Sediment microbial fuel cell sensor and method for monitoring methane emission

Abstract

The invention discloses a sediment microbial fuel cell sensor and method for monitoring methane emission. The sediment microbial fuel cell sensor comprises an anode, an external resistor, a reference electrode, a reference electrode chamber, a data collector and a monitoring terminal, the anode is buried in wetland bottom mud and is connected in series with the external resistor and the reference electrode; the reference electrode chamber floats in overlying water of wetland bottom mud, the reference electrode chamber is of a hollow cylindrical structure with an open bottom and a sealed top, the bottom of the reference electrode chamber is isolated from the overlying water by adopting a proton exchange membrane, an electrolyte solution is filled in the reference electrode chamber, and the reference electrode penetrates through the top of the reference electrode chamber and is inserted into the electrolyte solution; the external resistor is connected in parallel with a data collector, and the data collector sends collected electric signals to a monitoring terminal. Based on existing researches, the number of electrogenic bacteria in soil and the number of methanogens are found to have high correlation, so that the voltage of the sediment microbial fuel cell can be used as a monitoring index for monitoring the methane emission flux of the methanogens.

Description

Technical Field

[0001] The invention belongs to the technical field of ecological environmental protection, and in particular relates to a sediment microbial fuel cell sensor and method for monitoring methane emissions. Background Art

[0002] Wetland environments such as rice fields, ponds, lakes, rivers, and oceans produce greenhouse gas methane, and detecting methane emissions in these environments is of great significance for evaluating carbon emissions. Currently, many countries are conducting large-scale monitoring of methane emissions from global wetlands, but the methane detection methods used, such as the static chamber method (PLOS ONE, 2021, e0256796), infrared spectroscopy (Journal of Agricultural Meteorology, 2021, 77:160-165), and gas flux tower positioning monitoring method (Environmental Research Letter. 2021, 044038), all have problems such as cumbersome operation, high labor and detection costs.

[0003] Existing studies have found that electricity-producing bacteria are common in soil and wetland sediments, and Geobacter ( Geobacter )、Clostridium( Clostridium )、Pseudomonas( Pseudomonas ) and other electrogenic bacterial genera, and Desulfurobacterium ( Desulfobulbus )、Pseudomonas( Pseudomonas) and other electrogenic bacteria; studies have shown that both electrogenic bacteria and methanogens are anaerobic microorganisms, and both need to decompose soil organic matter to obtain the energy needed for growth. Both prefer a soil environment with a neutral pH, and some methanogens and electrogenic bacteria also form a symbiotic relationship through interspecies electron transfer. Therefore, the number of electrogenic bacteria in the soil is highly correlated with the number of methanogens (FEMS Microbiology Ecology, 2019, 95:fiz018); Therefore, the electricity production capacity of soil electrogenic bacteria can characterize the methane emissions of methanogens. The power generation capacity of soil electrogenic bacteria can be reflected by the voltage data of sediment microbial fuel cells (SMFCs) constructed in wetlands. However, since the voltage data is the difference between the cathode potential and the anode potential, and the cathodes of reported SMFCs are all immersed in the overlying water of wetlands such as rice fields, rivers and lakes, with dissolved oxygen as the electron acceptor (Science of Total Environment, 2020, 748:141544; Environmental Science, 2015, 36:3926-3934), the cathode potential often fluctuates due to changes in physical and chemical factors such as the dissolved oxygen concentration of the overlying water. In addition, rainfall and drought can also greatly affect the stability of the cathode potential, resulting in the SMFC voltage not being able to fully reflect the power generation capacity of electrogenic bacteria in the soil under field conditions.

[0004] Therefore, it is necessary to design the sensor so that the cathode potential is not affected by the properties of the wetland overlying water and the weather and remains constant. In this way, the difference in SMFC voltage only depends on the difference in the electricity production capacity of the electrogenic bacteria attached to the anode surface in the soil. The SMFC voltage can be used to accurately reflect the electricity production capacity of the soil electrogenic bacteria. Summary of the invention

[0005] The object of the present invention is to provide a sediment microbial fuel cell sensor and method for monitoring methane emissions.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions: A sediment microbial fuel cell sensor comprises an anode, an external resistor, a reference electrode, a reference electrode chamber, a data collector and a monitoring terminal; The anode is buried in the wetland bottom mud and connected in series with the external resistance and the reference electrode through a wire; The reference electrode chamber floats in the overlying water of the wetland sediment. The reference electrode chamber is a hollow cylindrical structure with an open bottom and a sealed top. The bottom is isolated from the overlying water by a proton exchange membrane. The reference electrode chamber is filled with an electrolyte solution. The reference electrode passes through the top of the reference electrode chamber and is inserted into the electrolyte solution. The external resistor is connected in parallel with a data collector, and the data collector is connected to the monitoring terminal via an electrical signal.

