reducing the total amount of pollution load for pollution sources, including loads from the department and domestic wastewater. This system was introduced by the amendment of the Water Pollution Control Law in 1978, and has been implemented since 1975 with the subject of chemical oxygen demand (COD).

  As a result, the pollution load related to Tokyo Bay has been steadily reduced, but the achievement rate of COD environmental standards is not satisfactory, and accompanying eutrophication due to nitrogen and phosphorus such as red tide Since problems also occur, in addition to the conventional COD, a total amount regulation for nitrogen content and phosphorus content has been newly implemented.

  Therefore, it is necessary to continuously monitor the nitrogen content and the phosphorus content, and particularly regarding phosphorus, Patent Document 1 proposes an apparatus that can continuously measure soluble phosphorus with high accuracy.

  Nitrogen is widely present and is also contained in natural water. However, nitrogen increases in water because it is contained in food, human waste, fertilizer, etc. Often comes from contamination.

  Nitrogen plays an important role in biological growth activities and is an essential element for microorganisms involved in biological treatment of wastewater. However, nitrogen is considered to be a cause of promoting eutrophication of lakes, marshes and the like, and an increase in nitrogen compounds in water is not preferable.

  As a method for removing nitrogen in waste water as described above, there is a biological nitrification denitrification method described in Non-Patent Document 1.

The biological nitrification denitrification method will be described. First, ammonia in water is converted into nitrous acid or nitric acid by the action of nitrifying bacteria under aerobic conditions. The produced nitric acid and nitrous acid are reduced in the order of NO ₃ ⁻ → NO ₂ ⁻ → NO → N ₂ O → N ₂ and removed as nitrogen gas by the action of denitrifying bacteria.

Non-patent document 1 describes the control of this biological nitrification denitrification process as follows. “Regarding the nitrogen removal process, technology for monitoring nitrification and denitrification reactions using sensors has been established to some extent, and technological development using this technology is active. Ion electrode methods, nitric acid / The UV absorbance method is mainly used to measure nitric acid. "
As a measuring device for monitoring ammonia nitrogen as described in this description, there is an ammonia analyzer ANTAXsc manufactured by HACH. As a measuring device for monitoring nitric acid / nitrite nitrogen, there is a UV type nitric acid meter NITRATAX manufactured by HACH. This measures the nitric acid + nitrite ion concentration. Further, there is a WTW VARiON system as an ion electrode type monitoring device for monitoring ammonia nitrogen and nitrate nitrogen. As described above, there is a measuring device for monitoring and controlling ammonia treatment nitrogen and nitrate nitrogen for water treatment process monitoring, but there is no device for monitoring nitrite nitrogen alone.

  For controlling the biological nitrification / denitrification process, a control method is often used in which the end point of the nitrification / denitrification reaction is detected and the oxygen supply is turned on / off using the above-described monitoring technique.

  In the nitrification step, ammonia nitrogen is generally oxidized under aerobic conditions to nitrite nitrogen via nitrite nitrogen. However, in order to denitrify, it is not necessary to oxidize to nitrate nitrogen, and it is sufficient to oxidize to nitrite nitrogen. This eliminates the need to supply oxygen necessary to oxidize nitrite nitrogen to nitrate nitrogen, leading to energy saving.

  However, since there is no technology that can monitor nitrite nitrogen in the water treatment process, it is common to oxidize ammonia nitrogen to nitrate nitrogen, although the required oxygen supply is increased.

  If there is a measurement device that can monitor nitrite nitrogen in water, the biological nitrification and denitrification method as described above can detect the stage in which ammonia nitrogen is oxidized to nitrite nitrogen, so energy-saving operation can be performed from the current level. It becomes possible.

  In recent years, a nitrogen removal method by anaerobic ammonia oxidation as shown in Non-Patent Document 2 has been proposed as a new biological nitrogen removal method.

The reaction of the anaerobic ammonium oxidation, NO ₂ ^- is reduced to NH ₂ OH, N ₂ H ₄ is produced from NH ₂ OH and which is reduced NH ₄ ⁺ and is denitrified to finally N ₂ gas . In terms of stoichiometry, it is represented by the following formula.
NH ₄ ⁺ + 1.32NO ₂ ⁻ + 0.066HCO ₃ ⁻ + 0.13H ⁺
→ 1.02N ₂ + 0.26NO ₃ ⁻ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O
The anaerobic ammonium oxidation, since anaerobic ammonium oxidizing bacteria perform denitrification of autotrophic and unnecessary organic carbon source as the hydrogen donor, the NH ₄ ⁺ half of the waste water NO ₂ ^- by oxidation Therefore, the amount of oxygen supply can be reduced, and the amount of excess sludge generated can be reduced. Application of anaerobic ammonia oxidation process is suitable for wastewater with high nitrogen concentration.

  In addition, the anaerobic ammonia oxidation method has a very high nitrogen removal rate compared with the conventional biological nitrification denitrification method. In the description of Non-Patent Document 3, the design load conditions of the conventional biological nitrification denitrification method and the anaerobic ammonia oxidation treatment are compared. It is shown that the value is one order larger. Moreover, as described in Non-Patent Document 4, the activity of anaerobic ammonia-oxidizing bacteria may be inhibited depending on the concentration of nitrite nitrogen as a substrate.

