阅读说明：本技术 一种高氯水样的cod测定方法和装置 (COD (chemical oxygen demand) determination method and device for high-chlorine water sample ) 是由 严百平 谢金强 张伟政 于 2020-07-09 设计创作，主要内容包括：本发明涉及水质检测领域,具体涉及一种高氯水样的COD测定方法和装置,包括依次管道连接的定量进样单元、反应单元和吸收装置,反应单元外设有恒温加热装置和光电测量装置,定量进样单元包括依次连通的气动装置、定量装置和多路阀,气动装置能通过管路向反应单元吹气,气动装置、定量装置、多路阀、恒温加热装置、光电测量装置均与控制单元电连。与现有技术相比,本发明所提供的一种高氯水样的COD测定方法和装置,能轻松应对小于50000mg/L的高氯水样的COD精准测量,测量稳定可靠,不会对液路造成潜在的堵塞风险,特别适合高氯水样COD在线监测领域,提高COD在线测定仪器的水体适应性,并且加入了废气的回收,避免有毒的氯化氢气体直接排到空气,造成大气污染。(The invention relates to the field of water quality detection, in particular to a COD (chemical oxygen demand) determination method and a COD determination device for a high-chlorine water sample, which comprise a quantitative sample introduction unit, a reaction unit and an absorption device which are sequentially connected through pipelines, wherein a constant-temperature heating device and a photoelectric measurement device are arranged outside the reaction unit, the quantitative sample introduction unit comprises a pneumatic device, a quantitative device and a multi-way valve which are sequentially communicated, the pneumatic device can blow air to the reaction unit through a pipeline, and the pneumatic device, the quantitative device, the multi-way valve, the constant-temperature heating device and the photoelectric measurement device are all electrically connected with a control unit. Compared with the prior art, the COD determination method and the device for the high-chlorine water sample can easily and accurately measure the COD of the high-chlorine water sample of which the concentration is less than 50000mg/L, are stable and reliable in measurement, do not cause potential blocking risk to a liquid path, are particularly suitable for the field of online monitoring of the COD of the high-chlorine water sample, improve the water body adaptability of an online COD determination instrument, add the recovery of waste gas and avoid the atmospheric pollution caused by directly discharging toxic hydrogen chloride gas into the air.)

1. The utility model provides a COD survey device of high chlorine water sample which characterized in that: the quantitative sampling device comprises a quantitative sampling unit (1), a reaction unit (2) and an absorption device (3) which are sequentially connected through pipelines, wherein a constant-temperature heating device (4) and a photoelectric measurement device (5) are arranged outside the reaction unit (2), the quantitative sampling unit (1) comprises a pneumatic device (1c), a quantitative device (1a) and a multi-way valve (1b) which are sequentially communicated, the pneumatic device (1c) can blow air to the reaction unit (2) through a pipeline, and the pneumatic device (1c), the quantitative device (1a), the multi-way valve (1b), the constant-temperature heating device (4) and the photoelectric measurement device (5) are electrically connected with a control unit (7).

2. The COD measuring device of the high chlorine water sample according to claim 1, characterized in that: the reaction unit (2) is a closed reaction chamber, an upper sealing valve (8) and a lower sealing valve (9) are respectively installed at the top and the bottom of the reaction chamber, the upper sealing valve (8) is communicated with the absorption device (3) through a first pipeline (10), the lower sealing valve (9) is connected with the quantitative sample introduction unit (1) through a second pipeline, and the upper sealing valve (8) and the lower sealing valve (9) are both electrically connected with the control unit (7).

3. The COD measuring device of the high chlorine water sample according to claim 2, characterized in that: a three-way valve (11) is arranged on the first pipeline (10), and the three-way valve (11) is electrically connected with the control unit (7).

4. The COD measuring device of the high chlorine water sample according to claim 1, characterized in that: constant temperature heating device (4) are including establishing around heater strip and setting on reaction unit (2) outer wall are in temperature sensor in reaction unit (2), heater strip and temperature sensor all with control unit (7) electricity is connected.

