Microbial electrolytic cell device for purifying phosphorus pollution by utilizing agricultural waste biochar

Abstract

The invention discloses a microbial electrolysis cell device and method for purifying phosphorus pollution by utilizing agricultural waste biochar. The device comprises an electrolytic tank main body (1) and a circulating system. The electrolytic tank main body (1) is of a single-chamber structure, and the constant-voltage power supply (12) is connected with the anode bar (2) and the cathode bar (3). And the cathode bar (3) adopts a composite structure of a permeable electrode shell (31) and a biochar electrode (32), so that the electrode is convenient to replace and recycle. The device can be further provided with a monitoring system and a reaction maintaining system, and automatic regulation and control are achieved. The method comprises the steps of microbial inoculation and biofilm formation, pretreatment feeding, calcium source supplementation, electrolytic adsorption coupling phosphorus removal, calcium phosphate recovery and the like, and efficient phosphorus removal and phosphorus resource recovery are achieved through the synergistic effect of electrochemistry and biological adsorption under the condition of low voltage (0.5-1.5 V). The method is suitable for treating multi-source phosphorus-containing wastewater in agriculture, industry, life and the like.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource recycling technology, specifically relating to a general-purpose device and method for purifying phosphorus pollution using biochar from common agricultural waste, which can be applied to the purification of various phosphorus-containing low-carbon wastewater and the recovery of phosphorus resources. Background Technology

[0002] With the continuous increase in intensive agricultural production, industrial wastewater discharge, and urban and rural domestic sewage discharge, large amounts of phosphorus-containing pollutants enter natural water bodies, becoming one of the main causes of eutrophication. Eutrophication not only disrupts the balance of aquatic ecosystems but can also lead to problems such as cyanobacterial blooms, decreased dissolved oxygen, and water quality deterioration, seriously affecting drinking water safety and the health of the aquatic environment. Therefore, developing efficient, economical, and sustainable phosphorus-containing wastewater treatment technologies is of significant practical importance.

[0003] Currently, common phosphorus-containing wastewater treatment technologies mainly include chemical precipitation, adsorption, biological methods, and electrochemical methods. Among them, chemical precipitation, while providing stable treatment results, suffers from high chemical consumption, high sludge production, and high operating costs; adsorption is simple to operate, but regeneration of the adsorbent is difficult after saturation, and it is prone to secondary pollution; biological methods are suitable for low-concentration phosphorus-containing wastewater, but they are sensitive to water quality fluctuations, have long treatment cycles, and are difficult to achieve efficient phosphorus recovery; electrochemical methods have advantages such as fast reaction speed, flexible operation, and good environmental compatibility, and have received widespread attention in recent years, but their high energy consumption and expensive electrode materials limit their large-scale application.

[0004] To reduce processing costs and achieve resource recovery, researchers have recently been exploring the combination of agricultural waste resource utilization with electrochemical technologies. Agricultural waste, such as straw, rice husks, and corn cobs, is widely available and produced in large quantities, but its resource utilization rate is generally low, often resulting in incineration or disposal, leading to resource waste and environmental pollution. Studies have shown that biochar prepared from agricultural waste through pyrolysis under limited oxygen conditions possesses a rich pore structure, a large specific surface area, and good surface functional group activity, making it an excellent adsorbent for the removal of phosphorus and heavy metals from water. Simultaneously, biochar exhibits good conductivity and biocompatibility, demonstrating its potential as an electrode material or electrode filler.

[0005] In recent years, microbial electrolysis cell technology has attracted attention due to its ability to drive pollutant conversion and achieve energy or resource recovery under low voltage conditions. Introducing biochar into the microbial electrolysis cell system can synergistically leverage its adsorption and electrochemical activity, enhancing phosphorus fixation and conversion. However, existing microbial electrolysis cell devices often suffer from problems such as complex structure, poor versatility, difficulty in electrode replacement, and insufficient precision in reaction environment control. For example, traditional cathodes are mostly fixed structures, making it difficult to replace and recycle the biochar after filling, limiting its sustainability in practical wastewater treatment; key parameters such as temperature, pH, and gas pressure lack effective monitoring and control methods during the reaction process, making it difficult to ensure microbial activity and reaction stability; furthermore, existing devices are mostly designed for single types of wastewater, making it difficult to adapt to the treatment needs of phosphorus-containing wastewater from multiple sources such as agriculture, industry, and domestic use.