  In the anaerobic ammonia oxidation treatment process as described above, denitrification is performed from ammonia nitrogen and nitrite nitrogen. Therefore, monitoring of ammonia nitrogen and nitrite nitrogen is important in process monitoring control. The nitrite nitrogen in the water to be treated in this process has a high concentration, and the nitrite nitrogen in the treated water resulting from the process has a low concentration. Therefore, it is advantageous that nitrite nitrogen monitoring in this process is possible over a wide concentration range. Moreover, it is desired to be able to measure quickly.

  Methods for measuring nitrite nitrogen in water include naphthylethylenediamine absorptiometry and ion chromatography (Non-Patent Document 5). In the naphthylethylenediamine spectrophotometry method, sulfanilamide is added to a sample, this is diazotized with nitrite ions, and N-1-naphthylethylenediamine is added to measure the absorbance of the red colored azo compound to quantify nitrite ions. Is. The quantification range by this method is 0.6 to 6 μg as nitrite ion, and the repeat analysis accuracy is 3 to 10% in terms of coefficient of variation. The quantification range of the ion chromatograph method is 0.5 to 40 mg / L as nitrite ion, and the repeated analysis accuracy is 2 to 10% as a coefficient of variation.

  In addition, although not an official method, there is a nitrite ion meter TiN-9003 from Toko Chemical Laboratory Co., Ltd. as a measurement method for laboratories (Non-patent Document 6).

  According to Non-Patent Document 6, this ion meter is a diaphragm electrode type dedicated meter for measuring nitrite ions. When the pH of the sample becomes 1.5 or less, the nitrite ion changes to nitrite. Nitrous acid enters the electrode through the diaphragm, and changes the pH of the electrolyte according to the concentration of nitrous acid. The diaphragm type nitrite ion electrode measures this pH change and detects the nitrite ion concentration. It is described that nitrite ions can be measured more quickly and stably with a simple operation by simply dropping a pH adjusting agent onto a sample. The measurement range of the nitrite ion meter TiN-9003 is 0.2 to 460 mg / L.

  This nitrite ion meter has a wider measurement range than the naphthylethylenediamine method and ion chromatograph method. However, sample water must be collected in a container, and after adding a pH adjuster, the electrode must be immersed and measured while stirring with a stirrer, so measurement by manned is fundamental and time is required.

  On the other hand, the flow injection analysis method is a method based on injecting a liquid sample into a liquid flowing continuously.

  A method of providing two flow paths for a reagent solution and a carrier liquid such as distilled water that does not affect the measurement and introducing the sample water into the flow of the carrier liquid is a common configuration.

  On the other hand, in the case of using a method called reverse flow injection analysis method in which sample water and carrier liquid are flowed at a constant flow rate instead of the reagent solution and the reagent solution is introduced into the carrier liquid flow, or an expensive reagent is used. After introducing the reagent solution into the carrier liquid flow, at the detector, provide a stopped-flow system that stops the flow, and a plurality of carrier liquid and reagent solution flow paths for a single sample water flow path. Various methods such as a method of analyzing multiple components have been proposed (Non-Patent Document 7).

  The flow injection analysis method has few moving parts, and is characterized in that the measurement can be performed by moving the solution side in the narrow tube, and therefore it is easy to make an apparatus.

  Electrochemical measurement methods are widely used in various fields such as the food field and the medical field because they are high-speed and high-sensitivity measurement methods. The electrochemical measurement method is an excellent measurement method in that the operation is simpler than the method using a chemical reaction. Methods used in electrochemical measurement include a measurement method that applies and holds a constant potential to the measurement electrode, such as voltammetry, and detects changes in the flowing current, and a potential of the measurement electrode, such as polarography. Various measurement methods such as a measurement method for detecting a change are used, and each of them measures the current flowing in the measurement electrode and the potential change of the measurement electrode.

JP 2008-196873 A

Water Environment Handbook, Japan Water Environment Society, Asakura Shoten, October 2006, p. 241 Fresh water technology handbook. 2004, Water Production Promotion Center, edited by the Water Production Technology Handbook Editorial Planning Committee, November 2004, p. 75 NEDO Development Organization, 2006 report, research on nitrogen removal technology in wastewater using by-products, p. 1-6 Physiological and ecological characterization of anaerobic ammonia oxidation (ANAHMOX) bacteria, 42nd Annual Meeting of Japan Society on Water Environment, p. 285 JIS K0102: 2008 “Industrial drainage test method” “Nitrite ion meter TiN-9003”, [online], Toko Chemical Laboratory Co., Ltd. [searched on January 18, 2009], Internet <URL: http: // www. kagaku. com / TOKO / tin9003. html> Rokuro Kuroda, Koichi Oguma, Hiroshi Nakamura, “Flow Injection Analysis”, Kyoritsu Publishing Co., Ltd., September 1990, pp. 50-117

  However, current measurement methods for nitrite nitrogen lack timeliness because it takes time from water collection from the water treatment process to detection of nitrite nitrogen. In the ion chromatographic method, since the upper limit of the nitrite nitrogen determination range is as low as about 40 mg / L, when the nitrite nitrogen has a high concentration, the sample water must be diluted and measured.