5. The COD measuring device of the high chlorine water sample according to claim 1, characterized in that: the pneumatic device (1c) is a peristaltic pump, the quantifying device (1a) is a quantifying pipe, a liquid level sensor is arranged in the quantifying pipe, two ends of the quantifying pipe are respectively communicated with the peristaltic pump and a pipeline of the multi-way valve (1b), and the liquid level sensor is electrically connected with the control unit (7).

6. The COD measuring device of the high chlorine water sample according to claim 1, characterized in that: the pneumatic device (1c) comprises a support (1cb) and a motor (1ca) fixedly arranged on the support (1cb), an output shaft of the motor (1ca) is fixedly connected with a lead screw, a sliding block (1cc) is in threaded connection with the lead screw, the quantifying device (1a) is a syringe, the syringe is fixedly arranged on the support (1cb), the sliding block (1cc) is fixedly connected with a piston rod of the syringe, and a liquid outlet of the syringe is communicated with the multi-way valve (1 b).

7. A COD determination method of a high-chlorine water sample is characterized by comprising the following steps:

step one, adding a water sample of COD to be detected with a certain volume into a reaction unit (2);

step two, adding concentrated sulfuric acid into the reaction unit (2) to form a mixed solution of concentrated sulfuric acid with the mass fraction of 5-70%;

thirdly, removing hydrogen chloride gas in the reaction unit (2) by adopting a stable chloride ion expelling method: heating the mixed solution in the reaction unit (2) and keeping the temperature at a target temperature, carrying out a chemical reaction on chloride ions in a COD water sample to be detected and sulfuric acid to generate hydrogen chloride gas, simultaneously blowing air into the reaction unit (2) through a pneumatic device (1c) in the reaction process until the hydrogen chloride gas generated in the reaction unit (2) is fully discharged into an absorption device (3), and absorbing the hydrogen chloride by an absorption substance in the absorption device (3);

step four, adding a mixed solution of potassium dichromate and silver sulfate in a certain proportion into the reaction unit (2), and carrying out a digestion reaction on the mixed solution at the temperature of 110-200 ℃ for 5-30 minutes;

and fifthly, the photoelectric measuring device (5) emits light rays with specific wavelength, the absorbance of the mixed solution in the reaction unit (2) is measured, and the control unit (7) calculates the COD value by comparing with the standard curve.

8. The method for measuring COD in a high-chlorine water sample according to claim 7, which is characterized in that: the air blowing time in the third step is 3-30 minutes.

9. The method for measuring COD in a high-chlorine water sample according to claim 7, which is characterized in that: and in the third step, a sectional heating method of rapid heating in the early stage and slow and stable heating in the later stage is adopted, so that the mixed solution is prevented from being boiled violently.

10. The method according to claim 7, wherein the target temperature in the third step is within ± 20 ℃ of the boiling point temperature of the mixed solution.

Technical Field

The invention relates to the field of water quality detection, in particular to a COD (chemical oxygen demand) determination method and device for a high-chlorine water sample.

Background

Chemical oxygen demand cod (chemical oxygen demand) is a very important parameter in the study of river pollution and properties of industrial wastewater and the management of operation of wastewater treatment plants. The method is characterized in that the amount of an oxidant consumed when a water sample is treated by a certain oxidant under a certain condition is used for reflecting the degree of pollution of a water body by reducing substances, and can be used as a comprehensive index of the relative content of organic matters.

The traditional COD on-line measuring instrument adopts potassium dichromate spectrophotometry, namely, the instrument respectively mixes a water sample with potassium dichromate and concentrated sulfuric acid under the control of a set program, silver sulfate is added as a catalyst, and mercury sulfate is complexed with chloride ions in a solution. The mixed solution is digested at 165 ℃ under high temperature and high pressure, and the reducing substances in the water sample react with the oxidant. Cr in the oxidizing agent⁶⁺Is reduced to Cr³⁺And the photoelectric measuring device detects the change of the signal, and the COD value is obtained after calculation through comparison of the standard curve.

