Method for treating sewage through bioelectrochemistry and plant air flotation technology

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for treating sewage by a bioelectrochemistry and plant air flotation technology. According to the invention, a microbial fuel cell, microbial electrolysis cell and plant air flotation multi-effect synergistic technology is adopted, organic matters are catalytically degraded through microorganisms, electricity or hydrogen is produced synchronously, the resource utilization of pollutants is realized, the residual electric energy of the microbial fuel cell can be used by the microbial electrolysis cell, and the energy consumption of an external source is reduced; the distribution of dissolved oxygen is optimized through multi-echelon aeration, the metabolism of aerobic / anoxic microorganisms is enhanced, and the treatment efficiency is improved; the plant air flotation adsorbs and absorbs nutritive salt through a root system, further purifies water quality, controls dissolved oxygen in stages, promotes synchronous nitrification and denitrification, and improves the total nitrogen removal rate. A chemical flocculant is replaced by the plant mucus, so that the use amount of the agent is reduced and the cost is reduced. The method has wide application prospects in the fields of industrial wastewater treatment, riverway restoration and the like, and the water treatment technology is promoted to be upgraded to the high-efficiency, low-carbon and recycling directions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and particularly relates to a method for treating sewage by using a bioelectrochemical synergistic plant air flotation technology. BACKGROUND

[0002] The most commonly used method for purifying oil-containing sewage is flocculation, which is to add a flocculating agent to the sewage, and the generated flocculating body adheres to the oil droplets and other impurities in the sewage, and then the density difference is used to remove them. Sewage contains many solid suspended matter, oil droplets and organic matter, which will cause corrosion, blockage and putrefactive bacteria proliferation of pipeline equipment. Since the oil droplets have negative electric properties, the colloids with positive electric properties are used to combine with the oil droplets, and the flocculation effect is achieved by using the principle of electric neutralization.

[0003] In the air flotation method, the air flotation oil-water separation technology is to pass gas into the sewage to be treated, the gas forms micro-bubbles through a bubble generating device, the micro-bubbles collide with and adhere to the oil droplets and impurity particles in the water, forming a flocculating body with a density smaller than that of water, and the flocculating body floats to the water surface under the action of buoyancy to overcome gravity and resistance, realizing the separation of oil phase and water phase, and solid phase and water phase. At present, for the air flotation method, the micro-nano air flotation machine is used to treat wastewater on the market. The micro-nano air flotation effect is a horizontal type dissolved air flotation machine, which is a commonly used device for treating solid-liquid separation in the sewage treatment industry, and can efficiently remove suspended solids, oil, glue and decolorized sludge in wastewater. The air flotation machine is the main equipment for the preliminary treatment of sewage. The Yude high-efficiency micro-nano superoxygen air flotation machine uses the principle of water-gas mixing high-speed rotation and precise cutting of water body, so as to generate a large number of micro-nano bubbles in the water, so that the air is attached to the suspended particles in the form of highly dispersed micro-bubbles, causing the state of density less than water, and making it float on the water surface by using the principle of buoyancy, so as to realize the solid-liquid separation of water treatment, which is a relatively advanced high-tech equipment.

[0004] Chemical method is the most widely used and lowest cost oil-water separation technology in petrochemical enterprises. Its mechanism involves complex physical and chemical processes. The currently accepted theories include interface film displacement theory, electric neutralization theory, double electric layer theory, adsorption bridge theory, and net capture and sweeping theory. Demulsifiers are solutions composed of various surfactants for water-in-oil (W / O) emulsion systems. By reducing the surface tension and interfacial strength of the oil-water interface, the original emulsion balance is broken, and water is quickly precipitated. Compared with demulsifiers, reverse demulsifiers target oil-in-water (O / W) emulsion systems. The dispersed phase is usually negatively charged, so it should have strong positive charge, surface activity, and flocculation ability. Flocculants act on oil droplets, solid particles, and colloidal particles suspended in wastewater, as well as other impurities, causing instability. The unstable impurities collide and stick together in water, forming flocculent bodies. Depending on their density, they float or sink. During the floating and sinking process, they collide and grow larger, eventually accumulating at the bottom or floating on the surface, completing water purification.

