CN114965611B - Microbial fuel cell sensor - Google Patents
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Abstract
The invention belongs to the technical field of new energy and environmental engineering, and provides a microbial fuel cell sensor which comprises a hollowed-out shell, a pretreatment layer, a miniature motor, an anode, a reference electrode, a Rujin capillary tube, a data acquisition part and an energy acquisition part. The microbial fuel cell sensor is of an open-circuit design, gets rid of the ancient plate mode of a traditional microbial fuel closed loop, simplifies the structure of the sensor to the greatest extent, reduces the equipment cost, improves the sensitivity, shortens the response time, and meets the actual application requirements; the direct current micro motor drives the anode to rotate, so that the sensor sensitivity is prevented from being reduced due to the too thick mixed bacterial film; the data acquisition part and the energy acquisition part can realize in-situ, online and real-time monitoring, and overcome the difficulty of remote transmission of field data; the pretreatment layer can reduce the interference of other substances (such as heavy metals) on the sensor, ensure the stable operation of the sensor, and can realize in-situ, rapid and real-time monitoring of the nitrate concentration in water.
Description
Technical Field
The invention belongs to the technical field of new energy and environmental engineering, and particularly relates to a microbial fuel cell sensor.
Background
Nitrate is one of the important existence forms of nitrogen element, is widely existing in natural water bodies, and the content of the nitrate in the water bodies is higher and higher along with the development of socioeconomic. Researches show that when the inorganic nitrogen content in the water body is more than 200mg/L, the algae bloom phenomenon can be possibly caused, and the red tide phenomenon is caused at the estuary and the bay, so that the water body is anoxic, a large amount of water body organisms die, and the ecological environment is seriously destroyed. Methemoglobinemia can be caused if humans drink water containing a large amount of nitrate for a long period of time. Although nitrate itself is not toxic to humans, it can be reduced to nitrite in humans, which has the ability to reduce ferric iron in hemoglobin to ferrous iron and denature newly produced red blood cells to lose oxygen carrying capacity, and the patient's body appears blue or bluish purple, which is known as blue infant disease in infants. In addition, nitrate is often present in water bodies along with acute contaminants such as tetrafluoroethylene pesticides and the like, and the acute contaminants are stably present through a series of biochemical actions, which is not beneficial to the normal operation of a drinking water treatment system and threatens the safety of drinking water. Therefore, timely and effective monitoring of nitrate in water is urgently needed to maintain the stability of the ecological system and ensure the drinking safety of human beings.
At present, the monitoring of nitrate in water is mainly carried out by a physical and chemical analysis method, and relies on complex large-scale instruments and equipment, so that the monitoring method is not suitable for the development of an online water quality monitoring system, for example, ultraviolet spectroscopy and ion chromatography require complicated sample pretreatment processes and professional operations, and the hysteresis of monitoring cannot rapidly cope with water quality changes and take effective measures. The portable ion selective electrode is developed to overcome the defect of heavy weight of large-scale monitoring equipment, however, the used selective permeable membrane is easy to be interfered by other ions, such as the influence of pH on the device is great, the reproducibility of the electrode is not strong, and the influence factors of the service life of the electrode are large, so that the electrode still has a plurality of problems for in-situ long-term monitoring. In recent years, the rising biosensor opens up a new way for environmental monitoring, while most researches focus on early warning of toxic substances, such as luminous bacteria, algae and biological fish water environment, methods and devices for detecting conventional pollutants such as nitrate have been developed, such as a biological enzyme sensor, which has higher selectivity and lower detection limit, however, because of shorter service life (about 5 days), enzyme activity is greatly affected by environment, so that the biological enzyme sensor cannot be widely applied in the field of environmental monitoring.
Disclosure of Invention
The invention provides a microbial fuel cell sensor, which aims to solve the problems that when a traditional closed-circuit microbial fuel cell sensor monitors nitrate in water, the response time of the device is relatively long, the stability of the device is poor due to the fact that other substances (such as heavy metal, ferric iron, sulfate and the like) in the water are easy to interfere, and the sensitivity of the sensor is reduced due to the fact that an aged biomembrane cannot be updated in time.
