A method for emptying and injecting arsenite removal in a subsurface flow constructed wetland enhanced by 2-line ferrihydrite particles

Abstract

The present invention belongs to the field of environmental protection and relates to a method for enhancing arsenic removal in a subsurface flow constructed wetland by evacuating and injecting 2-line ferrihydrite particles, which is mainly applied to efficiently and stably remove arsenic in a subsurface flow constructed wetland. Aiming at the defects of low arsenic adsorption capacity and easy adsorption saturation of conventional wetland fillers, as well as the arsenic desorption problem caused by arsenic reduction under anaerobic conditions, the present invention uses the evacuation and injection method to introduce 2-line ferrihydrite particles into the gaps of wetland fillers to achieve efficient and stable arsenic removal. The present invention also discovers the rule of controlling 2-line ferrihydrite particles by using the NaOH addition rate and stirring time, and prepares 2-line ferrihydrite particles with specific particle size specifications. The evacuation and injection method has the advantages of uniform particle introduction distribution, short time consumption, strong operability, etc. The present invention effectively enhances the arsenic removal efficiency of the subsurface flow constructed wetland, is applicable to treating arsenic-containing groundwater, river and lake water, industrial wastewater, etc., and controls the health hazards of the ecological environment caused by arsenic pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and particularly relates to a method for enhancing arsenic removal in a subsurface flow constructed wetland by evacuating and injecting goethite nanoparticles. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and is not necessarily to be regarded as an admission or any form of implication that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Heavy metals are highly toxic and not easily degraded in the environment. They can affect the ecological environment of aquatic animals and plants in the receiving water body. Along with the enrichment of the food chain, organisms will show symptoms of being harmed, resulting in developmental arrest or even death, causing damage to the structure and function of the ecosystem, and posing a potential threat to human health.

[0004] The subsurface flow constructed wetland is an ecological treatment technology that simulates natural processes to achieve wastewater purification. It mainly uses the synergistic effect of "plants - substrates - microorganisms" to remove pollutants in wastewater, and has the characteristics of low construction and operation costs, easy maintenance, convenient operation and management, and taking into account the landscape effect. Its application and scale in China are becoming more and more extensive.

[0005] In the subsurface flow constructed wetland system, the substrate provides a good attachment carrier for microorganisms and can adsorb pollutants in water. However, due to the defects of conventional fillers such as gravel and coarse sand, which have low arsenic adsorption capacity and are easily saturated by adsorption, and the problem of re - release caused by arsenic reduction under anaerobic conditions in the subsurface flow constructed wetland, the sustainable arsenic removal effect of the constructed wetland system is poor. At present, the method of directly adding adsorptive nanoparticles to the wetland to improve the arsenic removal effect has difficulties in controlling the particle size of the nanoparticles. Large - particle - size nanoparticles are easily blocked in the wetland system, and small - particle - size nanoparticles are not easily fixed in the gaps of the wetland substrate; it is difficult for the nanoparticles to be evenly distributed in the wetland system. Uneven distribution is easy to cause blockage, and local uneven distribution affects the overall function of the wetland system. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a method for enhancing arsenic removal in a subsurface flow constructed wetland by evacuating and injecting goethite nanoparticles, which improves the sustainable arsenic removal efficiency of the wetland system.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect of the present invention, there is provided a method for enhancing arsenic removal in a subsurface flow constructed wetland by evacuating and injecting goethite nanoparticles, including:

[0009] Preparing goethite nanoparticles by using Fe(NO3)3·9H2O solution and NaOH solution;

[0010] Collect 2-line ferrihydrite particles with a particle size range of 10 - 50 μm, freeze-dry them, and prepare a suspension containing 2-line ferrihydrite particles.

[0011] Empty the water in the subsurface flow wetland, inject the suspension containing 2-line ferrihydrite particles into the wetland system, fill the interstitial space of the wetland filler with the suspension until it is full, and complete the injection within 2 - 3 hours.

[0012] After the 2-line ferrihydrite particles enter the wetland system, let it stand for 6 - 10 hours to uniformly fix them in the interstitial space of the wetland filler, and then operate normally.

