Method for synchronously repairing water body through emergent aquatic plant-sediment microbial fuel cell

Abstract

The invention relates to the technical field of environmental governance, and discloses an emergent aquatic plant-sediment microbial fuel cell water body synchronous restoration method, which comprises the following steps: S1, constructing an emergent aquatic plant-SMFC coupling system, the emergent aquatic plant-SMFC coupling system comprises an emergent aquatic plant and an SMFC, and the SMFC comprises an anode electrode, a modified cathode electrode and an external resistor; emergent aquatic plants are planted around the anode electrode, so that the anode electrode is in contact with the bottom mud; s2, preparing a modified cathode electrode, and performing electrochemical oxidation modification on the cathode electrode to enhance the catalytic activity of the cathode electrode; s3, domesticating electroactive microorganisms: domesticating the emergent aquatic plant-SMFC coupling system at room temperature, and improving the electricity generation capacity of an anode electrode by introducing bottom mud rich in organic matters or exogenous inoculated microorganisms; and S4, starting and operating the system, and monitoring the concentration changes of chlorophyll a, ammonia nitrogen, total nitrogen and total phosphorus in the water body in real time. The invention provides a green, economic and efficient water bloom water body remediation technology which is suitable for ecological management of water bloom water bodies.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental governance, and particularly relates to a method for synchronously repairing water bodies by emergent plants - sediment microbial fuel cells. Background Art

[0002] A large amount of nitrogen and phosphorus nutrients are discharged into water bodies through agricultural runoff, industrial emissions and domestic sewage, resulting in an increase in the concentration of nutrients in the water bodies, thereby triggering frequent algal blooms in slow-flowing water bodies such as lakes, estuaries and bays. Algal bloom events not only damage the aquatic ecosystem, but also pose a threat to human health. Therefore, it is urgent to develop efficient and sustainable treatment technologies to reduce the negative impacts of algal blooms on water pollution and the ecosystem.

[0003] Domestic and foreign research has developed a variety of physical, chemical and biological treatment methods for treating algal bloom water bodies. Among them, hydrogen peroxide in the chemical method can not only effectively remove algae, but also the decomposition products are water and oxygen, which is a green algaecide with great application prospects. However, in actual application, directly adding hydrogen peroxide to remove algae faces the following problems: (1) Since hydrogen peroxide decomposes rapidly in water, it needs to be added multiple times to maintain the algae removal effect, resulting in a relatively high treatment cost; (2) Since hydrogen peroxide is a strong oxidant, improper operation may cause damage to personnel and equipment during storage, transportation and use, posing a great safety hazard. To overcome the above problems, in-situ generation of hydrogen peroxide to remove algae has become an optional method. For example, Patent CN202111426956.4 discloses a full-automatic algae control device and method for photocatalytic production of hydrogen peroxide to control the excessive growth of algae when algal blooms occur. Different from photocatalysis, Patent CN202011420278.6 discloses a method for in-situ driving electro-Fenton degradation of red tide / algal bloom algae based on SMFC.

[0004] Although the hydrogen peroxide generated in-situ based on photocatalysis and SMFC can continuously and low-cost remove algae in algal bloom water bodies, there are still the following defects: (1) Low hydrogen peroxide generation efficiency: The photocatalytic method relies on sunlight and can only operate during the day, and is restricted by the light intensity and reactor efficiency; Although the SMFC method can operate all day long, its hydrogen peroxide generation efficiency is limited by the insufficient concentration of organic matter in the sediment and the low catalytic activity of the cathode electrode, resulting in limited algae removal efficiency. (2) Insufficient removal effect on nitrogen and phosphorus pollution: After removing algae, a large amount of nitrogen and phosphorus are released by the decomposition of dead algae. Existing photocatalysis and SMFC technologies have not effectively removed these nutrients, resulting in possible secondary pollution of the water body and even triggering a new round of algal bloom outbreaks. (3) Risk of nitrogen and phosphorus release in the sediment: The sediment in algal bloom water bodies usually stores high concentrations of nitrogen and phosphorus substances. Under environmental condition changes such as a decrease in dissolved oxygen, these nutrients may be released into the water body, exacerbating the hydration problem and increasing the difficulty of treatment. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, a method for synchronous remediation of water bodies using emergent plants - sediment microbial fuel cells provided by the present invention makes full use of the ecological role of emergent plants and the catalytic characteristics of electrochemically modified cathodes to achieve efficient water body remediation through multiple mechanisms.