[0007] Furthermore, the anode is made of stainless steel, graphite or carbon felt.

[0008] Furthermore, the reference electrode is a silver chloride electrode.

[0009] Furthermore, the electrolyte solution is a saturated potassium chloride solution.

[0010] In one embodiment of the present invention, a solar panel is used to provide power for the data collector. The reference electrode chamber is fixed on a floating ring, and the floating ring allows the reference electrode chamber to float in the overlying water of the wetland bottom mud; a support rod is also fixed on the floating ring for setting up the solar panel.

[0011] The method for monitoring methane emissions using the sediment microbial fuel cell sensor comprises the following steps: Step 1, fixing a proton exchange membrane at the bottom opening of a reference electrode chamber, pouring an electrolyte solution into the reference electrode chamber, inserting a reference electrode through the top of the reference electrode chamber into the electrolyte solution, and floating the reference electrode chamber in the overlying water of the wetland sediment; Step 2, burying the anode in the wetland sediment and connecting it in series with the external resistance and the reference electrode through a wire; Step 3: connect the data collector to the external resistor in parallel, collect voltage data of the external resistor through the data collector, and send it to the monitoring terminal to obtain real-time voltage data for monitoring methane emissions.

[0012] The key to the present invention is to control the cathode potential without being disturbed by external factors and to keep it constant. Therefore, a silver chloride reference electrode is used as the cathode, and the cathode reaction is AgCl + e = Ag + Cl - , thereby using silver chloride rather than dissolved oxygen in the overlying water as the electron acceptor.

[0013] On the one hand, the sediment microbial fuel cell (SMFC) sensor for monitoring methane emissions provided by the present invention uses a reference electrode as a cathode and saturated potassium chloride as an electrolyte solution to ensure that the cathode reaction (AgCl + e = Ag +Cl - ) released Cl - Does not change the electrolyte solution Cl - The Ag produced by the cathode reaction is solid and will not change the ion concentration of the solution. On the other hand, the closed structure of the reference electrode chamber can also ensure that the electrolyte solution will not be diluted by rainfall, nor will it evaporate and dry due to long-term sunny and hot weather. The proton exchange membrane at the bottom of the reference electrode chamber allows a small amount of H + Entering the reference electrode chamber, the Cl produced by the cathode reaction -The pairing achieves charge balance, so it can achieve the purpose of stabilizing the cathode potential under field conditions. Therefore, the difference in SMFC voltage depends only on the difference in the power generation capacity of the electrogenic bacteria attached to the anode surface in the soil, and the SMFC voltage can be used to accurately reflect the power generation capacity of the electrogenic bacteria in the soil. Based on the inventor's previous research, it was found that the number of electrogenic bacteria in the soil is highly correlated with the number of methanogens, so the voltage of SMFC can be used as a monitoring indicator for monitoring the methane emission flux of methanogens.

[0014] The sensor of the present invention can monitor the methane emission flux remotely and in real time online. The monitoring result is intuitively presented in the form of a voltage curve. The sensor is light, labor-saving, low-cost, and the monitoring process is pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The structure diagram of the sediment microbial fuel cell sensor of the present invention is shown in FIG. 1 , wherein: 1 is an anode, 2 is a wire, 3 is an external resistor, 4 is a reference electrode, 5 is a reference electrode chamber, 6 is a floating ring, 7 is a proton exchange membrane, 8 is a data collector, 9 is a solar panel, 10 is a support rod, and 11 is a monitoring terminal.

[0016] Figure 2 The methane emission flux measured by the static box method in the field during the flooded growth period of rice in Example 1 and the voltage signal measured by the present invention, r in the figure represents the correlation coefficient between the methane emission flux and the voltage signal, p<0.001 indicates that the correlation between the methane emission flux and the voltage reaches an extremely significant level. The error bar is the standard error of three repeated samples.