The invention provides a microbial fuel cell sensor having the features that it comprises: the hollow shell is provided with an opening at the top and is internally used as a reaction cavity; the pretreatment layer is arranged on the hollowed-out shell, and water enters the reaction cavity after being pretreated by the pretreatment layer; the miniature motor is arranged at the top end of the hollowed-out shell; the anode is used for adsorbing electrogenesis bacteria, is positioned in the reaction cavity and is connected with the output end of the miniature motor through a conductive metal wire, so that the anode rotates under the drive of the miniature motor; the reference electrode is positioned in the reaction cavity and is arranged beside the anode; one end of the Rujin capillary tube is electrically connected with the reference electrode, and the other end of the Rujin capillary tube is separated from the anode by a preset distance; the data acquisition part is electrically connected with the anode, the reference electrode and the micro motor and is used for measuring the voltage between the anode and the reference electrode and controlling the rotation frequency of the micro motor; and the energy acquisition part is electrically connected with the anode and the micro motor and is used for collecting charges on the anode so as to supply power to the micro motor.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: the data collection part comprises a micro-control module, an analog-to-digital conversion module, a wireless communication module, a clock module and a data storage module, wherein the micro-controller sets the measurement frequency of the analog-to-digital conversion module and the rotation frequency of the micro motor according to the clock real-time module, the analog-to-digital conversion module measures the voltage between the anode and the reference electrode according to the measurement frequency, the micro-control module calculates the concentration of nitrate in the water body according to the voltage, the clock module records the time corresponding to each concentration, the data storage module stores the concentration and the time corresponding to each concentration to obtain monitoring data, and the wireless communication module sends the monitoring data to an external coordinator.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: the energy collection part comprises a charge pump, a super capacitor, a switch and a direct current converter, wherein the charge pump is electrically connected with the anode, electric energy on the anode is collected to charge the super capacitor, the super capacitor is automatically charged and discharged under the control of the switch, and the direct current converter boosts the electric energy released by the super capacitor and provides the boosted electric energy for the miniature motor.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: the hollow shell is a double-layer metal net, the pretreatment layer is formed by filling cellulose cation adsorbent in the double-layer metal net, the thickness of the pretreatment layer is 0.5 cm-1.5 cm, and the surface of the cellulose cation adsorbent is provided with surface active groups.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: wherein the surface active group is any one or more of aldehyde group, amino group or sulfonic group.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: wherein tungsten carbide nano particles are adhered to the surface of the anode, and the average load is 1.15mg/cm 2 。
The microbial fuel cell sensor provided by the invention can also have the following characteristics: wherein the anode is made of conductive, corrosion-resistant and biocompatible materials.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: wherein the predetermined distance is less than or equal to the outer diameter of the thin end of the rujin capillary.
The microbial fuel cell sensor provided by the invention can also have the following characteristics: wherein the culturing of the electrogenic bacteria on the anode comprises the following steps: step S1, a typical double-chamber microbial fuel cell is constructed, and an anode chamber and a cathode chamber are separated by a cation exchange membrane; step S2, injecting a mixed solution obtained by mixing an anode culture solution and inoculated anaerobic sludge according to a volume ratio of 4:1 into an anode chamber, and injecting a cathode culture solution into a cathode chamber; step S3, placing an anode in an anode chamber and connecting with the anode of the MFC, placing a counter electrode in a cathode chamber and connecting with the cathode of the MFC, and placing an Ag/AgCl reference electrode near a working electrode in the anode chamber; and S4, starting the MFC by adopting a constant anode potential intermittent feeding mode, replacing the cathode culture solution and the mixed solution in the anode chamber at regular time, and taking out the anode when the MFC obtains constant voltage output, namely, the maximum voltage of three continuous days is kept constant, so as to complete the culture of the electrogenesis bacteria.
Effects and effects of the invention
According to the microbial fuel cell sensor provided by the invention, a novel open-circuit microbial fuel cell nitrate sensor is constructed by the anode, the reference electrode, the data acquisition part and the energy acquisition part, nitrate is used as an electron acceptor, the pressure drop generated by competing electrons in the biological anode is used as a sensitive signal, and the nitrate concentration in the effluent can be monitored in situ and in real time after signal conversion and transmission. Compared with the traditional double-chamber or single-chamber closed loop sensor, the open-circuit design gets rid of the ancient board mode of the traditional microbial fuel closed loop, simplifies the structure of the sensor to the greatest extent, reduces the equipment cost, improves the sensitivity, shortens the response time, and meets the actual application requirements; the direct current micro motor drives the anode to rotate, so that the sensor sensitivity is prevented from being reduced due to the too thick mixed bacterial film; the data acquisition part and the energy acquisition part can realize in-situ, online and real-time monitoring, and overcome the difficulty of remote transmission of field data; the pretreatment layer can reduce the interference of other substances (such as heavy metals) on the sensor, and ensure the stable operation of the sensor.
In addition, compared with the traditional closed loop fuel cell sensor, the open circuit can not cause the conditions of anode pH drop and cathode pH rise, and the pH of the throttling solution does not need to be regulated. And the open circuit does not need long-distance electron transmission, reduces the electrode potential, improves the reaction rate of nitrate, further enhances the sensitivity of the sensor and shortens the response time.
