An ecological treatment device for simultaneous purification of landfill leachate and recovery of electric energy

Abstract

The application discloses a kind of ecological treatment equipment of garbage leachate purification and electric energy recovery synchronous, belong to garbage leachate processing technical field, including biological slow filter pond pretreatment device and artificial wetland-microbial fuel cell advanced treatment and energy production device, system uses three-dimensional current collection network electrode structure, through low impedance wire connection special energy recovery circuit, realize low voltage electric energy efficient collection, voltage boost and storage;Control module is according to real-time power density dynamic adjustment hydraulic retention time, realizes power generation and purification collaborative optimal control.The application improves biodegradability through biological slow filter pond, cooperates CW-MFC device, effectively solves the problems of large electrode loss, electric energy cannot be recovered, extensive operation control, low purification efficiency and the like of existing CW-MFC, can realize garbage leachate efficient denitrification and phosphorus removal, COD deep removal and electric energy recovery simultaneously, with the advantages of stable operation, intelligent controllable, low-carbon energy-saving, strong practicality and the like.

Description

[0001] This invention relates to the field of landfill leachate treatment technology, specifically to an ecological treatment device that simultaneously purifies landfill leachate and recovers electricity. Background Technology

[0002] Landfill leachate is characterized by high COD concentration, high ammonia nitrogen and total phosphorus loads, a variety of heavy metals, poor biodegradability, and drastic water quality fluctuations, classifying it as a typical high-concentration, recalcitrant organic wastewater. Traditional treatment processes generally suffer from low treatment efficiency, high operating costs, high energy consumption, inability to recover energy, and a tendency to cause secondary pollution. Currently, mainstream processes often employ a combination of anaerobic, aerobic, and membrane separation routes. While these can achieve pollutant discharge standards, they suffer from drawbacks such as high energy consumption, severe membrane fouling, complex operation and maintenance, and difficulties in concentrated wastewater disposal. Furthermore, the entire treatment process focuses solely on pollutant removal, failing to recover and utilize the chemical energy of the wastewater, which is inconsistent with the development direction of low-carbon and resource-based methods.

[0003] Constructed wetland-microbial fuel cell (CW-MFC) coupling technology can convert the chemical energy of organic matter into electrical energy while purifying water, making it an important research direction in the field of landfill leachate treatment. However, existing CW-MFC systems still have significant technical shortcomings in practical applications, as follows: First, the electrode structure has poor compatibility with the external circuit, resulting in extremely low energy recovery efficiency. Existing CW-MFC systems mostly use simple single-electrode connections, with unreasonable electrode layout, imperfect current collection networks, high wire impedance, and large contact resistance, leading to severe electron transfer losses. At the same time, they lack dedicated energy recovery circuits, resulting in low system output voltage and poor stability. It is difficult to effectively collect, boost, and store generated electricity, and there is a common problem of "generating electricity but not being able to use it," thus failing to realize the value of energy recovery.

[0004] Second, the operation and control methods are crude and cannot achieve optimal control of power generation efficiency. Existing CW-MFCs all operate with a fixed hydraulic retention time (HRT) and have not established a linkage mechanism between power generation parameters and hydraulic conditions. They cannot adaptively adjust the HRT according to real-time conditions such as output voltage and power density. When water quality fluctuates, microbial activity changes, or there are load shocks, the system is prone to problems such as decreased purification efficiency, power generation decline, ammonia nitrogen rebound, and unstable phosphorus removal, making it difficult to maintain efficient and stable operation in the long term.

[0005] In summary, existing CW-MFC technology cannot simultaneously solve key technical challenges such as high electrode-circuit connection losses, difficulty in recovering low-voltage energy, unstable operation due to fixed HRT, and inability to synergistically enhance purification and power generation. Therefore, it is difficult to meet the engineering requirements for efficient, stable, energy-efficient, and intelligent treatment of landfill leachate. Summary of the Invention

[0006] This invention addresses the problem of overly simplistic solutions in existing technologies by providing a significantly different approach. It offers an ecological treatment device that simultaneously purifies landfill leachate and recovers electricity. By optimizing the connection structure between the electrodes and the energy recovery circuit, and establishing a power generation efficiency control logic based on HRT regulation, it fundamentally overcomes the aforementioned deficiencies, achieving simultaneous and efficient purification, stable power generation, and intelligent adaptive operation. This solves the technical problems mentioned in the background, such as high electrode-circuit connection losses, difficulty in recovering low-voltage electricity, and unstable operation due to fixed HRT.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: An ecological treatment device that simultaneously purifies landfill leachate and recovers electricity includes a biological slow filter pretreatment device and an artificial wetland-microbial fuel cell deep treatment and production device, wherein the effluent from the biological slow filter pretreatment device is used as the influent from the artificial wetland-microbial fuel cell deep treatment and production device. The constructed wetland-microbial fuel cell deep processing and production device includes an anode, a cathode, packing material, wetland plants, and an energy recovery circuit. The anode and cathode are directly connected to the input terminal of the energy recovery circuit via wires. It also includes a control module, which is connected to the monitoring unit in the energy recovery circuit and the flow control valve located at the inlet of the constructed wetland-microbial fuel cell deep treatment and production device. The control module executes the following power generation efficiency control logic: The control module is configured to dynamically adjust the hydraulic residence time of the constructed wetland-microbial fuel cell by real-time monitoring of power generation parameters, so that the system is maintained in the optimal power generation range.

