An adjustable multi-stage flow-controlled electrocatalytic biological denitrification device and method

Abstract

This invention discloses an adjustable multi-stage flow-controlled electrocatalytic biological denitrification device and method. The device includes an anode chamber and a cathode chamber, within which multiple composite bioelectrodes are staggered, forming a through-flow-baffle flow composite channel. The electrodes function as hydraulic disturbance, electron transfer, and microbial carriers, constructing a flow-potential-microbial zoned coupling system to achieve simultaneous coupling of substrate mass transfer, electrochemical reaction, and biological metabolism. The system forms a gradient reaction zone along the water flow direction. By applying gradient potentials in zones and adjusting the electrode spacing and number, the ammonia oxidation, anaerobic ammonia oxidation, and denitrification pathways can be directionally controlled. Deep denitrification of high-ammonia-nitrogen, low-carbon-source wastewater can be achieved without external carbon sources or added nitrite. This invention features a compact structure, flexible control, high denitrification efficiency, and stable operation, significantly improving total nitrogen removal rate and system load resistance.

Description

Technical Field

[0001] This invention relates to the field of nitrogen-containing wastewater treatment, and in particular to an adjustable multi-stage flow-controlled electrocatalytic biological denitrification device and denitrification method. Background Technology

[0002] Biological denitrification of nitrogen-containing wastewater is a crucial step in wastewater treatment. Traditional biological denitrification primarily employs a nitrification-denitrification process, which involves gradually oxidizing ammonia nitrogen to nitrate, followed by denitrification reduction using an external organic carbon source to ultimately generate nitrogen gas. This approach suffers from drawbacks such as a long process flow, high energy consumption, significant organic carbon source consumption, and poor denitrification selectivity, making it difficult to meet the demands for low-carbon emissions and wastewater resource recovery.

[0003] Anaerobic ammonia oxidation technology can directly convert two substrates into nitrogen gas under anoxic conditions, using ammonia nitrogen as an electron donor and nitrite as an electron acceptor, without requiring an organic carbon source, thus offering significant energy-saving and carbon-reduction advantages. However, anaerobic ammonia oxidizing bacteria grow slowly and are sensitive to environmental conditions, and the reaction process easily produces nitrate byproducts, leading to incomplete denitrification. Furthermore, the insufficient supply of nitrite in actual wastewater makes it difficult to maintain a continuous and efficient reaction, limiting the stable application of this technology.

[0004] For example, patent (application number CN117923657A) discloses a wastewater treatment method and system based on an anaerobic ammonia oxidation reactor, which is superior to the traditional nitrification-denitrification process in improving nitrogen removal efficiency. However, this technology still has many limitations, such as the slow growth of Anammox functional bacteria (AnAOB), sensitivity to environmental conditions, and the easy generation of nitrate byproducts during the reaction, which reduces the thoroughness of nitrogen removal. Meanwhile, due to the presence of NO2 in actual wastewater... — The concentration is often too low, making it difficult to sustain the Anammox reaction and resulting in insufficient denitrification efficiency.

[0005] To enhance denitrification efficiency and substrate adaptability, existing technologies incorporate bioelectrochemical systems. These systems apply an external potential to drive electron transfer, thereby increasing the metabolic activity of electroactive microorganisms and anaerobic ammonia-oxidizing bacteria. However, existing electrocatalytic denitrification devices and methods still have significant shortcomings: the electrodes serve only as carriers for the electrochemical reaction and lack hydraulic control capabilities; the fluid flow state and the electrochemical reaction process are independent, failing to achieve synergistic coupling of mass transfer, electron transfer, and biological metabolism; the nitrogen conversion pathway is uncontrollable, making it difficult to maintain stable denitrification under low or no nitrite conditions; and the reactor structure and potential adjustment methods are simplistic, resulting in poor adaptability to different ammonia / nitrite ratios in the influent.

[0006] In summary, existing nitrogen removal technologies generally suffer from problems such as low mass transfer efficiency, uncontrollable nitrogen conversion pathways, high nitrite dependence, and poor system adjustability, failing to meet the demand for efficient and deep nitrogen removal from wastewater with high ammonia nitrogen and low carbon source. Therefore, developing an adjustable electrocatalytic biological nitrogen removal technology that integrates flow regime control, gradient potential, and biological transformation has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing electrocatalytic biological denitrification technologies, such as single electrode function, insufficient coupling between flow field and electric field, uncontrollable nitrogen conversion pathway, poor system adjustability, high dependence on nitrite, and complex operating structure, and to provide an adjustable multi-stage flow-controlled electrocatalytic biological denitrification device and denitrification method.

