Anaerobic baffle plate-microbial electrolysis-constructed wetland coupling process for rural domestic sewage treatment

Abstract

The invention discloses application of an anaerobic baffle plate-microbial electrolysis-constructed wetland coupling process in the aspect of rural domestic sewage treatment. The principle is based on a novel volatile fatty acid (VFAs) comprehensive utilization technology. The anaerobic baffle plate-microbial electrolysis-constructed wetland coupling process is mainly composed of a four-compartment anaerobic baffle plate reactor and a multi-section multi-stage microbial electrolysis and horizontal subsurface flow type constructed wetland coupling reactor, and the specific working process is as follows: (1) rural domestic sewage is used as inlet water, firstly enters the anaerobic baffle plate reactor and then enters the horizontal subsurface flow type constructed wetland coupling reactor; carrying out anaerobic hydrolysis to produce VFAs and gas production reaction; (2) starting a microbial electrolysis-constructed wetland coupling reactor; and (3) respectively introducing effluent and produced gas of the anaerobic baffled reactor into a microbial electrolysis-constructed wetland coupling reactor, integrally regulating and controlling the structure and activity of a microbial community, efficiently degrading VFAs into CO2 and CH4, and simultaneously removing nitrogen and phosphorus pollutants, thereby realizing the recycling of sewage treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of rural sewage treatment, and specifically relates to an anaerobic baffle-microbial electrolysis-constructed wetland coupling process for rural domestic sewage treatment. Background Art

[0002] Rural domestic sewage is widely distributed and has a large discharge volume, making it a key target for rural water environment improvement. Constructed wetlands are a treatment system that uses the synergistic effects of plants, soil, microorganisms, and substrates to remove pollutants in a controlled environment. They have the characteristics of low construction and operation costs and are widely used in rural sewage treatment. However, problems such as low pollutant load (hydraulic load, organic load, etc.), easy clogging, and the need to improve treatment efficiency have become the main factors restricting the application of constructed wetland projects.

[0003] In order to improve the siltation and blockage of artificial wetlands, increase the treatment load, and improve the effluent quality, it is necessary to carry out reasonable process combination and transformation. As an anaerobic bioreactor, anaerobic baffles have the effects of uniform water quality, regulating water volume, and improving the biodegradability of subsequent treatment. In addition, the microbial electrolysis cell technology has the characteristics of being able to utilize a variety of inorganic / organic substrates and high activity of power-producing microorganisms. Based on ecological principles, bioaugmentation measures can be adopted to improve the stability of the microbial community structure and the diversity of functional bacteria in the artificial wetland system. Therefore, the present invention proposes an anaerobic baffle-microbial electrolysis-artificial wetland coupling process for rural domestic sewage treatment: the influent is first treated by an anaerobic baffle reactor to generate a large amount of VFAs and biogas, and then the anaerobic reactor effluent and gas production are respectively introduced into a multi-stage multi-stage microbial electrolysis-artificial wetland coupling system, so as to achieve the synergistic improvement of the power-producing microbial flora in the treatment effect, as well as the regulation of biofilm thickness, the improvement of matrix blockage, the reduction of mass transfer resistance, etc., and finally enhance the overall treatment efficiency of the coupling system. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the engineering application defects of artificial wetlands in treating rural sewage, an anaerobic baffle-microbial electrolysis-artificial wetland coupling process and its application method are proposed to solve its shortcomings in anti-siltation and treatment of high organic load influent.

[0005] In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is:

[0006] An anaerobic baffle-microbial electrolysis-constructed wetland coupling process for rural domestic sewage treatment is designed, characterized in that rural domestic sewage flows from a sewage collection tank (1) into an anaerobic baffle reactor (3) through an inlet pipe, an anaerobic reactor inlet pump (2) is arranged on the inlet pipe, and the effluent from the sewage collection tank (1) is pumped into the anaerobic reactor (3) through the anaerobic reactor inlet (11). The effluent from the anaerobic reactor (3) is pumped into a horizontal subsurface flow artificial wetland (6) through an artificial wetland inlet pump (4), and the artificial wetland (6) is divided into a water distribution area (5), a main reaction area (7) and an outlet area (8), and the outlet pump (9) pumps the outlet water from the outlet area (8) into an outlet tank (10). The anaerobic baffle reactor (3) is composed of four cells (15) connected in series, and each cell is provided with an exhaust pipe (26) at the top. The partition (14) is used to separate the cells, and a reflector (13) is arranged under the partition (14). Water can flow through the folding plate (16) in sequence, and a guide plate (12) is provided at the end of the folding plate (16). The return sludge is returned to the sludge inlet (25) through the pipeline from the sludge outlet (23) under the action of the return sludge pump (24). The main reaction area (7) of the horizontal submerged flow artificial wetland (6) is composed of a plant layer (18), a soil layer (19), a filler layer (20), a gravel layer (21), and a compacted base layer (22). Six pairs of electrodes (34) are respectively inserted into the wetland filler layer (20), each pair of electrodes is respectively connected to the positive and negative electrodes of a constant voltage DC power supply (32), and an external resistor (33) is connected in series between each pair of electrodes and the constant voltage DC power supply (32). At the same time, the gas generated by the anaerobic reactor (3) is collected by the exhaust pipe (26) under the action of the vacuum pump (27), and then passes through a buffer tank (28) and a diffusion pipe (29) in sequence, and is introduced into the main reaction area (7) of the horizontal submerged flow artificial wetland (6). The diffusion pipe (29) is arranged in the gravel layer (21). The diffusion pipe (30) and the pressure monitoring meter (31) are used to monitor and discharge the high-pressure gas in the diffusion pipe.

