JP4714209B2 - COD automatic measuring instrument and COD measuring method using the same - Google Patents

Description

  The present invention relates to a COD automatic measuring instrument, and more particularly, to a COD automatic measuring instrument having a function of masking chloride ions in a solution with silver nitrate, and a COD measuring method using the same.

  Chemical oxygen demand (COD) is an indicator of water pollution. In factories and the like, generally, COD of wastewater is continuously measured using a COD automatic measuring instrument defined in JIS K0806-1997 (Non-patent Document 1). Monitoring is in progress.

  The COD automatic measuring instrument is an automated COD measurement method based on the method described in JIS K0102-1998 “17.100 ° C. Oxygen Consumption by Potassium Permanganate” (Non-Patent Document 2). . Specifically, the COD measurement method according to JIS K0102-1998 is as follows. First, sulfuric acid is added to the sample solution to make it acidic, and a silver nitrate solution is further added to precipitate chloride ions as silver chloride. Next, a known amount of potassium permanganate is added as an oxidizing agent and heated in a boiling water bath or an oil bath for 30 minutes to oxidize reducing substances such as organic substances. Thereafter, the sample solution is cooled to 60 to 80 ° C., and a sodium oxalate solution equivalent to the potassium permanganate is added. The residual sodium oxalate is back titrated with potassium permanganate, the amount of potassium permanganate consumed by the reducing substance in the sample solution is determined, and this is expressed as the equivalent amount of oxygen is COD. . The COD automatic measuring instrument automates a series of these operations.

  Since industrial wastewater generally has a low chloride ion concentration (for example, 500 mg / L or less), the amount of silver nitrate added in the COD automatic measuring instrument is small, and the amount of silver chloride produced is small. On the other hand, when the chloride ion concentration is high (for example, 3000 mg / L or more) as in the case of cleaning wastewater from incineration exhaust gas of industrial waste, the amount of silver nitrate added in the COD automatic measuring instrument increases, and the generated silver chloride The amount also increases. In conventional COD automatic measuring instruments, when a large amount of silver chloride is produced in this way, the silver chloride adheres to the inner walls of reaction vessels and piping, as well as to the surfaces of various sensors such as oxidation-reduction potential (ORP) electrodes in the reaction vessel. This was a cause of measurement error of the COD value. Further, even when the amount of silver chloride produced was small, silver chloride accumulated in the reaction vessel due to repeated measurement, resulting in the same measurement error. Further, when the COD value is small and this is accurately measured, it is necessary to increase the amount of the sample solution, and this increase in the amount of silver chloride produced may cause a COD value measurement error. .

In order to prevent such adhesion and accumulation of silver chloride, it is necessary to wash the measuring device for each measurement. However, when COD such as factory effluent is continuously monitored, it is described in JIS K0806-1997. Thus, the measurement cycle is defined as within one hour. In the conventional COD automatic measuring instrument, it is necessary to keep the reaction vessel at a high temperature during the measurement, and thus it is difficult to clean the measuring instrument for each measurement. In addition, if the amount of silver chloride produced by diluting the sample solution is reduced, blockage of the flow path of the COD automatic measuring instrument can be prevented, but the concentration of the reducing substance in the sample solution also decreases, so COD must be measured accurately. There were cases where it was difficult.
JIS K0806-1997 JIS K0102-1998 “17. Oxygen consumption by potassium permanganate at 100 ° C.”

  The present invention has been made in view of the above-mentioned problems of the prior art, and can sufficiently suppress the adhesion and accumulation of silver chloride on the inner wall of the reaction tank, the sensor surface, etc. It is an object of the present invention to provide a COD automatic measuring instrument capable of continuously measuring COD over a long period of time without performing dilution, and a method for measuring COD using the same.