[0008] Furthermore, the constructed wetland-microbial fuel cell deep treatment and production device adopts a vertical subsurface flow upflow structure or a vertical downflow structure, preferably a vertical subsurface flow upflow structure; and its interior is arranged from top to bottom as follows: wetland plants, cathode carbon felt and overlying water layer, fine sand filter layer, packing layer, anode carbon felt, and support layer. The filler is one of sponge iron, zeolite, and activated carbon, with sponge iron being preferred.

[0009] Furthermore, the anode carbon felt is composed of multiple anode carbon felt sheets connected in parallel or series to form a three-dimensional current collection network, which is completely immersed in the filler layer; The cathode carbon felt is composed of multiple cathode carbon felt sheets connected in parallel or series to form a cathode current collection network, located at the gas-liquid interface and distributed around the root system of wetland plants. Both the anode carbon felt and the cathode carbon felt are connected to the energy recovery circuit via low-impedance copper core wires.

[0010] Furthermore, both the anode carbon felt and the cathode carbon felt are carbon felts that have undergone acid hydrophilic treatment; The spacing between the anode carbon felt and the cathode carbon felt is 10-15cm, preferably 12cm.

[0011] Furthermore, the energy recovery circuit includes, in sequence along the direction of electrical energy transmission: an impedance matching unit, a boost unit, an energy storage unit, and a monitoring unit; The impedance matching unit is a maximum power point tracking controller used to dynamically match the internal resistance of the system; The boost unit is a DC-DC boost converter used to boost low voltage to a usable voltage; The monitoring unit is used to collect voltage and current data in real time and calculate power density.

[0012] Furthermore, the control module executes the following control logic based on the real-time power density: (1) When the power density is less than or equal to the low threshold Th2, extend the hydraulic residence time; (2) When the power density is greater than or equal to the high threshold Th1 and remains stable for a preset duration, shorten the hydraulic residence time; (3) When the power density is between Th2 and Th1, the current hydraulic residence time remains unchanged.

[0013] Furthermore, the hydraulic residence time can be adjusted within a range of 20 to 50 days, with an adjustment step of 5% to 10%.

[0014] Furthermore, the control module is also equipped with an early warning unit, which issues an early warning signal when the power density is lower than Th2 for 7 consecutive days.

[0015] Furthermore, the external fixed resistor of the constructed wetland-microbial fuel cell is 1000Ω; the data acquisition interval of the monitoring unit is 10 minutes.

[0016] Furthermore, the biological slow filter pretreatment device is equipped with a filter media layer, which consists of a gravel support layer, a multi-level filter media layer, and an overlying water layer from bottom to top. The multi-layer filter media includes, from bottom to top, an activated carbon layer, a biochar layer, and a quartz sand layer; the particle size of the quartz sand is 0.5-1.0 mm, and the particle size of both the activated carbon and biochar is 1.0-2.0 mm.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses a biological slow filter (BSSF) pretreatment device, which effectively reduces the influent load, removes heavy metals and suspended solids through the synergistic effect of mechanical interception, physical adsorption and biodegradation, and increases the BOD5 / COD of leachate from 25.36% to 31.17%, significantly improving biodegradability and providing a prerequisite for the efficient and stable operation of CW-MFC.

[0018] (2) The present invention adopts a three-dimensional anode current collection network and a cathode current collection network, and directly connects the energy recovery circuit with a low impedance copper core wire to optimize the electrode-circuit interface matching, significantly reduce contact resistance and electron transmission loss, and solve the problems of scattered electrode connection and large power generation leakage in the prior art.

[0019] (3) The energy recovery circuit of the present invention integrates MPPT impedance matching, DC-DC boost, energy storage and real-time monitoring units, which can effectively collect, boost and stably store the low voltage generated electricity of CW-MFC, realize the electricity generated can be used immediately, and solve the technical problems of low voltage cannot be recovered and low energy utilization rate.

