Water quality detection device and method for simultaneously detecting COD (Chemical Oxygen Demand) and total phosphorus

Abstract

The invention discloses a water quality detection device and method for simultaneously detecting COD (Chemical Oxygen Demand) and total phosphorus, and belongs to the technical field of water quality detection. The device mainly comprises a sampling module, a cleaning liquid storage tank, a digestion module, a developing module, a colorimetric module, a waste liquid storage tank, an electrode voltage control and current detection module, a control module, a display and operation module and an MCU. The digestion module is used for oxidizing reducing substances in the water sample by using an electrode and converting total phosphorus into orthophosphate; the color developing module is used for developing the orthophosphate; and the colorimetric module is used for detecting the RGB value of the color developing water sample. And the MCU stores a calculation model, calculates the COD concentration according to the digestion time and the electrode current, and calculates the total phosphorus concentration according to the RGB value of the water sample. The detection process comprises the following steps: starting the cleaning device; the digestion module is filled with the water sample for digestion, and COD is calculated; the water sample flows into a color developing module and a color developing agent is added; the colorimetric module is filled with the water sample to measure an RGB value and calculate the total phosphorus concentration; and finally cleaning the device again. The device realizes automatic continuous detection and cleaning of COD and total phosphorus.

Description

Technical Field

[0001] The invention belongs to the technical field of water quality detection, and particularly relates to a water quality detection device and method for simultaneously detecting COD and total phosphorus. Background Art

[0002] Water is the source of life and an important resource for all living things on Earth to survive. Water quality testing, as the basic work in water resource management and protection, is of great significance. COD (Chemical Oxygen Demand) and total phosphorus are both commonly used parameters in water quality testing. COD refers to the amount of oxidant consumed to oxidize the reducing substances in 1 liter of water sample under certain conditions, converted into oxygen consumption. It reflects the degree of pollution by reducing substances in water. This indicator is also one of the comprehensive indicators of the relative content of organic matter. Total phosphorus is the result of the water sample being digested and various forms of phosphorus are converted into orthophosphate, and is measured in milligrams of phosphorus per liter of water sample. Total phosphorus is an important indicator reflecting the eutrophication of water bodies.

[0003] Currently, the main methods for COD detection include chemical methods, optical methods, and advanced oxidation methods. Chemical methods use strong oxidants such as potassium permanganate and potassium dichromate to digest water samples under certain conditions (usually high temperature and high pressure). The oxidant consumption is then measured using titration, spectrophotometry, and other methods. Chemical methods offer good accuracy and stability, but they also have disadvantages such as long detection time, high operational difficulty, reagent consumption leading to secondary pollution, and high energy consumption due to the high temperature and high pressure required for the reaction. By combining continuous flow analysis with improved chemical methods, detection time and operational difficulty can be reduced, but secondary pollution and high energy consumption still pose challenges. Optical methods such as UV-visible spectroscopy and fluorescence emission spectroscopy offer advantages such as extremely fast detection speed, ease of continuous online detection, the absence of chemical reagents, and the lack of secondary pollution. However, they are affected by water turbidity and color, and their spectral characteristics vary due to the varying composition of different water bodies, resulting in poor generalization. Advanced oxidation methods mainly include photocatalytic oxidation, electrocatalytic oxidation, and photoelectrocatalytic oxidation. All three methods require no added oxidants, reducing secondary pollution. Photocatalysis is green and energy-efficient, but it's not conducive to calculating the equivalent oxygen consumption of the oxidation process. While COD can be calculated by adding a strong oxidant and measuring the oxidant consumption, the introduction of the oxidant still introduces secondary pollution. Electrocatalysis is a very convenient way to calculate COD, simply measuring the current during the oxidation process. However, electrocatalysis consumes more energy than photocatalysis. Photoelectrocatalysis combines the advantages of both photocatalysis and electrocatalysis, reducing energy consumption while also making COD measurement very convenient.

