KR20020064658A - Method for measuring chemical oxygen demand and apparatus thereof - Google Patents

Abstract

PURPOSE: To provide an apparatus for measuring chemical oxygen demand and a method therefor which generate no measurement errors by halide ions simpler and easy to process without using mercury nitrate, silver nitrate, and the like. CONSTITUTION: According to the method for measuring chemical oxygen demand and the apparatus for carrying out the measurement method, a fixed amount of a sample whose chemical oxygen demand is to be measured is collected. A predetermined amount of sulfuric acid is added to the sample, which is heated under an inert ambience to remove dissolved chloride ions present in the sample as a hydrogen chloride. Then, a fixed amount of an oxidation reagent for oxidizing the sample is added and heated, whereby a substance to be oxidized in the sample is oxidized. The residual oxidation reagent is coulometric titrated by a reagent solution for reduction. An amount of the residual excessive oxidation reagent is measured. An amount of the oxidation reagent consumed for oxidizing the substance to be oxidized of the sample is measured from the fixed amount of the oxidation reagent added beforehand. The chemical oxygen demand is calculated from the volume of the sample, and the measured value of the oxidation reagent consumed for oxidizing the substance to be oxidized in the sample.

Description

Method for measuring chemical oxygen demand and apparatus thereof

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

Conventionally, the measuring method of chemical oxygen demand amount detected the oxidizing substance in a detection sample using oxidizing agents, such as potassium permanganate and potassium nitrate. In this case, when a halogen element, especially chlorine ion, is contained in a detection sample, this chlorine ion will also be oxidized and the measured value of chemical oxygen demand will become high. For this reason, before the quantification of COD, the substance which reacts with the halogen ion which exists in a sample and forms a soluble complex was added, and oxidation of halogen ion was suppressed.

Mercury sulfate is used when the oxidizing agent is potassium nitrate. However, mercury is a hazardous substance that affects the human body regardless of inorganic or organic matter. Therefore, special care should be taken for the treatment of waste liquid after measurement. . In the case of using potassium permanganate as the oxidizing agent, silver nitrate is used as a substance to form a soluble complex, but this substance is also expensive, and another simple and low toxicity method for inhibiting chlorine ion is required.

The present invention has been made in view of the above circumstances, and in the method for measuring the chemical oxygen demand, the measurement of chemical oxygen demand without the use of mercuric sulfate, silver nitrate, or the like, and the measurement error due to the effect of halogen ions, which is simpler and easier to process, is performed. An object of the present invention is to propose an apparatus and a method thereof.

In the method for measuring the chemical oxygen demand of the present invention, a predetermined amount of a sample for measuring the chemical oxygen demand is collected, 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. A certain amount of the oxidizing reagent for oxidizing the sample was added to oxidize the pioxide in the sample, and the remaining oxidizing reagent was subjected to coulometric titration using a reagent solution for reducing to measure the amount of the remaining oxidizing reagent. The amount of the oxidizing reagent consumed to oxidize the blood oxide is measured from the difference between the amount of the oxidizing reagent added in a predetermined amount, and the chemical oxygen demand is determined from the measured value of the amount of the oxidizing reagent consumed to oxidize the blood oxide of the sample. It is characterized by calculating.

The oxidizing agent is a potassium nitrate solution, and the reducing reagent is ferric sulfate.

Preferably, the oxidant is a potassium permanganate solution, and the reducing reagent is a ferric sulfate solution.

An apparatus for measuring the chemical oxygen demand of the present invention includes a container for receiving a sample to be measured, a means for adding sulfuric acid to a sample contained in the container and heating it under an inert atmosphere, and adding a predetermined amount of an oxidizing reagent to the container to inert atmosphere. Titration means for titrating the remaining amount of the oxidizing reagent with the reducing reagent, and for titrating the amount of electricity with the reducing reagent from the volume of the sample to be measured and the amount of the oxidized sample added to the predetermined amount. And means for calculating the chemical oxygen demand from the amount of remaining oxidizing reagent calculated from the above.

1 is a flow chart illustrating a configuration of an apparatus of the present invention.

* Explanation of symbols for the main parts of the drawings

1: reaction vessel 2: heating heater

3: upper cover part 4: introduction tube of sample and chemical liquid

5: Introducing tube of washing water and chemical liquid 6: One pair of electrodes for electric quantity titration

7: fixed-quantity cylinder 8: chemical change cock

9: nitrogen gas introduction and drainage pipe 10: exhaust pipe

The method for measuring the chemical oxygen demand of the present invention does not use any harmful substances or expensive chemicals that form soluble complexes of conventional halogen ions when the sample water contains halogen ions such as seawater. It is to measure COD with higher precision by excluding effect. That is, sulfuric acid is added to the sample water for measuring the chemical oxygen demand in advance, and heated to produce a reaction represented by the following reaction formula, and the halogen ions present in the sample water are discharged out of the sample water as hydrogen halide. Measure it. And since the waste liquid after a measurement does not contain a hazardous substance, a process becomes simple and can measure COD easily.