[0006] In order to achieve the above object of the invention, the technical solution adopted by the present invention is: a method for synchronous remediation of water bodies using emergent plants - sediment microbial fuel cells, comprising the following steps:

[0007] S1, constructing an emergent plant - SMFC coupling system, the emergent plant - SMFC coupling system includes emergent plants and an SMFC, and the SMFC includes an anode electrode, a modified cathode electrode and an external resistor; plant the emergent plants around the anode electrode so that the anode electrode contacts the bottom mud;

[0008] S2, preparing the modified cathode electrode, and performing electrochemical oxidation modification on the cathode electrode to enhance its catalytic activity;

[0009] S3, domesticating electroactive microorganisms, placing the emergent plant - SMFC coupling system at room temperature for domestication, and improving the power generation capacity of the anode electrode by introducing bottom mud rich in organic matter or exogenous inoculation of microorganisms;

[0010] S4, starting and operating the system, and real - time monitoring the changes in the concentrations of chlorophyll a, ammonia nitrogen, total nitrogen and total phosphorus in the water body until the target treatment effect is achieved.

[0011] Further, in the above - mentioned method for synchronous remediation of water bodies using emergent plants - sediment microbial fuel cells, the anode electrode is a carbon felt, carbon rod, carbon cloth or carbon particle electrode, and the anode electrode is arranged in the bottom mud to promote the electron transfer of electroactive microorganisms.

[0012] Further, in the above - mentioned method for synchronous remediation of water bodies using emergent plants - sediment microbial fuel cells, the emergent plants include Cyperus alternifolius, Canna indica, Phragmites australis, Typha orientalis, Zizania latifolia, Scirpus validus, Acorus calamus or Sagittaria trifolia.

[0013] Further, in the above - mentioned method for synchronous remediation of water bodies using emergent plants - sediment microbial fuel cells, the cathode electrode is made of carbon felt, carbon rod or carbon cloth. The specific method for preparing the modified cathode electrode in S2 is: using an electrochemical workstation in the constant - current mode, setting the cathode electrode as the working electrode; using a carbon rod as the counter electrode, and the electrolyte is ammonium fluoride solution; performing oxidation treatment under constant - current conditions, then rinsing the cathode electrode with deionized water until neutral, and drying it at 55 °C for 10 hours to obtain the modified cathode electrode.

[0014] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, the parameters for oxidation treatment include: a constant current range of 1 - 1000 mA, an oxidation time of 1 - 60 minutes, and an ammonium fluoride solution concentration of 1 - 500 mM.

[0015] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, the modified cathode electrode is arranged at the water bloom water - air interface to enhance the utilization efficiency of oxygen and promote the generation of hydrogen peroxide.

[0016] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, the external resistor is connected in series with the anode electrode and the modified cathode electrode through a metal wire. The external resistor is located between the anode electrode and the cathode electrode; the metal wire is a platinum wire, a titanium wire, or a stainless steel wire; the resistance value range of the external resistor is 0 - 100000 Ω.

[0017] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, the specific process of domesticating electroactive microorganisms in S3 is as follows: slowly inject the effluent from the anode of the mature microbial fuel cell into the sediment where the anode electrode is located to promote the enhancement of microbial activity. When the anode output voltage increment is less than 5% for two consecutive cycles, it is regarded as the completion of domestication.

[0018] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, during the operation of the system in S4, regularly rinse the modified cathode electrode with deionized water to remove the precipitates on the electrode surface and improve the electrode performance and the system operation efficiency.