[0007] Preferably, for the structural design of the anaerobic baffle reactor, a three-phase separator is provided in front of each exhaust pipe and water outlet to ensure the three-phase separation effect of gas, liquid and solid sludge, to ensure that a high sludge concentration is maintained in each cell of the anaerobic reactor, and the gas produced by the anaerobic biochemical reaction in each cell is discharged from the reactor in time, avoiding the interference of the front-stage gas products with the rear-stage biochemical reaction, and ensuring the efficient production of VFAs by the anaerobic reaction. The guide plate and the reflector are perpendicular to each other. The cell width of the upflow zone is greater than the cell width of the downflow zone, thereby slowing down the rising flow rate of the upflow zone, which is conducive to the sedimentation and interception of sludge in the reaction zone. The spacing between the partitions gradually decreases along the direction of the water flow. The drainage effect of the guide plate and the reflector can promote the water flow to the central area of ​​the upflow zone, reduce the impact strength of the water flow when entering the cell, and play a role in uniform water distribution, buffering water flow, and increasing the sludge concentration of the reactor. For the structural design of artificial wetlands, reeds, cannas, calamus, etc. are selected as plants to provide organic matter and oxygen for the growth of microorganisms (including electrochemically active bacteria) through rhizosphere effect. 8-16mm ceramsite filter material is selected, which has high biofilm efficiency, small head loss, and strong pollution interception ability. For the structural design of the coupling system of microbial electrolysis and artificial wetlands, 6 pairs of electrodes are selected, the electrode material is carbon rod, and the cathode surface is coated with Pt catalyst.

[0008] According to the process flow described in claim 1, it is characterized in that the microbial electrolysis-constructed wetland coupling system adopts a multi-stage and multi-level design. The artificial wetland is divided into two sections, front and back. Two pairs of electrodes are inserted in the front section, and four pairs of electrodes are inserted in the back section. The number of electrodes in the back section is twice the number of the front section, so that the current density of the electrodes in the back section is larger and the internal resistance is smaller, which can enhance the synergistic degradation and specific degradation activity of the electrogenic bacteria. Moreover, the electrodes are not energized continuously, and an alternating working mode of power on / off is adopted to ensure the treatment effect while effectively reducing the operating energy consumption. The gas produced by the anaerobic reactor (the main components are CH4 and CO2) is input into the artificial wetland through a vacuum pump, and the gas is used to regulate the structure and activity of the wetland microbial community.

[0009] The above-mentioned anaerobic baffle-microbial electrolysis-constructed wetland coupling process for treating rural domestic sewage is characterized in that the process comprises the following steps:

[0010] (1) The influent passes through the anaerobic baffled reactor, where anaerobic hydrolysis occurs to produce VFAs and gas: the water temperature in the anaerobic baffled reactor is controlled at 35±2℃, the stirring rate is 80±20rpm / min, and the hydraulic retention time (HRT) of the anaerobic baffled reactor is 12h. Anaerobic sludge needs to be inoculated before the anaerobic reactor is started. The anaerobic reactor adopts a continuous flow operation mode. The vacuum pump pumps the exhaust pipe to a negative pressure at a constant rate to facilitate the smooth discharge of gases from each cell of the anaerobic reactor; (2) The microbial electrolysis and artificial wetland coupling system is started: First, the positive electrode (electrode type is carbon rod) of the microbial fuel cell or microbial electrolysis cell that has been running stably for more than one month is inserted into the artificial wetland, and a carbon rod with a Pt catalyst coated on the surface is used as the cathode, which is inserted into the artificial wetland together. Two pairs of electrodes are inserted in the front section of the wetland, and four pairs of electrodes are inserted in the back section of the wetland. Each pair of electrodes, a constant voltage DC power supply and an external resistor (10-20Ω) connected in series form a 1-stage microbial electrolysis cell system, and 6 pairs of electrodes constitute a 6-stage microbial electrolysis cell system. Next, the current change of the external resistor series circuit of each microbial electrolytic cell system is recorded. When the current of the electrolytic cell system of this level reaches a peak value and shows a downward trend, the wetland water is replaced. When the current peak values ​​generated after three consecutive water inflows are not much different, it can be considered that the surface of the anode electrode has been enriched with biofilm, and the system of this level is started; (3) The effluent and gas produced by the anaerobic reactor are respectively input into the microbial electrolysis and artificial wetland coupling system to integrate and regulate the structure and activity of the microbial community: each microbial electrolytic cell system is connected to an external constant voltage DC power supply with a voltage of 0.4-0.8V, a series external resistor of 10-20Ω, an HRT of 48h, and a power-on mode of 2h on / 0.5h off. A pressure relief valve is set on the gas diffusion pipe in the wetland. When the pressure threshold is exceeded, the dissipation pipe is opened (discharged into the atmosphere).

