Constructed wetland-microbial fuel cell coupled photocatalytic system for treating wastewater containing perfluorooctanoic acid

Abstract

The invention discloses a constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorine-containing caprylic acid wastewater, and relates to a constructed wetland microbial fuel cell coupled photocatalytic system. The invention aims to solve the problem that CW-MFC and photocatalysis are not combined to improve the removal rate of PFOA at present. The device comprises a reactor shell, a bottom filler layer, an anode region, a middle filler layer, a cathode region, wetland plants and an outer resistor, the bottom packing layer, the anode region, the middle packing layer and the cathode region are sequentially overlapped in the reactor shell from bottom to top, the cathode region loaded with a photocatalyst is connected with the anode region through an external resistor to form a circuit, a water inlet is formed in the lower part of the reactor shell, and a water outlet is formed in the upper part of the reactor shell. And the roots of the wetland plants penetrate through the cathode region and are planted in the middle filler layer. The invention belongs to the technical field of perfluorinated compound pollution remediation.

Description

Technical Field

[0001] The invention relates to an artificial wetland microbial fuel cell coupled photocatalytic system, belonging to the technical field of perfluorinated compound pollution remediation. Background Art

[0002] Perfluorooctanoic acid (PFOA), a Class 1 carcinogen, is currently widely present in surface water, air, soil and plants. Large-scale emissions of PFOA pose serious risks to ecosystems and human health, and PFOA still exists in wastewater treated by most sewage treatment plants. Although technologies such as advanced oxidation processes and nanofiltration can achieve effective removal of PFOA, these technologies are feasible on a laboratory scale and cannot be applied on a large scale. In addition, these methods of removing PFOA only separate PFOA from water without achieving the purpose of mineralization, and may produce more toxic metabolites. Therefore, it is necessary to develop an ecologically and cost-effective technology to remove PFOA from wastewater.

[0003] As an enhanced constructed wetland (CW) technology, constructed wetland-microbial fuel cell (CW-MFC) integrates substrates, plants and microorganisms to degrade various emerging pollutants, taking into account the dual functions of sewage treatment and biopower generation, and provides a sustainable and cost-effective method for PFOA pollution treatment. There is evidence that electrochemical stimulation of microorganisms can help improve the biodegradation of PFOA. In turn, some specific microorganisms can also produce bioelectricity during the degradation of PFOA, indicating that bioelectricity and PFOA biodegradation have complementary effects. However, long-term PFOA stress can change the microbial community structure, thereby inhibiting the denitrification performance and bioelectricity output of the CW-MFC system. Recently, a study has introduced photocatalysts into CW-MFC to improve the removal efficiency and promote power generation. However, there is no research on combining CW-MFC and photocatalysis to improve the removal rate of PFOA. Summary of the invention

[0004] The present invention aims to solve the problem that CW-MFC and photocatalysis have not yet been combined to improve the PFOA removal rate, and further proposes an artificial wetland microbial fuel cell coupled photocatalysis system for treating fluorooctanoic acid-containing wastewater.

[0005] The technical solution adopted by the present invention to solve the above problems is: the present invention comprises a reactor shell, a bottom filler layer, an anode region, a middle filler layer, a cathode region, wetland plants and an external resistor;

[0006] The bottom packing layer, the anode area, the middle packing layer and the cathode area are stacked in sequence from bottom to top in the reactor shell. The cathode area is connected to the anode area through an external resistor to form a circuit. A water inlet is provided at the bottom of the reactor shell, and a water outlet is provided at the top of the reactor shell. The roots of wetland plants pass through the cathode area and are planted in the middle packing layer.

[0007] Further, it also includes LED lights;

[0008] LED lights are set above the wetland plants.

[0009] Further, the bottom filler layer is composed of gravel, zeolite and quartz sand, and the middle filler layer is composed of quartz sand.

[0010] Furthermore, the cathode region is composed of five "tea bag cathodes" of identical size loaded with photocatalysts connected in series.

[0011] Furthermore, a stainless steel mesh is laid above the anode area as an electron collector, and the "tea bag cathodes" in the cathode area are connected in series with titanium wires.

[0012] Furthermore, the resistance of the external resistor is 200-1000Ω.

