A device and method for enhancing denitrification by biological electrochemical energy self-circulation under wet-dry cycles

Abstract

The application discloses a kind of enhanced denitrification device and method of biological electrochemical energy self-circulation under wet-dry alternation, and it relates to rainwater treatment technical field, device includes biological retention area and automatic control module;Biological retention area from bottom to top includes gravel drainage layer, filler layer, soil layer, water storage layer in sequence;First electrode is arranged in filler layer, and second electrode is arranged in soil layer;Automatic control module includes soil humidity sensor, super capacitor, LOGO controller, double-pole double-throw relay, voltage module, solar cell panel and battery.The device is used in the present application to promote the decomposition of organic matter and generate bioelectricity using microbial fuel cells during drought period, and to strengthen electron transfer denitrification by coupling microbial metabolism using microbial electrolysis cell with an external voltage during rainfall period, achieving efficient denitrification of the system by various measures.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rainwater treatment, more particularly to a device and method for enhanced denitrification by biological electrochemical energy self-circulation under dry-wet alternation. BACKGROUND

[0002] With the acceleration of urbanization, the contribution of urban stormwater runoff to nitrogen pollution of receiving water bodies is increasingly significant. As a key green infrastructure, the biological retention system is widely adopted and constructed. It has good removal effect on organic matter, total suspended solids, heavy metals and other pollutants in runoff. However, the traditional biological retention system lacks anoxic conditions and electron donors, resulting in unstable denitrification efficiency.

[0003] Biological electrochemical technology is an economical and effective green technology that improves the shortcomings of long start-up time and low denitrification rate of biological methods. It mainly includes microbial fuel cells (MFC) and microbial electrolysis cells (MEC). The former oxidizes organic matter by electroactive functional bacteria at the anode and releases electrons, which are transmitted to the cathode through an external circuit to form an electric current during oxygen reduction, achieving energy recovery. The latter activates the electron transfer pathway of electroactive denitrifying bacteria to improve the reduction efficiency of nitrate / nitrite to nitrogen.

[0004] In recent years, biological electrochemical technology has been introduced into artificial wetlands and biological retention systems, which can enhance electron transfer capacity, promote deep denitrification, and achieve simultaneous removal of nitrogen and organic matter and energy recovery. However, conventional MFC and MEC are usually applied to stable continuous wastewater treatment, which cannot adapt to the intermittent rainfall conditions of urban rainwater treatment. In addition, they require an external circuit, which is complex to maintain and increases costs. Moreover, they have the limitations of low energy recovery efficiency or excessive energy consumption, which cannot maximize their rainwater denitrification capacity in the unique microenvironment of dry-wet alternation.

[0005] Therefore, there is an urgent need for a denitrification method that can fully utilize the dry-wet alternation characteristics of rainwater, automatically switch operating states, achieve energy self-sufficiency and efficient electron transfer, and improve the removal capacity of biological retention systems for nitrogen pollutants. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application aims to provide a device and method for enhanced denitrification by biological electrochemical energy self-circulation under dry-wet alternation. The method couples MFC and MEC to the biological retention system, creating a denitrification process that does not require external energy supply, has energy self-circulation, rainfall self-adaptation, and carbon source and electron dual collaborative supply effect, solving the problem of unstable denitrification efficiency caused by weak electron supply capacity of traditional biological retention systems.

[0007] In order to achieve the above object, the present application adopts the following technical solutions:

[0008] The device for enhanced denitrification by biological electrochemical energy self-circulation under wetting and drying cycles comprises a biological retention zone and an automatic control module.

[0009] The biological retention zone comprises, from bottom to top, a gravel drainage layer, a filler layer, a soil layer and a water storage layer, the filler layer is provided with a composite electrode structure formed by using a titanium mesh as an electrode base and wrapping an electrically conductive carbon felt as a first electrode, the soil layer is provided with a composite electrode structure formed by using a titanium mesh as an electrode base and wrapping an electrically conductive carbon felt as a second electrode, water is introduced into the device at the top and discharged through a raised drain pipe provided in the gravel drainage layer at the bottom.

[0010] The automatic control module comprises a soil humidity sensor, a super capacitor, a LOGO controller, a double-pole double-throw relay, a voltage module, a solar cell panel and a battery.

