JPH0592711U - COD measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] Use the dilution water or blank water supply system required for COD measurement to clean the silver chloride adhering to the liquid junction and platinum electrode, and to check the congestion of various piping systems. In addition to avoiding deterioration and improving maintainability, the cost of the entire device will be reduced. [Constitution] COD of the reaction solution based on redox potential titration
In the COD measuring device for measuring the temperature, the discharge ports of the blank water supply pipe and the dilution water supply pipe are connected to the liquid junction 4 of the reference electrode 3.
And the platinum electrode 6 of the redox potential measuring electrode 5 are arranged so as to face each other.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention immerses the liquid junction part of the reference electrode and the platinum electrode of the redox potential measurement electrode in the reaction liquid diluted with sample water, and based on the redox potential titration, the reaction liquid COD (Chemical Oxygen Demand) The present invention relates to an improved technique of a COD measurement device by an oxidation method configured to measure the.

[0002]

[Prior Art]

 When measuring COD by the above-mentioned oxidation method, chloride ions contained in the sample water and a small amount of dilution water or blank water cause an error in the measured value. Therefore, silver nitrate was used as a reagent to mask this. When added to the reaction solution, this silver nitrate reacts with chloride ions to form silver chloride. If this silver chloride adheres to the liquid junction of the reference electrode or the platinum electrode of the oxidation-reduction potential measurement electrode, the measured value will be abnormal.Therefore, conventionally, the air outlet is exposed to the liquid junction or the platinum electrode. As described above, a pressurized air supply pipe is provided in the reaction tank, and silver chloride attached to the liquid junction or the platinum electrode is washed by bubbling pressurized air.

[0003]

[Problems to be solved by the device]

 However, as shown in FIG. 8, in addition to the reference electrode 3 and the oxidation-reduction potential measuring electrode 5, various supply pipes 8 to 12 such as reaction solution, reagent, dilution water, blank water, and titrant solution, and drainage solution are used. In addition to connecting the dedicated pressurized air supply pipe 24 for bubbling to the lid 2 of the reaction tank 1 in which the exhaust pipes 13 and 14 are congested, the maintainability becomes poor. There was room for improvement in that it was necessary to provide the exhaust pipe 14 with a cooler 25 for refluxing the reaction liquid that was evaporated along with the air into the reaction tank 1. The present invention has been made in view of such circumstances, and the above problems can be solved by a rational improvement that effectively uses a system required for COD measurement. The purpose is to provide a measuring device.

[0004]

[Means for Solving the Problems]

 In order to achieve the above object, in the first invention, in the COD measuring device described at the beginning, one outlet of each supply pipe of blank water for calibration and dilution water is made to face the liquid junction. It is characterized in that it is arranged so that the other ejection port faces the platinum electrode. The second invention is characterized in that the blank water supply pipe for calibration is branched and the discharge ports of the respective branch pipes are arranged so as to face the liquid junction and the platinum electrode.

[0005]

[Action]

 In both the first and second inventions described above, the liquid junction of the reference electrode and the platinum electrode of the redox potential measuring electrode are washed by supplying the dilution water or blank water required for the COD measurement.

[0006]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1 showing a COD measuring device according to one embodiment of the present invention, 1 is a reaction tank, and 2 is a lid for closing the upper opening of the reaction tank 1. 3 is a reference electrode having a liquid junction 4 at the lower end, 5 is an oxidation-reduction potential measuring electrode having a platinum electrode 6 at the lower end, and 7 is a collecting pipe in which a sample water supply pipe 8 and a reagent supply pipe 9 are assembled. , 10 is a diluting water supply pipe for diluting sample water, 11 is a blank water supply pipe for calibration, 12 is a titration liquid supply pipe, 13 is a drain pipe, and 14 is an exhaust pipe. The redox potential measuring electrode 5, and the tubes 7 to 14 are provided on the lid 2. Reference numeral 15 is a motor mounted on the lid 2.

As shown in FIG. 2, the outlet a of the dilution water supply pipe 10 is arranged so as to face the platinum electrode 6 of the oxidation-reduction potential measuring electrode 5, and the outlet b of the calibration blank water supply pipe 11 is provided. Are arranged so as to face the liquid junction 4 of the comparison electrode 3. The dilution water and blank water supply pipes 10 and 11 are connected to pressurized water supply devices 16 and 17 driven by pressurized air, and the pressurized water supply devices 16 and 17 are An air supply pipe that connects a dilution water or blank water inlet pipe 19 equipped with a pinch valve 18 to the bottom of the airtight tank 20 and also supplies air to the upper space of the airtight tank 20 by sharing the air pump 21. 22 is connected, and the dilution water and the blank water are pressure-fed to the reaction tank 1 by air by controlling the opening and closing of the solenoid valve V. After the COD measurement is completed, the dilution water is supplied to the platinum electrode 6. Moreover, by spraying blank water onto the liquid junction 4 under pressure, the silver chloride adhering to the platinum electrode 6 and the liquid junction 4 is washed away. Incidentally, 23 in the figure is a cylindrical electrode cover.