In addition, compared with the traditional closed loop sensor, the organic matter concentration is not easy to influence the open circuit voltage, and has better stability. The pretreatment layer wrapped near the electrode forms a protective barrier, so that the hydraulic impact of the sensor in water can be reduced, a certain buffer effect is achieved, and good environmental conditions are created for microorganisms adsorbed on the surface of the electrode.
Therefore, when the microbial fuel cell sensor provided by the invention is used for monitoring nitrate in water, the substrate in water can be degraded by means of the electroactive microorganisms enriched by the anode to perform power supply operation, no additional electric energy input is needed, and the microbial fuel cell sensor is energy-saving and environment-friendly; can play a certain role in purifying while monitoring the water quality; the equipment is simple to maintain and the running cost is low; the water quality change is directly converted into an electric signal which is easy to measure, and the structure is simple; the raw water is used as a culture medium, so that the nitrate concentration in water can be monitored in situ, quickly and in real time.
Drawings
FIG. 1 is a schematic diagram of the structure of a microbial fuel cell sensor in an embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of a microbial fuel cell sensor in an embodiment of the present invention;
FIG. 3 is a linear fit plot of pressure drop versus nitrate concentration in an embodiment of the invention;
FIG. 4 is a graph of the removal rate results for cellulose cation-sorbents in an example of the invention;
FIG. 5 is a comparison of sulfate interference results in an example of the present invention; and
fig. 6 is a comparison of ferric ion interference results in an example of the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement of the purposes and the effects of the present invention easy to understand, a microbial fuel cell sensor according to the present invention will be specifically described below with reference to the examples and the accompanying drawings.
Fig. 1 is a schematic structural view of a microbial fuel cell sensor in an embodiment of the present invention.
As shown in fig. 1, the microbial fuel cell sensor 100 includes a hollowed-out housing 101, a pretreatment layer 102, a micro-motor 103, an anode 104, a reference electrode 105, a rujin capillary 106, a data acquisition portion 107, and an energy acquisition portion 108.
The hollowed-out shell 101 is a double-layer stainless steel metal net, is open at the top and is internally used as a reaction cavity. The volume of the reaction cavity is 10 ml-50 ml. In this embodiment, the hollow housing 101 has an inner diameter of 5cm and an outer diameter of 6cm.
The pretreatment layer 102 is formed by filling a cellulose cation adsorbent in a double-layer stainless steel metal net 101, and the thickness of the pretreatment layer 102 is 0.5 cm-1.5 cm. The surface of the selected cellulose cation adsorbent is provided with surface active groups. The surface active group is any one or more of aldehyde group, amino group or sulfonic group. In this embodiment, the thickness of the pretreatment layer 102 is 1.0cm. The water body enters the reaction chamber after being pretreated by the pretreatment layer, so that the pretreatment layer 102 is used for removing heavy metal ions in water and organic matters which can be adsorbed by the heavy metal ions.
The packing thickness of the cellulose cation adsorbent in the double-layer stainless steel net should ensure that the adsorbent does not run off from the stainless steel net, and enough gaps should be reserved between the adsorbents to allow water to penetrate into the reaction cavity. The cellulose cation adsorbent needs to be replaced periodically, usually in two years, and can be taken out for verification by the formulated water body containing nitrate, and the cellulose cation adsorbent is replaced when the detected nitrate concentration deviates by more than 5% from the actual concentration.
The micro motor 103 is a direct current motor and is fixed with the top of the hollowed-out shell 101 through threads.
The anode 104 is used for adsorbing electrogenesis bacteria, is positioned in the reaction cavity, is connected with the output end of the micro motor 103 through a conductive metal wire 109, such as a titanium wire, and is driven by the micro motor 103 to rotate at fixed time.
The anode 104 can be used as anode material, and has the characteristics of conductivity, corrosion resistance and good biocompatibility. Anode 104 may be a graphite rod electrode (4 cm long, 2cm diameter) or a graphite felt electrode (1 cm x 5cm x 0.2 cm).
The tungsten carbide nano particles are stuck on the surface of the anode 104 by using 5w% Nafion solution as adhesive, and the average load is 1.15mg/cm 2 。
The anode 104 is washed with deionized water to remove surface impurities, soaked with 1mol/LNaOH for 1h, washed with deionized water, dried in a 50 ℃ oven, soaked with 1mol/L HCl for 1h, washed with deionized water, and dried for later use.
The reference electrode 105 is an Ag/AgCl electrode, is positioned in the reaction chamber, and is disposed beside the anode 104.
One end of the rujin capillary tube 106 is electrically connected with the reference electrode 105 through a titanium wire, and the other end is separated from the surface of the anode 104 by a predetermined distance. The predetermined distance is less than or equal to the outer diameter of the thin end of the gold capillary. In this example, the predetermined distance is 3mm.
