CN102298067A - Full-automatic on-line monitoring system of COD (chemical oxygen demand) and monitoring method thereof - Google Patents

Abstract

The invention relates to a COD automatic on-line monitoring system and a monitoring method thereof. The monitoring system includes a monitoring control device and an electric injector connected to it, an optical quantitative device, a multi-way adapter and a reaction pool. There are ventilation tubes connected between the electric injector and the optical quantitative device, and between the optical quantitative device and the reaction pool. The through adapter is connected with the optical quantitative device, the reaction pool, the input tube of the solution to be tested, the input tube of the standard solution, the input tube of the blank solution, the input tube of deionized water and the waste liquid discharge tube. Working electrode, auxiliary electrode and reference electrode connected to the device. The monitoring method is: measure the current change value of the standard solution with different concentrations, and the standard curve △I _c -C is automatically drawn by the monitoring control device, and the current change value △I _x of the solution to be tested is measured, and the monitoring control device finds the current change value from the standard curve. Get the corresponding COD value and display it. The invention has the advantages of accurate measurement, no pollution and high intelligence.

Description

A COD automatic online monitoring system and monitoring method thereof

technical field

The present invention relates to a water quality monitoring device, in particular to a COD full-automatic online monitoring system and monitoring method thereof, which utilize air pressure difference to automatically inject samples, automatically draw a standard curve △I _c -C, and automatically obtain the COD value of the water sample to be tested .

Background technique

Chemical oxygen demand (COD) refers to the amount of oxidant consumed when a strong oxidant is used to treat water samples under strong acid and heating conditions, expressed in O ₂ (mg/L), which reflects the reduction of substances in water (mainly organic matter) ) pollution degree is a comprehensive index to evaluate the degree of water pollution, and it is also one of the important parameters for water quality monitoring. In order to effectively curb the deteriorating environment of water bodies, my country has formulated control targets for the total discharge of COD pollution in the "Ninth Five-Year Plan", "Tenth Five-Year Plan" and "Eleventh Five-Year Plan".

The current COD monitoring methods are as follows: (1) The national standard method (GB11914-89, EPA410.4), this method first digests and refluxes the organic water sample with potassium dichromate solution at high temperature, and then quantitatively The COD value is calculated indirectly. The analysis time of this method is too long, and the total time for digestion and titration is up to 2 hours. The reaction process consumes a large amount of sulfuric acid, toxic mercury sulfate, potassium dichromate as an oxidant, and expensive silver sulfate, resulting in high cost and serious secondary pollution. (2) Ozone oxidation method is used to measure COD. Ozone can directly oxidize organic matter through cycloaddition, electrophile, and nucleophile in water, and partially oxidize organic matter indirectly through hydroxyl groups generated by decomposition. Because ozone itself is selective to the oxidation of organic matter, this method is limited in the monitoring of refractory organic wastewater. (3) Visible or ultraviolet spectrophotometry, which detects the total amount of organic substances by measuring the ultraviolet absorbance of organic substances at specific wavelengths. For specific wastewater, it is necessary to determine the most suitable ultraviolet absorption wavelength, which has great limitations and is quite troublesome to operate. (4) Photoelectric catalytic oxidation method, ultraviolet light irradiates the semiconductor TiO ₂ film electrode to generate electrons and holes. The photogenerated holes have a high redox potential and can oxidize most organic pollutants. The transfer of charges is expressed in the form of photocurrent Come out, get the corresponding COD value by detecting the current or electricity. This method is easy to recombine photogenerated electrons and holes, has low photocatalytic efficiency, only responds in the ultraviolet region, and has low utilization rate of sunlight, which has certain limitations in practical applications. (5) Electrochemical oxidation method, using direct electrolysis or electrocatalytic oxidation to convert refractory organic matter into biodegradable organic matter, and finally mineralized into CO ₂ and H ₂ O ₂ , by investigating the electrochemical parameters in the oxidation process The correlation between the amount of change and COD is quickly detected online. In recent years, _PbO2 electrode oxidation method and Cu electrode oxidation method have appeared. The PbO ₂ electrode is not resistant to chloride ion corrosion, and its life is short; lead ions may dissolve and cause secondary pollution; the working electrode must be regenerated under continuous high bias voltage, and high potential regeneration shortens the life of the electrode even more.