  As a result of intensive studies to achieve the above object, the present inventors have found that the temperature of the reaction vessel to which the silver nitrate solution is added is 50 ° C. in terms of the structure and operation (for example, the measurement cycle) in the conventional COD automatic measuring instrument. It is held at the above high temperature, and when a large amount of silver nitrate is added at such a high temperature to mask chloride ions, the generated silver chloride tends to solidify due to heat, and as a result, the inner wall of the reaction vessel or piping, Furthermore, it has been found that silver chloride is likely to adhere to and deposit on the surface of various sensors such as the ORP electrode in the reaction tank, resulting in measurement errors in the COD value. Furthermore, the present inventors have added a large amount of silver nitrate to mask chloride ions, and when added at a low temperature of less than 50 ° C., the produced silver chloride is easily dispersed in the sample solution by stirring, so that the reaction vessel It has been found that it is difficult to adhere to the inner wall, the sensor surface, etc., and the measurement error of the COD value hardly occurs, and the present invention has been completed.

That is, the COD automatic measuring instrument of the present invention is
(A) an ion concentration measurement unit for measuring the chloride ion concentration of the sample solution;
(B) a reaction tank connected in series or in parallel to the ion concentration measurement unit (A) and having a temperature in the range of −5 ° C. or more and less than 50 ° C .;
(C) a reaction vessel connected in series to the reaction vessel (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less;
(D) means for adding a silver nitrate solution to the reaction vessel (B);
(E) means for adding a silver nitrate solution to the reaction vessel (C);
(F) Control means electrically connected to the ion concentration measuring section (A) and the silver nitrate solution adding means (D) and (E),
Determining the amount of silver nitrate added to the sample solution based on the chloride ion concentration;
When the silver nitrate amount is not more than a threshold value, an amount of silver nitrate solution corresponding to the determined silver nitrate amount is added to the sample solution using the silver nitrate solution adding means (E),
When the amount of silver nitrate exceeds a threshold value, an amount of silver nitrate solution corresponding to the amount of silver nitrate exceeding the threshold value is added to the sample solution using the silver nitrate solution addition means (D), and then the reaction vessel Adding a silver nitrate solution in an amount corresponding to the threshold amount of silver nitrate using the silver nitrate solution addition means (E) to the sample solution transferred from (B) to the reaction vessel (C);
Control means for controlling the silver nitrate solution addition means (D) and (E),
(G) It has the structure based on the method as described in JIS K0102-1998 "Oxygen consumption by potassium permanganate at 17.100 degreeC", Comprising: In the said reaction vessel (C), after a silver nitrate solution addition Means for measuring the chemical oxygen demand of the sample solution;
It is characterized by providing.

In addition, the COD measurement method of the present invention includes:
(A) an ion concentration measurement unit for measuring the chloride ion concentration of the sample solution;
(B) a reaction tank connected in series or in parallel to the ion concentration measurement unit (A) and having a temperature in the range of −5 ° C. or more and less than 50 ° C .;
(C) a reaction vessel connected in series to the reaction vessel (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less;
(D) means for adding a silver nitrate solution to the reaction vessel (B);
(E) means for adding a silver nitrate solution to the reaction vessel (C);
(F) a control means electrically connected to the ion concentration measurement section (A) and the silver nitrate solution addition means (D) and (E);
(G) means for measuring a chemical oxygen demand having a configuration conforming to the method described in JIS K0102-1998 "Oxygen consumption by potassium permanganate at 17.100 ° C" ;
A method for measuring chemical oxygen demand of a sample solution using a COD automatic measuring instrument comprising:
Measuring the chloride ion concentration of the sample solution in the ion concentration measuring section (A);
By the control means (F),
Determining the amount of silver nitrate added to the sample solution based on the chloride ion concentration;
When the silver nitrate amount is not more than a threshold value, an amount of silver nitrate solution corresponding to the determined silver nitrate amount is added to the sample solution using the silver nitrate solution adding means (E),
When the amount of silver nitrate exceeds a threshold value, an amount of silver nitrate solution corresponding to the amount of silver nitrate exceeding the threshold value is added to the sample solution using the silver nitrate solution addition means (D), and then the reaction vessel (B) transferring the sample solution to the reaction vessel (C), and adding a silver nitrate solution in an amount corresponding to the threshold amount of silver nitrate to the sample solution using the silver nitrate solution adding means (E) When,
Measuring the chemical oxygen demand of the sample solution after addition of the silver nitrate solution by the chemical oxygen demand measurement means (G) in the reaction vessel (C);
It is the method characterized by including.

