A biochar-based constructed wetland and method for nitrogen and phosphorus removal and antibiotic degradation

Abstract

The present application relates to sewage treatment technical field, especially for a kind of biochar-based constructed wetland and for nitrogen and phosphorus removal and antibiotic degradation method, including constructed wetland pool, wetland plant and water inlet pipeline and water outlet pipeline;Pool is filled with quartz sand, biochar and gravel three layers of substrate from top to bottom in turn;Wetland plant yellow flag iris is planted in quartz sand layer;Water inlet pipeline is connected with the upper water inlet end of pool body, and water outlet pipeline is connected with the lower water outlet end;When operating, wastewater containing sulfamethoxazole is pumped into pool body by peristaltic pump, and sequentially flows through each substrate layer, and hydraulic retention time is 3~7 days;The present application is designed by the three-layer substrate layer structure of "quartz sand-biochar-gravel", improves the removal rate of sulfamethoxazole and total nitrogen, reduces N2O and CH4 greenhouse gas emissions, and inhibits the generation of toxic degradation products.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a biochar-based constructed wetland and a method for nitrogen and phosphorus removal and antibiotic degradation. Background Technology

[0002] Constructed wetlands, as a green and ecological wastewater treatment technology, rely on the synergistic effects of plant absorption, substrate adsorption, and microbial degradation. They are widely used in domestic sewage, wastewater treatment plant effluent, and aquaculture wastewater, offering advantages such as low operating costs, ease of operation, and good ecological landscape effects. However, with the increasing environmental risks of emerging antibiotic pollutants, the removal efficiency of traditional constructed wetlands for typical antibiotics such as sulfamethoxazole has become a technical bottleneck restricting their widespread application. Sulfamethoxazole, due to its widespread use and low biodegradability, easily remains in water bodies for extended periods and induces the development of antibiotic resistance genes, posing a potential threat to ecological safety and human health.

[0003] In recent years, researchers have conducted extensive research to improve the treatment of antibiotic-containing wastewater. For example, Chinese invention patent application CN116143295A discloses a method for removing typical antibiotics from aquaculture wastewater using an artificial wetland system. This technology employs a multi-layered matrix structure (12 layers in total, including maifanite, biochar, small-particle-size zeolite, and large-particle-size zeolite layers) alternating with zeolite and biochar, combined with salt-tolerant plants such as tussock moss and an intermittent water influent process (influent-retention-drainage-idle-refluent), achieving the removal of sulfamethoxazole and florfenicol from aquaculture wastewater. This technology increases the contact area between wastewater and biochar through the multi-layered alternating structure, reducing biochar loss, and increases the dissolved oxygen content of the system through intermittent water influent, promoting microbial degradation.

[0004] Experimental data show that its removal rate of sulfamethoxazole is 28.85%~79.81%, with an average removal rate of 57.50%, which is insufficient to meet increasingly stringent effluent quality requirements. Furthermore, its complex matrix structure makes installation cumbersome. While the multi-layer structure (up to 12 layers) using alternating zeolite and biochar increases the contact area, it also brings problems of high construction difficulty and maintenance costs. The alternating laying of matrices with different particle sizes may lead to uneven water flow distribution, affecting long-term operational stability. Antibiotics may generate more toxic intermediate products during degradation; the evaluation index is based solely on the removal rate of the parent compound, without analyzing the types of degradation products and ecological risks, making it difficult to fully guarantee effluent safety. In the denitrification process, strong greenhouse gases such as nitrous oxide and methane are inevitably generated, and the emission of these greenhouse gases is not controlled.

[0005] In existing technologies, aeration, addition of external carbon sources, and multi-stage series connection are often used to improve nitrogen removal efficiency. However, these methods have problems such as increased energy consumption, complex operation processes, and easy secondary pollution. In order to promote the degradation and removal of antibiotics, the research has tried to add special fillers and functional bacterial agents, but these methods may face defects such as high preparation costs, poor long-term operational stability, and low integration with the original wetland ecology. Summary of the Invention

[0006] The purpose of this invention is to provide a biochar-based constructed wetland and a method for nitrogen and phosphorus removal and antibiotic degradation. It has a simple structure and stable operation, and can efficiently remove antibiotics while synergistically controlling greenhouse gas emissions and the generation of toxic degradation products.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a biochar-based constructed wetland, comprising:

[0009] An artificial wetland pond is filled with a substrate, which, from top to bottom, consists of a quartz sand substrate layer, a biochar substrate layer, and a gravel substrate layer. The substrate filling height satisfies the ratio of gravel substrate layer: biochar substrate layer: quartz sand substrate layer = (1~3):(4~6):(2~4). The substrate particle size satisfies the ratio of gravel substrate layer > biochar substrate layer > quartz sand substrate layer. The artificial wetland pond has an upper inlet and a lower outlet on its sidewalls.

