JPH0137690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a measurement method that determines the COD value contained in sample water without the addition of silver salts and corrects it to the COD value determined by the official analytical method, and uses a large amount of expensive silver salts (silver nitrate, silver sulfate). We aim to significantly reduce the amount of silver salt used compared to the official analytical method, thereby significantly reducing the cost required to measure COD values, and to provide a method that can easily obtain accurate values. It is something to do. In the past, measurements were carried out using official analytical methods and automatic measuring devices, but as the price of silver has soared recently, reagent costs are high and COD Problems have arisen in which management costs are enormous and it is difficult to carry out measurements that comply with total volume regulations. The present invention is based on the fact that the addition of silver salts has been substantially eliminated using the official analytical method, and that a correction method corresponding to the function of silver salts has been found through experiments. In the official analytical method, it is absolutely necessary to add silver salt to interfere with chlorine ions and to have an oxidation catalytic effect. The inventors have investigated the interference of chlorine ions, especially when no silver salt is added. That is, the following experiment was carried out by manual analysis under conditions in which the addition of silver salt was omitted from the official analytical method. The result is the first
2 and 3. Figure 1 shows the results of adding sodium chloride to distilled water in stages and allowing the reaction between chlorine ions and potassium permanganate to occur for 10, 20, and 30 minutes. As is clear from these results, the amount of potassium permanganate consumed varies depending on the time the product is left in the boiling water bath, and the oxidation reaction hardly progresses after a reaction time of about 10 minutes. Furthermore, whether looking at 10 minutes, 20 minutes, or 30 minutes, the amount of potassium permanganate consumed increases linearly in proportion to the chloride ion concentration. Figure 2 shows a study conducted on river water, in which sodium chloride was added in stages and the COD value was determined. Although the COD values for each river were different, a straight line was obtained that was well parallel to the blank test value for sodium chloride alone. These results revealed that an accurate COD value can be determined by subtracting the blank test value according to the chloride ion concentration. Figure 3 shows a test conducted on inflow water from a sewage treatment plant, and the results were similar to those for river water. From the above results, it was found that the oxidation reaction of the COD target substance and chlorine ion with respect to potassium permanganate was a simultaneous reaction. As a result, potassium permanganate consumption due to chlorine ion concentration needs to be determined by actual measurement from the value of actual test water without the addition of silver salts and the value without the addition of silver salts in the same test water with standard addition of standard chlorine ions such as sodium chloride. There is. Therefore, the chlorine ion concentration in the sample water is measured using another method (ion electrode method), and the amount of potassium permanganate consumed, which is proportional to the chlorine ion content, is subtracted from the titration amount obtained in the sample water. Ion interference can be completely removed. In addition, for river water and inflow water from sewage treatment plants, we compared the COD values without the addition of silver salts and the official analysis method (silver salt addition method) from the standpoint of the catalytic action of silver salts.