[0005] Hydrocyclone method is a device that uses centrifugal separation and the principle of different oil and water densities. Oily wastewater is placed in a high-speed spiral cone. The density difference of the multi-phase medium produces different centripetal forces during the cyclone process, achieving separation. The structure usually has an overflow pipe at the top, a underflow pipe at the bottom, a cyclone chamber and a cone section in the middle. The material enters tangentially from the inlet. According to the function, it can be further divided into pre-separation area, main separation area, and underflow post-mixing area.

[0006] However, the treatment effect of wastewater containing certain specific components using conventional methods is not ideal, and the energy consumption of wastewater treatment using conventional technology is high. To achieve the "double carbon" goal, under the "double carbon" background, traditional wastewater treatment needs to gradually change to a new concept. Wastewater treatment cannot just be a system for removing pollutants, but a resource and energy plant that provides renewable resources and energy for itself and the surrounding area, contributing to social sustainable development. The low-carbon design technology points of the new concept wastewater treatment plant are studied.

[0007] As one of the secondary treatment alternatives, electrochemical AOPs have been increasingly applied in the treatment of wastewater containing high concentrations of chemicals. In addition to its high pollutant removal efficiency, electrochemical technology is superior to other technologies due to its simple process design, low installation cost, and no need for reagent addition. Through the action of an external electric field, electrochemical technology can induce direct or indirect redox reactions on the electrode surface or in the solution, achieving the decomposition of organic pollutants and thus realizing green and efficient treatment of chemical wastewater.

[0008] Electrochemical processes are a green and efficient water treatment technology, especially an effective way to remove refractory organic pollutants. Anodic oxidation reaction is mainly used to generate active oxygen (such as ·OH or O 2-The cathode reduction is mainly used for generating hydrogen atoms for reduction and dehalogenation. The equipment for degrading pollutants by the electrochemical oxidation and reduction process is simple, the reaction condition is mild, and the organic matters which are difficult to be degraded by traditional processes can be degraded. However, the single electrochemical treatment process cannot achieve the effect of completely degrading pollutants. Therefore, the combination of the electrochemical technology, the photocatalysis and the biological treatment technology is more beneficial to the advanced treatment of wastewater. SUMMARY

[0009] The technical problem to be solved by the present application is to provide a method for treating wastewater by a biological electrochemical and plant air flotation technology.

[0010] The method for treating wastewater by the biological electrochemical and plant air flotation technology comprises the following steps.

[0011] (1) The oily wastewater is treated by a microbial fuel cell (MFC) unit, in an anaerobic environment, the electricity-generating bacteria adsorb oily substances and degrade pollutants, and at the same time, the organic matters are decomposed to generate electric energy to power a microbial electrolysis cell;

[0012] (2) The oily wastewater enters the microbial electrolysis cell (MEC) unit for intensified decomposition, after the electrode is powered on, the oxidation reaction occurs at the anode to generate metal ions, the reduction reaction occurs at the cathode to generate H2 and OH - , the metal ions and OH - react to generate hydroxide and polynuclear hydroxyl complexes, and flocculation bodies are generated in the wastewater;

[0013] (3) The wastewater enters a plant air flotation bed unit, an aerator is arranged in the plant air flotation bed unit to further degrade the organic matters, the flocculation bodies floating on the water surface of the plant air flotation bed unit enter the release pipeline to be backflowed to the microbial electrolysis cell for reprocessing after reaching the water level, the qualified water is discharged or reused, the hydrogen is recycled, and the plant residues are prepared into biochar or biogas.

[0014] Preferably, the oily wastewater is pretreated by an oil separation tank to remove large particles of floating oil and suspended solids, and the pH is adjusted to neutral, and then the oily wastewater enters the microbial fuel cell unit.