[0008] In a first aspect, the present invention provides an adjustable multi-stage flow-controlled electrocatalytic biological denitrification device, comprising an electrocatalytic reactor, wherein the electrocatalytic reactor is provided with an anode chamber and a cathode chamber, and multiple composite bioelectrode units with both conductivity and porous structure are respectively arranged in the anode chamber and the cathode chamber. The electrode units are arranged in a staggered manner along the water flow direction to form an asymmetric flow channel structure. The composite bioelectrode units also serve as hydraulic disturbance components, electron transfer media and microbial attachment carriers, constructing a coupled system of flow state partitioning, potential partitioning and functional microbial partitioning inside the reactor. The liquid matrix forms a baffle path along the electrode gaps, and part of the fluid passes through the porous electrode structure to realize the synchronous coupling of substrate mass transfer, electrochemical reaction and microbial metabolism, forming a gradient reaction zone along the water flow direction.

[0009] Furthermore, the top of the electrocatalytic reactor is equipped with a cover plate with a wire and an exhaust port, and a rubber gasket is installed between the cover plate and the reactor body for sealing; an aeration port is installed at the bottom of the reactor; the composite bioelectrode unit is connected to an external DC power supply through a titanium wire via the reserved port; the reactor is equipped with an inlet peristaltic pump, the inlet is connected to the outlet of the peristaltic pump, and an overflow weir is installed in front of the outlet to achieve gas-liquid-solid three-phase separation.

[0010] This structure ensures the reactor operates in a sealed and stable manner, facilitates electrode wiring and venting, and achieves efficient separation of gas, liquid and solid, thereby improving the quality of the effluent and the safety of system operation.

[0011] Furthermore, the composite bioelectrode unit is composed of a porous ruthenium-iridium-plated titanium alloy mesh covered with conductive carbon felt.

[0012] The structure simultaneously provides a high specific surface area interface for microbial attachment and a stable electrochemical reaction interface.

[0013] Furthermore, a complex flow structure is formed inside the reactor, including a baffled path along the outside of the electrode and a trans-electrode mass transfer path through the porous structure of the electrode; the trans-electrode mass transfer path is accompanied by ion migration and electron transfer, enabling the fluid to participate in electrochemical reactions and biotransformation reactions simultaneously.

[0014] By constructing a composite flow field of baffles and throughflow, the efficiency of matrix mass transfer and interfacial contact is significantly enhanced, achieving a high degree of coupling between hydraulic flow, electrochemical reaction and biological metabolism.

[0015] Furthermore, the composite bioelectrode unit along the water flow direction forms a gradient functional reaction zone, with the front section being the ammonia oxidation and nitrite generation zone, the middle section being the anaerobic ammonia oxidation reaction zone, and the rear section being the nitrate reduction and denitrification reaction zone, realizing a multi-stage combined reaction of nitrogen transformation through multiple pathways. Achieve spatially ordered hierarchical separation of ammonia oxidation, anaerobic ammonia oxidation, and denitrification, avoiding reaction competition and interference, and improving the stability of the denitrification pathway and the depth of total nitrogen removal.

[0016] Furthermore, each composite bioelectrode unit is independently or in groups connected to a DC power supply, enabling the application of differentiated potentials to create a gradient potential field distributed along the water flow direction inside the reactor.

[0017] It can precisely regulate the electron supply and reaction intensity of each section, realize the directional control of the nitrogen conversion pathway, and solve the problems of single potential and uncontrollable reaction in traditional electrocatalytic systems.

[0018] Furthermore, electrode slots are provided in the anode chamber and the cathode chamber, which can adjust the electrode spacing and arrangement to change the flow structure and reaction zone distribution.

[0019] This makes the device structurally adjustable, allowing for flexible matching of the flow field and reaction zone according to the influent water quality, thus greatly improving its adaptability to wastewater with different loads.

[0020] Furthermore, uniform aeration micropores are set at the bottom of the reactor to regulate local dissolved oxygen and reaction environment, and to assist in controlling the reaction conditions of each functional reaction zone.

[0021] It can precisely control the local oxygen environment, enhance the reaction conditions of anaerobic ammonia oxidation and denitrification, while enhancing mass transfer, reducing biofilm blockage, and extending the stable operation cycle of the system.