The tip of the rujin capillary 106 is located as close to the surface of the electrode under investigation as possible, reducing the ohmic potential drop as much as possible. But not too close, otherwise, obvious shielding effect can be generated on the surface of the electrode to influence current distribution. In order to reduce the ohmic drop of the solution without producing a significant shielding effect and to increase the accuracy of the potentiometric data, the distance of the rufiu capillary 106 from the surface of the electrode should not be smaller than the outer diameter of the thin end of the Yu Lujin capillary.
The data acquisition unit 107 and the energy acquisition unit 108 are hermetically sealed together with the micro motor 103.
The anode 104 and the reference electrode 105 are electrically connected to the data acquisition unit 107 via a titanium wire, and the voltage between the anode and the reference electrode is measured. And the data acquisition part 107 is also electrically connected with the micro motor 103 to control the rotation frequency of the micro motor.
The anode 104 is electrically connected to the energy collection unit 108 by a titanium wire, and the micro motor 103 is electrically connected to the energy collection unit 108, so that the energy collection unit 108 collects electric charges from the anode 104 and supplies the electric charges to the micro motor 103.
Fig. 2 is a schematic diagram of the operation of a microbial fuel cell sensor in an embodiment of the present invention.
As shown in fig. 2, the microbial fuel cell sensor 100 workflow is as follows:
the data acquisition unit 107 includes a micro control module, an analog-to-digital conversion module, a wireless communication module, a clock module, and a data storage module. The microcontroller sets the measurement frequency of the analog-digital conversion module and the rotation frequency of the micro motor according to the clock real-time module, the analog-digital conversion module measures the voltage between the anode 104 and the reference electrode 105 according to the measurement frequency, the micro control module calculates the concentration of nitrate in the water body according to the voltage, the clock module records the time corresponding to each concentration, the data storage module stores the concentration and the time corresponding to each concentration to obtain monitoring data, and the wireless communication module sends the monitoring data to an external coordinator.
Specifically, the analog-to-digital conversion module is electrically connected with the anode 104 and the reference electrode 105 through titanium wires, and the micro-control module is electrically connected with the micro-motor 103. The micro control module is a microcontroller and is used for controlling and coordinating the operation of the whole equipment, and voltage data are set to be collected every 1 min. The analog-to-digital conversion module is an analog-to-digital converter, converts the acquired voltage into a digital signal, and obtains the nitrate concentration by an internal program of the microcontroller. The clock module is a real-time clock and records the time corresponding to each data; and (3) measuring. The data storage module stores the monitoring data, and the monitoring data before one month is automatically cleared in order to ensure sufficient storage space. The wireless communication module adopts a Zigbee wireless sensing technology, has the characteristics of short distance, low speed and high efficiency, and transmits real-time monitoring data to an external Zigbee coordinator so as to realize remote monitoring of nitrate.
As a further optimization, the microcontroller employs a 16-bit ultra low power mixed signal processor MSP430F149, commercially available from texas instruments. It integrates many analog circuit peripherals (e.g., ADC, DAC, analog comparator, etc.) and commonly used digital modules (e.g., SCI, SPI, PC, PWM, CAP, timer/timer) inside the chip.
As a further optimization, the digital-to-analog converter adopts an AD7194, which is a low-noise complete analog front end suitable for high-precision measurement applications. It integrates-a low noise 24-bit sigma-delta analog-to-digital converter (ADC), the low noise gain level on-chip means that small signals can be directly input.
The energy harvesting portion 108 includes a charge pump, a super capacitor, a switch, and a dc converter. The charge pump is electrically connected with the anode 104, electric energy on the anode 104 is collected to charge the super capacitor, the super capacitor is automatically charged and discharged under the control of the switch, and the direct current converter boosts the electric energy released by the super capacitor and provides the boosted electric energy to the load micro motor 103 and elements in the data acquisition part 107.
Specifically, the charge pump collects electrical energy from the anode 104, and the super capacitor serves as an energy storage capacitor to store the electrical energy. When the voltage values at the two ends of the energy storage capacitor reach the threshold value, the capacitor starts to discharge under the control of the switch, and the voltage is boosted to 5V through the direct current converter to supply power for the load, namely the miniature motor 103; when the voltage of the super capacitor is reduced to the threshold value, the switch is opened, and the super capacitor starts the charging process. The energy storage capacitor is automatically charged and discharged, the system is operated circularly, and the micro motor 103 works intermittently.