2NaCl + H ₂ SO ₄ → Na ₂ SO ₄ + 2HCl ↑

The measuring method of the chemical oxygen demand of this invention is demonstrated in order.

① Take a certain amount of sample to measure chemical oxygen demand (hereinafter abbreviated as COD). If the amount of COD is estimated to be large, the amount of collected is small. If the amount of COD is small, it is preferable to increase the accuracy of the measurement and to save the chemical used in the test. Usually a range of 1 ml to 5 ml is preferred.

Hereinafter, it is preferable to perform heat processing in inert atmosphere so that a sample may not be oxidized except an oxidizing agent. For example, it is preferable to carry out in nitrogen atmosphere of an inert gas.

(2) A predetermined amount (e.g., 10 times the amount of sulfuric acid) of sulfuric acid (rich sulfuric acid of a commercially available reagent) is added to the collected sample, and heated in an inert atmosphere (e.g., about 10 minutes at around 100 ° C) to be present in the sample. Dissolved halogen ions are removed from the sample liquid as hydrogen halide. Since the halogen ions contained in the sample liquid by the heat treatment in sulfuric acid, for example, sodium chloride dissolved as ions, become hydrogen chloride as shown in the above reaction equation by heat, the hydrogen chloride is acidic. Vaporization and removal from the sample liquid.

(3) Subsequently, a predetermined amount of an oxidizing reagent of known concentration is added to the sample water from which the halogen ions are removed, followed by heating in a inert atmosphere for a predetermined time (120 minutes in the JIS method) to oxidize the pioxide in the sample.

As the oxidizing reagent, potassium nichromate or potassium permanganate solution at a predetermined concentration can be used. In the case of potassium nitrate, the heating temperature is preferably about 120 minutes at 120 ° C. in the process method (JIS), for example. Usually, the oxidation in the oxidizing agent is carried out under sulfuric acid acid conditions, but in the present invention, sulfuric acid has already been added and acidified for the purpose of removing halogen ions, so it is not necessary to add sulfuric acid newly.

The heating temperature in the case of using potassium permanganate as the oxidizing agent is, for example, 30 minutes at 100 ° C in the process method (JIS), preferably at a lower temperature than in the case of potassium nitrate.

(4) After completion of the oxidation reaction, the amount of the remaining oxidizing reagent is added to a predetermined amount of the reducing reagent solution, and the electric quantity is titrated in an inert atmosphere to determine the amount of the remaining oxidizing reagent. At this time, it is preferable to dilute the sample liquid with distilled water in order to ensure the operability and the accuracy of the electricity quantity titration. When the oxidizing agent is potassium nitrate, a certain amount of ferric sulfate solution is added as a reducing reagent.

In the electric quantity titration, the added trivalent iron ions of ferric sulfate are supplied to the oxidant as divalent iron ions, and the amount of oxidant remaining reproducibly can be obtained by integrating the flowed current.

The same applies to the case where the oxidant is potassium permanganate, and the remaining oxidant can be quantified by titration of electricity.

(5) The amount of the oxidizing reagent which oxidized the pioxide can be calculated by subtracting from the amount of the oxidizing agent using the amount of the remaining oxidizing reagent determined by the above-mentioned electric quantity titration.

(6) It can be obtained by converting the amount of the sample and the amount of oxidizing reagent consumed by oxidation of the pioxide of the sample into the chemical oxygen demand amount (mg / L) contained in 1 liter of the sample.

An apparatus for measuring the chemical oxygen demand of the present invention includes a container for receiving a sample to be measured, a means for adding sulfuric acid to a sample contained in the container and heating it under an inert atmosphere, and adding a predetermined amount of an oxidizing reagent to the container to inert atmosphere. The amount of electricity by the reducing reagent from the means for heating under a predetermined amount, the titration means for titrating the remaining amount of the oxidizing reagent by adding a reducing sample, and the amount of the sample to be measured and the amount of the oxidizing reagent added to the predetermined amount. Means for calculating the chemical oxygen demand from the amount of the pioxide calculated from the titration value.

The apparatus for measuring the chemical oxygen demand of the present invention can be arranged as a single unit by arranging each means in advance in one container. For example, the container and the means for heating the container, an inlet and outlet for introducing an inert gas, an inlet for a sample or each reagent, and an electrode pair for titration of the amount of electricity can be disposed, and a waste liquid discharge part can be provided and integrated.

