Constructed wetland-bioelectro-fenton coupling system and method for treating sewage thereof

Abstract

The application discloses an artificial wetland-bioelectric Fenton coupling system, which comprises, from bottom to top, a gravel layer, a biological anode carbon felt, a wetland layer and a floating electric Fenton cathode; the biological anode carbon felt is buried in the gravel layer and the wetland layer; the floating electric Fenton cathode floats on the water surface of the wetland layer; the floating electric Fenton cathode comprises an air diffusion waterproof layer and a heterogeneous Fenton catalytic layer; the floating electric Fenton cathode floats up and down with the liquid surface, has a strong oxygen enrichment function, can cancel the aeration of a traditional Fenton reaction, simultaneously needs no additional iron salt catalyst for efficient catalytic oxidation, and increases the pH range of the Fenton reaction. The application combines the artificial wetland and the bioelectric Fenton system, utilizes the interception of the artificial wetland to easily degradable organic pollutants, provides sufficient electric energy for the electric Fenton process through the bioelectrochemical method, reduces the competition of easily degradable organic matters and PPCPs to hydroxyl radicals in the electric Fenton process, and improves the degradation efficiency of the PPCPs.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water treatment, specifically relating to an artificial wetland-bioelectric Fenton coupling system and a method for treating wastewater. Background Technology

[0002] Pharmaceuticals and personal care products (PPCPs) are a class of synthetically produced products, including prescription and over-the-counter drugs for human and animal health, cosmetics and fragrances for personal care, and household chemicals for improving quality of life. In recent years, due to the continuous growth of the global population, PPCPs have been used extensively. Coupled with the limited removal efficiency of traditional wastewater treatment plants for these pollutants, PPCPs are widely present in natural water bodies such as rivers and lakes in my country. Furthermore, compared to water bodies and organisms, soil and sediments are more important storage sites for PPCPs, especially in the topsoil layer (0–30 cm), where the average total mass ratio of PPCPs is 15.6 μg / kg. Long-term exposure of humans or animals to soil and water environments containing PPCPs poses a potential threat to their health.

[0003] Electro-Fenton oxidation, as a typical advanced oxidation method, boasts advantages such as high efficiency, mild reaction conditions, and simple equipment. It is highly effective in removing recalcitrant organic pollutants from water and is therefore frequently used for the pretreatment of recalcitrant wastewater or the advanced treatment of wastewater with stringent discharge standards. However, in actual wastewater treatment, single-use Fenton technology requires continuous addition of hydrogen peroxide or aeration. Additionally, constructed wetlands are a simple means of wastewater treatment and ecological restoration, but currently, organic wastewater often has high organic matter concentrations and complex compositions, making it difficult for constructed wetlands to treat.

[0004] The constructed wetland-bioelectro-Fenton coupling system utilizes the principle of a bioelectrochemical system driving electro-Fenton technology to modify traditional constructed wetlands. By leveraging the complementary effects of the two structures, electrochemistry is introduced into the ecological treatment of constructed wetlands, aiming to achieve better treatment results and obtain energy while removing pollutants. This system utilizes soil microorganisms to intercept and degrade organic pollutants in wastewater, and uses electrochemical processes to enhance pollutant removal. Furthermore, it utilizes small-molecule organic matter secreted by wetland plant roots and easily degradable organic matter in wastewater to provide ample organic carbon and electron donors for the bioelectrochemical system, achieving energy recovery and demonstrating good application potential. However, some researchers at home and abroad have studied the use of acrylic plates to fix the anode and electro-Fenton cathode for the catalytic oxidation and degradation of pollutants. This approach is not only computationally complex but also requires a large volume, is difficult to maintain, and cannot be applied to wetland environments. Other researchers have placed the electro-Fenton cathode close to the reactor, but this fails to achieve the cathode's air enrichment effect, resulting in poor airtightness and waterproof performance, which also precludes practical application. Summary of the Invention

