Wastewater treatment system and wastewater treatment method

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a wastewater treatment system and a wastewater treatment method, which realize a closed-loop system of'wastewater treatment-energy recovery-resource regeneration 'cooperative treatment by combining a microbial fuel cell with a sludge pyrolysis technology. According to the system, organic matters in wastewater are converted into electric energy by utilizing a microbial fuel cell system, meanwhile, the concentration of pollutants is reduced, generated sludge is subjected to two-stage pyrolysis after being subjected to dehydration pretreatment to prepare biochar, the biochar can be used for soil improvement, water purification and the like, and synthesis gas generated by pyrolysis is used for power generation to supplement energy consumption of the system. The resource utilization rate is effectively increased, the sludge yield is reduced, the treatment cost is reduced, and good environmental benefits and economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and specifically relates to a wastewater treatment system and a wastewater treatment method. Background Art

[0002] With the rapid development of industrialization and urbanization, the wastewater discharge is increasing day by day, and wastewater treatment has become an important task for environmental protection. The traditional wastewater treatment methods mainly aim to remove pollutants, with high energy consumption and insufficient realization of resource recovery and utilization. When treating a large amount of wastewater by the activated sludge method, a large amount of electricity is required for aeration, and the subsequent treatment cost of the generated excess sludge is high.

[0003] As a new wastewater treatment technology, the microbial fuel cell (MFC) technology can directly convert organic matter in wastewater into electric energy by using microorganisms, realizing energy recovery while treating wastewater, and has broad application prospects. However, the MFC technology still faces some challenges at present, such as the need to improve the power generation efficiency and the relatively high internal resistance, which limit its large-scale application.

[0004] On the other hand, sludge is a by-product in the wastewater treatment process, containing a large amount of organic matter, heavy metals, pathogens, etc. Traditional sludge treatment methods such as landfill and incineration not only occupy a large amount of land resources but also may cause secondary pollution. The technology of preparing biochar by sludge pyrolysis provides a new way for the resource utilization of sludge. Biochar can be used in fields such as soil improvement and adsorbents, and has high economic value. However, the sludge pyrolysis process requires a large amount of energy, and the quality of the pyrolysis products is greatly affected by the properties of the sludge.

[0005] At present, the research on combining the MFC technology with the sludge pyrolysis technology has gradually attracted attention, but the related technology is still in the development stage, with problems such as high system integration complexity and high treatment cost, and needs to be further optimized and improved. Summary of the Invention

[0006] Aiming at the problems in the prior art, the present invention provides a wastewater treatment system and a wastewater treatment method, which integrate wastewater treatment, energy recovery and resource regeneration by combining the microbial fuel cell with the sludge pyrolysis technology, improve the resource utilization rate, reduce the treatment cost and reduce environmental pollution.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a wastewater treatment system, including a microbial fuel cell system, a dehydration pretreatment device, a two-stage pyrolysis furnace, and a waste heat recovery system; The microbial fuel cell system is used to treat wastewater and generate electric energy. The water inlet of the microbial fuel cell system is connected to the wastewater source, the water outlet is used to discharge the up-to-standard effluent, and the excess sludge outlet is connected to the inlet of the dehydration pretreatment device; The dehydration pretreatment device is used to dehydrate the sludge generated by the microbial fuel cell system, and its outlet is connected to the feed inlet of the two-stage pyrolysis furnace; The two-stage pyrolysis furnace is used to pyrolyze the dehydrated sludge to produce biochar, bio-oil and syngas. The biochar outlet of the two-stage pyrolysis furnace is used to output biochar, and the bio-oil and syngas outlets are connected to the waste heat recovery system; The waste heat recovery system is used to recover the heat generated by pyrolysis, and its heat output end is respectively connected to the temperature control device of the microbial fuel cell system and the dehydration pretreatment device.

[0008] Specifically, the microbial fuel cell system includes an anode chamber, a cathode chamber and a proton exchange membrane. Geobacter sulfurreducens electroactive bacteria are domesticated in the anode chamber, and the cathode chamber uses a MnO2 / graphene composite catalyst.

