Microbial fuel cell and method for removing nitrogen and phosphorus by using cell anode chamber

Abstract

The invention relates to the technical field of water pollution control and resource utilization, in particular to a microbial fuel cell and a method for removing nitrogen and phosphorus by using a cell anode chamber. According to the microbial fuel cell, an anode of the microbial fuel cell is a carbon felt with an iron wire as a support, a cathode of the microbial fuel cell is a carbon brush, and anaerobic sludge is inoculated in an anode chamber. The invention provides a system for synchronously recovering nitrogen and phosphorus in urine based on a microbial fuel cell and a biochemical reaction, so as to realize efficient nitrogen removal and phosphorus recovery. According to the invention, triple functions of power generation, denitrification and phosphorus recovery of the microbial fuel cell are integrated, an innovative technical path of pollution control, energy regeneration and resource high value is formed, and a solution is provided for phosphorus recovery and wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution control and resource utilization, and more particularly to a microbial fuel cell and a method for removing nitrogen and phosphorus by utilizing the anode chamber of the cell. Background Art

[0002] Among the various technical paths for urine resource utilization, microbial fuel cell (MFC) technology has shown unique advantages. As a technology that combines wastewater treatment and power generation, MFC uses anaerobic microorganisms to oxidize organic matter in urine (urine contains about 10 g / L of organic matter, 90% of which is biodegradable) at the anode to generate H + , electrons, and other metabolites, directly converting chemical energy into electrical energy. Notably, the high concentrations of ammonia nitrogen and phosphate in urine, acting as a buffer, make its conductivity significantly superior to that of conventional wastewater, providing an ideal reaction matrix for MFC technology. Therefore, urine is not only a nutrient resource in the traditional sense, but also an excellent fuel for power generation in microbial fuel cells.

[0003] During the MFC urine treatment process, the effective removal of high concentrations of ammonia nitrogen is a key challenge. Ammonia nitrogen concentrations in normal human urine range from 0 to 3000 mg / L (as nitrogen). This high ammonia nitrogen load primarily originates from the alkaline environment of ammonium carbonate produced by urea hydrolysis. Anaerobic ammonium oxidation (Anammox) plays a key role in removing ammonia nitrogen from urine in an anaerobic environment in microbial fuel cells. The Anammox process relies on anaerobic ammonium-oxidizing bacteria, which directly convert ammonia nitrogen into nitrogen gas using nitrite as an electron acceptor under anaerobic conditions. Without the addition of nitrate or nitrite, iron plays a crucial role in the Anammox process. During the growth and metabolism of anaerobic ammonium-oxidizing bacteria, iron not only constitutes an essential element for cellular function but also directly participates in key biochemical reactions (Feammox). Under anaerobic conditions, the presence of iron ions can drive Feammox, an iron-based ammonia oxidation process. Feammox utilizes Fe³ to generate ammonia nitrogen. + Reduction and oxidation of ammonia generate nitrogen gas, nitrite, or nitrate. Iron can also synergize with elements such as sulfur and carbon to optimize and improve Anammox technology. Research has shown that the synergistic effect of iron and sulfur, with sulfide acting as an electron donor, enhances nitrogen removal and reduces the accumulation of nitrate and nitrite, thereby optimizing the balance between electron donors and acceptors, significantly improving nitrogen removal efficiency and the diversity of Anammox colonies. Therefore, integrating the power generation advantages of MFC with the denitrification mechanism of Feammox can achieve energy utilization of organic matter in urine while simultaneously addressing nitrogen pollution.