  According to the present invention, in a COD automatic measuring instrument that needs to keep the reaction tank at a high temperature during COD measurement, it is possible to sufficiently suppress the adhesion and accumulation of silver chloride on the inner wall of the reaction tank, the sensor surface, etc. It is possible to continuously measure COD over a long period of time without performing cleaning or dilution of the sample solution.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted. In the drawing, valves in the liquid feeding line are omitted.

For example, as shown in FIG. 1 or FIG.
(A) an ion concentration measurement unit for measuring the chloride ion concentration of the sample solution;
(B) a reaction tank connected in series (for example, FIG. 1) or in parallel (for example, FIG. 2) to the ion concentration measurement unit (A) and having a temperature in the range of −5 ° C. or more and less than 50 ° C .;
(C) a reaction vessel connected in series to the reaction vessel (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less;
(D) means for adding a silver nitrate solution to the reaction vessel (B);
(E) means for adding a silver nitrate solution to the reaction vessel (C);
(F) a control means electrically connected to the ion concentration measurement section (A) and the silver nitrate solution addition means (D) and (E);
(G) means for measuring chemical oxygen demand in the reaction vessel (C);
It is characterized by providing. The COD automatic measuring instrument of the present invention is not limited to that shown in FIGS.

  This COD automatic measuring instrument is used to measure the COD of solutions such as factory effluent, and in particular, COD such as washing wastewater of incineration exhaust gas from industrial waste, such as solutions with high chloride ion concentration. It is preferably used when measuring. In the present invention, a solution for measuring COD is referred to as a “sample solution”.

(A) Ion concentration measurement unit:
The ion concentration measuring unit (A) in the COD automatic measuring instrument of the present invention is not particularly limited as long as it can measure the chloride ion concentration of the sample solution. For example, the ion concentration measuring instrument (1 ) Sample solution tank (2). When measuring the COD of a sample solution in which a correlation is established between the chloride ion concentration and the conductivity, for example, a sample solution having a high concentration of chloride ions (for example, 1000 mg / L or more), the ion concentration A conductivity meter can be used as the ion concentration measuring instrument (1) used in the measuring section (A). Conductivity meters are easier to maintain than chlorine ion concentration meters, and are more reliable and less expensive. In such cases, measure the chloride ion concentration using a conductivity meter. Is preferred.

  The sample solution tank (2) is preferably provided with an overflow line. By constantly measuring the chloride ion concentration while overflowing the sample solution, the time lag between the chloride ion concentration measurement and the transfer of the sample solution to the reaction vessel (B) can be reduced.

  In this way, the ion concentration measuring unit (A) is provided in the COD automatic measuring instrument, and the chloride ion concentration of the sample solution is measured before the silver nitrate solution is added, so that chloride that is an interference substance in COD measurement is obtained. The amount of silver nitrate added to mask the product ions can be minimized, and the measurement cost can be reduced.

(B) Reaction tank:
The reaction tank (B) in the COD automatic measuring instrument of the present invention has a temperature in the range of −5 ° C. or more and less than 50 ° C. The reaction vessel (B) may be maintained at a temperature within the above range using a thermostatic bath (not shown) or the like, but from an economical viewpoint, it is simply installed in a room temperature environment without temperature control. Preferably it is.

  This reaction vessel (B) may be connected in series to the ion concentration measurement unit (A) as shown in FIG. 1, or in parallel to the ion concentration measurement unit (A) as shown in FIG. It may be connected.

  When the reaction vessel (B) is connected in series, a predetermined amount of the sample solution whose chloride ion concentration is measured in the ion concentration measurement unit (A) is transferred to the reaction vessel (B). Here, the sample solution may be transferred to the reaction vessel (B) in a lump after measuring the chloride ion concentration in the ion concentration measuring section (A), or the chloride solution in the ion concentration measuring section (A). You may transfer to a reaction tank (B), measuring ion concentration. In addition, an overflow line is provided in the sample solution tank (2) to constantly measure the chloride ion concentration while allowing the sample solution to overflow, and at the time of COD measurement, a part of the sample solution in which the chloride ion concentration is measured is added to the reaction tank ( B) may be transferred (FIG. 1). Of these, the chloride ion concentration is constantly measured while overflowing the sample solution from the viewpoint that the time lag between the measurement of the chloride ion concentration and the transfer of the sample solution to the reaction vessel (B) can be reduced. It is preferable to transfer a part of the sample solution to the reaction vessel (B) during COD measurement.