[0011] The soil humidity sensor is arranged on one side of the top of the soil layer and connected with the second electrode.

[0012] One end of the double-pole double-throw relay is connected with the soil humidity sensor, and the other end is connected with the first electrode.

[0013] One end of the voltage module is connected with the double-pole double-throw relay, and the other end is connected with the super capacitor.

[0014] One end of the LOGO controller is connected with the double-pole double-throw relay, and the other end is connected with the battery, and the battery is connected with the solar cell panel.

[0015] Preferably, the filler layer is a composite filler of wood chips, graphite and ceramic particles.

[0016] Preferably, the composite filler comprises, by volume percentage, 25-35% of wood chips, 8-12% of graphite powder and 55-65% of ceramic particles.

[0017] Preferably, the first electrode and the second electrode have a vertical spacing of 30cm.

[0018] The present application sets up a flooded zone by raising the drain pipe, i.e. a 30cm-thick filler layer in the middle of the biological retention zone, which is continuously saturated during rainfall, effectively prolonging the hydraulic retention time of rainwater. Meanwhile, the filler is improved to construct a composite filler of wood chips, graphite and ceramic particles, wood chips are used as a slow-release carbon source to promote heterotrophic denitrification, graphite particles are added to enhance the electrical conductivity, and ceramic particles are added to improve the adsorption capacity of the system, thus completing the structural improvement of the biological retention system.

[0019] Specifically, sawdust: as a sustainable natural carbon source, slowly releases biodegradable organic carbon, provides substrate for heterotrophic denitrifying bacteria and electroactive microorganisms, and improves the denitrification rate of the system; at the same time, it provides a porous structure to promote microbial attachment and reproduction.

[0020] Graphite powder: excellent electrical conductivity and chemical stability, significantly improve the overall electrical conductivity of the filler, and strengthen the electron transfer process; at the same time, the surface activity of graphite particles is high, which can promote the enrichment of electroactive microorganisms (such as Geobacter, Shewanella).

[0021] Ceramsite: plays a role in skeleton support, ensures the mechanical strength of the filter material and good hydraulic conditions; its rough surface provides a stable attachment substrate for functional microbial communities, maintains the water permeability of the system and the formation of oxygen / current gradient.

[0022] MFC dry period power storage for MEC rainfall period denitrification energy consumption, realize the zero external supply of electric energy; sawdust oxidation generates small molecule organic matter for rainfall period denitrification; realize the synergistic promotion of various measures to promote efficient denitrification. The present application adopts titanium mesh as the electrode matrix, and outer package conductive carbon felt to form a composite electrode structure, so as to balance the electrochemical performance and mechanical strength, improve the power generation efficiency of anode and the oxygen reduction capacity of cathode. At the same time, the electrode spacing is 30 cm to ensure that the system exhibits the best treatment efficiency.

[0023] Because of the randomness, instantaneity and regional difference of rainfall events, the present application realizes the intelligent dynamic switching of MFC / MEC working mode by real-time monitoring of humidity through soil humidity sensor and using LOGO controller and double-pole double-throw relay. The soil humidity sensor continuously monitors the soil moisture saturation in real time, and transmits the signal to the LOGO controller for logical judgment. The LOGO controller can dynamically adjust the power distribution in combination with the charge and discharge state of the super capacitor, realize the efficient closed loop of energy recovery-storage-release, and improve the energy efficiency.

[0024] Based on the above, the present application provides a kind of enhanced denitrification method of bioelectrochemical energy self-circulation under dry-wet alternation, comprising:

[0025] (1) the soil humidity sensor continuously monitors the soil moisture saturation in real time, and transmits the signal to the LOGO controller for logical judgment;

[0026] (2) when the soil moisture saturation is monitored to be greater than 60%, the LOGO controller determines that the system enters the rainfall period, and then supplies power to the double-pole double-throw relay, triggers the electrode polarity reversal, the soil layer becomes anode, and the filler layer becomes cathode. The device automatically switches to MEC mode operation, and the super capacitor starts discharging to provide power for MEC to strengthen the denitrification process.

