Method and system for electrochemical rapid analysis and detection of nitrogen element in water

Abstract

The invention belongs to the technical field of water quality detection and analysis, and discloses an electrochemical rapid analysis and detection method and system for nitrogen element in water, which takes water sample collection, filtration and digestion processes as a sample introduction and pretreatment unit, and takes electrolytic tank quantitative sample introduction, pH adjustment, electrochemical scanning and electrochemical reduction processes as an electrochemical treatment unit. A detection unit is composed of ammonia separation and collection and ammonia detection processes. The electrochemical analysis process is carried out in a special electrochemical reactor, and rapid analysis and detection of multiple parameters such as ammonia nitrogen, nitrate nitrogen, nitrite nitrogen and total nitrogen in water are realized through different detection process sequences. The invention provides a novel method and system for electrochemical analysis of nitrogen element pollution indexes in water, the system uses an electrochemical analysis technology to replace spectral analysis, and the system has the characteristics of no developing agent, environmental friendliness, environmental impurity interference resistance, wide applicable water quality range and multiple test indexes.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical analysis and detection of water quality, and relates to a method and system for rapid electrochemical analysis and detection of nitrogen in water. Background Art

[0002] Nitrogen is a common pollutant in water bodies. It has a wide range of sources and can easily lead to eutrophication of water bodies. my country has included many types of nitrogen pollutants in water bodies in water quality control projects. The analysis and detection of nitrogen pollution in water is an important part of controlling nitrogen pollution in water. It is of great significance to develop rapid and reliable water quality nitrogen pollutant analysis technology. Nitrogen pollutants in water can be mainly divided into suspended nitrogen particles, soluble organic nitrogen and inorganic nitrogen, among which inorganic nitrogen is mainly ammonia nitrogen, nitrate nitrogen and nitrite nitrogen. General water quality nitrogen pollution indicators include total nitrogen, total organic nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen. At present, my country has a series of standard detection methods for water quality nitrogen pollution indicators, which are mainly classified by spectrophotometry, ion chromatography, etc. However, the above methods may require the use of complex and toxic colorimetric reagents, or have problems such as long analysis time, expensive instruments, and susceptibility to environmental interference. They are difficult to apply to the scene requirements of green and rapid analysis of water quality. Therefore, it is urgent to develop new and more adaptable rapid water quality nitrogen pollutant detection and analysis technologies and equipment.

[0003] Electrochemical water quality analysis technology has the advantages of simple instruments and equipment, rapidity and sensitivity, and no need for complex reagents. It has good development prospects in the field of water quality sensing and detection. At present, ammonia-sensitive electrodes and ammonium ion-selective electrodes are used for quantitative detection of ammonia nitrogen in water. However, ammonia-sensitive electrodes are easily interfered by impurities in water, and ammonium ion-selective electrodes are easily interfered by dissolved metal ions and organic matter, resulting in large errors in practical applications. In addition, the existing electrochemical water quality analysis technology also has difficulty in achieving efficient and sensitive electrochemical quantitative detection of nitrate nitrogen, nitrite nitrogen and total nitrogen indicators. There is still a gap in the electrochemical technology and equipment system for comprehensive analysis of multiple nitrogen-containing pollutants in water.

[0004] Through the above analysis, the problems and defects of the existing technology are as follows: the electrochemical analysis and detection technology of nitrogen pollutants in water is difficult to cope with the analysis task of various nitrogen element indicators, and is easily affected by environmental interference, resulting in large errors, making the electrochemical water quality nitrogen element detection technology difficult to be widely used. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method and system for rapid electrochemical detection and analysis of nitrogen in water.