However, many industrial wastewater or near-sea water samples have high chloride ion content, and the accuracy of COD determination is affected by using a direct analysis method, resulting in a high measurement value, because chloride ions are not organic matter and do not belong to COD components, which brings troubles to industrial management and control and environmental monitoring. The traditional method is that before measuring COD, a concealing agent mercury sulfate is used in advance to react with chloride ions, and reactants do not appear in the detection light of the COD, so that the interference of the chloride ions can be eliminated, and the measurement accuracy is advanced. However, the method of eliminating mercury sulfate in advance can only eliminate water samples containing less than 2000mg/L of chlorine, and water samples containing too much chlorine still cause great deviation, so the COD on-line measuring instrument (analyzer) on the market at present has a certain capacity of eliminating chloride ions, but the measured value is still seriously high when meeting water samples containing high chlorine.

Disclosure of Invention

In order to overcome the defects of the technical defects, the invention provides a COD (chemical oxygen demand) determination method and a COD determination device for a high-chlorine water sample, and solves the problems of inaccurate high-chlorine water sample test, easy crystallization and unstable measurement of the traditional COD determination device.

The utility model provides a COD survey device of high chlorine water sample, the key lies in: the device comprises a quantitative sample introduction unit, a reaction unit and an absorption device which are sequentially connected through pipelines, wherein a constant temperature heating device and a photoelectric measurement device are arranged outside the reaction unit, the quantitative sample introduction unit comprises a pneumatic device, a quantifying device and a multi-way valve which are sequentially communicated, the pneumatic device can blow air to the reaction unit through the pipelines, and the pneumatic device, the quantifying device, the multi-way valve, the constant temperature heating device and the photoelectric measurement device are all electrically connected with a control unit. The method has the advantages that negative pressure can be generated in the quantitative device through the pneumatic device, at the moment, one path of valve in the multi-path valve is opened, water samples or reagents of the connected pipeline are pumped into the quantitative device, and the quantitative determination of the specific volume of the solution is completed when the water samples or reagents are stopped at specific points; then, all valves are closed by the multi-way valve, the air blowing unit generates positive pressure, the solution in the quantitative pipe can be pushed into the reaction unit, and the pneumatic device can also provide air blowing power for the reaction unit.

Preferably, the reaction unit is a closed reaction chamber, an upper sealing valve and a lower sealing valve are respectively installed at the top and the bottom of the reaction chamber, the upper sealing valve is communicated with the absorption device through a first pipeline, the lower sealing valve is connected with the quantitative sampling unit through a second pipeline, and both the upper sealing valve and the lower sealing valve are electrically connected with the control unit. The effect of this scheme is can be as required closed and open reaction chamber, with reaction unit and pneumatic means and absorbing device intercommunication or block.

Preferably, a three-way valve is arranged on the first pipeline and electrically connected with the control unit. The effect of this scheme is that can be as required selectively realize the reaction chamber with absorption device or external intercommunication or block.

Preferably, the constant temperature heating device comprises a heating wire wound on the outer wall of the reaction unit and a temperature sensor arranged in the reaction unit, and the heating wire and the temperature sensor are both electrically connected with the control unit. The effect of this solution is that the heating temperature can be accurately controlled.

Preferably, the pneumatic device is a peristaltic pump, the quantifying device comprises a quantifying pipe, two ends of the quantifying pipe are respectively communicated with the peristaltic pump and the multi-way valve, a liquid level sensor is arranged in the quantifying device, and the liquid level sensor is electrically connected with the control unit. The effect of this scheme is that the peristaltic pump produces the atmospheric pressure that is different from the atmospheric pressure through the inside hose of extrusion, produces the malleation when deciding in the buret to blow the air into reaction unit, produce the negative pressure when deciding in the buret, inhale the ration pipe with the sample, liquid level in the rising is extracted through the sensor perception, volume liquid.

Preferably, the pneumatic device comprises a support and a motor fixedly arranged on the support, an output shaft of the motor is fixedly connected with a lead screw, a slider is connected to the lead screw in a threaded manner, the quantifying device is an injector, the injector is fixedly arranged on the support, the slider is fixedly connected with a piston rod of the injector, and a liquid outlet of the injector is communicated with the multi-way valve. The effect of this scheme is that the motor rotates and drives the piston and move in the syringe, produces the malleation in deciding the syringe to blow the air into reaction unit, produce the negative pressure in the syringe, inhale the syringe with the liquid sample of certain volume.