[0004] The detection methods of total phosphorus can be divided into two categories according to whether or not a digestion pretreatment step is included.

[0005] The first category involves digestion pretreatment methods, which first use various pretreatment methods to convert total phosphorus into orthophosphate. The orthophosphate concentration is then measured and converted to total phosphorus concentration. This type of method is adopted by the national standard HJ636-2012. Pretreatment methods include chemical digestion, ultrasonic / UV / microwave-assisted digestion, UV digestion, electrode digestion, and advanced oxidation digestion. Methods for detecting orthophosphate include spectrophotometry, chromatography, and electrode detection. These methods offer advantages in terms of accuracy and versatility, but they also include a pretreatment step, making them relatively complex.

[0006] The second type is a method without digestion pretreatment, which directly detects the concentration of total phosphorus, mainly including electrode detection method, spectral method, etc. The advantage of this type of method is that it does not require the consumption of chemical reagents, the detection process is simple and fast, and it can achieve online real-time detection. However, in electrode detection, there are often impurities in the water that adhere to or corrode the electrodes, and the electrodes need to be maintained or replaced regularly; in spectral methods, physical and chemical indicators such as water sample turbidity, pH value, and components will affect the absorption spectrum, and usually compensation for different water samples is required to expand its scope of application.

[0007] In addition, the current total phosphorus detection for COD is mostly detected separately, and there are few methods for the joint detection of COD and total phosphorus. CN201110123476 proposes a combined colorimetric determination method for total phosphorus and chemical oxygen demand, which is based on the digestion of total phosphorus and chemical oxygen demand with Fenton reagent, and the use of malachite green-ammonium molybdate color developer to determine the total phosphorus concentration. Based on the competition mechanism between malachite green and COD, COD determination is achieved by measuring the residual amount of malachite green. The advantage is that the same digestion reagent is used, which reduces the number of reagents, and the same set of detection devices is used to complete the determination of the two parameters. However, due to the difference in the color developing reagents and the difference in the detection processes of the two, two separate detection processes are still required to detect total phosphorus and COD, which is not a true one-time detection to achieve the detection of two parameters. Xie Yingke et al. proposed a method for online determination of COD and total phosphorus in water quality based on Fenton reagent and a micro-spectrometer. This method, combined with ultrasound assistance, digests COD and total phosphorus using Fenton reagent. Malachite green and ammonium molybdate are used as colorants for COD and total phosphorus detection, respectively, and is combined with a micro-spectrometer to achieve COD and total phosphorus determination. Similar to the previous method, this method has the advantage of using the same digestion reagent and detection device, but still requires two separate color development and detection processes.

[0008] Therefore, the current total phosphorus detection of COD is mostly done separately, which is inefficient. In total phosphorus detection, after digestion, the concentration of orthophosphate ions is measured using instruments such as spectrophotometers, mass spectrometers, and chromatographs. These instruments are expensive and less portable. Summary of the Invention

[0009] To address these shortcomings, the present invention proposes a water quality testing device and method for simultaneously detecting COD and total phosphorus, which can simultaneously detect COD and total phosphorus to improve detection efficiency. The present invention uses RGB colorimetry instead of a spectrophotometer, mass spectrometer, or chromatograph, reducing costs and improving portability.

[0010] The present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a water quality detection device for simultaneously detecting COD and total phosphorus, comprising:

[0012] Sampling module, used for collecting water samples to be tested;

[0013] A cleaning liquid storage tank, which stores cleaning liquid for cleaning the modules and connecting pipes in the water quality detection device;

[0014] The digestion module has its inlet connected to the sampling module and the cleaning liquid storage tank through branch pipelines, and a No. 1 pump is set on the main pipeline, and independent valves are set on the branch pipelines. The digestion module uses electrodes to oxidize various reducing substances in the water sample and convert the total phosphorus in the water sample into orthophosphate;