[0006] In summary, existing technologies still suffer from problems such as low treatment efficiency, poor operational stability, difficulty in resource recovery, and inconvenient equipment maintenance when treating phosphorus-containing wastewater from multiple sources. There is an urgent need to develop a new type of treatment device with optimized structure, precise control, strong versatility, and the ability to recover phosphorus resources. Summary of the Invention

[0007] Technical problems to be solved This invention aims to solve the problems of existing microbial electrolysis cells in treating phosphorus-containing wastewater, such as complex structure, poor versatility, inconvenient electrode replacement, insufficient precision in reaction environment control, and difficulty in efficient recovery of phosphorus resources. It provides a universal purification device and method with optimized structure, convenient operation, precise control, and applicable to the treatment of phosphorus-containing wastewater from multiple sources and the realization of phosphorus resource recovery. Technical solution

[0008] This invention provides a device for purifying phosphorus pollution using biochar from agricultural waste. To achieve the above objective, this invention adopts the following technical solution.

[0009] A microbial electrolysis cell device for purifying phosphorus pollution using biochar from agricultural waste includes an electrolysis cell body (1), a circulation system, a monitoring system, and a reaction maintenance system.

[0010] The main body (1) of the electrolytic cell is a single-chamber structure, with an anode rod (2) and a cathode rod (3) inside. A constant voltage power supply (12) is connected to the anode rod (2) and the cathode rod (3) respectively. The cathode rod (3) is a composite structure, including a permeable electrode shell (31) and a biochar electrode (32) filled inside. The permeable electrode shell (31) is made of porous metal mesh or porous ceramic material with a pore size of 50~500μm, which ensures the free passage of ions and molecules while effectively trapping biochar particles. The biochar electrode (32) is made from agricultural waste through oxygen-limited pyrolysis at 400~700℃, with a specific surface area ≥300 m². 2 / g, with abundant porous structure and surface functional groups. The anode rod (2) adopts a titanium-based coated electrode, including a titanium substrate and a noble metal oxide coating on its surface, wherein the coating is one or a combination of IrO2-Ta2O5 or RuO2-IrO2, to improve the catalytic activity and corrosion resistance of the electrode.

[0011] The circulation system includes a feed pipe (4), a water inlet pipe (5), a water outlet pipe (6), an exhaust pipe (7), and a sewage discharge pipe (21). The feed pipe (4) is located at the top of the electrolytic cell body (1) and is used to transport microbial culture medium and pH buffer into the cell. The water inlet pipe (5) is located in the middle of the side wall of the electrolytic cell body (1) and is used to replenish the wastewater to be treated or adjust the concentration of the reaction system. The water outlet pipe (6) is located at the bottom of the side wall of the electrolytic cell body (1) and is used to discharge the treated wastewater. The exhaust pipe (7) is located at the top of the electrolytic cell body (1) and is connected to the gas pressure control valve (9) to discharge the gas generated during the reaction and maintain the stability of the system gas pressure. The sewage discharge pipe (21) is located at the bottom of the electrolytic cell body (1) and is used to discharge the deposited sludge and insoluble substances.

[0012] The monitoring system includes a pressure sensor (8), a pressure control valve (9), an electrochemical workstation (13), a pH sensor (14), a temperature sensor (15), and a level gauge (16). The pressure sensor (8) is located on the top of the electrolytic cell body (1) to monitor the pressure inside the cell in real time and is linked with the pressure control valve (9). When the pressure exceeds a preset threshold, the exhaust pipe (7) is automatically opened to release pressure. The electrochemical workstation (13) is connected to the anode rod (2) and the cathode rod (3) respectively to monitor the current, voltage, and electrode reaction efficiency during the electrolysis process in real time. The pH sensor (14) and the temperature sensor (15) are located on the side wall of the electrolytic cell body (1) to detect the acidity and alkalinity and temperature of the reaction solution, respectively. The level gauge (16) is located on the side wall of the electrolytic cell body (1) to monitor the liquid level in the cell. All monitoring data are transmitted to the PLC controller in real time to achieve precise control of the reaction system.