[0013] Further, the height of the gravel layer in the bottom filler layer is equal to the sum of the heights of the zeolite layer and the quartz sand layer.

[0014] Furthermore, the height of the anode region and the cathode region is one third of the middle filler layer.

[0015] The beneficial effects of the present invention are as follows: by sealing the stainless steel mesh electrode loaded with photocatalyst to the top of the "tea bag cathode", the present invention realizes the coupling of photocatalytic technology with artificial wetland-microbial fuel cell, and promotes the synergistic degradation of PFOA by photocatalyst and microorganisms. In addition, the system also has a good denitrification effect. At the same time, the introduction of photocatalytic technology has a positive effect on the detoxification metabolism of PFOA, reduces the toxicity of the system, increases the diversity of microorganisms, stimulates the activity of electroactive microorganisms, and thus improves the stability of the system's power generation capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the present invention;

[0017] Figure 1 In the figure, 1-water inlet, 2-bottom filler layer, 3-cathode area, 4-middle filler layer, 5-cathode area, 6-LED light, 7-wetland plant, 8-water outlet, 9-external resistor;

[0018] Figure 2 This is a diagram showing the denitrification effect of the artificial wetland-microbial fuel cell system in which the photocatalyst is introduced in Example 1;

[0019] Figure 3 is a comparison chart of PFOA outlet water concentration of CW-PMFC introduced with photocatalyst in Example 1 and CW-MFC not introduced with photocatalyst in Comparative Example 1;

[0020] Figure 4 is a comparison chart of PFOA removal rates of the CW-PMFC into which the photocatalyst is introduced in Example 1 and the CW-MFC into which the photocatalyst is not introduced in Comparative Example 1;

[0021] Figure 5 It is a comparison chart of the power generation capacity of the CW-PMFC introduced with the photocatalyst in Example 1 and the CW-MFC not introduced with the photocatalyst in Comparative Example 1. DETAILED DESCRIPTION

[0022] Specific implementation method 1: Figure 1 As shown, a constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater includes a reactor shell, a bottom filler layer 2, an anode region 3, a middle filler layer 4, a cathode region 5, wetland plants 7 and an external resistor 9;

[0023] The bottom packing layer 2, the anode area 3, the middle packing layer 4 and the cathode area 5 are stacked in sequence from bottom to top in the reactor shell. The cathode area 5 is connected to the anode area 3 through an external resistor 9 to form a circuit. A water inlet 1 is provided at the lower part of the reactor shell, and a water outlet 8 is provided at the upper part of the reactor shell. The roots of the wetland plants 7 pass through the cathode area 5 and are planted in the middle packing layer 4.

[0024] The bottom packing layer 2 is composed of gravel, zeolite and quartz sand, and the middle packing layer 4 is composed of quartz sand;

[0025] The cathode region 5 is composed of five “tea bag cathodes” of the same size loaded with photocatalysts connected in series;

[0026] A stainless steel mesh is laid above the anode area 3 as an electron collector, and the "tea bag cathodes" in the cathode area 5 are connected in series with titanium wires;

[0027] The resistance of the external resistor 9 is 200-1000Ω;

[0028] The height of the gravel layer in the bottom packing layer 2 is equal to the sum of the heights of the zeolite layer and the quartz sand layer;

[0029] The height of the anode region 3 and the cathode region 5 is one third of the middle filler layer.

[0030] Specific implementation method 2: Figure 2 As shown, it also includes an LED lamp 6;

[0031] The LED lamp 6 is arranged above the cathode region 5 .