[0027] This stage relies on the electrical energy stored in the super capacitor during the dry period to drive. The anode enhances nitrification under the applied voltage, and the cathode undergoes denitrification. On the one hand, the cathode directly provides electrons (2NO3 - +12H + +10e - →N2+6H2O); on the other hand, the small-molecule organic carbon source produced and enriched during the dry period participates in the reaction as an electron donor. The synergy of electron supply and organic carbon source significantly promotes the efficient reduction of nitrate nitrogen to nitrogen;

[0028] In this stage, nitrifying bacteria (such as Nitrosomonas and Nitrobacter) in the soil layer (anode area) are enhanced, and NH4 + is converted to NO3 - under aerobic conditions, providing a denitrification substrate.

[0029] In the filler layer cathode area, sulfur autotrophic denitrifying bacteria (such as Thiobacillus) and electroactive denitrifying bacteria (such as Pseudomonas) obtain electrons through an external voltage to reduce NO3 - to N2, completing autotrophic / heterotrophic coupled denitrification.

[0030] (3) When the soil water saturation is <30% and the rainwater residence time is >1h, the controller determines that it is in the dry period, at which time the power supply to the double-pole double-throw relay is cut off, the electrode polarity returns to the initial state, the soil layer is the cathode, and the filler layer is the anode. The system switches back to the MFC mode and operates, and microorganisms oxidize organic matter in the anode to produce electricity and store it in the super capacitor;

[0031] The core process of this stage is the oxidation of sawdust by anode microorganisms to produce electrons and protons. Electrons flow through the external circuit to the cathode, and protons migrate through the proton exchange medium to the cathode. In the cathode, dissolved oxygen accepts electrons and protons to be reduced to water (O2+4H + +4e - →2H2O), which drives the directional flow of electrons to generate electrical energy. The generated electrical energy is stored in the super capacitor to provide energy for the subsequent MEC mode. At the same time, the sawdust is decomposed into small-molecule organic carbon sources in the anode, which reserves key electron donors for the denitrification process during the rainy period. At this time, the dominant bacterial community is electroactive heterotrophic bacteria (such as Geobacter, Shewanella, etc.), which form a biofilm in the anode area. By oxidizing organic matter (COD) in sawdust-graphite filler to release electrons and transfer to the cathode, electricity generation and organic matter degradation are achieved in coordination. This stage realizes carbon source decomposition and conversion and electrical energy storage;

[0032] (4) The current humidity state does not meet any of the above trigger conditions, and the system will continue to monitor the environmental water level dynamically, waiting for the switching condition to be met. This stage helps the microbial community to self-regulate and enrich, providing a micro-ecological preparation for the next mode switching.

[0033] Through this closed-loop control logic based on the soil humidity threshold, the system can intelligently and autonomously adjust the working state, dynamically respond to the alternating changes of the environment, and does not require manual intervention.

[0034] Through the above technical solution, compared with the prior art, the present application has the following beneficial effects:

[0035] 1) Carbon source self-utilization: During the drought period, the MFC is used to oxidize and degrade sawdust into small molecule carbon sources that can be utilized by microorganisms. During the rainfall period, the accumulated carbon sources are used for denitrification in the system, realizing self-sufficient and recycling utilization of carbon sources, solving the problem of low utilization rate of carbon sources in traditional systems. The total nitrogen removal rate is significantly improved, and efficient and stable denitrification is realized.

[0036] 2) Energy self-circulation: The bioelectrochemical technology is fully utilized to produce and use electricity, dynamically respond to environmental changes without manual intervention, realize the dynamic switching of "photosynthesis energy storage" and "respiration energy consumption" similar to plants, realize energy "self-production and self-sale", and full-automatic operation with zero external energy supply.

[0037] 3) Rainfall self-adaptation: The system builds a dynamic reversal model of electrode polarity that is adapted to the natural dry and wet environment, uses a humidity sensor to sense the change of soil humidity, automatically drives a double-pole double-throw relay to switch the capacitor connection mode, realizes the dynamic reversal of the electrode polarity. According to the dry and wet conditions of the environment, different operation modes are automatically entered, the electrode microorganisms oxidize sawdust, the MFC generates electricity, and the capacitor stores energy during the drought period, and the capacitor discharges to supply MEC for enhanced denitrification during the rainfall period. It truly realizes the integration of microbial metabolism, electrochemical electron transfer and environmental trigger response mechanism in technical mechanism, effectively extends the service life of the system, and truly meets the environmental changes.

