Bioelectrochemical coupled iron-based artificial wetland device and application

Abstract

The invention discloses a bioelectrochemical coupled iron-based artificial wetland device and application, the device comprises a container, the top of the container is provided with a water supply device, the inner bottom of the container is paved with a supporting layer, the supporting layer is sequentially paved with a bioelectrochemical unit and a gravel layer, and aquatic plants are planted in the gravel layer; a plurality of water outlets are formed in positions, corresponding to the bioelectrochemical units, on the wall of the container; wherein the bioelectrochemical unit is formed by sequentially laying an upper cathode layer, an anode layer and a lower cathode layer from top to bottom, electrodes are horizontally embedded in each layer, and the bioelectrochemical unit is electrically connected with a power supply outside the container; and an aerator is also embedded in the anode layer and is connected with an air compressor outside the container through a ventilation pipeline. According to the device, multiple pollutants can be synchronously and efficiently removed through coupling of a multi-electrode bioelectrochemical structure, a controllable aerobic environment and iron-based filler chemical catalysis; meanwhile, by adjusting voltage and an aeration strategy, the device can quickly respond to water quality change, and is suitable for treating eutrophic water bodies with complex components.

Description

Technical Field

[0001] This invention relates to constructed wetlands, and more particularly to a bioelectrochemically coupled iron-based constructed wetland device and its application. Background Technology

[0002] Eutrophic water bodies such as rivers, lakes, nearshore waters, and aquaculture wastewater commonly suffer from complex pollution problems involving high ammonia nitrogen, high chemical oxygen demand (COD), high phosphorus, and antibiotic residues. Constructed wetland technology is widely used for the treatment of such wastewater due to its low cost and simple operation and maintenance. Constructed wetland packing materials, especially iron-based packing materials, play a crucial role in nitrogen and phosphorus removal in wetlands. Through iron and sulfur cycling, they can promote autotrophic denitrification and have a good adsorption effect on phosphorus. Furthermore, some studies have introduced bioelectrochemical systems into the ecological treatment of constructed wetlands, aiming to enhance electron transfer and pollutant transformation within the wetland system through electrode reactions.

[0003] However, constructed wetland systems coupled with traditional two-electrode bioelectrochemical systems are often limited by their single electron transport pathway and simple redox environment, resulting in significant shortcomings in electron utilization efficiency and synergistic removal of multiple pollutants. Furthermore, the difficulty in flexibly adjusting treatment efficiency according to influent load leads to poor adaptability to changes in operating conditions, thus limiting their practical application. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide an iron-based constructed wetland device with a multi-electrode bioelectrochemical system coupling that allows for flexible adjustment of treatment efficiency. The second purpose is to provide the application of this device in the treatment of eutrophic wastewater.

[0005] Technical Solution: The bioelectrochemically coupled iron-based constructed wetland device of the present invention includes a container with a water supply device at the top and a support layer made of crushed stone or gravel at the bottom. Bioelectrochemical units and a gravel layer are sequentially laid on the support layer. Aquatic plants are planted on the gravel layer. Multiple water outlets are provided on the container wall corresponding to the positions of the bioelectrochemical units. The bioelectrochemical unit is composed of a lower cathode layer made of pyrite, an anode layer made of volcanic rock, and an upper cathode layer made of iron-based filler, laid sequentially from bottom to top. Electrodes are horizontally embedded in each layer. The cathode electrodes are electrically connected to a power source outside the container via a series resistor, and the anode electrodes are directly electrically connected to the power source. An aerator is also embedded in the anode layer and connected to an air compressor outside the container via an air pipe.

[0006] In the bioelectrochemical unit, the pyrite in the lower cathode layer can undergo further denitrification under anaerobic conditions, and its oxidation product, Fe2O3, can adsorb phosphorus-containing pollutants. The volcanic rock in the anode layer has a porous structure, which can support nitrifying bacteria. Combined with the aerators laid in the anode area, a suitable aerobic environment is created for nitrifying bacteria, which can promote NH4+ production.4+ -N to NO 3- -N conversion; the iron-based filler in the upper cathode layer can promote the generation of hydroxyl radicals under aerobic cathode conditions, thereby degrading antibiotics.