[0020] (4) The present invention adopts intelligent control logic based on real-time adjustment of HRT according to power density, automatically extending / shortening hydraulic residence time according to power generation status, so that the system always maintains the optimal power generation and degradation range, and solves the problems of easy fluctuation in fixed HRT operation and unstable purification and power generation efficiency.

[0021] (5) The present invention preferably uses an upflow structure and sponge iron filler to enhance mass transfer efficiency and electron transfer, reduce the system internal resistance to 420.20Ω, and achieve a maximum power density of 3564.63mW / m 2 It simultaneously achieves deep phosphorus removal, stable nitrogen removal, and efficient COD degradation, avoiding ammonia nitrogen rebound and COD increase.

[0022] (6) The preferred sponge iron filler of the present invention can regulate the pH gradient of the cathode and anode, forming an alkaline cathode and a stable electrochemical microenvironment, enhancing the oxygen reduction reaction and heavy metal precipitation, and further improving the synergistic effect of purification and power generation.

[0023] (7) The present invention integrates deep purification of landfill leachate, synchronous power recovery and intelligent adaptive operation. It is stable in operation, simple in operation and maintenance, free from membrane pollution, low carbon and energy saving, and meets the needs of resource utilization and energy development.

[0024] This invention utilizes a two-stage cascaded process of biological slow filter pretreatment and CW-MFC deep treatment, combined with an optimized electrode-energy recovery circuit connection structure and power generation efficiency control logic based on HRT intelligent adjustment. This fundamentally solves the technical defects of existing CW-MFC systems, such as high electron transfer loss, inability to recover low-voltage energy, unstable operation of fixed HRT, and incomplete pollutant removal. While achieving efficient denitrification, deep phosphorus removal, and stable COD degradation of landfill leachate, it also efficiently converts and recovers the chemical energy of organic matter into electrical energy. It boasts significant advantages such as excellent purification effect, high power generation efficiency, stable operation, intelligent controllability, and low carbon emissions, making it highly applicable to engineering projects.

[0025] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0026] Figure 1 The diagram shows the structure of the ecological treatment equipment of the present invention; wherein (a) is a schematic diagram of the structure of a downflow constructed wetland-microbial fuel cell, and (b) is a schematic diagram of the structure of an upflow constructed wetland-microbial fuel cell. Figure 2 In different embodiments of the present invention, the constructed wetland-microbial fuel cell reduces the total phosphorus (TP) and ammonia nitrogen (NH4) content in landfill leachate. + Comparison of removal effects of total phosphorus (N) and chemical oxygen demand (COD); where (a) is the total phosphorus removal effect curve, (b) is the ammonia nitrogen removal effect curve, and (c) is the chemical oxygen demand removal effect curve. Figure 3 These are the pH change curves of the anode and cathode of the constructed wetland-microbial fuel cell as a function of operating time in different embodiments of the present invention; wherein (a) is the pH change curve of the cathode and (b) is the pH change curve of the anode. Figure 4 The diagram shows the polarization curves and power density curves of the constructed wetland-microbial fuel cell in different embodiments of the present invention; where (a) is the polarization curve and (b) is the power density curve. Figure 5 These are SEM images of microorganisms and their micromorphology on the packing surface before and after experiments in different embodiments of the present invention, showing the effects of artificial wetland-microbial fuel cell experiments. Detailed Implementation

[0027] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0028] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Example 1: An ecological treatment device that simultaneously purifies landfill leachate and recovers electricity includes a biological slow filter (BSSF) pretreatment unit and an constructed wetland-microbial fuel cell (CW-MFC) deep treatment and production unit, connected in series, with the effluent from the former directly used as the influent from the latter. Specifically: The BSSF pretreatment unit includes a container with an inlet and an outlet, such as an acrylic column. Water is evenly distributed at the top of the container, and the outlet is located 3.0 cm from the bottom. The operation is intermittent, with slow, even water distribution. The filter media layer inside the container consists of the following layers arranged from bottom to top: Support layer: The bottom is laid with gravel, with a thickness of 5.0cm and a gravel particle size of 9-12mm; Multi-layer filter media: Located above the support layer, from bottom to top, it consists of an activated carbon layer, a biochar layer, and a quartz sand layer, each layer laid independently; the quartz sand particle size is 0.5-1.0mm. Both activated carbon and biochar have a particle size of 1.0-2.0 mm. A quartz sand layer is located at the top, utilizing its own weight to inhibit the floating of the less dense activated carbon / biochar and providing initial mechanical retention. In this embodiment, the activated carbon layer is 15 cm thick, the biochar layer is 15 cm thick, and the quartz sand layer is 10 cm thick.

[0031] Overlying water layer: 5.0 cm high, used to stabilize hydraulic conditions.

[0032] The hydraulic retention time (HRT) of a biological slow filter (BSSF) pretreatment unit is 35-45 days.