The patent application document with the application number 200510023445.2 and the name "Chemical Oxygen Demand Electrochemical Analyzer" discloses a COD electrochemical analyzer consisting of a flow injection sampling system, an analysis and detection device and a data processing system. In the electrochemical system, the working electrode is a nano-oxide modified electrode. The detection device of this instrument is not tightly sealed and is prone to liquid leakage, and there is a risk of secondary pollution caused by metal dissolution in oxides, and the sensitivity is low.

The patent application document with the application number 200810010232.X and the title "A Device and Method for Measuring Chemical Oxygen Demand in Water Based on Flow Injection Sampling" simplifies the measurement steps, shortens the measurement time, and solves the problem of PbO ₂ electrode intolerance. Chloride ion corrosion and short service life, but it needs to be used in conjunction with electrochemical workstations and other instruments, and cannot be automatically diluted and cleaned, and cannot be detected online.

Contents of the invention

The invention mainly solves the technical problems that the original chemical oxygen demand measuring device has secondary pollution in the detection process, low sensitivity, cannot be automatically diluted and cleaned, and cannot be automatically detected online; it provides a sample solution with short response time, stable signal A COD automatic online monitoring system with small dosage, low detection limit, high sensitivity, and wide linear range and its monitoring method. The method does not use any toxic and harmful substances in the detection process, and does not produce secondary pollution after detection. It is environmentally friendly. Moreover, the dilution, cleaning, and monitoring operations are all automated. Just click the corresponding button, and the COD value will be directly displayed on the display screen after the measurement, without any manual conversion.

Another object of the present invention is to provide a COD automatic online monitoring system and its monitoring method, which uses BDD as the working electrode, has long service life, short response time, high sensitivity, low detection limit and large detection range, and is suitable for COD detection of various sewage and water bodies.

Another object of the present invention is to provide a COD automatic online monitoring system and monitoring method thereof, which accurately quantifies the solution entering the reaction pool each time through an optical quantitative device, avoids measurement errors caused by different volumes of solutions, and ensures COD Monitoring is more precise.

The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: the COD automatic online monitoring system of the present invention includes an electric injector, an optical quantitative device, a multi-way adapter, a reaction pool and a monitoring control device, the A gas exchange tube is connected between the electric injector and the optical quantitative device, between the optical quantitative device and the reaction pool, and the multi-way adapter is connected with a test solution input tube, a standard solution input tube, a blank solution input tube, The deionized water input pipe and the waste liquid discharge pipe, and the multi-way adapter are also communicated with the optical quantification device and the reaction pool through pipelines, and the reaction pool is provided with a working electrode, an auxiliary electrode and The reference electrode, the working electrode, the auxiliary electrode and the reference electrode are connected to the monitoring and control device through wires, and the monitoring and control device is also electrically connected to the electric injector, the optical quantitative device and the multi-way adapter respectively. The monitoring and control device is an intelligent device combining software and hardware, which controls the working status of the electric injector, optical quantitative device and multi-way adapter. Under the control of the monitoring and control device, the electric injector extracts the gas in the optical quantitative device through the ventilation tube, and the solution in the corresponding pipeline enters the optical quantitative device through the multi-way adapter, and the optical quantitative device quantifies the solution. When the solution reaches Quantitative value, the optical quantitative device sends a signal to the monitoring and control device, and the monitoring and control device sends a signal to the electric injector, and the electric injector passes the gas exchange tube and then presses the gas into the optical quantitative device, and the solution is passed by the optical quantitative device through the multi-pass transfer. At this time, the monitoring and control device applies a voltage on the working electrode to oxidize the organic matter in the solution into carbon dioxide and water, and the generated current signal is returned to the monitoring and control device, and the COD value is displayed after being processed by the monitoring and control device. After the measurement, the solution is discharged from the reaction pool through the multi-way adapter and the waste liquid pipe. The entire operation process is fully automated, and the staff only need to click the words "calibration" and "measurement" on the display screen of the monitoring and control device. After the measurement, the COD value will be directly displayed on the display screen without any manual conversion. Realize the automatic online detection of solution COD, with a high degree of intelligence. From the electrode to the solution, and the entire measurement process, no toxic and harmful substances are added and generated, and the environment is friendly, and there is no pollution and secondary pollution.