In use, the microbial fuel cell sensor 100 is placed in a body of water to be monitored. The water body is a water body with relatively stable microorganism and organic matter conditions, such as a drinking water source area, a pond lake with little fluctuation of the water body conditions, and the like. Before the water sample enters the sensor, heavy metal ions (Cu 2+ 、Hg 2+ 、Cr 6+ Etc.) and a portion of the suspended organics are first encapsulated in the fibers near the electrodeThe water sample after pretreatment enters a reaction chamber to be adsorbed by the cation adsorbent, microorganisms are gradually gathered on the anode 104 to form an electrogenesis bacterial film 200, electrons generated by organic matters which are degraded by the microorganisms and enter the reaction chamber are accumulated on the electrode in the process of forming the electrogenesis bacterial film 200, the electrode potential finally tends to be stable, and the organic matters in the water body continuously enter the organic matters in the reaction chamber to form the maximum open circuit potential without influencing the potential change. When Nitrate (NO) appears in water 3 - ) When the method is used, bioelectrochemical denitrification reaction can be carried out:
the reduction of the dissimilated nitrate to ammonium (DNRA) can also occur, and how the nitrate reacts is not predicted to date, but both reactions consume electrons accumulated on the electrode and thus create a voltage drop. Through an early-stage linear fitting experiment, the concentration of nitrate in water can be calculated according to the pressure drop, and the purpose of monitoring the nitrate in water is achieved.
Nitrate with different concentrations is added to an in-situ water source (also a water source of a place needing to be monitored) for the early linear fitting experiment, and then pressure drop and concentration tests are carried out. The experimental process is specifically as follows: when the sensor operates stably in the simulated water sample, 1mg/L, 5mg/L, 10mg/L, 20mg/L, 30mg/L and 40mg/L nitrate solutions are respectively prepared and introduced into the sensor at the flow rate of 5ml/min, the change condition of the voltage is recorded by utilizing a voltage data acquisition system, after each concentration is introduced, the voltage of the sensor is recovered to a stable state for 30min, and then the next nitrate concentration experiment is carried out. The test results are shown in FIG. 3.
FIG. 3 is a linear fit plot of pressure drop versus nitrate concentration in an embodiment of the invention.
As shown in FIG. 3, the pressure drop and the nitrate concentration show good linear relationship (R 2 = 0.9844), the concentration of nitrate in water can be calculated through the feedback of the voltage signal, and the purpose of monitoring the nitrate in water is achieved. When the nitrate concentration is lower than 1mg/LOr more than 40mg/L, the pressure drop is not obvious, and larger deviation exists.
When the water quality of the water body does not have large fluctuation, chemical energy in the water is converted into electric energy through electrogenerated bacteria on the surface of the anode, the whole sensor is in a stable electric storage state, when the electrode voltage is equal to the maximum open-circuit voltage value and maintained for 5min, the charge pump starts to charge the super capacitor, and if the open-circuit voltage is reduced and changed, the charging is immediately suspended, so that the accuracy of voltage drop data is ensured. When the voltage at two ends of the capacitor reaches a threshold value during charging, the capacitor starts to discharge, and the voltage is converted into 5V through direct current conversion and is supplied to a load. Under the condition of sufficient current, the super capacitor can be fully charged in tens of seconds, automatic circulation charging and discharging are easy to realize, and the load operates once at intervals.
The miniature direct current motor is started to drive the anode below to rotate, and the biomembrane (namely the electrogenesis bacterial film) on the surface of the anode and water generate shearing force in the tangential direction, so that the falling-off of the aged biomembrane is accelerated, the updating of the biomembrane is promoted, and the sensitivity of the sensor is ensured; the real-time clock enables all monitoring data to have corresponding time, data which cannot be sent in time are stored, and when the super capacitor discharges, the data are transmitted to the coordinator through the wireless communication technology Zigbee, so that the monitoring problem of a remote area is solved.
In order to verify the adsorption rate of the pretreatment layer to heavy metal ions in water, a removal rate experiment was performed. Cu of 1mg/L was formulated separately 2+ 、Hg 2+ 、Cr 6+ The solution of heavy metal ions is respectively passed through three identical self-made filter membranes filled with cellulose cation adsorbent with the thickness of 1cm at the flow rate of 5ml/min, and the concentration of the metal ions in water is detected by ICP-MS, so that the effect of the adsorbent on removing various heavy metal ions is obtained. The test results are shown in FIG. 4.
FIG. 4 is a graph showing the results of the removal rate of the cellulose cation-adsorbent in the example of the present invention.
As can be seen from fig. 4, after the water sample passes through the pretreatment layer 102, heavy metal ions Cu in the water 2+ 、Hg 2+ 、Cr 6+ The removal rate of the catalyst reaches 87%, 84% and 85%, respectively, and the removal efficiency is good.
The present example also examined the effect of different concentrations of interfering ions, sulfate and ferric ions, which are commonly available as electron acceptors, on the conventional closed circuit and sensor of the present example, resulting in fig. 5 and 6.
FIG. 5 is a comparison of sulfate interference results in an example of the present invention; fig. 6 is a comparison of ferric ion interference results in an example of the present invention.