[0009] Specifically, the electrodes of the microbial fuel cell system adopt a three-dimensional electrode structure, which is composed of activated carbon particles wrapped by carbon fiber cloth, with a specific surface area of up to 1200 m² / g and the internal resistance reduced to less than 80 Ω.

[0010] Specifically, the two-stage pyrolysis furnace includes a low-temperature dehydration section and a high-temperature pyrolysis section. The temperature of the low-temperature dehydration section is 150-250 °C, and the heat generated by the electricity generation of the microbial fuel cell is used to reduce the moisture content of the sludge from 80% to 40%; the temperature of the high-temperature pyrolysis section is 500-600 °C, and it stays for 30 minutes in an N2 atmosphere.

[0011] Specifically, 5% of FeCl3 based on the mass of the dehydrated sludge is added as a catalyst in the high-temperature pyrolysis section of the two-stage pyrolysis furnace.

[0012] Specifically, the wastewater treatment system further includes a biochar application device, which is used to use the biochar generated by pyrolysis as a soil conditioner or water purification filler.

[0013] Specifically, the wastewater treatment system realizes full-process dynamic simulation and optimization based on digital twin technology (such as ANSYS TwinBuilder).

[0014] The wastewater treatment method includes the following steps: S1. Introduce the wastewater into the microbial fuel cell system for treatment, use the anode microbial community to convert organic matter into electrons to generate electricity, and at the same time remove the COD in the wastewater to make the effluent meet the discharge standards; S2. Transport the surplus sludge generated by the microbial fuel cell system to the dehydration pretreatment device for dehydration treatment; S3. Feed the dehydrated sludge into a two-stage pyrolysis furnace for pyrolysis. First, utilize the waste heat generated by the microbial fuel cell for power generation in the low-temperature dehydration section to reduce the moisture content of the sludge, and then conduct a pyrolysis reaction in the high-temperature pyrolysis section to generate biochar, bio-oil, and syngas. S4. Collect the biochar produced by pyrolysis for soil improvement or water purification. S5. Transport the bio-oil and syngas produced by pyrolysis to the waste heat recovery system. The recovered heat is used for temperature control of the microbial fuel cell system and pre-treatment of sludge dehydration, and the syngas is used for power generation to supplement the system energy consumption.

[0015] Specifically, during the process of treating wastewater by the microbial fuel cell system, monitor the influent water quality and control the influent COD within the range of 500 - 1500 mg / L, ammonia nitrogen within the range of 50 - 100 mg / L, and pH within the range of 6.5 - 8.0.

[0016] Specifically, before pyrolyzing the sludge in the two-stage pyrolysis furnace, conduct microbial leaching treatment on the sludge, and use Thiobacillus ferrooxidans to remove more than 90% of heavy metals such as Cu / Pb.

[0017] Advantages of the present invention: 1. Improve resource utilization rate: Utilize the microbial fuel cell system to convert organic matter in wastewater into electric energy, and at the same time prepare biochar by sludge pyrolysis, realizing the resource utilization of wastewater and sludge and reducing resource waste.

[0018] 2. Reduce treatment cost: The syngas produced by pyrolysis is used for power generation to supplement the system energy consumption, and the combined process reduces the operating cost compared with single treatment. The sales revenue of biochar can further reduce the cost.

[0019] 3. Reduce environmental pollution: The microbial fuel cell system for treating wastewater reduces pollutant emissions. The biochar is reused as the cathode filler of the microbial fuel cell to adsorb cathode by-products and reduce the risk of greenhouse gas emissions. Microbial leaching of the sludge before pyrolysis to remove heavy metals reduces the risk of secondary pollution. Brief Description of the Drawings

[0020] The present invention will be further described below in conjunction with the drawings and embodiments.