As a preference, one end of the electric injector is provided with a motor, the other end is connected with the ventilation tube, the electric injector is provided with a piston, the piston is connected with a cylinder with a cavity inside, and the end surface of the other end of the cylinder is provided with There is a threaded hole, and the threaded hole is connected with a screw rod, and the screw rod is connected with the rotating shaft of the motor, and the motor is electrically connected with the monitoring and control device. The monitoring and control device controls the rotation of the motor, and the motor converts circular motion into linear motion through the screw, driving the piston to move up and down, thereby changing the air pressure in the optical quantitative device to realize the extraction and discharge of the solution.

As a preference, a locking groove is provided on the inner wall of the electric injector, and a locking member is provided on the side of one end of the connecting screw of the cylinder, and the head of the locking member is locked in the locking groove. A light blocking sheet is provided on the cylinder, and a photoelectric switch matching the light blocking sheet is provided on the side wall of the electric injector, and the photoelectric switch is electrically connected to the monitoring control device . When the piston moves up and down, the clamping member moves along the clamping groove to play a positioning and supporting role, making the movement of the piston more stable. When the piston moves down, once the light blocking sheet blocks the light source of the photoelectric switch, the photoelectric switch sends a signal to the monitoring and control device, and the monitoring and control device sends a signal to the motor to stop the piston from moving down or up. The process acts as a limiter. Because the cavity where the general piston is located is made of a precision glass tube, damage to the glass tube caused by the overrunning of the piston can be avoided.

As a preference, the photoelectric quantitative device includes a container and a three-way solenoid valve arranged on the container. The container is connected to the multi-way adapter through a pipeline, and the three-way solenoid valve is respectively connected through the ventilation tube and the electric injector, The reaction pools are connected, and a transmitter and a receiver are oppositely arranged on the side wall of the container, and the transmitter, the receiver and the three-way electromagnetic valve are respectively electrically connected with the monitoring and control device. This container is generally a glass tube. Since the liquid and glass in the glass tube are infiltrated, the surface area will tend to be the smallest under the action of surface tension and will be concave downward, so a meniscus is formed. Due to the refraction and reflection of light propagating in different media, the intensity of emitted and received light changes. In the case of liquid or empty pipe, when the incident light from the side is incident, the refraction angle is equal to the incident angle equal to 0°, the light does not refract, only a small amount of reflection is emitted, and the incident light is almost equal to the outgoing light; when the incident light hits the concave liquid When the surface is surfaced, due to the refraction and reflection of the light on the concave liquid surface, the outgoing light is reduced. After the signal is received by the monitoring and control device, after calculation and processing, the monitoring and control device sends a signal to the motor and the three-way solenoid valve to stop the extraction of the solution. , to achieve accurate quantitative liquid. Through two sets of transmitters and receivers, the liquid entering the reaction pool can be accurately quantified each time, ensuring that the quantitative error of each time is within 0.1%, and avoiding the measurement error caused by the inconsistent volume of the solution.

Preferably, the multi-way adapter is provided with several solenoid valves, and the solenoid valves are electrically connected to the monitoring and control device. The monitoring and control device controls the opening and closing of multiple electromagnetic valves on the multi-way adapter, so that the solution of which pipeline is extracted and the flow direction of the solution can be realized according to needs.

