JPH0727758A - Analytical method of nitrogen compound and phosphorus compound in water and photooxidation and decomposition apparatus - Google Patents

Abstract

PURPOSE:To measure a nitrogen compound and a phosphorus compound in a sample water in common and to perform a continuous analysis for many hours. CONSTITUTION:The sample water is supplied to a reaction tank, and it is heated to 90 deg.C. While the air is being supplied to the sample water, the sample water is irradiated with ultraviolet rays by a low-pressure mercury lamp, and a photooxidation and decomposition reaction is caused. After the photooxidation and decomposition reaction has been finished, a part of the sample water is taken into a measuring tank, and nitrate ions are measured at a wavelength of 220nm by an absorptiometer. Then, an ammonium molybdate solution and an L-ascorbic acid solution are added to the sample water which is left in the measuring tank, a coloring reaction is caused, and phosphate ions are measured at a wavelength of 880nm by an absorptiometer by using the colored liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing trace amounts of nitrogen compounds and phosphorus compounds contained in wastewater discharged from factories and business establishments and environmental water such as rivers and lakes. The present invention also relates to an oxidative decomposition apparatus which oxidizes nitrogen compounds and phosphorus compounds in the sample water by such an analysis method to convert them into nitrate ions and phosphate ions, respectively.

[0002]

2. Description of the Related Art In Japan, analysis methods for nitrogen compounds and phosphorus compounds in water are officially standardized by JIS K0102 and Environmental Agency Notification No. 140. Nitrogen compounds in water are present as nitrate ions, nitrite ions, ammonium ions or organic nitrogen. In the TN (total nitrogen) analysis method for measuring all nitrogen in these water, all nitrogen compounds are converted into nitrate ions for measurement, but ammonium ions and organic nitrogen are not easily oxidized to nitrate ions. Therefore, in the TN measurement, an alkaline potassium peroxodisulfate solution is added to sample water and heated at 120 ° C. for 30 minutes to oxidize all nitrogen compounds into nitrate ions. After cooling it, the pH was adjusted to 2-3, and the ultraviolet absorbance at a wavelength of 220 nm due to nitrate ions was measured.

On the other hand, phosphorus compounds in water are phosphate ions,
It exists as hydrolyzable phosphorus or organic phosphorus.
In TP (total phosphorus) measurement, potassium peroxodisulfate is added as an oxidant in a neutral state, and all phosphorus compounds are oxidized to phosphate ions by heating at 120 ° C. for 30 minutes. Since the phosphate ion does not have a unique light absorption,
To measure the phosphate ion, after cooling, an ammonium molybdate solution and an L-ascorbic acid solution are added as color formers to develop color, and the absorbance at a wavelength of 880 nm is measured.

In another TN measuring method, after oxidation to nitrate ions at a high temperature of 500 ° C. or higher using an oxidation catalyst, it is measured as a nitrogen oxide by a chemiluminescence method, or the nitrogen oxide is further analyzed in a redox reaction tube ( It is passed through about 600 ° C.) to decompose into nitrogen gas and measured as nitrogen by gas chromatography. As another method, a method of supplying ozone to sample water to oxidize ozone is also performed. The ozone oxidation is performed under alkaline conditions in TN measurement and under acidic conditions in TP measurement.

[0005]

There is no device that analyzes TN measurement and TP measurement in sample water with a common analyzer. This is because in the oxidation by an oxidant and the ozone oxidation, the pH condition at the time of oxidation is different such that the oxidation of the nitrogen compound is carried out under alkaline condition and the oxidation of the phosphorus compound is carried out under neutral condition or acidic condition. . In addition, in the oxidation method using an oxidant, since it is heated to a high temperature such as 120 ° C., which is higher than the boiling point of water, a reaction vessel having a pressure resistant structure is required, and the structure and operation of the oxidizer becomes complicated, resulting in high cost. is there.
Since the oxidant is consumed, it must be replenished frequently, which causes a problem of high running cost.

The method of oxidizing a nitrogen compound using a catalyst requires a high temperature such as 500 ° C. or higher, and the deterioration of the catalyst is severe. Not only is the device complicated in structure and difficult to maintain, but also analytical methods using catalysts are generally unsuitable for on-site use as monitors. Since the ozone oxidation method has a weak oxidizing power in the neutral range, both the oxidation of nitrogen compounds and the oxidation of phosphorus compounds are p.
A mechanism for adjusting H is required, and the structure of the device becomes complicated. Further, a pH adjusting liquid of acid and alkali is also required as a consumable item. In this way, the conventional analysis method not only cannot measure nitrogen compounds and phosphorus compounds in common, but also increases the cost and lacks the suitability as a continuous monitor.
Difficult to use.