[0032] Example

[0033] Embodiment 1

[0034] like Figure 1 As shown, a constructed wetland-microbial fuel cell system for strengthening the treatment of wastewater containing perfluorooctanoic acid by combined photocatalytic technology, the wetland system is a cylindrical structure, made of polypropylene, the main body of the wetland system is from bottom to top, the water inlet 1, the bottom filler layer 2 (0-40cm), the anode area 3 (40-45cm), the middle filler layer 4 (45-60cm), the cathode area 5 (60-65cm) and the water outlet 8, the bottom of the bottom filler layer 2 is provided with a water inlet 1 for wastewater to flow into the system, the upper part of the cathode area 5 is provided with a water outlet 8, the filler selected for the bottom filler layer 2 is 1-2cm gravel, 4-8mm zeolite and 2-4mm quartz sand to support and distribute the influent wastewater, wherein the height of the gravel layer is 20cm, and the height of the zeolite layer and the quartz sand layer are both 10cm. The anode area 3 is composed of domesticated coconut shell activated biochar particles, and a stainless steel mesh is laid on the top as an electron collector to enhance electron transfer, and the height of the anode area is 5cm. 1-2mm quartz sand is selected as an inert matrix to be filled in the middle packing layer 4 to support plant growth. Acorus calamus of the same growth stage and similar size is selected as the wetland plant 7 to be planted in the uppermost layer of the middle packing layer, and 11 plants are planted in each reactor. The cathode area 5 is at the top of the wetland system, and is composed of 5 "tea bag cathodes" of the same size loaded with photocatalysts connected in series with fine titanium wires. The anode area 3 and the cathode area 5 are connected by wires to form an external circuit. The external resistor 9 in the circuit is 1000Ω. The entire wetland system is wrapped with black shade cloth to prevent the production of algae and the photolysis of PFOA, and a round LED lamp 6 is placed above the cathode area to simulate sunlight to compensate for the lack of sunlight on the photocatalyst at night.

[0035] Production of "tea bag cathode": Cut the stainless steel mesh (3000 mesh) into 6×8cm rectangles, use silica sol to evenly load the photocatalytic material on the stainless steel electrode to form a photocatalytic cathode electrode (loading area is 6×4cm). At the same time, another stainless steel mesh (150 mesh) is cut into a "tea bag" shape, and the coconut shell biochar particles are loaded into the "tea bag". Then, the photocatalytic electrode is "sewn" to the top of the "tea bag" with titanium wire to prevent the buoyancy from causing the biochar particles to leak.

[0036] Domestication of coconut shell biochar particles: Coconut shell biochar particles were domesticated by inoculation biofilm method to obtain electrode microorganisms. Activated sludge was inoculated and placed in a container containing coconut shell biochar. Synthetic sewage was used as the microbial nutrient source, and an external conductive carbon rod was used as the air cathode to domesticate the microorganisms. Then, voltage monitoring was performed every day to observe the viscosity of the biochar surface. When the voltage was stable and the biochar surface was slightly sticky, it indicated that the microorganisms were successfully domesticated.

[0037] Start-up of the wetland system: The wetland system was inoculated with 2.5L of activated sludge diluted with tap water (activated sludge was taken from the secondary sedimentation tank of Wenchang Wastewater Treatment Plant in Harbin). Simulated wastewater (containing 300mg / L glucose, 200.00mg / L NaHCO) was continuously added to the wetland system from the bottom to the top of the wetland system by means of a peristaltic pump. 3 、61.00mg / LNH 4 Cl, 16.00mg / L KNO 3 、8.80mg / L KH 2 PO 4 、10.00mg / L MgSO 4 7H 2 O, 5.00mg / LFeSO 4 7H 2 O, 2.80mg / L CaCl 2 、3.00mg / L MnSO 4 ·H 2 O, 4.40mg / L ZnSO 4 7H 2 O and 4.00mg / LCuSO 4 ·5H 2 O), the hydraulic retention time is 3 days, until the performance of the system is stable.

[0038] Operation of the wetland system: After the artificial wetland-microbial fuel cell coupled photocatalytic system was successfully started, PFOA was added to each feed batch to make the concentration of PFOA in the influent water 10 μg / L.

[0039] Detection of the denitrification effect of the photocatalytic technology for treating wastewater containing perfluorooctanoic acid in the present invention by enhancing the artificial wetland-microbial fuel cell coupling photocatalytic system:

[0040] like Figure 2 As shown in the figure, the water quality of the system inlet 1 and outlet 8 is tested, and the ammonia nitrogen NH in the inlet wastewater is 4 + The average concentration of -N was 23.3 mg / L, and the nitrate nitrogen NO 3 -The average concentration of -N was 9.5 mg / L, the average concentration of total nitrogen TN was 15.5 mg / L and the average concentration of nitrite nitrogen NO 2 - The average concentration of -N is 0mg / L. After treatment by the wetland system, the ammonia nitrogen NH 4 + -N average concentration is 0.7mg / L, nitrate nitrogen NO 3 - The average concentration of -N is 1.1mg / L, the average concentration of total nitrogen TN is 0.3mg / L, and the nitrite nitrogen NO in the effluent is 2 - -N average concentration hardly increased, and the average removal rates of total nitrogen, ammonia nitrogen and nitrate nitrogen by the photocatalytic technology-enhanced artificial wetland-microbial fuel cell coupled photocatalytic system of the present invention were 97.6%, 96.9% and 88.7% respectively. By comparison, it can be obtained that the photocatalytic technology-enhanced artificial wetland-microbial fuel cell coupled photocatalytic system with the structure of the present invention has a good denitrification effect.