[0005] To overcome the problems existing in the prior art, one objective of this invention is to provide an constructed wetland-bioelectric Fenton coupling system. A second objective is to provide a method for wastewater treatment using the aforementioned constructed wetland-bioelectric Fenton coupling system. A third objective is to provide applications of this constructed wetland-bioelectric Fenton coupling system.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention provides an artificial wetland-bioelectric Fenton coupling system, comprising, from bottom to top, a gravel layer, a bioanode carbon felt, a wetland layer, and a floating electric Fenton cathode; the bioanode carbon felt is buried in the gravel layer and the wetland layer; the floating electric Fenton cathode floats on the water surface above the wetland layer; the floating electric Fenton cathode includes, from top to bottom, an air-diffusing waterproof layer and a heterogeneous Fenton catalytic layer; the air-diffusing waterproof layer is exposed to the air; the heterogeneous Fenton catalytic layer faces downwards towards the wetland layer.

[0008] Preferably, the gravel layer, bioanode carbon felt, wetland layer, and floating electro-Fenton cathode are uniformly distributed in the cylindrical acrylic reactor.

[0009] The gravel in the gravel layer has a particle size of 6-8 mm.

[0010] Preferably, the floating Fenton cathode is prepared by a method comprising the following steps:

[0011] S1. A waterproof material emulsion is coated on one side of the gas diffusion layer substrate and sintered at high temperature to form an air diffusion waterproof layer.

[0012] S2. The carbon black catalyst and the binder perfluorosulfonic acid polymer solution are mixed and coated on the other side of the gas diffusion layer substrate to form a heterogeneous Fenton catalyst layer, thereby obtaining the electric Fenton cathode.

[0013] S3. Fix a lightweight material around the electric Fenton cathode to make the electric Fenton cathode float on the water surface, thus obtaining a floating electric Fenton cathode.

[0014] More preferably, in step S1, the gas diffusion layer substrate is selected from one or more of carbon paper, carbon cloth, and carbon black paper.

[0015] More preferably, in step S1, the waterproof material is selected from one or more of polytetrafluoroethylene, polyimide, polyetheretherketone, polyphenylene sulfide, polyethersulfone, and polyetherimide.

[0016] More preferably, in step S1, the sintering temperature is 250-500℃. Even more preferably, the calcination time is 5-15 minutes, and the number of calcinations is 1-3 times.

[0017] More preferably, in step S1, the application amount is 0.001-1 mL / cm³. 2 .

[0018] More preferably, in step S2, the perfluorosulfonic acid polymer solution is a Nafion solution.

[0019] More preferably, in step S2, the mass-to-volume ratio of the carbon black catalyst to the perfluorosulfonic acid polymer solution is 1 mg:(4-8) μL.

[0020] More preferably, step S2 further includes mixing the carbon black catalyst, glass, binder perfluorosulfonic acid polymer solution, isopropanol, and water.

[0021] More preferably, in step S2, the coating process involves multiple coating layers, with each layer drying before applying the next.

[0022] More preferably, in step S3, the lightweight material is plastic. Even more preferably, the lightweight material is a plastic sealing cap.

[0023] More preferably, in step S3, the fixing method uses glue. Even more preferably, a counterweight can be added to adjust the density of the floating Fenton cathode.

[0024] The air-waterproof diffusion layer of the floating Fenton cathode is positioned facing the upper air layer of the constructed wetland system, its function being to enrich a large amount of oxygen through full contact with the atmosphere; the heterogeneous Fenton catalytic layer is positioned facing the wetland layer, its function being to utilize the oxygen enriched in the upper diffusion layer and the constructed wetland environment to catalyze the production of H2O2, which further reacts with Fe in the constructed wetland soil and water environment. 2+ The Fenton reaction catalyzes the generation of ·OH. Furthermore, the plastic sealing cap exhibits high stability, is not easily oxidized, and will not affect the floating of the Fenton cathode.