[0038] The application scenario of the method is wide, especially in the areas that require efficient denitrification, carbon emission reduction, intelligent management and resource and energy recycling. The following is the main application scenario analysis of the method: In the aspect of urban rainwater management, the facility is suitable for rainwater collection and treatment in urban roads, residential areas and other areas, reduces urban runoff pollution, improves the utilization efficiency of rainwater resources, and protects groundwater resources; In the aspect of industrial wastewater treatment, the facility can be used to treat a large amount of wastewater generated in industrial areas, reduce pollutant emissions, and realize the recycling of water resources; In the aspect of ecological restoration, the facility can be used for wetland restoration, river purification, etc., improve the service function of the ecological system, and enhance the beauty of the landscape.

[0039] As a demonstration city of sponge city construction in China, the method can be fully applied to local construction. Daqing is located in a high latitude area, and it rains a lot in summer. The facility can effectively collect and treat rainwater, improve the city's flood control and drainage capacity, reduce the risk of waterlogging, and improve the efficiency of rainwater resource utilization, achieving sustainable management of rainwater. For a large amount of wastewater generated by the local oil industry, the facility can be used for purification and treatment, reducing pollutant emissions and helping environmental protection. In the process of local ecological restoration and urban greening, it can also be applied to wetland restoration, providing new ideas for ecological restoration projects. In addition, the method has the characteristics of energy self-sufficiency, combined with the relatively complete solar power supply in the local area, reducing energy costs, and using waste plants and mineral modified fillers, which is efficient and economical. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0041] Figure 1 Figure A is a structure diagram of the device of the present application;

[0042] Figure 2 Figure B is a structure diagram of the device of the present application;

[0043] Figure 3 Figure C is a schematic diagram of the device during the drying period;

[0044] Figure 4 Figure D is a schematic diagram of the device during the rainfall period;

[0045] Figure 5 Figure E is a comparison chart of nitrate nitrogen removal in Example 1 for 120 days;

[0046] Figure 6 Figure F is a dry-wet alternating operation chart of BRS and BES-BRS in Example 1;

[0047] Figure 7 Figure G is a chart of nitrate nitrogen and ammonia nitrogen removal efficiency of BRS and BES-BRS during long-term operation in Example 2;

[0048] In the figures:

[0049] 1- water storage layer; 2- soil layer; 3- filler layer; 4- gravel drainage layer; 5- second electrode; 6- first electrode; 7- soil moisture sensor; 8- double-pole double-throw relay; 9- voltage module; 10- super capacitor; 11- LOGO controller; 12- battery; 13- solar panel. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0051] Embodiment 1

[0052] The enhanced denitrification method of bio-electrochemical energy self-circulation under dry-wet alternation adopted in this embodiment constructs a bio-electrochemical coupling biological retention system (BES-BRS) as an experimental group in a test device, and sets a conventional biological retention system (BRS) without an electrochemical module as a control group.

[0053] The experimental columns are all organic glass cylinders with a height of 100 cm and a diameter of 30 cm. The structure from bottom to top is as follows: a 20 cm gravel drainage layer, an internal particle size of 10-20 mm gravel, a 30 cm filler layer, the filler layer of the experimental group is a composite conductive filler, which is uniformly filled by mixing wood chips, graphite particles and ceramsite at a volume ratio of 3:1:6, the wood chips used are screened and treated to provide a sustainable carbon source; the graphite particles are used to improve the overall conductivity; the ceramsite is used to maintain a good pore structure, enhance the structural stability and microbial adhesion; the control group is filled with sandy soil, a 30 cm soil layer (mixed with brown soil and sand at a ratio of 2:8), a 20 cm water storage layer, and a rainwater inlet at the top.

[0054] The experimental group system is configured with a first electrode located in the filler layer and a second electrode located in the soil layer, connected with a super capacitor (2.7V 10F) and a double-pole double-throw relay, and combined with a humidity sensor to realize the switching of electrode polarity and energy self-circulation operation under dry-wet alternation.