Therefore, it is an object of the present invention to provide an analysis method that enables common measurement of nitrogen compounds and phosphorus compounds in sample water and that enables continuous analysis for a long time. . It is another object of the present invention to provide a convenient device for oxidizing both nitrogen compounds and phosphorus compounds into nitrate ions and phosphate ions by such an analytical method.

[0008]

The analysis method of the present invention includes the following steps (A) to (C) to analyze both nitrogen compounds and phosphorus compounds in water. (A) An oxidizing step of heating sample water to 50 to 100 ° C. and irradiating the sample water with ultraviolet rays while blowing a gas containing oxygen or ozone, and (B) absorbing nitrate ions of the oxidized sample water. Step of measuring by photometric method, (C) Step of adding a color-developing agent that selectively reacts with phosphate ion to oxidized sample water, and measuring the color-developing solution by absorptiometric method.

The photo-oxidative decomposition apparatus used in the analysis method of the present invention comprises an oxidation reaction tank having a sample water inlet / outlet port and a gas supply port,
An ultraviolet light source for irradiating the inside of the oxidation reaction tank with an ultraviolet ray and a heating means for heating the oxidation reaction tank are provided, and the sample water contained in the oxidation reaction tank is heated by the heating means to 50 to 1
While heating to 00 ° C and blowing a gas containing oxygen or ozone into the sample water from a gas supply port, the sample water is irradiated with ultraviolet rays from an ultraviolet light source to oxidize both nitrogen compounds and phosphorus compounds in the sample water. And nitrate and phosphate, respectively.

[0010]

When oxygen or ozone in the gas blown into the sample water is irradiated with ultraviolet rays, the following reaction occurs and oxygen atoms or ozone are generated in the water. O ₂ + UV (185 nm) → 2O O + O ₂ → O ₃ O ₃ + UV (254 nm) → O + O _{2 Since} oxygen atoms and ozone have oxidizing power, nitrogen compounds and phosphorus compounds in the sample water are oxidized to form nitrate ions and phosphorus ions, respectively. Change to acid ions.

If an organic compound is present, the unsaturated bond of the organic compound is cleaved. Ultraviolet absorption by the unsaturated bond causes interference of absorption peculiar to nitrate ion, but the interference is removed by cutting the unsaturated bond by oxygen atom or ozone. For example, NO in FIG.
Absorption spectrum a of sample water containing ₂ C ₆ H ₄ OH (sample water equivalent to 1 ppm in nitrogen concentration) before ultraviolet irradiation and absorption spectrum b after ultraviolet irradiation while blowing air.
It represents. In the sample water before ultraviolet irradiation, ultraviolet absorption of an unsaturated bond having a maximum absorption at about 340 nm and an absorption band at 400 nm or less is observed. When UV irradiation is performed while blowing air to cause photooxidative decomposition, the unsaturated bond disappears and only the spectrum specific to nitrate ion is detected. This greatly improves the accuracy of nitrate ion measurement. Sample water 50-100
The temperature is raised to 0 ° C. because the photooxidative decomposition reaction is greatly promoted by the heating.

[0012]

FIG. 1 shows one embodiment of the method of the present invention in the order of steps, and FIG. 2 shows a schematic structure of a measuring apparatus. FIG. 4 shows an example of a photo-oxidative decomposition tank for performing photo-oxidative decomposition. In the configuration diagram of FIG. 2, 2
Is a photo-oxidative decomposition tank, which is provided with a heating means so that it can be heated to 50 to 100 ° C., a means for supplying oxygen or air to the sample water, and a means for irradiating the sample water with ultraviolet rays.
The sample water after the nitrogen and phosphorus compounds are oxidized to nitrate ions and phosphate ions by the irradiation of ultraviolet rays in the photooxidation decomposition tank 2 is introduced into the measurement tank 8. Reference numeral 10 is an absorptiometer for measuring the absorbance of nitrate ions of the sample water in the measuring tank 8 and the amount of color development by the phosphate ions after the addition of the coloring agent as the absorbance. The ammonium molybdate solution and the L-ascorbic acid solution are measured by the measuring instruments 12 and 14 and mixed and supplied to the measuring tank 8 for the measurement of phosphate ions. Cleaning water is supplied to the photo-oxidative decomposition tank 2 and the measuring tank 8 for cleaning.