[0025] Preferably, the bioanode carbon felt is a carbon felt enriched with microorganisms.

[0026] More preferably, the bioanode carbon felt is a mixed bacterial system, wherein the microorganisms are specifically electrogenic microorganisms.

[0027] The described bio-electro-Fenton system involves burying a bio-anode carbon felt within a gravel and wetland layer, while a floating electro-Fenton cathode is exposed to air, using oxygen as the electron acceptor. A solid-liquid interface is formed between the wetland layer and the wastewater above the bio-electro-Fenton system, creating both anaerobic and aerobic environments. The bio-anode carbon felt performs anaerobic degradation of the wastewater, during which protons are transferred to the electro-Fenton cathode through the solid-liquid interface, while electrons generated simultaneously reach the cathode material through an external circuit.

[0028] Preferably, the wetland layer also includes phytoplankton.

[0029] The phytoplankton transport oxygen to their roots, creating an aerobic environment that provides a suitable habitat for microbial growth, thereby degrading pollutants in wastewater. Additionally, the phytoplankton roots can work in conjunction with soil microorganisms to adsorb and filter out small amounts of iron sludge.

[0030] Preferably, the bio-anode carbon felt and the floating electric Fenton cathode are connected to a power source via an external wire, and the power source and the resistor of the external circuit load are connected in parallel to form a bio-electric Fenton system.

[0031] Preferably, an outlet is provided above the floating Fenton cathode.

[0032] Preferably, a water inlet is provided below the gravel layer.

[0033] Preferably, the material of the wetland layer includes red clay and fine sand.

[0034] A second aspect of the present invention provides a method for wastewater treatment using the constructed wetland-bioelectric Fenton coupling system described in the first aspect, comprising the following steps:

[0035] 1) Wastewater is first filtered through a gravel layer for preliminary filtration; then, it is treated by anaerobic degradation using bio-anodized carbon felt.

[0036] 2) The anaerobic wastewater flows into the wetland layer, where materials and microorganisms adsorb and degrade the organic pollutants in the wastewater.

[0037] 3) The floating Fenton cathode floats on the surface of the wastewater on the wetland layer. The heterogeneous Fenton catalytic layer catalyzes the heterogeneous reaction to generate hydroxyl radicals and deeply removes organic matter from the wastewater.

[0038] Preferably, the wastewater flows in from an inlet below the gravel layer.

[0039] Preferably, the water treated in step 3) flows out through the outlet above the floating Fenton cathode.

[0040] Preferably, the bio-anode carbon felt and the floating Fenton cathode are connected to a power source and a voltage of 0.1-1V is applied.

[0041] Preferably, the hydraulic residence time is 6-18 hours.

[0042] The third aspect of this invention provides the application of the constructed wetland-bioelectric Fenton coupling system described in the first aspect in the treatment of PPCPs type wastewater.

[0043] Preferably, the PPCPs are selected from erythromycin, roxithromycin, diclofenac, ibuprofen, salicylic acid, sulfamethoxazole, carbamazepine, and 1,4-dioxane.

[0044] The beneficial effects of this invention are:

[0045] This invention provides an constructed wetland-bioelectro-Fenton coupling system. The floating electro-Fenton cathode can float up and down with the liquid surface, possessing extremely high oxygen enrichment capabilities. This eliminates the aeration process in traditional Fenton reactions, achieving highly efficient catalytic oxidation without the need for external iron salt catalysts, and expanding the pH range of the Fenton reaction. Building upon previous research on bioelectro-Fenton, this invention combines constructed wetlands with a bioelectro-Fenton system. It utilizes the constructed wetland's retention of readily degradable organic pollutants and employs bioelectrochemical methods to provide sufficient electrical energy for the electro-Fenton process while reducing competition between readily degradable organic matter and 1,4-dioxane-based hydroxyl radicals, thereby improving the degradation efficiency of typical PPCPs.