  On the other hand, when the reaction vessel (B) is connected in parallel, the sample solution is supplied to the sample solution vessel (2) to measure the chloride ion concentration and the sample solution is supplied to the reaction vessel (B). Alternatively, an overflow line may be provided in the sample solution tank (2) to constantly measure the chloride ion concentration while overflowing the sample solution, and the sample solution supplied to the sample solution tank (2) during COD measurement. A part may be supplied to the reaction tank (B) (FIG. 2). Of these, the chloride ion concentration is constantly measured while overflowing the sample solution from the viewpoint that the time lag between the measurement of the chloride ion concentration and the transfer of the sample solution to the reaction vessel (B) can be reduced. It is preferable to transfer a part of the sample solution to the reaction vessel (B) during COD measurement.

  In the present invention, a sample solution meter (3) may be provided in front of the reaction vessel (B) to measure the transfer amount (supply amount) of the sample solution (FIG. 1 or FIG. 2). The sample solution may be overflowed in the reaction vessel (B) so that a predetermined amount of the sample solution is transferred to B) (not shown).

  The amount of sample solution transferred to the reaction vessel (B) takes into account the amount of sample solution used for COD measurement and the amount of sample solution used for co-washing the reaction vessel (C) described later. And can be set as appropriate.

(C) Reaction tank:
The reaction tank (C) in the COD automatic measuring instrument of the present invention was connected in series to the reaction tank (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less using the heating device (4). Is. Examples of the heating device (4) include a boiling water bath and an oil bath.

  A predetermined amount of sample solution is transferred from the reaction vessel (B) to the reaction vessel (C). The transfer amount of the sample solution is usually measured by a sample solution meter (5) provided between the ion concentration measuring unit (A) and the reaction tank (B).

(D) Silver nitrate solution addition means:
The silver nitrate solution adding means (D) in the COD automatic measuring instrument of the present invention is for adding a silver nitrate solution to the reaction tank (B), and includes a silver nitrate solution storage tank (6) and a silver nitrate solution meter (7). It consists of. The silver nitrate solution adding means (D) (specifically, the silver nitrate solution meter (7)) is electrically connected to the control means (F) described later, and the silver nitrate solution meter (7) is connected to the control means (7). By controlling by F), the amount of the silver nitrate solution added to the reaction vessel (B) can be adjusted.

(E) Silver nitrate solution addition means:
The silver nitrate solution adding means (E) in the COD automatic measuring instrument of the present invention is for adding a silver nitrate solution to the reaction vessel (C), and includes a silver nitrate solution storage tank (6) and a silver nitrate solution meter (8). It consists of. The silver nitrate solution adding means (E) (specifically, the silver nitrate solution meter (8)) is electrically connected to the control means (F) described later, and the silver nitrate solution meter (8) is connected to the control means (8). By controlling by F), the amount of the silver nitrate solution added to the reaction vessel (C) can be adjusted. The silver nitrate solution storage tank (6) may be used in common with the silver nitrate solution storage tank of the silver nitrate solution addition means (D) as shown in FIGS. Also good.

(F) Control means:
The control means (F) in the COD automatic measuring instrument of the present invention includes the ion concentration measuring section (A) and the silver nitrate solution adding means (D) and (E) (specifically, the silver nitrate solution measuring instrument (7) and (8)), the amount of silver nitrate to be added to the sample solution is determined based on the chloride ion concentration measured in the ion concentration measuring section (A), and the silver nitrate solution adding means (D ) And (E).

  Specifically, first, an addition amount of silver nitrate with respect to the measured chloride ion concentration is determined based on a calibration curve between a preset chloride ion concentration and an addition amount of silver nitrate.