[0013] The reaction maintenance system includes a stirring device (10), baffles (11), a constant temperature water bath (17), a circulating water inlet pipe (18), a circulating water outlet pipe (19), and a circulating heating pump (20). The stirring device (10) consists of a stirring motor (101) and a stirring shaft (102). Two to four sets of inclined blade stirring paddles are installed on the stirring shaft (102). The stirring motor (101) drives the stirring shaft (102) to rotate, so that the wastewater is fully mixed with biochar and electrodes, and the mass transfer efficiency is enhanced. The baffles (11) are set vertically or inclined on the inner wall of the electrolytic cell body (1). There are two to four baffles, which are evenly distributed along the circumference to change the water flow path, force the circulating flow field, and prolong the wastewater residence time. The constant temperature water bath (17) is wrapped around the outside of the electrolytic cell body (1). The circulating heating pump (20) drives the circulating water to flow between the circulating water inlet pipe (18) and the circulating water outlet pipe (19) to achieve precise control of the reaction temperature.

[0014] The device also includes a PLC controller, which is electrically connected to a pressure sensor (8), a pressure control valve (9), an electrochemical workstation (13), a pH sensor (14), a temperature sensor (15), a level gauge (16), a stirring motor (101), a circulating heating pump (20), and a constant voltage power supply (12), respectively. The PLC controller is used to receive monitoring data and automatically adjust the operating status of each actuator according to a preset control strategy to realize the automated operation of the device.

[0015] The present invention also provides a method for purifying phosphorus pollution using the above-mentioned device, including steps such as microbial inoculation and biofilm formation, pretreatment and feeding, environmental control, electrolysis and adsorption reaction, product recovery and discharge. Electrogenic microbial communities (such as Geobacter and Shewanella) are inoculated into the main body of the electrolytic cell (1), and biofilm is cultured using a biochar electrode (32) as a carrier; phosphorus-containing wastewater is injected into the device, and calcium source is added as necessary according to the calcium ion concentration of the wastewater, and electrolysis and adsorption coupling reaction is carried out under low voltage (0.5~1.5V) conditions to precipitate and recover phosphorus in the wastewater in the form of calcium phosphate.

[0016] The phosphorus removal mechanism of this invention is based on the synergistic effect of electrochemical and bioadsorption: under the drive of an applied voltage, an oxygen evolution reaction occurs at the anode (2H₂O → O₂ + 4H₂O). + + 4e - Electrogenic microorganisms (such as *Geobacter* and *Shewanella*) in the cathode region oxidize organic carbon sources in the wastewater, releasing electrons which are then transferred to the cathode. Simultaneously, a reduction reaction (2H₂O + 2e⁻) occurs on the cathode surface. - → H2 + 2OH - This leads to a localized increase in pH in the cathode area. In an alkaline microenvironment, calcium ions (Ca) present in the wastewater, whether naturally present or added, cause a rise in pH.2+ ) and phosphate ions (PO4) 3- The calcium ions combine to form a poorly soluble calcium phosphate precipitate (Ca3(PO4)2 or hydroxyapatite), which is deposited on the surface of the biochar electrode (32). When the calcium ion concentration in the wastewater itself is insufficient, calcium sources such as calcium chloride (CaCl2) can be added through the feed pipe (4) to increase the calcium concentration in the reaction solution. 2+ The concentration is maintained within the range of 30–100 mg / L to ensure efficient formation of calcium phosphate precipitate. Meanwhile, the biochar electrode itself has abundant porous structure and oxygen-containing functional groups, which can further immobilize phosphate ions through physical and chemical adsorption, achieving a dual phosphorus removal effect of electrochemical precipitation and adsorption.

[0017] The single-chamber electrolytic cell structure simplifies the device composition and reduces manufacturing costs. The cathode rod adopts a composite structure of a permeable outer shell and an internal biochar electrode. The biochar electrode can be replaced and recycled separately, eliminating the need to replace the entire cathode rod, which greatly improves the sustainability and ease of maintenance of the device.

[0018] The device is suitable for treating phosphorus-containing wastewater from multiple sources, including agricultural wastewater, industrial wastewater, and domestic wastewater. It has a good purification effect on phosphorus-containing wastewater of different concentrations and qualities. By adjusting parameters such as voltage and reaction time, it can adapt to different treatment needs and has good process flexibility.