[0007] Preferably, the iron-based filler is iron filings, pyrite, or a mixture of iron filings and biochar; more preferably, when the iron-based filler is a mixture of iron filings and biochar, the mass ratio of iron filings to biochar is 6~10:1.

[0008] Preferably, the thickness of the support layer is 3-7 cm, the thickness of each layer in the bioelectrochemical unit is 10-20 cm, and the thickness of the gravel layer is 3-7 cm.

[0009] Preferably, the particle size of the crushed stone or gravel in the supporting layer is 10-20 mm; the particle size of the pyrite in the lower cathode layer is 8-10 mm; the particle size of the volcanic rock in the anode layer is 6-10 mm; the particle size of the iron-based filler in the upper cathode layer is 3-8 mm; and the particle size of the gravel in the gravel layer is 10-20 mm.

[0010] Preferably, both the cathode electrode and the anode electrode are graphite felt electrodes with a length of 15-20 cm, a width of 5-10 cm, and a thickness of 0.3-0.7 cm.

[0011] Preferably, the power supply is a voltage-adjustable power supply, and the resistance value of the resistor is 500~1500 Ω; more preferably, the adjustable voltage range of the power supply is 10~30 V, and when the pollutant load increases, the electrochemical activity of the system can be enhanced by increasing the operating voltage to achieve emergency enhanced treatment.

[0012] Preferably, the aquatic plants include one or more of canna lilies, calamus, and reeds.

[0013] Preferably, an outlet is provided on the container wall at the corresponding position of each layer of the bioelectrochemical unit; more preferably, the outlet is located 1-3 cm from the bottom boundary of each layer of the bioelectrochemical unit; even more preferably, a sampling port is also provided on the container wall at a position strictly at the same height as each of the above outlets.

[0014] The eutrophic wastewater treatment method of the present invention includes the following steps: S1, activated sludge is inoculated into the aforementioned bioelectrochemical coupled iron-based constructed wetland device and microbial domestication is carried out. Then, eutrophic sewage is added until it covers the gravel layer, and the wastewater is discharged after standing for 36-60 hours. S2 continuously supplies the eutrophic wastewater to be treated through a water supply device for treatment.

[0015] Preferably, in step S2, the hydraulic retention time of the eutrophic wastewater is 24-48 h.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The device optimizes the electron transfer path and promotes the generation efficiency of hydroxyl radicals by coupling the multi-electrode bioelectrochemical structure, the controllable aerobic environment and the chemical catalysis of iron-based filler, and constructs a suitable alternating environment for nitrification and denitrification, which can achieve simultaneous and efficient removal of multiple pollutants such as antibiotics, nitrogen and phosphorus; 2. Based on the variable voltage system and the controllable aeration oxygen environment regulation system, the device has good operational stability and the ability to cope with shock loads. It can quickly respond to water quality changes by adjusting the voltage and aeration strategy, and is suitable for treating aquaculture tailwater with complex composition and other eutrophic water bodies. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a bioelectrochemically coupled iron-based constructed wetland device. Figure 2 This is a graph showing the statistical results of enrofloxacin removal rate after the device has been running continuously for 3 months. Figure 3 This is a graph showing the statistical results of the total nitrogen removal rate of the unit after three months of continuous operation. Figure 4 This is a graph showing the statistical results of the total phosphorus removal rate of the device after three months of continuous operation. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0019] Figure 1 The attached diagrams are labeled as follows: water supply device-1, power supply-2, anode electrode-3, cathode electrode-4, resistor-5, upper cathode layer-6, anode layer-7, lower cathode layer-8, support layer-9, outlet-10, sampling port-11, aerator-12, ventilation pipeline-13, air compressor-14, gravel layer-15, container-16.

[0020] Example 1: Construction of a multi-electrode bioelectrochemically coupled iron-based constructed wetland device Four types of multi-electrode bioelectrochemically coupled iron-based constructed wetland devices were established: Fe 0 -CW (zero-valent iron enhanced constructed wetland), FeS2-CW (pyrite enhanced constructed wetland), Fe 0 -BC-CW (Iron-Biochar Composite Enhanced Constructed Wetland), Fe 0 -FeS2-BC-CW (zero-valent iron-pyrite-biochar composite reinforced constructed wetland), q-CW (control group constructed wetland).