[0015] A color development module, whose inlet and outlet are connected to the digestion module and the colorimetric module respectively, and the inlet and outlet are provided with independent valves, and the module is used to develop the color of orthophosphate in the digested water sample;

[0016] A colorimetric module is used to detect the RGB value of the water sample after color development. The inlet and outlet of the colorimetric module are provided with independent valves;

[0017] The waste liquid storage tank is connected to the outlet of the colorimetric module and is used to store waste liquid. When the cleaning liquid storage tank is started, the cleaning liquid flows through the digestion module, the color development module and the colorimetric module in sequence;

[0018] The electrode voltage control and current detection module is used to provide the working voltage for the digestion module, detect the electrode current, and record the digestion time;

[0019] Control module, used to control valves, pumps and light sources;

[0020] Display and operation module, used to control the opening and closing of the device and display the test results;

[0021] The MCU is connected to the colorimetric module, electrode voltage control and current detection module, control module, display and operation module, and is used to calculate the COD concentration based on the digestion time and electrode current, calculate the total phosphorus concentration based on the RGB value of the water sample, and display the calculation results through the display and operation module; it also receives operation instructions from the display and operation module and sends control instructions to the control module.

[0022] As a preferred embodiment of the present invention, the MCU stores a COD concentration calculation model and a total phosphorus concentration calculation model;

[0023] The COD concentration calculation model is as follows:

[0024]

[0025] Among them, t0 is the digestion start time, t1 is the digestion end time, I0 is the base current, I1 is the digestion current, k COD is the fitting parameter, c COD is the COD concentration;

[0026] The total phosphorus concentration calculation model is as follows:

[0027] c TP =k R c TP,R +k G c TP,G +k B c TP,B

[0028]

[0029] Among them, c TP is the total phosphorus concentration, c TP,R 、c TP,G 、c TP,B are the total phosphorus concentrations calculated based on the R, G, and B channels, respectively. R 、k G 、k B is the fitting parameter, R, G, B are the values ​​of the three channels R, G, B respectively, a R 、a G 、a B 、b R 、b G 、b B are the fitting parameters respectively.

[0030] As a preferred embodiment of the present invention, the digestion module includes a digestion tank, electrodes located in the digestion tank and an ultraviolet light source whose illumination range covers the anode surface in the electrode, and the water inlet and outlet of the digestion tank serve as the inlet and outlet of the digestion module.

[0031] As a preferred embodiment of the present invention, the ultraviolet light source is an ultraviolet lamp with a wavelength less than 385 mm.

[0032] As a preference of the present invention, the electrodes are a three-electrode system.

[0033] As a preferred embodiment of the present invention, the color development module includes a color development pool, a color developer storage tank, a No. 2 pump and a color development valve. The No. 2 pump and the color development valve are located on the connecting pipeline between the color developer storage tank and the color development pool, and the water inlet and outlet of the color development pool serve as the inlet and outlet of the color development module.

[0034] As a preferred embodiment of the present invention, the colorimetric module includes a colorimetric cell, a light source and a color sensor. The light source is a visible light source, and the color sensor is installed on the outer wall of the transparent colorimetric cell to test the RGB value of the water sample in the colorimetric cell.

[0035] As a preference of the present invention, the visible light source is a white LED lamp.

[0036] In a second aspect, the present invention provides a detection method for a water quality detection device for simultaneously detecting COD and total phosphorus, comprising the following steps:

[0037] S1, start the cleaning liquid storage tank to clean the digestion module, color development module and colorimetric module;

[0038] S2, control the water sample to flow in until the digestion module is full, and turn off pump No. 1;

[0039] S3, applies voltage to the electrodes in the digestion module, records the digestion start time, digestion end time and digestion current, and transmits them to the MCU to calculate the COD concentration;

[0040] S4, control the water sample to flow into the color development module until it fills the color development module, and turn off pump No. 1; automatically add excess color development agent during the process of the water sample flowing into the color development module;

[0041] S5, controls the water sample to flow in until it fills the colorimetric module, tests the RGB value of the water sample, and transmits it to the MCU to calculate the total phosphorus concentration;

[0042] S6, start the cleaning liquid storage tank, clean the digestion module, color development module and colorimetric module, and the test ends.