[Table] As is clear from the above table, the specific oxidation rate (river: average 1.1, treatment plant: 1.2) is shown depending on the contents of the sample water, the measurement location, and the target sample water. By multiplying the COD value at the time of addition by the oxidation rate coefficient, a value that closely matches the COD value determined by the official analytical method can be obtained. The method of the present invention is based on the results of the experiments described above, and involves measuring the chloride ion concentration in the sample water, determining the amount of potassium permanganate consumed by the chloride ions in the sample water, and then determining the amount of potassium permanganate consumed by the chlorine ions in the sample water. Add potassium permanganate to the sample water without adding salt and find the total consumption. Subtract the potassium permanganate consumption due to chlorine ions from this total consumption to obtain the actual measurement without adding silver salt. Obtain the results, divide the measurement results by the official analysis method (JISK0102) by this actual measurement result to find the oxidation rate coefficient, and multiply this coefficient by the actual measurement results for subsequent water tests without the addition of silver salts.
It is characterized by obtaining COD values. According to this method, the number of measurements performed using the official analytical method that requires the addition of a silver salt can be greatly reduced, and therefore the cost required for measurements can be significantly reduced. As is clear from the above, an accurate COD value can be obtained by multiplying the actual measurement result obtained without the addition of silver salt by the oxidation rate coefficient. Hereinafter, the fourth embodiment of the method of the present invention will be explained.
This will be explained using the block diagram shown in the figure. In this example, a preliminary measurement is first performed on the same sample water, and then the actual measurement is performed. Then, at certain regular intervals or as necessary, measurements are performed based on the official analysis method specified in JISK0102 to determine the oxidation rate coefficient and correct the results of the above-mentioned main measurements. The reagents used here are based on JISK0102. (1) Regarding preliminary measurements, first send an appropriate amount (for example, 300 ml) of test water 1, such as river water or wastewater, to test tank 3 using pop-up 2 and store it there. The water test tank 3 has a built-in chlorine ion electrode or sodium ion electrode (hereinafter referred to as ion electrode) 4 for measuring the chloride ion concentration, and the sample water 1'
An output voltage corresponding to the chloride ion concentration in the sample is obtained. The output voltage of the ion electrode 4 is applied to a voltmeter 5, and the result is sent to a computer 6.
transmitted to and stored. After measuring the chloride ion concentration, the computer 6 opens the valve 7 and sends the sample water 1' to the scale 8 for weighing, and when it reaches, for example, 10 ml, closes the valve 7 and sends the sample water 1' to the scale 8 for weighing. The operation of sending it to reaction tank 9 is performed in step 2.
Repeat several times to supply 20 ml of test water to the reaction tank 9.
Similarly, the valve 11 of the dilution water tank 10 is opened to send the dilution water 12 to the weigher 8, 20 ml is weighed out, the valve 11 is closed, and it is supplied to the reaction tank 9. Then, the pump 14 attached to the sulfuric acid tank 13 is operated for a certain period of time,
Sulfuric acid 15 is directly supplied to reaction tank 9. A reference electrode for the redox potential method is inserted into this channel and is used as a liquid junction. Subsequently, the valve is opened to operate the pump 16, and the potassium permanganate solution 18 is pumped from the potassium permanganate solution tank 17.
is supplied to a 10 ml reaction tank 9. After the above operations are completed, 60 ml of the mixed solution in the reaction tank 9 is heated to raise the temperature according to a predetermined temperature rise curve. After a certain period of time has elapsed, the computer 6
The pump 20 connected to the sodium oxalate tank 19 is operated, and the sodium oxalate solution 21 is sent to the weigher 8 and weighed.
ml is supplied to the reaction tank 9 to stop the reaction of the mixed solution. After the reaction has stopped, the computer 6 opens the valve 22 and operates the pump 16 to supply the potassium permanganate solution 18 at a constant flow rate to the reaction tank 9 for reaction. The end point of the reaction by titration of the potassium permanganate solution is detected, for example, by the redox potential method. When the computer 6 detects this reaction end point,
Immediately stop the pump 16 and close the valve 22. Then, from the time required for titration using the pump 16, the computer 6 calculates
The COD value is calculated, and the dilution amount of the test water is determined according to the previously measured and stored chloride ion concentration value. (2) Regarding the main measurement Based on the results of the preliminary measurement described above, the computer 6 determines the amount of dilution of the test water 1' so that the titration amount of potassium permanganate is 4 to 6 ml. Specifically, the amount of test water 1' supplied to the reaction tank 9 was set in the range of 10 to 100 ml, and the amount of dilution water 12
The supply amount of each is determined so that it is in the range of 90 to 0 ml and the total amount of both is 100 ml. Based on this determination, the computer 6 sequentially controls the opening and closing of the valves 7 and 11 to supply test water 1' and dilution water 12 to the reaction tank 9 in the same manner as described above. Thereafter, 10 ml each of sulfuric acid 15 and potassium permanganate solution 18 are sent to the reaction tank 9 in the same procedure, and the mixed solution is heated and raised in temperature according to a predetermined temperature rise curve. After 30 minutes, sodium oxalate solution 21 is added to the mixed solution in the 10 ml reaction tank 9 to stop the reaction. Then, the valve 22 is opened, and the pump 16 supplies the potassium permanganate solution 18 at a constant flow rate to the reaction tank 9 for titration. The computer 6 calculates the amount of potassium permanganate according to the chlorine ion concentration contained in the main measurement, subtracts the calculation result from the titration amount of potassium permanganate in the main measurement, and calculates the amount of potassium permanganate when no silver salt is added. Determine the COD value and then multiply it by the oxidation rate coefficient due to silver salt to indicate the COD value according to the official analytical method. When implementing such a method, COD based on the official analytical method in which silver salt is added at a certain period.
By calculating the value, storing the result in the computer 6, and automatically correcting the oxidation rate coefficient of the silver salt, it is possible to always obtain the correct COD value. The operation for measuring the COD value when silver salt is added is almost the same as the operation when no silver salt is added. The most different point is that in the above measurement operation, for example, silver nitrate is added to the mixed solution in the reaction tank 9, and then it is heated according to a predetermined temperature increase curve. This official analytical method may be carried out at appropriate intervals in actual measurements. For example, 1 day
Once again, the computer 6 operates the pump 25 provided in the silver nitrate solution tank 24 twice, and the sample water, sulfuric acid, potassium permanganate solution, and a mixed solution of dilution water added as necessary are mixed. For example, 5 ml of silver nitrate solution 26 is added and reacted in reaction tank 9. Then, titrate potassium permanganate using the same procedure as above to determine the COD value. Obtained by this official analytical method
For sample water with the same composition as the COD value, the COD value measured without the addition of silver salt is calculated, and the value obtained by dividing the COD value with silver salt by the COD value without addition of silver salt is the oxidation rate coefficient by the silver salt catalyst. Coefficient computer 6
The value is stored and stored until the next official analysis method is carried out, and then multiplied by the repeatedly obtained measurement results without the addition of silver salts to obtain the COD value. As is clear from the above explanation, according to the method of the present invention, the composition of the sample water (the ratio of substances with different reaction rates with potassium permanganate and the mixing ratio of substances with different oxidation rates by the silver salt catalyst) If there is no change, it is sufficient to add silver salt at least once a day.
Reagent cost is 1/24th. Further, as a means for confirming that the composition of the sample water does not change, the check function mode of the apparatus according to the method of the present invention is used. This mode has a function that allows continuous and automatic measurement of sample water of the same composition with and without silver salt added. Use this check function to measure sample water, and compare and examine the corrected COD value by multiplying the obtained COD value without silver salts by the silver salt catalyst oxidation rate coefficient and the COD value with silver salts to determine if there is a difference. Confirm that there is no change in the composition of the sample water. In addition, if a difference occurs, the amount of potassium permanganate consumed by chlorine ions and the oxidation coefficient are determined again through experiments, and the results are input into the computer and dealt with accordingly. In addition, even in the official analysis method, it has been found that the variation in COD values increases when suspended organic matter is mixed in, so the sample water used in this experiment was also made from water with suspended matter removed. used.