  In particular, the anaerobic ammonia oxidation treatment process has a very high nitrogen removal rate and a short treatment time compared to the conventional biological nitrification denitrification method. Also, normal processing may be hindered by the concentration of nitrite nitrogen. Therefore, it is required to measure the nitrite nitrogen concentration more quickly and control the treatment process.

  In order to solve the above-mentioned problems, an object of the present invention is to provide a nitrite nitrogen measuring method and apparatus capable of measuring a nitrite nitrogen concentration range wide and capable of being measured quickly and with high accuracy.

The nitrite nitrogen measuring method of the present invention that achieves the above object is a reaction solution in which sample water and an acidic reagent solution of any one of a sulfuric acid solution, a hydrochloric acid solution, a citric acid solution, an acetic acid solution, and a nitric acid solution are mixed. The reagent solution is supplied as a carrier liquid to the flow cell at a predetermined speed, and the potential of the working electrode is 270 to 480 mV with respect to the Ag / AgCl reference electrode between the working electrode and the counter electrode arranged in the flow cell. A voltage is applied so that the nitrite nitrogen concentration in the sample water is measured based on a current or a charge flowing between the working electrode and the counter electrode .

The nitrite nitrogen measuring apparatus of the present invention that achieves the above object is a reaction solution in which a sample water is mixed with an acidic reagent solution of a sulfuric acid solution, a hydrochloric acid solution, a citric acid solution, an acetic acid solution, or a nitric acid solution. However , the potential of the working electrode is 270 to 270 with respect to the Ag / AgCl reference electrode between the flow cell introduced with the reagent solution as a carrier liquid at a predetermined rate, and the working electrode and the counter electrode arranged in the flow cell. A measuring means for applying a voltage of 480 mV and measuring a nitrite nitrogen concentration in the sample water based on a current or a charge flowing between the working electrode and the counter electrode. It is said.

  Therefore, according to the above invention, the concentration of nitrite nitrogen in the solution can be measured quickly and with high accuracy.

The schematic block diagram which showed the nitrite nitrogen measuring apparatus which concerns on Embodiment 1 of this invention. The characteristic view which showed the pattern of the current measured by the flow injection analysis method. The characteristic view which showed the relationship (in the case of a nitrite nitrogen standard solution density | concentration 200 mg-N / L) of the maximum electric current measured with the sulfuric acid density | concentration in a reagent solution, and the sulfuric acid density | concentration. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 0.6 mL / L, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 3 mL / L, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 6 mL / L, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 15 mL / L, and the measured electric current value. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 30 mL / L, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the sulfuric acid density | concentration in a reagent solution is 60 mL / L, and the measured electric current value. The characteristic view which shows the relationship (in the case of nitrite nitrogen standard solution density | concentration of 100 mg-N / L) of the electric quantity computed from the applied voltage and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 270 mV, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 300 mV, and the measured electric current value. The characteristic view which showed the relationship between the quantity of electricity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 315mV, and the measured electric current value. The characteristic view which showed the relationship between the quantity of electricity computed from the nitrite nitrogen standard liquid density | concentration in case an applied voltage is 330 mV, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 360 mV, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 400 mV, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case an applied voltage is 450 mV, and the measured electric current value. The characteristic view which showed the relationship of the electric quantity computed from the nitrite nitrogen standard solution in case an applied voltage is 480 mV, and the measured electric current value. The characteristic view which showed the relationship (in the case of nitrite-nitrogen standard solution density | concentration of 100 mg-N / L) of the electric quantity computed from the flow rate of a reagent solution and a carrier liquid, and the electric current value detected on the conditions of the flow rate. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the flow rate of a reagent solution and a carrier liquid is 0.3 mL / min, and the measured electric current value. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the flow rate of a reagent solution and a carrier liquid is 0.45 mL / min, and the measured electric current value. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the flow rate of a reagent solution and a carrier liquid is 0.6 mL / min, and the measured electric current value. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the flow rate of a reagent solution and a carrier liquid is 0.9 mL / min, and the measured electric current value. The characteristic view which showed the relationship between the electric quantity computed from the nitrite nitrogen standard solution density | concentration in case the flow rate of a reagent solution and a carrier liquid is 1.2 mL / min, and the measured electric current value. The characteristic view which shows the electric current pattern measured when the flow rates of the reagent solution and the carrier liquid are 0.45 mL / min and 1.2 mL / min. The characteristic view which showed the relationship of the electric quantity (mC) computed from the detected electric current value when measuring with sample amount (microliter) and the sample amount. The characteristic view which shows the electric current pattern detected when sample amount is 100 microliters and 600 microliters. The characteristic view which showed the relationship between the density | concentration (0-20 mg-N / L) of a nitrous acid nitrogen standard solution, and the electric quantity ((micro | micron | mu) C) calculated from the measured electric current value. A characteristic diagram showing measurement accuracy. The selectivity test result of the nitrite nitrogen measuring method which concerns on this invention. The comparison result of the nitrite nitrogen measuring method and official method which concern on this invention. The schematic block diagram which showed the nitrite nitrogen measuring apparatus which concerns on Embodiment 2 of this invention.