[0011] Preferably, the biogas (mainly CH4 and CO2) produced by the anaerobic baffle reactor is diffused into the wetland through the gas diffusion tube, which has the following effects: (1) It provides inorganic carbon sources and hydrogen as electron donors for specific functional microorganisms (such as autotrophic denitrifying bacteria), thereby improving the denitrification performance of the coupled system; (2) It utilizes the vibration, shearing, friction and other effects of the rising airflow and bubbles on the biofilm attached to the solid surface to enhance the water vapor scouring intensity, regulate the biofilm thickness on the solid surface of the matrix, soil, electrode, etc., and alleviate the matrix clogging phenomenon; (3) It reduces the mass transfer resistance of the coupled system, improves the supply of nutrients such as oxygen, the release of biochemical reaction products such as CO2, and the utilization of H2 produced near the cathode.

[0012] Regarding gas collection and pipeline pressure safety measures, for the biogas produced by the anaerobic reactor, the gas is first pumped into a buffer tank filled with clean water through a vacuum pump, and then diffused to the wetland through a diffusion pipe. The gas flow rate in the diffusion pipe is: 8m / s (wetland startup), 5m / s (wetland normal operation). Use a dissipation pipe and a pressure test gauge to monitor the pressure in the pipe to be lower than the threshold of 0.5Mpa to ensure pressure safety.

[0013] The main beneficial effects of the present invention are as follows:

[0014] 1) Propose a sewage treatment process based on the coupling of multiple reaction principles to achieve the technology of comprehensive utilization of VFAs: Generally, the carbon source type that can be directly utilized by methanogens in anaerobic digestion systems is acetic acid. In addition to acetic acid that can be directly utilized by methanogens, sewage or sludge also contains a large amount of multi-carbon volatile organic fatty acids (VFAs). These multi-carbon volatile organic fatty acids cannot be directly utilized by methanogens. They need to be hydrolyzed and fermented to produce acetic acid during the anaerobic digestion process before they can be utilized by methanogens. Therefore, the anaerobic digestion process is relatively complicated, and the untimely utilization of acids causes the low gas production rate of biogas. Therefore, there are metabolic barriers in traditional anaerobic digestion or anaerobic fermentation, that is, substrates mainly composed of small molecular organic matter (VFAs) cannot be fully utilized. On the other hand, sewage containing organic pollutants can produce a large amount of VFAs through anaerobic or aerobic fermentation processes, and these VFAs have high economic value. Traditional VFAs utilization technology mainly produces methane, alcohol, degradable plastics and other substances through anaerobic digestion or biosynthesis. As an emerging bioelectrochemical technology, the principle of microbial electrolysis cell is to use electrogenic microorganisms to degrade organic matter and generate hydrogen or methane. The types of substrates that can be used in microbial electrolysis cells are very rich, including small molecular organic acids such as acetic acid, propionic acid, and butyric acid. Since VFAs can accumulate rapidly in the fermentation broth through anaerobic reactions, and at the same time, VFAs can be used as an effective carbon source donor for microbial electrolysis reactions, it solves the organic substrate metabolic barriers of traditional anaerobic digestion / fermentation. Therefore, based on the feasibility of microbial electrolysis of VFAs, a product of anaerobic fermentation of sewage, a new anaerobic reaction-microbial electrolysis-constructed wetland coupling technology with VFAs as the medium is proposed to enhance the comprehensive utilization of VFAs, which not only increases the directional production of VFAs, but also improves the organic matter degradation rate of microbial electrolysis-constructed wetlands, so that the three form an enhanced technical system that can fully utilize VFAs through the cascade utilization design of organic matter.