Sulfate interference experimental protocol: 0.3698g, 0.4438g, 0.5177g and 0.5917g of sodium sulfate are respectively weighed and dissolved in 1L of simulated water (corresponding to 250mg/L, 300mg/L, 350mg/L and 400mg/L of SO) 4 2- ) The sensor of the embodiment and the common commercial closed circuit sensor are sequentially fed at a flow rate of 5ml/min, the voltage change of the two sensors is recorded by a voltage acquisition system, and after each concentration is fed, the next concentration experiment is performed after the sensor voltage is recovered to a stable state for 30 min.
Ferric ion interference experimental protocol: weighing 0.0014g, 0.0019g, 0.0024g and 0.0029g of ferric trichloride respectively, dissolving in 1L of simulated water (equivalent to 0.3mg/L, 0.4mg/L, 0.5mg/L and 0.6mg/L of Fe) 3+ ) The operation was consistent with the sulfate.
From the experimental results of fig. 5 and 6, it can be seen that the stability of the sensor of this embodiment is very little affected by the interfering ions, and the stability is better than that of the conventional closed-circuit sensor.
When the sensor of the embodiment is used, the sensor can be placed in a water body to be monitored to culture the electrogenerated bacteria in situ, and can also be used for rapidly culturing the electrogenerated bacteria in a laboratory. The in-situ culture of the electrogenesis bacteria requires a long time, and the electrogenesis can be carried out for monitoring about 2 months. The sensor for culturing the electrogenesis bacteria in the laboratory can be placed into the water body to be monitored after being cultured for about 2 weeks, and the sensor can be normally monitored and used after about 1-2 days.
The culturing of the electrogenic bacteria on the anode comprises the following steps:
step S1, a typical double-chamber microbial fuel cell is constructed, and an anode chamber and a cathode chamber are separated by a cation exchange membrane;
step S2, injecting a mixed solution obtained by mixing an anode culture solution and inoculated anaerobic sludge according to a volume ratio of 4:1 into the anode chamber, and injecting a cathode culture solution into the cathode chamber;
step S3, placing the anode in the anode chamber and connecting with the anode of the MFC, placing a counter electrode in the cathode chamber and connecting with the cathode of the MFC, and placing an Ag/AgCl reference electrode in the anode chamber near the working electrode;
and S4, starting the MFC by adopting a constant anode potential intermittent feeding mode, replacing the cathode culture solution and the mixed solution in the anode chamber at regular time, and taking out the anode when the MFC obtains constant voltage output, namely the maximum voltage of three continuous days is kept constant, so as to complete the culture of the electrogenerated bacteria.
Specifically, the preparation steps of the anode mixed bacterial film laboratory in the laboratory are as follows: a typical dual-chamber microbial fuel cell was constructed using plexiglas with anode and cathode chamber liquid volumes of 50mL and 50mL, respectively, separated by a cation exchange membrane. The anode graphite rod was fixed to the top of the reactor (MFC, common commercial fuel cell sensor) with titanium wire. The cathode (counter electrode) is a carbon fiber brush with the length of 3cm and the diameter of 2cm, surface impurities are washed off by deionized water, soaked by acetone for 24 hours, then put into a muffle furnace, burned for 30 minutes at 400-600 ℃, finally put into deionized water for flushing, and then put into a baking oven at 50 ℃ for drying for standby. An Ag/AgCl electrode was inserted near the anode as a reference electrode. The anode culture solution simulates the water quality of natural water, and comprises the following components:
TABLE 1 composition of anode culture solution
| Composition of the components | Concentration (g/L) |
| CH 3 COONa | 1.64 |
| NH 4 Cl | 0.31 |
| CaCl 2 ·2H 2 0 | 0.1 |
| MgCl 2 ·6H 2 O | 0.1 |
| KH 2 PO 4 | 4.4 |
| K 2 HPO 4 ·3H 2 O | 3.4 |
| Mineral solution | 12.5mL/L |
| Vitamin solution | 5mL/L |
The catholyte had the following composition:
TABLE 2 catholyte composition table
| Composition of the components | Concentration (g/L) |
| K 3 [Fe(CN) 6 ] | 16.64 |
| KH 2 PO 4 | 4.4 |
| K 2 HPO 4 ·3H 2 O | 3.4 |
The anode culture solution and inoculated anaerobic sludge are mixed according to the ratio of 4:1 and injected into an anode chamber, and the anaerobic sludge is obtained from the residual sludge of an anaerobic tank of a sewage treatment plant. The catholyte is directly injected into the cathode chamber, and the bottoms of the two chambers are both uniformly reacted by using a magnetic stirrer.