  The present invention relates to a nitrite nitrogen measuring method and apparatus capable of automatic measurement continuously and rapidly with high accuracy. Hereinafter, the nitrite nitrogen measuring device and the nitrite nitrogen measuring device of the present invention will be described in detail by exemplifying the nitrite nitrogen measuring device according to the embodiment of the present invention. The measurement method and the nitrite nitrogen measuring device are not limited to the embodiment, and can be appropriately changed in design as long as the effects of the present invention are not impaired.

(Embodiment 1)
The nitrite nitrogen measuring apparatus 1 according to Embodiment 1 of the present invention shown in FIG. 1 measures the nitrite nitrogen concentration by flow injection analysis. Flow injection analysis is a method in which a reagent solution and a carrier liquid are flowed at a constant flow rate, and sample water to be measured is introduced into this flow for measurement. Examples of sample water include waste water discharged from manufacturing industries such as sewage treatment plants, food manufacturing industries, textile industries, and chemical industries.

  The nitrite nitrogen measuring apparatus 1 is provided with a sulfuric acid solution as a reagent solution. The flow injection analysis means 2 includes an injection valve 3, a mixer 4 and a flow cell 5. The flow injection analysis means 2 electrochemically measures the nitrite nitrogen concentration in the sample water.

  A sulfuric acid solution is exemplified as the reagent solution to be supplied to the nitrite nitrogen measuring apparatus 1, but a hydrochloric acid solution, a citric acid solution, an acetic acid solution, a nitric acid solution, or the like can be used without any problem if it is an acidic solution.

  The injection valve 3 is an injection means for injecting the carrier liquid and the reagent solution or sample water. The illustrated injection valve 3 is a six-way rotary valve type. Thin tubes 31 to 35 are connected to the injection valve 3 as flow paths. The narrow tube 31 is a tube constituting a flow path for injecting the carrier liquid supplied by the pump P2. The thin tube 32 is a tube constituting a flow path for injecting the sample water supplied by the pump P3. The thin tube 33 is a tube constituting a sample loop. The narrow tube 34 is a tube constituting a flow path for supplying a carrier liquid containing sample water to the mixer 4. The thin tube 35 is a tube for transferring the sample water overflowed from the sample loop (the thin tube 33) to the drain bottle 7 which is a drain part.

  The injection valve 3 is configured to inject the carrier liquid and the sample water, but may be configured to inject the carrier liquid and the reagent solution. Further, the form of the injection means is not limited to the six-way rotary valve type such as the injection valve 3, and examples thereof include a syringe type and a proportional injector type.

  The mixer 4 mixes the carrier liquid, the reagent solution, and the sample water. As the mixer 4, a known mixer that is used for flow injection analysis using electrochemical detection may be used. A narrow tube 34 and thin tubes 41 and 42 are connected to the mixer 4. The narrow tube 41 is a tube constituting a flow path for injecting the reagent solution supplied by the pump P1. The narrow tube 42 is a tube constituting a flow path for injecting the carrier liquid containing the sample water and the reagent supplied from the mixer 4 into the flow cell 5. The reaction rate can be increased by appropriately heating these thin tube portions involved in chemical reaction with a heating device (not shown). As a result, it is possible to further speed up the measurement.

  Connected to the flow cell 5 is a thin tube 51 for transferring the carrier liquid supplied through the thin tube 42 to the drain bottle 7.

  Moreover, the inside of the flow cell 5 is comprised from a working electrode, a reference electrode, a counter electrode, and electrolyte solution. The working electrode inside the flow cell 5 of the nitrite nitrogen measuring apparatus 1 according to the embodiment of the present invention is made of glassy carbon, the reference electrode is made of Ag / AgCl, and the counter electrode is made of SUS316 or the like. The type of each electrode such as the working electrode, the reference electrode, and the counter electrode is not limited to the combination of the above-described electrodes and the like, and a type / combination that does not hinder measurement is appropriately selected.

  The flow cell 5 is provided between the working electrode and the counter electrode, which is generated based on the reaction between the sample water and the reagent solution contained in the carrier liquid supplied from the mixer 4 while keeping the voltage of the working electrode with respect to the reference electrode constant by the potentiostat 8. Detects current changes.

  The applied voltage of the working electrode with respect to the reference electrode was 270 to 480 mV. However, the range of the applied voltage is not limited to this range, and is appropriately set to a value that does not hinder measurement. As an electrochemical measurement method, coulometry, chronoamperometry, or the like is used.

  Further, the temperature inside the flow cell 5 and the nitrite nitrogen measuring device 1 and the installation environment is measured by a measuring device (not shown), and the measured signal is transmitted to the computer 9.

  A sulfuric acid solution having a sulfuric acid concentration of 0.6 to 60 mL / L was prepared as a reagent solution for the nitrite nitrogen measuring apparatus 1 of the present invention. However, the sulfuric acid concentration of the sulfuric acid solution is not limited to this range, and is appropriately set to a value that does not hinder measurement.

  The carrier liquid uses pure water. However, as long as the carrier liquid is inactive with respect to the sample water and the reagent solution, ultrapure water or a fluorine-based inert liquid may be used instead of pure water.