[0046] Specifically, compared with the prior art, the present invention has the following advantages:

[0047] The carbon material of the air-diffusion waterproof layer has good electrical conductivity, high stability, high waterproof performance, and is loose and porous, with extremely high oxygen enrichment function, so no additional aeration device is required.

[0048] The heterogeneous Fenton catalyst layer can utilize Fe in the wetland layer 2+ The Fenton reaction occurs, Fe 2+ It is continuously regenerated under electrocatalysis, in which the cathodic reduction reaction can enhance Fe 2+ The regeneration efficiency greatly reduces the amount of iron salt added and the amount of iron sludge generated. Attached Figure Description

[0049] Figure 1 The images show the front view (a), top view (b), and bottom view (c) of a floating Fenton cathode.

[0050] Figure 2 Diagram of an artificial wetland-bioelectric Fenton coupling system;

[0051] Figure 3 This is a diagram showing the oxygen enrichment of a floating Fenton cathode.

[0052] Figure 4Graph showing the degradation effect of typical PPCPs by an constructed wetland-bioelectric Fenton coupling system;

[0053] Figure 5 The graph shows the H2O2 production of a floating Fenton cathode under an applied current.

[0054] Among them, 1 is the gravel layer, 2 is the bio-anode carbon felt, 3 is the wetland layer, 4 is the sewage, 5 is the floating Fenton cathode, 6 is duckweed, 7 is the outlet, 8 is the inlet, 9 is the power source, and 10 is the titanium wire conductor. Detailed Implementation

[0055] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0056] Example 1

[0057] 1. The preparation method of the electro-Fenton cathode in this embodiment is as follows:

[0058] 1.1 Coat the side of the carbon cloth (9cm in diameter) with conductive carbon black with PTFE (polytetrafluoroethylene). The amount of PTFE coating is 2.5mL. After drying, place it in a muffle furnace and sinter at 350℃ for 10min. Repeat twice to form an air-diffusion waterproof layer and obtain waterproof carbon cloth.

[0059] 1.2 Weigh 225mg of carbon black (specification: XC-72) into a plastic bottle, add 3-4 glass beads, add 250μL of deionized water and shake for 20s, add 1000μL of 5wt% Nafion solution (perfluorosulfonic acid type polymer) and 500μL of isopropanol, and evenly coat it on the other side of the waterproof carbon cloth (opposite to the waterproof side). Coat it in multiple layers, and only coat the next layer after each coating layer has dried, to form a heterogeneous Fenton catalyst layer, and obtain the electric Fenton cathode.

[0060] 1.3 Finally, use AB glue to fix it in the plastic cover, thus obtaining the floating Fenton cathode. Figure 1 .

[0061] 2. The constructed wetland-bioelectric Fenton coupling system in this embodiment is as follows: Figure 2 As shown, the details are as follows:

[0062] The reactor comprises, from bottom to top, a gravel layer 1, a bioanode carbon felt 2, a wetland layer 3, and a floating Fenton cathode 5, all evenly distributed within a cylindrical acrylic reactor. The bioanode carbon felt 2 is buried within the gravel layer 1 and the wetland layer 3. The floating Fenton cathode 5 floats on the surface of wastewater 4 above the wetland layer 3. The floating Fenton cathode 5 includes an air-diffusing waterproof layer and a heterogeneous Fenton catalytic layer. The air-diffusing waterproof layer is directly exposed to the air, while the heterogeneous Fenton catalytic layer faces downwards towards the wetland layer 3.

[0063] The bio-anode carbon felt 2 and the floating electric Fenton cathode 5 are connected to the power supply 10 through an external titanium wire 9. The power supply 10 is connected in parallel with the resistor of the external circuit load to form a bio-electric Fenton system.

[0064] The bottom of the reactor near the gravel layer 1 is provided with inlets 8 on both sides, which are connected to a wastewater storage tank for PPCPs wastewater to enter; the top of the reactor near the floating Fenton cathode 5 is provided with an outlet 7.