Preferably, a pretreatment system is connected between the input pipe of the solution to be tested and the multi-way adapter. The pretreatment system is mainly some filtering equipment to filter the large particles of impurities and suspended solids in the solution to be tested, so as to prevent some large particles of impurities contained in the heavily polluted sewage from entering the pipeline and causing pipeline blockage, and reduce the impact of some impurities on the measurement. Interference and contamination of the reaction cell and electrodes.

Preferably, a stirrer is provided at the bottom of the reaction pool, the stirrer is electrically connected to the monitoring and control device, and the working electrode is a BDD membrane electrode. When the solution to be tested or the standard solution enters the reaction pool, the monitoring and control device sends a signal to start the stirrer, so as to avoid the error caused by the uneven concentration of the solution during the reaction process and make the measurement more accurate. The BDD film electrode is a boron-doped diamond film electrode. It is used as a working electrode with an area of 0.2-0.5cm ² . The metal platinum sheet is used as an auxiliary electrode, and the silver/silver chloride electrode is used as a reference electrode. BDD membrane electrode has good electrical conductivity, wide electrochemical window, low background current, high chemical stability, and is not easily polluted by organic adsorption. These excellent characteristics make it very suitable for the electrodeposition of organic pollutants. Chemical analysis. In addition, the BDD membrane electrode has high mechanical strength and corrosion resistance. As an electrode material, it also has a high oxygen evolution potential, which means that more stable operation effects and higher current efficiency can be obtained when treating sewage. BDD membrane electrode has long service life, short response time, high sensitivity, low detection limit and large detection range.

Preferably, the monitoring control device includes a single-chip microcomputer and a motor drive circuit connected to the single-chip microcomputer, an electrode control and acquisition circuit, a solenoid valve control circuit, a stirrer control circuit and a display circuit, a button circuit, a motor drive circuit and the motor The electrode control and acquisition circuits are connected with the working electrode, auxiliary electrode, and reference electrode. The solenoid valve control circuit is connected with the three-way solenoid valve on the photoelectric quantitative device and the solenoid valve on the multi-way adapter. The stirrer control circuit It is connected with the stirrer of the reaction pool, and the single-chip microcomputer is also connected with the photoelectric switch on the electric injector, and the transmitter and receiver on the photoelectric quantitative device. The display circuit and the button circuit can also adopt an integrated touch display screen, which is easy to operate, compact in structure, and has a good man-machine interface.

The monitoring method of the COD automatic on-line monitoring system of the present invention is that the monitoring and control device sends out a control signal to control the electric injector, the multi-way adapter, and the optical quantitative device, and the electric injector is extracted from the optical quantitative device through a ventilation tube. The gas in the corresponding pipeline enters the optical quantitative device through the multi-way adapter, and the optical quantitative device quantifies the solution. When the solution reaches the quantitative value, the optical quantitative device sends a signal to the monitoring and control device, and the monitoring and control device then Send a signal to the electric injector, and the electric injector will press the gas into the optical quantitative device through the ventilation tube, and then the solution will enter the reaction pool from the optical quantitative device through the multi-way adapter. At this time, the monitoring and control device applies a voltage on the working electrode , the organic matter in the solution is oxidized into carbon dioxide and water, and the generated current signal is returned to the monitoring and control device, and the COD value is displayed after being processed by the monitoring and control device. The liquid tube is discharged; each time before measuring the standard solution or the solution to be tested, measure the blank solution once to obtain the current I ₀ ; the current of the standard solution is I _c , and the current change value of the standard solution is △I _c =I _c - I ₀ , measure the current change value of standard solutions with different concentrations, and the monitoring and control device automatically draws the curves of the current change values of standard solutions with different concentrations and the corresponding COD concentration to obtain the standard curve △I _c -C, and measure the solution to be tested The current change value of ΔI _x is compared with the standard curve, and finally the COD value of the solution to be tested is obtained and displayed by the monitoring and control device.