[0019] Phosphorus resources are recovered in the form of calcium phosphate, realizing the resource utilization of phosphorus in wastewater; at the same time, biochar is prepared from agricultural waste, realizing waste-to-waste treatment, reducing treatment costs, and the recovered biochar can also be used as a soil conditioner, forming a closed-loop resource system.

[0020] Through real-time monitoring by multiple sensors and automatic regulation by a PLC controller, precise control of key parameters such as temperature, pH, air pressure, and liquid level is achieved, ensuring the activity of microorganisms and the stability of the electrolytic reaction. The stirring device and the baffle work together to enhance mass transfer efficiency and improve the completeness of the reaction.

[0021] Through multi-stage operation mode control, the adsorption, electrolysis, and sedimentation stages can be flexibly switched according to water quality and treatment objectives to optimize energy consumption and treatment efficiency; low voltage (0.5~1.5V) operation conditions reduce energy consumption and are suitable for large-scale promotion and application.

[0022] Employing electrochemical and adsorption coupling technology, no chemical reagents are required, avoiding the secondary pollution problems of sludge caused by chemical precipitation methods; the biochar electrode is derived from agricultural waste and can be recycled after use, making the entire process environmentally friendly. Attached Figure Description

[0023] Figure 1 Schematic diagram of the overall structure of a biochar cathode phosphorus recovery microbial electrolysis cell.

[0024] Figure 2 Workflow flowchart (including steps such as microbial inoculation and biofilm formation, pretreatment and feeding, calcium source supplementation, environmental control, electrolysis and adsorption reaction, real-time monitoring and control, multi-stage operation mode control, product recovery and discharge).

[0025] 1-Electrolytic cell body; 2-Anode rod; 3-Cathode rod; 31-Cathode shell; 32-Biochar electrode; 4-Feed pipe; 5-Water inlet pipe; 6-Water outlet pipe; 7-Exhaust pipe; 8-Pressure sensor; 9-Pressure control valve; 10-Stirring device; 101-Stirring motor; 102-Stirring shaft; 11-Baffle; 12-Constant voltage power supply; 13-Electrochemical workstation; 14-pH sensor; 15-Temperature sensor; 16-Level gauge; 17-Constant temperature water bath jacket; 18-Circulating water inlet pipe; 19-Circulating water outlet pipe; 20-Circulating heating pump; 21-Sewage pipe Detailed Implementation

[0026] like Figure 1 As shown, the present invention provides a phosphorus recovery bioelectrolysis cell device based on agricultural waste biochar electrode, including an electrolysis cell body (1), an anode rod (2), a cathode rod (3), a cathode shell (31), a biochar electrode (32), a feed pipe (4), a water inlet pipe (5), a water outlet pipe (6), an exhaust pipe (7), a pressure sensor (8), a pressure control valve (9), a stirring device (10); a stirring motor (101); a stirring shaft (102); a baffle plate (11); a constant voltage power supply (12); an electrochemical workstation (13); a pH sensor (14); a temperature sensor (15); a level gauge (16); a constant temperature water bath jacket (17); a circulating water inlet pipe (18); a circulating water outlet pipe (19); a circulating heating pump (20); and a sewage discharge pipe (21).

[0027] In this invention, the main body (1) of the electrolytic cell is preferably a cylindrical structure with a pointed bottom, and the material is preferably a high-strength, corrosion-resistant material such as high borosilicate glass or organic glass, more preferably high borosilicate glass; the inner diameter is preferably 200~300mm, more preferably 250mm; the height is preferably 400~500mm, more preferably 450mm; the top cover is preferably a corrosion-resistant polymer material, more preferably polytetrafluoroethylene; and the bottom cone angle is preferably 150°.

[0028] In this invention, the anode rod (2) is a titanium-based coated electrode, preferably made of industrial pure titanium TA2; the diameter is preferably 15-25 mm, more preferably 20 mm; the length is preferably 300-400 mm, more preferably 350 mm. The surface is preferably coated with a mixed metal oxide coating such as IrO2-Ta2O5 or RuO2-IrO2, which possesses catalytic activity and corrosion resistance, more preferably with an Ir:Ta molar ratio of 7:3 and a coating loading of 12 g / m². 2 The electrode has an IrO2-Ta2O5 coating. An M10 threaded interface is provided on the top of the electrode for connecting the power cord.