[0065] Duckweed 6 is planted on the wetland layer 3;

[0066] The material of the wetland layer 3 is a mixture of red clay and fine sand in a mass ratio of 7:3.

[0067] 3. Method for treating PPCPs-type wastewater using an constructed wetland-bioelectric Fenton coupling system

[0068] 3.1. Titanium wires are used to connect the anode and cathode to form a closed circuit. The experiment is set with an applied voltage of 0.4V, and the system current is 2mA when stable. The initial pH of the wastewater is 8.5.

[0069] 3.2 PPCPs wastewater flows into the gravel layer 1 through inlet 8 for preliminary filtration; then, the wastewater undergoes anaerobic degradation treatment using the bio-anode carbon felt 2. The bio-electric Fenton system involves burying the bio-anode carbon felt 2 within the gravel layer 1 and wetland layer 3, while the floating Fenton cathode 5 is exposed to air, using oxygen as the electron acceptor. The wetland layer 3 and the upper wastewater 4 of the bio-electric Fenton system form a solid-liquid interface, thus creating both anaerobic and aerobic environments. During the anaerobic degradation treatment of the wastewater by the bio-anode carbon felt 2, the protons generated are transferred to the Fenton cathode 5 through the solid-liquid interface, while the electrons generated simultaneously reach the Fenton cathode 5 through an external circuit.

[0070] 3.3 The anaerobic wastewater flows into wetland layer 3, where the materials and microorganisms adsorb and degrade the organic pollutants in the wastewater.

[0071] 3.4. Wastewater passing through wetland layer 3 gradually overflows to form wastewater 4 above the wetland layer. The floating Fenton cathode 5 floats on the surface of the wastewater 4 above the wetland layer. The air-waterproof diffusion layer of the floating Fenton cathode 5 is placed facing the upper air of the constructed wetland system, and its function is to enrich a large amount of oxygen through full contact with the atmosphere. The heterogeneous Fenton catalytic layer is placed facing the wetland layer, and its function is to utilize the oxygen enriched by the diffusion layer above and the oxygen in the constructed wetland environment to catalyze the production of H2O2, which further reacts with Fe in the soil water environment of the constructed wetland. 2+ Heterogeneous reactions are carried out to generate hydroxyl radicals and to deeply remove organic matter from wastewater;

[0072] 3.4 The wastewater treated by the electro-Fenton flowed out through outlet 7.

[0073] Experimental Analysis

[0074] 1. To demonstrate the oxygen-enriching function of the floating electro-Fenton cathode, the experiment compared the constructed wetland-bioelectric Fenton system equipped with the floating electro-Fenton cathode with a conventional constructed wetland-bioelectric Fenton system. The results are as follows: Figure 3 (Where, constructed wetland-bioelectric Fenton systems with floating electric Fenton cathodes are represented by E-CW-MFC; constructed wetland-bioelectric Fenton systems are represented by CW-MFC). The results show that constructed wetland-bioelectric Fenton systems with floating electric Fenton cathodes contain higher dissolved oxygen, which is more conducive to the enhanced degradation of the cathode Fenton reaction.

[0075] 2. With an applied voltage of 0.4V, the effective area of ​​the floating Fenton cathode is 254 cm². 2 A constructed wetland-bioelectric Fenton coupling system was constructed with a 9cm distance between the anode and cathode. The composition and concentration of the influent were as follows: NH4Cl 0.07g / L, NaHCO3 1g / L, K2HPO4 0.03g / L, C6H... 12 O6 0.15g / L, CH3COONa 0.1g / L, trace elements 1mL / L, vitamins 1mL / L.

[0076] The initial pH of the system influent was 8.5, and the influent time was 12 hours. The concentrations of carbamazepine and 1,4-dioxane in the effluent were measured. Results are as follows: Figure 4 The artificial wetland-bioelectric Fenton coupling system of this embodiment achieved a removal rate of 65% for carbamazepine and a removal rate of 77% for 1,4-dioxane, indicating that the artificial wetland-bioelectric Fenton coupling system has a good removal effect on typical PPCPs.