[0019] Furthermore, for the above method for synchronously repairing water bodies using emergent plants - sediment microbial fuel cells, during the operation of the system in S4, by real - time monitoring the concentration changes of chlorophyll a, ammonia nitrogen, total nitrogen, and total phosphorus in the water body, dynamically adjust the electrochemical parameters of the cathode electrode and the planting density of emergent plants according to the monitoring results.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) Efficiently remove and degrade water bloom algae. The electroactive microorganisms on the anode electrode of the SMFC simultaneously catalyze the decomposition of organic matter in the sediment of the water bloom water body and the organic matter secreted by the rhizosphere of emergent plants, generating a large number of electrons. The electrons reach the cathode via the metal wire and the external resistor, and are used to in - situ generate hydrogen peroxide, thereby efficiently removing algae. At the same time, the dead water bloom algae sink to the sediment, and the electroactive microorganisms can also utilize the organic matter decomposed from the water bloom algae to further promote the generation of hydrogen peroxide, realizing the continuous and efficient removal and degradation of water bloom algae.

[0022] (2) Efficiently remove the nitrogen and phosphorus nutrients released during the degradation of bloom algae, and avoid water quality deterioration and the recurrence of blooms. On the one hand, emergent plants directly absorb nitrogen and phosphorus elements in eutrophic water bodies through their growth; on the other hand, emergent plants form a microenvironment containing aerobic, facultative, and anaerobic zones through rhizosphere oxygen secretion in the root area of the plants. This microenvironment can promote the nitrification-denitrification of nitrogen and aerobic phosphorus storage by microorganisms in the sediment, thereby enhancing the removal efficiency of nitrogen and phosphorus nutrients in eutrophic water bodies.

[0023] (3) Reduce the release of nitrogen and phosphorus nutrients in the water sediment. The present invention reduces the release of nitrogen in the water sediment through the absorption of nitrogen in the sediment by the growth of emergent plants and the enhancement of denitrification of sediment microorganisms by rhizosphere oxygen secretion; it reduces the release of phosphorus in the water sediment through the rhizosphere oxygen secretion of emergent plants and the increase of the redox potential of the sediment by the SMFC anode electrode, thereby reducing the release of phosphorus through the iron-sulfur-phosphorus cycle.

[0024] (4) The present invention combines microbial electrochemical technology and plant ecology, and improves the efficiency and sustainability of the restoration of bloom water bodies through the self-regulating ability of natural ecosystems. This method can not only effectively control the growth of bloom algae, but also solve the nitrogen and phosphorus pollution problems in water bodies at the same time, providing a new environmentally friendly solution for the treatment of bloom water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of the device for efficiently removing algae, nitrogen, and phosphorus of the present invention;

[0026] Figure 2 It is the change of the amount of in-situ generated hydrogen peroxide with time in Example 1;

[0027] Figure 3 It is the change of chlorophyll a in the bloom water body with time in Example 1;

[0028] Figure 4 It is the change of ammonia nitrogen and total nitrogen concentrations with time in Example 1;

[0029] Figure 5 It is the change of ammonia nitrogen and total nitrogen concentrations with time in Example 1;

[0030] Figure 6 It is the change of total phosphorus concentration with time in Example 1;

[0031] Among them: 1, sediment; 2, anode electrode; 3, bloom water body; 4, cathode electrode; 5, emergent plant; 6, light source; 7, metal wire; 8, external resistance. DETAILED DESCRIPTION OF THE INVENTION

[0032] The specific embodiments of the present invention will be described below to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0033] Example 1

[0034] Step 1: As shown in Figure 1 , construct an emergent plant - SMFC coupling system. The height of the sediment 1 is set to 15 cm, and the sediment is taken from Yao Lake in Nanchang and filtered through a 2 - mm sieve. Optionally, the anode electrode 2 is made of carbon felt, with an apparent size of 30.0 cm × 10.0 cm × 1.0 cm. A circular hole with a diameter of 2.0 cm is cut in the center of the anode electrode, and the anode electrode is curled into a cylinder, stitched with titanium wire. Then, the emergent plant 5 is planted on the anode electrode (5 Cyperus alternifolius plants with a height of 46.2 - 54.4 cm, and the roots pass through the circular hole cut in the anode electrode). Finally, the anode electrode is placed in the sediment, with the circular hole facing up and located at the top of the sediment. The height of the eutrophic water body 3 is set to 20 cm.