  Next, when the amount of silver nitrate is not more than the threshold, no silver nitrate solution is added in the reaction vessel (B), and the predetermined amount of the sample solution in the reaction vessel (B) is kept as it is at 50 ° C. or more and 100 ° C. or less. It is transferred to a reaction vessel (C) controlled to a temperature in the range, and in this reaction vessel (C), an amount of silver nitrate solution corresponding to the determined silver nitrate amount is added to the sample solution by means of silver nitrate solution addition means (E). Add with stirring. Stirring may be performed by a stirrer (9) as shown in FIGS. 1 and 2, or by bubbling (not shown).

  On the other hand, when the amount of silver nitrate exceeds the threshold, first, in the reaction vessel (B) having a temperature in the range of −5 ° C. or more and less than 50 ° C., an amount of silver nitrate solution corresponding to the amount of silver nitrate exceeding the threshold Is added to the sample solution with stirring by the silver nitrate solution adding means (D). Next, a predetermined amount of the sample solution in the reaction vessel (B) is transferred to the reaction vessel (C), and in the reaction vessel (C) controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less, the silver nitrate having the above threshold value is obtained. An amount of silver nitrate solution corresponding to the amount is added to the sample solution with stirring by the silver nitrate solution adding means (E). Stirring may be performed by a stirrer (10) as shown in FIGS. 1 and 2, or by bubbling (not shown).

  The threshold is usually determined by the specifications of the COD automatic measuring instrument, etc., but as described above, if a large amount of silver nitrate is added at a high temperature, the silver chloride is likely to be solidified by heat, so the threshold is as small as possible. More specifically, it is preferably 5 ml or less in terms of the amount of 200 g / L silver nitrate solution.

  As described above, an amount of silver nitrate corresponding to the amount of silver nitrate exceeding the threshold is added to the sample solution at a relatively low temperature of −5 ° C. or more and less than 50 ° C. Even when silver chloride is generated, it is possible to suppress the solidification of silver chloride due to heat, and the silver chloride is uniformly dispersed in the sample solution and chlorinated on the inner walls of the reaction vessels (B) and (C) and the sensor surface. Silver adhesion and accumulation can be suppressed. Since such an effect is larger as the temperature of the reaction vessel is lower, the temperature of the reaction vessel (B) is preferably in the range of −5 to 40 ° C., which corresponds to the amount of silver nitrate exceeding the threshold at this temperature range. It is preferred to add the amount of silver nitrate solution to be added. Moreover, in this invention, it is especially preferable that the reaction tank (B) is simply installed in the environment of room temperature, without controlling temperature from an economical viewpoint.

(G) Chemical oxygen demand (COD) measuring means:
The COD measuring means (G) in the COD automatic measuring instrument of the present invention measures the COD of the sample solution after addition of the silver nitrate solution in the reaction vessel (C) controlled to a temperature in the range of 50 ° C. to 100 ° C. There is no particular limitation as long as it is possible.

  Examples of such COD measuring means (G) include those based on the method described in JIS K0102-1998 “17. Oxygen consumption by potassium permanganate at 100 ° C.”, for example, ORP electrode as shown in FIG. (11), a titrator (12), a reagent storage tank (13), a reagent meter (14), and a titration controller (15) electrically connected to and controlling them. However, the COD measuring means (G) is not limited to this. Specifically, COD measurement is performed by the following method.

  First, sulfuric acid is added (a sulfuric acid storage tank and a sulfuric acid meter are not shown), and a predetermined amount of potassium permanganate solution is added as an oxidizing agent to the sample solution after addition of the silver nitrate solution adjusted to sulfuric acid acidity. The sulfuric acid may be added before the silver nitrate solution is added, may be added simultaneously with the silver nitrate solution, or may be added after the silver nitrate solution is added. The sample solution is then heated at 100 ° C. for 30 minutes. Thereby, reducing substances such as organic substances in the sample solution are oxidized by potassium permanganate. Thereafter, a predetermined amount of sodium oxalate solution is added (sodium oxalate storage tank and sodium oxalate meter are not shown), and the reaction vessel (C) is cooled to a temperature in the range of 50 ° C. to 60 ° C. Back titration with a potassium manganate solution measures the amount of potassium permanganate consumed in the oxidation reaction. The amount of oxygen corresponding to the consumption of potassium permanganate is the chemical oxygen demand (COD) of the sample solution. The end point of the back titration can be determined by measuring the redox potential of the sample solution using the ORP electrode (11).