[0043] Furthermore, before detecting the COD and total phosphorus of the water sample, the fitting parameters in the COD concentration calculation model and the total phosphorus concentration calculation model are calibrated with a standard water sample.

[0044] The beneficial effects of the present invention are:

[0045] (1) Detect two parameters, COD and total phosphorus, at one time.

[0046] (2) Compared with the national standard method, the digestion process does not require the addition of chemical reagents, thus avoiding secondary pollution. The digestion conditions are mild, and high temperature and high pressure are not required, thus reducing energy consumption.

[0047] (3) RGB colorimetry reduces detection costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the structure of a water quality detection device for simultaneously detecting COD and total phosphorus. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the specific implementation manner of the present invention is not limited thereto.

[0050] The present invention adopts a photoelectrocatalytic oxidation digestion method. The principle is: when photons with energy higher than the semiconductor band gap width irradiate the semiconductor material, the electrons in the semiconductor valence band jump to the conduction band, generating photogenerated holes and photogenerated electrons. The strong oxidizing ability of photogenerated holes and the reducing ability of photogenerated electrons cause the semiconductor photocatalyst to trigger a series of photocatalytic reactions. However, the activated electrons and holes can easily meet and annihilate inside or on the surface of the semiconductor, making the efficiency of photocatalytic oxidation low. In addition, the photocatalytic oxidation reaction is not convenient for measuring the equivalent oxygen consumption during the reaction. Photoelectrocatalytic oxidation is based on photocatalysis, and an external voltage is applied to drive the photogenerated electrons into the auxiliary electrode, reducing the simple recombination of photogenerated electrons and holes and improving the oxidation efficiency. The substances participating in the digestion process can be quantified by measuring the current, which greatly facilitates the determination of COD.

[0051] The mechanism of photoelectrocatalysis can be expressed as follows:

[0052] Anodic reaction:

[0053] TiO2+hv→TiO2(e - )+TiO2(h + ) (1)

[0054] TiO2(h + )+OH - →TiO2+·OH (2)

[0055] TiO2(h + ) + reducing substance → product (3)

[0056] OH + reducing substance → product (4)

[0057] Wherein, TiO2 is titanium dioxide, hv is ultraviolet light, and formula (1) shows that under ultraviolet light, the electrons in TiO2 (e - ) jumps from the valence band to the conduction band and becomes a free electron, leaving a hole TiO2 (h + );OH -is the hydroxide ion in water, and ·OH is the hydroxyl radical, a highly oxidizing active substance. The reducing substances in formulas (3) and (4) are mainly organic matter in water and also include other reducing ions. The products are mainly CO2, the products of the oxidation of water and various reducing ions.

[0058] Cathode reaction:

[0059] 4e - +O2+4H + →2H2O (5)

[0060] 2e - +2H + →H2 (6)

[0061] The reducing substances in the water, including various forms of phosphorus, are oxidized by holes and hydroxyl radicals (·OH) at the anode, thus achieving the purpose of digestion.

[0062] Generally speaking, the more positive the value of a semiconductor's valence band, the stronger the oxidizing power of the holes, while the less negative the value of the conduction band, the stronger the reducing power of the electrons. The more positive the value of the TiO2 valence band, the stronger the oxidizing power of the holes. This indicates that the holes generated by TiO2 have a stronger oxidizing power, making it suitable for the strong oxidant requirements of COD and total phosphorus digestion. Therefore, TiO2 is selected as the anode material, and the cathode acts as a conductor. An inert electrode such as a platinum electrode or a graphite electrode can be used, and Ag / AgCl is selected as the reference electrode to form a three-electrode system. This three-electrode system facilitates control of electrode voltage and current detection.