[0015] In view of anaerobic reactions, the present invention proposes a new type of baffle reactor. In the four compartments of the reactor, the microbial community in each compartment shows a good population distribution, and each compartment is domesticated and cultivated with a microbial community that is adapted to the sewage quality and environmental conditions of the compartment. In order to promote the separation of anaerobic acid production phase reaction and methanogenic phase reaction along the process, the spacing between the partitions is gradually reduced along the water flow direction, and the anaerobic fermentation process is controlled in the fermentation acid production stage by shortening the HRT, that is, the baffle reactor is dominated by hydrolytic acid-producing bacteria, the growth of methanogenic bacteria is inhibited, and the maximum cumulative concentration of VFAs is obtained by using the organic matter in the influent. At the same time, in order to avoid excessive acidification of the first compartment affecting the stable operation of the system, a sludge return system is added, which can not only increase the pH value of the compartment, inhibit the growth of filamentous bacteria, dilute toxic and harmful substances in the influent, but also maintain a higher sludge concentration in the compartment. The above technical effects can effectively promote the production of VFAs in the system. It should be pointed out that the sludge return system uses a return sludge pump to directly return to the sludge inlet of the anaerobic reactor through a pipeline, instead of the traditional method of first returning to the sludge storage tank and then returning from the storage tank to the sludge inlet. The traditional method will cause the sludge in the intermediate sludge tank to produce methane and other reactions, destroying the microbial community structure of the baffle reactor. Therefore, the direct sludge return method is also considered from the perspective of increasing the VFAs production of the system.

[0016] The novel baffle reactor adopted by the present invention, in order to avoid the adverse effect of the partial pressure of gas in the system on the VFAs production of the system, is provided with a three-phase separator and an independent exhaust pipe at the top of each cell (before each exhaust pipe and water outlet), and the biogas (CH4, CO2 and other gases) produced by the anaerobic reaction is promptly removed, so that the intermediate metabolites in different cells can carry out independent extracellular organic matter hydrolysis reaction and VFAs production reaction of the hydrolyzate under different gas partial pressure conditions, and ensure the different stages of the acid production reaction. In addition, by reasonably setting the partition spacing, the width of the upflow zone is made greater than the downflow zone, slowing down the rising flow rate of the upflow zone, which is conducive to the sedimentation and interception of the sludge in the reactor in the main reaction zone. A guide plate is provided at the end of the baffle, which can make the water flow to the central area of ​​the upflow zone, and avoid the impact when the water flow enters the chamber, which plays a role in uniform water distribution, buffering water flow, and increasing the sludge concentration of the reactor, thereby facilitating the growth of fermentation acid-producing bacteria and increasing the VFAs production of the system.

[0017] Anaerobic fermentation acid production is generally divided into three stages: the first stage is the hydrolysis of complex organic matter, such as sugars, fats and proteins, into simple soluble monomers or dimers; the second stage is the acid-producing fermentation bacteria converting the simple organic matter produced in the hydrolysis stage into VFAs and alcohols, such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid and ethanol; the third stage is the hydrogen-producing acetic acid-producing bacteria converting the organic acids and alcohols containing more than two carbon atoms produced in the fermentation acid production stage, except for acetic acid, into acetic acid, hydrogen and CO2. The present invention adopts a baffle reactor, and targets anaerobic microbial communities, and regulates the hydrolysis of extracellular polymers and the intracellular NADH / NAD through reactor design and reaction condition control. + level, and the anaerobic fermentation process is controlled in the second stage (fermentation acid production stage), thereby achieving strict control of the fermentation products, that is, using rural domestic sewage to obtain the maximum cumulative concentration of VFAs. In addition, since the concentration ratio of various substances in the fermentation broth VFAs can stimulate the extracellular electron transfer activity of electrogenic bacteria and affect the microbial community structure in the subsequent microbial electrolysis reaction system, the appropriate anaerobic reactor type (i.e., baffle) is selected by comparing the water quality of the effluent (i.e., fermentation broth) of different anaerobic reactors, and the baffle reactor structure is improved to make the concentration ratio of various substances in the effluent VFAs of the baffle reactor suitable for the microbial community in the microbial electrolysis-constructed wetland coupling system, that is, it is easier to establish an "electrical environment mutual trophic" relationship between the conductive bacteria and acidogenic bacteria, methanogens, etc. in the coupling system. This method of constructing a microbial community based on VFAs as a substrate is more suitable for the microbial electrolysis reaction system than the traditional microbial community structure established based on acetic acid as a substrate. Therefore, the economic benefits of degrading VFAs using the microbial electrolysis-constructed wetland coupling system are more prominent.

[0018] The formation of the above-mentioned "electrical-environmental mutualism" relationship is not only related to the concentration ratio of various substances in the influent VFAs, but also related to the introduction of the microbial electrolysis system and the introduction of anaerobic gas production into the wetland. Since the microbial electrolysis system is introduced into the artificial wetland, it is beneficial to promote the activity of the wetland microbial population by providing additional electrons. Since CH4 and CO2 are introduced into the wetland, the thickness of the biofilm on the surface of the matrix and the electrode in the coupling system is regulated by providing inorganic carbon sources, electron donors, water vapor scouring, and reducing the mass transfer resistance at the gas-liquid-solid interface, thereby alleviating the blockage of the matrix. By establishing a microbial community with an "electrical-environmental mutualism" relationship, the coupling system shows a good treatment effect, effectively solving the technical problems of artificial wetland systems in terms of siltation blockage, high load, and removal of difficult-to-degrade organic matter.