  An example of the operation of the nitrite nitrogen measuring apparatus 1 will be described with reference to FIG. The reagent solution, the carrier liquid, and the sample water are respectively sent by pumps P1, P2, and P3 to capillaries connected to each pump at a constant speed. The sample water is sent to the drain part (drain bottle 7) by the pump P3. The sample water in the sample bottle 6 is supplied to the injection valve 3 through the thin tube 32 by the pump P3. The sample water measured by the injection valve 3 and the thin tube 33 of the sample loop rides on the flow of the carrier liquid provided through the thin tube 31 by switching the route of the injection valve 3 and enters the mixer 4 through the thin tubes 33 and 34. Supplied. At this time, nitrite nitrogen contained in the sample water reacts with the reagent solution injected through the thin tube 41. When this reaction solution reaches the flow cell 5 through the thin tube 42, the current corresponding to the nitrite nitrogen concentration in the sample water is measured in the flow cell 5. The current measured by the flow cell 5 changes under the influence of the reaction temperature and the like. Therefore, under the voltage control between the electrodes by the potentiostat 8, the current measured for the nitrite nitrogen concentration in the flow cell 5 is input to the computer 9 and integrated, and calculation processing such as correction by the temperature measurement value is performed. Is displayed as a measured value of nitrite nitrogen concentration. The measured value of nitrous acid nitrogen concentration is output to the outside as a transmission output for biological treatment process control.

  The carrier liquid containing the reagent solution and the sample water that has passed through the flow cell 5 is guided to the drain bottle 7 as a waste liquid through the thin tube 51.

  FIG. 2 is a characteristic diagram showing a current pattern measured by a flow injection analysis method. FIG. 2 shows the results obtained by measuring a nitrite-nitrogen standard solution of the same concentration as sample water and measuring the same concentration of nitrite-nitrogen standard solution three times at intervals of 6 minutes.

  With reference to FIGS. 3-9, the result of having examined about the sulfuric acid concentration in the reagent solution of measurement conditions is shown.

  In the nitrite nitrogen measuring apparatus 1 of FIG. 1, a reagent was prepared so that the sulfuric acid concentration was 0.6 to 60 mL / L under the conditions shown in Table 1, and the sample water was measured. As the sample water, 0, 100, 200, 300 mg-N / L nitrite nitrogen standard solution was used and injected from the injection valve 3 for measurement.

  FIG. 3 shows the relationship between the sulfuric acid concentration in the reagent solution and the maximum current (in the case of nitrite nitrogen standard solution 200 mg-N / L). As shown in FIG. 3, the maximum current increased as the sulfuric acid concentration in the reagent solution increased.

  4 to FIG. 9 show that when the concentration of the sulfuric acid solution as the reagent solution is 0.6 to 60 mL / L in the nitrite nitrogen measuring apparatus 1 of FIG. The quantity of electricity (mC) calculated from the current value measured by the flow cell 5 with respect to the nitrous acid nitrogen standard solution concentration of L is shown. 4 to 9, the vertical axis represents the amount of electricity (mC) calculated based on the current value measured by the flow cell 5, and the horizontal axis represents the nitrite nitrogen concentration ( mg-N / L).

  As is apparent from FIGS. 4 to 9, when the sulfuric acid concentration in the reagent solution was 0.6 to 60 mL / L, nitrite nitrogen in a concentration range of 0 to 300 mg-N / L could be measured.

  It is preferable that the amount of reagent used is small because the running cost is low. In addition, the measurement waste liquid in this apparatus has a low pH and needs to be neutralized at the time of disposal. Considering such a case, it is more preferable that the sulfuric acid concentration used for the measurement is low because the running cost is low. The sulfuric acid concentration in the reagent solution is set to a low concentration within the allowable range of measurement accuracy.

  10 to 18 show the results of examining the applied voltage among the measurement conditions.

  In the nitrous acid nitrogen measuring apparatus 1 of FIG. 1, a sulfuric acid solution is used as a reagent solution under the conditions shown in Table 2, and 0, 100, 200, 300, 400, 500 mg-N / L of nitrite is used as sample water from the injection valve 3. A nitrogen standard solution was injected, the applied voltage was changed from 270 mV to 480 mV, the current value was measured with the flow cell 5, and the amount of electricity was calculated from the current value.

  FIG. 10 is a characteristic diagram showing the relationship between the applied voltage and the amount of electricity calculated from the measured current value (when the nitrite nitrogen standard solution concentration is 100 mg-N / L). In this applied voltage range, the amount of electricity calculated from the current value decreased as the applied voltage increased.

  11 to FIG. 18 show that in the nitrite nitrogen measuring apparatus 1 of FIG. 1, the applied voltage is 270 to 480 mV under the conditions of Table 2, and the nitrite nitrogen standard solution concentration is 0 to 500 mg-N / L. The amount of electricity (mC) calculated from the current value measured by the flow cell 5 is shown.

Since the determination coefficients (R ² ) shown in FIGS. 11 to 18 are all R ² > 0.9, it is shown that the measurement can be performed accurately in the range of the applied voltage of 270 to 480 mV under the conditions of Table 2. . Since the applied voltage affects sensitivity and the like, it is appropriately set within a range that does not hinder measurement.

  19 to 25 show the results of studying the flow rates of the reagent solution and the carrier liquid.