The container containing the sample number to be measured is not particularly specified, and any one can be used as long as it has a lid capable of inserting an electrode for heating and titration of electricity, stirring the solution and sealing. Cylindrical corrosion-resistant containers, such as beakers and flasks, used in ordinary chemical experiments can be used. A heating heater is disposed below the vessel outside. In order to make the container an inert atmosphere, it is preferable to set it as the outlet of hydrogen chloride and nitrogen gas which generate | occur | produce a nitrogen inlet and an outlet.

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

The means for adding a predetermined amount of an oxidizing reagent to the vessel and heating it under an inert atmosphere is a predetermined amount of an oxidizing agent for measuring a normal COD is added to the vessel. The heating atmosphere is heated in an inert atmosphere under a nitrogen stream.

In a titration means for titrating the remaining amount of the oxidizing reagent by adding a reducing reagent and titrating the amount of electricity, a pair of electrodes for titrating the quantity of electricity placed in the vessel in advance by adding a predetermined amount of a reducing reagent for measuring the oxidant remaining in the vessel. Is inserted into the liquid surface, the sample solution is added with an inert gas, the mixture is stirred, and the end point of the titration is detected by the change of the electrical amount of the reduction by electrolysis of iron ions, and the amount of oxidant remaining after residual is measured.

The means for calculating the chemical oxygen demand from the amount of the target to be measured and the amount of the oxidized oxide calculated from the amount of the oxidizing reagent added by the reducing reagent from the amount of the oxidizing reagent added, the amount of the sample to be consumed in the oxidation quantified by the titration. The amount of oxidation to be present from the amount of the oxidant and the amount of the oxidation amount (mg / L) contained in one liter from the amount of the sample used are calculated and displayed.

When nitric acid is used as the oxidizing agent, a predetermined amount of oxidizing agent solution is added and heated for a predetermined time, distilled water is added to dilute the reaction solution, and electric quantity titration is performed using a ferric sulfate solution to the reducing reagent solution. The remaining oxidant is measured.

In the electric quantity titration, the added trivalent iron ions of ferric sulfate are electrolyzed and supplied to the oxidant as divalent iron ions. In the meantime, COD can be calculated | required reproducibly by integrating the electric current which flowed.

Hereinafter, it demonstrates concretely by an Example.

(Example 1)

The structural flow of the measuring apparatus used in the present Example is shown in FIG. In the columnar reaction vessel 1, a heater 2 for heating is arranged on the outer circumference, and the upper lid portion 3 has an introduction tube 4 of the sample and the chemical liquid, a washing water and a nitrogen gas introduction tube 5, and nitrogen. A gas introduction and drain pipe 9, an exhaust pipe 10, and a pair of electrodes 6 for electric quantity titration are mounted.

In the middle of the sample introduction tube 4, a sample, distilled water, sulfuric acid, an oxidizing agent solution of a standard concentration, and a reagent solution for reduction are connected through an electric charge cylinder 7 and an end thereof with a potion replacement cock 8. The predetermined amount required is then weighed and injected into the reaction vessel.

Nitrogen gas is introduced into the reaction vessel 1 through the washing and nitrogen gas introduction pipe 5 or the nitrogen introduction and drain pipe 9, and the solution is stirred with this nitrogen gas at the time of heating of the chlorine ion removal and titration of electricity. . The nitrogen gas which enters from the washing | cleaning and nitrogen gas introduction tube 5 raises the pressure in the reaction container 1, and discharges the liquid after a measurement from the nitrogen gas introduction and discharge tube 9.

A predetermined amount of sample is injected into the reaction vessel 1 by injecting the chemical liquid replacement cock 8 into the reaction vessel 1. Thereafter, the chemical liquid replacement cock 8 is operated to add sulfuric acid, which is quantified by the metering cylinder, to the vessel 1, and nitrogen gas is introduced into the reaction vessel 1 through the introduction of nitrogen gas and the drainage pipe 9 to the reaction vessel 1 After making the inside of inert atmosphere into inert atmosphere, a sample liquid is heated to about 100 degreeC 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 nitrogen gas and removed. After removing the hydrogen halide, potassium nichromate liquid of a predetermined concentration is metered into the metering cylinder 7 and added to the container 1 and heated to a predetermined temperature (160 ° C.) for 10 minutes. Subsequently, distilled distilled water and ferric sulfate solution were respectively weighed and added to the metering cylinder 7, and the electrode 6 for electric quantity titration was inserted into the sample mixture, and the electrode 6 was stirred with nitrogen gas. The change in the output potential is read by a display unit (not shown), and the amount of oxidant remaining after oxidizing the pioxide in the sample is quantified. From this quantity, the amount of oxidant used to oxidize the pioxide is calculated. From the volume of the sample used and the amount of oxidant consumed, a COD value indicating the amount of oxidation (mg / L) in 1 liter is calculated.

