JP2001104945A - Oxidative decomposition reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidative decomposition reactor capable of respectively converting a nitrogen compd. and a phosphorus compd. in sample water to nitrate ions and phosphate ions by inexpensive and simple constitution. SOLUTION: Sample water is put in the phosphorus oxidative decomposition tank 10 and a nitrogen oxidative decomposition tank 12 of a photoxidation reactor 8 by about 100 ml and the pH of the sample water in the phosphorus oxidative decomposition tank 10 is adjusted to about 9-11 and the pH of the sample water in the nitrogen oxidative decomposition tank 1 is adjusted to about 11. A low pressure mercury lamp 16 is lighted while clean air is blown in the sample waters from the lower parts of the reaction pipes of both oxidative decomposition tanks 10, 12 to perform photooxidation reaction for about 40 min. Light irradiation is performed in the nitrogen oxidative decomposition tank 12 in the presence of a photocatalyst 14 to convert a nitrogen compound to nitrate ions by photocatalystic reaction and on the other hand, oxidation is performed in the phosphorus oxidative decomposition tank 10 by light irradiation to convert a phosphorus compd. to phosphate ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for analyzing trace amounts of nitrogen compounds and phosphorus compounds, which are eutrophic components contained in wastewater discharged from factories and offices, and environmental waters such as rivers, lakes, and seawater. It relates to the oxidative decomposition reactor used.

[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.

[0004] Other practical TN measurement methods include:
After being oxidized to nitrate ions at a high temperature of 500 ° C. or more using an oxidation catalyst such as platinum, it is measured as nitrogen oxide by a chemiluminescence method, or the nitrogen oxide is further passed through a redox reaction tube (about 600 ° C.). It is decomposed into nitrogen gas and measured 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]

In the official oxidation method using an oxidizing agent or ozone oxidation, oxidation of a nitrogen compound is performed under alkaline conditions, and oxidation of a phosphorus compound is performed under neutral or acidic conditions. In this case, TN and TP in the sample water could not be decomposed at the same time due to different pH conditions, so that it was difficult to combine TN measurement and TP measurement in one device. 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. Therefore, a pressure-resistant reactor is required, and the structure and operation of the oxidizing apparatus become complicated, resulting in a high price. 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 nitrogen compounds using a catalyst requires a high-temperature furnace which is operated at a high temperature of 500 ° C. or more, which not only complicates the structure of the apparatus but also makes the use of a high-temperature catalyst unsuitable for maintenance. It has been shunned for some time. Further, TP cannot be measured by this method. The ozone oxidation method has a problem that the oxidation conditions of TP and TN are different (TN: alkaline, TP: acidic) as in the official method.

[0007] Tahara, the present inventor, irradiates sample water with ultraviolet light and oxidizes phosphorus compounds in the sample water to generate phosphate ions so that TN and TP in the sample water can be commonly measured. And a nitrogen / TOC oxidation reaction tank that irradiates sample water with ultraviolet light in the presence of a photocatalyst and oxidizes nitrogen compounds and total organic carbon in the sample water to produce nitrate ions and carbon dioxide, respectively. An analysis device provided with the same has been proposed (see JP-A-9-281099). In this case, two types of light sources that emit light with different wavelength ranges are installed around the center and surroundings in each of the phosphorylation reaction tank and the nitrogen / TOC oxidation reaction tank, but the role played by the light sources is the same in both oxidation reaction tanks. Therefore, it is uneconomical to use two sets of light sources, and there has been a problem that the configuration is complicated.

An object of the present invention is to provide an oxidative decomposition reactor capable of converting a nitrogen compound in a sample water into nitrate ions and a phosphorus compound into phosphate ions with a low-cost and simple configuration.

[0009]

The oxidative decomposition reactor of the present invention comprises a nitrogen oxidative decomposition tank provided with a photocatalyst therein and a phosphorylation decomposition tank not provided with a photocatalyst disposed opposite to each other. At least the opposing surfaces are made of a material that transmits ultraviolet light, a light source is provided between the two oxidative decomposition tanks, and the light source irradiates the two oxidative decomposition tanks with ultraviolet light. In the decomposition tank, the phosphorus compound is oxidatively decomposed into phosphate ions.