[0033] In this embodiment, the effective volume of the plexiglass column is approximately 15L, the inner diameter is 20.0cm, and the height is 60.0cm; the column body does not require light shielding.

[0034] In this embodiment, the single influent volume was 5.0L, the hydraulic retention time (HRT) was 40 days, and the experimental ambient temperature was 25±3℃; samples were taken for monitoring every 3 days.

[0035] The function of the BSSF pretreatment unit is to remove suspended solids, some organic matter and heavy metals from landfill leachate through mechanical interception, physical adsorption, chemical complexation and aerobic / anaerobic degradation of the biofilm formed on the surface of the filter media, and to increase the BOD5 / COD of the leachate from 25.36% to 31.17%, thereby improving the biodegradability of the leachate.

[0036] In this embodiment, the CW-MFC deep processing and production capacity device, such as... Figure 1As shown in (b), a vertical subsurface-to-upflow structure is adopted, with water entering from the bottom and exiting from the top. For example, a polypropylene tank. The outer wall of the container is wrapped with a black plastic film to block light and prevent algae growth. The internal structural layers of the container include, from top to bottom, the following: Wetland plants: In this example, two water hyacinth plants were used, with a plant height of 24.0±2.0cm and a fresh weight of 75.0±5.0g. They were used after being hydroponically acclimatized for 2 weeks. Cathode carbon felt and overlying water layer: The cathode carbon felt is a hydrophilic-treated annular hollow carbon felt with a thickness of 5.0 mm, an inner diameter of 10.0 cm, and an outer diameter of 20.0 cm; the overlying water layer has a thickness of 3.0 cm. Fine sand filter layer: particle size 0.1-0.3cm, thickness 3.0cm; Filler layer: The thickness is 10.0 cm. In this embodiment, DRI sponge iron is used as the filler. Anode carbon felt: Same specifications as cathode, and undergoes the same hydrophilic treatment; Support layer: gravel with a particle size of 0.9-1.2cm and a thickness of 4.0cm.

[0037] Both the cathode and anode carbon felts are treated with an acid hydrophilic method: first soaked in 1M H2SO4 for 24 hours, then rinsed with deionized water 5 times, then bathed in a 90℃ water bath for 30 minutes, and finally dried at 80℃ for 24 hours.

[0038] The anode carbon felt is completely submerged in the filler layer, while the cathode carbon felt is located at the gas-liquid interface and distributed around the roots of wetland plants.

[0039] The spacing between the cathode and anode carbon felts is 10-15 cm. In this embodiment, the spacing is 12 cm.

[0040] The aforementioned structural layers collectively constitute the reaction carrier and spatial environment of the constructed wetland-microbial fuel cell (CW-MFC), providing the necessary conditions for electrochemically active microorganisms to attach, grow, and reproduce on the anode carbon felt surface, forming a stable electrochemically active biofilm. The formation and maturation of this electrochemically active biofilm is the core foundation for achieving pollutant degradation, electron transfer, and simultaneous power generation. Therefore, before the equipment is officially put into operation with landfill leachate, the CW-MFC unit needs to be inoculated and acclimatized. The specific process is as follows: First, the inoculum solution was prepared: sludge supernatant from the secondary sedimentation tank of an urban wastewater treatment plant was taken, and a nutrient solution containing 1.0 g glucose, 0.15 g ammonium chloride, and 0.03 g potassium dihydrogen phosphate was added and dissolved in 20 mL of ultrapure water. After adding the nutrient solution, the container was sealed and placed in a constant temperature shaking incubator. The inoculum was enriched and cultured at 37°C and 120 r / min for 48 h to obtain an inoculum solution containing highly active electrochemical microorganisms.

[0041] Subsequently, a gradient acclimatization strategy was adopted to start up the CW-MFC device: 20 mL of the above-mentioned inoculum solution was injected into the anode carbon felt through the silicone tube every 3 days, and the nutrient solution was replaced with fresh solution once a week; at the same time, the output voltage of the system was continuously monitored by a paperless recorder. When the output voltage was maintained stably for 72 hours without significant fluctuations, it indicated that a mature and stable electrochemically active biofilm had been successfully formed on the electrode surface, and the CW-MFC device was successfully started up and could be formally introduced into the landfill leachate pretreated by the biological slow filter to enter the continuous operation stage.

[0042] In this embodiment, the container is a 5.0L polypropylene drum with a top and bottom diameter of 21.0cm and 19.0cm respectively, and a height of 26.0cm.

[0043] In this embodiment, the effluent from the BSSF pretreatment unit is fed into the container of the CW-MFC unit at a constant flow rate of 20 mL / min by a peristaltic pump; the operating cycle is: continuous operation for 30 days, with water quality monitored every 48 hours; the ambient temperature is 25±3℃. The aforementioned equipment also includes an energy recovery circuit and a control module.

