JP3495994B2 - Method and apparatus for measuring chemical oxygen demand - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improved method for measuring chemical oxygen demand (COD), and more particularly to a method for measuring chemical oxygen demand in which the influence of halogen ions present in a sample is reduced. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, a method for measuring a chemical oxygen demand has been to detect an oxidizable substance in a detection sample using an oxidizing agent such as potassium permanganate or potassium dichromate. In this case, when the sample element contains halogen elements, especially chlorine ions, the chlorine ions are also oxidized and the measured value of the chemical oxygen demand increases. Therefore, before the quantitative determination of COD, a substance that reacts with a halogen ion present in the sample to form a soluble complex is added to suppress the oxidation of the halogen ion.

As the substance that forms this soluble complex, when the oxidizing agent is potassium dichromate, mercury sulfate is used. However, mercury is a toxic substance which affects the human body regardless of whether it is inorganic or organic. Special care must be taken when treating the waste liquid after the measurement. Further, when potassium permanganate is used as an oxidant, silver nitrate is used as a substance that forms a soluble complex, but this substance is also expensive, and another simple and less toxic chloride ion suppression method is required. ing.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is simpler and easier to treat halogen without using mercury sulfate or silver nitrate in the method for measuring the chemical oxygen demand. It is an object of the present invention to propose an apparatus and method for measuring a chemical oxygen demand that does not cause a measurement error due to the influence of ions.

[0005]

The method for measuring chemical oxygen demand according to the present invention comprises: collecting a fixed amount of a sample for measuring the chemical oxygen demand; adding a predetermined amount of sulfuric acid to the sample; The solution is heated under to remove dissolved chlorine ions present in the sample as hydrogen chloride, and then a certain amount of an oxidizing reagent that oxidizes the sample is added and heated to oxidize an oxide in the sample, and the remaining oxidizing reagent is removed. The amount of the remaining oxidizing reagent was measured by performing coulometric titration using a reducing reagent solution, and the oxidizing reagent consumed to oxidize the oxidant from the difference from the amount of the oxidizing reagent added in a fixed amount in advance. The amount of chemical oxygen is measured and the chemical oxygen demand is calculated from the volume of the sample and the measured value of the amount of the oxidizing reagent consumed to oxidize the material to be oxidized in the sample.

Preferably, the oxidizing reagent is a potassium dichromate solution and the reducing reagent is ferric sulfate.

It is preferable that the oxidizing reagent is a potassium permanganate solution and the reducing reagent is a ferric sulfate solution.

The chemical oxygen demand measuring device of the present invention comprises:
A container for containing the sample to be measured, a means for adding sulfuric acid to the sample contained in the container and heating the sample in an inert atmosphere, and a predetermined amount of an oxidizing reagent added to the container and heating in an inert atmosphere Means, titration means for coulometrically titrating the remaining amount of the oxidizing reagent with a reducing reagent, and calculation from the coulometric titration value by the reducing reagent from the volume of the sample to be measured and the amount of the fixed amount of oxidizing reagent added And a means for calculating the chemical oxygen demand amount from the amount of the remaining oxidizing reagent.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for measuring the chemical oxygen demand of the present invention, when the sample water contains halogen ions such as seawater, conventional halogen ions which form a soluble complex and expensive substances are used. COD is measured without using any chemicals to improve the accuracy by eliminating the influence of halogen ions. That is, sulfuric acid is previously added to sample water for measuring the chemical oxygen demand and heated to cause a reaction as shown in the following reaction formula to cause halogen ions present in the sample water as hydrogen halide to be converted into sample water. After discharging it outside, the chemical oxygen demand is measured. Further, since the waste liquid after the measurement does not contain a harmful substance, the treatment is also simplified, and the COD measurement can be simplified.

2NaCl + H ₂ SO ₄ → Na ₂ SO ₄ + 2H
Cl ↑ The method for measuring the chemical oxygen demand of the present invention will be described step by step.

A certain amount of a sample for measuring the chemical oxygen demand (hereinafter abbreviated as COD) is taken. When the estimated amount of COD is large, the collected amount is small, and when the amount of COD is small, it is preferable that the collected amount is large in order to improve the accuracy of the measurement and save the chemicals used in the test. Usually, the range of 1 ml to 5 ml is preferable.

In the following, it is desirable that the heat treatment is carried out in an inert atmosphere so that the sample is not oxidized by means other than the oxidizing agent. For example, it is preferably performed under a nitrogen stream of an inert gas.

A predetermined amount (for example, 10 times the amount of the sample) of sulfuric acid (concentrated sulfuric acid as a commercially available reagent) is added to the collected sample and heated in an inert atmosphere (for example, about 100 ° C. for about 10 minutes).
Then, the dissolved halogen ions present in the sample are removed from the sample solution as hydrogen halide. By this heat treatment in sulfuric acid, halogen ions contained in the sample solution, for example, sodium chloride dissolved as ions, become hydrogen chloride as shown in the above reaction formula due to heat, and the sample solution becomes acidic. Therefore, hydrogen chloride is vaporized and removed from the sample solution.

