A denitrification method by using an electrically conductive membrane bioreactor for anaerobic ammonia oxidation of low-concentration nitrite wastewater

Abstract

This invention relates to the field of wastewater treatment technology, and more particularly to a method for anaerobic ammonia oxidation denitrification in a conductive membrane bioreactor for wastewater with low concentrations of nitrite. Anaerobic ammonia-oxidizing bacteria are inoculated into a conductive membrane bioreactor; the bioreactor is connected to a DC power supply, with a conductive membrane assembly as the cathode and a three-dimensional porous or fibrous conductive carbon material with a high specific surface area as the anode, and a positive bias is applied to the anode; nitrogen-containing wastewater with a nitrite to ammonia nitrogen molar ratio of 1:1.5 to 1:5 is introduced into the electro-enhanced membrane bioreactor, where the anaerobic ammonia-oxidizing bacteria use the conductive carbon material at the anode as an extracellular electron acceptor for biological denitrification. This invention, based on a conductive membrane bioreactor, achieves efficient denitrification even under nitrite-deficient conditions through a dual approach of "electroadsorption enrichment + electrostimulation enhancement." This method is simple to operate, energy-saving, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more particularly to a conductive membrane bioreactor method for anaerobic ammonia oxidation denitrification of low-concentration nitrite wastewater. Background Technology

[0002] Anaerobic ammonium oxidation (Anammox) produces nitrite (NO2) - Ammonia nitrogen (NH4) is an electron acceptor. + Anaerobic ammonia oxidation (ANAO) uses electrons as a donor to generate nitrogen gas under anaerobic conditions. Compared with traditional denitrification processes, ANAO has advantages such as saving external carbon sources, saving oxygen supply energy, reducing excess sludge production, and reducing greenhouse gas emissions, and is therefore considered a promising new denitrification process. However, nitrogen in wastewater mainly exists in the form of ammonia nitrogen, and the required nitrite must be provided through upstream treatment steps. This requires the integration of pretreatment processes, such as partial denitrification (PDN) or partial nitrification (PN), which respectively increases the operating costs associated with external carbon sources and aeration. In addition, these processes require strict control to maintain theoretically stoichiometric NO2 levels. - NH4 + The ratio is 1.32:1. This stringent requirement increases the energy consumption of the process and limits its practical application.

[0003] To overcome the dependence on nitrite and strict limitations on influent ratios in traditional anaerobic ammonia oxidation processes, the extracellular electron transfer capabilities of anaerobic ammonia oxidizing bacteria have been explored in recent years. Extracellular electron transfer refers to the process by which anaerobic ammonia oxidizing bacteria utilize insoluble extracellular electron acceptors, such as graphene oxide or the anode in a microbial electrolysis cell, as electron acceptors to oxidize ammonia nitrogen, thereby achieving ammonia nitrogen removal. Using this process eliminates the need for strict control of the theoretically stoichiometric NO2. - NH4 + The ratio of 1.32:1 reduces the proportion of nitrite required for conversion in pre-denitrification (PDN) or partial nitrification (PN), thereby reducing operating costs associated with external carbon sources and aeration. However, the current nitrogen removal rate of this process is relatively low, limiting its practical application. Therefore, it is necessary to find ways to increase the rate of extracellular electron transfer.

[0004] Considering that bacteria exchange electrons with extracellular acceptors, shortening the extracellular electron transport pathway can accelerate the extracellular electron transport process, thereby enabling denitrification using the extracellular electron transport process of anaerobic ammonia oxidizing bacteria. Based on this idea, the Anammox Membrane Bioreactor (Anammox MBR) process can effectively retain bacteria and maintain a high sludge concentration within the reactor, thereby achieving the enrichment and cultivation of anaerobic ammonia oxidizing bacteria and providing a foundation for subsequent enhanced denitrification. Summary of the Invention