[0022] On the other hand, the present invention also provides an adjustable multi-stage flow-controlled electrocatalytic biological denitrification method, employing the above-mentioned apparatus, comprising the following steps: S1: Nitrogen-containing wastewater is introduced into the reactor, forming a baffle path between the staggered composite bioelectrodes, with some fluid passing through the porous structure of the electrodes. S2: When fluid passes through the electrode, it achieves synchronous coupling of electrochemical reaction and microbial metabolism through the electron transfer path on the electrode surface; S3: Apply differential potentials to electrodes at different positions to create a gradient potential distribution, so that ammonia oxidation, anaerobic ammonia oxidation and denitrification reactions occur sequentially along the water flow direction; S4: Adjust the electrode layout parameters and potential distribution to control the nitrogen conversion pathway in stages.

[0023] Furthermore, by adjusting the electrode spacing, number of electrodes, electrode potential, and fluid residence time, a stable flow-potential-microorganism coupling regulation mechanism is formed to adapt to the treatment needs of wastewater with different nitrogen source ratios.

[0024] By achieving coordinated control of multiple parameters, the system can maintain efficient nitrogen removal even under conditions of low nitrite and low carbon source, thus broadening the scope of engineering applications and improving operational stability.

[0025] The beneficial effects of this invention are: 1. Constructing a multi-stage reaction system coupled with flow regime, potential, and microorganisms, overcoming the limitations of traditional enhancement mechanisms: This invention, through the staggered arrangement of composite bioelectrodes, forms a composite flow regime dominated by electrodes within the reactor, and further constructs a cross-electrode mass transfer pathway, enabling the fluid to simultaneously participate in electrochemical reactions and microbial metabolic processes as it traverses the electrodes. Unlike existing technologies that rely solely on baffles to extend residence time or achieve single reaction functions through electrode partitioning, this invention achieves the synergistic coupling of hydraulic flow, electron transfer, and biological reactions, transforming nitrogen conversion from a random coupling to a controllable gradient reaction process.

[0026] 2. No external carbon source or NO2 required. — The self-supply mechanism: The system achieves NO2 production through the synergistic effect of electrochemical ammonia oxidation and anaerobic ammonia oxidation reactions in the anodic region. — In-situ generation and recycling, without the need for external NO2. — And organic carbon sources, suitable for high NH4 content + Low C / N ratio wastewater treatment.

[0027] 3. Enhanced Electrochemical-Biological Synergistic Pathway Optimization and Spatial Regulation Capability: By constructing gradient potential distributions and reaction zones, multi-pathway synergistic transformations of ammonia nitrogen oxidation, nitrate reduction, and nitrogen generation are achieved, overcoming the limitations of traditional anaerobic ammonia oxidation systems in controlling NO2. — Dependence and NO3 — Residual issues.

[0028] 4. Composite bioelectrode structure enhances microbial enrichment and electron transfer: The ruthenium-iridium-titanium-carbon felt composite bioelectrode used has high conductivity and large specific surface area, which is conducive to the enrichment of electroactive microorganisms and anaerobic ammonia-oxidizing bacteria, thereby improving electron transfer efficiency and reaction rate.

[0029] 5. Enhanced total nitrogen removal capacity and engineering application adaptability: This invention achieves high nitrogen removal capacity and engineering application adaptability in low NO2 environments. — Or no NO2 — It can still achieve efficient nitrogen removal under certain conditions, significantly improving the total nitrogen removal load of the system. Moreover, the device has a modular structure and strong adjustability, and has good prospects for engineering applications. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram showing the spatial location of the electrodes and the hydraulic flow. Figure 3 For the operation of an adjustable multi-stage flow-controlled electrocatalytic biological nitrogen removal device, NH4 + NO2 - and NO3 - effluent concentration diagram; Figure 4 For NH4+ along the process in an adjustable multi-stage flow-controlled electrocatalytic biological nitrogen removal device + NO2 - and NO3 - Concentration change graph; Figure 5 The graph shows the cyclic voltammetry analysis of the bioelectrode unit under different voltage conditions. Figure 6 This is an electrochemical impedance spectroscopy analysis of the bioelectrode unit under different voltage conditions.

[0031] The components include: top cover plate 1, sealing gasket 2, electrode slot 3, transverse inspection hole 4, water inlet 5, anode titanium wire 6, anode composite bioelectrode 7, peristaltic pump 8, wire and exhaust port 9, overflow weir 10, water outlet 11, electrocatalytic reactor 12, DC power supply anode wire 13, DC power supply 14, DC power supply cathode wire 15, cathode titanium wire 16, bottom aeration port 17, anode chamber 18, cathode chamber 19, and cathode composite bioelectrode 20. Detailed Implementation

[0032] To make the objectives, advantages and features of the present invention more apparent, the following detailed description of the embodiments further illustrates the present invention.

