JP3269195B2 - Method for analyzing nitrogen compounds and phosphorus compounds in water and photo-oxidative decomposition device - Google Patents

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 offices and in environmental water such as rivers and lakes. The present invention also relates to an oxidative decomposition apparatus that oxidizes nitrogen compounds and phosphorus compounds in sample water to nitrate ions and phosphate ions, respectively, by such an analysis method.

[0002]

2. Description of the Related Art In Japan, methods for analyzing nitrogen compounds and phosphorus compounds in water are publicly standardized by JIS K0102 and Notification No. 140 of the Environment Agency. 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 of the nitrogen in water, all the nitrogen compounds are changed to nitrate ions for measurement. However, ammonium ions and organic nitrogen are hardly oxidized to nitrate ions. Therefore, in the TN measurement, an alkaline potassium peroxodisulfate solution is added to the sample water and heated at 120 ° C. for 30 minutes to oxidize all nitrogen compounds to nitrate ions. After cooling, the pH was adjusted to 2-3 and the UV absorbance at a wavelength of 220 nm due to nitrate ions was measured.

On the other hand, phosphorus compounds in water are phosphate ions,
Present as hydrolysable phosphorus or organic phosphorus.
In the TP (total phosphorus) measurement, potassium peroxodisulfate is added as an oxidizing agent in a neutral state, and all phosphorus compounds are oxidized to phosphate ions by heating at 120 ° C. for 30 minutes. Since phosphate ions do not have a specific light absorption,
In order to measure phosphate ions, 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 measurement method, after oxidation to nitrate ions at a high temperature of 500 ° C. or more using an oxidation catalyst, measurement is made as nitrogen oxide by a chemiluminescence method, or nitrogen oxide is further added to a redox reaction tube ( (About 600 ° C.) to decompose into nitrogen gas and measure it as nitrogen by gas chromatography. As another method, ozone is supplied to a sample water to oxidize ozone. The ozone oxidation is performed under alkaline conditions in TN measurement and under acidic conditions in TP measurement.

[0005]

There is no apparatus for analyzing TN measurement and TP measurement in sample water with a common analyzer. This is because, in the oxidation by an oxidizing agent or ozone oxidation, the pH conditions at the time of oxidation are different, such that oxidation of a nitrogen compound is performed under alkaline conditions and oxidation of a phosphorus compound is performed under neutral or acidic conditions. . In addition, the oxidizing method using an oxidizing agent heats to a high temperature such as 120 ° C., which is higher than the boiling point of water. is there.
Since the oxidizing agent is consumed, it must be replenished frequently, and there is a problem that the running cost is increased.

The method of oxidizing a nitrogen compound using a catalyst requires a high temperature of 500 ° C. or more, and the catalyst is severely deteriorated. Not only is the device complicated in structure and difficult to maintain, but the analytical method using a catalyst is generally unsuitable for on-site use as a monitor. In the ozone oxidation method, since the oxidizing power in the neutral region is weak, both the oxidation of the nitrogen compound and the oxidation of the phosphorus compound are p
A mechanism for adjusting H is required, and the structure of the device becomes complicated. Further, a pH adjusting solution of an acid and an alkali is also required as a consumable. As described above, the conventional analysis method cannot not only measure the nitrogen compound and the phosphorus compound in common, but also increases the cost and lacks suitability as a continuous monitor.
Difficult to use.

Accordingly, an object of the present invention is to provide an analysis method which enables common measurement of a nitrogen compound and a phosphorus compound in a sample water and enables continuous analysis for a long time. . Another object of the present invention is to provide an apparatus which is advantageous for oxidizing a nitrogen compound and a phosphorus compound together to convert them into nitrate ions and phosphate ions by such an analysis 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) heating the sample water to 50 to 100 ° C. and irradiating the sample water with ultraviolet rays while blowing a gas containing oxygen or ozone; (B) absorbing the nitrate ions of the oxidized sample water A step of measuring by a photometric method, and (C) a step of adding a coloring agent that selectively reacts with phosphate ions to the oxidized sample water, and measuring the coloring solution by an absorptiometric method.

The photo-oxidative decomposition apparatus used in the analysis method of the present invention is an oxidation reaction tank having a sample water inlet / outlet and a gas supply port for blowing a gas containing oxygen or ozone into the sample water contained therein, An ultraviolet light source for irradiating ultraviolet rays to the sample water in the tank, and a heating means for heating the sample water contained in the oxidation reaction tank to 50 to 100 ° C., comprising a nitrogen compound and a phosphorus compound in the sample water. Both are oxidized into nitrate ions and phosphate ions, respectively.

[0010]

When ultraviolet rays are irradiated on oxygen and ozone in the gas blown into the sample water, the following reaction occurs, and oxygen atoms and 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 nitrate ions and phosphorus, respectively. Change to acid ion.