[0021] Figure 1 It is the flow chart of the collaborative treatment of microbial fuel cell and sludge pyrolysis for preparing biochar in the present invention; Figure 2 It is the step flow chart of the wastewater treatment method provided by the present invention. Detailed Embodiments

[0022] In order to make the technical means, creative features, achieved objectives and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0023] As Figure 1 shown, the wastewater treatment system described in this embodiment includes a microbial fuel cell (MFC) system, a dehydration pretreatment device, a two-stage pyrolysis furnace, and a waste heat recovery system. The specific steps are as follows: First, the water inlet of the MFC system is connected to the wastewater source, which treats the wastewater and generates electricity. The outlet discharges the up-to-standard effluent, and the residual sludge outlet is connected to the dehydration pretreatment device; then, after the dehydration pretreatment device dehydrates the sludge, the dehydrated sludge is sent to the two-stage pyrolysis furnace; finally, the two-stage pyrolysis furnace produces biochar, bio-oil and syngas. The biochar is used for resource utilization, and the bio-oil and syngas enter the waste heat recovery system, and the recovered heat is used for the temperature control of the MFC system and sludge dehydration.

[0024] Among them, in the microbial fuel cell (MFC) system: Anode microbial community: Electroactive bacteria such as Geobacter sulfurreducens are domesticated to form a biofilm on the anode surface, converting organic matter (such as COD) into electrons (reaction formula ).

[0025] Cathode strengthening strategy: Using MnO2 / graphene composite catalyst to reduce the oxygen reduction overpotential and improve the cathode reaction efficiency ( ).

[0026] Three-dimensional electrode structure: Using carbon fiber cloth to wrap activated carbon particles, the specific surface area reaches 1200 m² / g, the internal resistance is reduced to 80 Ω, and the power density breaks through 1.2 kW / m³ (only 0.3 kW / m³ for traditional flat electrodes).

[0027] Among them, the production of biochar from sludge pyrolysis: 1. Pyrolysis process parameters Two-stage pyrolysis: Low-temperature dehydration stage (150 - 250 °C): Utilizing the waste heat generated by MFC power generation, the moisture content of the sludge is reduced from 80% to 40%, and the energy consumption is reduced.

[0028] High-temperature pyrolysis stage (500 - 600 °C): Staying for 30 minutes in an N2 atmosphere, the biochar yield reaches 35 - 40% (calculated based on dry sludge), and the calorific value is 18 - 22 MJ / kg.

[0029] Catalyst modification: Adding 5% of FeCl3 by mass of the dehydrated sludge to promote tar decomposition, increasing the specific surface area of the biochar to 800 m² / g, and enhancing the heavy metal adsorption capacity.

[0030] 2. Product value extension Soil conditioner: Biochar with a pH of 8.5 - 9.5 and a CEC (cation exchange capacity) of 35 cmol / kg can repair acidic soil.

[0031] Water quality purification filler: Biochar loaded with nano zero-valent iron (nZVI) has a removal rate of Cr(VI) up to 98% and an adsorption capacity of 25 mg / g.

[0032] Among them, during co-treatment: 1. Energy closed-loop: The syngas (H2 / CO) generated by pyrolysis is used for power generation to supplement the energy consumption of the MFC system, achieving a net energy output of 15%.

[0033] 2. Material cycle: Biochar is reused as the cathode filler in the MFC. Its porous structure improves the oxygen transfer efficiency by 20%, and at the same time, the adsorption of cathode by-products (such as nitrous oxide) reduces greenhouse gas emissions.

[0034] Co-treatment reduces the operating cost compared to single treatment.

[0035] Such as Figure 2 shown, the wastewater treatment method described in this embodiment includes the following steps: S1. Introduce the wastewater into the microbial fuel cell system for treatment. Utilize the anode microbial community to convert organic matter into electrons to generate electricity, and at the same time remove COD in the wastewater to make the effluent meet the discharge standards. S2. Transport the excess sludge generated by the microbial fuel cell system to the dehydration pretreatment device for dehydration treatment. S3. Feed the dehydrated sludge into a two-stage pyrolysis furnace for pyrolysis. First, use the waste heat generated by the microbial fuel cell for power generation in the low-temperature dehydration section to reduce the moisture content of the sludge, and then carry out pyrolysis reaction in the high-temperature pyrolysis section to generate biochar, bio-oil and syngas. S4. Collect the biochar generated by pyrolysis for soil improvement or water quality purification. S5. Transport the bio-oil and syngas generated by pyrolysis to the waste heat recovery system. The recovered heat is used for temperature control of the microbial fuel cell system and sludge dehydration pretreatment, and the syngas is used for power generation to supplement the system energy consumption.