[0063] Since the essence of redox reaction is the transfer of electrons, the amount of electricity passing through the electrode during the reaction can be converted into equivalent oxygen consumption, thereby calculating COD. The amount of electricity can be calculated by integrating the current, thus obtaining the COD concentration c COD The calculation formula is:

[0064]

[0065] Where t0 is the digestion start time, t1 is the digestion end time, that is, the time when the digestion current no longer changes, I0 is the base current, that is, the current when the current no longer changes, I1 is the electrode current, k COD To be determined parameters.

[0066] Use the least squares method to fit the k in equation (6) COD .make:

[0067] y=c COD (7)

[0068]

[0069] Using COD standard solutions of different concentrations to perform n measurements, we can obtain n sets of measurement data [y1, y2, ... y n ],[x1,x2,…x n ], then:

[0070]

[0071] The digestion process calculates the COD concentration and simultaneously converts various forms of phosphorus into orthophosphate. Simply measuring the orthophosphate concentration allows calculation of the total phosphorus concentration. Currently, orthophosphate concentration is typically measured using instruments such as spectrophotometers, mass spectrometers, and chromatographs, which are costly and lack portability. The present invention uses RGB colorimetry instead of these instruments to reduce costs and improve portability.

[0072] First, orthophosphate undergoes a color development reaction to obtain a colored solution. The color development method of orthophosphate is the ammonium molybdate method. Its principle is: in an acidic medium, orthophosphate reacts with ammonium molybdate to form a phosphomolybdic heteropoly acid in the presence of antimony salt, which is immediately reduced by ascorbic acid to form a blue complex. Its chemical formula is:

[0073]

[0074] The process of RGB colorimetry is as follows: In a dark box, without interference from ambient light, a light source is vertically irradiated on the blue solution in the cuvette. The emitted light is partially absorbed by the solution and enters the color sensor to obtain RGB. The concentration is calculated based on RGB. The principle is as follows:

[0075] The total absorbance during the process of light from the light source to the RGB sensor is:

[0076]

[0077] Among them, A total (λ) is the total absorbance of light with wavelength λ from the light source to the sensor, I0(λ) is the original light intensity at the light source, I1(λ) is the light intensity at the sensor, and A m (λ) is the absorbance of the substance to be tested, A o (λ) is the absorbance of the substance other than the substance to be tested. Here we assume that I0(λ), A o (λ) remains unchanged.

[0078] According to Lambert-Beer law:

[0079] A m (λ)=K m (λ)lc TP (12)

[0080] Among them, K m (λ) is the molar absorption coefficient of the substance to be measured at wavelength λ, l is the thickness of the absorption layer, c TP is the concentration of the substance to be tested.

[0081] After the light signal hits the RGB sensor, it is converted into RGB three-channel signals:

[0082] P i =α i ∫I1(λ)K i (λ)dλ,i=1,2,3 (13)

[0083] Among them, P i Refers to the value of one of the RGB channels, i=1, 2, 3 are R, G, B, α i For channel P i Gain, K i (λ) is the wavelength λ, channel P i spectral responsivity.

[0084] The combined equations (11-13) yield:

[0085]

[0086] Since the integral form of the model is difficult to fit, it is approximately replaced by a discretized form:

[0087]

[0088] Where Δλ i is the wavelength range corresponding to the i-th segment. The above formula can be transformed into the following form:

[0089]

[0090] Among them, n R 、n G 、n B 、a Ri 、b Ri 、a Gi 、b Gi 、a Bi 、b Bi is a parameter to be determined. In this invention, in order to simplify the complexity of the model, n is taken R =n G =n B =1.