[0013] The present invention uses the evacuation and injection method to introduce 2-line ferrihydrite particles into the subsurface flow constructed wetland system. The 2-line ferrihydrite particles have a high arsenic adsorption capacity and strong adsorption stability, which helps to improve the arsenic adsorption capacity of the wetland matrix and control the arsenic desorption caused by arsenic reduction. The present invention also discovers the rule of controlling 2-line ferrihydrite particles by using the NaOH addition rate and stirring time, and prepares 2-line ferrihydrite particles with specific particle size specifications. The evacuation and injection method has the advantages of uniform particle distribution, short time consumption, and strong operability. The present invention effectively enhances the arsenic removal efficiency of the subsurface flow constructed wetland, is suitable for treating arsenic-contaminated groundwater, river and lake water, sewage treatment plant effluent, industrial wastewater, etc., and controls the ecological and environmental health hazards caused by arsenic pollution.

[0014] In the second aspect of the present invention, there is provided the above-prepared enhanced subsurface flow constructed wetland.

[0015] In the third aspect of the present invention, there is provided the application of the above enhanced subsurface flow constructed wetland in arsenic removal.

[0016] Advantages of the present invention

[0017] (1) Conventional subsurface flow constructed wetlands for arsenic removal have the defects of low arsenic adsorption capacity of the filler and easy adsorption saturation, as well as the problem of poor adsorption stability caused by arsenic reduction and arsenic desorption in the anaerobic environment of the subsurface flow wetland. The present invention uses the evacuation and injection method to introduce 2-line ferrihydrite particles into the subsurface flow wetland system. The 2-line ferrihydrite particles have a high arsenic adsorption capacity and strong adsorption stability, which helps to improve the arsenic adsorption capacity of the wetland matrix and control the arsenic desorption caused by arsenic reduction. The present invention also discovers the rule of controlling 2-line ferrihydrite particles by using the NaOH addition rate and stirring time, and prepares 2-line ferrihydrite particles with specific particle size specifications. Introducing 2-line ferrihydrite particles into the interstitial space of the wetland filler by the evacuation and injection method has the advantages of uniform particle distribution, short time consumption, and strong operability. The present invention effectively enhances the arsenic removal efficiency of the subsurface flow wetland, is suitable for treating arsenic-contaminated groundwater, river and lake water, sewage treatment plant effluent, industrial wastewater, etc., and controls the ecological and environmental health hazards caused by arsenic pollution.

[0018] (2) The method of the present invention is simple, highly practical, and easy to promote. Description of the Drawings

[0019] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] Figure 1 It is a schematic flow chart of the preparation and introduction of goethite nanoparticles with two wires into the subsurface flow wetland of the present invention.

[0021] Figure 2 It is the adsorption isotherm of arsenic by different filler particle sizes and goethite nanoparticles with two wires in Example 1 of the present invention.

[0022] Figure 3 It is a comparison chart of arsenic removal by the subsurface flow constructed wetland system with or without the introduction of goethite nanoparticles with two wires of the present invention. Detailed Description of the Invention

[0023] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0024] A method for emptying and injecting goethite nanoparticles with two wires to enhance arsenic removal in a subsurface flow constructed wetland, which is mainly applied to efficiently and stably remove arsenic in a subsurface flow constructed wetland. The law of controlling goethite nanoparticles with two wires by using the NaOH addition rate and stirring time is discovered. Goethite nanoparticles with specific particle size specifications are prepared, and the goethite nanoparticles with two wires are introduced into the wetland filler gaps by the emptying and injection method. The goethite nanoparticles with two wires have a high arsenic adsorption capacity and strong adsorption stability, which can improve the arsenic adsorption capacity of the wetland matrix and control the arsenic desorption caused by arsenic reduction. Introducing the goethite nanoparticles with two wires into the wetland filler gaps by the emptying and injection method has the advantages of uniform particle distribution, short time consumption, strong operability, etc., ensuring the efficient and stable removal of arsenic in the subsurface flow constructed wetland.

[0025] The arsenic removal method of the present invention is applicable to treating arsenic-contaminated groundwater, river and lake water, sewage treatment plant effluent, industrial wastewater, etc., to avoid the health hazards of the ecological environment caused by arsenic pollution.