[0033] like Figure 1 As shown, the present invention provides an adjustable multi-stage flow-controlled electrocatalytic biological denitrification device, the core of which is an electrocatalytic reactor 12 equipped with an anode chamber 18 and a cathode chamber 19. The two chambers are connected and sealed by bolts and rubber gaskets. The top is provided with a wire and an exhaust port 9, and the bottom is provided with a bottom aeration port 17 to achieve closed operation of the reactor and gas release.

[0034] Composite bioelectrodes (7, 20) are respectively installed in the anode chamber 18 and the cathode chamber 19. These electrodes consist of a conductive carbon felt coated with a ruthenium-iridium-titanium alloy mesh, possessing high conductivity, biocompatibility, and corrosion resistance, which is beneficial for the directional enrichment and stable adhesion of electroactive microbial membranes. The anode / cathode composite bioelectrodes are connected to an external DC power supply 14 via titanium wires (6, 16) to provide a constant potential for the electrochemical reaction.

[0035] The inlet 5 of the reactor anode chamber is connected to the raw water storage container via an inlet peristaltic pump 8, pumping the pretreatment substrate into the chamber. Under the action of the anode composite electrode, the substrate reacts with the loaded electroactive functional bacteria, converting NH4+ into NH4+. + With NO2 - Converted into N2 and a small amount of NO3 - Simultaneously, anodic electrochemical oxidation can partially decompose NH4+. + Directly oxidized to NO2 - Used for self-supplied Anammox reactions to construct "low NO2 influent". - Or no NO2 - The denitrification pathway of “”.

[0036] NO3 generated at the anode - As the liquid flows into the cathode chamber, it is reduced to NO2 by the denitrifying / electroactive bacteria supported on the cathode composite bioelectrode. - NH4 + Alternatively, N2 can be used to further achieve deep denitrification. The cathode chamber is equipped with an outlet 11 and a three-phase separation overflow weir 10 to separate the effluent from gas and particulate matter, thereby improving the system's operational stability.

[0037] In the device structure, both the anode and cathode cavities are equipped with slots 3 and transverse inspection holes 4, which can realize the spatial arrangement and replacement adjustment of the electrode plates, enhancing modular maintenance performance. The bottom aeration port 17 provides controllable gas disturbance, which is beneficial to mass transfer enhancement, sludge granulation, and biofilm stability.

[0038] During operation, by adjusting parameters such as DC voltage, number and arrangement of electrodes, and aeration rate, different NH4 levels can be flexibly adapted. + / NO2 - The optimal influent loading ratio enables efficient and stable nitrogen removal. No external carbon source or NO2 supplementation is required throughout the entire reaction process. - It has near-zero carbon addition denitrification capability and is particularly suitable for high NH4 content environments. + The need for engineered treatment of wastewater with low C / N ratio.

[0039] Device Example 1: This embodiment provides an electrocatalytic biological denitrification device using a ruthenium-iridium-titanium-carbon felt composite bioelectrode. It includes an anode chamber 18 and a cathode chamber 19, physically separated and disposed on an electrocatalytic reactor 12, and an anode composite bioelectrode 7 disposed within the anode chamber and a cathode composite bioelectrode 20 disposed within the cathode chamber. The anode and cathode composite electrodes are respectively composed of a ruthenium-iridium-titanium alloy metal mesh framework and a conductive carbon felt covering its exterior, exhibiting good conductivity, biocompatibility, and corrosion resistance.

[0040] The anode composite bioelectrode 7 is disposed in the anode chamber 18, and its carbon felt surface is loaded with electroactive microorganisms and anaerobic ammonia-oxidizing bacteria, enabling it to operate without the addition of NO2. — Achieving NH4 under certain conditions + The conversion to N2 occurs; simultaneously, the anode, driven by an applied potential, can assist in the electrochemical oxidation of NH4. + NO2 formation - It provides an electron acceptor for the Anammox reaction, constructing an internally self-supplied NO2 system. — Loop path.

[0041] To enhance mass transfer and reaction efficiency within the system, the anode chamber is designed as a bottom-in, top-out through-flow structure, with water introduced from the bottom of the chamber. For example... Figure 2 As shown, six composite bioelectrodes (7, 20) are staggered within the chamber. Water first enters from the bottom of the first electrode and flows sequentially through the subsequent five electrodes in a "baffle flow" manner. This long-flow design ensures sufficient reaction time between the water, microorganisms, and electrodes. Simultaneously, a portion of the water flows through the porous electrode plates, forming a "throughflow," further increasing the contact area and residence time between the ions to be treated and the electrodes and surface microorganisms, collectively constituting an enhanced "throughflow-baffle flow" composite hydraulic path.