[0035] Step 2: Modify the cathode electrode. Optionally, the cathode electrode 4 is made of carbon felt, with an apparent size of Φ10.0 cm × 1.0 cm. Using an electrochemical workstation (Biological VSP - 300 from France) in the constant - current mode, the cathode electrode is set as the working electrode, and the carbon rod is set as the counter electrode. The constant current is set to 200 mA, the oxidation time is set to 30 min, and the ammonium fluoride concentration is 50 mM. After oxidation treatment, the cathode electrode is rinsed with deionized water until neutral and dried at 55 °C for 10 h. Then, a circular hole with a diameter of 2.0 cm is cut in the center of the modified cathode electrode to allow the emergent plant to pass through, and the cathode electrode is placed 0.5 cm below the water surface.

[0036] Step 3: Set the simulated sunlight. Optionally, 2 groups of 18 - W LED lights are selected as the light source 6, and the light source is 50.0 cm away from the water surface of the eutrophic water body, and the light - dark ratio is set to 12 h / 12 h.

[0037] Step 4: Connect the current loop. Optionally, the metal wire 7 is made of titanium wire, connecting the anode electrode and the modified cathode electrode. Optionally, the external resistance 8 is set to 1000 Ω and is connected in series between the anode electrode and the cathode electrode.

[0038] Step 5: Start the system. Use a syringe to inject 100 mL of the anode effluent of the microbial fuel cell with sodium acetate as the organic substrate into the anode carbon felt electrode. Slowly inject the bloom water body onto the sediment by siphon until the water body reaches a height of 20 cm. The bloom algae in the bloom water body is Microcystis aeruginosa, with an algal density of 2.5×108 cells / L, chlorophyll a of 108 μg / L, total phosphorus of 2.0 mg / L, total nitrogen of 8.0 mg / L (ammonia nitrogen 2.0 mg / L, nitrate nitrogen 6.0 mg / L), transparency of 24 cm, permanganate index of 42 mg / L, and sodium chloride concentration of 0.07 mg / L, so that the solution conductivity is 167 μS / cm.

[0039] Step 6: Domesticate electroactive microorganisms. Place the emergent plant-SMFC coupled system at room temperature (25±2 °C) for domestication. Replace the bloom water body every 2 days, which is one cycle. When the increment of the output voltage is less than 5% for two consecutive cycles, it indicates that the coupled system is successfully started.

[0040] Step 7: Analyze the hydrogen peroxide content. Replace the external resistance with 50 Ω, replace the bloom water body in Step 5, remove Microcystis aeruginosa, and keep other water quality conditions the same. Continuously operate for 10 d, regularly sample, and analyze the change in the hydrogen peroxide concentration in the liquid phase.

[0041] Step 8: Operate the system. Replace the bloom water body again and keep the water quality conditions the same as in Step 5. Operate for 45 d, regularly sample, and analyze the concentrations of chlorophyll a, ammonia nitrogen, total nitrogen, and total phosphorus in the liquid phase.

[0042] Control Example 1:

[0043] Operate the control group with only SMFC, that is, without the effect of emergent plants, and keep other operating conditions the same as in Example 1.

[0044] Control Example 2:

[0045] Operate the control group of emergent plant-SMFC, that is, the cathode electrode of SMFC is not modified, and keep other operating conditions the same as in Example 1.