  Thereafter, the sample solutions in the reaction tanks (B) and (C) are transferred to the silver recovery tank (16), and after silver chloride is separated and recovered, it is discharged.

  The means for transferring the sample solution in the COD automatic measuring instrument of the present invention is not particularly limited, and may be transferred using a pump or may be transferred in an extruding manner by applying pressure (all not shown).

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
Using the COD automatic measuring instrument shown in FIG. 2, the COD of industrial waste incineration exhaust gas cleaning wastewater (chloride ion concentration: 3000 mg / L or more) was continuously measured. Each measurement was carried out by automatic control in the following order. A silver nitrate solution having a concentration of 200 g / L was used, and the threshold value of the amount of silver nitrate was set to 5 ml in terms of the amount of the silver nitrate solution. FIG. 2 does not show a sulfuric acid storage tank, a sulfuric acid meter, a sodium oxalate solution storage tank, a sodium oxalate solution meter, and a diluting water flow path. However, sulfuric acid, a sodium oxalate solution, and diluting water are also not shown. Added by automatic control. Each solution was prepared according to the method described in JIS K0102-1998 “Oxygen consumption by potassium permanganate at 17.100 ° C.”. Moreover, the electrical conductivity meter was used as an ion concentration measuring device (1), and the washing waste_water | drain in the reaction tank (B) was stirred by bubbling instead of the stirrer (9).

  First, the washing waste water (sample solution) was overflowed in the sample solution tank (2), and the chloride ion concentration of the sample solution was constantly measured by the ion concentration measuring device (1). Next, at the time of COD measurement, 160 ml of a part of the sample solution was supplied to a reaction vessel (B) installed in a room temperature environment. Thereafter, the control means (F) determines the addition amount of the silver nitrate solution corresponding to the addition amount of silver nitrate with respect to the measured chloride ion concentration based on the following Table 1, and the silver nitrate solution is used as a sample solution as follows. Added.

  When the determined addition amount of the silver nitrate solution is not more than the threshold (5 ml), the reaction vessel (B) is not added with the silver nitrate solution, and the reaction vessel (C) is co-washed with the sample solution in the reaction vessel (B). After that, 67 ml of the sample solution in the reaction tank (B) was transferred to the reaction tank (C). After adding 33 ml of diluted water and 10 ml of sulfuric acid (1 + 2) to this, the determined amount of silver nitrate solution was weighed with a silver nitrate solution meter (8) and added to the reaction vessel (C) with stirring. During this time, the temperature of the reaction vessel (C) was controlled at 100 ° C.

  On the other hand, when the determined addition amount of the silver nitrate solution exceeds the threshold value (5 ml), the excess amount (for example, 4 ml when the determined addition amount of the silver nitrate solution is 9 ml) is added to the silver nitrate solution meter. Weighed in (7) and added to the reaction vessel (B) installed in a room temperature environment while stirring by bubbling (not shown). Next, after the reaction vessel (C) was co-washed with this sample solution, 67 ml of the sample solution in the reaction vessel (B) was transferred to the reaction vessel (C). After adding 33 ml of diluting water and 10 ml of sulfuric acid (1 + 2) to this, a silver nitrate solution of the threshold amount (5 ml) was weighed with a silver nitrate solution meter (8) and stirred with a stirrer (10) (reaction vessel ( To C). During this time, the temperature of the reaction vessel (C) was controlled at 100 ° C.