[0019] 2) Improve the economy of the process in engineering application scenarios: The anaerobic baffle reactor has a simple structure, no moving parts, and low construction and operating costs. The microbial electrolysis cell uses relatively low-priced electrode materials. The multi-stage and multi-stage design features not only save energy consumption by using the intermittent operation mode of alternating power on / off of multiple electrodes on the basis of ensuring stable purification efficiency, but also the intermittent power-on operation mode can effectively slow down the deposition of anode salt crystals and ensure the effective biological activity of the anode biofilm. Overall, the coupling system embodies good cost control characteristics and has promotion potential in the field of rural sewage treatment.

[0020] 3) Multi-stage and multi-level design ideas and details: For the microbial electrolysis-constructed wetland coupling system, a multi-stage and multi-level electrode layout is adopted. This is designed based on the characteristics of wetland organic matter degradation, that is, the degradation of organic matter in sewage mainly occurs in the first half of the wetland. Therefore, in the sewage in the second half of the wetland, the pollutants mainly exist in the form of difficult-to-degrade organic matter. In view of the above-mentioned organic matter characteristics, the electrode layout is improved from asymmetric to approximately symmetrical by increasing the number of electrodes in the second half of the wetland (the number of electrodes in the second half is twice that in the first half). Under the symmetrical layout conditions, electrons in the system can be transferred to the cathode from multiple directions, and the electron transfer efficiency is high, which increases the current density of the bioelectrocatalytic reaction. At the same time, the dense number of electrodes can reduce the internal resistance of the system, stimulate plant growth and development, expand the anoxic environment space represented by the area near the cathode, and give full play to the biochemical synergistic effect of the microbial population in the "electrical environment mutual trophy" relationship of the coupling system, thereby improving the treatment effect of difficult-to-degrade organic matter.

[0021] 4) Anaerobic gas production regulates the biofilm thickness of the microbial electrolysis-constructed wetland coupling system: The biogas (mainly composed of CH4 and CO2) produced by the anaerobic baffled reactor is diffused into the wetland through the gas diffusion tubes arranged in the wetland, producing the following effects: (1) It provides inorganic carbon sources and hydrogen (the cathode of the microbial electrolysis system produces hydrogen, methane and other gases) as electron donors for specific functional microorganisms (such as autotrophic denitrifying bacteria, etc.), without the need to add additional organic carbon sources, thereby improving the denitrification performance of the wetland system under low carbon source inflow conditions; (2) It utilizes the rising airflow and The bubbles produce vibration, shear, friction and other effects on the biofilm attached to the solid surface of the matrix, soil, electrode, etc. The disturbance effect on the matrix layer gradually increases during the rising process of the bubbles, which enhances the water vapor scouring intensity, regulates the thickness of the biofilm on the solid surface of the matrix, soil, electrode, etc., avoids excessive thickness, and alleviates the matrix clogging phenomenon; (3) Reduce the mass transfer resistance of the coupling system: There are different mass transfer resistances such as gas-liquid, gas-solid, solid-liquid in the microbial electrolysis-constructed wetland coupling reaction system, which differ greatly between different interfaces, forming a differentiated gas phase concentration gradient, which affects the growth and metabolism of functional microorganisms. There is a discontinuous gas, liquid, and solid coexistence system on the surface of the filler, electrode and soil in the coupling system. The hydraulic state of the horizontal flow of sewage in the system has limited improvement on the mass transfer resistance of the three-phase interface. The present invention proposes an anaerobic reactor gas production introduction coupling system. Due to the diffusion and disturbance of the introduced gas, the concentration gradient, which is the only diffusion driving force, is improved, which effectively reduces the mass transfer resistance of the three-phase interface, improves the supply of nutrients such as oxygen, the release of biochemical reaction products such as CO2, and the utilization of H2 produced near the cathode. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the anaerobic baffle-microbial electrolysis-constructed wetland coupling process structure of the present invention.

[0023] Figure symbols: 1-sewage collection tank, 2-anaerobic reactor inlet pump, 3-anaerobic baffle reactor, 4-artificial wetland inlet pump, 5-water distribution area, 6-horizontal submerged artificial wetland, 7-main reaction area, 8-water outlet area, 9-artificial wetland outlet pump, 10-water outlet tank, 11-anaerobic reactor inlet, 12-guide plate, 13-reflection plate, 14-partition, 15-cell, 16-folding plate, 17-anaerobic reactor outlet, 18-plant layer, 19-soil layer, 20-filling layer, 21-gravel layer, 22-compacted base, 23-sludge outlet, 24-return sludge pump, 25-sludge inlet, 26-exhaust pipe, 27-vacuum pump, 28-buffer tank, 29-diffusion pipe, 30-dissipation pipe, 31-pressure monitoring meter DETAILED DESCRIPTION

[0024] The technical solution of the present invention is clearly and completely described below in conjunction with specific embodiments.