[0010] The wetland plants, namely yellow iris, are planted in a quartz sand substrate layer at a planting density of 40-60 plants / m².

[0011] The water inlet pipe is connected to the water body to be treated on one side and to the upper water inlet of the artificial wetland pool on the other side.

[0012] The water outlet pipe is connected to the lower water outlet end.

[0013] Preferably, the particle size of the quartz sand matrix layer is 2-4 mm, the particle size of the biochar matrix is ​​6-10 mm, and the particle size of the gravel matrix is ​​10-20 mm.

[0014] Preferably, the planting density of the yellow iris is 50 plants / m².

[0015] Secondly, the present invention also provides a method for using biochar-based constructed wetlands for nitrogen and phosphorus removal and antibiotic degradation, comprising the following steps:

[0016] Step 1: Turn on the peristaltic pump to start the constructed wetland pond;

[0017] Step 2: The wastewater to be treated enters the constructed wetland pond through the inlet pipe, passing sequentially through the quartz sand matrix layer, the biochar matrix layer, and the gravel matrix layer;

[0018] Step 3: The treated water is discharged through the lower outlet and the outlet pipe, resulting in purified water.

[0019] Preferably, the artificial wetland pond operates in an intermittent flow mode with a hydraulic retention time of 3 to 7 days.

[0020] Preferably, the wastewater to be treated is effluent from a sewage treatment plant, aquaculture wastewater, or farmland wastewater.

[0021] Preferably, the wastewater to be treated contains sulfamethoxazole pollutant.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention achieves functional complementarity through a layered matrix design and proportion of "quartz sand-biochar-gravel". The upper layer of quartz sand has a small particle size and strong interception capacity, which can remove suspended particulate matter in the water first and avoid clogging of the biochar matrix pores; the middle layer of biochar is the core functional layer, whose rich pores and active functional groups can not only serve as a slow-release carbon source to accelerate nitrogen conversion, but also adsorb and catalyze the degradation of SMX, while removing phosphorus through surface group complexation; the lower layer of gravel has a large particle size, ensuring smooth water permeability and improving hydraulic conductivity.

[0024] 2. This invention further enhances the pollutant removal effect through the synergistic effect of iris and layered matrix.

[0025] 3. This invention requires no additional aeration, carbon source or microbial agent addition, has low operating energy consumption and controllable cost, and the biochar has a high degree of integration with the wetland environment and strong long-term operating stability.

[0026] 4. This invention improves the removal efficiency of nitrogen, phosphorus and sulfamethoxazole while reducing greenhouse gas emissions, and at the same time limits the generation of toxic degradation products of sulfamethoxazole, thereby improving the safety of effluent. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the biochar-based constructed wetland in this invention.

[0028] In the diagram: 1. Constructed wetland pond; 2. Wetland plants; 3. Inlet pipe; 4. Quartz sand matrix layer; 5. Biochar matrix layer; 6. Gravel matrix layer; 7. Upper inlet end; 8. Lower outlet end; 9. Peristaltic pump; 10. Outlet pipe. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: Construction of a bio-carbon-based constructed wetland

[0031] like Figure 1 As shown, a biochar-based constructed wetland includes a constructed wetland pool 1, wetland plants 2, an inlet pipe 3, and an outlet pipe 10. The constructed wetland pool 1 is a cylindrical pool with an inner diameter of 0.4m and a height of 1.2m. The substrate filling inside the constructed wetland pool 1 is divided into three layers:

[0032] Upper layer: 20cm high quartz sand (particle size 2~4mm) is filled as quartz sand matrix layer 4;

[0033] Middle layer: Biochar (particle size 6~10mm) with a height of 50cm is filled as biochar matrix layer 5;

[0034] Lower layer: Filled with gravel (10~20mm in diameter) to a height of 10cm, as gravel matrix layer 6.

