A long-term on-line ammonia nitrogen monitoring sensor for sewage based on electrochemical balance

Abstract

The application provides a sewage long-term online ammonia nitrogen monitoring sensor based on electrochemical balance, which comprises a conductive substrate, a reference electrode, a working electrode and a counter electrode arranged on the conductive substrate in sequence, an extension area arranged at the rear end of the working electrode as a contact area, and a POT-MWCNTs solid contact layer, an ammonium ion selective membrane layer and an amphoteric ion copolymer coating layer arranged on the contact area in sequence. The sensor is fast in response, stable, efficient and persistent, and can realize long-term online ammonia nitrogen monitoring of sewage.

Description

Technical Field

[0001] This invention relates to the field of wastewater ammonia nitrogen monitoring technology, specifically to a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium. Background Technology

[0002] Ammonia nitrogen concentration in wastewater is widely regarded as a core indicator for evaluating the operational efficiency of biological wastewater treatment processes (especially nitrification and denitrification) and for determining whether the effluent quality of wastewater treatment plants meets standards. Real-time and accurate monitoring of ammonia nitrogen concentration is not only a crucial guarantee for achieving compliant wastewater discharge, but also an effective way to realize intelligent control of wastewater treatment plants, reduce energy consumption, and lower operating costs. Currently, precision aeration technology based on real-time online ammonia nitrogen concentration feedback control has matured. By dynamically adjusting operating parameters such as aeration intensity, aeration duration, and carbon source dosage, aeration energy consumption and external carbon source consumption can be significantly reduced, thereby achieving significant economic and environmental benefits while meeting stringent discharge standards. This intelligent control mode based on real-time monitoring aligns with increasingly stringent requirements for wastewater discharge risk management.

[0003] However, currently widely used ammonia nitrogen analysis methods, such as the traditional Nessler's reagent colorimetric method, ion chromatography, and spectrophotometry, while possessing high sensitivity and reliability, generally suffer from significant drawbacks, including complex and cumbersome analytical procedures, time-consuming and labor-intensive sample pretreatment, and strong dependence on equipment. Furthermore, these laboratory analytical methods typically require manual sampling and laboratory analysis, resulting in long detection feedback cycles (usually several hours or even days), leading to significantly insufficient timeliness of analytical results. Simultaneously, the numerous manual operation steps easily introduce operational errors or human biases, resulting in poor repeatability and stability of detection results. Therefore, these methods struggle to provide real-time, accurate, and reliable water quality data for automated operation control modules in wastewater treatment plants, failing to effectively support the instantaneous decision-making and dynamic control needs of wastewater treatment processes, severely hindering further development of wastewater treatment process optimization. Therefore, there is an urgent need to develop a highly stable and accurate online electrochemical potential sensor for ammonia nitrogen detection, thereby achieving accurate and long-term real-time monitoring of wastewater ammonia nitrogen.

[0004] Solid-state ionophore selective electrode (S-ISM) sensors, based on ion carriers, offer significant advantages such as low detection limits, no need for external power supplies, fast response speeds, and low costs, leading to their widespread application in various fields. S-ISM sensors can achieve trace detection limits down to the microgram per liter (μg / L). Furthermore, the solid-state structure avoids the problems of leakage, evaporation, and inconvenient maintenance associated with traditional liquid-based potential electrodes. However, current S-ISM sensor technology still faces certain technical bottlenecks. First, S-ISM sensors are prone to signal drift during long-term continuous monitoring due to the formation of a water film at the interface between the electrode membrane and the solid, resulting in decreased stability of the potential readings. Second, in complex aquatic environments such as wastewater and groundwater, biofilm adhesion (biocontamination) easily occurs on the electrode surface, further reducing sensitivity and accuracy, and even causing the electrode to fail within days.