As a preference, each time a solution is to be measured, the reaction tank must be rinsed with the solution: under the control of the monitoring and control device, the solution is sent to the optical quantitative device through the multi-way adapter, and then the optical quantitative device Through the multi-way adapter to the reaction pool; then the solution is discharged from the reaction pool through the multi-way adapter from the waste liquid discharge pipe.

The beneficial effects of the present invention are: BDD membrane electrode is selected as the working electrode, which has good electrical conductivity, a wide electrochemical window, a very low background current, high chemical stability, and is not easily polluted by organic adsorption. BDD Membrane electrode has high mechanical strength and corrosion resistance, high oxygen evolution potential, and can get more stable operation effect and higher current efficiency when treating sewage. From the electrode to the solution, and the entire measurement process, no toxic and harmful substances are added and generated, and the environment is friendly, and there is no pollution and secondary pollution. The pressure difference is used for sample injection and liquid discharge, and the optical quantitative device quantifies the solution to ensure that the volume of the solution entering the reaction pool is consistent, making COD monitoring more accurate. The cleaning and monitoring operations are simple and fully automated. The staff only need to click the words "calibration" and "measurement" on the display screen. After the measurement, the COD value will be directly displayed on the display screen without any manual conversion. Realize the automatic online detection of solution COD, with a high degree of intelligence.

Description of drawings

Fig. 1 is a schematic diagram of a system connection structure of the COD automatic on-line monitoring system of the present invention.

Fig. 2 is a schematic structural view of the electric injector in the COD automatic on-line monitoring system of the present invention.

Fig. 3 is a schematic structural view of the optical quantitative device in the COD automatic on-line monitoring system of the present invention.

Fig. 4 is a circuit principle connection block diagram of the monitoring and control device in the COD automatic on-line monitoring system of the present invention.

Detailed ways

The technical solutions of the present invention will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Embodiment 1: The COD automatic online monitoring system of this embodiment, as shown in Figure 1, includes an electric injector 1, an optical quantitative device 2, a multi-way adapter 3, a reaction pool 4 and a monitoring and control device 5, and an electric injector 1 A ventilation tube 6 is connected between the optical quantitative device 2 and between the optical quantitative device 2 and the reaction pool 4 . There are many pipelines inside the multi-way adapter 3, and there are a plurality of electromagnetic valves 27 on the multi-way adapter 3, and each electromagnetic valve controls the on-off between the internal pipelines. The solution input pipe 7 to be tested is connected to the multi-way adapter 3 through the pretreatment system 28, and the multi-way adapter 3 is also connected with two standard solution input pipes 8, blank solution input pipe 9, and deionized water input pipe 10. And the waste liquid discharge pipe 11, the multi-way adapter 3 is also communicated with the optical quantitative device 2 and the reaction cell 4 through the pipeline respectively, and the working electrode 12, the auxiliary electrode 13 and the reference electrode 14 are inserted in the reaction cell 4, and the BDD film The electrode (boron-doped diamond film electrode) is the working electrode, the metal platinum sheet is the auxiliary electrode, and the silver/silver chloride electrode is the reference electrode. These three electrodes are connected to the monitoring and control device 5 through wires, and a stirring device is installed at the bottom of the reaction pool. Device 29, agitator 29, solenoid valve 27, electric injector 1, optical quantitative device 2, multi-way adapter 3 are connected to monitoring and control device 5 through wires respectively.

As shown in Figure 2, one end of the electric injector 1 is equipped with a motor 15, and the other end is a glass tube connected with a ventilation tube 6. There is a piston 16 in the glass tube, and a cylinder 17 with a cavity inside is connected to the piston 16. The cylinder 17 The other end of the nut is connected with a nut 37, and one end of the nut and a screw rod 18 is threaded, and the other end of the screw rod 18 is connected with the rotating shaft on the motor 15. There is a slot 19 on the inner wall of the electric injector 1 near the side of the motor 15 , and a screw is transversely connected to the nut 37 to form a locking member 20 , and the head of the screw is stuck in the slot 19 . A light blocking sheet 21 is connected under the nut 37, and there is a photoelectric switch 22 matching the light blocking sheet 21 on the side wall of the electric injector 1 near the lower end of the card slot 19. The photoelectric switch 22 and the motor 15 pass through the monitoring and control device 5 respectively. wire connection.