[0015] Preferably, in the microbial fuel cell unit, a biofilm is attached to the anode surface, and organic matters in the wastewater are directly converted into electricity in the anode oxidation process under anaerobic environment, and the biological cathode removes nitrogen and phosphorus in the water through activated sludge and aerobic nitrification process under aeration requirement.

[0016] Preferably, the microbial electrolysis cell unit provides required electricity through the microbial fuel cell unit, and the anode generates oxidation reaction, and generated metal ions include Al 3+ , Fe 3+ .

[0017] Preferably, in the microbial electrolysis cell unit, generated flocculation bodies remove oil droplets in the wastewater through the way of entrapment, bridging and adsorption, and H2 micro-bubbles generated in the cathode electrolysis wrap the oil droplets into the bubbles and then adhere to the flocculation bodies, and the hydrogen-producing bacteria in the microbial electrolysis cell also convert organic matters into hydrogen gas, and remove nitrogen and phosphorus pollutants.

[0018] Preferably, the plant air floatation bed unit comprises aquatic / hygrophyte and oil-tolerant submerged plants, the aquatic plants are planted on the artificial floatation bed, and the bottom submerged plants are arranged to cooperatively treat the wastewater, and a micro-nano aerator is arranged to periodically perform multi-gradient aeration in the water.

[0019] Preferably, the aquatic / hygrophyte comprises reed, calabash, cattail, duckweed, green canna, iris, arrowhead, purple canna, and as a further preferred, the aquatic / hygrophyte is cattail; the oil-tolerant submerged plant comprises any one of or a combination of Ceratophyllum demersum and Potamogeton crispus, and as a further preferred, the oil-tolerant submerged plant is the combination of Ceratophyllum demersum and Potamogeton crispus.

[0020] Preferably, a plurality of plants are planted on the plant air floatation bed, and a foam board is used as a floatation bed carrier, and the distance between adjacent plants is adapted.

[0021] Preferably, the hydraulic retention time is at least 2 hours.

[0022] Preferably, the dissolved gas pressure of the plant air floatation bed unit is controlled to be 0.3-0.5 MPa, the gas-water ratio is 1:3-1:5, and the pH is 6.5-7.5.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The biological electrochemical system (BES) catalytically degrades organic matters through microorganisms, synchronously generates electricity or hydrogen, and realizes resource utilization of pollutants; multi-gradient aeration optimizes the distribution of dissolved oxygen, strengthens aerobic / anaerobic microbial metabolism, and improves the treatment efficiency; the plant air floatation purifies the water quality through root adsorption and absorption of nutrient salts (such as nitrogen and phosphorus), and forms a multi-stage treatment chain.

[0025] (2) Plant root system enriches microorganism and organic matter, promoting in-situ degradation of sludge; air flotation unit separates suspended solids through micro-bubbles, reducing sludge production; the whole system replaces traditional chemical agents with biological-electrochemical-plant synergistic effect, reducing the risk of secondary pollution.

[0026] (3) Multi-technology synergistic effect principle

[0027] MFC: Using electrogenic bacteria (such as Geobacter) to oxidize organic matter to generate electricity, suitable for low-concentration organic wastewater (COD 500-2000 mg / L). The electrochemically active bacteria attached to the anode surface can degrade the organic matter in the residual sludge to generate electrons transferred to the anode surface, while protons migrate to the cathode area. The electrons on the anode surface are transferred to the cathode through an external circuit, combined with the cathode electron acceptor (O2, NO 3- -N, NO 2- -N), to generate the corresponding reduction products, achieving simultaneous treatment of anode biological sludge and cathode wastewater and recovery of electrical energy.

[0028] MEC: External voltage drives hydrogen-producing bacteria (such as Clostridium) to convert organic matter into hydrogen gas, suitable for high-concentration wastewater (COD > 3000 mg / L).

[0029] Synergistic points: The residual electrical energy of MFC can power MEC, reducing external energy consumption; the hydrogen byproduct of MEC can be reused as energy or chemical raw materials.