[0005] Currently, existing research has explored introducing conductive polymer materials (such as multi-walled carbon nanotubes (MWCNTs) and conductive polymers like PEDOT) between the S-ISM sensor membrane and the solid electrode contact layer. These methods can reduce interfacial resistance and suppress the formation of interfacial water films to some extent, but they cannot fundamentally solve the problem of biofouling during long-term use of S-ISM sensors. Furthermore, the long-term stability of these conductive materials in wastewater is also challenging. For example, MWCNTs may aggregate, and conductive polymers may gradually degrade or experience a decrease in electrochemical stability, leading to a significant reduction in reliability during long-term continuous monitoring. Hydrophilic modification of the electrode membrane surface (such as introducing polyethylene glycol (PEG), graphene oxide (GO), or silica (SiO2) nanoparticles) can effectively reduce the adhesion and contamination of microorganisms and their metabolites on the electrode surface. However, increased hydrophilicity of the S-ISM sensor membrane surface leads to the adsorption and retention of more water molecules, exacerbating the water layer formation problem at the membrane-solid electrode contact interface and causing a significant drift in the electrode potential reading. This signal drift phenomenon is particularly pronounced during long-term continuous monitoring, severely limiting the accuracy and stability of the electrode during long-term use. Therefore, there is an urgent need to develop an S-ISM ammonia nitrogen electrochemical potential sensor that can simultaneously suppress water film formation and biofouling, in order to achieve real-time online monitoring of ammonia nitrogen in wastewater with high stability and accuracy. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium.

[0007] The technical solution of this invention is:

[0008] A long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium includes a conductive substrate. A reference electrode, a working electrode, and a counter electrode are sequentially arranged on the upper surface of the conductive substrate from one side to the other along the width direction. The front ends of the reference electrode, working electrode, and counter electrode all extend to the front edge of the conductive substrate, and the rear ends extend along the length direction to the rear part of the conductive substrate, together forming an electrochemical reaction working area. The extended area at the rear end of the working electrode serves as a contact area, and the rear end of the counter electrode surrounds the contact area.

[0009] A POT-MWCNTs solid contact layer is provided above the contact area, an ammonium ion selective film layer is provided above the POT-MWCNTs solid contact layer, and an amphoteric copolymer coating is provided above the ammonium ion selective film layer.

[0010] Furthermore, the reference electrode, working electrode, and counter electrode are arranged at equal intervals, with the working electrode located at the center of the conductive substrate. The reference electrode, working electrode, and counter electrode have a wire contact strip on the side near the front end of the conductive substrate. The wire contact strip and the electrochemical reaction working area are connected by a long, thin transition strip. The area on the upper surface of the conductive substrate other than the electrochemical reaction working area is encapsulated with a dielectric protective coating.

[0011] Note: By rationally arranging the reference electrode, working electrode, and counter electrode, a stable and rapid monitoring process can be ensured.

[0012] Furthermore, the conductive substrate has a length of 35-40 mm, a width of 10-15 mm, and a thickness of 0.5-1 mm, and the contact area is circular.

[0013] Note: By properly controlling the size of the conductive substrate, overall portability can be improved while ensuring monitoring effectiveness.

[0014] Furthermore, the conductive substrate is made of glass carbon plate or dense graphite sheet.

[0015] Note: By selecting a suitable conductive substrate material, conductivity and excellent physical properties can be ensured.

[0016] Furthermore, the reference electrode, working electrode, and counter electrode are printed on the conductive substrate using screen printing technology. The printing method is as follows: First, the conductive substrate is ultrasonically cleaned for 15-20 minutes and dried. Then, carbon ink is printed 1-2 times at the working electrode position, with a total printing thickness of 8-20µm. The substrate is then dried and cured at 80-120℃ for 10-20 minutes. Next, AgCl ink is printed once at the reference electrode position, with a printing thickness of 8-20µm. The substrate is then dried and cured at 80-120℃ for 10-20 minutes. Finally, platinum ink is printed 1-2 times at the counter electrode position, with a total printing thickness of 8-20µm. The substrate is then dried and cured at 80-120℃ for 10-20 minutes.

[0017] Note: By properly controlling the printing parameters of each electrode, the printing position can be ensured to be accurate.

[0018] Further, the preparation method of the POT-MWCNTs solid contact layer is as follows: 3~4 mg of multi-walled carbon nanotubes are added to 1~2 mL of poly(3-octylthiophene-2,5-diyl), dispersed in 1~2 mL of tetrahydrofuran solution, and ultrasonically treated for 30~60 s. The resulting suspension is centrifuged at 18000~20000 rpm for 10~15 min. The separated solid material POT-MWCNTs is redispersed in 1~2 mL of tetrahydrofuran as POT-MWCNTs suspension. 10~15 μL of POT-MWCNTs suspension is dropped onto the surface of a conductive substrate and allowed to evaporate at room temperature.