  In the nitrite nitrogen measuring apparatus 1 of FIG. 1, a current value measured by injecting a nitrite nitrogen standard solution of 0 to 500 mg-N / L as sample water from the injection valve 3 under the conditions of Table 3 and measuring with the flow cell 5. From this, the amount of electricity was calculated. The flow rates of the reagent solution and the carrier liquid were changed in the range of 0.3 to 1.2 mL / min.

  19 to 24, a sulfuric acid solution is used as a reagent solution, a 0-500 mg-N / L nitrite nitrogen standard solution is injected as sample water from an injection valve, and the flow rates of the reagent solution and the carrier solution are 0.3- This is the result of calculating the amount of electricity (mC) from the current value measured by the flow cell 5 while changing to 1.2 mL / min.

  FIG. 19 shows the relationship between the flow rate of the reagent solution and the carrier liquid and the amount of electricity calculated from the measured current value (in the case of a nitrite nitrogen standard solution concentration of 100 mg-N / L). In the flow rate range of the reagent and carrier liquid shown in Table 3, the amount of electricity increased as the flow rate decreased.

  20 to 24 show the nitrite-nitrogen measuring apparatus 1 of FIG. 1, changing the flow rates of the reagent solution and the carrier liquid in the range of 0.3 to 1.2 mL / min under the conditions of Table 3, and 0 to 500 mg. It is the result of calculating the amount of electricity (mC) from the current value measured by the flow cell 5 in the N / L nitrite nitrogen standard solution.

Since the determination coefficients (R ² ) shown in FIGS. 20 to 24 are all R ² > 0.9, the flow rate of the carrier liquid is within the range of 0.3 to 1.2 mL / min under the conditions in Table 3. It shows that nitrite nitrogen concentration can be measured.

  FIG. 25 is a characteristic diagram showing a pattern of measurement current when the flow rates of the reagent solution and the carrier liquid are 0.45 mL / min and 1.2 mL / min. As shown in FIG. 25, the slower the flow rate, the broader the current change pattern. Also, the slower the flow rate, the longer the time for detecting the current. When the flow rate of the reaction solution is increased, the time change pattern of the measurement current becomes sharper, and when the flow rate is decreased, it is broader. In the flow injection analysis method, since the flow velocity generally affects the sensitivity of measurement, the flow velocity is appropriately set within a range that does not hinder measurement.

  The flow rate affects the chemical reaction between the reagent solution containing sulfuric acid and the sample water in the mixer, and also affects the redox reaction on the working electrode in the flow cell 5.

  Since the running cost can be reduced when the amount of the reagent solution and the carrier liquid used is small, it is preferable that the flow rate is low. On the other hand, since the time during which the current is measured becomes longer by slowing down the flow rate, the measurement interval required for one measurement becomes longer. The flow rate should be set as late as possible within the allowable range of measurement accuracy and measurement interval.

  26 and 27 show the results of studying the sample amount.

  In the nitrite-nitrogen measuring apparatus 1 in FIG. 1, 100 mg-N / L nitrite-nitrogen standard solution as sample water under the conditions shown in Table 4 is used with sample amounts of 50, 100, 200, 400, and 600 μL from the injection valve 3. The current was measured with the flow cell 5, and the amount of electricity was calculated.

  FIG. 26 is a characteristic diagram showing the relationship between the amount of sample (μL) and the amount of electricity (mC) calculated from the measured current value. In FIG. 26, a line connecting the amount of electricity at a sample amount of 200 μL and the zero point (0, 0) is indicated by a straight line.

  As shown in FIG. 26, the larger the sample amount, the larger the amount of electricity. Under the conditions in Table 4, the amount of electricity is not proportional to the sample amount. The amount of electricity of sample amounts 50, 100, and 200 μL is along the above-mentioned straight line. On the other hand, the sample quantities of 400 and 600 μL are located below the straight line. However, if the measurement conditions such as sulfuric acid concentration, sample quantity, flow rate of the reagent and carrier liquid are optimized, it will be on the straight line. Conceivable.

  FIG. 27 shows current measurement patterns with sample amounts of 100 μL and 600 μL. The larger the sample amount, the larger the maximum current, and the longer the time during which the current is measured.

  From this result, a test was conducted by selecting 200 μL as a sample amount in which the amount of electricity is relatively proportional to the amount of sample and the amount of electricity is as large as possible. However, the amount of sample is not limited to this value, and is appropriately selected within a range that does not hinder measurement.

  FIG. 28 shows the results of studying the measurement range.

  In the nitrite-nitrogen measuring apparatus 1 in FIG. 1, a sample amount of 200 μL is injected from the injection valve 3 using 0 to 20 mg-N / L nitrite-nitrogen standard solution as sample water under the conditions in Table 5, and the flow cell 5 The current value was measured with and the amount of electricity was calculated.

  FIG. 28 is a characteristic diagram showing the relationship between the concentration of nitrite nitrogen standard solution (0 to 20 mg-N / L) and the amount of electricity calculated from the current value.

The coefficient of determination (R ² ) in FIG. 28 is as high as 0.996, indicating that measurement can be performed even in the range where the nitrite nitrogen concentration is 20 mg-N / L or less under the conditions in Table 5.