  Next, 10 ml of 5 mmol / L potassium permanganate solution is added to the reaction vessel (C) controlled at 100 ° C. while stirring with a stirrer (10), and the reaction vessel (C) is heated at 100 ° C. for 30 minutes. did. Thereafter, 10 ml of a 12.5 mmol / L sodium oxalate solution was added to the reaction vessel (C) while stirring with a stirrer (10), and then the reaction vessel (C) was cooled to 50 to 60 ° C. The COD value of the sample solution was measured by back titration with a potassium permanganate solution. The end point of the back titration was determined by measuring the redox potential of the sample solution with the ORP electrode (11). After completion of the measurement, the sample solutions in the reaction tanks (B) and (C) were transferred to the silver recovery tank (16) to separate and recover the silver chloride, and then the sample solution was discharged.

  This measurement was performed at a cycle of 1 hour. After 23 measurements, the system was automatically cleaned, and the measurement and cleaning were repeated at this cycle. Although COD measurement was carried out continuously for 180 days, this COD automatic measuring instrument did not show a large measurement error in the COD value, and it was confirmed that COD measurement was possible stably over a long period of time.

(Comparative Example 1)
Using the COD automatic measuring instrument shown in FIG. 3, the COD of industrial waste incineration exhaust gas cleaning wastewater (chloride ion concentration: 3000 mg / L or more) was continuously measured. Each measurement was carried out by automatic control in the following order. A silver nitrate solution having a concentration of 200 g / L was used, and the addition amount of the silver nitrate solution was 13 ml to prevent insufficient masking of chloride ions. Further, although FIG. 3 does not show a sulfuric acid storage tank, a sulfuric acid meter, a sodium oxalate solution storage tank, and a sodium oxalate solution meter, sulfuric acid and sodium oxalate solution were also added by automatic control. Each solution was prepared according to the method described in JIS K0102-1998 “Oxygen consumption by potassium permanganate at 17.100 ° C.”. Moreover, the conductivity meter was used as an ion concentration measuring device (1).

  After washing the reaction tank (C) with the washing waste water (sample solution), 67 ml of the sample solution was transferred to the reaction tank (C). After adding 33 ml of diluted water and 10 ml of sulfuric acid (1 + 2) to this, the above-mentioned amount of silver nitrate solution was weighed with a silver nitrate solution meter (8) and added to the reaction vessel (C) while stirring with a stirrer (10). . During this time, the temperature of the reaction vessel (C) was controlled at 100 ° C.

  Next, 10 ml of 5 mmol / L potassium permanganate solution is added to the reaction vessel (C) controlled at 100 ° C. while stirring with a stirrer (10), and the reaction vessel (C) is heated at 100 ° C. for 30 minutes. did. Thereafter, 10 ml of a 12.5 mmol / L sodium oxalate solution was added to the reaction vessel (C) while stirring with a stirrer (10), and then the reaction vessel (C) was cooled to 50-60 ° C. The COD value of the sample solution was measured by back titration with a potassium permanganate solution. The end point of the back titration was determined by measuring the redox potential of the sample solution with the ORP electrode (11). After completion of the measurement, the sample solution in the reaction tank (C) was transferred to the silver recovery tank (16), and after silver chloride was separated and recovered, the sample solution was discharged.

  When this measurement was carried out at a cycle of 1 hour, the COD value increased greatly at 3 hours from the start of the measurement. Therefore, the measurement was stopped, and the inside of the reaction vessel (C) and the surface of the ORP electrode (11) were visually observed. Silver chloride was deposited on the bottom of the reaction vessel (C), and silver chloride was adhered to the surface of the ORP electrode (11).

  As described above, according to the present invention, even in a COD automatic measuring instrument that needs to keep the reaction vessel at a high temperature during COD measurement, the adhesion and accumulation of silver chloride on the inner wall of the reaction vessel, the sensor surface, etc. Therefore, it is possible to continuously measure COD over a long period of time without performing cleaning for each measurement or dilution of the sample solution.

  Therefore, the COD automatic measuring instrument of the present invention is useful for long-term continuous COD measurement, particularly COD measurement of cleaning wastewater from incineration exhaust gas of industrial waste.

It is a schematic diagram which shows an example of the COD automatic measuring device of this invention. It is a schematic diagram which shows the other example of the COD automatic measuring device of this invention. It is a schematic diagram which shows the conventional COD automatic measuring device.