FIG. 4 shows an example of the photooxidation reaction tank 2.
(A) is a top view and (B) is a front sectional view. FIG. 4 shows an inner cylinder type photo-oxidative decomposition tank, in which a low-pressure mercury lamp 22 for irradiating ultraviolet rays is provided in the reaction tank 20 and is in direct contact with sample water in the reaction tank 20. The low-pressure mercury lamp 22 has a short-wavelength ultraviolet light, for example, 185 nm. An air inlet 24, a sample water inlet 26, and a sample water outlet 28 are provided at the bottom of the reaction tank 20, and joints are provided at these inlets and outlets so that a tube can be connected. In order to discharge the overflow liquid at the time of introducing the sample liquid, a side tube 30 is provided at the upper part of the reaction tank 20.
Is provided. The side tube 30 is also provided with a joint for tube connection.

The reaction tank 20 is made of aluminum, a cartridge heater 32 and a temperature sensor 34 are embedded, and the temperature of the reaction tank 20 is controlled to about 90.degree. Reaction tank 2
The periphery of 0 is covered with a heat insulating material 36 as a heat insulating material.
The inner surface of the reaction tank 20 is mirror-polished to have a mirror structure for multiple reflection of ultraviolet rays. The material of the reaction tank 20 is not limited to aluminum, but stainless steel, glass, or the like can be used. Also in the case of stainless steel, it is preferable to mirror-polish to form a mirror structure. In the case of glass, since Pyrex glass does not transmit ultraviolet rays, it is possible to form a mirror structure by forming a silver mirror or an aluminum vapor deposition film on the inner surface and by forming a silver mirror or aluminum vapor deposition film on the outer surface in the case of ultraviolet ray transmitting glass. If the reaction tank 20 has a mirror structure, the ultraviolet radiation can be effectively used, and the decomposition efficiency is significantly improved.

The ultraviolet radiation source is not limited to the low-pressure mercury lamp 22, but any light source capable of emitting ultraviolet light with strong energy, such as an excimer laser, a deuterium lamp, a xenon lamp, or a Hg-Zn-Pb lamp, can be used. it can. The low-pressure mercury lamp is convenient because it is inexpensive and has a long life and is suitable as a monitor. As the low-pressure mercury lamp 22, an ultraviolet lamp made of ultraviolet-transparent glass with a diameter of about 18 mm is a discharge current of 0.8 A and a discharge voltage of 100 V.
It is processed into a U shape. Attach this to two reaction vessels,
If immersed in the sample water, the amount of water in the reaction tank 20 is about 100 m.
It becomes l. 23 is a power transformer for lighting the low-pressure mercury lamp 22, and 37 is a temperature controller for controlling the temperature of the reaction tank 20. At the time of oxidative decomposition, the low pressure mercury lamp 22 is turned on, the sample water in the reaction tank 20 is irradiated with ultraviolet rays, and air is supplied from the air inlet 24 at about 0.1 liter / minute.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. The sample water is supplied to the reaction tank 20 through the sample inlet 26 while being measured after the large dirt is removed by a filter or the like. Reaction tank 20
Then, the sample water is heated to 90 ° C., and air is supplied from the air inlet 24 while the low pressure mercury lamp 22 is supplied for 20 minutes.
The sample water is irradiated with the ultraviolet rays. It is considered that the next reaction occurs in the reaction tank 20 due to the irradiation of ultraviolet rays. O ₂ + UV (185 nm) → 2O O + O ₂ → O ₃ O ₃ + UV (254 nm) → O + O ₂ O + O ₃ → 2O ₂ (O, O ₃ ) + (nitrogen compound, phosphorus compound) → nitrate ion, phosphate ion (O , O ₃ ) + unsaturated compound → saturated compound, CO ₂ ,
H ₂ O

After the photo-oxidative decomposition is completed, a part or all of the sample water in the reaction tank 20 is taken out to the measuring tank 8 and the absorptiometer 10 is used.
To measure nitrate ion at a wavelength of 220 nm. next,
An ammonium molybdate solution and an L-ascorbic acid solution are added to the measuring tank 8 to cause a color reaction. Phosphate ion of the color-developed liquid is measured with an absorptiometer 10 at a wavelength of 880 nm.