[0005] The purpose of this invention is to provide a conductive membrane bioreactor method for anaerobic ammonia oxidation denitrification in wastewater with low concentrations of nitrite. This method enhances the extracellular electron transport rate through a dual approach of "anodic electroadsorption enrichment + external electric field stimulation." Specifically, this invention employs a conductive membrane bioreactor with a three-dimensional porous or fibrous conductive carbon material with a high specific surface area as the anode and a positive bias applied. Electrostatic adsorption causes negatively charged anaerobic ammonia-oxidizing bacteria to accumulate on the anode surface, thereby shortening the extracellular electron transport path. Simultaneously, the external electric field stimulates the anaerobic ammonia-oxidizing bacteria to secrete more cytochrome c, enhancing electron shuttle-mediated extracellular electron transport. When treating nitrite-deficient wastewater, the anaerobic ammonia-oxidizing bacteria directly use the anodic conductive carbon material as an extracellular electron acceptor for biological denitrification, achieving highly efficient denitrification.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a method for anaerobic ammonia oxidation denitrification in a conductive membrane bioreactor for low-concentration nitrite wastewater, wherein anaerobic ammonia oxidizing bacteria are inoculated into the conductive membrane bioreactor; The conductive membrane bioreactor is connected to a DC power supply, with the conductive membrane assembly as the cathode and a three-dimensional porous or fibrous conductive carbon material with a high specific surface area as the anode. A positive bias voltage is applied to the anode, and the negatively charged anaerobic ammonia-oxidizing bacteria are enriched on the anode surface by electrostatic adsorption. Nitrogenous wastewater with a concentration lower than that required by the traditional anaerobic ammonia oxidation denitrification process is introduced into a membrane bioreactor. The molar ratio of nitrite to ammonia nitrogen in the nitrogenous wastewater is lower than the theoretical value of 1.32:1 in the traditional anaerobic ammonia oxidation denitrification process, i.e., 1:1.5 to 1:5. Anaerobic ammonia oxidizing bacteria use anolyl conductive carbon material as an extracellular electron acceptor for biological denitrification.

[0008] In the above technical solution, the applied voltage to the conductive membrane reactor is 0~1.0 V, the corresponding anode potential is 0~0.35 V vs. Ag / AgCl, and the cathode potential is 0~-0.65 V vs. Ag / AgCl, wherein the applied voltage, anode potential, and cathode potential do not include 0.

[0009] In the above technical solution, the three-dimensional porous or fibrous conductive carbon material with high specific surface area further includes one of carbon fiber brushes, carbon felt, and foamed carbon. The anode uses a conductive carbon material with a rough surface and high specific surface area, which can provide sufficient attachment sites for anaerobic ammonia-oxidizing bacteria while maintaining good electron transfer performance.

[0010] In the above technical solution, the conductive membrane bioreactor further includes a reactor shell, an anode, a cathode, and a DC power supply; The reactor shell is provided with an inlet at the bottom and an outlet at the top; The anode is located inside the reactor; The cathode is located inside the reactor; The positive terminal of the DC power supply is connected to the anode, and the negative terminal of the DC power supply is connected to the cathode.

[0011] In the above technical solution, the conductive film assembly further includes one of a hollow fiber film assembly, a tubular film assembly, and a flat sheet film assembly.

[0012] In the above technical solution, the membrane in the conductive membrane assembly is either an ultrafiltration membrane or a microfiltration membrane.

[0013] The principle of this invention: Anaerobic ammonia oxidizing bacteria possess certain electrochemical activity. Under the combined action of conductive materials and an applied electric field, they can establish an extracellular electron transport pathway by exchanging electrons between redox-active components on their cell surface and an external electrode. Specifically, the conductive anode provides a high specific surface area attachment interface and electron exchange platform for anaerobic ammonia oxidizing bacteria, promoting bacterial attachment, accumulation, and biofilm formation on its surface. The applied voltage provides a continuous and stable electrochemical driving force within the reactor, promoting the participation of redox-active components related to extracellular electron transport in electron migration. This shortens the electron transport distance, forms a continuous electron transport pathway, reduces electron transport resistance, and improves the electron exchange efficiency and metabolic activity between anaerobic ammonia oxidizing bacteria and the electrode, thereby enhancing the nitrogen conversion process and achieving biological denitrification based on enhanced extracellular electron transport.