[0029] In this invention, the cathode rod (3) adopts an inner and outer layered structure, including an outer permeable electrode shell (31) and an inner biochar electrode (32). The electrode shell (31) is preferably made of a permeable metal or ceramic porous material with a pore size of 50~150μm, more preferably a 316L stainless steel sintered filter element with a pore size of 100μm; the inner diameter is preferably 20~30mm, more preferably 25mm; the length is preferably 300~400mm, more preferably 350mm. The biochar electrode (32) is preferably made of biochar pyrolyzed in an oxygen-limited environment at 400~700℃, more preferably at a pyrolysis temperature of 600℃; the particle size is preferably 20~40 mesh, more preferably 30 mesh.

[0030] In this invention, the feed pipe (4), water inlet pipe (5), water outlet pipe (6), exhaust pipe (7) and sewage pipe (21) are preferably made of polyvinyl chloride or polypropylene, more preferably polyvinyl chloride, and are equipped with electric ball valves.

[0031] In this invention, the pressure sensor (8) is preferably a diffused silicon pressure sensor, more preferably a MIK-P300 type; the pressure control valve (9) is preferably a two-position two-way solenoid valve, which is linked with the pressure sensor (8); the electrochemical workstation (13) is preferably a general-purpose electrochemical workstation, more preferably a CHI660E type; the pH sensor (14) is preferably an industrial online pH electrode, more preferably an E-201-C, equipped with a polytetrafluoroethylene sheath, with a measurement range of 0~14. The temperature sensor (15) is preferably a PT100 platinum resistance temperature sensor, equipped with a stainless steel sheath, with a measurement accuracy of ±0.1℃; the level gauge (16) is preferably a magnetic float level gauge, more preferably a UHZ-519 type, equipped with a high and low level alarm switch; all of the above sensors need to be electrically connected to the PLC controller.

[0032] In this invention, the stirring motor (101) is preferably a DC brushless geared motor; the speed adjustment range is preferably 0~300rpm; the power is preferably 40~80W, more preferably 60W. The stirring shaft (102) is preferably made of 316L stainless steel and fitted with a polytetrafluoroethylene sleeve; the length is preferably 300~400mm, more preferably 350mm; the number of stirring blades is preferably 2~4 sets, more preferably 3 sets, the blades are uniformly fixed to the stirring shaft (102) at a 45° angle, the distance between the lowest blade and the bottom of the reactor is preferably 30~70mm, more preferably 50mm; the spacing between each set of blades is preferably 60~100mm, more preferably 80mm.

[0033] In this invention, the baffles (11) are evenly distributed circumferentially along the inner wall of the reactor, preferably in the form of 2 to 4 pieces, more preferably 4 pieces; the material is preferably polytetrafluoroethylene or 316L stainless steel, more preferably polytetrafluoroethylene; the length is preferably 250 to 350 mm, more preferably 300 mm. In this invention, the constant temperature water bath jacket (17) and the main body of the electrolytic cell (1) are designed as an integrated unit, with a double-layer structure. The material is preferably high borosilicate glass or organic glass, more preferably high borosilicate glass. The jacket thickness is preferably 20~40mm, more preferably 30mm. The circulating water inlet (18) is located at the bottom. The circulating water outlet (19) is located at the top. The material of the above-mentioned pipe is preferably polyvinyl chloride or polypropylene, more preferably polyvinyl chloride. The above-mentioned circulating heating pump (20) is preferably a precision constant temperature water bath circulator, and the pump flow rate is preferably 10~20L / min, more preferably 15L / min. The circulating pipeline material is preferably DN15 heat-resistant silicone tube, wrapped with heat insulation cotton.

[0034] The present invention provides a method for purifying and recovering phosphorus pollution in wastewater using the above-mentioned device, comprising the following steps: A mixed bacterial solution of electrogenic microorganisms, including *Geobacter sulfurreducens* and *Shewanella oneidensis*, with strong extracellular electron transfer capabilities, was added to the main body (1) of the electrolytic cell. The inoculum amount was 5% to 10% of the reaction liquid volume. A nutrient medium containing sodium acetate (1.0 to 2.0 g / L) was added to the main body (1) of the electrolytic cell through the feed pipe (4) as the carbon source. Biofilm culture was carried out under the conditions of 0.3 to 0.5 V and 30 °C for 7 to 21 days until a stable electrogenic current (≥0.5 mA) was detected by the electrochemical workstation (13), indicating that the biofilm was successfully attached to the surface of the biochar electrode (32). After the biofilm was attached, the waste liquid of the culture medium was discharged, and the formal operation stage began.