Table 1 shows the recovery rates when nitrogen compounds and phosphorus compounds were measured using standard substances by this method. The recovery rate indicates the ratio of the nitrogen compounds and phosphorus compounds in the sample water oxidized to nitrate ions and phosphate ions, respectively. A recovery rate of 100% means that all nitrogen compounds and phosphorus compounds were oxidized and converted into nitrate ions and phosphate ions, respectively. The concentration of nitrogen and phosphorus of each standard substance was 1 ppm (w / v).

[0019]

[Table 1] Component recovery rate (%) Nitrogen compound NaNO ₂ 103 NO ₂ C ₆ H ₄ OH 101 NH ₄ Cl 101 (NH ₄ ) ₂ SO ₂ 98 HOOCCH ₂ CH (NH ₂ ) COOH 99 Phosphorus compound (HOCH ₂ ) ₂ CHONO ₂ PO ₃ 98 C ₆ H ₅ Na ₂ PO ₄ 106 CH ₃ P (C ₆ H ₅ ) ₃ Br 94

From the results of Table 1, the recovery rate is almost 1 in all cases.
The value is 00%, which is a good value. As described above, it has been clarified that both the nitrogen compound and the phosphorus compound are oxidized in the reaction tank 20 to be converted into nitrate ion and phosphate ion, respectively, and both the nitrogen compound and the phosphorus compound can be measured by one analyzer.

Here, using the photo-oxidative decomposition tank of FIG. 4, the sample water containing 1 ppm of methyltriphenylphosphonium bromide as a standard sample was measured and the temperature effect and aeration effect at the time of ultraviolet irradiation are shown in FIG. explain. First, when the sample water is heated to 60 ° C. and the case where air is supplied from the air inlet 26 and the case where it is not supplied are compared, there is a difference in recovery rate of about three times. It can be seen that the supply of air during the irradiation of ultraviolet rays effectively acts on the oxidation by oxygen atoms or ozone. When comparing the case where the temperature was changed while supplying air to the sample water during UV irradiation, there was a difference in the recovery rate between 60 ° C and 80 ° C, and the oxidation reaction was promoted at higher temperatures. Is clear.

FIG. 6 shows the results of measuring the effect of multiple reflection of ultraviolet rays on the inner surface of the reaction vessel. A comparison is made between a case where the inner surface of the reaction tank 20 is mirror-finished so as to reflect ultraviolet rays, and b where it is not. The sample water was an ammonium chloride aqueous solution containing 1 ppm of nitrogen, the temperature was set to 90 ° C., and air was supplied at about 100 ml / min. As a result, the multi-reflection of ultraviolet rays has a remarkable effect on the photo-oxidative decomposition reaction.

The photo-oxidation decomposition tank 2 can be modified in various ways. For example, if the sample water is seawater or salty water,
The reaction tank is preferably made of glass. FIG. 7 shows an example of an inner cylinder type photooxidation decomposition tank in which the reaction tank is made of glass. (A) is a top view and (B) is a front sectional view.
An air inlet 24, a sample inlet 26, and a sample outlet 28 are provided at the bottom of a glass reaction tank 40 such as Pyrex, and an overflow liquid outlet 30 is provided as a side tube at the top. A metal protective tank 42 having good thermal conductivity is provided in contact with the outside of the reaction tank 40 at the side and bottom of the reaction tank 40, and the cartridge heater 32 and the temperature sensor 34 are embedded in the protective tank 42. The other structure is the same as that of FIG. 4, the low-pressure mercury lamp 22 is mounted in the reaction tank 40, and the outside of the protection tank 42 is covered with the heat insulating material 36.

In the photooxidation decomposition tank of FIGS. 4 and 7, the sample inlet 26 is not limited to the bottom portion, but may be provided at the side portion or the upper portion. Further, when the sample inlet is provided at the bottom, the sample inlet and the air inlet may be merged, and a common one inlet may be provided at a portion connected to the reaction tank.

FIG. 8 shows an example of an outer cylinder type photooxidation decomposition tank in which an ultraviolet light source is arranged outside the reaction tank. In FIG. 8, the two low-pressure mercury lamps 50 are arranged outside the reaction tank 52. The reaction tank 52 is made of ultraviolet transparent glass.
Reference numeral 54 is a support member for the reaction tank 52. Illustrations of the air inlet, sample inlet, sample outlet, overflow liquid outlet, etc. are simplified. In order to perform multiple reflection of ultraviolet rays, an outer tube 55 for reflecting ultraviolet rays is provided outside the low pressure mercury lamp 50. A heater 56 is provided outside the outer cylinder 55. Comparing the inner cylinder type photo-oxidative decomposition tank and the outer cylinder type photo-oxidative decomposition tank, the inner cylinder type can effectively utilize radiation, but the ultraviolet lamp is apt to be contaminated. The outer cylinder type has the opposite characteristic.