[0006] The technical solution of the present invention:

[0007] A system for rapid electrochemical analysis and detection of nitrogen in water, comprising:

[0008] The sampling and pretreatment unit includes a water sample collector, a filter and a digester; the water sample collector is used to extract water samples, and the water samples are sent to the filter through a pump and then to the digester or directly to the digester for pretreatment; the filter is used to remove trace suspended matter in the water sample before entering the digester for digestion; the digester mineralizes the organic matter in the water sample into inorganic matter, and in this process the organic nitrogen substances are completely oxidized into nitrate nitrogen; all types of nitrogen are converted into ammonia nitrogen for final quantification; the ratio of nitrate nitrogen and nitrite nitrogen is analyzed by electrochemical method, and the concentration of nitrate nitrogen and nitrite nitrogen is quantitatively calculated by indirect calculation;

[0009] The electrochemical treatment unit includes an electrolytic cell quantitative sampling module, a pH adjustment module and an electrochemical workstation module; in the electrolytic cell quantitative sampling module, a quantitative extraction device is used to feed part of the pretreated water sample into the electrolytic cell, so as to provide an accurate water sample volume for subsequent water quality index data calculation; the pH adjustment module adjusts the pH of the pretreated water sample to 12-14 by quantitatively injecting alkali solution into the electrolytic cell, thereby improving the conductivity of the pretreated water sample and providing conditions for subsequent ammonia volatilization separation; the electrochemical scanning or electrochemical reduction operation is carried out using the three-electrode mode of the electrochemical workstation module, wherein the electrochemical scanning analysis uses a cyclic voltammetry test method or a coulometric titration method, and the ratio of nitrate to nitrite is determined by analyzing the ratio of nitrate to nitrite signals; the electrochemical reduction operation electrocatalyzes the reduction of nitrate and nitrite to ammonium by applying negative electricity to the working electrode;

[0010] The detection unit uses an ammonia separation device to treat the effluent from the electrochemical treatment unit, transfers and enriches the ammonia in the effluent; and then uses an ammonia test electrode to measure the ammonia concentration of the enriched solution.

[0011] Furthermore, the digester utilizes microwave, plasma, and high-temperature chemical digestion to completely oxidize organic matter in water.

[0012] Furthermore, the electrochemical treatment unit mainly adopts an electrochemical workstation and a three-electrode system to analyze the water sample in the cathode chamber of the electrolytic cell. The cathode chamber and the anode chamber of the electrolytic cell are separated by a bipolar membrane to prevent nitrogen-containing ion exchange between the cathode chamber and the anode chamber; the anode electrolyte of the electrolytic cell is sulfuric acid, and the electrolysis of water and oxygen evolution reaction mainly occur during the electro-reduction treatment process; the volume of the cathode chamber of the electrolytic cell is a fixed value, and the top is designed as a slope to promote bubble transfer; the high end of the slope is connected to one end of a U-shaped tube, and the other end of the U-shaped tube has a sealing valve and a free liquid surface; the bottom of the cathode chamber of the electrolytic cell is provided with a water inlet and outlet and a sealing valve; the function of the U-shaped tube is to automatically adjust the pressure of the cathode chamber of the electrolytic cell to prevent excessive pressure caused by cathode gas production during the cathode electro-reduction process.

[0013] Furthermore, the cathode chamber of the electrolytic cell is switched between two valves to allow water samples to enter and exit the cathode chamber of the electrolytic cell, as well as to be flushed with clean water.

[0014] Furthermore, the analyzed water samples can be discharged after the pH is finally adjusted to neutral, without causing potential environmental pollution;

[0015] Furthermore, in the entire system, various nitrogen species are converted into ammonia nitrogen through pretreatment and electrochemical conversion; the acid solution is used to absorb the ammonia volatilized from the sample at the outlet of the electrochemical treatment unit under the condition of an air-permeable and water-tight diaphragm to achieve ammonia separation; the ammonium ions in the acid solution are analyzed using a mature ammonia analysis electrode to avoid interference from environmental impurities and extend the service life of the ammonia analysis electrode.