[0091] The three channel components of R, G, and B and the total phosphorus concentration c TP The models between can be calculated as follows:

[0092]

[0093] where c TP,R 、c TP,G 、c TP,B are the total phosphorus concentrations calculated based on the R, G, and B channels, respectively. Use the least squares method to fit equation (17), taking the R channel as an example, and the same applies to the other two channels. Let y = c TP,R , x=[lnR,1] T , the group data is measured through experiments, Y=[y1,y2,…y n ] represents a set of known total phosphorus concentrations, X=[x1,x2,…x n ] is obtained by converting the measured R channel component, then:

[0094]

[0095] Similarly, we can calculate b G 、lna G 、b B 、lna B .

[0096] The total phosphorus concentration c calculated from the three RGB channel information is obtained through the above formula TP,R 、c TP,G 、c TP,B ; The results of the three-channel calculations are combined to obtain the final total phosphorus concentration c TP Calculation formula:

[0097] c TP =k R c TP,R +k G c TP,G +k B c TP,B (19)

[0098] where k R , k G , k B To be determined parameters.

[0099] Since there is collinearity of independent variables in formula (19), that is, c TP,R 、c TP,G 、c TP,B There is a strong linear relationship, and it is difficult to overcome the collinearity problem using conventional least squares method. Therefore, the present invention uses partial least squares method to fit equation (19), for example, using the plsregress function in the matlab function package for fitting.

[0100] like Figure 1 As shown, the present invention provides a water quality detection device, comprising:

[0101] Sampling module 1, used for collecting water samples to be tested;

[0102] A cleaning liquid storage tank 2 stores cleaning liquid for cleaning the modules and connecting pipes in the water quality detection device;

[0103] Digestion module 6 is used to oxidize various reducing substances in the water sample. During this process, total phosphorus is converted into orthophosphate;

[0104] A color development module 8, for developing the color of orthophosphate;

[0105] Colorimetric module 10, for detecting orthophosphate concentration;

[0106] A waste liquid storage tank 12, used for storing waste liquid;

[0107] The electrode voltage control and current detection module 14 is used to provide the working voltage for the digestion module 6 and detect the electrode current and record the digestion time;

[0108] Control module 16, used to control valves, pumps and lights;

[0109] Display and operation module 13, used to control the opening and closing of the device and display the test results;

[0110] MCU15 is connected to the colorimetric module, electrode voltage control and current detection module, control module, display and operation module, and is used to calculate the COD concentration based on the digestion time and electrode current, calculate the total phosphorus concentration based on the RGB value of the water sample, and display the calculation results through the display and operation module; it also receives operation instructions from the display and operation module and sends control instructions to the control module.

[0111] In one embodiment of the present invention, digestion module 6 comprises: a UV lamp 61, a digestion cell 62, and electrodes 63. UV lamp 61 is a UV light source with a wavelength less than 385 nm. Electrode 63 is a three-electrode system, wherein the anode is a titanium dioxide thin film electrode, the cathode is an inert electrode, which can be a platinum electrode or a graphite electrode, and the reference electrode can be an Ag / AgCl electrode. The UV light source's illumination range must cover the anode surface of the three-electrode system.

[0112] The color development module 8 includes a color developer storage tank 81 and a color development pool 84 .

[0113] The colorimetric module 10 includes: a light source 101, a colorimetric cell 102, and a color detection module 103. The light source 101 is a visible light source with stable light intensity and spectrum, which can be a white LED, and the color detection module (103) can be a color sensor or a camera.

[0114] The flow path connection of the device is as follows: the outlet of the sampling module 1 is connected to valve No. 1 3, the outlet of the cleaning liquid storage tank 2 is connected to valve No. 2 4, the two valve outlets are connected to the inlet of pump No. 1 5 through a tee pipe, the outlet of pump No. 1 5 is connected to the inlet of the digestion tank 62, the outlet of the digestion tank 62 is connected to the inlet of valve No. 3 7, the outlet of valve No. 3 7 is connected to the inlet of the color development tank 84, the outlet of the color development tank 84 is connected to the inlet of valve No. 4 9, the outlet of valve No. 4 9 is connected to the inlet of the colorimetric cell 102, the outlet of the colorimetric cell 102 is connected to the inlet of valve No. 5 11, and the outlet of valve No. 5 11 is connected to the waste liquid storage tank 12; the outlet of the color developer storage tank 81 is connected to the inlet of valve No. 6 82, the outlet of valve No. 6 82 is connected to the inlet of pump No. 2 83, and the outlet of pump No. 2 83 is connected to the inlet of the color development tank 84.