As shown in Figure 3, the photoelectric quantitative device 2 includes a container 23 and a three-way solenoid valve 24 installed on the top of the container 23. The bottom of the container 23 is connected to the multi-way adapter 3 through a pipeline, and the three-way solenoid valve 24 is passed through respectively. The ventilation tube 6 is connected to the glass tube of the electric injector 1 and the reaction pool 4, and two sets of transmitters 25 and receivers 26 are installed oppositely on the side wall of the container 23, and the transmitter 25, the receiver 26 and the three-way solenoid valve 24 respectively pass through The wire is connected to the monitoring control device 5 .

As shown in Figure 4, the monitoring control device 5 comprises a single-chip microcomputer 30 and a motor drive circuit 31 connected to the single-chip microcomputer 30, an electrode control and acquisition circuit 32, a solenoid valve control circuit 33, an agitator control circuit 34 and a display circuit 35 and a button circuit. 36 constitute the touch display screen, the motor drive circuit 31 is connected to the motor 15, the electrode control and acquisition circuit 32 is connected to the working electrode 12, the auxiliary electrode 13, and the reference electrode 14, and the solenoid valve control circuit 33 is connected to the photoelectric quantitative device 2. The solenoid valve 24 is connected to the solenoid valve 27 on the multi-way adapter 3, the stirrer control circuit 34 is connected to the stirrer 29 of the reaction tank 4, and the single-chip microcomputer 30 is also connected to the photoelectric switch 22 and the photoelectric quantitative device 2 on the electric injector 1. The transmitter 25 and receiver 26 on it are connected.

Working process: The monitoring and control device 5 sends control signals to control the electric injector 1, the multi-way adapter 3, and the optical quantitative device 2. The electric injector 1 extracts the gas in the optical quantitative device 2 through the ventilation tube 6, and the solution in the corresponding pipeline passes through The multi-way adapter 3 enters the optical quantification device 2, and the solution is quantified by the optical quantification device 2. When the solution reaches the quantitative value, the optical quantification device 2 sends a signal to the monitoring control device 5, and the monitoring control device 5 sends a signal to the motor The motor of the syringe 1 is used to press the gas into the optical quantitative device 2 through the electric injector 1 through the ventilation tube 6, and the solution enters the reaction pool 4 from the optical quantitative device 2 through the multi-way adapter 3. At this time, the monitoring control device 5 Apply a 2.5V voltage on the working electrode 12 to oxidize the organic matter in the solution into carbon dioxide and water, and the generated current signal is returned to the monitoring and control device 5, and the COD value is displayed after the processing of the monitoring and control device 5. After the measurement, the solution is re- It is discharged from the reaction pool 4 through the multi-way adapter 3 and the waste liquid discharge pipe 11.

The monitoring method of the above-mentioned COD automatic online monitoring system is:

1. Rinse the electrode and reaction cell with deionized water: under the cooperation of the electric injector, multi-way adapter and optical quantitative device, the deionized water is pumped into the reaction cell from the deionized water input pipe by using the air pressure difference, and then from the The waste liquid discharge pipe discharges;

2. Connect the blank solution input tube, first rinse the electrode and the reaction cell with the blank solution, then take 3mL of the blank solution (0.1Mol/L Na ₂ SO ₄ solution) and inject it into the reaction cell, and apply a voltage of 2.5V on the working electrode , start the stirrer to stir at a uniform speed, the monitoring and control device records the It curve of the current changing with time, and reads the current value I ₀ at this time in 120 seconds;

3. Connect the standard solution input tube, first rinse the electrode and the reaction cell with the standard solution, then take 3mL COD standard sample solution (glucose solution prepared with a blank solution of 0.1Mol/L Na ₂ SO ₄ ), put it on the working electrode Apply 2.5V voltage, and when it reaches 120 seconds, the monitoring and control device reads the current value I _c at this time, and obtains the current change value △I _c =I _c -I ₀ ;