Preferably, the second pipeline is further connected with an auxiliary blowing device. The effect of this scheme is in order to further improve the effect of blowing.

Preferably, the control unit comprises a controller and a display.

The COD measuring method of the high-chlorine water sample is characterized by comprising the following steps:

step one, adding a certain volume of COD water sample to be detected into a reaction unit;

step two, adding concentrated sulfuric acid into a reaction unit to form a mixed solution of the concentrated sulfuric acid with the mass fraction of 5-70%;

thirdly, removing hydrogen chloride gas in the reaction unit by adopting a stable chloride ion expelling method: heating the mixed solution in the reaction unit and keeping the temperature at a target temperature, carrying out chemical reaction on chloride ions in a COD water sample to be detected and sulfuric acid to generate hydrogen chloride gas, simultaneously blowing air into the reaction unit through a pneumatic device in the reaction process until the hydrogen chloride gas generated in the reaction unit is fully discharged into an absorption device, wherein the hydrogen chloride is absorbed and treated by an absorption substance in the absorption device, the absorption substance can be absorption liquid or solid absorption substance, the hydrogen chloride is absorbed or adsorbed through physical or chemical reaction, and the absorption liquid can be alkaline solution, such as sodium hydroxide solution;

step four, adding a certain proportion of mixed solution of potassium dichromate and silver sulfate into a reaction unit, and carrying out digestion reaction on the mixed solution at the temperature of 110-200 ℃ for 5-30 minutes;

fifthly, the photoelectric measuring device emits light rays with specific wavelengths, the absorbance of the mixed solution in the reaction unit is measured, and the control unit calculates the COD value by comparing with a standard curve;

and step six, discharging the mixed solution of the reaction unit, and then carrying out next COD measurement.

Preferably, the air blowing time in the third step is 3-30 minutes.

Preferably, a segmented heating method of rapid heating in the early stage and slow and stable heating in the later stage is adopted in the third step, so that the mixed solution is prevented from being boiled violently.

Preferably, the target temperature in the third step is the boiling temperature of the mixed solution +/-20 ℃.

Preferably, the absorbing substance in step three is an alkaline solution, and toxic hydrogen chloride gas is reacted into other substances by means of a chemical reaction.

Preferably, the absorbing substance in the third step is an absorbing block, and the hydrogen chloride gas is absorbed by a physical adsorption method.

Has the advantages that: compared with the prior art, the COD determination method and the device for the high-chlorine water sample can easily and accurately measure the COD of the high-chlorine water sample of which the concentration is less than 50000mg/L, are stable and reliable in measurement, do not cause potential blocking risk to a liquid path, are particularly suitable for the field of online monitoring of the COD of the high-chlorine water sample, improve the water body adaptability of an online COD determination instrument, add the recovery of waste gas and avoid the atmospheric pollution caused by directly discharging toxic hydrogen chloride gas into the air.

Drawings

FIG. 1 is a schematic structural view of embodiment 1 of the present invention;

fig. 2 is a schematic structural diagram of the quantitative sampling unit 1 in embodiment 2.

Detailed description of the invention

In order to make the technical solutions of the present invention better understood, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1

As shown in fig. 1, a COD measuring device for a high chlorine water sample comprises a peristaltic pump 1c, a quantitative tube 1a, a plurality of rows of valves 1b, a reaction unit 2 and an absorption device 3, which are sequentially connected by a pipeline, wherein two ends of the quantitative tube 1a are respectively communicated with the peristaltic pump and the plurality of rows of valves 1b, a liquid level sensor is arranged in the quantitative tube 1a, the reaction unit 2 is a closed reaction chamber, an upper sealing valve 8 and a lower sealing valve 9 are respectively installed at the top and the bottom of the reaction chamber, the upper sealing valve 8 is communicated with the absorption device 3 through a pipeline one 10, a three-way valve 11 is arranged on the pipeline one 10, the lower sealing valve 9 is connected with the plurality of rows of valves 1b through a pipeline two, a constant temperature heating device 4 and a photoelectric measurement device 5 are arranged outside the reaction unit 2, the constant temperature heating device 4 comprises a heating wire wound on the outer wall of the reaction unit 2 and a temperature sensor arranged in the reaction unit 2, the peristaltic pump 1c, the multi-row linkage valve 1b, the liquid level sensor, the upper sealing valve 8, the lower sealing valve 9, the three-way valve 11, the heating wires, the temperature sensor and the photoelectric measuring device 5 are all electrically connected with the control unit 7.