The MFC (fuel cell sensor) is started by adopting a constant anodic potential intermittent feeding mode, the anode of the MFC is connected with a working electrode (anode graphite rod), the cathode of the MFC is connected with a counter electrode, and the anodic potential is kept at-290 mv relative to an Ag/AgCl reference electrode (relative to SHE+197 mv). The double-chamber solution was changed daily with a syringe. When the MFC has obtained a constant voltage output, i.e. the maximum voltage for three consecutive days remains substantially constant, the anode is removed from the MFC and placed in the sensor reaction chamber, and the anodic mixed film culture is completed, which takes approximately two weeks.
In the fuel cell sensor of this embodiment, the cathode, the proton exchange membrane and the external circuit are omitted, and the fuel cell sensor is an open circuit sensor, and the electrode reaction equation is as follows:
①CH 3 COO - +2H 2 O→2CO 2 +7H + +8e -
②
therefore, compared to conventional closed loop fuel cell sensors, the open circuit does not result in a drop in anode pH and an increase in cathode pH, eliminating the need to adjust the pH of the solution.
Effects and effects of the examples
According to the microbial fuel cell sensor provided by the embodiment, the novel open-circuit microbial fuel cell nitrate sensor is constructed by the anode, the reference electrode, the data acquisition part and the energy acquisition part, nitrate is used as an electron acceptor, the pressure drop generated by competing electrons in the biological anode is used as a sensitive signal, and the nitrate concentration in the effluent can be monitored in situ and in real time after signal conversion and transmission. Compared with the traditional double-chamber or single-chamber closed loop sensor, the open-circuit design gets rid of the ancient board mode of the traditional microbial fuel closed loop, simplifies the structure of the sensor to the greatest extent, reduces the equipment cost, improves the sensitivity, shortens the response time, and meets the actual application requirements; the direct current micro motor drives the anode to rotate, so that the sensor sensitivity is prevented from being reduced due to the too thick mixed bacterial film; the data acquisition part and the energy acquisition part can realize in-situ, online and real-time monitoring, and overcome the difficulty of remote transmission of field data; the cellulose adsorbent pretreatment layer on the outer layer can reduce the interference of other substances (such as heavy metals) on the sensor and ensure the stable operation of the sensor.
In addition, compared with the existing microbial fuel cell sensor, the following advantages are provided in the embodiment:
(1) Compared with the traditional closed loop fuel cell sensor, the open circuit can not cause the condition that the pH of the anode is reduced and the pH of the cathode is increased, and the pH of the throttling solution is not required to be regulated.
(2) The open circuit does not need long-distance electron transmission, reduces the electrode potential, improves the reaction rate of nitrate, further enhances the sensitivity of the sensor and shortens the response time;
(3) Compared with the traditional closed loop sensor, the organic matter concentration is not easy to influence the open circuit voltage, and has better stability;
(4) Heavy metal ions in water are removed through a cellulose cation adsorbent, so that the stability of the sensor is improved; the adsorbent wrapped near the electrode forms a protective barrier, so that the hydraulic impact of the sensor in water can be reduced, a certain buffer effect is achieved, and good environmental conditions are created for microorganisms adsorbed on the surface of the electrode.
(5) The micro DC motor can accelerate the update of the biomembrane on the surface of the electrode, so that a thicker biomembrane is not formed, the activity of microorganisms is effectively maintained, and the sensitivity of the sensor is ensured;
(6) Wireless signal transmission is carried out through Zigbee, so that the wireless sensor can be well suitable for field wireless sensor monitoring tasks.
Therefore, when the microbial fuel cell sensor provided by the embodiment monitors nitrate in water, the substrate in water can be degraded by means of the electroactive microorganisms enriched by the anode to supply power for operation, no additional electric energy input is needed, and the microbial fuel cell sensor is energy-saving and environment-friendly; can play a certain role in purifying while monitoring the water quality; the equipment is simple to maintain and the running cost is low; the water quality change is directly converted into an electric signal which is easy to measure, and the structure is simple; the raw water is used as a culture medium, so that the nitrate concentration in water can be monitored in situ, quickly and in real time.
The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.
In practical application, the data acquisition part and the energy acquisition part can be packaged in a shell, and then a display screen is arranged outside the shell and used for displaying monitoring results and real-time.
Claims (10)
1. A microbial fuel cell sensor for monitoring the concentration of nitrate in a body of water, comprising:
the hollow shell is provided with an opening at the top and is internally used as a reaction cavity;
the pretreatment layer is arranged on the hollowed-out shell, and the water body enters the reaction cavity after being pretreated by the pretreatment layer;
the miniature motor is arranged at the top end of the hollowed-out shell;
the anode is used for adsorbing electrogenesis bacteria, is positioned in the reaction cavity and is connected with the output end of the miniature motor through a conductive metal wire so as to rotate under the drive of the miniature motor;
the reference electrode is positioned in the reaction cavity and is arranged beside the anode;
one end of the Rujin capillary tube is electrically connected with the reference electrode, and the other end of the Rujin capillary tube is separated from the anode by a preset distance;
the data acquisition part is electrically connected with the anode, the reference electrode and the micro motor and is used for measuring the voltage between the anode and the reference electrode and controlling the rotation frequency of the micro motor; and
and the energy acquisition part is electrically connected with the anode and the micro motor and is used for collecting charges on the anode so as to supply power to the micro motor.