When an organic compound is present, the unsaturated bond of the organic compound is cleaved. Ultraviolet absorption by the unsaturated bond interferes with the specific absorption of nitrate ion, but the interference is removed by cutting the unsaturated bond by oxygen atoms or ozone. For example, 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.
Is expressed. The sample water before ultraviolet irradiation has a maximum absorption at about 340 nm and an ultraviolet absorption of unsaturated bond having an absorption band at 400 nm or less. When photo-oxidative decomposition is performed by irradiating ultraviolet rays while blowing air, unsaturated bonds disappear, and only a spectrum specific to nitrate ions is detected. This greatly improves the accuracy of nitrate ion measurement. Sample water 50-100
The reason why the temperature is raised to ° C. is that the heating greatly promotes the photooxidative decomposition reaction.

[0012]

FIG. 1 shows an embodiment of the method of the present invention in the order of steps, and FIG. 2 shows a schematic configuration 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.
Is a photo-oxidation 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 ultraviolet irradiation in the photo-oxidative decomposition tank 2 is led to the measurement tank 8. Reference numeral 10 denotes an absorptiometer that measures the absorbance of nitrate ions in the sample water in the measurement tank 8 and the amount of color developed by the phosphate ions after the addition of the coloring agent as the absorbance. In order to measure phosphate ions, an ammonium molybdate solution and an L-ascorbic acid solution are measured and mixed by the measuring devices 12 and 14, respectively, and supplied to the measuring tank 8. Wash water is supplied to the photo-oxidative decomposition tank 2 and the measurement tank 8 for washing.

FIG. 4 shows an example of the photo-oxidation 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 a reaction tank 20, and directly contacts sample water in the reaction tank 20. The low-pressure mercury lamp 22 has a luminance at a short wavelength ultraviolet ray, 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 tubes can be connected. In order to discharge the overflow liquid at the time of introducing the sample liquid, a side pipe 30
Is provided. The side tube 30 is also provided with a joint for tube connection.

The reaction tank 20 is made of aluminum, has a cartridge heater 32 and a temperature sensor 34 embedded therein, and the temperature of the reaction tank 20 is controlled to about 90 ° C. 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 in order to reflect ultraviolet rays multiple times. The material of the reaction tank 20 is not limited to aluminum, and stainless steel, glass, or the like can also be used. In the case of stainless steel as well, it is preferable to make a mirror structure by mirror polishing. In the case of glass, since Pyrex glass does not transmit ultraviolet rays, the inner surface has a mirror structure using a silver mirror or an aluminum vapor-deposited film, and in the case of ultraviolet-transmissive glass, the mirror structure can be formed by forming a silver mirror or an aluminum vapor-deposited film on the outer surface. If the reaction tank 20 has a mirror structure, the ultraviolet radiation can be effectively used, and the decomposition efficiency can be significantly improved.

The ultraviolet radiation source is not limited to the low-pressure mercury lamp 22, and any light source that can emit ultraviolet light with strong energy, such as an excimer laser, a deuterium lamp, a xenon lamp, and a Hg-Zn-Pb lamp, can be used. it can. Low-pressure mercury lamps are advantageous because they are inexpensive and have a long life and are suitable as monitors. An ultraviolet lamp made of ultraviolet transmitting glass having a diameter of about 18 mm as the low-pressure mercury lamp 22 has a discharge current of 0.8 A and a discharge voltage of 100 V.
It is processed into a U shape. This is installed in two reaction tanks,
If immersed in the sample water, the amount of water in the reaction tank 20 is about 100 m
It becomes l. Reference numeral 23 denotes a power transformer for turning on the low-pressure mercury lamp 22, and reference numeral 37 denotes 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, ultraviolet rays are irradiated on the sample water in the reaction tank 20, 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 via the sample inlet 26 while being measured, after large dirt is removed in advance by a filter or the like. Reaction tank 20
The sample water is heated to 90 ° C., and air is supplied from the air inlet 24 while the low-pressure mercury lamp 22
Irradiates the sample water with ultraviolet rays. It is considered that the following reaction has occurred in the reaction tank 20 by this ultraviolet irradiation. 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 completion of the photo-oxidative decomposition, a part or all of the sample water in the reaction tank 20 is taken out to the measurement tank 8 and the spectrophotometer 10
Is measured 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 ions of the colored solution are measured at a wavelength of 880 nm by the absorptiometer 10.

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

[0019]

Table 1 Component recovery (%) 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 shown in Table 1, the recovery rate was almost 1 in all cases.
00%, which is a good value. Thus, it was revealed that in the reaction tank 20, both the nitrogen compound and the phosphorus compound were oxidized and converted into nitrate ions and phosphate ions, respectively, and both the nitrogen compound and the phosphorus compound could be measured by one analyzer.