[0025] Embodiment 1:

[0026] Anaerobic baffle-microbial electrolysis-constructed wetland coupling process structure Figure 1 As shown, it mainly includes: sewage flows from a sewage collection tank (1) into an anaerobic baffle reactor (3) through an inlet pipe, an anaerobic reactor inlet pump (2) is arranged on the inlet pipe, and the effluent of the sewage collection tank (1) is pumped into the anaerobic reactor (3) through the anaerobic reactor inlet (11). The effluent of the anaerobic reactor (3) is pumped into a horizontal subsurface artificial wetland (6) through an artificial wetland inlet pump (4), and the artificial wetland (6) is divided into a water distribution area (5), a main reaction area (7) and an outlet area (8), and the outlet pump (9) pumps the outlet of the outlet area (8) into an outlet tank (10). The anaerobic baffle reactor (3) is composed of four cells (15) connected in series, and each cell is provided with an exhaust pipe (26) at the top. The partition (14) is used to separate the cells, and a reflector (13) is arranged under the partition (14). Water can flow through the folding plate (16) in sequence, and a guide plate (12) is provided at the end of the folding plate (16). The return sludge is returned to the sludge inlet (25) through the pipeline from the sludge outlet (23) under the action of the return sludge pump (24). The main reaction area (7) of the horizontal submerged flow artificial wetland (6) is composed of a plant layer (18), a soil layer (19), a filler layer (20), a gravel layer (21), and a compacted base layer (22). Six pairs of electrodes (34) are respectively inserted into the wetland filler layer (20), each pair of electrodes is respectively connected to the positive and negative electrodes of a constant voltage DC power supply (32), and an external resistor (33) is connected in series between each pair of electrodes and the constant voltage DC power supply (32). At the same time, the gas generated by the anaerobic reactor (3) is collected by the exhaust pipe (26) under the action of the vacuum pump (27), and then passes through a buffer tank (28) and a diffusion pipe (29) in sequence, and is introduced into the main reaction area (7) of the horizontal submerged flow artificial wetland (6). The diffusion pipe (29) is arranged in the gravel layer (21). The diffusion pipe (30) and the pressure monitoring meter (31) are used to monitor and discharge the high-pressure gas in the diffusion pipe.

[0027] Embodiment 2:

[0028] The above-mentioned anaerobic baffle-microbial electrolysis-constructed wetland coupling process is used to treat rural domestic sewage: the COD concentration of a rural domestic sewage is 158.24 mg / L, the total nitrogen concentration is 33.84 mg / L, and the total phosphorus concentration is 0.475 mg / L. The anaerobic baffle-microbial electrolysis-constructed wetland coupling process is used for treatment, and the specific steps are as follows:

[0029] Step 1: The influent passes through the anaerobic baffled reactor, where anaerobic hydrolysis occurs to produce VFAs and gas: the water temperature in the anaerobic baffled reactor is controlled to be 35±2°C, the stirring rate is 80±20rpm / min, and the hydraulic retention time (HRT) of the anaerobic baffled reactor is 12h. Anaerobic sludge needs to be inoculated before the anaerobic reactor is started. The anaerobic reactor adopts a continuous flow operation mode. The vacuum pump draws the exhaust pipe to negative pressure at a constant rate to facilitate the smooth discharge of gas from each cell of the anaerobic reactor.

[0030] Step 2: Start the coupling system of microbial electrolysis and artificial wetland: First, insert the positive electrode (electrode type is carbon rod) of the microbial fuel cell or microbial electrolysis cell that has been running stably for more than one month into the artificial wetland, and insert the carbon rod with Pt catalyst coated on the surface as the cathode into the artificial wetland together. Insert 2 pairs of electrodes in the front section of the wetland and 4 pairs of electrodes in the back section of the wetland. Each pair of electrodes and a constant voltage DC power supply and an external resistor (10-20Ω) in series form a 1-level microbial electrolysis cell system, and 6 pairs of electrodes constitute a 6-level microbial electrolysis cell system. Then, record the current change of the external resistor series circuit of each level of the microbial electrolysis cell system. When the current of the electrolysis cell system at this level reaches a peak value and shows a downward trend, replace the wetland water inlet. When the current peak value generated after three consecutive water inflows is not much different, it can be considered that the surface of the anode electrode has been enriched with biofilm, and the startup of this level of system is complete.

[0031] Step three, the effluent and gas produced by the anaerobic reactor are respectively input into the microbial electrolysis and artificial wetland coupling system to integrate and regulate the structure and activity of the microbial community: each stage of the microbial electrolysis cell system is connected to an external constant voltage DC power supply with a voltage of 0.4-0.8V, an external resistance in series of 10-20Ω, an HRT of 48h, and a power-on mode of 2h on / 0.5h off. A pressure relief valve is set on the gas diffusion pipe in the wetland, and the dissipation pipe is opened (discharged into the atmosphere) when the pressure threshold is exceeded.