[0035] The phosphorus-containing wastewater to be treated is injected into the main body of the electrolytic cell (1) through the inlet pipe (5). The liquid level is monitored by the level gauge (16) and controlled to reach 60%~80% of the volume of the main body of the electrolytic cell (1). The calcium ion concentration in the wastewater is detected. When Ca 2+ When the concentration is below 30 mg / L, calcium sources such as calcium chloride (CaCl2) are added to the reaction solution through the feed pipe (4) to make the Ca... 2+ A concentration of 30-100 mg / L provides sufficient calcium ions for the calcium phosphate precipitation reaction.

[0036] Start the circulating heating pump (20) and adjust the reaction temperature to 25~35℃ through the constant temperature water bath jacket (17); monitor the pH value of the reaction solution through the pH sensor (14). If the pH deviates from the range of 6.5~8.0, add pH buffer through the feed pipe (4) to adjust the pH to the set range.

[0037] Turn on the constant voltage power supply (12), control the voltage to 0.5~1.5V, start the stirring device (10), and set the stirring speed to 50~200 rpm to ensure that the wastewater is in full contact with the anode rod (2), cathode rod (3), and biochar electrode (32). During electrolysis, oxygen evolution reaction occurs at the anode, and the electrogenic microorganisms in the cathode region oxidize the organic carbon source in the wastewater, releasing electrons, creating a reducing environment and increasing the local pH value in the cathode region. This promotes the combination of phosphate ions and calcium ions to form calcium phosphate precipitate, which is deposited on the surface of the biochar electrode (32). At the same time, the biochar electrode further fixes phosphate ions through physical adsorption and chemical adsorption. The reaction time is 2~8 hours, depending on the initial phosphorus concentration of the wastewater.

[0038] During the reaction, the monitoring system collects real-time data on air pressure, pH, temperature, liquid level and electrochemical properties. The PLC controller automatically judges and adjusts the system according to the preset thresholds: when the air pressure exceeds the set threshold, the air pressure control valve (9) is automatically opened to release pressure through the exhaust pipe (7); when the pH deviates from the set range, the system automatically prompts or starts the device to add pH buffer for adjustment; when the temperature deviates from the set range, the power of the circulating heating pump (20) is automatically adjusted; when the liquid level is lower than the set value, the water inlet pipe (5) is automatically opened to replenish the water.

[0039] According to the wastewater quality and treatment objectives, the PLC controller can perform multi-stage operation mode control: Adsorption stage: turn off the constant voltage power supply (12), only start the stirring device (10), and use the biochar electrode (32) to adsorb phosphorus for 0.5~2 hours; Electrolysis stage: turn on the constant voltage power supply (12), maintain the set voltage, and carry out electrochemical conversion for 2~6 hours; Sedimentation stage: turn off the stirring device (10) and the constant voltage power supply (12), and let it settle for 0.5~1.5 hours to allow insoluble impurities to settle; Discharge stage: open the effluent pipe (6) to discharge the treated wastewater, and open the sewage pipe (21) to discharge the bottom impurities.

[0040] After the reaction is completed, the insoluble precipitate and bacterial mud deposited at the bottom are discharged through the sewage pipe (21) and then further treated. The treated wastewater is discharged through the outlet pipe (6) or circulated through the inlet pipe (5). The used biochar electrode (32) can be taken out from the cathode rod (3), reused after regeneration, or recycled as a soil conditioner after cleaning and drying.

[0041] Example 1: Following step 1, microbial inoculation and biofilm formation were completed (inoculation with a mixed culture of Geobacter and Shewanella, biofilm culture for 14 days, with the electrogenic current stabilizing at 0.8 mA). CaCl2 was added to the wastewater to increase the Ca... 2+ The concentration was 50 mg / L. Comparative experiments were conducted to treat agricultural wastewater (pig farm biogas slurry, diluted to 15 mg / L TP), industrial wastewater (electroplating plant phosphorus-containing wastewater, 25 mg / L TP, containing heavy metals), and domestic sewage (campus sewage, 8 mg / L TP) under the same conditions (voltage 1.0V, temperature 30℃, pH 7.0, reaction time 6h). The results showed that the phosphorus removal rate was 92% for agricultural wastewater, 88% for industrial wastewater, and 96% for domestic sewage, verifying the versatility of this invention.