[0019] Note: The preparation method of the POT-MWCNTs solid contact layer of the present invention optimizes the ion flow in the electrode and reduces the leaching rate of the ion carrier, which has the advantage of ensuring the stability of the potential response. The prepared POT-MWCNTs solid contact layer is uniform, dense and structurally stable.

[0020] Furthermore, the preparation method of the ammonium ion selective film layer is as follows: 6.5-7 parts by mass of the dodecyloxo-macrocyclic compound C 40 H 64 O 12 A selective membrane mixture is prepared by uniformly mixing 92-93 parts of plasticizer and 0.5-1 parts of tetraoctylammonium chloride. The selective membrane mixture is then mixed with 49-51 parts of polyvinyl chloride and placed together in 148-152 parts of tetrahydrofuran. The mixture is ultrasonically mixed to obtain an ammonium ion selective membrane solution. The ammonium ion selective membrane solution is drop-coated onto the POT-MWCNTs solid contact layer and dried at room temperature in the dark for 36-48 hours to obtain an ammonium ion selective membrane layer. The plasticizer is dibutyl phthalate.

[0021] Note: By introducing the dodecyloxo-macrocyclic compound C 40 H 64 O 12 As an ammonium ion carrier, its carbonyl group interacts with ammonium ions in a tetrahedral configuration, achieving highly selective recognition and response to target ions.

[0022] Furthermore, the ammonium ion selective membrane layer also contains PTFE hydrophobic modified particles. The preparation method of the ammonium ion selective membrane layer with added PTFE hydrophobic modified particles is as follows: polytetrafluoroethylene nanoparticles are uniformly dispersed in tetrahydrofuran solution, and after ultrasonic treatment for 10-15 min, a uniformly mixed dispersion is prepared with a mass concentration of 4-5%. The dispersion is mixed with the ammonium ion selective membrane solution at a volume ratio of 1:1, and then uniformly drop-coated onto the surface of the POT-MWCNTs solid contact layer. The membrane is dried at room temperature in the dark for 36-48 h to obtain the ammonium ion selective membrane layer.

[0023] Explanation: By adding hydrophobic modified polytetrafluoroethylene (PTFE) particles to modify the electrode surface, the negative charge and roughness of the electrode surface are effectively reduced, and its hydrophobicity is improved, thereby inhibiting the formation of water film and suppressing the obstruction of electron transfer by water layer penetration.

[0024] Furthermore, the preparation method of the zwitterionic copolymer coating is as follows: the zwitterionic copolymer is prepared into an aqueous solution with a mass concentration of 0.5±0.05%, and uniformly coated onto the surface of the ammonium ion selective membrane layer by drop coating or dip coating, and naturally dried at room temperature for 24~36h to form a hydrophilic nanochannel coating.

[0025] Note: Introducing a zwitterionic copolymer coating can inhibit biofilm growth.

[0026] Furthermore, the zwitterionic copolymer is trifluoroethyl methacrylate or sulfobetaine methacrylate.

[0027] Note: Trifluoroethyl methacrylate or sulfobetaine methacrylate have good inhibitory effects on biofilms.

[0028] The beneficial effects of this invention are:

[0029] This invention introduces a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, which incorporates the dodecaoxy macrocyclic compound C. 40 H 64 O 12As an ammonium ion carrier, its carbonyl group interacts with ammonium ions in a tetrahedral configuration, achieving highly selective recognition and response to target ions. Simultaneously, PTFE modification of the electrode surface effectively reduces surface negative charge and roughness, enhancing its hydrophobicity and thus inhibiting water film formation and suppressing the obstruction of electron transfer by water layer permeation. A POT-MWCNTs solid contact layer structure was designed to optimize ion flow within the electrode and reduce the leaching rate of the ion carrier, ensuring the stability of the potential response. Finally, a self-assembled zwitterionic copolymer coating was introduced to inhibit biofilm growth through the formation of a stable hydration layer and the principle of electrode surface neutrality, constructing hydrophilic nanochannels with a pore size of approximately 1 nm. This balances the electrocoulombic driving force between the ion layer and charge layer at the electrode interface in the wastewater environment, ensuring ion flux and potential stability, and significantly reducing signal drift. Ultimately, a fast-responding, stable, efficient, and continuous long-term online ammonia nitrogen monitoring sensor for wastewater was obtained. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, according to the present invention.