[0042] The six composite bioelectrodes (7, 20) have clearly defined functional zones: the first electrode initially withstands the impact of water flow, retaining a portion of organic matter and debris through physical and gravitational forces; the first three electrodes form the anode region, where electrochemical ammonia oxidation occurs on the electrode surface, converting a portion of NH4+ into nitrogen. + Converted to NO2 - This provides the necessary electron acceptor for the anammox process within the system, enabling self-supply of nitrite. Simultaneously, anammox bacteria are also enriched on the anode electrode surface, synergistically participating in the denitrification reaction. The latter three electrodes form the cathode region, where electrochemical nitrate reduction and biological denitrification processes mainly occur, converting the NO3 produced earlier into nitrogen. - Reduced to N2 or NO2 - The internal circulation returns the material to the anode area for reuse.

[0043] Finally, the treated water flows out through the overflow weir 10, achieving three-phase separation of gas, liquid and solid.

[0044] The cathode composite bioelectrode 20 is disposed in the cathode chamber 19, and its surface is loaded with denitrifying bacteria. Under electrical drive, it can transfer NO3 from the anode. - Reduced to NO2 - Or N2, to achieve multi-path nitrogen conversion and NO3 - Deep removal. The cathode chamber also employs a through-flow-baffle flow electrode arrangement to enhance NO3 removal. - Migration efficiency and electrochemical reduction reaction rate.

[0045] The electrocatalytic reactor 12 is provided with a constant potential by a DC power supply 14. The anode and cathode composite bioelectrodes are respectively connected to the positive and negative terminals of the power supply through titanium wires via conductive ports, driving electron flow to promote electrochemical reactions and microbial electron transfer.

[0046] The system is equipped with a microporous bottom aeration port 17 at the bottom to enhance the distribution of dissolved oxygen and mass transfer efficiency within the chamber. The effluent system includes an overflow weir 10 and a three-phase separation device; after gas-liquid-solid phase separation, the effluent is discharged from the outlet 11.

[0047] To improve the system's recycling efficiency, the anode effluent is returned to the anode inlet 5 via a liquid circulation pump, achieving efficient substrate circulation and continuous nitrogen conversion. The inlet peristaltic pump 8 inputs the pre-degraded substrate into the anode chamber 18, and the effluent system is connected to a hose to guide the treated liquid to the collection unit or subsequent treatment unit.

[0048] To further enhance electrode stability and adhesion performance, the electrode carbon felt is made of a three-dimensional conductive polymer material and fixed to the surface of a metal skeleton by titanium wires. This structure not only improves the adhesion ability of microorganisms but also enhances the conductivity of the electrode and extends its service life.

[0049] In summary, the electrocatalytic biological denitrification device shown in this embodiment can operate in low NO2 environments. - Or no NO2 - This system achieves highly efficient nitrogen removal under influent conditions without the need for an external carbon source. It boasts stable operation, a compact structure, and excellent engineering adaptability and replicability. By constructing a through-flow / baffle flow fluid path, employing multiple staggered composite electrodes, and controlling electrical parameters, it significantly enhances the activity of the reaction interface and nitrogen removal efficiency, making it ideal for high-NH4+ environments. + Low-carbon wastewater provides a sustainable and controllable denitrification pathway.

[0050] The advantages of this implementation method are illustrated through two experimental cases: Experimental Example 1: like Figure 1As shown, this embodiment employs an electrocatalytic bioreactor with an effective volume of 900 mL, wherein the effective volumes of the anode and cathode chambers are both 450 mL. Composite bioelectrodes are respectively installed in the anode and cathode chambers and connected to a DC power supply via an external circuit to provide stable and adjustable potential conditions. Both the anode and cathode composite bioelectrodes utilize a mesh-like iridium-plated titanium substrate as a framework, covered with conductive carbon felt to ensure excellent conductivity, corrosion resistance, and microbial adhesion performance.

[0051] The anode and cathode chambers were respectively inoculated with anaerobic ammonia-oxidizing bacteria sludge that had been acclimatized in a solid waste laboratory and activated sludge from a wastewater treatment plant, so that the system simultaneously possessed electroactive microorganisms, anaerobic ammonia-oxidizing bacteria, and denitrifying functional bacteria. Before starting the experiment, the pH of the reaction solution in both chambers was uniformly adjusted to 7.0 to facilitate the synergistic growth of electrochemical reactions and functional microorganisms.

[0052] During operation, the influent ammonia nitrogen concentration is controlled at 255 mg NH4. + With a nitrogen concentration of -N / L, the influent enters the reactor from the bottom of the anode chamber. As it flows through multiple staggered composite bioelectrodes, it forms a typical through-flow / baffle flow hydraulic path. This flow pattern significantly prolongs the contact time between the substrate and the electrode surface and promotes the stepwise conversion of nitrogen at different electrode interfaces. The system operated continuously for 83 days, with influent and effluent samples collected every 3 days. NH4+ was measured using a UV spectrophotometer. + -N, NO2 — -N, NO3 — Indicators such as -N and total nitrogen, nitrogen concentration in the effluent, such as Figure 3 As shown.