[0010] By ultraviolet irradiation with a common light source in the nitrogen oxidative decomposition tank and the phosphorylation decomposition tank, the nitrogen compound is converted to nitrate ions together with the photocatalytic reaction in the nitrogen oxidation decomposition tank, and the phosphorus compound is converted to phosphate ions in the phosphorylation decomposition tank. You. Thus, by using a common light source, the cost of the oxidative decomposition reactor can be reduced and the structure can be simplified. A preferred example of the photocatalyst is titanium dioxide. In a photocatalyst, electrons and holes are generated on the surface by irradiation with light of 400 nm or less, and each causes a redox reaction. That is, O ₂ ^- and OH ^- are generated as the active species. In the nitrogen oxidative decomposition tank, a nitrogen compound is converted into nitrate ions by the oxidation-reduction reaction (photocatalytic reaction) and oxidation (photolysis reaction) by irradiation with ultraviolet rays. On the other hand, in the phosphorylation decomposition tank,
Since there is no photocatalyst, the phosphorus compound is converted to phosphate ions only by the photolysis reaction. If a photocatalyst is present in the phosphoric acid decomposition tank, phosphate ions and the photocatalyst may react depending on conditions such as pH, and phosphate ions may precipitate as phosphates. There is no light catalyst.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Around a nitrogen oxidative decomposition tank and a phosphorylation decomposition tank, another light source that emits light having a wavelength range different from that of the light source is provided, and both oxidative decomposition tanks are irradiated with light from the other light sources. It is preferable that at least a part of the surface is made of a material that transmits light from another light source. As ultraviolet rays having different wavelength ranges, it is preferable to use ultraviolet rays of 300 to 400 nm generated from black light and 185 nm and 254 nm ultraviolet rays generated from a low-pressure mercury lamp.

When the sample water is irradiated with ultraviolet rays of 185 nm or 254 nm, the following reaction occurs, and oxygen atoms and ozone are generated in the water. These oxygen atoms and ozone promote oxidation of nitrogen compounds and phosphorus compounds. O ₂ + UV (185 nm) → 2O O + O ₂ → O ₃ O ₃ + UV (254 nm) → O + O ₂ Oxygen atoms and ozone also have oxidizing power, so that nitrogen compounds and phosphorus compounds in the sample water are simultaneously strongly oxidized to nitrate ions. And phosphate ions. Thereby, the hardly decomposable nitrogen compound and phosphorus compound can also be oxidatively decomposed.

[0013]

FIG. 1 schematically shows an entire analyzer to which the present invention is applied. The sample water is continuously supplied from the lower part of the adjustment tank 4 by the pump 2, overflows from the upper part of the adjustment tank 4, and is discharged. The sample water in the adjustment tank 4 is supplied to a phosphorylation decomposition tank 10 and a nitrogen oxidative decomposition tank 12 of an oxidative decomposition reactor 8 through a valve 6 provided at the bottom thereof. Both oxidative decomposition tanks 10 and 12 are cylindrical reaction tubes made of Pyrex glass and having a bottom. A photocatalyst is not mounted in the phosphorylation decomposition tank 10, but a plate-like TiO ₂ photocatalyst 14 is mounted in the nitrogen oxidation decomposition tank 12. This photocatalyst 14 is made of TiO on the surface of the Ti net.
_Two layers are formed, and TiO ₂ powder and powdered glass are sintered thereon, and manufactured under the conditions described in JP-A-9-276694. Both oxidation decomposition tanks 10,
A low-pressure mercury lamp 16 is provided between the two. The output of the low-pressure mercury lamp 16 is 20 W, and through the ballast 18,
It is electrically connected to a 100 V AC power supply.

Clean air is supplied from the lower part of both oxidative decomposition tanks 10 and 12 to perform oxidation and stirring.
Further, a pH adjusting solution is added to both the oxidative decomposition tanks 10 and 12. At the lower part of both oxidative decomposition tanks 10 and 12, there are provided outlets for taking out the sample water after the oxidation reaction, and at each outlet there are provided valves 20 and 22 for sending the sample water to the measuring cell of the absorptiometer 26. And their valves 20,
The flow path downstream of 22 passes through the switching valve 24 to the light absorbing portion 26.
Are connected to the measurement cell. Both oxidation decomposition tanks 10 and 12
In the lower part of the column, there are further provided valves 28 and 30 for drainage, and valves 32 and 34 of flow paths for supplying washing water for washing the reaction vessel after draining the sample water. The measuring cell of the absorptiometer 26 is provided with an optical system (described in detail in FIG. 2) for optically measuring the nitrogen concentration and the phosphorus concentration.

Referring to FIG. 2, the light absorption part 26 will be described in detail. The measurement cell 36 allows the sample water sent from either of the oxidative decomposition tanks 10 and 12 to flow through the valve 38, and transmits the light from the light source 40 in the range from ultraviolet to near infrared. For this purpose, a transmission window made of quartz glass is provided. Reference numeral 42 denotes a valve for draining the sample water or the washing water after the measurement.

The light source 40 is preferably a xenon flash lamp which emits light in a range from ultraviolet to near infrared and has a long life. 44 is a power supply for the light source 40. Measurement cell 36
Has an optical path length of 10 mm, a coloring agent inlet is provided at the top,
After the TN measurement and before the TP measurement, the color formers 48 and 50 are transferred from the tank to the measurement cell 36 by the peristaltic pump 46 and added. The color forming agents 48 and 50 react with phosphate ions to form a color. Specifically, JIS K0102
The coloring agent 48 is an ammonium molybdate solution, and 50 is an L-ascorbic acid solution.