[0036] Among them, during the process of treating wastewater in the microbial fuel cell system, monitor the influent water quality and control the influent COD within the range of 500 - 1500 mg / L, ammonia nitrogen within the range of 50 - 100 mg / L, and pH within the range of 6.5 - 8.0.

[0037] Among them, before pyrolyzing the sludge in the two-stage pyrolysis furnace, carry out microbial leaching treatment on the sludge, and use Thiobacillus ferrooxidans to remove more than 90% of heavy metals such as Cu / Pb.

[0038] Example 1: Application in a domestic sewage treatment plant In a sewage treatment plant with a daily treatment capacity of 5,000 tons of domestic sewage, the wastewater treatment system of the example played an important role. The microbial fuel cell (MFC) system consists of 12 groups of modular reactors arranged in an orderly manner, forming a reaction structure with stable treatment capacity. In the anode chamber, researchers carefully domesticated electroactive bacteria such as Geobacter sulfurreducens, and these electroactive bacteria closely adhered to the anode surface, forming a vibrant biofilm.

[0039] When domestic sewage flows into the MFC system, the anode microbial community initiates metabolic activities. They use the organic matter in the sewage as a substrate, and through the bioelectrochemical metabolic process, convert the organic matter into electrons. The electrons are transferred through the external circuit to form an electric current, and then electrical energy is generated. At the same time, a large amount of COD in the wastewater is removed. After detection, when the influent water quality is stably controlled at COD 800 mg / L, ammonia nitrogen 70 mg / L, and pH around 7.0, the COD removal rate of the treated effluent is as high as 90%, the power generation density reaches 1.2 W / m², and the generated electrical energy is sufficient to meet 30% of the power demand of the plant area, providing considerable energy support for the daily operation of the sewage treatment plant.

[0040] The treated sewage meets the discharge standards, and the generated excess sludge is transported to the dehydration pretreatment device. Here, the sludge undergoes a series of physical treatments to remove a large amount of water. Subsequently, the dewatered sludge enters a two-stage pyrolysis furnace. The low-temperature dehydration section cleverly utilizes the waste heat generated by MFC power generation to control the temperature between 150 - 250 °C. In this temperature range, the moisture content of the sludge smoothly drops from 80% to 40%, not only saving additional energy consumption but also creating good conditions for subsequent pyrolysis reactions. Then, the sludge enters the high-temperature pyrolysis section, where it continuously reacts for 30 minutes at a high temperature of 550 °C under the protection of an N2 atmosphere. At the same time, 5% of the mass of the dehydrated sludge of FeCl3 is added as a catalyst, which greatly promotes the pyrolysis reaction. Finally, the biochar yield reaches 38%. These biochars are transported to 2,000 mu of surrounding farmland for soil improvement.

[0041] After detection, the bulk density of the soil without biochar improvement is 1.45 g / cm³, the field water holding capacity is 25%, and the organic matter content is 1.2%; after improvement with biochar, the bulk density of the soil drops to 1.2 g / cm³, the structure is looser, the field water holding capacity increases to 32%, the water and fertilizer retention capacity is significantly enhanced, and the organic matter content increases to 1.8%. Comparative planting experiments show that the average mu yield of crops on the unimproved soil is 800 kg, and the protein content of agricultural products is 10%; after improvement of the soil, the average mu yield of crops increases to 950 kg, and the protein content of agricultural products increases to 13%, and the yield and quality of crops are significantly improved.

[0042] Example 2: Food processing plant wastewater treatment Food processing plants produce a large amount of high COD wastewater every day, with a content of about 1200 mg / L. Faced with this problem, the MFC system of the embodiment adopts a series of targeted optimization measures. The researchers first carefully screened and domesticated the anode microbial community so that it can better adapt to the environment of high concentration of organic matter. At the same time, MnO2 / graphene composite catalyst is used in the cathode chamber, and conductive hydrogel (PAM / CNT composite membrane) is introduced. This composite membrane is like a bridge, which greatly reduces the internal resistance of MFC to below 50Ω, thereby significantly improving the power generation efficiency.