  In FIG. 29, the reproducibility of the measured value by the nitrite nitrogen measuring apparatus 1 is shown. FIG. 29 shows the results of measuring the nitrite nitrogen standard solution 100 mg-N / L at 6-minute intervals in the nitrite nitrogen measuring device 1 of FIG.

  FIG. 29 shows that the coefficient of variation of 53 measurement values is 0.7%, which can be measured with good reproducibility.

  The result of having examined the selectivity of various nitrogen forms by the nitrite nitrogen measuring method according to the present invention will be described.

  In the nitrite nitrogen measuring apparatus 1 of FIG. 1, four types of sample water of nitrate nitrogen, ammonia nitrogen, nitrite nitrogen and a mixture of three types of nitrogen were prepared and measured under the conditions of Table 7. . The measurement results are shown in FIG.

  Only nitrite nitrogen was measured for nitrate nitrogen, ammonia nitrogen, nitrite nitrogen and a mixture of three nitrogen forms.

  Therefore, it was confirmed that the measurement method according to the present invention can selectively measure nitrite nitrogen with respect to various nitrogen forms.

  Next, a comparative test result between the nitrite nitrogen measuring method and the official method (naphthylethylenediamine absorptiometry) according to the present invention will be described.

  In the nitrite nitrogen measuring apparatus 1 of FIG. 1, under the conditions shown in Table 8, the nitrite-treated water of the activated sludge dehydrated filtrate and the nitrite-treated water of the inorganic synthetic wastewater were appropriately diluted and measured as sample water. The same sample water was also measured by the official method. The result is shown in FIG.

  The correlation between the measurement result of the present invention and the measurement result by the official method is high, and the slope of the regression line is 1.00, which shows that the measurement value by both measurement methods has almost no error and can be measured with high accuracy.

(Embodiment 2)
The nitrite nitrogen measuring apparatus 10 according to the second embodiment of the present invention shown in FIG. 32 measures the nitrite nitrogen concentration by flow injection analysis. The nitrite nitrogen measuring apparatus 10 according to the second embodiment of the present invention is configured to flow a reagent solution at a constant flow rate in flow injection analysis, and to measure by introducing sample water to be measured into this flow. The analysis is performed by the same method as the nitrite nitrogen measuring apparatus 1 according to the first embodiment of the present invention. Therefore, the measurement conditions, the types of reagents used, and the like are the same as those of the nitrite nitrogen measuring apparatus 1 described in the first embodiment, and the nitrite nitrogen measuring apparatus 10 is the same as the nitrite nitrogen measuring apparatus 1. Are denoted by the same reference numerals, and detailed description thereof is omitted.

  The nitrite nitrogen measuring apparatus 10 is provided with a sulfuric acid solution as a reagent solution. The flow injection analysis means 11 includes an injection valve 3 and a flow cell 5. The nitrite nitrogen concentration in the sample water is electrochemically measured by the flow injection analysis means 11.

  The injection valve 3 is an injection means for injecting sample water into the reagent solution. The illustrated injection valve 3 is a six-way rotary valve type. The injection valve 3 is connected with thin tubes 32, 33, 35, 43, and 44 as flow paths. The thin tube 43 is a tube constituting a flow path for injecting the reagent solution supplied by the pump P4. The thin tube 32 is a tube constituting a flow path for injecting the sample water supplied by the pump P3. The thin tube 33 is a tube constituting a sample loop. The thin tube 44 is a tube that constitutes a flow path for supplying a reagent solution containing sample water to the flow cell 5. The thin tube 35 is a tube for transferring the sample water overflowed from the sample loop (the thin tube 33) to the drain bottle 7 which is a drain part.

  The form of the injection means is not limited to the six-way rotary valve type such as the injection valve 3, and for example, a syringe type or a proportional injector type may be used.

  The reaction rate can be increased by appropriately heating a thin tube part (for example, the thin tube 44) involved in the chemical reaction with a heating device (not shown). As a result, it is possible to further speed up the measurement.

  Connected to the flow cell 5 is a thin tube 51 for transferring a reagent solution or sample water supplied through the thin tube 44 to the drain bottle 7.

  Moreover, the inside of the flow cell 5 is comprised from a working electrode, a reference electrode, a counter electrode, and electrolyte solution. The working electrode inside the flow cell 5 of the nitrite nitrogen measuring apparatus 10 according to the embodiment of the present invention is made of glassy carbon, the reference electrode is made of Ag / AgCl, and the counter electrode is made of SUS316 or the like. The type of each electrode such as the working electrode, the reference electrode, and the counter electrode is not limited to the combination of the above-described electrodes and the like, and a type / combination that does not hinder measurement is appropriately selected.

  The flow cell 5 detects a change in current between the working electrode and the counter electrode, which is generated based on the reaction between the sample water supplied from the thin tube 44 and the reagent solution, while keeping the voltage of the working electrode with respect to the reference electrode constant by the potentiostat 8.

  The applied voltage of the working electrode with respect to the reference electrode was 270 to 480 mV. However, the range of the applied voltage is not limited to this range, and is appropriately set to a value that does not hinder measurement. As an electrochemical measurement method, coulometry, chronoamperometry, or the like is used.