Example 2

As shown in fig. 1 and fig. 2, a COD measuring device for a high chlorine water sample comprises a syringe 1a, a disc valve 1b, a reaction unit 2 and an absorption device 3, which are sequentially connected by a pipeline, wherein the pneumatic device 1c comprises a motor 1ca and a piston 1cb, the syringe 1a and the motor 1ca are both fixedly arranged on a support 1cb, an output shaft of the motor 1ca is fixedly connected with a lead screw, a slider 1cc is connected to the lead screw by a thread, the slider 1cc is fixedly connected to a piston rod of the syringe, a liquid outlet of the syringe is communicated with the disc valve 1b, the reaction unit 2 is a closed reaction chamber, an upper sealing valve 8 and a lower sealing valve 9 are respectively arranged at the top and the bottom of the reaction chamber, the upper sealing valve 8 is communicated with the absorption device 3 through a pipeline one 10, a three-way valve 11 is arranged on the pipeline one 10, the lower sealing valve 9 is connected with the disc valve 1b through a pipeline two, reaction unit 2 is equipped with constant temperature heating device 4 and photoelectric measurement device 5 outward, constant temperature heating device 4 includes around establishing heater strip on the outer wall of reaction unit 2 and setting are in temperature sensor among the reaction unit 2, motor 1ca, disc valve 1b, level sensor, upper seal valve 8, lower seal valve 9, three-way valve 11, heater strip, temperature sensor and photoelectric measurement device 5 all with the control unit 7 electricity is connected.

Example 3

A water sample determination method of a COD determination device for a high-chlorine water sample is carried out according to the following steps:

step one, a peristaltic pump 1c continuously rotates forwards to generate negative pressure, at the moment, a certain valve in a multi-row linkage valve 1b is opened, so that a to-be-detected water sample of a pipeline connected with the peristaltic pump is pumped to a quantitative tube 1a, a sensor senses the liquid level in pumping and rising, the pump is stopped at a specific point position, the quantification of the specific volume of the solution is completed, then, the multi-row linkage valve 1b closes all valves, an upper sealing valve 8 and a lower sealing valve 9 are opened, the peristaltic pump 1c rotates reversely, positive pressure is generated above the quantitative tube 1a, and the to-be-detected water sample in the quantitative tube 1a can be pushed into a reaction chamber 2;

step two, the peristaltic pump 1c continuously rotates forwards to generate negative pressure, at the moment, a certain valve in the multi-row linkage valve 1b is opened, so that concentrated sulfuric acid in a pipeline connected with the peristaltic pump is pumped to the quantitative pipe 1a, the sensor senses the liquid level in the pumping process, the pump is stopped at a specific point position, the quantification of the specific volume of the solution is completed, then, the multi-row linkage valve 1b closes all valves, the upper sealing valve 8 and the lower sealing valve 9 are opened, the peristaltic pump 1c rotates reversely, positive pressure is generated above the quantitative pipe 1a, the concentrated sulfuric acid in the quantitative pipe 1a can be pushed into the reaction chamber 2, and a mixed solution with the mass fraction of the concentrated sulfuric acid being 5% is formed;

step three, opening an upper sealing valve 8 and a lower sealing valve 9, controlling a three-way valve 11 to be communicated with an absorption device 3 instead of air, and controlling a heating wire and a temperature sensor to enable the temperature of the mixed liquid in the reaction chamber 2 to rise to 100 ℃, enabling chloride ions to be subjected to chemical reaction with concentrated sulfuric acid to generate hydrogen chloride, wherein the hydrogen chloride generated by the reaction is dissolved in the mixed liquid to become a hydrochloric acid solution because the hydrogen chloride is easily dissolved in water, and controlling a peristaltic pump 1c to reversely rotate at the moment to continuously blow air into the reaction chamber for 3 minutes, and the mixed liquid volatilizes hydrogen chloride gas because the hydrochloric acid solution is highly volatile, and the continuously blown water transfers the hydrogen chloride gas to the absorption device 3 to be absorbed by a sodium hydroxide solution, so that the hydrogen chloride gas is prevented from being directly discharged into the air, and air pollution or possible poisoning is avoided;