[0115] The signal connections of the device are as follows: valve No. 1 3, valve No. 2 4, pump No. 1 5, ultraviolet lamp 61, valve No. 3 7, valve No. 6 82, pump No. 2 83, valve No. 4 9, light source 101, and valve No. 5 11 are connected to the control module 16; the electrode 63 is connected to the electrode voltage control and current detection module 14; the color detection module 103, the electrode voltage control and current detection module 14, the control module 16, and the display and operation module 13 are connected to the MCU 15.

[0116] A detection method for the above-mentioned water quality detection device is provided, and the detection steps are as follows:

[0117] S1. Close valves 3 and 82, open valves 4, 7, 9, and 11, start pump 5, and clean the device;

[0118] S2. Turn off pump 5, turn off 4, open valve 3, turn on pump 5 until the digestion tank 62 is filled with the water sample to be tested, turn off pump 5, close valves 3 and 7, turn on the UV lamp 61, apply voltage to the electrode 63, and digest the water sample for a period of time;

[0119] S3. Calculate COD concentration based on digestion current;

[0120] S4. Open valves 3, 7, 82, turn on pumps 5 and 83 for a while, turn off pumps 5 and 83, close valves 7 and 9, and allow the color to develop for a while;

[0121] S5. Open valves 7 and 9, turn on the pump 5 for a period of time, turn off the pump 5, close valves 9 and 11, turn on the light source 101, and the color detection module 103 performs colorimetric detection;

[0122] S6. calculating the total phosphorus concentration based on the measured RGB;

[0123] S7. Open valves 9, 11, and 4, close valve 3, start pump 5, and clean the device.

[0124] In step S3, COD concentration c COD The calculation formula is:

[0125]

[0126] Among them, t0 is the digestion start time, t1 is the digestion end time, that is, the time when the digestion current no longer changes, I0 is the base current, that is, the current when the current no longer changes, I1 is the digestion current, k CoD is the fitting parameter.

[0127] Total phosphorus concentration c TP The calculation formula is:

[0128] c TP =k R c TP,R +k G c TP,G +k B c TP,B

[0129]

[0130]

[0131] Among them, c TP is the total phosphorus concentration, R, G, and B are the three color components obtained by the sensor, and c TP,R 、c TP,G 、c TP,B are the total phosphorus concentrations calculated based on the R, G, and B channels, respectively. R 、k G 、k B 、n R 、n G 、n B 、a BR 、a G 、a B 、b R 、b G 、b B is the fitting parameter.

[0132] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A water quality detection device for simultaneously detecting COD and total phosphorus, characterized in that: include: Sampling module, used for collecting water samples to be tested; A cleaning liquid storage tank, which stores cleaning liquid for cleaning the modules and connecting pipes in the water quality detection device; The digestion module has its inlet connected to the sampling module and the cleaning liquid storage tank through branch pipelines, and a No. 1 pump is set on the main pipeline, and independent valves are set on the branch pipelines. The digestion module uses electrodes to oxidize various reducing substances in the water sample and convert the total phosphorus in the water sample into orthophosphate; A color development module, whose inlet and outlet are connected to the digestion module and the colorimetric module respectively, and the inlet and outlet are provided with independent valves, and the module is used to develop the color of orthophosphate in the digested water sample; A colorimetric module is used to detect the RGB value of the water sample after color development. The inlet and outlet of the colorimetric module are provided with independent valves; The waste liquid storage tank is connected to the outlet of the colorimetric module and is used to store waste liquid. When the cleaning liquid storage tank is started, the cleaning liquid flows through the digestion module, the color development module and the colorimetric module in sequence; The electrode voltage control and current detection module is used to provide the working voltage for the digestion module, detect the electrode current, and record the digestion time; Control module, used to control valves, pumps and light sources; Display and operation module, used to control the opening and closing of the device and display the test results; MCU, which is connected to the colorimetric module, electrode voltage control and current detection module, control module, display and operation module, and is used to calculate the COD concentration based on the digestion time and electrode current, calculate the total phosphorus concentration based on the RGB value of the water sample, and display the calculation results through the display and operation module; It also receives operation instructions from the display and operation module and sends control instructions to the control module.

2. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 1, characterized in that, The MCU stores the COD concentration calculation model and the total phosphorus concentration calculation model; The COD concentration calculation model is as follows: Among them, t0 is the digestion start time, t1 is the digestion end time, I0 is the base current, I1 is the digestion current, k COD is the fitting parameter, c COD is the COD concentration; The total phosphorus concentration calculation model is as follows: c TP =k R c TP,R +k G c TP,G +k B c TP,B Among them, c TP is the total phosphorus concentration, c TP,R 、c TP,G 、c TP,B are the total phosphorus concentrations calculated based on the R, G, and B channels, respectively. R 、k G 、k B is the fitting parameter, R, G, B are the values ​​of the three channels R, G, B respectively, a R 、a G 、a B 、b R 、b G 、b B are the fitting parameters respectively.

3. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 1, characterized in that, The digestion module includes a digestion tank, electrodes located in the digestion tank and an ultraviolet light source whose illumination range covers the anode surface in the electrode. The water inlet and outlet of the digestion tank serve as the inlet and outlet of the digestion module.

4. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 3, characterized in that, The ultraviolet light source is an ultraviolet lamp with a wavelength less than 385 mm.

5. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 3, characterized in that, The electrodes are a three-electrode system.

6. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 1, characterized in that, The color development module includes a color development pool, a color developer storage tank, a second pump and a color development valve. The second pump and the color development valve are located on the connecting pipeline between the color developer storage tank and the color development pool. The water inlet and outlet of the color development pool serve as the inlet and outlet of the color development module.

7. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 1, characterized in that, The colorimetric module includes a colorimetric cell, a light source and a color sensor. The light source is a visible light source. The color sensor is installed on the outer wall of the transparent colorimetric cell to test the RGB value of the water sample in the colorimetric cell.

8. A water quality detection device for simultaneously detecting COD and total phosphorus according to claim 7, characterized in that, The visible light source is a white LED lamp.

9. A detection method based on a water quality detection device for simultaneously detecting COD and total phosphorus according to claim 2, characterized in that: The following steps are involved: S1, start the cleaning liquid storage tank to clean the digestion module, color development module and colorimetric module; S2, control the water sample to flow in until the digestion module is full, and turn off pump No. 1; S3, applies voltage to the electrodes in the digestion module, records the digestion start time, digestion end time and digestion current, and transmits them to the MCU to calculate the COD concentration; S4, control the water sample to flow into the color development module until it fills the color development module, and turn off pump No. 1; automatically add excess color development agent during the process of the water sample flowing into the color development module; S5, controls the water sample to flow in until it fills the colorimetric module, tests the RGB value of the water sample, and transmits it to the MCU to calculate the total phosphorus concentration; S6, start the cleaning liquid storage tank, clean the digestion module, color development module and colorimetric module, and the test ends.

10. The detection method of a water quality detection device for simultaneously detecting COD and total phosphorus according to claim 9, characterized in that: Before detecting COD and total phosphorus in water samples, the fitting parameters in the COD concentration calculation model and the total phosphorus concentration calculation model are calibrated with standard water samples.

Images