[0021] 1. Fe 0 -CW Construction A cubic glass container with dimensions of 20×10×60 cm is used. A peristaltic pump is installed at the top of the container as a water supply device 1, and a 5 cm thick support layer 9 composed of pebbles with a particle size of 10-20 mm is laid at the bottom of the container.

[0022] On the support layer 9, bioelectrochemical units and a gravel layer are laid in sequence. The gravel layer is made of gravel with a particle size of 10-20 mm and a thickness of 5 cm. At the same time, a canna lily (1 plant) is planted on the gravel layer. The bioelectrochemical unit is made of: a lower cathode layer 8 with a thickness of 15 cm composed of pyrite with a particle size of 10-20 mm, an anode layer 7 with a thickness of 15 cm composed of volcanic rock with a particle size of 6-10 mm, and an upper cathode layer 6 with a thickness of 15 cm composed of iron filings with a particle size of 3-8 mm, laid in sequence from bottom to top.

[0023] Each layer has a graphite felt electrode horizontally embedded 3 cm from the bottom boundary. The cathode electrode 4 has a size of 19×8×0.5 cm and is connected to the power supply 2 via a copper wire after being connected in series with a resistor 5 with a resistance of 1000 Ω. The anode electrode 3 has a size of 18×8×0.5 cm and is directly connected to the power supply 2 via a copper wire. The power supply 2 is a voltage adjustable power supply, and the output voltage can be adjusted between 10V, 20V, and 30V.

[0024] The anode layer 7 is also equipped with an aerator 12, which is connected to the air compressor 14 through the air pipe 13.

[0025] An outlet 10 is provided on the container wall at a position 2 cm from the bottom boundary of each layer of the bioelectrochemical unit, and a sampling port 11 is provided at a position strictly at the same height as each of the outlets 10.

[0026] 2. Construction of FeS2-CW Reference Fe 0 The difference in the construction of -CW is that the bioelectrochemical unit is composed of: a lower cathode layer 8 with a thickness of 15 cm made of pyrite with a particle size of 8-10 mm, an anode layer 7 with a thickness of 15 cm made of volcanic rock with a particle size of 6-10 mm, and an upper cathode layer 6 with a thickness of 15 cm made of pyrite with a particle size of 8-10 mm, laid out sequentially from bottom to top.

[0027] 3. Fe 0 -BC-CW Construction Reference Fe 0The construction of -CW differs in that the bioelectrochemical unit consists of: a 15 cm thick lower cathode layer 8 composed of pyrite with a particle size of 8-10 mm, a 15 cm thick anode layer 7 composed of volcanic rock with a particle size of 6-10 mm, and a 15 cm thick upper cathode layer 6 composed of a mixture of iron filings and biochar with a particle size of 3-8 mm, laid out sequentially from bottom to top. The mass ratio of iron filings to biochar is 8:1.

[0028] 4. Fe 0 Construction of FeS2-BC-CW Reference Fe 0 The construction of -CW differs in that the bioelectrochemical unit consists of: a 15 cm thick lower cathode layer 8 composed of pyrite with a particle size of 8-10 mm; a 15 cm thick anode layer 7 composed of volcanic rock with a particle size of 6-10 mm; and a 15 cm thick upper cathode layer 6 composed of a mixture of iron filings, pyrite, and biochar with a particle size of 3-8 mm, laid out sequentially from bottom to top. The mass ratio of iron filings, pyrite, and biochar is 4:4:1.

[0029] 5. Construction of q-CW Reference Fe 0 The difference in the construction of -CW is that the bioelectrochemical unit is composed of: a lower cathode layer 8 with a thickness of 15 cm made of pyrite with a particle size of 8-10 mm, an anode layer 7 with a thickness of 15 cm made of volcanic rock with a particle size of 6-10 mm, and an upper cathode layer 6 with a thickness of 15 cm made of quartz sand with a particle size of 3-8 mm, laid out sequentially from bottom to top.