[0044] The input of the energy recovery circuit is electrically connected to the cathode and anode carbon felt of the CW-MFC device, while the output is used to power the energy storage device or directly drive a low-power load. A paperless recorder is used to automatically collect voltage data every 10 minutes.

[0045] The specific topology and connection method of this circuit are as follows: (1) Electrode layout and connection method: Anode carbon felt: It is composed of multiple anode carbon felt sheets connected in parallel or series to form a three-dimensional current collection network; Cathode carbon felt: Composed of multiple cathode carbon felt sheets connected in parallel or series, distributed around the root system of wetland plants, and partially exposed to the atmosphere; Connecting wires: Both the anode carbon felt and the cathode carbon felt are connected to the energy recovery circuit of the external circuit via low-impedance copper core wires. The initial matching resistance of the external circuit is 500-2000Ω.

[0046] (2) Energy recovery circuit topology: The energy recovery circuit includes the following modules connected in sequence: Impedance matching unit: a maximum power point tracking (MPPT) controller used to dynamically match the internal resistance of CW-MFC (the internal resistance varies with HRT, water quality, and microbial activity, ranging from 420-588Ω), so that the device always operates at the maximum power output point; Boost Unit: A DC-DC boost converter used to boost the low voltage (80-800mV) output of CW-MFC to a usable voltage level (such as 3.3V or 5V). Energy storage unit: including a supercapacitor bank and / or rechargeable battery, for storing the recovered electric energy; Monitoring unit: including a paperless recorder or a single-chip microcomputer monitoring module, for recording in real time the power generation parameters such as output voltage, current, power, etc., and providing data input for the control module.

[0047] The above connection method realizes the direct, low-loss, and stable electrical connection between the wetland electrode and the energy recovery system, ensures the efficient transmission of electrons, and is the key structural basis for realizing synchronous power generation and electric energy recovery.

[0048] The control module is signal-connected to the monitoring unit in the energy recovery circuit and the flow control valve (such as a peristaltic pump) arranged at the water inlet of the CW-MFC device, and executes the following power generation efficiency control logic: adjusting the hydraulic retention time (HRT) of the CW-MFC device in real time to keep the power generation power density of the device within a preset optimal range. The specific steps of the control logic are as follows: Step 1, Initial setting: When the device starts up, set the initial HRT to 25 - 35 days. In this embodiment, it is set to 30 days.

[0049] Step 2, Real-time monitoring: Through the above monitoring unit, continuously or intermittently collect the real-time output voltage U and real-time output current I of the CW-MFC, and calculate the real-time power density Pd.

[0050] Step 3, Efficiency evaluation: Compare the real-time power density Pd with a preset first threshold Th1 (high threshold) and second threshold Th2 (low threshold), where Th1 > Th2.

[0051] Step 4, HRT adjustment: When Pd ≤ Th2, the control module sends an instruction to the flow control valve to increase the HRT and reduce the influent flow rate, gradually extend the HRT in steps of 5% - 10%, and the maximum does not exceed 50 days; When Pd ≥ Th1 and remains stable continuously for a preset duration (such as 72 hours), the control module sends an instruction to the flow control valve to shorten the HRT and increase the influent flow rate, gradually shorten the HRT in steps of 5% - 10%, and the minimum is not less than 20 days; When Th2 < Pd < Th1, keep the current HRT unchanged.

[0052] The HRT adjustment range of the CW-MFC advanced treatment and power generation device is 20 - 50 days.

[0053] Step 5, Early warning protection: When Pd still remains lower than Th2 continuously for a preset duration (such as 7 days) after adjustment, the system issues an early warning signal.

[0054] Through the above logic, automatic optimal control of power generation efficiency is achieved, significantly improving system stability and energy recovery efficiency.

[0055] Example 2: The only difference from Example 1 is that: like Figure 1 As shown in (a), the CW-MFC device uses a vertical downflow.

[0056] Everything else is the same as in Example 1.

[0057] Example 3: The only difference from Example 1 is that: The packing layer inside the CW-MFC unit uses zeolite (ZEO).

[0058] Everything else is the same as in Example 1.

[0059] Example 4: The only difference from Example 1 is that: The packing layer inside the CW-MFC unit uses activated carbon (GAC).

[0060] Everything else is the same as in Example 1.

[0061] Example 5: The only difference from Example 1 is that: The CW-MFC unit uses a vertical downflow design and its internal packing layer is made of zeolite.

[0062] Everything else is the same as in Example 1.

[0063] Example 6: The only difference from Example 1 is that: The CW-MFC unit uses a vertical downflow design, and its internal packing layer is made of activated carbon.