[0016] A method for rapid electrochemical analysis and detection of nitrogen in water, comprising:

[0017] Step 1: The water sample is sucked into the filter through the water sample collector and the pump. After the filter removes the suspended particles, the water sample enters the digester to completely mineralize the organic matter, and the nitrogen element in the organic matter is converted into nitrate nitrogen; or the water sample is sucked into the digester through the water sample collector and the pump to completely mineralize the organic matter, and the nitrogen element in the organic matter is converted into nitrate nitrogen;

[0018] Step 2: After the water sample has been injected and pretreated by the unit, alkali is added to adjust the pH before entering the electrolytic cell, and cyclic voltammetry scanning is performed to determine the ratio of nitrate and nitrite; the electrochemical reduction process reduces nitrate nitrogen and nitrite nitrogen to ammonia nitrogen through the electrocatalytic reduction of the working electrode;

[0019] NO3 - +8e - +9H + →NH4 +

[0020] NO2 - +6e - +7H + →NH4 +

[0021] Step 3: The effluent from the cathode chamber of the electrolytic cell enters the detection unit, uses the acid to absorb the ammonia in the alkaline sample through the bipolar membrane, and uses the ammonia sensor electrode to analyze the ammonium concentration in the dilute sulfuric acid;

[0022] NH3·H2O→H2O+NH 3(gas)

[0023] 2NH 3(gas) +H2SO4→(NH4)2SO4.

[0024] Beneficial effects of the present invention:

[0025] First, a new solution is proposed for the rapid analysis and detection of current electrochemical water quality nitrogen pollution indicators. Through digestion, pH adjustment, electrochemical scanning, electrochemical reduction, ammonia separation, and multiple injections, the quantitative determination of various nitrogen forms is achieved, and the interference of impurities in the water sample on the analysis can be avoided. The method has a wide range of water quality applications.

[0026] Second, the technical solution of the present invention utilizes electrochemical methods to rapidly determine a variety of nitrogen pollution indicators without the need for colorimetric agents, and is more environmentally friendly.

[0027] Third, the technical solution of the present invention utilizes filtration, digestion and electrochemical technology to ultimately convert various forms of nitrogen in water into ammonia nitrogen concentration in an acid solution, thereby avoiding the problem of environmental interferences on ammonia detection electrodes and overcoming the technical bias that electrochemical ammonia nitrogen testing is affected by interferences, resulting in unstable testing.

[0028] Fourth, compared with the traditional electrochemical method of directly analyzing the concentration of nitrate and nitrite in water, the technical solution of the present invention indirectly analyzes the concentration of nitrate nitrogen and nitrite nitrogen by analyzing the ratio of nitrate and nitrite and the final ammonium concentration, avoiding the problem of decreased test accuracy due to passivation or poisoning of the working electrode.

[0029] The technical solution of the present invention combines electrochemical technology with water sample pretreatment methods and ammonia nitrogen electrochemical sensing detection to achieve quantitative analysis and detection of various forms of nitrogen elements in water in one process, filling the technical gap in the electrochemical water quality analysis and detection industry. Under the background of green and sustainable development strategy, the technical solution of the present invention has the advantages of being fast, low-cost and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the operation flow of the method and system for rapid electrochemical analysis of nitrogen in water provided by an embodiment of the present invention;

[0031] Figure 2 is a schematic structural diagram of an electrocatalytic reactor provided by an embodiment of the present invention;

[0032] In the figure: 1a, reference electrode; 1b, cathode electrode; 1c, counter electrode; 2a, anode chamber with an opening; 2b, cathode chamber of fixed volume with a sloped top; 3a, anolyte; 3b, cathode liquid (water sample); 4, bipolar membrane; 5, U-shaped sealing tube; 6a, control valve at the top of cathode chamber; 6b, control valve at the bottom of cathode chamber; 7a, water inlet and outlet at the top of cathode chamber; 7b, water inlet and outlet at the bottom of cathode chamber. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0034] like Figure 1 As shown, the electrochemical rapid detection and analysis method and system of nitrogen in water provided by the embodiment of the present invention includes a sampling and pretreatment unit, an electrochemical analysis unit, and a detection unit. Specifically, it includes: ① water sample collection process, ② filtration process, ③ digestion process, ④ electrolytic cell and quantitative sampling process, ⑤ pH adjustment process, ⑥ electrochemical scanning process, ⑦ electrochemical reduction process, ⑧ ammonia separation and collection process, and ⑨ ammonia detection process.