[0046] Results: In the operation stage, the concentration of hydrogen peroxide in the water body of the emergent plant-SMFC coupled system with the modified cathode gradually increases and stabilizes at 3.17±0.15 mg / L, which is significantly higher than that of the emergent plant-SMFC coupled system with the unmodified cathode (1.81±0.08 mg / L, Figure 2 ) and the SMFC system (1.36±0.14 mg / L, Figure 2) This indicates that the electrochemically oxidized modification significantly improves the catalytic activity and selectivity of the cathode electrode, thereby enhancing the hydrogen peroxide generation capacity. Meanwhile, the coupling of emergent plants and SMFC promotes electricity generation through rhizosphere organic matter secretion, improves the current efficiency of the system, and further increases the hydrogen peroxide production.

[0047] Regarding the removal of bloom algae, the emergent plant-SMFC coupling system with the modified cathode can reduce the chlorophyll a concentration in the water body from the initial 108.2 ± 6.1 μg / L to 0 μg / L in only 12 days, while the emergent plant-SMFC coupling system and the SMFC system with the unmodified cathode require 24 days and 30 days respectively ( Figure 3 ). This result shows that the modified cathode significantly improves the algae removal efficiency, and the synergistic effect of emergent plants and SMFC further enhances the overall algae removal ability of the system.

[0048] Regarding the treatment of nitrogen pollution, in the initial stage of operation of the emergent plant-SMFC coupling system with the modified cathode, the ammonia nitrogen concentration in the water body briefly increases and then rapidly decreases, dropping to 0 mg / L within 28 days ( Figure 4 ), while the unmodified cathode system requires 32 days to completely remove ammonia nitrogen. In contrast, although the ammonia nitrogen concentration in the water body of the SMFC system gradually decreases in the later stage of operation, it only drops to 2.68 ± 0.14 mg / L at 45 days, still higher than the initial concentration of 2.13 ± 0.09 mg / L, showing significant removal insufficiency ( Figure 4 ). Regarding the total nitrogen removal, at 45 days, the total nitrogen concentration in the water body of the emergent plant-SMFC coupling system with the modified cathode drops to 1.13 ± 0.26 mg / L, significantly lower than that of the unmodified cathode system (6.56 ± 0.67 mg / L) and the SMFC system (16.46 ± 0.54 mg / L) ( Figure 5 ). In addition, the total nitrogen concentration of the SMFC system significantly increases in the initial stage of operation and is still higher than the initial concentration (8.06 ± 0.43 mg / L) finally. These results show that the electrochemical modification significantly improves the nitrogen pollution removal ability of the cathode, and at the same time, the emergent plants further enhance the denitrification effect of the system through the regulation of the rhizosphere microenvironment.

[0049] Regarding the treatment of phosphorus pollution, the emergent plant-SMFC coupling system with the modified cathode shows excellent total phosphorus removal effect. After 45 days of operation, the total phosphorus concentration in the water body drops to 0.24 ± 0.06 mg / L, significantly lower than that of the unmodified cathode system (0.85 ± 0.07 mg / L) and the SMFC system (3.35 ± 0.14 mg / L) ( Figure 6)。In contrast, the total phosphorus concentration in the SMFC system increased significantly during operation and was finally still higher than the initial concentration of 2.01±0.08 mg / L, showing a significant deficiency in phosphorus pollution control. The emergent plant-SMFC coupling system with a modified cathode not only effectively avoided the secondary release of total phosphorus but also significantly enhanced the phosphorus removal efficiency, which benefited from the improvement of the cathode catalytic performance by electrochemical modification and the synergistic enhancement of the active absorption of phosphorus nutrients by emergent plants and the rhizosphere microorganisms.

[0050] In summary, the emergent plant-SMFC coupling system based on a modified cathode in the present invention has successfully improved the hydrogen peroxide generation efficiency through multiple mechanisms, thereby increasing the removal speed and efficiency of bloom algae. In addition, through the regulation of the rhizosphere microenvironment of emergent plants and the catalytic enhancement of the electrochemically modified cathode, this system has significantly improved the removal efficiency of ammonia nitrogen, total nitrogen, and total phosphorus in the water body, while effectively inhibiting the release of nitrogen and phosphorus nutrients in the sediment, achieving the synchronous and efficient treatment of algae removal and pollution control in bloom water bodies, and providing an efficient, green, and sustainable technical solution for water body ecological restoration.