[0077] 3. Under an applied current of 2 mA, with a 1 g / L sodium bicarbonate buffer solution as the electrolyte and an initial pH of 8.5, and using a carbon plate as the anode, the amount of H₂O₂ produced by the floating Fenton cathode under this current was investigated. The results are as follows: Figure 5 The yield of H2O2 was 0.33 mg / L after 60 min, indicating that the bio-carbon Fenton cathode has a high catalytic ability for the H2O2 generation reaction.

[0078] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An artificial wetland-bioelectric Fenton coupling system, characterized in that, The system comprises, from bottom to top, a gravel layer, a bio-anode carbon felt, a wetland layer, and a floating Fenton cathode; the floating Fenton cathode floats on the water surface above the wetland layer; the floating Fenton cathode includes, from top to bottom, an air-diffusing waterproof layer and a heterogeneous Fenton catalytic layer; the air-diffusing waterproof layer is exposed to the air; the heterogeneous Fenton catalytic layer faces downwards towards the wetland layer; The floating Fenton cathode is prepared by a method comprising the following steps: S1. A waterproof material emulsion is coated on one side of the gas diffusion layer substrate and sintered to form an air diffusion waterproof layer; S2. The carbon black catalyst and the binder perfluorosulfonic acid polymer solution are mixed and coated on the other side of the gas diffusion layer substrate to form a heterogeneous Fenton catalyst layer, thereby obtaining the electric Fenton cathode. S3. Fix a lightweight material around the electric Fenton cathode to make the electric Fenton cathode float on the water surface, thus obtaining a floating electric Fenton cathode. The gas diffusion layer substrate is selected from one or more of carbon paper, carbon cloth, and carbon black paper; In step S2, the perfluorosulfonic acid polymer solution is a Nafion solution; The mass-to-volume ratio of the carbon black catalyst to the perfluorosulfonic acid polymer solution is 1 mg:(4-8) μL; The bioanode carbon felt is a carbon felt enriched with microorganisms; The bio-anode carbon felt and floating electric Fenton cathode are connected to a power source via external wires. The power source and the resistor of the external circuit load are connected in parallel to form a bio-electric Fenton system.

2. The constructed wetland-bioelectric Fenton coupling system according to claim 1, characterized in that, In step S1, the waterproof material is selected from one or more of polytetrafluoroethylene, polyimide, polyetheretherketone, polyphenylene sulfide, polyethersulfone, and polyetherimide; And / or, the sintering temperature is 250-500℃.

3. The constructed wetland-bioelectric Fenton coupling system according to claim 1, characterized in that, In step S3, the lightweight material is plastic.

4. The constructed wetland-bioelectric Fenton coupling system according to claim 1, characterized in that, The wetland layer also includes phytoplankton.

5. The constructed wetland-bioelectric Fenton coupling system according to claim 1, characterized in that, The floating Fenton cathode is provided with an outlet above it; And / or, an inlet is provided below the gravel layer.

6. A method for wastewater treatment using the constructed wetland-bioelectric Fenton coupling system according to any one of claims 1-5, characterized in that, Includes the following steps: 1) Wastewater is first filtered through a gravel layer; then, it is treated by anaerobic degradation using a bio-anodized carbon felt. 2) The wastewater after anaerobic degradation flows into the wetland layer, where the materials and microorganisms in the wetland layer respectively intercept and degrade the organic pollutants in the wastewater; 3) The floating Fenton cathode floats on the surface of the wastewater on the wetland layer, and the heterogeneous Fenton catalytic layer catalyzes the heterogeneous reaction to generate hydroxyl radicals and remove organic matter from the wastewater.

7. The application of the constructed wetland-bioelectric Fenton coupling system according to any one of claims 1-5 in the treatment of PPCPs type wastewater.

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