[0008] Incidentally, the COD measurement of the reaction solution obtained by adding 60 ml of diluting water to 40 ml of an aqueous solution of sodium chloride having a concentration of 4.1 g / L as sample water was repeated without carrying out the above washing, When the change in the titration curve at that time was examined and seen, it is clear from Fig. 3 (A) showing the result of the first measurement and Fig. 3 (B) showing the result of the 16th measurement that it was impossible to measure. While the titration curve changed greatly, when performing COD measurement under the same conditions as above, the platinum electrode 6 was washed with diluting water and the liquid junction 4 was washed with blank water for 60 seconds each. However, as is clear from FIG. 4 (A) showing the result of the first measurement and FIG. 4 (B) showing the result of the 50th measurement, a large change in the titration curve was observed even after repeating the COD measurement 50 times. There wasn't. This proved correctly that the silver chloride adhering to the platinum electrode 6 and the liquid junction 4 was effectively washed and removed by the dilution water and the blank water.

In addition to the above washing, during the reaction waiting time before titration, the airtight tank 20 of the pressurized water supply device 16 is emptied, and pressurized air is supplied from the dilution water supply pipe 10 toward the platinum electrode 6. When bubbling was performed for 100 seconds, the COD measurement was repeated 159 times, as is clear from FIG. 5A showing the first measurement result and FIG. 5B showing the 159th measurement result. However, there was almost no change in the titration curve. It should be added that with this level of bubbling, the amount of the reaction liquid that is evaporated along with the air is insignificant, and a cooler for refluxing the reaction liquid is not required.

As shown in FIG. 6, by connecting the dilution water supply pipe 10 to the cylindrical electrode cover 23, the electrode cover 23 is used to wash the silver chloride adhering to the platinum electrode 6 with the dilution water. It is possible to take the form. The outlet a of the dilution water supply pipe 10 is exposed to the liquid junction 4 to wash the liquid junction 4 with diluted water, and the outlet b of the blank water supply pipe 11 is connected to the platinum electrode 6. It is also possible to carry out a mode in which the platinum electrode 6 is washed with blank water to face the above. Further, depending on the concentration of the sample water for which COD is to be measured, dilution water may not be required. In this case, the airtight tank 20 is emptied or the water level is lowered to add water from the diluted water supply pipe 10. The compressed air may be blown toward the liquid junction 4 or the platinum electrode 6 in the form of air cleaning. At this time, since the air is not bubbled, the reaction liquid does not accompany the air and evaporates, and therefore the reaction liquid No cooler for reflux is required. Alternatively, some devices may not be equipped with the dilution water supply pipe itself. In this case, as shown in FIG. 7, the calibration blank water supply pipe 11 is branched so that each branch pipe 11a, The discharge ports c and d of 11b may be arranged so as to face the liquid junction 4 and the platinum electrode 6, and the silver chloride adhering to the liquid junction 4 and the platinum electrode 6 may be washed with blank water. ..

[0011]

[Effect of the device]

 As described above, in both the first and second inventions, the liquid junction and the white gold electrode are rationalized by effectively using the supply system of the dilution water or the blank water required for the COD measurement. By adopting a form in which cleaning is performed, it is no longer necessary to use a pressurized air supply system dedicated to cleaning, as in the past, and a cooler for refluxing the reaction liquid that evaporates with the air is no longer required, and congestion of the piping system is eliminated. In addition to avoiding the increase in cost and improving the maintainability, a significant cost reduction has been achieved.

[Brief description of drawings]

FIG. 1 is a simplified plan view of a COD measuring device.

FIG. 2 is an explanatory view showing a cleaning state of a supply system of dilution water and blank water, a platinum electrode and a liquid junction.

3 (A) and 3 (B) are graphs showing changes with time of a titration curve during COD measurement in a state where the cleaning function is stopped.

4 (A) and (B) are graphs showing changes over time in a titration curve during COD measurement when washing was performed with dilution water and blank water.

5 (A) and 5 (B) are graphs showing the change over time of the titration curve during COD measurement when bubbling cleaning was performed in addition to cleaning with dilution water and blank water.

FIG. 6 is a partial cross-sectional view showing a cleaning mode of a platinum electrode by supplying dilution water using an electrode cover.

FIG. 7 is an explanatory view showing a cleaning mode of a liquid junction part and a platinum electrode by branch supply of blank water for calibration.

FIG. 8 is a simplified plan view of a conventional COD measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reaction tank, 3 ... Comparison electrode, 4 ... Liquid junction part, 5 ... Redox potential measurement electrode, 6 ... Platinum electrode, 10 ... Dilution water supply pipe, 11 ...
Blank water supply pipe, 11a, 11b ... Branch pipe, a, b, c,
d ... Discharge port.

Claims (2)

[Scope of utility model registration request] 1. A structure in which a liquid junction part of a reference electrode and a platinum electrode of a redox potential measuring electrode are immersed in a reaction liquid in a reaction tank, and COD of the reaction liquid is measured based on redox potential titration. In the COD measuring device described above, one discharge port of each supply pipe of the calibration blank water and the dilution water is arranged so as to face the liquid junction, and the other discharge port is arranged so as to face the platinum electrode. A COD measuring device characterized by being provided. 2. A structure in which the liquid junction part of the reference electrode and the platinum electrode of the redox potential measuring electrode are immersed in the reaction liquid in the reaction tank, and the COD of the reaction liquid is measured based on the redox potential titration. In the COD measuring device described above, the blank water supply pipe for calibration is branched, and the discharge port of each branch pipe is arranged so as to face the liquid junction and the platinum electrode. .