[0053] Depending on the applied potential conditions, the reaction process can be divided into the following five stages: Phase 1 (0 V, 0-12 days): Under conditions where no external potential is applied, the reactor operates in an anaerobic state. During this phase, the NH4+ in the influent... + -N mainly migrated with the water flow in the anode chamber, and no obvious electrochemical oxidation was observed. NO2 in the system... — The -N concentration remains low, making it difficult to sustain a sufficient substrate supply for the anaerobic ammonium oxidation reaction. Therefore, NH4+ concentrations are low during this stage. + -N conversion was low, and the total nitrogen removal rate was close to zero.

[0054] Phase Two (0.6 V, 13–33 days): After applying a potential of 0.6 V to the anodic and cathode composite bioelectrode, a stable electrochemical driving environment begins to form within the system. Influent NH4 + During the process of NH4+ ions traversing the anodic composite bioelectrode, an electrochemically assisted oxidation reaction occurs on the anode surface, resulting in the partial oxidation of NH4+.+ -N is directly oxidized to produce NO2. — -N; simultaneously, anaerobic ammonia-oxidizing bacteria utilize the generated NO2 — -N and residual NH4 + -N undergoes the Anammox reaction, producing N2 and a small amount of NO3. — -N.

[0055] NO3 generated — After entering the cathode chamber with the water flow, -N is reduced to NO2 on the surface of the cathode composite bioelectrode under the synergistic action of electro-driven and denitrifying functional bacteria. — -N, and partially refluxed back to the anode chamber to continue participating in the anaerobic ammonia oxidation reaction. During this stage, the system gradually establishes a "nodal production of NO2" process. — -N- Cathode regeneration NO2 — The synergistic substrate supply mechanism of "-N" improved the total nitrogen removal rate to 46.1% ± 2.0%.

[0056] Phase 3 (1.0 V, 34–58 days): When the potential increases to 1.0 V, the electrochemical oxidation on the anodic side is further enhanced, and NH4+... + -N in the anode chamber to NO2 — -N and NO3 — The conversion rate of -N increases. Under the action of the through-flow-baffle flow between multi-stage electrodes, the influent achieves a stepwise conversion of nitrogen forms: NH4+ + →NO2 — →NO3 — .

[0057] Meanwhile, NO3 in the cathode chamber — The electroreduction reaction of -N is further enhanced, increasing the internal NO2 content of the system. — A more stable nitrogen supply is beneficial for the continuous anaerobic ammonia oxidation reaction. The total nitrogen removal rate increased to 55.3% ± 4.0% during this stage, indicating that the electrocatalytic-biological synergistic mechanism is gradually becoming dominant.

[0058] Phase Four (1.4 V, 59–83 days): When the potential is further increased to 1.4 V, the anode ammonia oxidation and cathode nitrate reduction processes are synergistically enhanced, forming a stable multi-pathway nitrogen conversion network within the system. Influent NH4 + -N is efficiently oxidized in the anode region and rapidly enters the anaerobic ammonium oxidation reaction pathway, while NO3- is reacted at the cathode. — The deep reduction of -N further reduces nitrate accumulation.

[0059] Under the hydraulic conditions of through-flow and baffle flow, nitrogen is repeatedly transformed and utilized between multiple electrodes, ultimately increasing the total nitrogen removal rate to 65.3% ± 4.4%.

[0060] Phase 5 (1.8 V, 84–105 days): When the applied potential is further increased to 1.8 V, the NH4+ on the anode side… + The electrochemical oxidation capacity of -N is further enhanced, and NO3 on the cathode side... — The -N reduction process is simultaneously enhanced, and the nitrogen conversion rate within the system continues to increase. During this stage, the anode reacts with NH4+. + The activation and transformation of -N, the regeneration and reduction of oxidized nitrogen at the cathode, and the anaerobic ammonia oxidation reaction form a more efficient synergistic effect, thereby reducing NO2 inside the reactor. — -N supply and consumption tend to reach a dynamic equilibrium. (Combined) Figure 4 As shown, the concentration of ammonia nitrogen gradually decreases along the direction of water flow, while the concentration of nitrite nitrogen shows a trend of first increasing and then decreasing. Nitrate nitrogen accumulates in the early stage and decreases significantly in the later stage, indicating that nitrogen is transformed in stages along the flow.