[0031] Figure 2 This is a top view of a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, according to the present invention.

[0032] Figure 3 This is a cross-sectional view of the contact area of ​​a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, according to the present invention.

[0033] Figure 4 This is a schematic diagram illustrating the ion selection mechanism and stability and balance optimization of a long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, according to the present invention.

[0034] Figure 5 These are six months of monitoring data of the sensor's electrochemical potential in the experimental examples of this invention.

[0035] Among them, 1-conductive substrate, 11-wire contact strip, 12-transition strip, 2-reference electrode, 3-working electrode, 4-counter electrode, 5-electrochemical reaction working area, 51-contact area, 6-POT-MWCNTs solid contact layer, 7-ammonium ion selective film layer, 8-zwitterionic copolymer coating. Detailed Implementation

[0036] Example 1: A long-term online ammonia nitrogen monitoring sensor for wastewater based on electrochemical equilibrium, such as... Figure 1As shown, the device includes a conductive substrate 1, which is 37 mm long, 12 mm wide, and 0.8 mm thick. The conductive substrate 1 is made of glassy carbon plate. A reference electrode 2, a working electrode 3, and a counter electrode 4 are sequentially arranged along the width direction from one side to the other on the upper surface of the conductive substrate 1. The front ends of the reference electrode 2, working electrode 3, and counter electrode 4 all extend to the front edge of the conductive substrate 1, and their rear ends extend along the length direction to the rear part of the conductive substrate 1, together forming an electrochemical reaction working area 5. The extended area at the rear end of the working electrode 3 serves as a contact area 51. Figure 2 As shown, the rear end of the counter electrode 4 surrounds the contact area 51, which is circular. The reference electrode 2, the working electrode 3, and the counter electrode 4 are arranged at equal intervals. The working electrode 3 is located at the center of the conductive substrate 1. The reference electrode 2, the working electrode 3, and the counter electrode 4 have a wire contact strip 11 on the side near the front end of the conductive substrate 1. There is a thin strip-shaped transition strip 12 between the wire contact strip 11 and the electrochemical reaction working area 5. The area on the upper surface of the conductive substrate 1, except for the electrochemical reaction working area 5, is encapsulated with dielectric protective paint.

[0037] The reference electrode 2, working electrode 3, and counter electrode 4 are printed on the conductive substrate 1 using screen printing technology. The printing method is as follows: First, the conductive substrate 1 is ultrasonically cleaned for 16 minutes and dried. Then, carbon ink is printed once at the working electrode 3 with a printing thickness of 15µm, and dried and cured at 100℃ for 15 minutes. AgCl ink is printed once at the reference electrode 2 with a printing thickness of 15µm, and dried and cured at 100℃ for 15 minutes. Platinum ink is printed once at the counter electrode 4 with a printing thickness of 12µm, and dried and cured at 100℃ for 15 minutes.

[0038] like Figure 1 and Figure 3 As shown, a POT-MWCNTs solid contact layer 6 is provided above the contact area 51, an ammonium ion selective film layer 7 is provided above the POT-MWCNTs solid contact layer 6, and an amphoteric copolymer coating 8 is provided above the ammonium ion selective film layer 7.

[0039] The preparation method of POT-MWCNTs solid contact layer 6 is as follows: 3.5 mg of multi-walled carbon nanotubes (MWCNTs) were added to 1.5 mL of poly(3-octylthiophene-2,5-diyl) (POT), dispersed in 1.5 mL of tetrahydrofuran solution, and sonicated for 45 s using a probe-type ultrasonic instrument. The resulting suspension was centrifuged at 19000 rpm for 12 min. The separated solid material POT-MWCNTs was redispersed in 1.5 mL of tetrahydrofuran as POT-MWCNTs suspension. 12 μL of POT-MWCNTs suspension was dropped onto the surface of conductive substrate 1 and allowed to evaporate at room temperature.