4. Repeat steps 2 and 3 to obtain the current change values of COD standard sample solutions with different concentrations, and the monitoring and control device automatically makes a standard curve △I _c -C;

5. COD determination of the sample to be tested: Repeat step 2, record the current I ₀ , connect the input tube of the solution to be tested, first rinse the electrode and the reaction cell with the solution to be tested, then take 3mL of the solution to be tested, and apply it to the working electrode 2.5V voltage, when it reaches 120 seconds, the monitoring and control device reads the current value I _x at this time, and obtains the current change value △I _x =I _x -I ₀ , and the monitoring and control device finds out the value corresponding to △I _x on the standard curve The concentration value is the COD value of the sample to be tested and displayed on the display.

The invention adopts the BDD membrane electrode as the working electrode, has long service life, short response time, stable signal, only 3-8 minutes for a single measurement, no pollution and secondary pollution in the whole measurement process, and relatively small error. The monitoring operation is simple and convenient, just click the words "calibration" and "measurement" on the display screen, and the COD value will be directly displayed on the display screen after the measurement, with reliable performance, large detection range, high sensitivity and low detection limit , which integrates detection, data processing, storage and transmission, is suitable for COD detection of various sewage, drinking water and seawater.

Claims (10)

1. A COD automatic online monitoring system, characterized in that it includes an electric injector (1), an optical quantitative device (2), a multi-way adapter (3), a reaction pool (4) and a monitoring control device (5), A ventilation tube (6) is connected between the electric injector (1) and the optical quantitative device (2), between the optical quantitative device (2) and the reaction pool (4), and the multi-way adapter ( 3) There are input tubes for the solution to be tested (7), standard solution input tubes (8), blank solution input tubes (9), deionized water input tubes (10) and waste liquid discharge tubes (11). The connector (3) is also communicated with the optical quantification device (2) and the reaction pool (4) respectively through pipelines, and the reaction pool (4) is provided with a working electrode (12), an auxiliary electrode (13) and the reference electrode (14), the working electrode (12), the auxiliary electrode (13) and the reference electrode (14) are connected to the monitoring control device (5) through wires, and the monitoring control device (5) also They are respectively electrically connected to the electric injector (1), the optical quantitative device (2), and the multi-way adapter (3). 2. The COD automatic online monitoring system according to claim 1, characterized in that one end of the electric injector (1) is provided with a motor (15), and the other end is connected with the ventilation tube (6). (1) There is a piston (16) inside, and a cylinder (17) with a cavity inside is connected to the piston (16). The end surface of the other end of the cylinder (17) is provided with a threaded hole, the threaded hole and a screw rod (18), the screw (18) is connected to the rotating shaft of the motor (15), and the motor (15) is electrically connected to the monitoring and control device (5). 3. The COD automatic online monitoring system according to claim 2, characterized in that a slot (19) is provided on the inner wall of the electric injector (1), and the cylinder (17) is connected with a screw ( The side of one end of 18) is provided with a clamping piece (20), the head of the clamping piece (20) is clamped in the said slot (19), and the said column (17) is provided with a stop Light sheet (21), the side wall of the electric injector (1) is provided with a photoelectric switch (22) matching the light blocking sheet (21), the photoelectric switch (22) and the The monitoring control device (5) is electrically connected. 4. The COD automatic online monitoring system according to claim 1, characterized in that the photoelectric quantitative device (2) includes a container (23) and a three-way solenoid valve (24) on the container (23) , the container (23) is connected to the multi-way adapter (3) through the pipeline, and the three-way solenoid valve (24) is connected to the electric injector (1) and the reaction pool (4) through the ventilation tube (6) respectively, The side wall of the container (23) is oppositely provided with a transmitter (25) and a receiver (26), and the transmitter (25), the receiver (26) and the three-way solenoid valve (24) are respectively connected with the The monitoring control device (5) is electrically connected. 