[0017] Figure 3 The methane emission flux measured by the static box method in the summer of 2024 and the voltage signal measured by the present invention in Example 2, and the methane emission flux measured by the static box method in the winter of 2023 and the voltage signal measured by the present invention, r in the figure represents the correlation coefficient between the methane emission flux and the voltage signal in summer and winter, p<0.001 indicates that the correlation between the methane emission flux and the voltage reaches an extremely significant level. The error bar is the standard error of three repeated samples. DETAILED DESCRIPTION

[0018] The preferred embodiments of the present invention will be described in detail below in conjunction with examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0019] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0020] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources. Example 1

[0021] In a rice field in Jiangning District, Nanjing, gas collection was carried out using the static box method starting from the first day after transplanting. At the same time, three boxes were set up as three replicates, each of which was about 5 cm deep in the soil and covered the rice. Gas was collected once every six days, and three replicate gas samples were collected each time. The sampling time was 14:00-16:00 until the 61st day after transplanting. The gas was stored in a 20 mL vacuum gas sampling bottle, and the methane concentration was determined by gas chromatography.

[0022] At the same time, on the third day after transplanting, the location of gas collection in the static box was constructed as follows Figure 1 The three sensors shown are used as three replicates. The anode stainless steel tube 1 (φ3.0 cm×20 cm) is completely inserted into the bottom mud, and the titanium wire conductor 2 is led out. The reference electrode chamber 5 has an inner diameter of 5 cm and a height of 5 cm. The proton exchange membrane 7 with a diameter of 6 cm is fixed to the foam float 6 by screws at the bottom. The closed reference electrode chamber 5 is filled with 95 mL of saturated potassium chloride solution. The diaphragm end of the reference electrode 4 is immersed in the potassium chloride solution. The reference electrode 4 is connected in series with the anode 1 through a 1000 Ω external resistor 3. The data logger 8 is used to record and remotely send a voltage data to the monitoring terminal 11 at 15:00 every day until the 61st day after transplanting.

[0023] like Figure 2 As shown, there is a very significant correlation between the voltage of the sensor constructed by the present invention and the methane emission flux. Example 2

[0024] In the artificial wetland in the greenhouse of Nanjing Normal University Xianlin Campus, three sensors were built with reference to Example 1, and a data collector was used to record and remotely send a voltage data every 15 minutes. At the same time, the static box method was used for gas collection, and three boxes were arranged as three repetitions, each box was about 5 cm into the wetland sediment, and one day in summer and winter was selected respectively. Gas was collected 5 times within 40 hours, and 3 repeated gas samples were collected each time. The gas was stored in a 20 mL vacuum gas collection bottle, and the methane concentration in the collected gas was determined by gas chromatography.

[0025] like Figure 3 As shown, the sensor voltage and methane emission flux constructed in the summer of the present invention are significantly higher than the sensor voltage and methane emission flux in winter; and on the same day, the methane emission flux is also higher during the period when the sensor voltage is higher, indicating that the sensor voltage has a good correlation with the methane emission flux and can be used as an indicator for monitoring the methane emission flux.

Claims

1. A sediment microbial fuel cell sensor, characterized in that: It comprises an anode (1), an external resistor (3), a reference electrode (4), a reference electrode chamber (5), a data acquisition device (8) and a monitoring terminal (11); The anode (1) is buried in the wetland sediment and is connected in series with the external resistor (3) and the reference electrode (4) via a conductor (2); The reference electrode chamber (5) floats in the overlying water of the wetland sediment. The reference electrode chamber (5) is a hollow cylindrical structure with an open bottom and a sealed top. The bottom is isolated from the overlying water by a proton exchange membrane (7). The reference electrode chamber (5) contains an electrolyte solution. The reference electrode (4) passes through the top of the reference electrode chamber (5) and is inserted into the electrolyte solution. The external resistor (3) is connected in parallel with a data collector (8), and the data collector (8) transmits the collected electrical signals to a monitoring terminal (11).

2. The sediment microbial fuel cell sensor according to claim 1, characterized in that: The material of the anode (1) is stainless steel, graphite or carbon felt.

3. The sediment microbial fuel cell sensor according to claim 1, characterized in that: The reference electrode (4) is a silver chloride electrode.

4. The sediment microbial fuel cell sensor according to claim 3, characterized in that: The electrolyte solution is a saturated potassium chloride solution.

5. A method for monitoring methane emissions using a sediment microbial fuel cell sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1, fixing a proton exchange membrane (7) at the bottom opening of a reference electrode chamber (5), pouring an electrolyte solution into the reference electrode chamber (5), inserting a reference electrode (4) through the top of the reference electrode chamber (5) into the electrolyte solution, and floating the reference electrode chamber (5) in the overlying water of the wetland sediment; Step 2, burying the anode (1) in the wetland sediment, and connecting it in series with the external resistor (3) and the reference electrode (4) through the wire (2); Step 3, connecting the data collector (8) and the external resistor (3) in parallel, collecting voltage data of the external resistor (3) through the data collector (8), and sending it to the monitoring terminal (11), so as to obtain real-time voltage data for monitoring methane emissions.

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