[0004] Currently, agricultural production relies primarily on phosphate fertilizers derived from phosphate rock mining, yet global phosphate rock resources are facing a severe shortage. Recent studies estimate that, at current mining rates, the world's economically exploitable phosphate rock reserves will only last approximately 50 years. This resource crisis has made phosphorus recovery from wastewater particularly important. Urine, rich in phosphorus (200-800 mg / L), offers a promising source for phosphorus recovery. Traditional wastewater treatment processes often recover phosphorus through chemical precipitation to form struvite (MgNH₄PO₄·6H₂O), but this method suffers from high reagent consumption and low product value. This technology, due to the presence of iron ions, exhibits unique advantages in phosphorus recovery when treating urine. When phosphate in urine interacts with iron ions, violet iron ore (Fe₃(PO₄)₂·8H₂O) spontaneously forms without microbial mediation. Its unique crystal structure and chemical properties make it highly valuable for practical applications. In the field of new energy, vivianite is a key precursor of lithium iron phosphate (LiFePO4), a cathode material for lithium-ion batteries. Its current market price is as high as $10,000 per ton, which has significant economic value. In the field of environmental remediation, vivianite's layered structure and surface active sites make it resistant to lead (Pb²⁺) and arsenic (As³⁺ / As 5 Vitriol has a strong adsorption capacity for toxic heavy metals such as calcium (⁺) and cadmium (Cd²⁺). In agriculture, violet iron ore can serve as a high-quality slow-release phosphate fertilizer. Its phosphorus release cycle in neutral soil environments can reach 120 days, increasing phosphorus utilization by 3.2 times compared to traditional phosphate fertilizers, significantly reducing phosphorus loss and environmental pollution. Furthermore, its deep blue crystal form is highly sought after in mineral collections and jewelry design. Using MFC to recover phosphorus from urine and generate violet iron ore not only addresses phosphorus pollution in wastewater treatment but also creates a "pollutant-resource-high-value product" transformation pathway.

[0005] Traditional wastewater treatment processes often recover phosphorus through chemical precipitation to form struvite (MgNH₄PO₄·6H₂O). However, this method suffers from high reagent consumption and low product value. It cannot simultaneously address phosphorus pollution in wastewater treatment and achieve a "pollutant-resource-high-value product" transformation path. Summary of the Invention

[0006] This invention provides a microbial fuel cell and a method for removing nitrogen and phosphorus using the cell's anode chamber. It also proposes a system for simultaneously recovering nitrogen and phosphorus from urine based on the coordinated biochemical reactions of the microbial fuel cell, achieving efficient denitrification and phosphorus recovery. This invention integrates the triple functions of microbial fuel cells for power generation, denitrification, and phosphorus recovery, forming an innovative technological path of "pollution control, energy regeneration, and resource maximization," providing a solution for phosphorus recovery and wastewater treatment.

[0007] In a first aspect, the present invention provides a microbial fuel cell, which uses a dual-chamber H-type microbial fuel cell with nitrogen-phosphorus wastewater with a low carbon-nitrogen ratio as the anode chamber matrix and potassium ferrocyanide as the cathode chamber matrix. The anode chamber is inoculated with anaerobic sludge, and the anode electrode is composed of iron wire interlaced with carbon felt.

[0008] Preferably, the anode of the microbial fuel cell is a carbon felt with an iron wire as a support, the cathode is a carbon brush, and anaerobic sludge is inoculated in the anode chamber.

[0009] Preferably, the microbial fuel cell is manufactured by using nitrogen-phosphorus wastewater with a low carbon-nitrogen ratio as the matrix of the anode chamber, inoculating iron-rich anaerobic sludge in the anode chamber, and potassium ferrocyanide and sodium chloride solution as the matrix of the cathode chamber. The two polar chambers are separated by a proton exchange membrane and fixed by snaps.

[0010] Preferably, nitrogen is introduced into the anode chamber, and phosphate in the wastewater is oxidized by the anode iron wire to release divalent iron to form cyanite.

[0011] Preferably, the cathode is a carbon brush composed of carbon fiber and high-purity titanium wire.

[0012] Preferably, a constant temperature magnetic stirrer is installed at the bottom of the anode chamber.

[0013] Preferably, the rotation speed of the constant temperature magnetic stirrer is 500-600 rpm and the temperature is 34-36°C.

[0014] Preferably, the anaerobic sludge inoculated in the anode chamber is anaerobic granular sludge with an initial concentration of 2000-2500 mg / L.

[0015] Preferably, the ammonia nitrogen concentration of the nitrogen and phosphorus wastewater in the anode chamber is 1 to 3000 mg / L.

[0016] Preferably, the initial pH value of the anode solution is 6-8.

[0017] In a second aspect, the present invention provides a method for using a microbial fuel cell to remove nitrogen and phosphorus using the anode chamber of the cell, wherein nitrogen and phosphorus wastewater with a low carbon-nitrogen ratio is introduced into the anode chamber of the cell to remove nitrogen and phosphorus.