[0064] Everything else is the same as in Example 1.

[0065] The leachate used in this embodiment of the invention was taken from the anaerobic digester of a municipal solid waste incineration power plant in Wuhu City. It was collected in batches in March and May 2024 in a sealed, light-protected manner. The water quality indicators are shown in Table 1. Table 1 Water quality parameters of landfill leachate

[0066] After treatment by the BSSF unit, the effluent is used as the feed water for the CW-MFC unit, and its water quality parameters are shown in Table 2: Table 2. Water quality parameters of the influent to the CW-MFC unit

[0067] Table 3 shows the organic matter content and biodegradability of the influent and effluent from the devices in Examples 1-4: Table 3. Organic matter index and biodegradability of influent and effluent from the apparatus in Examples 1-4

[0068] Table 3 shows that the combined BSSF and CW-MFC process system improved the biodegradability of landfill leachate. After BSSF pretreatment, the effluent BOD5 / COD ratio increased from 25.36% at the influent level to 31.17%, indicating a significant improvement in biodegradability. This change is mainly attributed to the BSSF's ability to effectively degrade recalcitrant organic matter (humus, etc.) and inorganic pollutants (nitrite, FeO, Fe). 2+ Mn 2+ The interception and adsorption effects of CW-MFC (such as zeolite packing) increase the relative proportion of readily biodegradable components, providing favorable conditions such as usable carbon sources for subsequent biological treatment. During the advanced treatment stage of CW-MFC, biodegradability continues to improve, with the BOD5 / COD ratio of the effluent from the CW-MFC unit reaching 35.93%-38.82%. This trend indicates that recalcitrant organic matter is further transformed, and the metabolic activity of microorganisms continues to increase. Example 1 (upflow sponge iron CW-MFC) showed the best improvement in biodegradability, with the BOD5 / COD ratio increasing from 31.17% in the influent to 38.82%. Example 2 (downflow sponge iron CW-MFC) experienced a decrease in mass transfer efficiency due to the water flow pattern, resulting in a slightly lower improvement in biodegradability compared to Example 1, verifying the synergistic effect of the upflow structure on leachate purification and biodegradability improvement. The biodegradability improvement effects of Examples 3 (zeolite packing) and 4 (activated carbon packing) were inferior to those of sponge iron packing.

[0069] The effects of the CW-MFC devices in Examples 1-6 on TP and NH4 were measured respectively. + The purification effects of -N and COD, the results are as follows Figure 2 As shown.

[0070] Depend on Figure 2 It can be seen that CW-MFC supports TP and NH4. + The removal efficiency of -N and COD shows a significant dependence on the type of packing material and the flow regime. Regarding TP removal, DRI-Down, relying on sponge ferroelectrochemical precipitation, achieves deep phosphorus removal within the first 6 days, with effluent TP remaining stable at near-zero levels. ZEO-Up, relying on the synergistic effect of zeolite ion exchange and upflow oxidation, shows a steady decrease throughout the process, achieving stable compliance within 30 days. GAC-Up relies on polyphosphate-accumulating bacteria for enhanced biological phosphorus removal in the later stages, but GAC-Down's efficiency is less than 55%, highlighting the significant impact of the flow regime on the performance of this packing material. NH4 + Regarding -N removal efficiency, the ZEO group achieved stable and efficient performance throughout the entire process, relying on ion exchange and biological nitrification. GAC-Up saw enhanced nitrification after the biofilm matured. DRI-Up had lower efficiency initially but rapid degradation later. DRI-Down, however, suffered from Fe... 0Corrosion consumes oxygen and inhibits nitrifying bacteria, leading to ammonia nitrogen rebound and accumulation. Regarding COD removal efficiency, GAC-Up shows significantly enhanced mineralization after the biofilm matures; ZEO-Up relies on the synergistic effect of rapid initial adsorption and subsequent biodegradation; DRI-Up achieves only moderate removal; and DRI-Down promotes Fe removal in the anoxic zone. 2+ The formation of stable complexes with organic matter leads to extremely low or even increased COD removal rates. The preferred DRI-Up type CW-MFC of this invention exhibits excellent and balanced performance in the comprehensive removal of the three types of pollutants. Compared with various downflow schemes, it effectively avoids problems such as limited phosphorus removal, ammonia nitrogen rebound, and low COD removal rates, proving that the combination of upflow structure and sponge iron packing is the key to achieving efficient purification and simultaneous power generation.

[0071] The pH change characteristics of the cathode and anode of the CW-MFC devices in Examples 1-6 were measured respectively, and the results are as follows: Figure 3 As shown.