[0014] The beneficial effects of this invention are as follows: (1) The present invention uses a conductive anaerobic ammonia oxidation membrane bioreactor, which utilizes the membrane's retention effect to effectively enrich microorganisms and maintain a high sludge concentration in the reactor; at the same time, it enriches anaerobic ammonia oxidizing bacteria through anodic electroadsorption, allowing the bacteria to directly attach to the electron acceptor surface, and utilizes the aggregation growth characteristics of anaerobic ammonia oxidizing bacteria to significantly shorten the extracellular electron transfer path. (2) The method of the present invention stimulates anaerobic ammonia-oxidizing bacteria to secrete cytochrome c by applying an external electric field, thereby enhancing the extracellular electron transfer ability mediated by electron shuttles; (3) The present invention can achieve efficient denitrification under the condition that the nitrite concentration is lower than the theoretical requirement of the traditional anaerobic ammonia oxidation denitrification process. It breaks through the strict requirements of the traditional anaerobic ammonia oxidation process on the theoretical ratio of influent ammonia nitrogen and nitrite, and reduces the dependence of the pre-nitrification or partial denitrification process on the nitrite generation ratio and control precision. (4) Compared with the traditional anaerobic ammonia oxidation process that relies on precise supply of nitrite, the present invention is beneficial to reduce the aeration requirements of the pre-nitrification process or the amount of external carbon source added in the pre-denitrification process, thereby reducing the overall system's operating energy consumption and treatment costs, and has good prospects for promotion and application. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 This is a schematic diagram of the conductive membrane bioreactor structure used in the method of the present invention; Figure 2 This is a photograph of bacteria attached to a carbon fiber brush inside reactor R2 in Example 1; Figure 3 This shows the changes in total nitrogen removal efficiency in Example 1; In the diagram: 1. Inlet tank, 2. Inlet pump, 3. Inlet pipe, 4. Circulating vacuum pump, 5. Constant temperature water bath, 6. Reactor, 7. Conductive membrane assembly, 8. Carbon fiber brush, 9. Outlet pipe, 10. Vacuum gauge, 11. Outlet pump, 12. DC power supply, 13. Stirrer, 14. Outlet tank. Detailed Implementation

[0017] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0018] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0019] like Figure 1 As shown, anaerobic ammonia-oxidizing bacteria are inoculated into a conductive membrane bioreactor. The conductive membrane bioreactor is connected to a DC power supply, with a conductive membrane module as the cathode and a three-dimensional porous or fibrous conductive carbon material with a high specific surface area as the anode. Sludge is retained through the conductive membrane module, and bacteria are enriched through the anode. A positive bias voltage is applied to the anode, and the negatively charged anaerobic ammonia-oxidizing bacteria are enriched on the carbon brush surface by electrostatic adsorption. When treating wastewater, the concentration ratio of nitrite to ammonia nitrogen is 1:1.5 to 1:5, which stimulates bacteria to perform biological denitrification using the carbon brush as an extracellular electron acceptor.

[0020] The relevant material parameters of the single carbon fiber brush in Example 1 are shown in Table 1.