[0061] Under these operating conditions, the reactor exhibited optimal nitrogen removal performance, with the total nitrogen removal rate increasing to 83.7% ± 3.1%, indicating that the constructed composite bioelectrode structure and the through-flow-baffle flow coupled hydraulic path can achieve efficient stepwise conversion and deep removal of nitrogen under high applied potential conditions. Figure 5 As shown, the redox peaks of the electrode change significantly under different applied voltages, indicating that increasing the potential can significantly enhance the electrocatalytic activity and electron transfer capacity of the electrode. Figure 6 As shown, the radius of the electrode impedance arc decreases with increasing applied potential, indicating that the electron transfer resistance of the electrocatalytic system is reduced and the reaction kinetics are significantly improved.

[0062] The above results demonstrate that the electrocatalytic biological nitrogen removal device constructed in this invention can continuously provide usable substrates for the anaerobic ammonia oxidation reaction without the addition of additional nitrite through the synergistic effect of anode ammonia nitrogen electrochemical oxidation and cathode nitrate electroreduction. This system, through the synergistic design of multi-stage composite bioelectrodes and a throughflow-baffle flow structure, significantly enhances nitrogen mass transfer, reaction efficiency, and system stability, exhibiting excellent nitrogen removal potential and engineering application value.

[0063] Experimental Example 2: In this embodiment, a small-scale electrocatalytic bioreactor (effective volume 0.8 L) and a conventional upflow anaerobic sludge blanket (UASB) reactor (effective volume 8 L) are coupled to further optimize nitrogen removal. Both reactors are inoculated with acclimated anaerobic ammonia-oxidizing bacteria sludge. The UASB reactor had achieved stable operation before coupling, maintaining a total nitrogen removal rate of approximately 78.20 ± 1.20%. During the coupled operation, the effluent from the UASB reactor first enters the electrocatalytic bioreactor for secondary treatment, and then is recirculated (recirculation ratio 0.6) back into the UASB reactor. A gradient voltage (0 V, 0.6 V, 1.0 V, 1.6 V) is applied to the electrocatalytic bioreactor using a constant potential control device.

[0064] Experimental results show that the adjustable multi-stage flow-controlled electrocatalytic biological nitrogen removal device and method provided by this invention increases the total nitrogen removal rate to 90.24±2.51% and the total nitrogen removal speed to 1.86 kgN / m³. 3 / d, an improvement of approximately 12.04% compared to a single UASB system. Further analysis revealed residual NH4 in the UASB effluent. + Partially converted to NO2 through electrocatalysis — The NO2 — It can be directly used as a substrate for anaerobic ammonia oxidation, thereby promoting nitrogen cycling and enhancing the overall nitrogen removal performance of the system.

[0065] Therefore, the enhanced anaerobic ammonia oxidation system and the system for rapidly increasing total nitrogen removal load provided in the above two embodiments have the following beneficial effects: 1) Superior electrode performance, enhancing electron transfer and reactivity. The composite bioelectrode used in this invention has higher conductivity and more stable electrochemical characteristics than traditional carbon rod or titanium wire electrodes, significantly promoting redox reactions and accelerating nitrogen conversion. Simultaneously, its surface structure facilitates the formation of a dense and stable biofilm, enhancing microbial adhesion and activity, and ensuring long-term stable operation of the system.

[0066] 2) High efficiency and low carbon footprint, combining substrate adaptability with nitrogen removal performance. Compared with the traditional Anammox process, the system of this invention can effectively remove nitrogen from various NH4 groups. + / NO2 — Under proportional conditions, it exhibits high denitrification efficiency and adaptability, avoiding dependence on precise influent ratios and offering greater operational flexibility. This technology can achieve highly efficient denitrification without the need for external organic carbon sources, significantly reducing operating costs and achieving the goals of energy conservation, emission reduction, and resource recycling.

[0067] 3) Modular design, flexible engineering application. The system of this invention has a compact structure and high modularity, which can be flexibly combined and expanded according to different water quality conditions and treatment scales. It is easy to install, has a long maintenance cycle, and low operation requirements, making it suitable for large-scale engineering applications and possessing good potential for promotion.

[0068] 4) Enhanced coupling effect to improve total nitrogen removal load. This invention achieves NH4+ removal by efficiently coupling the electrocatalytic process with anaerobic ammonia oxidation. + To NO2 — Partial directional conversion forms a positive cycle substrate supply mechanism, which significantly improves the total nitrogen removal load and system stability.