step four, after chloride ions in the mixed solution are removed, controlling and adding a mixed solution of potassium dichromate and silver sulfate in a certain proportion, closing the upper sealing valve 8 and the lower sealing valve 9, heating the mixed solution to 110 ℃ for digestion, maintaining the digestion process for 5 minutes, and reducing the potassium dichromate into trivalent chromium ions (Cr ions)³⁺) Then, the temperature is reduced to 90 ℃;

step five, the photoelectric measuring device 5 emits light with a specific wavelength, the absorbance of the mixed solution in the reaction unit 2 is measured, the deeper the color is, the higher the absorbance is, the higher the concentration of the COD to be measured in the water sample is, the controller can calculate the COD value through the comparison of the standard curve, and the COD value is displayed through the display;

and step six, switching the three-way valve 11 back to an air channel, discharging the solution in the reaction chamber 2, and carrying out next COD measurement.

Example 4

The water sample determination method of the COD determination device for the high-chlorine water sample comprises the following steps:

step one, a peristaltic pump 1c continuously rotates forwards to generate negative pressure, at the moment, a certain valve in a multi-row linkage valve 1b is opened, so that a to-be-detected water sample of a pipeline connected with the peristaltic pump is pumped to a quantitative tube 1a, a sensor senses the liquid level in pumping and rising, the pump is stopped at a specific point position, the quantification of the specific volume of the solution is completed, then, the multi-row linkage valve 1b closes all valves, an upper sealing valve 8 and a lower sealing valve 9 are opened, the peristaltic pump 1c rotates reversely, positive pressure is generated above the quantitative tube 1a, and the to-be-detected water sample in the quantitative tube 1a can be pushed into a reaction chamber 2;

step two, the peristaltic pump 1c continuously rotates forwards to generate negative pressure, at the moment, a certain valve in the multi-row linkage valve 1b is opened, so that sulfuric acid in a pipeline connected with the peristaltic pump is pumped to the quantitative tube 1a, the sensor senses the liquid level in the pumping process, the pump is stopped at a specific point position, the quantification of the specific volume of the solution is completed, then, the multi-row linkage valve 1b closes all valves, the upper sealing valve 8 and the lower sealing valve 9 are opened, the peristaltic pump 1c rotates reversely, positive pressure is generated above the quantitative tube 1a, and concentrated sulfuric acid in the quantitative tube 1a can be pushed into the reaction chamber 2 to form a mixed solution with the mass fraction of the concentrated sulfuric acid being 20%;

step three, opening an upper sealing valve 8 and a lower sealing valve 9, controlling a three-way valve 11 to be communicated with an absorption device 3 instead of air, and controlling a heating wire and a temperature sensor to enable the temperature of the mixed liquid in the reaction chamber 2 to rise to 130 ℃, enabling chloride ions to be subjected to chemical reaction with concentrated sulfuric acid to generate hydrogen chloride, wherein the hydrogen chloride generated by the reaction is dissolved in the mixed liquid to become a hydrochloric acid solution because the hydrogen chloride is easily dissolved in water, and controlling a peristaltic pump 1c to reversely rotate at the moment to continuously blow air into the reaction chamber for 15 minutes, and because the hydrochloric acid solution is highly volatile, the mixed liquid can volatilize hydrogen chloride gas, and the continuously blown water transfers the hydrogen chloride gas to the absorption device 3 to be absorbed by a sodium hydroxide solution, so that the hydrogen chloride gas is prevented from being directly discharged into the air, and air pollution or possible poisoning is avoided;

step four, after chloride ions in the mixed solution are removed, controlling and adding a mixed solution of potassium dichromate and silver sulfate in a certain proportion, closing the upper sealing valve 8 and the lower sealing valve 9, heating the mixed solution to 180 ℃ for digestion, maintaining the digestion process for 10 minutes, and reducing the potassium dichromate into trivalent chromium ions (Cr ions)³⁺) Then, the temperature is reduced to 90 ℃;