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

No1 does not remove chlorine with distilled water that does not contain chlorine ions or phosphides, and No2 adjusts chlorine ions to 20000 mg / L, which is almost the same as seawater, without chlorine removal. Otherwise, No3 was adjusted to 20000 mg / L of chlorine ions in distilled water containing no oxidized water and approximately 10 minutes of heating (100 ° C.) as a chlorine removal treatment. When chlorine ions were adjusted to 20000 mg / L in distilled water, which was about the same as that of seawater, and agitation was performed by heating (100 ° C.) for 10 minutes and nitrogen gas as a chlorine removal treatment, No5 was used for distilled water containing no chlorine oxide. Is adjusted to 20000 mg / L, which is about the same as sea water, and heating (100 ° C.) for 5 minutes and stirring with nitrogen gas are performed as chlorine removal treatment. Is adjusted to 20000 mg / L, which is about the same as sea water, and heating (100 ° C.) is carried out for 15 minutes and stirring with nitrogen gas as the chlorine removal treatment. When heating (100 ° C.) was stirred for 10 minutes and nitrogen gas was applied to a solution containing no chlorine, No8 adjusted the standard solution to 220 mg / L in the oxidized substance, and the chlorine ion was almost equal to 20000 mg in seawater. / L and heating (100 ° C) for 10 minutes and stirring with nitrogen gas as chlorine removal treatment, No9 adjusts the standard solution 220 mg / L to the chlorine oxide to chlorine ions 20000 mg / When adjusting to L and heating (120 ° C.) for 10 minutes and stirring with nitrogen gas as the chlorine removal treatment, No10 adjusts the standard solution 220 mg / L to the oxidized substance to give chlorine ions 20000 mg / L almost the same as seawater. , And heating (140 ° C.) as a chlorine removal treatment. The COD of each of 3 samples was measured under the condition of 10 minutes and stirring with nitrogen gas. The results and averages are shown in Table 1. Other conditions: 2 ml of the sample, 20 ml of concentrated sulfuric acid, and the component of the standard solution were potassium phthalate.

As shown in Table 1, No1 is a so-called blank test, which is the zero point of the instrument. The effect of a chlorine removal process is demonstrated by comparison with this blank value.

The influence of chlorine contained in No 2 extends until it cannot be measured without the chlorine removal treatment. No3 is a case where stirring is not performed, and No4 is a case where stirring is performed, and has shown the effect of chlorine removal by stirring. No4, N05, and No6 show the influence of the heating time of chlorine removal.

Therefore, according to the experiments No1 to No6, the sample containing the chlorine ion concentration at the seawater level can be completely treated by performing stirring with nitrogen gas at a heating temperature of 100 ° C. for a heating time of 10 minutes or more as a chlorine removal treatment. Able to know.

Even when comparing the case of containing chlorine ions of No7 and No8 which have the same amount of oxidant and does not contain chlorine ions, the value of COD becomes a prescribed amount so that the chlorine removal treatment of the present invention does not affect the phosphate contained in the sample. I can see that it does not. Increasing the heating temperature of No9 and No10 to 140 degreeC will show some influence on the pioxide contained in a sample.

In the method for measuring the chemical oxygen demand of the present invention, even when halogen ions are present in the sample water, measurement can be performed with the same precision as in the case where no halogen ions are present without using a conventional hazardous substance or expensive chemicals.

Therefore, since the waste liquid after measurement does not contain a hazardous substance etc., waste liquid can be processed easily.

Claims (4)

Take a certain amount of sample to measure chemical oxygen demand, A predetermined amount of sulfuric acid was added to the sample and heated in an inert atmosphere to remove dissolved chlorine ions present in the sample as hydrogen chloride, Subsequently, a predetermined amount of an oxidizing reagent that oxidizes the sample is added thereto, followed by heating to oxidize the pioxide in the sample, The amount of the remaining oxidizing reagent is measured by titrating the remaining oxidizing reagent with a reducing reagent solution. From the amount of the oxidizing reagent added in a certain amount in advance, the amount of the oxidizing reagent consumed to oxidize the pioxide of the sample is measured, A method for measuring the chemical oxygen demand, characterized in that the chemical oxygen demand is calculated from the measured value of the capacity of the sample and the amount of the oxidizing reagent consumed to oxidize the pioxide of the sample. The method of claim 1, And the oxidizing agent is a potassium nitrate solution, and the reducing reagent is ferric sulfate (III). The method of claim 2, And said oxidizing agent is a potassium permanganate solution and said reducing reagent is a ferric sulfate (III) solution. A container for holding the sample to be measured, means for adding sulfuric acid to a sample contained in the container and heating in an inert atmosphere, means for adding a predetermined amount of an oxidizing reagent to the container for heating in an inert atmosphere, and An apparatus for measuring the chemical oxygen demand amount having a titration means for titrating the amount of electricity remaining with a reagent for reducing, and a means for calculating a chemical oxygen demand amount from the capacity of the sample to be measured and the titration value of the electricity amount.