Then, a certain amount of an oxidizing reagent having a known concentration is added to the sample water from which the halogen ions have been removed, and the sample water is heated in an inert atmosphere for a predetermined time (120 minutes in the official method (JIS)) to oxidize the sample. Oxidize.

As the oxidizing reagent, potassium dichromate or potassium permanganate solution having a predetermined concentration can be used. In the case of potassium dichromate, the heating temperature is preferably 120 ° C. for about 120 minutes in the official method (JIS), for example. Usually, the oxidation with the above-mentioned oxidizing agent is carried out under the condition of sulfuric acid acidity, but in the case of the present invention, since sulfuric acid has already been added to make it acidic for the purpose of removing halogen ions,
There is no need to add fresh sulfuric acid.

The heating temperature when potassium permanganate is used as the oxidant is, for example, 100 in the official method (JIS).
It is preferable to carry out at 30 ° C. for 30 minutes at a lower temperature than in the case of potassium dichromate.

After the completion of the oxidation reaction, a predetermined amount of the reducing reagent solution is added to the remaining amount of the oxidizing reagent and coulometric titration is performed in an inert atmosphere to determine the amount of the remaining oxidizing reagent. At this time, it is preferable to dilute the sample solution with distilled water in order to ensure operability and accuracy of coulometric titration. When the oxidizing agent is potassium dichromate, a fixed amount of ferric sulfate solution is added as a reducing reagent.

In the coulometric titration, the added trivalent iron ions of ferric sulfate are electrolyzed to be provided as an divalent iron ion in the oxidizing agent, and during that period, the current flowing is integrated to remain with good reproducibility. The amount of oxidant is required.

The same applies when the oxidizing agent is potassium permanganate, and the remaining oxidizing agent can be quantified by coulometric titration.

By subtracting the amount of the remaining oxidizing reagent obtained by the above-mentioned coulometric titration from the amount of the oxidizing agent used, the amount of the oxidizing reagent that has oxidized the oxide can be calculated.

Obtained by converting the capacity of the sample and the measured value of the amount of the oxidizing reagent consumed for the oxidation of the sample to be oxidized into the chemical oxygen demand (mg / L) contained in 1 liter of the sample. To be

The chemical oxygen demand measuring device of the present invention comprises:
A container for containing the sample to be measured, a means for adding sulfuric acid to the sample contained in the container and heating the sample in an inert atmosphere, and a predetermined amount of an oxidizing reagent added to the container and heating in an inert atmosphere Means, titration means for coulometrically titrating the remaining amount of the oxidizing reagent by adding a reducing reagent, and coulometric titration with the reducing reagent from the volume of the sample to be measured and the amount of the fixed amount of oxidizing reagent added. And a means for calculating the chemical oxygen demand from the amount of the oxide to be calculated from the value.

The chemical oxygen demand measuring device of the present invention comprises:
Each means can be pre-deployed in one container to form one unit. For example, a container and a means for heating the container, an inlet / outlet port for an inert gas, an inlet port for a sample or each reagent, and an electrode pair for coulometric titration may be provided, and a waste liquid may further be provided with an outlet part for integration. it can.

The container for containing the sample water to be measured is not particularly specified, and any container can be used as long as it can be inserted with an electrode for heating and coulometric titration, can stir the solution, can be sealed and has a lid. Cylindrical corrosion-resistant containers such as beakers and flasks used in ordinary chemical experiments can be used. A heater is provided below the outside of the container. In order to create an inert atmosphere in the container, it is preferable to provide a nitrogen inlet and an outlet to serve as outlets for hydrogen chloride and nitrogen gas generated.

The means for adding sulfuric acid to the sample contained in the container and heating it under an inert atmosphere is to add the sample and a predetermined amount of sulfuric acid to the container and heat the container from the outside under a nitrogen gas stream. By heating, the halogen ions present in the sample become a halogenated gas and are discharged out of the container together with the nitrogen gas. This halogenated gas can be prevented from scattering to the outside by passing it through a solid alkali such as sodium hydroxide or an aqueous solution.

Means for adding a predetermined amount of an oxidizing reagent to the container and heating it under an inert atmosphere is a conventional C in the container.
A predetermined amount of oxidant for measuring OD is added. The heating atmosphere is heated in an inert atmosphere under a nitrogen stream.

In the titration means for coulometrically titrating the remaining amount of the oxidizing reagent by adding the reducing reagent, a predetermined amount of the reducing reagent for measuring the oxidizing agent remaining in the container is added and preliminarily provided in the container. A pair of electrodes for coulometric titration were inserted into the liquid surface, the sample solution was flowed with an inert gas and stirred, and the end point of the titration was detected and left by detecting the change in the amount of electricity due to the electrolysis of iron ions.
Metering the oxidant amount in existence.