[0042] Example 2: Following step 1, microbial inoculation and biofilm formation were completed (biofilm culture for 14 days, with the electrostatic current stable at 0.8 mA). CaCl2 was added to the wastewater to increase the Ca... 2+ The concentration was 50 mg / L. Under the same process conditions (voltage 1.0V, temperature 30℃, pH 7.0, TP 8 mg / L from campus domestic sewage), the phosphorus removal efficiency of biochar electrodes made from different agricultural wastes was compared. Corn stalks, rice husks, and peanut shells were used to prepare biochar through pyrolysis at 600℃ under limited oxygen conditions. The results showed that corn stalk biochar achieved a phosphorus removal rate of 94%, rice husk biochar 91%, and peanut shell biochar 89%. All three biochar materials exhibited good phosphorus removal capabilities, with corn stalk biochar showing the highest phosphorus removal rate (462 m²). 2The phosphorus removal efficiency was highest ( / g). Experiments show that this invention has good adaptability to biochar raw materials, and different agricultural wastes can be used as cathode materials.

[0043] Example 3: Following step 1, microbial inoculation and biofilm formation were completed (biofilm culture for 14 days, with the electrostatic current stable at 0.8 mA). Using campus domestic wastewater (TP 8 mg / L) as the target, CaCl2 was added to the wastewater to increase the Ca... 2+ The effect of different applied voltages on phosphorus removal efficiency was investigated at a concentration of 50 mg / L. The reaction was conducted at a fixed temperature of 30℃, pH 7.0, and reaction time of 6 h, with voltages set at 0.5V, 0.8V, 1.0V, 1.2V, and 1.5V. Results showed that the phosphorus removal rate was 78% at 0.5V, 89% at 0.8V, 96% at 1.0V, 97% at 1.2V, and 97% at 1.5V. The phosphorus removal rate significantly increased from 0.5V to 1.0V; however, the removal rate tended to stabilize above 1.0V. Considering both removal efficiency and energy consumption, the optimal operating voltage is recommended to be 0.8–1.0V. The biochar electrode was also subjected to five regeneration cycles. After each use, it was regenerated by soaking in 0.1 mol / L HCl for 2 h. After five cycles, the phosphorus removal rate remained above 88%, indicating that the biochar electrode has good regenerability.

Claims

1. A microbial electrolytic cell device for purifying phosphorus pollution using agricultural waste biochar, comprising an electrolytic cell body (1) and a circulation system; characterized in that: The main body (1) of the electrolytic cell is a single-chamber structure, with an anode rod (2) and a cathode rod (3) inside. A constant voltage power supply (12) is connected to the anode rod (2) and the cathode rod (3) respectively. The cathode rod (3) is a composite structure, including a permeable electrode shell (31) and a biochar electrode (32) filled inside. The biochar electrode (32) can be removed from the permeable electrode shell (31) for replacement. The circulation system includes a feed pipe (4), a water inlet pipe (5), a water outlet pipe (6), an exhaust pipe (7), and a sewage discharge pipe (21), which are used to input raw materials and wastewater, output treated wastewater and waste materials, and maintain the normal working state of the electrolytic cell.

2. The apparatus according to claim 1, characterized in that, The anode rod (2) is a titanium-based coated electrode, comprising a titanium substrate and a metal oxide coating on its surface. The coating is one or a combination of IrO2-Ta2O5 or RuO2-IrO2, and has high oxygen evolution overpotential and catalytic selectivity.

3. The apparatus according to claim 1, characterized in that, The permeable electrode shell (31) is made of porous metal mesh or porous ceramic material with a pore size of 50~500μm; the biochar electrode (32) is made by pyrolysis of agricultural waste in an oxygen-limited environment at 400~700℃, with a specific surface area ≥300 m². 2 / g; Waste biochar electrodes (32) can be used directly as soil conditioners.

4. The apparatus according to claim 1, characterized in that, It also includes a monitoring system, which includes a pressure sensor (8), a pressure control valve (9), an electrochemical workstation (13), a pH sensor (14), a temperature sensor (15), and a level gauge (16) for real-time monitoring and control of the pressure, electrochemical parameters, pH, temperature, and level in the reactor.