[0018] In summary, the present invention has the following beneficial effects: This invention utilizes microbial fuel cells in conjunction with iron-based ammonia oxidation technology to remove high-concentration ammonia nitrogen, achieving a denitrification efficiency of 80%. Compared to conventional microbial fuel cell denitrification, the entire denitrification and phosphorus removal process is performed solely in the anode chamber, eliminating the need for patented multipolar microbial fuel cells. Furthermore, the denitrification process eliminates the need for additional nitrite and carbon source additions and enhances the power generation performance of the microbial fuel cell, helping to reduce wastewater treatment costs.

[0019] The electroactive bacteria of the present invention enrich and degrade organic matter in the wastewater at the anode, converting chemical energy into electrical energy. Potassium ferrocyanide is used as an electron acceptor at the cathode, generating a redox potential difference that allows electrons on the anode to spontaneously pass through an external circuit to the cathode. Phosphate in the wastewater reacts with divalent iron released after oxidation of the anode iron wire to form cyanite. At the same time, the anode also removes ammonia nitrogen simultaneously due to iron-based ammonia oxidation and anaerobic ammonia oxidation. By controlling the reaction conditions, the present invention generates cyanite in the MFC anode chamber, achieving recovery rates of soluble phosphorus, ammonia nitrogen, and organic matter in the wastewater of 99%, 80%, and over 80%, respectively.

[0020] 3. The present invention can generate high value-added blue iron ore without adding chemical agents, PO4 3- The removal rate is close to 100%. Compared to struvite as a slow-release fertilizer, violet iron ore has multiple values, such as being a precursor for lithium battery cathode materials and a catalyst, significantly improving the economic benefits of the process.

[0021] 4. The maximum output voltage and power density of the microbial fuel cell of the present invention are 0.74 V and 11.0 W / m respectively. 3 .

[0022] 5. The reactor of the present invention has a simple structure, a short reaction cycle and no secondary pollution.

[0023] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory and are not intended to limit the scope of protection of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is a graph comparing the changes in ammonia nitrogen concentration and pH over time in the anolyte according to an embodiment of the present invention; Figure 2 is the NH in the anolyte in the embodiment of the present invention. 4+ with NO 3⁻ 、NO 2⁻ Concentration change over time comparison chart; Figure 3 is the PO4 in the anolyte in the embodiment of the present invention 3- Concentration change over time comparison chart; Figure 4 When the present invention is run for 12 days, different NH 4+ XRD patterns of anolyte precipitates at different concentrations; Figure 5 Graph showing voltage, polarization and power density during operation of a microbial fuel cell in an embodiment of the invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions were carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0026] Example In this example, four H-type dual-chamber microbial fuel cells were operated simultaneously. Each chamber had a volume of 250 mL and was separated by a proton exchange membrane. The cathode and anode electrodes were pretreated carbon brushes and iron wire carbon felt, respectively. The anaerobic sludge inoculated into the anode chamber was anaerobic granular sludge from a UASB reactor at a wastewater treatment plant. The anode chamber matrix contained 300, 500, 1000, and 2000 mg / L NH 4+ The corresponding microbial fuel cell devices were designated MFC1, MFC2, MFC3, and MFC4, respectively. The catholyte was a mixture of 50 mM potassium ferrocyanide and 100 mM NaCl. The electrodes of the microbial fuel cell were connected to a 1000 Ω external resistor via wires. To maintain anaerobic conditions in the anode compartment, nitrogen was flushed for 5 minutes before startup. The anode compartment of the microbial fuel cell was placed on a thermostatic magnetic stirrer and the device was started at 35 ± 1°C and a rotation speed of 500–600 rpm.

[0027] The experimental results are as follows: like Figure 1 As shown in the figure, organic matter can be rapidly degraded in the first 6 days of operation of the four groups of microbial fuel cells, but the organic matter concentration tends to be stable after 15 days of operation, and the COD removal rate reaches a peak of 88.2%, 81.8%, 83.1% and 77.4%, respectively.

[0028] like Figure 2 As shown, within the first three days of operation of the microbial fuel cell, NH4 + The concentration dropped rapidly. After 3 days, the NH4 + The removal rates were 62.4%, 75.1%, 63.9%, and 71.1%, respectively. In comparison, NO⁻ and NO⁻ concentrations gradually increased within three days of operation, while the NO⁻ and NO⁻ produced within 4 to 12 days were rapidly consumed. After 18 days, ammonia nitrogen concentrations in the microbial fuel cells remained essentially stable. By 30 days of operation, the ammonia nitrogen removal rates for all groups of microbial fuel cells were 80 ± 0.5%.