Explanation of symbols

  A ... Ion concentration measuring part; B, C ... Reaction tank; D, E ... Silver nitrate solution adding means; F ... Control means; G ... COD measuring means; 1 ... Ion concentration measuring instrument; Sample solution meter; 4 ... Heating device; 6 ... Silver nitrate solution storage tank; 7, 8 ... Silver nitrate solution meter; 9, 10 ... Stirrer; 11 ... ORP electrode; 12 ... Titrator; ... Reagent meter; 15 ... Titration controller; 16 ... Silver recovery tank.

Claims (2)

(A) an ion concentration measurement unit for measuring the chloride ion concentration of the sample solution;
(B) a reaction tank connected in series or in parallel to the ion concentration measurement unit (A) and having a temperature in the range of −5 ° C. or more and less than 50 ° C .;
(C) a reaction vessel connected in series to the reaction vessel (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less;
(D) means for adding a silver nitrate solution to the reaction vessel (B);
(E) means for adding a silver nitrate solution to the reaction vessel (C);
(F) Control means electrically connected to the ion concentration measuring section (A) and the silver nitrate solution adding means (D) and (E),
Determining the amount of silver nitrate added to the sample solution based on the chloride ion concentration;
When the silver nitrate amount is not more than a threshold value, an amount of silver nitrate solution corresponding to the determined silver nitrate amount is added to the sample solution using the silver nitrate solution adding means (E),
When the amount of silver nitrate exceeds a threshold value, an amount of silver nitrate solution corresponding to the amount of silver nitrate exceeding the threshold value is added to the sample solution using the silver nitrate solution addition means (D), and then the reaction vessel Adding a silver nitrate solution in an amount corresponding to the threshold amount of silver nitrate using the silver nitrate solution addition means (E) to the sample solution transferred from (B) to the reaction vessel (C);
Control means for controlling the silver nitrate solution addition means (D) and (E),
(G) It has the structure based on the method as described in JIS K0102-1998 "Oxygen consumption by potassium permanganate at 17.100 degreeC", Comprising: In the said reaction tank (C), after a silver nitrate solution addition Means for measuring the chemical oxygen demand of the sample solution;
A COD automatic measuring instrument comprising: (A) an ion concentration measurement unit for measuring the chloride ion concentration of the sample solution;
(B) a reaction tank connected in series or in parallel to the ion concentration measurement unit (A) and having a temperature in the range of −5 ° C. or more and less than 50 ° C .;
(C) a reaction vessel connected in series to the reaction vessel (B) and controlled to a temperature in the range of 50 ° C. or more and 100 ° C. or less;
(D) means for adding a silver nitrate solution to the reaction vessel (B);
(E) means for adding a silver nitrate solution to the reaction vessel (C);
(F) a control means electrically connected to the ion concentration measurement section (A) and the silver nitrate solution addition means (D) and (E);
(G) means for measuring a chemical oxygen demand having a configuration conforming to the method described in JIS K0102-1998 "Oxygen consumption by potassium permanganate at 17.100 ° C" ;
A method for measuring chemical oxygen demand of a sample solution using a COD automatic measuring instrument comprising:
Measuring the chloride ion concentration of the sample solution in the ion concentration measuring section (A);
By the control means (F),
Determining the amount of silver nitrate added to the sample solution based on the chloride ion concentration;
When the silver nitrate amount is not more than a threshold value, an amount of silver nitrate solution corresponding to the determined silver nitrate amount is added to the sample solution using the silver nitrate solution adding means (E),
When the amount of silver nitrate exceeds a threshold value, an amount of silver nitrate solution corresponding to the amount of silver nitrate exceeding the threshold value is added to the sample solution using the silver nitrate solution addition means (D), and then the reaction vessel (B) transferring the sample solution to the reaction vessel (C), and adding a silver nitrate solution in an amount corresponding to the threshold amount of silver nitrate to the sample solution using the silver nitrate solution adding means (E) When,
Measuring the chemical oxygen demand of the sample solution after addition of the silver nitrate solution by the chemical oxygen demand measurement means (G) in the reaction vessel (C);
A COD measurement method comprising:

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