Means for calculating the chemical oxygen demand from the volume of the sample to be measured and the amount of the oxide to be calculated from the coulometric titration value of the reducing reagent from the amount of the fixed amount of the oxidizing reagent added Then, based on the amount of oxidant that was present from the amount of oxidant consumed by oxidation determined by titration and the amount of sample used, the amount of oxidizable substance contained in 1 liter (mg
COD converted as / L) is calculated and displayed.

When dichromic acid is used as the oxidant, a predetermined amount of the oxidant solution is added and heated for a predetermined time, and then distilled water is added to dilute the reaction solution to form a sulfuric acid solution in the reducing reagent solution. Coulometric titration with iron solution. The amount of remaining oxidant is measured. In the coulometric titration, the added trivalent iron ions of ferric sulfate are electrolyzed and provided as divalent iron ions to the oxidizing agent. Meanwhile, the COD is obtained with good reproducibility by integrating the flowing current.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples.

(Embodiment 1) FIG. 1 shows the configuration flow of the measuring apparatus used in this embodiment. A heating heater 2 is provided on the outer periphery of the cylindrical reaction vessel 1, and a sample / chemical solution introduction pipe 4, a wash water and nitrogen gas introduction pipe 5 are provided on the upper lid 3.
A nitrogen gas introduction and drain pipe 9, an exhaust pipe 10 and a pair of electrodes 6 for coulometric titration are attached.

In the middle of the sample introducing pipe 4, a sample, distilled water,
Sulfuric acid, a standard concentration oxidant solution, and a reducing reagent solution are connected. Then, a required predetermined amount is measured and injected into the reaction container. Nitrogen gas is introduced into the reaction vessel 1 through the cleaning and nitrogen gas introduction pipe 5 or the nitrogen introduction and drain pipe 9.
The solution was agitated with this nitrogen gas during heating for removing chlorine ions and coulometric titration. The nitrogen gas introduced from the cleaning and nitrogen gas introduction pipe 5 raises the pressure in the reaction vessel 1 and the measured liquid is discharged from the nitrogen gas introduction and discharge pipe 9.

A predetermined amount of the sample in the reaction container 1 is operated by the chemical liquid switching cock 8 and measured by the metering cylinder to measure the reaction container 1.
Inject. After that, the chemical solution switching cock 8 is operated to add sulfuric acid quantified by the quantification cylinder to the container 1, nitrogen gas is introduced into the reaction container 1 through the nitrogen gas introduction and drain pipe 9, and the reaction container 1 is placed in an inert atmosphere. And then add 1
Heat to about 00 ° C. for about 10 minutes. By this heating, the halogen ions contained in the sample become hydrogen halide and are discharged to the outside from the exhaust pipe 10 together with the nitrogen gas and removed.
After removing the hydrogen halide, a potassium dichromate solution having a predetermined concentration is weighed by the metering cylinder 7 and added into the container 1 and heated at a predetermined temperature (160 ° C.) for 10 minutes. Next, add distilled water for dilution and ferric sulfate solution to the metering cylinder 7 respectively.
Then, the electrode 6 for coulometric titration is inserted into the sample mixture, and the change in the potential output by the electrode 6 is read on the display unit (not shown) while stirring the solution with nitrogen gas. The amount of the remaining oxidant that oxidizes the oxide to be quantified is quantified.
From this quantitative value, the amount of oxidizing agent used to oxidize the oxide is calculated. From the volume of the sample used and the amount of the oxidant consumed, the COD value indicating the amount of oxidizable substance (mg / L) in 1 liter is calculated.

The effect of removing halogen ions in the sample will be described.