2. A microbial fuel cell sensor according to claim 1, wherein:
wherein the data collection part comprises a micro control module, an analog-to-digital conversion module, a wireless communication module, a clock module and a data storage module,
the micro control module sets the measuring frequency of the analog-digital conversion module and the rotating frequency of the micro motor according to the clock module, calculates the concentration of nitrate in the water body according to the voltage,
the clock module records the corresponding time of each concentration,
the analog-to-digital conversion module measures the voltage between the anode and the reference electrode according to the measurement frequency,
the data storage module stores the concentration and obtains monitoring data at the moment corresponding to each concentration,
the wireless communication module transmits the monitoring data to an external coordinator.
3. A microbial fuel cell sensor according to claim 2, wherein:
wherein the energy collection part comprises a charge pump, a super capacitor, a switch and a direct current converter,
the charge pump is electrically connected with the anode, electric energy on the anode is collected to charge the super capacitor, the super capacitor is automatically charged and discharged under the control of the switch, and the direct current converter boosts the electric energy released by the super capacitor and provides the boosted electric energy for the miniature motor.
4. A microbial fuel cell sensor according to claim 1, wherein:
the hollow shell is a double-layer metal net, the pretreatment layer is formed by filling cellulose cation adsorbent in the double-layer metal net, the thickness of the pretreatment layer is 0.5 cm-1.5 cm, and the surface of the cellulose cation adsorbent is provided with surface active groups.
5. A microbial fuel cell sensor according to claim 4, wherein:
wherein the surface active group is any one or more of aldehyde group, amino group or sulfonic group.
6. A microbial fuel cell sensor according to claim 1, wherein:
wherein tungsten carbide nano particles are adhered to the surface of the anode, and the average load is 1.15mg/cm 2 。
7. A microbial fuel cell sensor according to claim 1, wherein:
wherein the anode is made of conductive, corrosion-resistant and biocompatible materials.
8. A microbial fuel cell sensor according to claim 1, wherein:
wherein the volume of the reaction cavity is 10 ml-50 ml.
9. A microbial fuel cell sensor according to claim 1, wherein:
wherein the predetermined distance is less than or equal to the outer diameter of the thin end of the gold capillary.
10. A microbial fuel cell sensor according to claim 1, wherein:
wherein the culturing of the electrogenic bacteria on the anode comprises the steps of:
step S1, a typical double-chamber microbial fuel cell is constructed, and an anode chamber and a cathode chamber are separated by a cation exchange membrane;
s2, injecting a mixed solution obtained by mixing an anode culture solution and inoculated anaerobic sludge according to a volume ratio of 4:1 into the anode chamber, and injecting a cathode culture solution into the cathode chamber;
step S3, placing the anode in the anode chamber and connecting with the anode of the MFC, placing a counter electrode in the cathode chamber and connecting with the cathode of the MFC, and placing an Ag/AgCl reference electrode near the working electrode in the anode chamber;
and S4, starting the MFC by adopting a constant anode potential intermittent feeding mode, replacing the cathode culture solution and the mixed solution in the anode chamber at regular time, and taking out the anode when the MFC obtains constant voltage output, namely the maximum voltage of three continuous days is kept constant, so as to complete the culture of the electrogenerated bacteria.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US3960673A (en) * | 1970-06-09 | 1976-06-01 | Fischer & Porter Co. | Technique for continuously analyzing the concentration of ozone dissolved in water |
| CN207623276U (en) * | 2017-12-29 | 2018-07-17 | 环境保护部南京环境科学研究所 | Utilize the device of microbiological fuel cell evaluating water quality organic contamination situation |
| CN110398529A (en) * | 2018-04-25 | 2019-11-01 | 浙江自常环保技术有限公司 | A kind of BOD water quality monitoring method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3960673A (en) * | 1970-06-09 | 1976-06-01 | Fischer & Porter Co. | Technique for continuously analyzing the concentration of ozone dissolved in water |
| CN207623276U (en) * | 2017-12-29 | 2018-07-17 | 环境保护部南京环境科学研究所 | Utilize the device of microbiological fuel cell evaluating water quality organic contamination situation |
| CN110398529A (en) * | 2018-04-25 | 2019-11-01 | 浙江自常环保技术有限公司 | A kind of BOD water quality monitoring method |
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