[0055] The test uses artificially configured rainwater (rainfall intensity 0-10 mm), and the influent NO3 - -N concentration is 12±2 mg / L, and NH4 + -N concentration is 5±2 mg / L, and the system operation cycle is 4 days of dry period and 1 day of rainfall period. The experiment is continuously operated for 120 days, and the influent and effluent samples are periodically collected for nitrogen analysis.

[0056] The experimental results are as follows: after 120 days of operation verification, the removal rates of nitrate nitrogen and ammonia nitrogen of the system are stably 75~80% and 95~98% respectively, which are increased by more than 25% compared with the system without electrochemical enhancement; the real-time removal efficiency of nitrate nitrogen under dry-wet alternation is as high as 80~83%, which is increased by more than 25% compared with the control group.

[0057] Embodiment 2

[0058] Based on the embodiment 1, the adaptability and denitrification performance of the method of the application under the condition of moderate rain are further simulated.

[0059] The influent is artificial simulated rainwater (rainfall intensity 0-25mm), NO3 - -N concentration is 13±3mg / L, NH4 + -N is 3±2mg / L. The experimental period is the same as that of the dry period of 4 days and the rainfall period of 1 day, and the system is continuously operated for 90 days. The nitrogen concentration changes in the influent and effluent are continuously monitored during the system operation, and the stability and response efficiency of the system under high impact hydraulic conditions are evaluated.

[0060] The test results are as follows:

[0061] NO3 - -N removal rate is maintained at 85~91%;

[0062] NH4 + -N removal rate is 92~95%;

[0063] The capacitive discharge and polarity reversal during the rainfall period can still successfully drive the electrochemical denitrification;

[0064] Compared with the traditional BRS system, the removal rate of NO3 - -N is still improved by 15~25%.

[0065] The results show that: the method of the application still has good self-adaptability and denitrification stability under the condition of change of rainfall intensity, and the polarity switching and capacitive discharge process do not appear delay or failure phenomenon. It shows that the application has high nitrogen removal effect under the conditions of light rain and moderate rain.

[0066] Embodiment 3

[0067] Based on the embodiment 1, the adaptability and denitrification performance of the method of the application under the condition of heavy rain are further simulated.

[0068] The influent is artificial simulated rainwater (rainfall intensity 25-50mm), NO3 - -N concentration is 12±3mg / L, NH4 + -N is 4±2mg / L. The experimental period is the same as that of the dry period of 4 days and the rainfall period of 1 day, and the system is continuously operated for 60 days. The nitrogen concentration changes in the influent and effluent are continuously monitored during the system operation, and the stability and response efficiency of the system under high impact hydraulic conditions are evaluated.

[0069] The test results are as follows:

[0070] NO3 - -N removal rate is maintained at 72~75%;

[0071] NH4 +-N removal rate is 83~87%;

[0072] During periods of rainfall, capacitor discharge and polarity reversal can still successfully drive electrochemical denitrification.

[0073] The results show that the method of the present invention still possesses good adaptability and denitrification stability under conditions of continued increase in rainfall intensity, and no hysteresis or failure occurs in the polarity switching and capacitor discharge processes. This indicates that the present invention still has a highly efficient denitrification effect even under heavy rain conditions.

[0074] Example 4

[0075] This embodiment is used to verify the effect of the frequency variation of the dry-wet alternation cycle on the denitrification effect of the system of the present invention. The influent water quality and other conditions are kept the same as in Example 1, and only the operating cycle is adjusted as follows: 2 days for the dry period and 1 day for the rainy period.

[0076] Even with increased rainfall frequency and shorter dry periods, the system can still perform charge-discharge cycles and polarity switching operations.

[0077] After 60 days of continuous operation, the system is in stable condition, with an average capacitor charging voltage of 2.3V. During the rainy season, it can maintain a current output of 0.08~0.12mA to drive the electrochemical denitrification process.

[0078] The average nitrogen removal efficiency of the system is as follows:

[0079] NO3 - -N removal rate is 88~91%;

[0080] NH4 + -N removal rate is 94~96%;

[0081] The duration of capacitor discharge was slightly shorter than that of the long drying period (approximately 2-2.5 hours), but the denitrification efficiency was still significantly better than that of the control group;

[0082] Compared to the BRS system, the nitrogen removal capacity is improved by 25-38%.