[0043] During the wastewater treatment process, the MFC system efficiently converts organic matter in the wastewater into electrical energy and removes a large amount of COD. The treated sludge first enters the dehydration pretreatment device for preliminary dehydration. Before entering the two-stage pyrolysis furnace, the sludge is treated using microbial leaching (Thiobacillus ferrooxidans) technology, successfully removing more than 90% of heavy metals such as Cu / Pb, effectively reducing the risk of secondary pollution of subsequent pyrolysis products.

[0044] The two-stage pyrolysis furnace operates according to the set parameters. The low-temperature dehydration section uses the waste heat from the MFC to further reduce the moisture content of the sludge. The high-temperature pyrolysis section performs pyrolysis reactions at a high temperature of 500-600°C to generate biochar, bio-oil and synthesis gas. The biochar produced by pyrolysis is put into use as a water purification filler. With its rich pore structure and good adsorption performance, it deeply adsorbs the trace organic matter and heavy metals remaining in the wastewater. After testing, the removal rate of biochar for Cr(VI) is as high as 98%, and the adsorption capacity reaches 25mg / g, which further improves the effluent water quality, enables the treated wastewater to meet strict emission standards, and realizes the recycling of water resources. At the same time, the production and application of biochar also brings additional economic benefits to food processing plants.

[0045] Example 3: Chemical Park Wastewater Treatment The composition of wastewater in chemical parks is extremely complex, including a variety of organic pollutants, heavy metal ions and difficult-to-degrade compounds. In order to effectively treat these wastewaters, the implementation example uses digital twin technology (ANSYS TwinBuilder) to conduct a comprehensive dynamic simulation and optimization of the entire wastewater treatment system.

[0046] Through the digital model, the operating parameters of the MFC system were deeply analyzed. For example, the electrode spacing was set at 5 cm and the hydraulic retention time was controlled at 12 hours to study their effects on the treatment effect. After 10 simulations and adjustments, the optimal combination of operating parameters was determined. In terms of the two-stage pyrolysis furnace, the set temperature of the low-temperature dehydration section was 80 °C and the treatment time was 2 hours; the temperature of the high-temperature pyrolysis section was 500 °C and the time was 3 hours, and the addition amount of the catalyst FeCl3 was 5% of the mass of the dehydrated sludge, and refined optimization was carried out. During the operation of the optimized system, the removal efficiency of various pollutants in the wastewater by the MFC system was greatly improved, and the power generation performance was also significantly enhanced.

[0047] The two-stage pyrolysis furnace operates stably under the optimized parameters. The low-temperature dehydration section makes full use of the waste heat generated by the MFC for power generation and efficiently reduces the moisture content of the sludge. Under the precisely controlled temperature and time conditions in the high-temperature pyrolysis section, with the addition of an appropriate amount of FeCl3 catalyst accounting for 5% of the mass of the dehydrated sludge, both the yield and quality of biochar have been greatly improved. The biochar is reused as the cathode filler of the MFC. Its unique porous structure improves the oxygen transfer efficiency by 20%, and at the same time effectively adsorbs the cathode by-products, reducing greenhouse gas emissions. The overall energy efficiency ratio of the system reaches more than 1.3, realizing efficient and stable operation, not only reducing the operating cost but also improving the resource utilization rate, providing a strong guarantee for the sustainable development of chemical industrial parks.

[0048] Example 4: Treatment of printing and dyeing factory wastewater The wastewater from printing and dyeing factories has the characteristics of complex composition and high chroma, making it extremely difficult to treat. The wastewater treatment system in the example took a series of special measures according to the characteristics of printing and dyeing wastewater. A pretreatment process was added before the MFC system. First, the coagulation and precipitation technology was used to remove some suspended solids and macromolecular organic matter in the wastewater, and then the adsorption process was used to further remove refractory organic matter and chroma, reducing the treatment burden of the subsequent MFC system.