The light transmitted through the measuring cell is condensed on a half mirror 54 by a condensing lens 52 disposed on the transmitted light path, and is split by the half mirror 54. The half mirror 54 has a wavelength characteristic set so that transmitted light has a wavelength of less than 250 nm and reflected light has a wavelength of 250 nm or more. The transmitted light is used for TN measurement and the reflected light is used for TP measurement.
A calibration filter 56 is disposed on the optical path between the condenser lens 62 and the half mirror 54.

An interference filter 58, a condenser lens 62 and an optical sensor 66 are arranged on the transmitted light path of the half mirror 54, and the interference filter 6 is disposed on the reflected light path of the half mirror 54.
0, a condenser lens 64 and an optical sensor 68 are arranged. Silicon photodiodes are suitable as the optical sensors 66 and 68. 220n of the interference filter 58 on the transmitted light side
m, the interference filter 60 on the reflected light side has a transmission peak at 880 nm. Silicon photodiode light sensor 6
Nos. 6, 68 select those having characteristics having sensitivity to a wavelength of 200 to 1000 nm. The signals detected by the optical sensors 66 and 68 are taken into the arithmetic unit 72 via the preprocessing unit 70. The pre-processing unit 70 performs differential amplification and logarithmic amplification, and the calculation unit 72 calculates the concentrations of the nitrogen compound and the phosphorus compound.
It is displayed on the display unit 74.

The procedure for measuring the nitrogen concentration and the phosphorus concentration will be described with reference to FIGS. About 100 ml of sample water is collected from the adjustment tank 4 into the reaction tubes of both the oxidative decomposition tanks 10 and 12. About 1 ml of a 1M-NaOH solution is added to the phosphorylation / decomposition tank 10 to adjust the pH of the sample water to about 9 to 11, and about 1 ml of the 1M-NaOH solution is added to the nitrogen oxidization / decomposition tank 12. The pH of the water is adjusted to about 11. Clean air is constantly blown into the sample water at a rate of about 200 ml / min from the lower portions of the reaction tubes of both oxidative decomposition tanks 10 and 12. The low-pressure mercury lamp 16 is turned on, and the photo-oxidation reaction is performed for about 40 minutes. In the nitrogen oxidation decomposition tank 12, light irradiation is performed in the presence of the photocatalyst 14 to cause a photocatalytic reaction, while in the phosphorylation decomposition tank 10, only light irradiation is performed to cause photolysis.

After completion of the photooxidation reaction, acid is injected into the sample water in the nitrogen oxidative decomposition tank 12 to adjust the pH to about 2, and the sample water is transferred to the measurement cell 36. 2 by spectrophotometry
The absorbance at 20 nm is measured to determine TN. Thereafter, the measurement cell 36 is cleaned. For the cleaning of the measurement cell 36, the oxidative decomposition tank after the measurement, in this case, the nitrogen oxidative decomposition tank 12, is washed with washing water flowing from the reaction tube of the oxidative decomposition tank 12 to the measurement cell 36 via a pipe. These components are discharged from the valve 42 and are washed.

Next, after the sample water in the phosphorylation / decomposition tank 10 is transferred to the measurement cell 36, an ammonium molybdate solution and an L-ascorbic acid solution are added to the sample water as color formers, as in the official method. About 10 to develop color
After standing for a minute, the absorbance at 880 nm is measured by the absorption spectrophotometry to determine TP. After the TP measurement, the measurement cell 36 is washed.

Either the sample water in the nitrogen oxidative decomposition tank 12 or the sample water in the phosphorylation decomposition tank 10 may be measured first. In this embodiment, the phosphate ions and the color former are reacted in the measurement cell, but they may be reacted in the phosphorylation / decomposition tank. In that case, if the TN measurement is performed during the reaction between the phosphate ion and the color former, the measurement time can be reduced. In addition, p of the sample water treated in the nitrogen oxidative decomposition tank 12
The H adjustment may be performed in the measurement cell 36.

FIG. 4 is a schematic diagram showing another embodiment of the oxidative decomposition reactor. A plurality of black lights 76 are provided around the phosphorylation decomposition tank 10 and the nitrogen oxidation decomposition tank 12. The black light 76 is electrically connected to a 100 V AC power supply via the ballast 18. The black light 76 irradiates ultraviolet rays having a wavelength of 300 to 400 nm to improve the photolytic reaction ability in the phosphorylation decomposition tank 10 and the photocatalytic reaction ability in the nitrogen oxidation decomposition reaction tank 12.