[0029] like Figure 3 As shown, PO4 in four groups of microbial fuel cells 3⁻ Phosphate removal is almost complete within 9-12 days, with a phosphate removal rate approaching 100%. After 12 days of operation, the sediment in the anode chamber of the microbial fuel cell was filtered and dried, turning dark blue. Figure 4 It is the XRD characterization of the sludge samples before and after the reaction. By comparing with the cyanite standard card, it can be seen that the characteristic diffraction peaks of the sludge after the reaction match the characteristic diffraction peaks (11.148°, 13.144°, 20.966°, 27.066°, 30.086°) of the cyanite standard card (card number 75-1186), and the MFC3 and MFC4 peak intensities are higher and the peak shapes are sharper, indicating that its cyanite content is higher and the crystal form is better.

[0030] like Figure 5 As shown in the figure, the output voltage of the four groups of microbial fuel cells rose rapidly after startup, reached the maximum value and stabilized after about 5 hours, at which time the output voltage was 0.72±0.04, 0.70±0.04, 0.70±0.02 and 0.74±0.02 V, respectively. The power density of the microbial fuel cell reached its maximum around the 12th day, and the power density of MFC4 was significantly higher than that of the other three groups, reaching 11.0 W / m 3 about.

[0031] From the above examples, it can be seen that PO4 in the anode chamber 3- Oxidation with the anode wire to form Fe 2+ The reaction generates blue iron ore which is completely removed. And NH4 + The increase in concentration will lead to a decrease in pH value and promote the increase in iron ion concentration, thereby increasing the crystallinity of blue iron ore. In the early stage of microbial fuel cell operation, the generation and consumption of NO2⁻ and NO3⁻ in the anode liquid indicate that Feammox and Anammox occurred in the microbial fuel cell reactor. + Through the bio-electrochemical synergistic pathway, the removal rate can reach 80±0.5%. + It is beneficial to increase the voltage and output power of the microbial fuel cell and reduce the internal resistance of the entire microbial fuel cell system.

[0032] The foregoing description is merely an exemplary embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A microbial fuel cell, characterized in that: A double-chamber H-type microbial fuel cell is used with nitrogen-phosphorus wastewater with a low carbon-nitrogen ratio as the anode chamber matrix and potassium ferrocyanide as the cathode chamber matrix. The anode chamber is inoculated with anaerobic sludge, and the anode electrode is composed of iron wire interlaced with carbon felt.

2. The microbial fuel cell according to claim 1, characterized in that The microbial fuel cell is manufactured by separating the two polar chambers with a proton exchange membrane and fixing them with buckles.

3. The microbial fuel cell according to claim 1, characterized in that Nitrogen is introduced into the anode chamber, and phosphate in the wastewater is oxidized by the anode iron wire to release divalent iron to generate violet iron ore.

4. The microbial fuel cell according to claim 1, characterized in that The cathode is a carbon brush composed of carbon fiber and high-purity titanium wire.

5. The microbial fuel cell according to claim 1, characterized in that: A constant temperature magnetic stirrer is installed at the bottom of the anode chamber.

6. The microbial fuel cell according to claim 1, characterized in that: The rotation speed of the constant temperature magnetic stirrer is 500-600 rpm and the temperature is 34-36°C.

7. The microbial fuel cell according to claim 1, characterized in that: The anaerobic sludge inoculated in the anode chamber is anaerobic granular sludge with an initial concentration of 2000-2500 mg / L.

8. The microbial fuel cell according to claim 1, characterized in that: The ammonia nitrogen concentration of the nitrogen and phosphorus wastewater in the anode chamber is 1-3000 mg / L.

9. The microbial fuel cell according to claim 1, characterized in that: The initial pH value of the anode solution is 6-8.

10. A method for removing nitrogen and phosphorus by utilizing the microbial fuel cell according to any one of claims 1 to 9 in the anode chamber of the cell, characterized in that: Nitrogen and phosphorus wastewater with a low carbon-nitrogen ratio is introduced into the anode chamber of the battery to remove nitrogen and phosphorus.

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