[0030] Multi-stage aeration control:

[0031] Controlling dissolved oxygen in stages (such as alternating aerobic and anoxic conditions) to promote simultaneous nitrification and denitrification (SND), with total nitrogen removal rate improved to more than 85%, while inhibiting filamentous bacteria expansion. In the plant air flotation bed unit (or integrated plant water treatment system), according to the different needs of dissolved oxygen concentration in different treatment stages and microbial reactions, the aeration unit with different aeration intensity, different bubble size or different aeration mode is designed and implemented as needed in space (horizontal direction, vertical depth) and / or time (process direction), forming a stable and controllable dissolved oxygen concentration gradient distribution (such as aerobic → anoxic → anaerobic) in a single reactor or closely coupled system, to achieve efficient synergistic removal of pollutants (COD, nitrogen, phosphorus, etc.), optimize mass transfer efficiency, strengthen air flotation separation effect and reduce energy consumption.

[0032] Plant air flotation enhancement:

[0033] Plant root system (such as cattail) secretes electron shuttles (such as quinones), enhancing the electron transfer efficiency of MFC / MEC; air flotation micro-bubbles carry pollutants to float up, reducing the load of subsequent treatment.

[0034] (4) Operation cost optimization

[0035] Low energy consumption: MFC's self-generated electricity replaces traditional aeration energy consumption (saving 40%-60%), and the hydrogen produced by MEC partially offsets this electricity consumption. Low chemical consumption: Plant mucus replaces chemical flocculants (such as PAC), reducing flotation unit chemical costs by 70%. This technology combination has broad application prospects in industrial wastewater treatment, river restoration, and other fields, driving water treatment technology towards higher efficiency, lower carbon emissions, and resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Flow chart of the method of the present invention;

[0037] Figure 2 This is a working principle diagram of the microbial fuel cell unit in the present invention;

[0038] Figure 3 This is a working principle diagram of the microbial electrolysis cell unit in the present invention;

[0039] Figure 4 This is a structural diagram of a plant air-floating bed unit of the present invention;

[0040] Figure 5 It is a front view of the microbial fuel cell, microbial electrolysis cell, and plant air floating bed unit structure of the present invention;

[0041] Figure 6 It is a three-dimensional diagram of the structure of the microbial fuel cell, microbial electrolysis cell, and plant aeration bed unit in the present invention.

[0042] In the figure, 1 is a microbial fuel cell; 2 is a microbial electrolytic cell; 3 is a plant floating bed; 4 is a rotating motor; 5 is a micro-nano aerator; 6 is a cathode wire; 7 is an anode wire; 8 is an inlet of a plant gas floating bed unit; 9 is an artificial floating bed; 10 is an electrolytic cell anode; 11 is a circular graphite felt; 12 is a sewage inlet; 13 is a graphite rod shaft; 14 is an electrolytic cell sewage inlet; 15 is an electrolytic cell outlet. DETAILED DESCRIPTION

[0043] The accompanying drawings are for illustrative purposes only, and the present invention will be described in detail below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the present invention can be purchased through conventional commercial channels.

[0044] Example 1

[0045] like Figure 1 As shown, a method for treating sewage using bioelectrochemical synergistic plant flotation technology includes the following steps:

[0046] (1) Oil-containing wastewater is treated by a microbial fuel cell (MFC) unit. In an anaerobic environment, electricity-producing bacteria adsorb oily substances and degrade pollutants, while decomposing organic matter to generate electricity for the microbial electrolysis cell;

[0047] (2) The oil-containing wastewater enters the microbial electrolysis cell (MEC) unit for enhanced decomposition. After the electrodes are powered on, oxidation occurs at the anode, generating metal ions, and reduction occurs at the cathode, generating H2 and OH-. The metal ions and OH- react to form hydroxides and polynuclear hydroxyl complexes, and flocculation bodies are generated in the wastewater;

[0048] (3) The wastewater enters the plant air flotation bed unit, where an aerator is installed to further degrade organic matter. The flocculation bodies floating on the water surface of the plant air flotation bed unit enter the release pipeline to return to the microbial electrolysis cell for reprocessing after reaching the water level. The treated water is discharged or reused, hydrogen is recycled, and plant residues are used to prepare biochar or biogas.