No. 1 is a case where chlorine removal treatment is not performed with distilled water containing no chlorine ions and oxides, and No. 2 is chlorine water in distilled water containing no oxides, which is almost the same as seawater.
When it is adjusted to 20000mg / L and chlorine is not removed, No3
Is to adjust the chlorine ion in distilled water that does not contain oxides to 20000 mg / L, which is almost the same as seawater, and heat it as chlorine removal treatment (1
(00 ° C) for 10 minutes, No. 4 has chlorine ions in distilled water that does not contain oxides, which is almost the same as seawater, 20,000 m.
Adjust to g / L and heat (100 ° C) as chlorine removal treatment to 1
When stirring was performed for 0 minutes and nitrogen gas, No5 was
Chloride ion was adjusted to 20000mg / L, which is almost the same as seawater, in distilled water that did not contain oxides and heated as chlorine removal treatment (100
(° C) for 5 minutes and stirring with nitrogen gas, No
No. 7 is 6 when chlorine ion is adjusted to 20000 mg / L which is almost the same as seawater in distilled water that does not contain oxides and heating (100 ° C.) is carried out for 15 minutes as a chlorine removal treatment and stirring is performed with nitrogen gas. When the standard solution 220 mg / L was prepared for the oxide, and the solution containing no chlorine ions was heated (100 ° C.) for 10 minutes as a chlorine removal treatment and stirred with nitrogen gas, No. 8 was the standard for the oxide. When liquid 220mg / L was adjusted, chlorine ion was adjusted to 20000mg / L, which is almost the same as seawater, and heating (100 ° C) was performed for 10 minutes as chlorine removal treatment, and stirring was performed with nitrogen gas, No9 was oxidized. Adjust 220mg / L of standard solution to make chlorine ion almost the same as seawater 20
Adjusted to 000mg / L and heated for chlorine removal (120 ℃)
No. 1 when stirring for 10 minutes and nitrogen gas
For 0, the standard solution was adjusted to 220 mg / L for the oxide, chlorine ions were adjusted to about 20000 mg / L, which is almost the same as seawater, and heating (140 ° C.) for 10 minutes and stirring with nitrogen gas were performed as chlorine removal treatment. In this case, the COD of each of the three samples was measured under the conditions of. The results and average values are shown in Table 1. Other conditions: 2 ml of sample, 20 ml of concentrated sulfuric acid, and the standard solution is potassium phthalate.

[0036]

[Table 1] As shown in Table 1, No. 1 is a so-called blank test and becomes the zero point of the instrument. The effect of chlorine removal treatment will be explained by comparison with this blank value.

The effect of chlorine contained in No. 2 extends to unmeasurable without chlorine removal treatment. No
No. 3 is the case without stirring, No. 4 is the case with stirring, and shows the effect of chlorine removal by stirring. No4, N
O5 and No6 show the influence of the heating time for chlorine removal.

Therefore, according to the experiments from No. 1 to No. 6, samples containing chlorine ion concentration at seawater level were completely treated by stirring with nitrogen gas at a heating temperature of 100 ° C. for a heating time of 10 minutes or more as chlorine removal treatment. I know what I can do.

Even if the amounts of oxides are the same and no chlorine ion is contained in No. 7 and No. 8 chlorine ion are compared,
It can be seen that the value of OD is a specified value and that the chlorine removal treatment of the present invention does not affect the oxides contained in the sample. When the heating temperature of No. 9 and No. 10 is raised to 140 ° C., a slight effect appears on the oxides contained in the sample.

[0040]

According to the method for measuring the chemical oxygen demand of the present invention, even when halogen ions are present in the sample water, there is no need to use conventional harmful substances or expensive chemicals, Similar accuracy can be measured.

Therefore, since the waste liquid after the measurement does not contain harmful substances, the waste liquid can be easily treated.

[Brief description of drawings]

FIG. 1 is a flow sheet illustrating the configuration of the device of the present invention.

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-9-21794 (JP, A) JP-A-5-322830 (JP, A) JP-A-8-101188 (JP, A) JP-A-11- 132997 (JP, A) JP-A-56-111465 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/26-27/49 G01N 1/00-1/34 G01N 33/18

Claims (4)

(57) [Claims] 1. A fixed amount of a sample for measuring the chemical oxygen demand is sampled, and a predetermined amount of sulfuric acid is added to the sample and heated under an inert atmosphere to remove dissolved chlorine ions present in the sample as hydrogen chloride. Then, a certain amount of an oxidizing reagent that oxidizes the sample is added and heated to oxidize the oxidant in the sample, and the remaining oxidizing reagent is subjected to coulometric titration with a reducing reagent solution to determine the amount of the remaining oxidizing reagent. Measure and measure the amount of oxidizing reagent consumed to oxidize the oxidant of the sample from the amount of the oxidizing reagent added in advance in a predetermined amount, and to consume the volume of the sample and oxidize the oxidant of the sample A method for measuring a chemical oxygen demand, comprising: calculating a chemical oxygen demand from the measured oxidation reagent amount. 2. The method for measuring a chemical oxygen demand according to claim 1 , wherein the oxidizing reagent is a potassium dichromate solution, and the reducing reagent is ferric (III) sulfate. 3. The method for measuring chemical oxygen demand according to claim 1 , wherein the oxidizing reagent is a potassium permanganate solution and the reducing reagent is a ferric sulfate (III) solution. 4. A container for containing a sample to be measured, a means for adding sulfuric acid to the sample contained in the container and heating the sample in an inert atmosphere, and an inert gas by adding a predetermined amount of an oxidizing reagent to the container. It has means for heating in an atmosphere, titration means for coulometric titration of the residual amount of the oxidizing reagent with a reducing reagent, and means for calculating the chemical oxygen demand from the capacity of the sample to be measured and the coulometric titration value. Measuring device for chemical oxygen demand.