[0035] The electrolytic cell structure used in the electrochemical analysis unit is as follows Figure 2 As shown, it includes a reference electrode, a working electrode, a counter electrode, a bipolar membrane, an anode and cathode chamber, a water inlet and outlet, and a voltage-stabilizing U-tube.

[0036] During the execution of the specific process, ① water sample collection process, use a pump to suck water sample, and selectively enter ② filtration or ③ digestion process through the program; ② filtration process effluent is selectively controlled by the program to enter ③ digestion or ④ electrolytic cell quantitative injection process; ④ electrolytic cell quantitative injection is controlled by the program to perform ⑤ pH adjustment or ⑦ electrochemical reduction process; ⑤ pH adjustment is alkaline and then the program controls the execution of ⑥ electrochemical scanning or ⑦ electrochemical reduction or effluent to ⑧ ammonia separation and collection process; ⑦ electrochemical reduction is followed by effluent to ⑧ ammonia separation and collection process; ⑧ ammonia separation and collection is followed by quantitative sampling to enter ⑨ ammonia detection process.

[0037] Ammonia nitrogen analysis flow path: ①→②→④→⑤→⑧→⑨; that is, ① after the water sample is collected, the insoluble substances are removed through the ② filtration process to eliminate the interference of insoluble nitrogen; ④ a quantitative (known volume) water sample enters the electrolytic cell and the concentrated alkali solution is added quantitatively through ⑤ to make the pH reach above 12; all the liquid in the electrolytic cell is transferred to the ⑧ ammonia separation part, and the ammonia in the water sample is separated through membrane separation and known volume acid absorption. Finally, the ammonia nitrogen concentration of the acid absorption liquid is measured by the ⑨ ammonia analysis electrode, and the ammonia nitrogen concentration of the water sample is calculated by the following formula:

[0038]

[0039] Among them, c 水样氨氮 The final analysis results show that the concentration of ammonia nitrogen in water (in terms of nitrogen) is in g / L; c 酸吸收氨氮 is the ammonia nitrogen concentration detected by the ammonia analysis electrode, in mol / L; V 酸吸收液 V is the volume of acid used in the ammonia separation process, in L; 进入电解池水样 is the volume of water sample entering the electrolytic cell, in L;

[0040] Total nitrogen analysis flow path: ①→③→④→⑤→⑦→⑧→⑨; that is, after ① water sample collection, it enters ③ digestion process, all types of nitrogen elements are digested and converted into nitrate nitrogen, ④ quantitative (known volume) water sample enters the electrolytic cell and through ⑤ quantitative addition of concentrated alkali solution to make the pH reach above 12; after ⑦ electrochemical reduction process, the nitrate ions (i.e. nitrate nitrogen) are all reduced to ammonia nitrogen by the electrocatalytic reduction of the working electrode, and then undergo the same analysis process of ammonia nitrogen, the total nitrogen concentration of the water sample is calculated by the following formula:

[0041]

[0042] where c 水样总氮 is the final analysis of the water quality ammonia nitrogen concentration (in nitrogen), unit is g / L; the meanings of other symbols are the same as in formula 1;

[0043] Soluble inorganic nitrogen analysis flow path: ①→②→④→⑤→⑦→⑧→⑨; It is not difficult to see that the soluble inorganic nitrogen analysis process is the same operation of total nitrogen analysis on filtered and undigested water samples, and its concentration can be obtained by analogy with the same calculation method for total nitrogen;

[0044] Soluble nitrogen analysis flow path: ①→②→③→④→⑤→⑦→⑧→⑨; It is not difficult to see that the soluble nitrogen analysis process is to analyze the total nitrogen of the filtered water sample, and its concentration can be obtained by the same calculation method as the total nitrogen;