[0049] The MFC system uses the Geobacter sulfurreducens strain that has been screened and cultivated for a long time. This strain has strong adaptability and degradation ability to printing and dyeing wastewater. During the treatment process, the microbial fuel cell efficiently removes the organic matter in the wastewater and generates electricity at the same time. The treated sludge enters the two-stage pyrolysis furnace for pyrolysis after dehydration pretreatment.

[0050] The biochar produced by pyrolysis is used for the advanced treatment of printing and dyeing wastewater after being loaded with nano zero-valent iron (nZVI). The synergistic effect of biochar and nano zero-valent iron enables its removal rate of Cr(VI) to reach 98%, and the adsorption capacity to reach 25 mg / g. After the treatment of the printing and dyeing wastewater, the chroma is significantly reduced, and all pollutant indexes meet the discharge standards. The treated water can be recycled for the printing and dyeing production process, realizing the recycling of water resources, greatly reducing the water consumption cost of the printing and dyeing factory, and at the same time reducing environmental pollution, achieving good environmental and economic benefits.

[0051] Example 5: Treatment of papermill wastewater The papermill discharges a large amount of wastewater every day, which contains high concentrations of organic pollutants such as lignin and cellulose, as well as a certain amount of chemical additives and heavy metal ions. The wastewater treatment system of the example plays a key role in the treatment of papermill wastewater.

[0052] The microbial fuel cell system optimized the anode microbial community according to the characteristics of papermaking wastewater. Microbial strains such as Geobacter sulfurreducens that can efficiently degrade lignin and cellulose were screened out and domesticated to adapt to the complex environment of papermaking wastewater. A special catalyst was used in the cathode chamber to improve the efficiency of the oxygen reduction reaction. When the influent COD was 1500 mg / L, ammonia nitrogen was 80 mg / L, and pH was about 7.2, the MFC system effectively converted the organic matter in the wastewater into electric energy and removed a large amount of COD at the same time.

[0053] The treated sludge enters a two-stage pyrolysis furnace after dehydration pretreatment. In the low-temperature dehydration stage, the waste heat generated by MFC power generation is used to reduce the sludge moisture content from 80% to 40%. In the high-temperature pyrolysis stage, it stays for 30 minutes at 580 °C in an N2 atmosphere, and FeCl3 catalyst accounting for 5% of the mass of the dehydrated sludge is added. The biochar produced by pyrolysis has a rich pore structure and a large specific surface area, and has a strong adsorption capacity for the residual heavy metal ions and organic pollutants in papermaking wastewater. The biochar is used in the sewage treatment link of the papermill to further improve the effluent quality. At the same time, the syngas produced by pyrolysis is used for power generation, supplementing the energy consumption of the system and reducing the production cost.

[0054] Example 6: Treatment of electroplating plant wastewater The electroplating plant wastewater contains a large amount of heavy metal ions such as chromium, nickel, copper, etc., as well as highly toxic and harmful substances such as high-concentration cyanide. The wastewater treatment system of the example provides an effective solution for the treatment of electroplating plant wastewater.

[0055] Before the wastewater enters the MFC system, pretreatment is carried out first. The chemical precipitation method is used to remove most heavy metal ions, and then cyanide is decomposed through redox reactions. The pretreated wastewater enters the MFC system, which adopts a microbial community resistant to heavy metals and cyanide, as well as special electrode materials. During the treatment process, the microbial fuel cell not only removes the residual organic matter and some heavy metal ions in the wastewater, but also generates electricity.

[0056] After the treated sludge undergoes dehydration pretreatment, it enters a two-stage pyrolysis furnace. During the pyrolysis process, the low-temperature dehydration section utilizes the waste heat generated by the MFC for power generation, and the high-temperature pyrolysis section is carried out at 520 °C under a nitrogen atmosphere. The biochar produced by pyrolysis is loaded with specific metal chelating agents, which have strong adsorption selectivity for the residual heavy metal ions in the wastewater. After detection, the content of heavy metal ions in the treated wastewater is far lower than the discharge standard. The biochar can also be used in certain links during the production process of electroplating factories, such as adsorbing impurities in the electrolyte, realizing the recycling of resources, reducing production costs, and effectively reducing the environmental pollution of electroplating factory wastewater.