[0032] After the process system has been running stably for 30 days, the effluent quality is tested. Considering that the artificial wetland system is composed of complex microbial communities and has strong ecological characteristics, the sampling time is set at 8:00, 15:00, and 19:00 on the same day, and each sampling is carried out at an interval of 7 days. The results of 15 samples obtained on 5 sampling days were analyzed for components, and the average COD concentration of the samples was 14.4 mg / L, the removal rate was 0.909, the total nitrogen concentration was 6.7 mg / L, the removal rate was 0.802, and the total phosphorus concentration was 0.14 mg / L, and the removal rate was 0.705. The test results show that the anaerobic baffle-microbial electrolysis-artificial wetland coupling process has the full-time organic matter removal and nitrogen and phosphorus removal efficiency, and the anti-siltation ability is significantly improved, and it has the potential to be applied to rural sewage treatment.

[0033] The pressure threshold of the wetland gas diffusion tube was set at 0.5 MPa. According to the pressure monitoring indication, the coupling process did not exceed the limit during the actual operation cycle, meeting the safety standards of actual sewage treatment application scenarios.

[0034] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An anaerobic baffle-microbial electrolysis-constructed wetland coupling process for rural domestic sewage treatment, characterized in that: Rural domestic sewage flows from a sewage collection tank (1) into an anaerobic baffled reactor (3) through an inlet pipe. An anaerobic reactor inlet pump (2) is arranged on the inlet pipe to pump the effluent from the sewage collection tank (1) into the anaerobic reactor (3) through an anaerobic reactor inlet (11). The effluent from the anaerobic reactor (3) is pumped into a horizontal subsurface artificial wetland (6) by an artificial wetland inlet pump (4). The artificial wetland (6) is divided into a water distribution area (5), a main reaction area (7) and an outlet area (8). The outlet pump (9) pumps the outlet water from the outlet area (8) into an outlet tank (10). The anaerobic baffled reactor (3) is composed of four cells (15) connected in series, and each cell is provided with an exhaust pipe (26) at the top. A partition (14) is used to separate the cells, and a reflector (13) is arranged under the partition (14). Water can flow through the folding plate (16) in sequence, and a guide plate (12) is provided at the end of the folding plate (16). The return sludge flows back to the sludge inlet (25) through the pipeline from the sludge outlet (23) under the action of the return sludge pump (24). The main reaction area (7) of the horizontal submerged flow artificial wetland (6) is composed of a plant layer (18), a soil layer (19), a filler layer (20), a gravel layer (21), and a compacted base layer (22). Six pairs of electrodes (34) are respectively inserted into the wetland filling layer (20), each pair of electrodes is respectively connected to the positive and negative electrodes of a constant voltage DC power supply (32), and an external resistor (33) is connected in series between each pair of electrodes and the constant voltage DC power supply (32). At the same time, the gas generated by the anaerobic reactor (3) is collected by the exhaust pipe (26) under the action of the vacuum pump (27), and then passes through the buffer tank (28) and the diffusion pipe (29) in sequence, and is introduced into the main reaction area (7) of the horizontal submerged flow artificial wetland (6). The diffusion pipe (29) is arranged in the gravel layer (21). The dissipation pipe (30) and the pressure monitoring meter (31) are used to monitor and remove the high-pressure gas in the diffusion pipe.

2. The process according to claim 1, characterized in that: Three-phase separation can be achieved before each exhaust pipe (26) and water outlet (17) of the anaerobic baffle reactor (3). The guide plate (12) and the reflector (13) are perpendicular to each other; because the water flows through the cells (15) in sequence, the water flow in each cell (15) rises or falls, and the width of the cell (15) in the upflow area is greater than the width of the cell (15) in the downflow area, thereby slowing down the rising flow rate in the upflow area, which is conducive to the sedimentation and retention of sludge in the reaction area; the spacing of the partitions (14) gradually decreases along the direction of the water flow. The drainage effect of the guide plate (12) and the reflector (13) can promote the water flow to the central area of ​​the upflow area, reduce the impact strength of the water flow when entering the cell (15), and play a role in uniform water distribution, buffering water flow, and increasing the sludge concentration of the reactor.

3. The process according to claim 1, characterized in that: The horizontal subsurface flow artificial wetland (6) uses reeds, cannas, calamus and other plants to provide organic matter and oxygen for the growth of microorganisms (including electrochemically active bacteria) through the rhizosphere effect. The artificial wetland (6) uses 8-16mm ceramsite filter material, which has high biofilm efficiency, low head loss and strong sewage interception capacity.

4. The process according to claim 1, characterized in that: The materials of the six pairs of electrodes (34) are carbon rods, wherein the cathode surface is coated with platinum (Pt) catalyst.