[0040] The preparation method of ammonium ion selective film layer 7 is as follows: 6.9 parts by mass of dodecyloxo-macrocyclic compound C 40 H 64 O 12 92.4 parts of plasticizer dibutyl phthalate and 0.7 parts of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture was mixed with 50 parts of polyvinyl chloride and placed together in 150 parts of tetrahydrofuran. The mixture was ultrasonically mixed evenly to obtain an ammonium ion selective membrane solution. The ammonium ion selective membrane solution was drop-coated onto the POT-MWCNTs solid contact layer 6 and dried at room temperature in the dark for 40 hours to obtain the ammonium ion selective membrane layer 7.

[0041] The zwitterionic copolymer coating 8 was prepared as follows: the zwitterionic copolymer was prepared into an aqueous solution with a mass concentration of 0.5%, and uniformly coated onto the surface of the ammonium ion selective membrane layer 7 by drop coating. It was then allowed to dry naturally at room temperature for 30 hours to form a hydrophilic nanochannel coating with a pore size of approximately 1 nm. The zwitterionic copolymer was trifluoroethyl methacrylate. The room temperature was 25℃.

[0042] Example 2: This example differs from Example 1 in that the preparation method of the ammonium ion selective film layer 7 is as follows: 6.9 parts by mass of the dodecyloxo-macrocyclic compound C 40 H 64 O 12 92.4 parts of plasticizer dibutyl phthalate and 0.7 parts of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture was mixed with 50 parts of polyvinyl chloride and placed together in 150 parts of tetrahydrofuran. The mixture was then ultrasonically mixed evenly to obtain an ammonium ion selective membrane solution.

[0043] Polytetrafluoroethylene nanoparticles were uniformly dispersed in a tetrahydrofuran solution and ultrasonically treated for 12 min to prepare a uniformly mixed dispersion with a mass concentration of 4.5%. The dispersion was mixed with the ammonium ion selective membrane solution at a volume ratio of 1:1 and then uniformly drop-coated onto the surface of the POT-MWCNTs solid contact layer 6. The membrane was dried at room temperature in the dark for 40 h to obtain the ammonium ion selective membrane layer 7.

[0044] Example 3: The difference between this example and Example 1 is that the conductive substrate 1 has a length of 35mm, a width of 10mm, a thickness of 0.5mm, and is made of dense graphite sheet.

[0045] Example 4: The difference between this example and Example 1 is that the conductive substrate 1 has a length of 40mm, a width of 15mm, and a thickness of 1mm, and the material of the conductive substrate 1 is glass carbon plate.

[0046] Note: The dimensions of the conductive substrate 1 are adjusted proportionally, and both the glass carbon plate and the dense graphite sheet have electrical conductivity and excellent physical properties.

[0047] Example 5: This example differs from Example 1 in that the reference electrode 2, working electrode 3, and counter electrode 4 are printed on the conductive substrate 1 using screen printing technology. The printing method is as follows: First, the conductive substrate 1 is ultrasonically cleaned for 15 minutes and dried. Then, carbon ink is printed once at the working electrode 3, with a printing thickness of 8µm, and dried and cured at 80°C for 10 minutes. AgCl ink is printed once at the reference electrode 2, with a total printing thickness of 8µm, and dried and cured at 80°C for 10 minutes. Platinum ink is printed once at the counter electrode 4, with a printing thickness of 8µm, and dried and cured at 80°C for 10 minutes.

[0048] Example 6: This example differs from Example 1 in that the reference electrode 2, working electrode 3, and counter electrode 4 are printed on the conductive substrate 1 using screen printing technology. The printing method is as follows: First, the conductive substrate 1 is ultrasonically cleaned for 20 minutes and dried. Then, carbon ink is printed twice at the working electrode 3, with a total printing thickness of 20µm. The substrate is then dried and cured at 120°C for 20 minutes. Then, AgCl ink is printed once at the reference electrode 2, with a printing thickness of 20µm. The substrate is then dried and cured at 120°C for 20 minutes. Finally, platinum ink is printed twice at the counter electrode 4, with a total printing thickness of 20µm. The substrate is then dried and cured at 120°C for 20 minutes.