FIG. 5 is a schematic structural view showing still another embodiment of the oxidative decomposition reactor. Low pressure mercury lamp 1 as in FIG.
6, the phosphorylation and decomposition tank 10a and the nitrogen oxidative decomposition tank 1
2a is arranged. Both oxidation decomposition tanks 10a, 12a
Is a cylindrical reaction tube made of Pyrex glass and sealed at both ends. The two oxidative decomposition tanks 10a and 12a are provided with the axial direction being vertical.
A sample water inlet and a clean air inlet are provided below 0a and 12a, and a sample outlet is provided at the upper end side of the side wall.

A spiral partition wall 80 is provided inside the phosphorylation / decomposition tank 10a, and the sample water introduced into the phosphorylation / decomposition tank 10a flows through the phosphorylation / decomposition tank 10a along the partition wall 80. It is guided to the sample water outlet while patrol. A spiral partition wall 82 is provided inside the nitrogen oxidative decomposition tank 12a, and the sample water introduced into the nitrogen oxidative decomposition tank 12a travels in the nitrogen oxidative decomposition tank 12a along the partition wall 82. It is led to the sample water outlet. The partition wall 82 is formed by coating titanium dioxide as a photocatalyst on the surface of a titanium wire net having a wire diameter of 0.3 mm and a pitch of 0.5 mm. As a method for manufacturing the partition 82, a titanium wire mesh is baked in a heating furnace at 800 ° C. for 30 minutes to form a titanium oxide thin film on the surface of the titanium wire mesh, and then anatase-type titanium dioxide having high photocatalytic activity is produced. The method of applying was used. If the photocatalyst is applied directly to the titanium wire mesh, the photocatalyst may peel off,
By forming a titanium oxide thin film having high adhesion on the surface of the titanium wire netting, peeling of the photocatalyst can be prevented.
The surface of the partition wall 82 formed in this manner becomes uneven. No photocatalyst is provided on the partition wall 80 of the phosphorylation decomposition tank 10a. A low-pressure mercury lamp 16 provided between the two oxidative decomposition tanks 10a and 12a is
It is electrically connected to a V AC power supply.

When the low-pressure mercury lamp 16 is turned on to irradiate the two oxidative decomposition tanks 10a and 12a with ultraviolet light while flowing the sample water through the two oxidative decomposition tanks 10a and 12a, phosphoric acid is decomposed in the phosphorylation and decomposition tank 10a by a photolysis reaction. The compounds are converted into phosphate ions, and the nitrogen compounds are converted into nitrate ions by a photocatalytic reaction in the nitrogen oxidative decomposition tank 12a. With such a configuration, it can be applied to continuous measurement.

[0027]

According to the oxidative decomposition reactor of the present invention, a nitrogen oxidative decomposition tank provided with a photocatalyst therein and a phosphorylation decomposition tank not provided with a photocatalyst are disposed opposite to each other, and a light source is provided between both oxidative decomposition tanks. UV irradiation is applied to both oxidative decomposition tanks from the light source, and nitrogen compounds are oxidized and decomposed into nitrate ions in the nitrogen oxidative decomposition tank, and phosphorus compounds are oxidized and decomposed into phosphate ions in the phosphorylation and decomposition tank. Thus, the cost of the oxidative decomposition reactor can be reduced and the structure can be simplified.

[Brief description of the drawings]

FIG. 1 is a flow diagram schematically showing an entire analyzer to which the present invention is applied.

FIG. 2 is a schematic configuration diagram showing an absorption spectrometer in the analyzer.

FIG. 3 is a flowchart showing the operation of the present invention.

FIG. 4 is a schematic sectional view showing another embodiment of the oxidative decomposition reactor.

FIG. 5 is a schematic sectional view showing still another embodiment of the oxidative decomposition reactor.

[Explanation of symbols]

 Reference Signs List 8 oxidation decomposition reactor 10 phosphorylation decomposition tank 12 nitrogen oxidation decomposition tank 14 photocatalyst 16 low-pressure mercury lamp

Claims (2)

[Claims] 1. A nitrogen oxidative decomposition tank provided with a photocatalyst therein and a phosphorylation decomposition tank not provided with a photocatalyst are disposed opposite to each other, and at least opposing surfaces of both oxidative decomposition tanks are made of a material through which ultraviolet light is transmitted. A light source is provided between the oxidative decomposition tanks, and the light source irradiates the two oxidative decomposition tanks with ultraviolet rays. The nitrogen oxidative decomposition tank oxidizes nitrogen compounds to nitrate ions, and the phosphorylation decomposition tank oxidizes phosphorus compounds to phosphate ions. An oxidative decomposition reactor designed to decompose. 2. A light source that emits light having a different wavelength range from the light source is provided around the nitrogen oxidative decomposition tank and the phosphorylation decomposition tank, and both oxidative decompositions are irradiated with light from the other light source. The oxidative decomposition reactor according to claim 1, wherein at least a part of the surface of the tank is made of a material that transmits light from the other light source.