[0026] In some embodiments, for the preparation of 2-line ferrihydrite microparticles, a 0.1-1M Fe(NO3)3·9H2O solution is prepared and stirred at 100-300 r / min. Meanwhile, a 1M NaOH solution is added to the Fe(NO3)3·9H2O solution per cubic meter at a rate of 1-10 L / min, and the pH is adjusted to about 7.5. Stirring is continued for 5-10 minutes. According to the technical principle that the particle size is positively correlated with the NaOH addition rate and stirring time, the particle size of the 2-line ferrihydrite microparticles is adjusted by controlling the NaOH addition rate and stirring time.

[0027] In some embodiments, the 2-line ferrihydrite microparticle suspension is repeatedly sieved and washed 2-3 times using 250-mesh and 1250-mesh sieves, and 2-line ferrihydrite microparticles with a particle size range of 10-50 μm are collected.

[0028] In some embodiments, the prepared 2-line ferrihydrite microparticles are freeze-dried and stored in a low-temperature environment at 4°C, and used within 3 months after preparation to avoid structural deformation and affect the application effect.

[0029] In some embodiments, before injecting the 2-line ferrihydrite microparticles into the subsurface flow constructed wetland system, the water in the subsurface wetland needs to be drained to allow the microparticles to be fixed in the gaps of the wetland filler through sedimentation and adsorption.

[0030] In some embodiments, the concentration of the 2-line ferrihydrite microparticle suspension is calculated based on the dynamic adsorption amount of arsenic by the 2-line ferrihydrite microparticles and the demand for arsenic removal, and the preferred concentration range is between 5-50 g / L.

[0031] In some embodiments, a suspension containing 2-line ferrihydrite microparticles is prepared and injected into the wetland system through an inlet pipe until the suspension fills the gaps of the subsurface wetland filler, and the injection is completed within 2 hours.

[0032] In some embodiments, after the 2-line ferrihydrite microparticles enter the wetland system, they are left standing for 6-10 hours to be uniformly fixed in the gaps of the wetland filler, and then the system can operate normally.

[0033] In some embodiments, 2-line ferrihydrite microparticles with particle sizes of 10-20 μm, 20-35 μm, and 35-50 μm are respectively selected according to different wetland filler particle sizes of 1-3 cm, 4-6 cm, and 7-10 cm to better load the 2-line ferrihydrite microparticles in the gaps of the wetland filler and improve the uniformity and stability of the loading.

[0034] The following combines specific embodiments to further elaborate on the present invention. It should be noted that the specific embodiments are explanations rather than limitations of the present invention.

[0035] Example 1:

[0036] Construct a subsurface flow wetland system with a wetland substrate depth of 0.6 m, filled with three 20-cm-thick base layers, including 0-20 cm of coarse gravel (diameter 7-10 mm), 20-40 cm of medium gravel (diameter 4-6 mm), and 40-60 cm of fine gravel (diameter 1-3 mm). The arrangement of the substrate is designed to promote the uniform distribution of 2-line ferrihydrite particles in the wetland bed substrate. By introducing 10 g / L of 10-20 μm 2-line ferrihydrite particles into the subsurface flow wetland system using the evacuation injection method, they are evenly distributed in the gaps between the wetland fillers. In the wetland, reeds are planted at a density of 10 plants / m 2 . When the system stabilizes, arsenic-containing wastewater is injected into the wetland system through the inlet device, passing through the wetland substrate from top to bottom, and the purified water is discharged through the drainage device.

[0037] From Figure 2 the adsorption isotherms of arsenic by different filler particle sizes and 2-line ferrihydrite particles, it can be seen that the adsorption capacity of traditional gravel is low and it is easy to reach adsorption saturation, while 2-line ferrihydrite particles have a higher adsorption capacity.