[0049] Note: The parameters of the screen printing technology for the reference electrode 2, working electrode 3, and counter electrode 4 can be adjusted reasonably within the given parameter range.

[0050] Example 7: The difference between this example and Example 1 is that the preparation method of the POT-MWCNTs solid contact layer 6 is as follows: 3 mg of multi-walled carbon nanotubes are added to 1 mL of poly(3-octylthiophene-2,5-diyl), dispersed in 1 mL of tetrahydrofuran solution, and ultrasonically treated for 30 s. The resulting suspension is centrifuged at 18000 rpm for 10 min. The separated solid material POT-MWCNTs is redispersed in 1 mL of tetrahydrofuran as a POT-MWCNTs suspension. 10 μL of the POT-MWCNTs suspension is dropped onto the surface of the conductive substrate 1 and allowed to evaporate at room temperature.

[0051] Example 8: The difference between this example and Example 1 is that the preparation method of the POT-MWCNTs solid contact layer 6 is as follows: 4 mg of multi-walled carbon nanotubes are added to 2 mL of poly(3-octylthiophene-2,5-diyl), dispersed in 2 mL of tetrahydrofuran solution, and ultrasonically treated for 60 s. The resulting suspension is centrifuged at 20,000 rpm for 15 min. The separated solid material POT-MWCNTs is redispersed in 2 mL of tetrahydrofuran as a POT-MWCNTs suspension. 15 μL of the POT-MWCNTs suspension is dropped onto the surface of the conductive substrate 1 and allowed to evaporate at room temperature.

[0052] Note: When preparing the POT-MWCNTs solid contact layer 6, the parameters of the electrochemical deposition method can be reasonably adjusted within the given parameter range.

[0053] Example 9: The difference between this example and Example 2 is that polytetrafluoroethylene nanoparticles are uniformly dispersed in tetrahydrofuran solution, and after ultrasonic treatment for 10 min, a uniformly mixed dispersion is prepared with a mass concentration of 4%.

[0054] Example 10: The difference between this example and Example 2 is that polytetrafluoroethylene nanoparticles are uniformly dispersed in tetrahydrofuran solution, and after ultrasonic treatment for 15 minutes, a uniformly mixed dispersion is prepared with a mass concentration of 5%.

[0055] Note: The parameters for preparing PTFE hydrophobic modified particles can be adjusted reasonably within the given parameter range.

[0056] Example 11: This example differs from Example 1 in that the preparation method of the ammonium ion selective film layer 7 is as follows: 6.5 parts by mass of the dodecyloxo-macrocyclic compound C 40 H 64 O 12 92 parts of plasticizer dibutyl phthalate and 0.5 parts of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture was mixed with 49 parts of polyvinyl chloride and placed together in 148 parts of tetrahydrofuran. The mixture was ultrasonically mixed evenly to obtain an ammonium ion selective membrane solution. The ammonium ion selective membrane solution was drop-coated onto the POT-MWCNTs solid contact layer 6 and dried at room temperature in the dark for 36 hours to obtain the ammonium ion selective membrane layer 7.

[0057] Example 12: This example differs from Example 1 in that the preparation method of the ammonium ion selective film 7 is as follows: 7 parts by mass of the dodecyloxo-macrocyclic compound C 40 H 64 O 1293 parts of plasticizer dibutyl phthalate and 1 part of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture was mixed with 51 parts of polyvinyl chloride and placed together in 152 parts of tetrahydrofuran. The mixture was ultrasonically mixed evenly to obtain an ammonium ion selective membrane solution. The ammonium ion selective membrane solution was drop-coated onto the POT-MWCNTs solid contact layer 6 and dried at room temperature in the dark for 48 hours to obtain the ammonium ion selective membrane layer 7.

[0058] Note: The selection of ammonium ion-selective membrane layer 7 is the main innovation of this invention, and the parameters in Example 1 or Example 2 are preferred for optimal effect.