[0045] Nitrate nitrogen and nitrite nitrogen analysis flow path: ①→②→④→⑤→⑥→⑦→⑧→⑨, analysis principle: nitrate and nitrite have different reduction potentials in electrochemical voltammetry scanning. The reduction peak intensity I of the two is analyzed by electrochemical analysis. NO3 -:I NO2 -ratio can obtain the concentration ratio of nitrate nitrogen and nitrite nitrogen; it is not difficult to see that the difference between soluble inorganic nitrogen and ammonia nitrogen, I NO3 -:I NO2 -ratio can be used to obtain the concentration of nitrate nitrogen and nitrite nitrogen, and the concentration of nitrate and nitrite in water samples can be calculated by the following formulas:

[0046]

[0047] where c 水样硝态氮 、c 水样亚硝态氮 are the nitrate nitrogen concentration and nitrite nitrogen concentration of the water sample, in g / L; Some represent the proportion of nitrate reduction signal intensity in electrochemical analysis, The part represents the proportion of the reduction signal intensity of nitrite in electrochemical analysis;

[0048] Soluble organic nitrogen: the difference between soluble nitrogen and soluble inorganic nitrogen;

[0049] In the quantitative sampling process of the electrolytic cell, the water sample is injected into the cathode chamber from the water inlet and outlet at the bottom of the cathode chamber 7b and the valve 6b, and the excess water sample is discharged through the 5U-shaped tube, the valve 6a, and the water outlet 7a; after the electrochemical treatment of the sample is completed, it is discharged through the water inlet and outlet at the bottom of the cathode chamber 7b;

[0050] In the electrochemical scanning process ⑥, three electrodes are used for testing. The electrochemical workstation uses the reference electrode 1a as the reference, applies a cyclic scanning potential to the working electrode 1b, records the current change, and calculates the peak intensity ratio of nitrate and nitrite on the basis of calibrating the reduction peak positions of nitrate and nitrite. The working part of the working electrode 1b can be made of copper, silver, nickel, gold, iron, platinum and their alloys; the working part of the counter electrode 1c can be made of titanium, ruthenium iridium titanium, iridium tantalum titanium;

[0051] In the ⑦ electrochemical reduction process, a constant current is applied between the working electrode 1b and the counter electrode 1c, and the cell voltage is monitored. A reduction reaction occurs on the working electrode 1b, and a small amount of gas that may be produced at the cathode is retained in the cathode chamber by the action of the 5U-type tube;

[0052] In the ammonia separation and collection process (⑧), the effluent from the previous process enters the separation module and is separated from the dilute sulfuric acid by a water-proof and breathable membrane. Under alkaline conditions, ammonium ions or ammonia molecules are unstable and easily volatilize ammonia gas. Under the action of concentration difference and acid-base neutralization, ammonia gas is absorbed and enriched by dilute sulfuric acid to achieve ammonia separation and collection;

[0053] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A rapid electrochemical analysis and detection system for nitrogen in water, characterized in that: include: The sampling and pretreatment unit includes a water sample collector, a filter and a digester; the water sample collector is used to extract water samples, and the water samples are sent to the filter through a pump and then to the digester or directly to the digester for pretreatment; The filter is used to remove trace suspended matter in the water sample before entering the digester for digestion; the digester mineralizes the organic matter in the water sample into inorganic matter, and in this process the organic nitrogen substances are completely oxidized into nitrate nitrogen; all types of nitrogen are converted into ammonia nitrogen for final quantification; the ratio of nitrate nitrogen and nitrite nitrogen is analyzed by electrochemical method, and the concentration of nitrate nitrogen and nitrite nitrogen is quantitatively calculated indirectly; An electrochemical treatment unit, including an electrolytic cell quantitative sampling module, a pH adjustment module and an electrochemical workstation module; In the electrolytic cell quantitative sampling module, a quantitative extraction device is used to feed part of the pretreated water sample into the electrolytic cell, providing an accurate water sample volume for subsequent water quality index data calculation; the pH adjustment module adjusts the pH of the pretreated water sample to 12-14 by quantitatively injecting alkali solution into the electrolytic cell, thereby improving the conductivity of the pretreated water sample and providing conditions for subsequent ammonia volatilization separation; the three-electrode mode of the electrochemical workstation module is used to carry out electrochemical scanning or electrochemical reduction operations, wherein the electrochemical scanning analysis uses a cyclic voltammetry test method or a coulometric titration method to determine the ratio of nitrate to nitrite by analyzing the ratio of nitrate and nitrite signals; the electrochemical reduction operation applies negative electricity to the working electrode to electrocatalyze the reduction of nitrate and nitrite to ammonium; The detection unit uses an ammonia separation device to treat the effluent from the electrochemical treatment unit, and transfers and enriches the ammonia in the effluent; The ammonia test electrode is then used to measure the ammonia concentration of the enriched solution.