step five, the photoelectric measuring device 5 emits light with a specific wavelength, the absorbance of the mixed solution in the reaction unit 2 is measured, the deeper the color is, the higher the absorbance is, the higher the concentration of the COD to be measured in the water sample is, the controller can calculate the COD value through the comparison of the standard curve, and the COD value is displayed through the display;

and step six, switching the three-way valve 11 back to an air channel, discharging the solution in the reaction chamber 2, and carrying out next COD measurement.

Example 5

The water sample determination method of the COD determination device for the high-chlorine water sample comprises the following steps:

step one, a motor 1ca rotates to drive a piston in an injector 1a to reciprocate to generate negative pressure, at the moment, a certain path of valve in a disc valve 1b is opened, so that a water sample to be detected of a pipeline connected with the valve is pumped into the injector 1a, a pump is stopped at a specific point position, the quantification of the specific volume of a solution is completed, then, the disc valve 1b closes all valves, an upper sealing valve 8 and a lower sealing valve 9 are opened, and the motor 1ca rotates to drive the piston in the injector 1a to reciprocate to push the water sample to be detected in the injector 1a into a reaction chamber 2;

step two, the motor 1ca rotates to drive the piston in the injector 1a to reciprocate to generate negative pressure, at the moment, a certain path of valve in the disc valve 1b is opened, so that concentrated sulfuric acid in a pipeline connected with the valve is pumped to the injector 1a, a pump is stopped at a specific point position, the quantification of the specific volume of the solution is completed, then, the disc valve 1b closes all the valves, the upper sealing valve 8 and the lower sealing valve 9 are opened, the motor 1ca rotates to drive the piston in the injector 1a to reciprocate to push the concentrated sulfuric acid in the injector 1a to the reaction chamber 2, and a mixed solution with the mass fraction of the concentrated sulfuric acid being 70% is formed;

step three, opening an upper sealing valve 8 and a lower sealing valve 9, controlling a three-way valve 11 to be communicated with an absorption device 3 instead of air, and controlling a heating wire and a temperature sensor to enable the temperature of the mixed solution in the reaction chamber 2 to rise to 120 ℃, enabling chloride ions to be subjected to chemical reaction with concentrated sulfuric acid to generate hydrogen chloride, wherein the hydrogen chloride generated by the reaction is dissolved in the mixed solution to become a hydrochloric acid solution because the hydrogen chloride is easily soluble in water, and controlling a peristaltic pump 1c to reversely rotate at the moment to continuously blow air into the reaction chamber for 30 minutes, and because the hydrochloric acid solution is highly volatile, the mixed solution can volatilize hydrogen chloride gas, and the continuously blown water transfers the hydrogen chloride gas to the absorption device 3 to be absorbed by a sodium hydroxide solution, so that the hydrogen chloride gas is prevented from being directly discharged into the air, and air pollution or possible poisoning is avoided;

step four, after chloride ions in the mixed solution are removed, controlling and adding a mixed solution of potassium dichromate and silver sulfate in a certain proportion, closing the upper sealing valve 8 and the lower sealing valve 9, heating the mixed solution to 200 ℃ for digestion, maintaining the digestion process for 20 minutes, and reducing the potassium dichromate into trivalent chromium ions (Cr ions)³⁺) Then, the temperature is reduced to 90 ℃;

step five, the photoelectric measuring device 5 emits light with a specific wavelength, the absorbance of the mixed solution in the reaction unit 2 is measured, the deeper the color is, the higher the absorbance is, the higher the concentration of the COD to be measured in the water sample is, the controller can calculate the COD value through the comparison of the standard curve, and the COD value is displayed through the display;

and step six, switching the three-way valve 11 back to an air channel, discharging the solution in the reaction chamber 2, and carrying out next COD measurement.

Finally, it should be noted that the above-mentioned description is only a preferred embodiment of the present invention, and those skilled in the art can make various similar representations without departing from the spirit and scope of the present invention.