[0083] The results verify that the method of the present invention has strong adaptability and energy self-balancing ability under different climatic conditions, and is suitable for rainwater purification and denitrification applications in rainy or intermittent rainfall areas.

[0084] Example 5

[0085] This example is used to verify whether the energy produced by MFC and stored in the super capacitor under natural wet-dry cycle conditions can meet the discharge energy required for electrochemical denitrification during the rainfall period, so as to achieve the goal of energy self-circulation of the system. The operation cycle is: 4 days of dry period, 3 hours of rainfall period. The system is equipped with a humidity sensor (threshold RH < 30% triggers dry period) to control the double-pole double-throw relay to switch the capacitor polarity, and a super capacitor with a capacity of 2F and a rated voltage of 2.7V is used for energy storage and discharge.

[0086] By monitoring the average output voltage and current of the system during the dry period, the average output voltage of the system during the dry period is 0.65V, the average current is 0.3mA, and the continuous power generation is 96 hours. The voltage is stabilized at 2.3-2.5V by the voltage boosting module, and the final charging voltage of the super capacitor is 2.45V, so the charging energy is about 6J. The system enters the discharge mode during the rainfall period, with an average discharge voltage of 2.025V and a discharge current of 0.2mA, and the discharge time is 3 hours, and the discharge energy is 3.96J.

[0087] The system successfully charges the super capacitor with about 6.0J of energy by MFC power generation during the dry period, which is enough to support the about 4J discharge load required for electrochemical denitrification during the rainfall period. It shows that the system can realize energy self-circulation and polarity control function under wet-dry cycle without relying on external energy.

[0088] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0089] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for enhanced denitrification by bio-electrochemical energy self-cycling under wet-dry cycles, characterized in that, The device comprises a biological retention zone and an automatic control module. The biological retention zone comprises, from bottom to top, a gravel drainage layer, a filler layer, a soil layer, and a water storage layer. The automatic control module comprises a soil humidity sensor, a super capacitor, a LOGO controller, a double-pole double-throw relay, a voltage module, a solar panel, and a battery. The soil humidity sensor is arranged on one side of the top of the soil layer and connected with the second electrode. One end of the double-pole double-throw relay is connected with the soil humidity sensor, and the other end is connected with the first electrode. One end of the voltage module is connected with the double-pole double-throw relay, and the other end is connected with the super capacitor. One end of the LOGO controller is connected with the double-pole double-throw relay, and the other end is connected with the battery.

2. The device according to claim 1, wherein, The battery is connected with the solar panel.

3. The device according to claim 2, wherein, The filler layer is a composite filler of wood chips, graphite, and ceramsite.

4. The device according to claim 3, wherein, The composite filler comprises, by volume percentage, 25-35% of wood chips, 8-12% of graphite powder, and 55-65% of ceramsite.

5. A method for enhanced denitrification by bio-electrochemical energy self-cycling under wet-dry cycles, characterized in that, The upper and lower spacing of the first electrode and the second electrode is 30 cm. The device of claim 4 comprises: (1) The soil humidity sensor continuously monitors the soil moisture saturation in real time and transmits signals to the LOGO controller for logical judgment. (2) When the soil moisture saturation is greater than 60%, the LOGO controller determines that the system enters the rainfall period, and immediately supplies power to the double-pole double-throw relay to trigger the electrode polarity reversal, the soil layer becomes the anode, and the filler layer becomes the cathode, and the device automatically switches to the microbial electrolysis cell mode operation, and the super capacitor starts discharging to provide power for the microbial electrolysis cell to strengthen the denitrification process. (3) When the soil moisture saturation is less than 30% and the rainwater residence time is greater than 1 h, the controller determines that it enters the drought period, at which time the power supply to the double-pole double-throw relay is cut off, the electrode polarity returns to the initial state, the soil layer is the cathode, and the filler layer is the anode, and the system switches back to the microbial fuel cell mode operation, and the microorganisms oxidize organic matter at the anode to generate electricity and store it in the super capacitor. (4) If the current humidity state does not meet any of the above trigger conditions, the system will continue to monitor the environmental water level dynamically and wait for the switching conditions to be met.

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