2. The electrochemical rapid analysis and detection system for nitrogen in water according to claim 1 is characterized in that: The digester utilizes microwave, plasma, and high-temperature chemical digestion to completely oxidize organic matter in water.

3. The electrochemical rapid analysis and detection system for nitrogen in water according to claim 1 is characterized in that: The electrochemical treatment unit mainly adopts an electrochemical workstation and a three-electrode system to analyze the water sample in the cathode chamber of the electrolytic cell. The cathode chamber and the anode chamber of the electrolytic cell are separated by a bipolar membrane to prevent nitrogen-containing ion exchange between the cathode chamber and the anode chamber. The anode electrolyte of the electrolytic cell is sulfuric acid, and the electrolysis of water and oxygen evolution reaction mainly occur during the electro-reduction treatment process. The volume of the cathode chamber of the electrolytic cell is a fixed value, and the top is designed as a slope to promote bubble transfer; the high end of the slope is connected to one end of a U-shaped tube, and the other end of the U-shaped tube has a sealing valve and a free liquid surface; the bottom of the cathode chamber of the electrolytic cell is provided with a water inlet and outlet and a sealing valve; the function of the U-shaped tube is to automatically adjust the pressure of the cathode chamber of the electrolytic cell to prevent excessive pressure caused by cathode gas production during cathode electro-reduction.

4. The electrochemical rapid analysis and detection system for nitrogen in water according to claim 1 is characterized in that: The cathode chamber of the electrolytic cell is switched between two valves to allow water samples to enter and exit the cathode chamber of the electrolytic cell, and to be flushed with clean water.

5. A detection method for the electrochemical rapid analysis and detection system of nitrogen in water as claimed in claim 1, characterized in that: Here are the steps: Step 1: The water sample is sucked into the filter through the water sample collector and pump. After the filter removes the suspended particles, the water sample enters the digester to completely mineralize the organic matter and convert the nitrogen in the organic matter into nitrate nitrogen; or The water sample is sucked into the digester through the water sample collector and the pump to completely mineralize the organic matter, and the nitrogen element in the organic matter is converted into nitrate nitrogen; Step 2, the water sample after the sampling and pretreatment unit is added with alkali to adjust the pH and then enters the electrolytic cell to carry out cyclic voltammetry scanning to determine the ratio of nitrate and nitrite; The electrochemical reduction process reduces nitrate nitrogen and nitrite nitrogen to ammonia nitrogen through the electrocatalytic reduction of the working electrode; <h2 style=";text-align:left;direction:ltr">NO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> +8e<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> +9H<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> →NH4<h2 style=";text-align:left;direction:ltr"> + NO2 - +6e - +7H + →NH4 + Step 3: The effluent from the cathode chamber of the electrolytic cell enters the detection unit, uses the acid to absorb the ammonia in the alkaline sample through the bipolar membrane, and uses the ammonia sensor electrode to analyze the ammonium concentration in the dilute sulfuric acid; NH3·H2O→H2O+NH 3(gas) 2NH 3(gas) +H2SO4→(NH4)2SO4。

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