[0057] Control for the change in the anode microbial community of the microbial fuel cell system: Referring to Example 1, instead of domesticating Geobacter sulfurreducens electroactive bacteria in the anode chamber of the microbial fuel cell system, ordinary activated sludge is used. During the wastewater treatment process, due to the lack of microorganisms that can efficiently convert organic matter into electrons, the power generation efficiency drops significantly, and the power generation density is only 0.2 W / m², far lower than 1.2 W / m² in Example 1. At the same time, the COD removal rate in the wastewater also decreases significantly, only reaching 60%, and it is impossible to stably meet the discharge standard for the effluent, indicating that a specific anode microbial community plays a key role in the energy recovery and pollutant removal of the system.

[0058] Control for the change in the temperature of the low-temperature dehydration section of the two-stage pyrolysis furnace: According to Example 1, the temperature of the low-temperature dehydration section of the two-stage pyrolysis furnace is set at 100 °C. At this temperature, when using the waste heat generated by the microbial fuel cell for power generation to dehydrate the sludge, the moisture content of the sludge can only be reduced from 80% to 60%, and it is impossible to achieve the effect of reducing to 40% in the example. This leads to an increase in energy consumption in the subsequent high-temperature pyrolysis section, a decrease in the biochar yield to 30%, and a decline in the quality of the biochar, with poor adsorption performance and soil improvement effects, indicating that an appropriate temperature for the low-temperature dehydration section is crucial for the entire pyrolysis process and product quality.

[0059] Comparison of influent water quality exceeding the set range: Based on Example 1, the influent COD was increased to 2000 mg / L, the ammonia nitrogen was increased to 150 mg / L, and the pH was adjusted to 9.0. The microbial fuel cell system was overloaded, the activity of the anode microbial community was inhibited, the power generation efficiency decreased significantly, and the power generation density dropped to 0.5 W / m². At the same time, the COD removal rate was only 70%, and the effluent could not meet the discharge standards. In addition, the excessive ammonia nitrogen and inappropriate pH also affected the pyrolysis effect of the sludge in the two-stage pyrolysis furnace, and both the biochar yield and quality decreased, proving that strictly controlling the influent water quality within the set range of the invention is crucial for the stable operation and treatment effect of the system.

[0060] Comparison of no catalyst added in the high-temperature pyrolysis section of the two-stage pyrolysis furnace: Referring to Example 1, no FeCl3 accounting for 5% of the mass of the dehydrated sludge was added as a catalyst in the high-temperature pyrolysis section of the two-stage pyrolysis furnace. The pyrolysis reaction was not sufficient, the tar decomposition was incomplete, the specific surface area of the biochar was only 600 m² / g, lower than 800 m² / g when the catalyst was added. The adsorption capacity of the biochar for heavy metals also decreased significantly, and the removal rate of Cr(VI) was only 80%, far lower than 98% in the example. Moreover, the biochar yield decreased to 32%, indicating that adding a catalyst in the high-temperature pyrolysis section is of great significance for improving the quality and yield of biochar.

[0061] Comparison of no sludge microbial leaching treatment: According to Example 2, the sludge was not subjected to microbial leaching treatment before pyrolysis in the two-stage pyrolysis furnace. The biochar produced by pyrolysis contained a large amount of heavy metals such as Cu / Pb. When used as a water purification filler, it could not effectively purify the water quality and might even cause secondary pollution. At the same time, due to the presence of heavy metals, when the biochar was used for soil improvement, it would pose a potential hazard to the soil ecological environment and affect the growth of crops, highlighting the importance of sludge microbial leaching treatment in reducing the risk of secondary pollution.