  Further, the temperature inside the flow cell 5 and the nitrite nitrogen measuring device 10 and the installation environment is measured by a measuring instrument (not shown), and the measured signal is transmitted to the computer 9.

  A sulfuric acid solution having a sulfuric acid concentration of 0.3 to 30 mL / L was prepared as a reagent solution of the nitrite nitrogen measuring apparatus 10 of the present invention. However, the sulfuric acid concentration of the sulfuric acid solution is not limited to this range, and is appropriately set to a value that does not hinder measurement.

  An example of the operation of the nitrite nitrogen measuring apparatus 10 will be described with reference to FIG. The reagent solution is fed to the narrow tube 44 at a constant speed by the pump P4. The sample water in the sample bottle 6 is supplied to the injection valve 3 through the thin tube 32 by the pump P3, and is sent to the drain part (drain bottle 7). The sample water measured by the injection valve 3 and the thin tube 33 of the sample loop rides on the flow of the reagent solution provided through the thin tube 43 by switching the route of the injection valve 3 and flows into the flow cell 5 through the thin tubes 33 and 44. Supplied. At this time, nitrite nitrogen contained in the sample water reacts with the reagent solution. When this reaction solution passes through the thin tube 44 and reaches the flow cell 5, a current corresponding to the nitrite nitrogen concentration in the sample water is measured in the flow cell 5. The current measured by the flow cell 5 changes under the influence of the reaction temperature and the like. Therefore, under the voltage control between the electrodes by the potentiostat 8, the current measured for the nitrite nitrogen concentration in the flow cell 5 is input to the computer 9 and integrated, and calculation processing such as correction by the temperature measurement value is performed. Is displayed as a measured value of nitrite nitrogen concentration. The measured value of nitrous acid nitrogen concentration is output to the outside as a transmission output for biological treatment process control.

  The carrier liquid containing the reagent solution and the sample water that has passed through the flow cell 5 is guided to the drain bottle 7 as a waste liquid through the thin tube 51.

  Similarly to the nitrite nitrogen measuring device 1 according to the first embodiment, the nitrite nitrogen measuring device 10 according to the second embodiment dilutes 0-500 mg-N / L nitrite nitrogen in water. It was confirmed by experiment that it could be measured without any problems.

  According to the nitrite nitrogen measuring device 10 according to the second embodiment, piping and a pump for circulating the carrier liquid are unnecessary, so the number of device parts can be reduced, and the nitrite nitrogen measuring device 10 is simplified. be able to. In addition, by reducing the number of pumps, the measurement accuracy of the nitrite-nitrogen measuring apparatus 10 is improved because the measurement accuracy does not decrease due to the flow rate fluctuation of the reduced pump. Furthermore, since the number of solutions (reagent solution, sample water) required for the measurement is two, the number of containers for storing the solution can be reduced, and operations such as solution replenishment are reduced.

  As described above, as shown in Embodiments 1 and 2, according to the nitrite nitrogen measuring method and the nitrite nitrogen measuring apparatus of the present invention, nitrite nitrogen can be monitored in the water treatment process, and nitrite nitrogen can be monitored. Process control using concentration measurement signals enables energy-saving operation of wastewater treatment by biological nitrification denitrification.

  Moreover, the nitrite nitrogen measuring apparatus of this invention can measure without diluting 0-500 mg-N / L nitrite nitrogen in water. Furthermore, it is possible to measure quickly and accurately, unattended and continuously.

  Therefore, the nitrite nitrogen measuring device of the present invention can be used for monitoring and controlling an anaerobic ammonia oxidation process for treating high nitrite nitrogen-containing water.

DESCRIPTION OF SYMBOLS 1,10 ... Nitrite nitrogen measuring apparatus 2, 11 ... Flow injection analysis means 3 ... Injection valve 4 ... Mixer 5 ... Flow cell 6 ... Sample bottle 7 ... Drain bottle 8 ... Potentiostat 9 ... Computer (measuring means)
31-35, 41-44, 51 ... capillary

Claims (2)

Supply a reaction solution, which is a mixture of sample water and an acidic reagent solution of sulfuric acid solution, hydrochloric acid solution, citric acid solution, acetic acid solution, or nitric acid solution, to the flow cell at a predetermined rate using the reagent solution as a carrier solution. Then , a voltage is applied between the working electrode arranged in the flow cell and the counter electrode so that the potential of the working electrode is 270 to 480 mV with respect to the Ag / AgCl reference electrode, and the working electrode and the counter electrode are A method for measuring nitrite nitrogen, comprising measuring a nitrite nitrogen concentration in the sample water based on a current or a charge flowing between them. A reaction cell in which an acidic reagent solution of any one of a sulfuric acid solution, a hydrochloric acid solution, a citric acid solution, an acetic acid solution, and a nitric acid solution is mixed with sample water is introduced into the flow cell at a predetermined rate using the reagent solution as a carrier liquid. ,
A voltage is applied between the working electrode and the counter electrode between the working electrode and the counter electrode so that the potential of the working electrode is 270 to 480 mV with respect to the Ag / AgCl reference electrode. And a measuring means for measuring a nitrite nitrogen concentration in the sample water based on a current or a charge flowing through the nitrite nitrogen measuring device.

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