[0059] Example 13: The difference between this example and Example 1 is that the zwitterionic copolymer coating 8 is prepared by: preparing a zwitterionic copolymer into an aqueous solution with a mass concentration of 0.45%, uniformly coating it onto the surface of the ammonium ion selective membrane layer 7 by drop coating, and naturally drying it at room temperature for 24 hours to form a hydrophilic nanochannel coating. The zwitterionic copolymer is trifluoroethyl methacrylate.

[0060] Example 14: The difference between this example and Example 1 is that the zwitterionic copolymer coating 8 is prepared by: preparing a zwitterionic copolymer into an aqueous solution with a mass concentration of 0.55%, uniformly coating it onto the surface of the ammonium ion selective membrane layer 7 by dip coating, and naturally drying it at room temperature for 36 hours to form a hydrophilic nanochannel coating. The zwitterionic copolymer is sulfobetaine methacrylate.

[0061] Note: The zwitterionic copolymers trifluoroethyl methacrylate or sulfobetaine methacrylate have high chemical stability and a good inhibitory effect on biofilm adhesion.

[0062] Experimental Example: The electrochemical equilibrium-based long-term online ammonia nitrogen monitoring sensor for wastewater prepared in Example 1 was applied to a real wastewater environment to monitor ammonia nitrogen in the wastewater. Figure 4 It can be seen that NH4 in wastewater + First, after diffusing in water, it passes through the nanochannels (approximately 1 nm) formed by the zwitterionic copolymer coating 8 to the surface of the ammonium ion selective membrane layer 7. Simultaneously, the zwitterionic copolymer coating 8 blocks the adhesion and penetration of biological contaminants, subsequently allowing NH4 to... + The PTFE hydrophobically modified particles, combined with the substrate of the ammonium ion selective membrane layer 7, form charge separation on both sides of the membrane layer 7. This effectively prevents water from penetrating into the ammonium ion selective membrane layer 7 and affecting NH4+. + The binding process with the ammonium ion-selective membrane layer 7 substrate;

[0063] Subsequently, the ionic charge accumulated at the interface of the ammonium ion-selective film layer 7 is converted into an electron chemical potential difference by the POT-MWCNTs solid contact layer 6. This electron chemical potential difference is collected by the conductive substrate 1 and transmitted to the electrochemical workstation via the wire connected to the front end of the working electrode 3. The collected open-circuit voltage signal is then processed, such as... Figure 5 As shown in the figure, the horizontal axis represents time, and the vertical axis represents the NH4 converted from the voltage signal. + The concentration, and the resulting pattern, is represented by NH4. + The dynamic changes in concentration over time reflect a stable ammonia nitrogen signal;

[0064] The electrochemical equilibrium-based long-term online ammonia nitrogen monitoring sensor for wastewater of this invention can achieve an accuracy of over 90% in monitoring ammonia nitrogen in wastewater, far exceeding the accuracy of existing commercial in-situ ion sensors (less than 50%). It can achieve real-time in-situ monitoring for up to one month in a real wastewater environment.