[0030] Comparative Example 1: Construction of a single-electrode bioelectrochemically coupled iron-based constructed wetland device SC-CW A 20×10×60 cm cubic glass container is used. A peristaltic pump is installed at the top of the container as a water supply device, and a 5 cm thick support layer of crushed stone or gravel with a particle size of 10-20 mm is laid at the bottom of the container.

[0031] A single-electrode bioelectrochemical system unit and a gravel layer are sequentially laid on the support layer. The gravel layer is composed of gravel with a particle size of 10-20 mm and is 5 cm thick. A canna lily plant is also placed in the gravel layer. The single-electrode bioelectrochemical system unit consists of a 15 cm thick anode layer made of volcanic rock with a particle size of 6-10 mm, and a 15 cm thick upper cathode layer made of a mixture of iron filings and biochar with a particle size of 3-8 mm, laid sequentially from bottom to top. The mass ratio of iron filings to biochar is 8:1.

[0032] Each layer has a graphite felt electrode horizontally embedded 3 cm from the bottom boundary. The cathode electrode measures 19×8×0.5 cm and is connected to the power supply via a copper wire after being connected in series with a 1000 Ω resistor. The anode electrode measures 18×8×0.5 cm and is directly connected to the power supply via a copper wire. The output voltage of the power supply is fixed at 20 V.

[0033] The anode layer is also equipped with an aerator, which is connected to an air compressor through a ventilation pipeline.

[0034] On the container wall, each layer of the single-electrode bioelectrochemical system unit has an outlet 3 cm from the bottom boundary, and a sampling port is also provided at the same height as each of the outlets.

[0035] Experimental Example 1: Evaluation of the Treatment Effect of Eutrophic Wastewater 1. Handling methods Activated sludge (obtained from a wastewater treatment plant) with a mixed liquor suspended solids concentration (MLSS) of 3000 mg / L was inoculated into the gravel layer of the bioelectrochemically coupled iron-based constructed wetland devices obtained in Example 1 and Comparative Example 1, respectively. After inoculation, the sludge was allowed to stand and adhere. Microbial acclimatization was then initiated for a total of 4 weeks. After acclimatization, simulated seawater aquaculture tailwater was added until it covered the gravel layer, and the sludge was allowed to stand for 48 hours before being drained. The simulated seawater aquaculture wastewater is continuously supplied through a water supply device, with a hydraulic retention time set to 48 hours for treatment.

[0036] The method for preparing simulated marine aquaculture wastewater is as follows: Take 800 mL of deionized water, and add 30 g of sea salt, 0.0305 g of ammonium chloride, 0.0485 g of sodium nitrate, 0.0030 g of sodium nitrite, 0.0176 g of potassium dihydrogen phosphate, 0.0937 g of glucose, and 0.001 g of enrofloxacin in sequence. Stir to dissolve and then bring the volume to 1 L to obtain simulated marine aquaculture wastewater.

[0037] 2. Analysis of Treatment Effects After three months of stable operation, water samples were collected from the bottom outlet for water quality analysis.

[0038] The methods for analyzing water quality indicators are shown in Table 1 below.

[0039] Table 1. Water Quality Index Analysis Methods

[0040] Enrofloxacin (ENR) removal rate test results are as follows: Figure 2 As shown, Fe 0 The FeS2-BC-CW group showed the highest removal rate of ENR, reaching 92%; while Fe 0-CW group, FeS2-CW group and Fe 0 The removal rates of Fe in the -BC-CW group were 56%, 61%, and 65%, respectively, while those in the q-CW group were only 35%. These results indicate that Fe 0 The components in the FeS2-BC-CW group are fully coupled, resulting in a significant synergistic effect. Its removal efficiency for typical antibiotics far exceeds that of single or binary material systems, and is more than 150% higher than that of unenhanced systems.

[0041] The results of the total nitrogen (TN) removal rate determination are as follows: Figure 3 As shown, Fe 0 The FeS2-BC-CW group achieved a TN removal rate of up to 91%; Fe 0 -CW group, FeS2-CW group and Fe 0 The TN removal rate of the -BC-CW group was between 52% and 55%, while the q-CW group had a lower nitrogen removal capacity, with a total nitrogen removal rate of only 33%. The results indicate that Fe... 0 The FeS2-BC-CW group, through a biochar-enhanced electron transport network, synergistically utilizes zero-valent iron and pyrite as composite electron donors, achieving highly efficient autotrophic denitrification under the drive of an external electric field. This solves the problem of denitrification in wastewater with a low carbon-to-nitrogen ratio, and its denitrification efficiency is nearly twice that of the proportional system.