5. The process according to claim 1, characterized in that: The microbial electrolysis-constructed wetland coupling system adopts a multi-stage and multi-level design. The artificial wetland (6) is divided into two sections. Two pairs of electrodes are inserted in the front section and four pairs of electrodes are inserted in the rear section. The number of electrodes in the rear section is twice that of the front section, so that the current density of the rear section electrode is larger and the internal resistance is smaller, which can enhance the synergistic degradation and specific degradation activity of the electrochemical microbial population. Furthermore, the electrodes are not energized continuously, and an alternating working mode of power on / off is adopted to ensure the treatment effect while effectively reducing the operating energy consumption. The gas (mainly composed of CH4 and CO2) produced by the anaerobic reactor (3) is input into the artificial wetland (6) through the vacuum pump (27), and the gas is used to regulate the structure and activity of the wetland microbial community.

6. A method for treating rural domestic sewage using the anaerobic baffle-microbial electrolysis-constructed wetland coupling process described in claims 1-5, characterized in that , the method comprises the following steps: (1) The influent passes through the anaerobic baffled reactor, where anaerobic hydrolysis occurs to produce VFAs and gas; (2) Start-up of the microbial electrolysis and artificial wetland coupling system; (3) The effluent and gas produced by the anaerobic reactor are respectively input into the microbial electrolysis and artificial wetland coupling system to integrate and regulate the structure and activity of the microbial community.

7. The method according to claim 6, characterized in that The specific operation steps of the method are as follows: (1) The influent passes through the anaerobic baffled reactor, where anaerobic hydrolysis occurs to produce VFAs and gas: the water temperature in the anaerobic baffled reactor is controlled at 35±2°C, the stirring rate is 80±20rpm / min, and the hydraulic retention time (HRT) of the anaerobic baffled reactor is 12h. Anaerobic sludge must be inoculated before the anaerobic reactor is started. The anaerobic reactor adopts a continuous flow operation mode. The vacuum pump draws the exhaust pipe to a negative pressure at a constant rate to facilitate the smooth discharge of gas from each cell of the anaerobic reactor; (2) Startup of the microbial electrolysis and artificial wetland coupling system: First, the positive electrode (electrode type is carbon rod) of a microbial fuel cell or microbial electrolytic cell that has been running stably for more than one month is inserted into the artificial wetland. A carbon rod coated with a Pt catalyst is used as the cathode and inserted into the artificial wetland together. Two pairs of electrodes are inserted in the front section of the wetland, and four pairs of electrodes are inserted in the back section of the wetland. Each pair of electrodes and a constant voltage DC power supply and an external resistor (10-20Ω) in series form a 1-level microbial electrolytic cell system. Six pairs of electrodes constitute a 6-level microbial electrolytic cell system. Next, record the current changes of the external resistor series circuit of each level of the microbial electrolytic cell system. When the current of the electrolytic cell system at this level reaches a peak value and shows a downward trend, replace the wetland water inlet. When the current peaks generated after three consecutive water inflows are not much different, it can be considered that the surface of the anode electrode has been enriched with biofilm, and the startup of this level of the system is complete; (3) The effluent and gas produced by the anaerobic reactor are respectively input into the microbial electrolysis and artificial wetland coupling system to integrate and regulate the structure and activity of the microbial community: each stage of the microbial electrolysis cell system is connected to an external DC power supply with a voltage of 0.4-0.8V, an external series resistance of 10-20Ω, an HRT of 48h, and a power-on mode of 2h / 0.5h. A pressure relief valve is installed on the gas diffusion pipe in the wetland. When the pressure threshold is exceeded, the dissipation pipe is opened (discharged into the atmosphere).

8. The process according to claim 7, characterized in that: The biogas (mainly CH4 and CO2) produced by the anaerobic baffled reactor is diffused into the wetland through the gas diffusion tube, which has the following effects: (1) It provides inorganic carbon sources and hydrogen as electron donors for specific functional microorganisms (such as autotrophic denitrifying bacteria), thereby improving the denitrification performance of the coupled system; (2) It utilizes the vibration, shearing, and friction effects of rising airflow and bubbles on the biofilm attached to the solid surface to enhance the water vapor scouring intensity, regulate the biofilm thickness on the solid surface of the matrix, soil, electrode, etc., and alleviate the matrix clogging phenomenon; (3) The mass transfer resistance of the coupled system is reduced, which improves the supply of nutrients such as oxygen, the release of biochemical reaction products such as CO2, and the utilization of H2 produced near the cathode.

9. The process according to claim 7, characterized in that: The biogas generated by the anaerobic reactor in step (1) is first pumped into a buffer tank filled with clean water by a vacuum pump, and then diffused to the wetland through a diffusion pipe. The gas flow rate in the diffusion pipe is: 8m / s (wetland startup), 5m / s (wetland normal operation). The gas pressure in the diffusion pipe is monitored by a dissipation pipe and a pressure detection gauge to be lower than the threshold of 0.5Mpa to ensure the safety of the gas pressure.

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