[0041] Comparative Example 1

[0042] In the comparative example 1, during the preparation process of the "tea bag cathode", the stainless steel electrode is not loaded with a photocatalyst, and the LED lamp disposed above the cathode area is removed, and the remaining operations are the same as those of the embodiment 1.

[0043] The performance comparison of PFOA removal effect and electricity generation capacity of the constructed wetland-microbial fuel cell system enhanced by photocatalytic technology for treating wastewater containing perfluorooctanoic acid and the constructed wetland-microbial fuel cell system without photocatalytic technology was carried out:

[0044] like Figure 3 As shown, in the artificial wetland-microbial fuel cell system enhanced by photocatalytic technology, the concentration of PFOA in the effluent is lower, with an average concentration of 0.2 mg / L.

[0045] like Figure 4 As shown in the figure, the removal efficiency of PFOA by the artificial wetland-microbial fuel cell system enhanced by photocatalysis technology (97.49% on average) is higher than that by the artificial wetland-microbial fuel cell system without photocatalysis technology (95.93%). The above results show that the introduction of photocatalysis technology to enhance the artificial wetland-microbial fuel cell system can effectively improve the removal of PFOA.

[0046] like Figure 5As shown, in the previous embodiment 1 and comparative example 1, the voltage output of the wetland system was relatively stable, with an average maximum voltage range of 0.381-0.457 V. However, after adding PFOA, the biopower generation of the artificial wetland-microbial fuel cell system enhanced by photocatalytic technology was more stable than that of the artificial wetland-microbial fuel cell system without photocatalytic technology.

[0047] The above results show that the artificial wetland-microbial fuel cell system enhanced by photocatalytic technology can effectively enhance the removal of perfluorooctanoic acid and improve the stability of power generation capacity, which can improve the shortcomings of existing technologies.

[0048] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater, characterized in that: It comprises a reactor shell, a bottom filler layer (2), an anode region (3), a middle filler layer (4), a cathode region (5), wetland plants (7) and an external resistor (9); A bottom packing layer (2), an anode region (3), a middle packing layer (4) and a cathode region (5) are sequentially stacked from bottom to top in a reactor shell; the cathode region (5) is connected to the anode region (3) via an external resistor (9) to form a circuit; a water inlet (1) is provided at the bottom of the reactor shell; a water outlet (8) is provided at the top of the reactor shell; and the roots of wetland plants (7) pass through the cathode region (5) and are planted in the middle packing layer (4).

2. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 1, characterized in that: Also includes an LED lamp (6); The LED lamp (6) is arranged above the cathode region (5).

3. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 1, characterized in that: The bottom packing layer (2) is composed of gravel, zeolite and quartz sand, and the middle packing layer (4) is composed of quartz sand.

4. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 1, characterized in that: The cathode region (5) is composed of five "tea bag cathodes" of the same size loaded with photocatalysts connected in series.

5. A constructed wetland microbial fuel cell system for treating fluorooctanoic acid-containing wastewater according to claim 1 or 4, characterized in that: A stainless steel mesh is laid above the anode area (3) as an electron collector, and the "tea bag cathodes" in the cathode area (5) are connected in series with titanium wires.

6. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 1, characterized in that: The resistance of the external resistor (9) is 200 to 1000Ω.

7. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 3, characterized in that: The height of the gravel layer in the bottom filler layer (2) is equal to the sum of the heights of the zeolite layer and the quartz sand layer.

8. The constructed wetland microbial fuel cell coupled photocatalytic system for treating fluorooctanoic acid-containing wastewater according to claim 1, characterized in that: The height of the anode region (3) and the cathode region (5) is one third of the height of the middle filler layer.

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