[0042] The results of the total phosphorus (TP) removal rate determination are as follows: Figure 4 As shown, Fe 0 The removal rate of FeS2-BC-CW group can reach 89%; Fe 0 -CW group, FeS2-CW group and Fe 0 The TP removal rate in the BC-CW group was between 71% and 75%, while that in the q-CW group was only 45%. The results indicate that Fe... 0 The FeS2-BC-CW system provides a dual iron source (Fe 0 The combination of FeS2 and biochar ensures a continuous supply of iron ions, and together with the adsorption of biochar, a stable "adsorption-precipitation" phosphorus removal network is formed, which has a significant and stable phosphorus removal effect.

Claims

1. A bioelectrochemically coupled iron-based constructed wetland device, characterized in that, The device includes a container (16) with a water supply device (1) on top and a support layer (9) made of crushed stone or gravel laid at the bottom inside. Bioelectrochemical units and a gravel layer (15) are laid on the support layer (9) in sequence. Aquatic plants are planted on the gravel layer (15). Multiple water outlets (10) are provided on the wall of the container (16) at positions corresponding to the bioelectrochemical units. The bioelectrochemical unit is composed of a lower cathode layer (8) made of pyrite, an anode layer (7) made of volcanic rock, and an upper cathode layer (6) made of iron-based filler, laid from bottom to top. Each layer has horizontally embedded electrodes. The cathode electrode (4) is electrically connected to the power source (2) outside the container (16) by a series resistor (5), and the anode electrode (3) is directly electrically connected to the power source (2). The anode layer (7) is also embedded with an aerator (12), which is connected to the air compressor (14) outside the container (16) through a ventilation pipe (13).

2. The apparatus according to claim 1, characterized in that, The iron-based filler is iron filings, pyrite, or a mixture of iron filings and biochar.

3. The apparatus according to claim 2, characterized in that, When the iron-based filler is a mixture of iron filings and biochar, the mass ratio of iron filings to biochar is 6~10:

1.

4. The apparatus according to claim 1, characterized in that, The thickness of the support layer (9) is 3-7 cm, the thickness of each layer in the bioelectrochemical unit is 10-20 cm, and the thickness of the gravel layer (15) is 3-7 cm.

5. The apparatus according to claim 1, characterized in that, The particle size of the crushed stone or gravel in the support layer (9) is 10~20 mm; the particle size of the pyrite in the lower cathode layer (8) is 8~10 mm; the particle size of the volcanic rock in the anode layer (7) is 6~10 mm; the particle size of the iron-based filler in the upper cathode layer (6) is 3~8 mm; and the particle size of the gravel in the gravel layer is 10~20 mm.

6. The apparatus according to claim 1, characterized in that, The cathode electrode (4) and anode electrode (3) are both graphite felt electrodes with a length of 15-20 cm, a width of 5-10 cm, and a thickness of 0.3-0.7 cm.

7. The apparatus according to claim 1, characterized in that, The power supply (2) is a voltage adjustable power supply, and the resistance of the resistor (5) is 500~1500 Ω.

8. The apparatus according to claim 1, characterized in that, The aquatic plants include one or more of canna lilies, calamus, and reeds.

9. A method for treating eutrophic wastewater, characterized in that the steps include... include: S1, In the iron-based constructed wetland device with bioelectrochemical coupling as described in any one of claims 1 to 8, activated sludge is inoculated and microbial domestication is carried out, then eutrophic sewage is added until it covers the gravel layer, and after standing for 36 to 60 hours, it is drained. S2, through the water supply device (1), continuously supplies the eutrophic wastewater to be treated for treatment.

10. The eutrophic wastewater treatment method according to claim 9, characterized in that, In step S2, the hydraulic retention time of the eutrophic wastewater is 24-48 h.

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