5. The apparatus according to claim 4, characterized in that, The pressure sensor (8) is connected to the pressure control valve (9) and controls the opening and closing status of the exhaust pipe (7) by monitoring the internal pressure of the reactor; the electrochemical workstation (13) is connected to the anode rod (2) and the cathode rod (3) respectively, and monitors the current, voltage and electrode reaction efficiency in the electrolysis process in real time.

6. The apparatus according to claim 1, characterized in that, It also includes a reaction maintenance system, which includes a stirring device (10), a baffle (11), a constant temperature water bath (17), a circulating water inlet pipe (18), a circulating water outlet pipe (19), and a circulating heating pump (20). The stirring device (10) includes a stirring motor (101) and a stirring shaft (102). The stirring paddles are set in 2 to 4 groups and are evenly arranged on the stirring shaft (102). The baffle (11) is set in 2 to 4 pieces vertically or obliquely and is evenly distributed on the inner wall of the reactor. It works in conjunction with the stirring device (10) to form a forced circulating flow field and enhance the mass transfer efficiency. The constant temperature water bath (17) is wrapped around the outside of the electrolytic cell body (1). The circulating heating pump (20) drives the circulating water to flow between the circulating water inlet pipe (18) and the circulating water outlet pipe (19) to achieve precise control of the reaction temperature.

7. The apparatus according to claim 4 or 6, characterized in that, It also includes a PLC controller, which is electrically connected to a pressure sensor (8), a pressure control valve (9), a stirring motor (101), a constant voltage power supply (12), an electrochemical workstation (13), a pH sensor (14), a temperature sensor (15), a level gauge (16), and a circulating heating pump (20), and automatically controls the stirring speed, heating power, water flow and voltage of the equipment through real-time monitoring.

8. A method for purifying phosphorus pollution, based on the apparatus of claim 1, wherein the apparatus further comprises the monitoring system of claim 4 and the reaction maintenance system of claim 6, characterized in that, The process includes the following steps: (1) Microbial inoculation and biofilm formation: Electrolytic microbial communities are inoculated into the main body (1) of the electrolytic cell, and biofilm is formed using a biochar electrode (32) as a carrier. The biofilm formation time is 7-21 days until a stable electrolytic current is detected; (2) Pretreatment and feeding: The phosphorus-containing wastewater to be treated is injected into the main body (1) of the electrolytic cell through the inlet pipe (5), and the liquid level is controlled to the preset range; the calcium ion concentration in the wastewater is detected, and when Ca 2+ When the concentration is insufficient, calcium source is supplemented through feed pipe (4) to increase the Ca concentration in the reaction solution. 2+ The concentration reaches 30~100 mg / L; (3) Environmental control: Adjust the reaction temperature to 25~35℃ and adjust the pH of the reaction solution to 6.5~8.0; (4) Electrolysis and adsorption reaction: Turn on the constant voltage power supply (12), control the voltage to 0.5~1.5V, start the stirring device (10), carry out electrolysis and adsorption reaction, and the reaction time is 2~8 hours; During the reaction, oxygen evolution reaction occurs at the anode, and microorganisms in the cathode area oxidize organic matter to release electrons, generate a reducing environment and increase the local pH value, promote the combination of phosphate ions and calcium ions to generate calcium phosphate precipitate, which is deposited on the surface of biochar electrode (32); (5) Product recovery and discharge: After the reaction is completed, let it stand to precipitate, recover the calcium phosphate precipitate, discharge the treated wastewater that meets the standards, and discharge the solid waste through the sewage pipe (21).

9. The method according to claim 8, characterized in that, The phosphorus-containing wastewater to be treated includes one or more of the following: agricultural wastewater, industrial wastewater, or domestic wastewater.

10. The method according to claim 8, characterized in that, The step (4) also includes multi-stage operation mode control: during the adsorption stage, the constant voltage power supply (12) is turned off, and only the stirring device (10) is started to adsorb phosphorus using the biochar electrode (32) for 0.5 to 2 hours; during the electrolysis stage, the constant voltage power supply (12) is turned on to maintain the set voltage for electrochemical conversion for 2 to 6 hours; during the precipitation stage, the stirring device (10) and the constant voltage power supply (12) are turned off, and the precipitation is allowed to stand for 0.5 to 1.5 hours.

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