[0049] As shown in Figure 2 , the microbial fuel cell (MFC) technology, as the most common wastewater treatment and power generation function method in microbial electrochemical systems, has gradually shown great potential in the field of wastewater treatment. In MFC technology, organic matter in wastewater can be directly converted into electrical energy during the anode oxidation process, thereby offsetting the energy consumption required for wastewater treatment. The biological cathode can exhibit high nitrogen removal performance superior to traditional activated sludge and aerobic nitrification processes under lower aeration requirements. In addition, MFC technology can still effectively treat influent wastewater at low temperatures and chemical oxygen demand loads.

[0050] As shown in Figure 3 , the microbial electrolysis cell (MEC) is a technology that uses external electrical energy to enhance the decomposition of substrates and achieve hydrogen recovery (or other chemicals such as methane). The power generation mechanism of MEC technology is the same as that of the electricity-producing microorganisms in the anode biofilm in MFC technology; however, the start-up of MEC technology requires a weak voltage provided by an external circuit to oxidize and reduce pollutants in wastewater at the anode and cathode, respectively, through the electrolysis process, converting them into easily biodegradable low-molecular-weight, low-toxicity substances, thereby facilitating biological treatment. Through electrolysis, complete mineralization of organic matter can be achieved, thereby completely converting persistent organic pollutants into harmless substances such as CO2 and H2O, to achieve the purpose of wastewater purification. Meanwhile, electrons and protons combine on the surface of the electrode cathode, thereby producing hydrogen, which also provides a new approach to biological hydrogen production.

[0051] The microbial electrochemical system can recycle CO2, CO3 2- and HCO3- Microbial electrolysis cells (MECs) have the characteristics of easier operation and flexible adjustment configuration. The operation of MECs combined with AD (Anaerobic digestion) can reduce the deposition of volatile fatty acids, improve the hydrolysis / acid production rate, and increase the methanogenic activity through in-situ and ex-situ modes. The in-situ mode is to carry out the AD reaction process in the MEC reactor, and the ex-situ mode is to operate the MEC as a post-treatment unit in a separate reactor to improve the biodegradability of organic matter, enhance the stability of AD, recover nutrients, and upgrade biogas. In single / double-chamber MECs, electrons are generated in the anode chamber through electrolysis or substrate oxidation processes and reach the cathode to produce methane using acetic acid or H2. MECs use water oxidation at the anode to generate electrons (e-) and protons (H+) in the presence of an external potential, which are transported to the cathode, where electro-active microorganisms (e.g., Geobacter, Desulfovibrio, Desulfosarcina, Symbiobacterium, Chlorella, and Micractinium) utilize them in redox reactions. In addition, bacteria rely heavily on electron exchange, so various extracellular electron transfer mechanisms are required: direct interspecies electron transfer (DIET) and indirect interspecies electron transfer (IIET). DIET occurs through biofilms, promoting long-range transfer of electrons from the biofilm to the anode surface through cell membrane-bound cytochromes or conductive pili (nanowires). IIET occurs through the mediation of H2, with microbial redox mediators (electron shuttles) such as redox-active proteins or formate dehydrogenase acting as catalysts. In this case, electro-active bacteria (EAB) are capable of accepting electrons from the electrode through direct interspecies electron transfer, through electron shuttling, or through the oxidation of hydrogen or other compounds produced by microorganisms.

[0052] As shown in Figure 4 , several plants are cultivated on each plant floating bed, and foam boards are used as floating bed carriers with an appropriate distance between adjacent plants. The plant floating bed technology has obvious nitrogen removal effect, provides habitats for birds and fish, beautifies the landscape, protects the shore, blocks light, and suppresses algae, etc., and has multiple ecological benefits. It is widely used in ecological restoration projects of lakes and rivers and has achieved good results. The mechanism of organic pollutant removal by plant floating beds is mainly biological absorption and degradation, including plant root absorption, root excretion regulation, and microbial degradation attached to plant roots. The advantages of this biological remediation method are high safety and less secondary pollution.