5. The COD automatic online monitoring system according to claim 1, characterized in that the multi-way adapter (3) is provided with several solenoid valves (27), the solenoid valves (27) and the The monitoring and control device (5) described above is electrically connected. 6. The COD automatic on-line monitoring system according to claim 1 or 2 or 4 or 5, characterized in that there is a preset Handling system (28). 7. The COD automatic online monitoring system according to claim 1 or 2 or 4 or 5, characterized in that the bottom of the reaction pool (4) is provided with an agitator (29), the agitator (29) and the The above-mentioned monitoring and control device (5) is electrically connected, and the above-mentioned working electrode (12) is a BDD membrane electrode. 8. The COD automatic online monitoring system according to claim 7, characterized in that the monitoring control device (5) includes a single-chip microcomputer (30) and a motor drive circuit (31) connected to the single-chip microcomputer (30), electrode control And collection circuit (32), solenoid valve control circuit (33), agitator control circuit (34), display circuit (35), button circuit (36), motor drive circuit (31) is connected to the motor (15) , the electrode control and acquisition circuit (32) is connected to the working electrode (12), auxiliary electrode (13), and reference electrode (14), the solenoid valve control circuit (33) and the three-way electromagnetic valve on the photoelectric quantitative device (2) The valve (24) is connected to the solenoid valve (27) on the multi-way adapter (3), the agitator control circuit (34) is connected to the agitator (29) of the reaction tank (4), and the single-chip microcomputer (30) It is also connected with the photoelectric switch (22) on the electric injector (1), the transmitter (25) and the receiver (26) on the photoelectric quantitative device (2). 9. A monitoring method of the COD automatic on-line monitoring system according to claim 1, characterized in that the monitoring and control device (5) sends a control signal to control the electric injector (1), multi-channel transfer Device (3), optical quantitative device (2), the electric injector (1) extracts the gas in the optical quantitative device (2) through the ventilation tube (6), and the solution in the corresponding pipeline passes through the multi-way adapter ( 3) Enter the optical quantification device (2), the solution is quantified by the optical quantification device (2), when the solution reaches the quantitative value, the optical quantification device (2) sends a signal to the monitoring control device (5), the monitoring control device (5 ) and then send a signal to the electric injector (1), the electric injector (1) passes the gas exchange tube (6) and then presses the gas into the optical quantitative device (2), and the solution is then transferred by the optical quantitative device (2) through a multi-channel The device (3) enters the reaction pool (4), at this time, the monitoring and control device (5) applies a voltage to the working electrode (12), oxidizing the organic matter in the solution into carbon dioxide and water, and the generated current signal is returned to the monitoring and control device (5), the COD value is displayed after the treatment of the monitoring and control device (5). After the measurement, the solution is discharged from the reaction pool (4) through the multi-way adapter (3) and the waste liquid discharge pipe (11); Before measuring the standard solution or the solution to be tested, measure the blank solution once to obtain the current I ₀ ; the current of the standard solution is I _c , and the current change value of the standard solution is △I _c =I _c - I ₀ , measure different concentrations The current change value of the standard solution, the monitoring and control device (5) automatically draws the curves of the current change value of the standard solution with different concentrations and the corresponding COD concentration, and obtains the standard curve △I _c -C, and measures the current of the solution to be tested The change value is △I _x , and then compared with the standard curve, and finally the monitoring and control device (5) automatically obtains the COD value of the solution to be tested and displays it. 10. The monitoring method according to claim 9, characterized in that each time before measuring a solution, the reaction tank must be rinsed with the solution: under the control of the monitoring control device (5), the solution is The multi-way adapter (3) to the optical quantitative device (2), and then from the optical quantitative device (2) to the reaction pool (4) through the multi-way adapter (3); then the solution is passed from the reaction pool (4) Discharge from the waste liquid discharge pipe (11) through the multi-way adapter (3).

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