[0035] The substrate filling height ratio is gravel substrate layer 6: biochar substrate layer 5: quartz sand substrate layer 4 = 1:5:2, and the particle size satisfies gravel substrate layer 6 > biochar substrate layer 5 > quartz sand substrate layer 4. The sidewalls of the constructed wetland pool 1 are equipped with an upper inlet end 7 and a lower outlet end 8.

[0036] Wetland plant 2 is yellow iris, planted in quartz sand substrate layer 4 at a planting density of 50 plants / m². Before transplanting, yellow iris seedlings with a height of 20-30 cm and uniform growth were selected and cultured in clean water for 7 days. After the root system has grown well, they were transplanted to artificial wetland pond 1.

[0037] One side of the inlet pipe 3 is connected to the water to be treated via a peristaltic pump 9, and the other side is connected to the upper inlet end 7; the outlet pipe 10 is connected to the lower outlet end 8, ensuring that the water to be treated is discharged after being processed through each matrix layer in sequence.

[0038] Example 2: Biochar-based constructed wetlands for nitrogen and phosphorus removal and antibiotic degradation

[0039] 1. Experimental setup

[0040] The biochar-based constructed wetland of Example 1 was used as the experimental group, and a control group was set up at the same time. The control group was a traditional gravel-based constructed wetland. The difference between the control group and the experimental group was that the middle layer of biochar was replaced with gravel of the same particle size (6~10 mm). The rest of the structure (20cm of quartz sand in the upper layer, 10cm of gravel in the lower layer, plant configuration, and pool size) was the same as the experimental group.

[0041] 2. Operating Method

[0042] The peristaltic pump 9 is turned on, and the water to be treated enters the constructed wetland tank 1 from the upper inlet 7 through the inlet pipe 3. The water is then treated through the quartz sand matrix layer 4, the biochar matrix layer 5 (the control group used a gravel matrix layer), and the gravel matrix layer 6. The treated water is discharged from the lower outlet 8, resulting in purified water. The constructed wetland operates in an intermittent flow mode, with a hydraulic retention time set to 72 hours.

[0043] 3. Influent water quality

[0044] The water body to be treated simulates the effluent from a wastewater treatment plant. The influent water quality indicators are: TN 22.45 mg / L, NH4+ + -N 7.82mg / L, NO3 - -N 13.56 mg / L, COD 21.58 mg / L, TP 1.17 mg / L. Sulfadiazine (SMX) was added to bring the SMX concentration in the influent to 201.8 μg / L.

[0045] 4. Sampling and Detection Methods

[0046] After the system is running stably, collect water samples from the inlet and outlet ends and measure the following indicators:

[0047] Standard water quality indicator: NH4 + -N, NO3 - -N, TN, TP, and COD should be measured in accordance with the "Methods for Monitoring and Analysis of Water and Wastewater" (Fourth Edition);

[0048] SMX concentration: determined by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS);

[0049] Greenhouse gas emissions: N2O and CH4 gases were detected using a static chamber-gas chromatography method with an Agilent GC8090 gas chromatograph.

[0050] Degradation product analysis: The effluent was detected and identified using a precision mass quadrupole time-of-flight mass spectrometer (Agilent 6540).

[0051] 5. Experimental Results

[0052] (1) Removal effect of conventional pollutants

[0053] The experimental results are shown in Table 1:

[0054] Table 1 Removal effect of conventional pollutants

[0055] The results showed that the experimental group of this invention had significantly better removal efficiency for conventional pollutants than the control group, especially in terms of TN removal rate and NO3 removal rate. - The -N removal rate indicates that the middle layer biochar matrix effectively enhances the denitrification process as a slow-release carbon source.

[0056] (2) Antibiotic SMX removal effect

[0057] The experimental results are shown in Table 2:

[0058] Table 2. Antibiotic SMX Removal Efficacy

[0059] The results showed that the SMX removal rate of the experimental group of this invention reached 85.70%, which was significantly higher than that of the control group (27.99%), proving that the introduction of biochar matrix layer 5 plays a key role in antibiotic removal.

[0060] (3) Greenhouse gas emissions

[0061] The results of greenhouse gas emission flux measurements are shown in Table 3:

[0062] Table 3 Average Greenhouse Gas Emission Flux

[0063] The results showed that the N2O emission flux in the experimental group of this invention was reduced by about 80% and the CH4 emission flux was reduced by about 40% compared with the control group, demonstrating that biochar matrix significantly reduced greenhouse gas emissions by optimizing carbon source supply and regulating microbial metabolism.