Here, the temperature effect and the aeration effect at the time of ultraviolet irradiation are shown in FIG. 5 based on the results of measurement of a sample water containing 1 ppm of methyltriphenylphosphonium bromide as a standard sample using the photooxidative decomposition tank of FIG. explain. First, when the case where air is supplied from the air inlet 26 and the case where air is not supplied in a state where the sample water is heated to 60 ° C. is compared, the recovery rate is about three times larger. It can be seen that oxidation by oxygen atoms or ozone is effectively acting by supplying air during ultraviolet irradiation. When comparing the case where the temperature was changed while supplying air to the sample water at the time of ultraviolet irradiation, a difference was observed in the recovery rate between 60 ° C and 80 ° C. The higher the temperature, the faster the oxidation reaction was promoted. Is evident.

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

The photo-oxidative decomposition tank 2 can be variously modified. 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 photo-oxidative 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 at the top as a side tube. At the side and bottom of the reaction tank 40, a metal protection tank 42 having good heat conductivity is provided in contact with the outside of the reaction tank 40, and the cartridge heater 32 and the temperature sensor 34 are embedded in the protection tank 42. The other structure is the same as that of FIG. 4. The low-pressure mercury lamp 22 is installed in the reaction tank 40, and the outside of the protection tank 42 is covered with a heat insulating material 36.

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

FIG. 8 shows an example of an outer cylindrical photo-oxidative decomposition tank in which an ultraviolet light source is arranged outside the reaction tank. In FIG. 8, two low-pressure mercury lamps 50 are arranged outside the reaction tank 52. The reaction tank 52 is formed of an ultraviolet transmitting glass.
54 is a support member for the reaction tank 52. The illustration of the air inlet, the sample inlet, the sample outlet, the overflow liquid outlet, and the like is simplified. In order to perform multiple reflection of ultraviolet rays, an outer cylinder 55 for reflecting ultraviolet rays is provided outside the low-pressure mercury lamp 50. Reference numeral 56 denotes a heater, which is provided outside the outer cylinder 55. Comparing the inner cylinder type photo-oxidation decomposition tank and the outer cylinder type photo-oxidation decomposition tank, the inner cylinder type can effectively utilize radiation, but the ultraviolet lamp is liable to be stained. The outer cylinder type has the opposite characteristics.

The analysis method of the present invention always has a recovery rate of 10
It does not mean that it must be used under the condition of 0%. For example, the recovery rate in the method of the present invention and the established method using the oxidation with an oxidizing agent and the spectrophotometry is 10%.
By preliminarily measuring a certain correlation with the analysis value in a state of less than 0%, it is possible to use even a state in which the recovery rate is less than 100%.

[0027]

According to the present invention, the sample water is heated to 50 to 100 ° C., and while the gas containing oxygen or ozone is blown, the sample water is irradiated with ultraviolet rays to cause an oxidation reaction, and the nitrogen in the sample water is increased. After converting the compound and the phosphorus compound into nitrate and phosphate ions, respectively, the nitrate and phosphate ions were respectively analyzed. Therefore, it is necessary to analyze both the nitrogen compound and the phosphorus compound with one analyzer. Can be. In addition, since the method uses physical means of irradiating sample water with ultraviolet rays while blowing a gas containing oxygen or ozone, consumables are extremely reduced and maintenance work is facilitated. Oxidation efficiency is increased by heating the sample water and supplying a gas containing oxygen or ozone. Thus, the use of the method of the present invention makes it possible to monitor nitrogen compounds and phosphorus compounds at low cost. Also, the configuration is simple.

[Brief description of the drawings]

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

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

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

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

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

FIG. 6 is a diagram of measured data showing the multiple effect of ultraviolet light in the photooxidative decomposition reaction of a nitrogen compound.

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

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

[Explanation of symbols]

 2 Photo-oxidation decomposition tank 8 Measurement tank 12, 14 Measuring instrument 10 Absorbance meter 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

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁷ Identification code FI G01N 33/18 G01N 33/18 B

Claims (2)

(57) [Claims] 1. An analysis method comprising the following steps (A) to (C) for analyzing nitrogen compounds and phosphorus compounds in water. (A) heating the sample water to 50 to 100 ° C. and irradiating the sample water with ultraviolet rays while blowing gas containing oxygen or ozone; (B) absorbing nitrate ions of the oxidized sample water (C) a step of adding a coloring agent that selectively reacts with phosphate ions to the oxidized sample water, and measuring the coloring solution by an absorptiometric method. 2. An oxidation reaction tank having a sample water inlet / outlet and a gas supply port for blowing a gas containing oxygen or ozone into the sample water contained therein, and an ultraviolet ray for irradiating the sample water in the oxidation reaction tank with ultraviolet rays. An apparatus for photo-oxidative decomposition of a nitrogen compound and a phosphorus compound, comprising: a light source; and heating means for heating the sample water contained in the oxidation reaction tank to 50 to 100 ° C.