[0062] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A wastewater treatment system, comprising a microbial fuel cell system, a dehydration pretreatment device, a two-stage pyrolysis furnace, and a waste heat recovery system; The microbial fuel cell system is used to treat wastewater and generate electric energy. The water inlet of the microbial fuel cell system is connected to a wastewater source, the water outlet is used to discharge up-to-standard effluent, and the excess sludge outlet is connected to the inlet of the dehydration pretreatment device; The dehydration pretreatment device is used to dehydrate the sludge generated by the microbial fuel cell system, and its outlet is connected to the feed inlet of the two-stage pyrolysis furnace; The two-stage pyrolysis furnace is used to pyrolyze the dehydrated sludge to produce biochar, bio-oil, and syngas. The biochar outlet of the two-stage pyrolysis furnace is used to output biochar, and the bio-oil and syngas outlets are connected to the waste heat recovery system; The waste heat recovery system is used to recover the heat generated by pyrolysis, and its heat output end is respectively connected to the temperature control device of the microbial fuel cell system and the dehydration pretreatment device.

2. The wastewater treatment system according to claim 1, wherein: The microbial fuel cell system includes an anode chamber, a cathode chamber, and a proton exchange membrane. Geobacter sulfurreducens electroactive bacteria are domesticated in the anode chamber, and the cathode chamber uses a MnO2 / graphene composite catalyst.

3. The wastewater treatment system according to claim 2, characterized in that: The electrodes of the microbial fuel cell system adopt a three-dimensional electrode structure, which is composed of activated carbon particles wrapped in carbon fiber cloth, with a specific surface area of up to 1200 m² / g and an internal resistance reduced to below 80 Ω.

4. The wastewater treatment system according to claim 1, characterized in that: The two-stage pyrolysis furnace includes a low-temperature dehydration section and a high-temperature pyrolysis section. The temperature of the low-temperature dehydration section is 150 - 250 °C, and the waste heat generated by the microbial fuel cell is used to reduce the moisture content of the sludge from 80% to 40%; the temperature of the high-temperature pyrolysis section is 500 - 600 °C, and it stays for 30 minutes in an N2 atmosphere.

5. The wastewater treatment system according to claim 4, characterized in that: 5% of FeCl3 based on the mass of the dehydrated sludge is added as a catalyst in the high-temperature pyrolysis section of the two-stage pyrolysis furnace.

6. The wastewater treatment system according to claim 1, characterized in that: The wastewater treatment system further includes a biochar application device, which is used to use the biochar generated by pyrolysis as a soil conditioner or a water purification filler.

7. The wastewater treatment system according to claim 1, characterized in that: The wastewater treatment system realizes full-process dynamic simulation and optimization based on digital twin technology.

8. A wastewater treatment method using the wastewater treatment system according to any one of claims 1-7, characterized in that, It includes the following steps: S1. Introduce the wastewater into the microbial fuel cell system for treatment. Use the anode microbial community to convert organic matter into electrons to generate electric energy, and at the same time remove COD in the wastewater to make the effluent meet the standards for discharge; S2. Transport the excess sludge generated by the microbial fuel cell system to the dehydration pretreatment device for dehydration treatment; S3. Send the dehydrated sludge into the two-stage pyrolysis furnace for pyrolysis. First, use the waste heat generated by the microbial fuel cell in the low-temperature dehydration section to reduce the moisture content of the sludge, and then carry out a pyrolysis reaction in the high-temperature pyrolysis section to generate biochar, bio-oil, and syngas; S4. Collect the biochar generated by pyrolysis; S5. Transport the bio-oil and syngas generated by pyrolysis to the waste heat recovery system. The recovered heat is used for the temperature control of the microbial fuel cell system and the sludge dehydration pretreatment, and the syngas is used for power generation to supplement the system energy consumption.

9. The wastewater treatment method according to claim 8, characterized in that: During the process of treating wastewater by a microbial fuel cell system, monitor the influent water quality and control the influent COD within the range of 500 - 1500 mg / L, ammonia nitrogen within the range of 50 - 100 mg / L, and pH within the range of 6.5 - 8.

0.

10. The wastewater treatment method according to claim 8, characterized in that: Before pyrolyzing sludge in a two-stage pyrolyzer, perform microbial leaching treatment on the sludge and use Thiobacillus ferrooxidans to treat and remove Cu / Pb heavy metals.

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