Claims

1. A long-term on-line ammonia nitrogen monitoring sensor for sewage based on electrochemical equilibrium, characterized in that, The application relates to an electrochemical sensor, which comprises a conductive substrate (1), a reference electrode (2), a working electrode (3) and a counter electrode (4) arranged on the upper surface of the conductive substrate (1) from one side to the other side along the width direction, the front ends of the reference electrode (2), the working electrode (3) and the counter electrode (4) extend to the front end edge of the conductive substrate (1), and the rear ends extend to the rear part of the conductive substrate (1) along the length direction and jointly form an electrochemical reaction working area (5), wherein an extension area arranged at the rear end of the working electrode (3) is used as a contact area (51), and the rear end of the counter electrode (4) surrounds the contact area (51). A POT-MWCNTs solid contact layer (6) is arranged above the contact area (51), an ammonium ion selective membrane layer (7) is arranged above the POT-MWCNTs solid contact layer (6), and a zwitterionic copolymer coating layer (8) is arranged above the ammonium ion selective membrane layer (7). The preparation method of the POT-MWCNTs solid contact layer (6) is as follows: 3-4 mg of multi-walled carbon nanotubes are added into 1-2 mL of poly (3-octylthiophene-2, 5-diyl), dispersed in 1-2 mL of tetrahydrofuran solution, and ultrasonically treated for 30-60 s; the obtained suspension is centrifuged at a centrifugal speed of 18000-20000 rpm for 10-15 min; the separated solid material POT-MWCNTs is redispersed in 1-2 mL of tetrahydrofuran as a POT-MWCNTs suspension; and 10-15 muL of the POT-MWCNTs suspension is dropped on the surface of the conductive substrate (1) and evaporated at room temperature. The preparation method of the ammonium ion selective membrane layer (7) is as follows: 6.5-7 parts of dodecaoxacyclo compound C 40 H 64 O 12 , 92-93 parts of a plasticizer, and 0.5-1 part of tetraoctylammonium chloride are uniformly mixed to obtain a selective membrane mixture, then the selective membrane mixture is mixed with 49-51 parts of polyvinyl chloride, and is uniformly mixed in 148-152 parts of tetrahydrofuran by ultrasonic mixing, to obtain an ammonium ion selective membrane solution, wherein the plasticizer is dibutyl phthalate. PTFE hydrophobic modified particles are further added in the ammonium ion selective membrane layer (7), polytetrafluoroethylene nanoparticles are uniformly dispersed in tetrahydrofuran solution, and a uniformly mixed dispersion liquid is prepared after ultrasonic treatment for 10-15 min, the mass concentration of the dispersion liquid is 4-5%, the dispersion liquid and the ammonium ion selective membrane liquid are mixed according to a volume ratio of 1:1, the mixed liquid is uniformly dropped on the surface of the POT-MWCNTs solid contact layer (6), and the ammonium ion selective membrane layer (7) is obtained after drying at room temperature for 36-48 h under light-proof conditions.

2. The long-term on-line ammonia nitrogen monitoring sensor based on electrochemical balance for sewage according to claim 1, characterized in that, The reference electrode (2), the working electrode (3) and the counter electrode (4) are arranged at equal intervals, the working electrode (3) is located at the center of the conductive substrate (1), the reference electrode (2), the working electrode (3) and the counter electrode (4) are lead contact strips (11) near the front end of the conductive substrate (1), the lead contact strips (11) and the electrochemical reaction working area (5) are transition strips (12) in an elongated strip shape, and the regions on the upper surface of the conductive substrate (1) except the electrochemical reaction working area (5) are packaged by dielectric protective paint.

3. The long-term on-line ammonia nitrogen monitoring sensor based on electrochemical balance according to claim 1, characterized in that, The length of the conductive substrate (1) is 35-40 mm, the width is 10-15 mm, and the thickness is 0.5-1 mm, and the contact area (51) is circular.

4. The long-term on-line ammonia nitrogen monitoring sensor based on electrochemical balance according to claim 1, characterized in that, The material of the conductive substrate (1) is a glass carbon plate or a dense graphite sheet.

5. The long-term on-line ammonia nitrogen monitoring sensor based on electrochemical balance according to claim 1, characterized in that, The reference electrode (2), the working electrode (3) and the counter electrode (4) are printed on the conductive substrate (1) by a screen printing technology, and the printing method is as follows: first, the conductive substrate (1) is cleaned by ultrasonic for 15-20 min, dried, and then 1-2 times of carbon ink printing is performed at the position of the working electrode (3), the total printing thickness is 8-20 µm, and the printing is dried and cured at a temperature of 80-120 ℃ for 10-20 min; 1 time of AgCl ink printing is performed at the position of the reference electrode (2), the printing thickness is 8-20 µm, and the printing is dried and cured at a temperature of 80-120 ℃ for 10-20 min; 1-2 times of platinum ink printing is performed at the position of the counter electrode (4), the total printing thickness is 8-20 µm, and the printing is dried and cured at a temperature of 80-120 ℃ for 10-20 min.

6. The long-term on-line ammonia nitrogen monitoring sensor based on electrochemical balance according to claim 1, characterized in that, The preparation method of the zwitterionic copolymer coating (8) is as follows: the zwitterionic copolymer is prepared into an aqueous solution with a mass concentration of 0.5±0.05%, the aqueous solution is uniformly coated on the surface of the ammonium ion-selective membrane layer (7) by a drop coating or dip coating method, and the coating is naturally dried at room temperature for 24-36 h to form a hydrophilic nanochannel coating.

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