[0038] Example 2:

[0039] A method for enhancing arsenic removal in a subsurface flow constructed wetland by evacuating and injecting 2-line ferrihydrite particles. Construct a subsurface flow constructed wetland system with a wetland substrate depth of 0.6 m, filled with coarse gravel (diameter 4-6 mm; porosity 38%). 10 g / L of 20-35 μm 2-line ferrihydrite particles are introduced into the subsurface flow constructed wetland system using the evacuation injection method to form uniformly distributed 2-line ferrihydrite particles in the wetland system. Reeds are planted in the wetland at a density of 20 plants / m 2 . Through the inlet device, wastewater containing heavy metal As is injected into the wetland system. As can be seen from Figure 3 (B), after 300 days, the concentration of As in the effluent is 37.1 ± 2.41 μg / L, and the average removal rate of As by the subsurface flow constructed wetland system is 70%. In the wetland artificial system (A) without adding 2-line ferrihydrite particles, the concentration of As is much higher than the influent because after the substrate adsorption reaches saturation, As is released back into the water body again, causing secondary pollution to the water body.

[0040] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for emptying and injecting 2-line ferrihydrite particles to enhance arsenic removal in a subsurface flow constructed wetland, characterized in that, Comprising: Preparing 2-line ferrihydrite particles using a Fe(NO3)3·9H2O solution and a NaOH solution; Collecting 2-line ferrihydrite particles with a particle size range of 10 - 50 μm, freeze-drying them, and preparing a suspension containing the 2-line ferrihydrite particles; Emptying the water in the subsurface flow wetland, injecting the suspension containing the 2-line ferrihydrite particles into the wetland system until the interstitial spaces of the subsurface flow wetland filler are filled, and completing the injection within 2 - 3 hours; After the 2-line ferrihydrite particles enter the wetland system, let it stand for 6 - 10 hours to uniformly fix them in the interstitial spaces of the wetland filler, and then operate normally; Selecting 2-line ferrihydrite particles with particle sizes of 10 - 20 μm, 20 - 35 μm, and 35 - 50 μm according to different wetland filler particle sizes of 1 - 3 cm, 4 - 6 cm, and 7 - 10 cm respectively; The method for preparing 2-line ferrihydrite particles includes: preparing a 0.1 - 1M Fe(NO3)3·9H2O solution, stirring at 100 - 300 r / min, and simultaneously adding a 1M NaOH solution to the Fe(NO3)3·9H2O solution per cubic meter at a rate of 1 - 10 L / min, adjusting the pH to 7.5, and continuing to stir for 5 - 10 minutes; Adjusting the particle size of the 2-line ferrihydrite particles by controlling the addition rate of NaOH and the stirring time.

2. The method for arsenic removal from subsurface flow constructed wetland enhanced by goethite particles with evacuation injection 2-line as claimed in claim 1, wherein, Repeatedly sieving and washing the 2-line ferrihydrite particle suspension 2 - 3 times.

3. The method for removing arsenic from subsurface flow constructed wetland enhanced by goethite particles with evacuation injection 2-line as claimed in claim 1, wherein, After freeze-drying, the 2-line ferrihydrite particles are stored in a low-temperature environment of 4 - 5°C and used within 3 months after preparation.

4. The method for arsenic removal from horizontal subsurface flow constructed wetland enhanced by goethite particles with evacuation injection 2-line as claimed in claim 1, wherein The concentration range of the suspension containing the 2-line ferrihydrite particles is between 5 - 50 g / L.

5. The method for removing arsenic by evacuating and injecting 2-line ferrihydrite particles to strengthen the subsurface flow constructed wetland according to claim 1, characterized in that, The depth of the wetland substrate is 0.6 m, filled with 3 base layers with a depth of 20 cm each, including coarse gravel with a diameter of 7 - 10 mm in the range of 0 - 20 cm, medium gravel with a diameter of 4 - 6 mm in the range of 20 - 40 cm, and fine gravel with a diameter of 1 - 3 mm in the range of 40 - 60 cm; Or, the depth of the wetland substrate is 0.6 m, filled with coarse gravel with a diameter of 4 - 6 mm and a porosity of 38%.

6. A subsurface flow constructed wetland enhanced with 2-line ferrihydrite particles prepared by the method of evacuating and injecting 2-line ferrihydrite particles for arsenic removal according to any one of claims 1 - 5.

7. The application of the subsurface flow constructed wetland enhanced as claimed in claim 6 in arsenic removal.

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