[0064] (4) Degradation product analysis

[0065] Seven degradation products were detected and five transformation pathways were deduced from the effluent from constructed wetlands. Pathways I-IV were common pathways, while degradation products present in pathway V were only detected in the control group constructed wetland. Compared to the two groups of constructed wetlands with different substrates, the control group showed a higher detection frequency of degradation products. SMX exhibited more degradation pathways in the control group, indicating that the addition of biochar not only promoted the adsorption and degradation of SMX by constructed wetlands but also limited some SMX degradation pathways to a certain extent, reducing the formation of toxic degradation products.

[0066] Pathway I: During the hydrogenation process, the NO bond of isoxazole is broken, forming the intermediate SMX.+ SMX + The second electron and two protons undergo hydrogenation to produce TP256. The breaking of the NO bond is one of the main pathways for the degradation of SMX in constructed wetlands with different substrates.

[0067] Pathway II: SMX undergoes hydroxylation via hydroxyl radical degradation, which further attacks the isoxazole ring C=C, followed by electrophilic substitution to generate TP288. The C atom on the aromatic ring of TP288 is further substituted by hydroxyl groups, and the reaction of the hydroxyl group with ortho-aniline yields TP274.

[0068] Pathway III: The sulfonyl SN bond of SMX is hydrolyzed and broken to produce 4-aniline sulfonic acid (TP173) and 3-amino-5-methylisoxazole (TP99). The amino groups on the two TP99 groups combine to form N=N to form TP193.

[0069] Pathway IV: The sulfonamide bond of SMX breaks to produce TP190.

[0070] Pathway V: Ammonia-oxidizing bacteria oxidize SMX to TP283, and the CS bond of the 4-nitro group on TP283 breaks to further form TP162 and TP139.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biochar-based constructed wetland, characterized in that, include: An artificial wetland pond (1) is filled with a matrix, which consists of a quartz sand matrix layer (4), a biochar matrix layer (5), and a gravel matrix layer (6) from top to bottom. The matrix filling height satisfies the ratio of gravel matrix layer (6): biochar matrix layer (5): quartz sand matrix layer (4) = (1~3): (4~6): (2~4). The matrix particle size satisfies the ratio of gravel matrix layer (6) > biochar matrix layer (5) > quartz sand matrix layer (4). The artificial wetland pond (1) has an upper water inlet (7) and a lower water outlet (8) on its sidewalls. Wetland plants (2), wherein the wetland plants (2) are yellow irises, planted in quartz sand substrate layer (4) at a planting density of 40~60 plants / m²; Water inlet pipe (3), one side of which is connected to the water body to be treated, and the other side is connected to the upper water inlet end (7) of the artificial wetland pool (1); Water outlet pipe (10) is connected to the lower water outlet end (8).

2. The biochar-based constructed wetland according to claim 1, characterized in that: The quartz sand matrix layer (4) has a particle size of 2-4 mm, the biochar matrix layer (5) has a particle size of 6-10 mm, and the gravel matrix layer (6) has a particle size of 10-20 mm.

3. The biochar-based constructed wetland according to claim 1, characterized in that: The planting density of the yellow iris is 50 plants / m².

4. A biochar-based constructed wetland and a method for nitrogen and phosphorus removal and antibiotic degradation according to any one of claims 1-3, characterized in that: Includes the following steps: Step 1: Turn on the peristaltic pump (9) to start the artificial wetland pond (1); Step 2: The wastewater to be treated enters the artificial wetland pool (1) through the inlet pipe (3), and passes through the quartz sand matrix layer (4), the biochar matrix layer (5) and the gravel matrix layer (7) in sequence. Step 3: The treated water is discharged through the lower outlet (8) and the outlet pipe (10) to obtain purified water.

5. The biochar-based constructed wetland and its method for nitrogen and phosphorus removal and antibiotic degradation according to claim 4, characterized in that: The artificial wetland pond (1) operates in an intermittent flow mode, with a hydraulic retention time of 3 to 7 days.

6. The biochar-based constructed wetland and its method for nitrogen and phosphorus removal and antibiotic degradation according to claim 4, characterized in that: The wastewater to be treated includes effluent from sewage treatment plants, aquaculture wastewater, and agricultural wastewater.

7. The biochar-based constructed wetland and its method for nitrogen and phosphorus removal and antibiotic degradation according to claim 6, characterized in that: The wastewater to be treated contains sulfamethoxazole contaminant.

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