Claims

1. A method for synchronously repairing water bodies by using an emergent plant-sediment microbial fuel cell, characterized in that, It includes the following steps: A method for synchronous remediation of water body by emergent plant-sediment microbial fuel cell S1. Construct an emergent plant-SMFC coupling system. The emergent plant-SMFC coupling system includes an emergent plant and an SMFC. The SMFC includes an anode electrode, a modified cathode electrode and an external resistor. Plant the emergent plant around the anode electrode so that the anode electrode contacts the bottom mud; S2. Prepare the modified cathode electrode and perform electrochemical oxidation modification on the cathode electrode to enhance its catalytic activity; S3. Domesticate electroactive microorganisms. Place the emergent plant-SMFC coupling system at room temperature for domestication. By introducing bottom mud rich in organic matter or exogenous inoculation of microorganisms, improve the power generation capacity of the anode electrode; S4. Start and run the system, and monitor the changes in the concentrations of chlorophyll a, ammonia nitrogen, total nitrogen and total phosphorus in the water body in real time until the target treatment effect is achieved.

2. The method for synchronously repairing water bodies by emergent plants-sediment microbial fuel cells according to claim 1, characterized in that, The anode electrode is a carbon felt, carbon rod, carbon cloth or carbon particle electrode, and the anode electrode is arranged in the bottom mud to promote the electron transfer of electroactive microorganisms.

3. The method for synchronously repairing water bodies by emergent plants - sediment microbial fuel cells according to claim 1, characterized in that, The emergent plants include Cyperus alternifolius, Canna indica, Phragmites australis, Typha orientalis, Zizania latifolia, Scirpus validus, Acorus calamus or Sagittaria trifolia.

4. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 1, wherein The cathode electrode is made of carbon felt, carbon rod or carbon cloth. The specific method for preparing the modified cathode electrode in S2 is as follows: Use an electrochemical workstation in the constant current mode, set the cathode electrode as the working electrode; use a carbon rod as the counter electrode, and the electrolyte is ammonium fluoride solution; perform oxidation treatment under constant current conditions, then rinse the cathode electrode with deionized water until neutral, and dry it at 55°C for 10 hours to obtain the modified cathode electrode.

5. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 4, wherein, The parameters of the oxidation treatment include: the constant current range is 1-1000 mA, the oxidation time is 1-60 minutes, and the concentration of ammonium fluoride solution is 1-500 mM.

6. The method for synchronously repairing water body by emergent plants - sediment microbial fuel cell according to claim 1, characterized in that The modified cathode electrode is arranged at the interface between the water bloom water body and the air to enhance the utilization efficiency of oxygen and promote the generation of hydrogen peroxide.

7. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 1, characterized in that The external resistor is connected in series with the anode electrode and the modified cathode electrode through a metal wire. The external resistor is located between the anode electrode and the cathode electrode; the metal wire is a platinum wire, titanium wire or stainless steel wire; the resistance value range of the external resistor is 0-100000 Ω.

8. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 1, characterized in that, The specific method for domesticating electroactive microorganisms in S3 is as follows: Slowly inject the effluent from the anode of the mature microbial fuel cell into the bottom mud where the anode electrode is located to promote the enhancement of microbial activity. When the increment of the anode output voltage is less than 5% in two consecutive cycles, it is considered that the domestication is completed.

9. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 1, characterized in that, When the system runs in S4, regularly rinse the modified cathode electrode with deionized water to remove the precipitates on the electrode surface and improve the electrode performance and system operation efficiency.

10. The method for synchronously repairing water body by emergent plant-sediment microbial fuel cell according to claim 1, wherein When the system runs in S4, by monitoring the changes in the concentrations of chlorophyll a, ammonia nitrogen, total nitrogen and total phosphorus in the water body in real time, dynamically adjust the electrochemical parameters of the cathode electrode and the planting density of the emergent plants according to the monitoring results.

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