[0069] 5) Aligns with the "dual-carbon" strategy, offering significant environmental and economic benefits. This invention reduces external carbon source input and energy consumption while achieving deep nitrogen removal and compliant wastewater discharge, meeting the needs of the current "dual-carbon" strategy and green sustainable development. It has broad application prospects in the fields of wastewater treatment and resource utilization.

[0070] The above embodiments have provided a detailed description of the technical solution of the present invention. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various modifications, but any modifications that are equivalent to or similar to the present invention fall within the scope of protection of the present invention.

[0071] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. An adjustable multi-stage flow-controlled electrocatalytic biological nitrogen removal device, comprising an electrocatalytic reactor (12), wherein the electrocatalytic reactor is provided with an anode chamber (18) and a cathode chamber (19), characterized in that: Multiple composite bioelectrode units (7) with both conductivity and porous structure are respectively set in the anode chamber (18) and the cathode chamber (19). Each electrode unit is arranged in a staggered manner along the water flow direction to form an asymmetric flow channel structure. The composite bioelectrode unit (7) also serves as a hydraulic disturbance component, an electron transfer medium and a microbial attachment carrier, constructing a coupling system of flow zone, potential zone and functional microbial zone inside the reactor. The liquid matrix forms a baffle path along the electrode gap, and some fluid passes through the porous electrode structure to realize the synchronous coupling of substrate mass transfer, electrochemical reaction and microbial metabolism, forming a gradient reaction zone along the water flow direction.

2. The apparatus as described in claim 1, characterized in that: The electrocatalytic reactor (12) is equipped with a cover plate (1) with a wire and an exhaust port (9) at the top. A rubber gasket (2) is installed between the cover plate and the reactor body to seal the cover plate. A bottom aeration port (17) is provided at the bottom of the reactor. The composite bioelectrode unit (7) is connected to an external DC power supply (14) through a titanium wire (6) via the reserved port (9). The reactor is equipped with an inlet peristaltic pump (8). The inlet (5) is connected to the outlet of the peristaltic pump. An overflow weir (10) is set in front of the outlet (11) to achieve gas-liquid-solid three-phase separation.

3. The apparatus as described in claim 1, characterized in that: The composite bioelectrode unit (7) is composed of a porous ruthenium-iridium-titanium alloy mesh covered with conductive carbon felt.

4. The apparatus as claimed in claim 1, characterized in that: The reactor interior forms a complex flow structure, including a baffled path along the outer side of the electrode and a trans-electrode mass transfer path that traverses the porous structure of the electrode. The trans-electrode mass transfer path is accompanied by ion migration and electron transfer, enabling the fluid to participate in electrochemical and biotransformation reactions simultaneously.

5. The apparatus as described in claim 4, characterized in that: The composite bioelectrode unit along the water flow direction forms a gradient functional reaction zone. The front section is the ammonia oxidation and nitrite generation zone, the middle section is the anaerobic ammonia oxidation reaction zone, and the rear section is the nitrate reduction and denitrification reaction zone, realizing a multi-stage combined reaction of nitrogen transformation through multiple pathways.

6. The apparatus as claimed in claim 1, characterized in that: Each composite bioelectrode unit (7) is independently or in groups connected to a DC power supply (14), which can apply differentiated potentials and construct a gradient potential field distributed along the water flow direction inside the reactor.

7. The apparatus as claimed in claim 1, characterized in that: Electrode slots (3) are provided in the anode chamber (18) and the cathode chamber (19) to adjust the electrode spacing and arrangement, thereby changing the flow structure and reaction zone distribution.

8. The apparatus as claimed in claim 1, characterized in that: Uniform aeration micropores are set at the bottom of the reactor to regulate local dissolved oxygen and reaction environment, and to assist in controlling the reaction conditions of each functional reaction zone.

9. A tunable multi-stage flow-controlled electrocatalytic biological nitrogen removal method, employing the apparatus described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Nitrogen-containing wastewater is introduced into the reactor, forming a baffle path between the staggered composite bioelectrodes, with some fluid passing through the porous structure of the electrodes. S2: When fluid passes through the electrode, it achieves synchronous coupling of electrochemical reaction and microbial metabolism through the electron transfer path on the electrode surface; S3: Apply differential potentials to electrodes at different positions to create a gradient potential distribution, so that ammonia oxidation, anaerobic ammonia oxidation and denitrification reactions occur sequentially along the water flow direction; S4: Adjust the electrode layout parameters and potential distribution to control the nitrogen conversion pathway in stages.

10. The method as described in claim 9, characterized in that: By adjusting the electrode spacing, number of electrodes, electrode potential, and fluid residence time, a stable flow-potential-microorganism coupling regulation mechanism is formed to adapt to the treatment needs of wastewater with different nitrogen source ratios.

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