[0053] The principle of the air floatation oil-water separation technology is to pass gas into the sewage to be treated, the gas forms micro-bubbles through a bubble generator, the micro-bubbles collide with and adhere to oil droplets and impurity particles in the water to form flocs with a density less than that of water, the flocs float to the water surface under the action of buoyancy to separate the oil phase from the water phase and the solid phase from the water phase.

[0054] The plant floatation bed 3 unit comprises hydrophytes / wetland plants and oil-resistant submerged plants, the hydrophytes are planted on the artificial floatation bed, the bottom submerged plants are matched to cooperatively treat the sewage, and a micro-nano aerator is arranged to periodically perform multi-gradient aeration in the water.

[0055] Therefore, the dissolved oxygen is one of important factors for the biological floatation purification of water bodies. The dissolved oxygen in the water body has two main sources, one is from the atmosphere, and the gas exchange is often carried out at the interface between the water body and the atmosphere to make the oxygen in the atmosphere enter the water body, and the exchange speed depends on the horizontal and vertical movement speed of the water flow, which is the main source in the water body. The other is the oxygen released by the aquatic plants through photosynthesis, which can also accelerate the reoxygenation process of the water body.

[0056] Experiments prove that the oxygen released by the aquatic plants in the light irradiation water body above 0.5 m is basically absorbed below 0.5 m. Therefore, the maximum value of photosynthesis in the water often does not appear in the surface layer or the deep layer, but in a certain depth under the water. This is because under the condition of clear weather, the light intensity in the surface layer is too large, and the light inhibition phenomenon occurs in the photosynthesis process. If the reoxygenation process is very slow under the condition of static water, the dissolved oxygen in the water cannot be supplemented in time, and the water is in an anaerobic state: the organic pollutants will be converted into organic acids and reducing gases, thereby causing the water quality to decrease. The submerged plant + plant floatation method is developed according to the above action mechanism, and the floatation bed plant + submerged plant: the hydrophytes are planted on the artificial floatation bed, and the bottom submerged plants are matched to cooperatively treat the sewage, which can maximize the gas exchange between the water and the atmosphere and accelerate the reoxygenation process. At the same time, the water is periodically aerated, and the concentration is reasonably designed to maintain the activity of the submerged plants and the hydrophytes, so that the biological photosynthesis can be ensured; the biological can also absorb the nitrogen, phosphorus and other nutrients in the water to form the basic nutrients of the food chain of the ecological system and ensure the energy flow in the ecological system, so that the purification effect can be fully played.

[0057] As Figure 4 , 5As shown, the oil-containing wastewater is first pretreated by an oil separation tank to remove large particles of floating oil and suspended solids, and the pH is adjusted to neutral, and then enters the microbial fuel cell 1 unit. A rotating motor 4 is provided on one side of the microbial fuel cell 1 unit, a circular graphite felt 11 is provided in the microbial fuel cell 1 unit, and a sewage inlet 12 is provided on the other side wall. The anode surface is attached with a biofilm. In an anaerobic environment, the organic matter in the wastewater is directly converted into electrical energy during the oxidation process at the anode. The biological cathode removes nitrogen and phosphorus in the water through activated sludge and aerobic nitrification process under aeration requirement. A cathode wire 6 and an anode wire 7 are provided to connect the microbial electrolysis cell 2 unit.

[0058] In the microbial electrolysis cell 2 unit, the required power is provided by the microbial fuel cell 1 unit. The anode and the cathode are both attached with a biofilm. The anode undergoes an oxidation reaction, and the generated metal ions include Al 3+ , Fe 3+ . An electrolysis cell sewage inlet 14 is provided at the bottom of the microbial electrolysis cell 2 unit. A pipeline is also provided, so that the flocculation body floating on the water surface of the plant air floatation bed 3 unit will enter the release pipeline and return to the microbial electrolysis cell for reprocessing after reaching the water level. In the microbial electrolysis cell 2 unit, the generated flocculation body removes oil droplets in the wastewater by means of net capture, sweeping, bridging and adsorption. The cathode electrolysis generates H2 micro-bubbles, which wrap the oil droplets into bubbles and then adhere to the flocculation body. The hydrogen-producing bacteria in the microbial electrolysis cell also convert organic matter into hydrogen gas, while removing nitrogen and phosphorus pollutants. The plant mucilage replaces the chemical flocculant (such as PAC), greatly reducing the amount of chemicals used.