[0072] Depend on Figure 3 It can be seen that the pH of the anode and cathode in the CW-MFC system exhibits a clear gradient distribution of "cathode alkalinity and anode weak acidity," with significant differences between operating conditions. The cathode pH generally increases over time, with the 30-day average being DRI (8.51) > GAC (8.33) > ZEO (7.92). The DRI sponge iron condition showed the highest cathode pH, consistently maintaining a strongly alkaline range of 8.5-8.9, which is conducive to the cathode oxygen reduction reaction. Similarly, the DRI anode pH was higher than other conditions, mostly between 8.5 and 8.7, while the zeolite and activated carbon conditions showed relatively lower anode pH, fluctuating between 6.5 and 7.0. Further comparison of flow patterns reveals that the cathode pH in the upflow (Up) system is generally higher than that in the downflow (Down) system. For example, the pH of GAC-Up on day 30 was 8.61, higher than that of GAC-Down (8.41), indicating that the upflow structure is more conducive to the stratification of the anaerobic environment at the anode and the aerobic environment at the cathode, indirectly strengthening the alkaline environment at the cathode. The DRI group exhibited the most significant pH gradient between the anode and cathode, with the anode becoming alkaline (pH ≥ 8.5) from day 12 onwards. Besides the inherent high pH characteristic of the packing material, this was primarily due to the hydrogen release reaction from iron corrosion. These pH distribution characteristics confirm that the sponge iron packing material combined with the upflow structure can effectively regulate the system's acid-base environment, forming a stable electrochemical gradient. This ensures the synergistic effect of the alkaline environment at the cathode and the weakly acidic conditions at the anode, thereby enhancing electrochemical reactions such as the precipitation of heavy metal hydroxyl complexes. This is a crucial environmental foundation for achieving efficient purification and simultaneous power generation in this invention.

[0073] The maximum output voltage of the CW-MFC devices in Examples 1-6 was measured, and the unit is mV. The results are shown in Table 4.

[0074] The power generation performance, polarization curves, and power density curves of the CW-MFC devices in Examples 1-6 were tested as follows: Figure 4 As shown, the statistical parameters include internal resistance and maximum power density, the former in Ω and the latter in mW / m. 2 The results are shown in Table 4.

[0075] Table 4. Statistics on Maximum Output Voltage and Power Generation Performance of the Embodiments

[0076] Depend on Figure 4 It is evident that the sponge iron-upflow (DRI-Up) combination corresponding to Example 1 exhibits an absolute advantage in power generation performance: its voltage curve shows the highest peak value, and its voltage decay is the slowest across the entire current density range. The corresponding power density curves show that the maximum power density under DRI-Up conditions is significantly higher than that of GAC-Up (granular activated carbon-upflow) and ZEO-Up (zeolite-upflow), reaching 1.5-2 times higher than GAC-Up and ZEO-Up, respectively. Simultaneously, the voltage and power density of the downflow schemes (DRI-Down, GAC-Down, ZEO-Down) are far lower than their corresponding upflow schemes, and they decay rapidly. This data directly confirms that the sponge iron filler combined with the upflow structure can effectively reduce the system's internal resistance and enhance electron transfer efficiency, which is the core technological guarantee for the high-efficiency power generation of this invention.

[0077] As shown in Table 4, the maximum output voltage of Example 1 can reach 772mV, the internal resistance is only 420.20Ω, and the maximum power density can reach 3564.63mW / m 2 This indicates that the upflow structure combined with the conductive sponge iron packing can significantly enhance electron transfer efficiency, reduce system internal resistance, and enable the microbial fuel cell to output higher power under low internal resistance conditions, achieving stable and efficient energy recovery. Although Example 2 still maintains high power generation performance, all parameters are slightly lower than in Example 1, indicating that the downflow method weakens the contact efficiency between the matrix and the packing, leading to a slight decrease in power generation performance. In Examples 3 and 4, the maximum output voltage is significantly reduced, the internal resistance is significantly increased, and the maximum power density is also significantly reduced. This indicates that although zeolite and activated carbon have certain adsorption capacity, they do not possess the conductivity of sponge iron, resulting in power generation performance inferior to the sponge iron packing in Example 1.

[0078] SEM observation and analysis were performed on the packing material of the CW-MFC device before and after the experiment in Examples 1-6. The results are as follows: Figure 5 As shown.

[0079] Depend on Figure 5It was observed that dense microbial aggregates formed on the surfaces of the GAC and ZEO groups, mainly composed of rod-shaped, cocci, and filamentous bacteria, accompanied by a network structure formed by a large number of EPS (explosive permeable material). The DRI group, however, formed a porous and loose corrosion product layer due to the corrosion reaction. While this enhanced microbial adhesion, the bacterial community was not visually observed. SEM analysis at the microscopic level showed that different flow regimes affected the uniformity of the biofilm, with upflow being more conducive to microbial community development, further illustrating the significant effect of microbial degradation on pollutant removal.