[Brief explanation of drawings]

Figures 1, 2 and 3 are the COD of the present invention.
FIG. 4 is a diagram for explaining the principle of the value measurement method, and is a block diagram of an apparatus for carrying out an embodiment of the method of the present invention. 1, 1'...Water test, 2...Pump, 3...Water test tank, 4...Ion electrode, 5...Voltmeter, 6...Computer, 7...Valve, 8...Weighing meter, 9...
... Reaction tank, 10 ... Dilution tank, 11 ... Valve,
13... Sulfuric acid tank, 14... Valve, 15... Sulfuric acid, 16... Pump, 17... Potassium permanganate solution tank, 19... Sodium oxalate solution tank, 20... Pump, 24... Silver nitrate solution Tank, 2
5...Pump.

Claims (1)

[Claims] 1. Measure the chlorine ion concentration in the test water to determine the amount of potassium permanganate consumed by the chlorine ions in the test water, and then add potassium permanganate to the test water without adding silver salt. The amount of potassium permanganate consumed by the chlorine ions is subtracted from the total amount of potassium permanganate consumed to obtain the actual measurement result when no silver salt is added. The oxidation rate coefficient is obtained by dividing the measurement result when silver salt is added for the same test water as the above test water, and this oxidation rate coefficient is multiplied by the actual measurement result for the subsequent test water without the addition of silver salt.
A COD value measurement method characterized by obtaining a COD value.