[0059] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A method for treating sewage using bioelectrochemical and plant flotation technology, characterized in that: The steps include: (1) Oily wastewater is treated by a microbial fuel cell unit. Under an anaerobic environment, electrogenic bacteria adsorb oily substances and degrade pollutants, while decomposing organic matter to generate electricity to power the microbial electrolysis cell. (2) The oily wastewater enters the microbial electrolysis cell unit for enhanced decomposition. After the electrodes are energized, an oxidation reaction occurs at the anode to generate metal ions, and a reduction reaction occurs at the cathode to generate H2 and OH. - , metal ions and OH - The reaction generates hydroxides and polynuclear hydroxyl complexes, and floccules are formed in the wastewater; (3) Wastewater enters the plant flotation bed unit, where an aerator is installed to further degrade organic matter. When the flocs floating on the water surface of the plant flotation bed unit reach the water level, they will enter the release pipe and flow back to the microbial electrolysis cell for reprocessing. The water that meets the standards will be discharged or reused, hydrogen will be recovered and utilized, and plant residues will be used to prepare biochar or biogas.

2. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 2, characterized in that: The oily wastewater is first pretreated in a grease trap to remove large floating oil particles and suspended solids, and the pH is adjusted to neutral before entering the microbial fuel cell unit.

3. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 1, characterized in that: In the microbial fuel cell unit, a biofilm is attached to the anode surface. Under anaerobic conditions, organic matter in the wastewater is directly converted into electrical energy during the anode oxidation process. Under aeration requirements, the biocathode removes nitrogen and phosphorus from the water through activated sludge and aerobic nitrification processes.

4. The method for treating sewage by bio-electrochemical coordinated plant flotation technology according to claim 1, characterized in that: The microbial electrolysis cell unit provides the required electricity through the microbial fuel cell unit, and an oxidation reaction occurs at the anode to generate metal ions including Al 3+ 、Fe 3+ .

5. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 1, characterized in that: In the microbial electrolysis cell unit, the generated flocs remove oil droplets from the sewage through netting, sweeping, bridging, and adsorption; cathode electrolysis produces tiny bubbles of H2, which wrap the oil droplets in the bubbles and then adhere to the flocs. The hydrogen-producing bacteria in the microbial electrolysis cell also convert organic matter into hydrogen, while removing nitrogen and phosphorus pollutants.

6. The method for treating sewage by bio-electrochemical coordinated plant flotation technology according to claim 1, characterized in that: The plant air floating bed unit includes aquatic / wet plants and oil-resistant submerged plants. Aquatic plants are planted on the artificial floating bed and combined with bottom submerged plants to synergistically treat sewage. At the same time, a micro-nano aerator is set to periodically perform multi-gradient aeration in the water.

7. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 6, characterized in that: Aquatic / wet plants include reeds, gourds, cattails, duckweed, green-leaf canna iris, lily of the valley, arrowhead, and purple-leaf canna. Oil-resistant submerged plants include either duckweed or foxtail algae, or a combination of both.

8. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 7, characterized in that: Several plants are cultivated on a plant floating bed, with foam boards used as floating bed carriers, and the distances between adjacent plants are adapted.

9. The method for treating sewage by bio-electrochemical synergistic plant flotation technology according to claim 1, characterized in that: The hydraulic retention time is at least 2 hours.

10. The method for treating sewage by bio-electrochemical coordinated plant flotation technology according to claim 1, characterized in that: The dissolved air pressure of the plant air floating bed unit is controlled to be 0.3-0.5 MPa, the air-water ratio is 1:3-1:5, and the pH is 6.5-7.5.

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