[0080] The present invention has been described by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvement made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, shall be within the protection scope of the present invention.

Claims

1. An ecological treatment device that simultaneously purifies landfill leachate and recovers electricity, characterized in that: It includes a biological slow filter pretreatment device and an artificial wetland-microbial fuel cell deep treatment and production device, and the effluent from the biological slow filter pretreatment device is used as the influent from the artificial wetland-microbial fuel cell deep treatment and production device. The constructed wetland-microbial fuel cell deep treatment and production device includes an anode, a cathode, packing material, wetland plants, and an energy recovery circuit, and the anode and cathode are directly connected to the input terminal of the energy recovery circuit through wires. It also includes a control module, which is connected to the monitoring unit in the energy recovery circuit and the flow control valve located at the inlet of the constructed wetland-microbial fuel cell deep treatment and production device. The control module executes the following power generation efficiency control logic: The control module is configured to dynamically adjust the hydraulic residence time of the constructed wetland-microbial fuel cell by real-time monitoring of power generation parameters, so that the system is maintained in the optimal power generation range.

2. The ecological treatment equipment for simultaneous purification of landfill leachate and recovery of electricity as described in claim 1, characterized in that: The constructed wetland-microbial fuel cell deep treatment and production device adopts a vertical subsurface flow upflow structure or a vertical downflow structure; and its interior is arranged from top to bottom as follows: wetland plants, cathode carbon felt and upper water layer, fine sand filter layer, filler layer, anode carbon felt, and support layer. The filler is one of sponge iron, zeolite, and activated carbon.

3. The ecological treatment equipment for simultaneous purification of landfill leachate and recovery of electricity as described in claim 2, characterized in that: The anode carbon felt is composed of multiple anode carbon felt sheets connected in parallel or in series to form a three-dimensional current collection network, which is completely immersed in the filler layer; The cathode carbon felt is composed of multiple cathode carbon felt sheets connected in parallel or in series to form a cathode current collection network, located at the gas-liquid interface and distributed around the roots of wetland plants. Both the anode carbon felt and the cathode carbon felt are connected to the energy recovery circuit via low-impedance copper core wires.

4. The ecological treatment equipment for simultaneous purification of landfill leachate and recovery of electricity according to claim 2, characterized in that: Both the anode carbon felt and the cathode carbon felt are carbon felts that have undergone acid hydrophilic treatment. The distance between the anode carbon felt and the cathode carbon felt is 10-15 cm.

5. The ecological treatment equipment for simultaneous purification of landfill leachate and recovery of electricity as described in claim 1, characterized in that: The energy recovery circuit includes, in sequence along the direction of power transmission: an impedance matching unit, a boost unit, an energy storage unit, and a monitoring unit; The impedance matching unit is a maximum power point tracking controller, used to dynamically match the internal resistance of the system; The boost unit is a DC-DC boost converter used to boost low voltage to a usable voltage; The monitoring unit is used to collect voltage and current in real time and calculate power density.

6. The ecological treatment equipment for simultaneous purification of landfill leachate and recovery of electricity according to claim 5, characterized in that: The control module executes the following control logic based on the real-time power density: (1) When the power density is less than or equal to the low threshold Th2, extend the hydraulic residence time; (2) When the power density is greater than or equal to the high threshold Th1 and remains stable for a preset duration, shorten the hydraulic residence time; (3) When the power density is between Th2 and Th1, the current hydraulic residence time remains unchanged.

7. An ecological treatment device for simultaneous purification of landfill leachate and recovery of electricity according to claim 6, characterized in that: The hydraulic residence time can be adjusted within a range of 20 to 50 days, with an adjustment step of 5% to 10%.

8. An ecological treatment device for simultaneous purification of landfill leachate and recovery of electricity according to claim 5, characterized in that: The control module is also equipped with an early warning unit, which issues an early warning signal when the power density is lower than Th2 for 7 consecutive days.

9. An ecological treatment device for simultaneous purification of landfill leachate and recovery of electricity according to claim 1, characterized in that: The external fixed resistor of the constructed wetland-microbial fuel cell is 1000Ω; the data collection interval of the monitoring unit is 10 minutes.

10. An ecological treatment device for simultaneous purification of landfill leachate and recovery of electricity according to claim 1, characterized in that: The biological slow filter pretreatment device is provided with a filter media layer, which consists of a gravel support layer, a multi-level filter media layer, and an overlying water layer from bottom to top. The multi-layered filter media includes, from bottom to top, an activated carbon layer, a biochar layer, and a quartz sand layer; the quartz sand has a particle size of 0.5-1.0 mm, and the activated carbon and biochar both have a particle size of 1.0-2.0 mm.

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