[0021] Table 1 Characteristic parameters of a single carbon fiber brush

[0022] Example 1 Three conductive membrane bioreactors were established. The anode material was a carbon fiber brush, and its parameters are shown in Table 1. The cathode material was a conductive membrane assembly composed of carbon nanotube hollow fiber membranes. Different applied voltages were applied to the three reactors: the control group R0 had no applied voltage; the experimental groups R1 and R2 had applied voltages of 0.5 V and 1.0 V, respectively, with corresponding anode potentials of 0.23 V vs. Ag / AgCl and 0.35 V vs. Ag / AgCl, and cathode potentials of -0.27 V vs. Ag / AgCl and -0.65 V vs. Ag / AgCl, respectively. The simulated wastewater had an ammonia nitrogen concentration of 250 mg / L and a nitrite concentration of 150 mg / L. The anaerobic ammonia oxidation sludge was obtained from laboratory domestication and culture, with a sludge concentration of 3000 ± 500 mg / L in each reactor.

[0023] The biological nitrogen removal efficiency under nitrite-deficient influent conditions in Test Example 1: like Figure 2 As shown, a large number of anaerobic ammonia-oxidizing bacteria adhered to the surface of the carbon fiber brush, indicating that the reactor effectively retained and enriched anaerobic ammonia-oxidizing bacteria. The bacteria's attachment to the anode shortened the extracellular electron transfer path. Figure 3 As shown, during the operating cycle, the total nitrogen removal rate of the control group R0 was only about 60%, while the total nitrogen removal rates of the experimental groups R1 and R2 were about 78% and 90%, respectively. No obvious hydrogen evolution peak was observed in the cyclic voltammetry curve of the electrified group, which ruled out the electrode oxidation effect. This proves that the electrified group can still remove excess ammonia nitrogen by enhancing extracellular electron transfer under nitrite deficiency conditions.

[0024] The above embodiments are merely preferred examples of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A conductive membrane bioreactor method for anaerobic ammonia oxidation denitrification of low-concentration nitrite wastewater, characterized in that: Anaerobic ammonia-oxidizing bacteria were inoculated into a conductive membrane bioreactor; The conductive membrane bioreactor is connected to a DC power supply, with the conductive membrane assembly as the cathode and a three-dimensional porous or fibrous conductive carbon material with a high specific surface area as the anode, and a positive bias voltage is applied to the anode. Nitrogenous wastewater is introduced into a membrane bioreactor, wherein the molar ratio of nitrite to ammonia nitrogen in the nitrogenous wastewater is 1:1.5 to 1:5, and anaerobic ammonia-oxidizing bacteria perform biological denitrification using the anode as an extracellular electron acceptor.

2. The anaerobic ammonia oxidation denitrification method for a conductive membrane bioreactor according to claim 1, characterized in that: The conductive membrane reactor is subjected to a voltage of 0~1.0 V, with a corresponding anode potential of 0~0.35 V vs. Ag / AgCl and a cathode potential of 0~-0.65 V vs. Ag / AgCl. The applied voltage, anode potential, and cathode potential do not include 0.

3. The anaerobic ammonia oxidation denitrification method for a conductive membrane bioreactor according to claim 1, characterized in that: The three-dimensional porous or fibrous conductive carbon material with high specific surface area includes one of carbon fiber brushes, carbon felt, and carbon foam.

4. The anaerobic ammonia oxidation denitrification method for a conductive membrane bioreactor according to claim 1, characterized in that: The conductive membrane bioreactor includes a reactor shell, an anode, a cathode, and a DC power supply; The reactor shell is provided with an inlet at the bottom and an outlet at the top; The anode is located inside the reactor; The cathode is located inside the reactor; The positive terminal of the DC power supply is connected to the anode, and the negative terminal of the DC power supply is connected to the cathode.

5. The anaerobic ammonia oxidation denitrification method for a conductive membrane bioreactor according to claim 1, characterized in that: The conductive membrane assembly includes one of hollow fiber membrane assembly, tubular membrane assembly, and flat sheet membrane assembly.

6. The anaerobic ammonia oxidation denitrification method for a conductive membrane bioreactor according to claim 1, characterized in that: The membrane in the conductive membrane assembly is either an ultrafiltration membrane or a microfiltration membrane.

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