The analysis method of the present invention does not necessarily have a recovery rate of 10.
It does not mean that it must be used under the condition of 0%. For example, the recovery rate of the method of the present invention and the conventional established method using oxidation with an oxidant and absorption spectrophotometry is 10 or less.
By measuring in advance a certain correlation with the analysis value in the state of less than 0%, it can be used even in the state of the recovery rate of less than 100%.

[0027]

INDUSTRIAL APPLICABILITY In the present invention, the sample water is heated to 50 to 100 ° C., while the gas containing oxygen or ozone is blown, the sample water is irradiated with ultraviolet rays to cause an oxidation reaction, and nitrogen in the sample water is caused. After converting the compound and phosphorus compound into nitrate ion and phosphate ion respectively, and then analyze nitrate ion and phosphate ion respectively, analyze both nitrogen compound and phosphorus compound with one analyzer. You can In addition, since the method uses a physical means of irradiating the sample water with ultraviolet rays while blowing a gas containing oxygen or ozone, the consumables are remarkably small and the maintenance work becomes easy. Further, by heating the sample water and supplying a gas containing oxygen or ozone, the oxidation efficiency is increased. Thus, the use of the method of the present invention makes it possible to inexpensively monitor nitrogen compounds and phosphorus compounds. Also, its configuration is simple.

[Brief description of drawings]

FIG. 1 is a flow chart of an embodiment showing an analysis method of the present invention.

FIG. 2 is a block diagram schematically showing an example of an apparatus that realizes the analysis method of the present invention.

FIG. 3 is a diagram showing absorption spectra of a nitrogen-containing unsaturated organic compound before and after ultraviolet irradiation.

FIG. 4 is a diagram showing an example of a photo-oxidative decomposition apparatus of the present invention, (A) is a top view and (B) is a front sectional view.

FIG. 5 is a diagram of measurement data showing the effects of temperature and oxygen on the photooxidative decomposition reaction of phosphorus compounds.

FIG. 6 is a diagram of measurement data showing the multiple effect of ultraviolet rays on the photooxidative decomposition reaction of nitrogen compounds.

FIG. 7 is a diagram showing another example of the photo-oxidative decomposition apparatus of the present invention, (A) is a top view, and (B) is a front sectional view.

FIG. 8 is a diagram showing still another example of the photo-oxidative decomposition apparatus of the present invention, (A) is a top view and (B) is a front sectional view.

[Explanation of symbols]

 2 Photo-oxidation decomposition tank 8 Measuring tank 12, 14 Measuring instrument 10 Absorptiometer 20, 40, 52 Reaction tank 22 Low pressure mercury lamp 24 Air inlet 26 Sample water inlet 28 Sample outlet 32 Heater 34 Temperature sensor 37 Temperature controller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01N 31/00 N

Claims (2)

[Claims] 1. An analytical method for analyzing nitrogen compounds and phosphorus compounds in water, which comprises the following steps (A) to (C). (A) An oxidizing step of heating sample water to 50 to 100 ° C. and irradiating the sample water with ultraviolet rays while blowing a gas containing oxygen or ozone, and (B) absorbing nitrate ions of the oxidized sample water. Step of measuring by photometric method, (C) Step of adding a color-developing agent that selectively reacts with phosphate ion to oxidized sample water, and measuring the color-developing solution by absorptiometric method. 2. An oxidation reaction tank having a sample water inlet / outlet port and a gas supply port, an ultraviolet light source for irradiating the inside of the oxidation reaction tank with ultraviolet rays, and a heating means for heating the oxidation reaction tank,
The sample water contained in the oxidation reaction tank is heated to 50 to 100 ° C. by the heating means, and a gas containing oxygen or ozone is blown into the sample water from the gas supply port while the sample light is supplied from the ultraviolet light source. A photo-oxidative decomposition device that irradiates sample water with ultraviolet rays to oxidize both nitrogen compounds and phosphorus compounds in the sample water to form nitrate ions and phosphate ions, respectively.