A method for removing ammonia nitrogen by using microalgae coupled with a bio-electric wetland system

Abstract

The application belongs to the field of water environment treatment, and particularly relates to a method for removing ammonia nitrogen by using microalgae coupled with a biological electric wetland. The method specifically couples microalgae sewage treatment technology, electrochemical technology and wetland technology, uses microalgae and plant photosynthesis oxygen near the cathode to promote the conversion of ammonia nitrogen into nitrate nitrogen in the cathode area, and after the reduction of the nitrate nitrogen at the cathode, the remaining nitrate nitrogen flows into the anode chamber for anaerobic denitrification, so that efficient removal of ammonia nitrogen is realized. In addition, the system also has good removal effect on organic matter and phosphorus elements. Compared with the traditional denitrification process, the application has the advantages of saving aeration units, not producing sludge, simple operation, good treatment effect and the like, and has great application potential in the field of water environment treatment.

Description

Technical Field

[0001] This invention belongs to the field of water environment management, specifically relating to a method for removing ammonia nitrogen using a microalgae-coupled bioelectric wetland system. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Water environment degradation is a major concern in modern society. Currently popular nitrogen removal technologies mainly rely on bacterial nitrification and denitrification processes, which suffer from high energy and resource consumption. Moreover, this method is not suitable for natural water bodies with excessive nitrogen levels.

[0004] Constructed wetlands are a typical, cost-effective, and efficient water environment treatment technology. They simulate the structure and function of natural wetlands, utilizing the synergistic physical, chemical, and biological effects of the packing materials, aquatic plants, and microorganisms within the system. Through the physicochemical processes of the packing materials (interception, filtration, sedimentation, adsorption, absorption, ion exchange, and complexation reactions) and the absorption by plants and decomposition by microorganisms, wastewater is efficiently purified. Currently, constructed wetlands have become an important means of ecological restoration and wastewater treatment, and are a widely used wastewater treatment technology globally.

[0005] The compatibility of wetland electrochemical systems with the natural redox gradients existing vertically in constructed wetlands and microbial electrochemical systems has become a promising technology. Bioelectrochemical systems represent a novel low-energy / resource-consumption wastewater treatment model. Microbial electrochemical systems, without external energy input, use electrogenic microorganisms as catalysts to metabolically degrade organic pollutants in the environment, directly converting the chemical energy of organic matter into electrical energy. This achieves both efficient pollutant removal and power generation, representing a novel energy regeneration technology. Bioelectrochemical systems utilize electrochemically active microorganisms to oxidize organic matter and produce electrons, protons, and other metabolic products, demonstrating the potential for renewable energy production during wastewater treatment.

[0006] Patent CN110683648A discloses a wastewater denitrification system and method that couples a microbial fuel cell with an artificial wetland. Through the deep coupling of artificial wetland and microbial fuel cell technologies, organic matter is removed simultaneously, but its ammonia nitrogen removal efficiency still needs to be improved. Summary of the Invention

[0007] As described in the background section, existing denitrification processes suffer from high energy consumption and are unsuitable for natural water bodies. Traditional constructed wetlands have limited pollutant removal capabilities. To address these technical issues, this invention provides a method for removing ammonia nitrogen using a microalgae-coupled bioelectrochemical wetland system. This method establishes a microalgae-coupled bioelectrochemical wetland system by combining microalgae, a bioelectrochemical system, and a wetland system. It utilizes photosynthetic oxygen production by microalgae near the cathode to promote the oxidation of most NH4+ by ammonia-oxidizing and nitrite-oxidizing bacteria. + Converted to NO2 - and NO3 - The nitration reaction is completed, and at the same time, the organic matter is oxidized in the anode chamber, generating electrons that reach the cathode through an external circuit to react with NO2. - and NO3 - Denitrification is performed, and the remaining nitrate nitrogen flows into the anode chamber for removal through denitrification. This invention provides a novel method for ammonia nitrogen removal, and this system has significant potential for water purification.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A first aspect of the present invention provides a microalgae-coupled bioelectric wetland system, comprising: a vertical subsurface flow bioelectric wetland system;

[0010] The vertical subsurface flow bioelectric wetland system is a continuous subsurface flow constructed wetland system. The water flow direction is from top to bottom, and the wetland structure from bottom to top consists of an impermeable layer, a matrix layer, a water body layer, and wetland plants. The anode is located in the matrix layer, and the cathode is located in the near-water surface layer of the water body layer. A diaphragm is installed between the cathode chamber and the anode chamber, and the cathode and anode are electrically connected.

[0011] The cathode chamber is equipped with microalgae and aerobic sludge.

[0012] Microalgae are photosynthetic organisms with highly efficient nitrogen and phosphorus removal capabilities, offering significant advantages in wastewater treatment and enabling efficient pollutant removal. In microbial electrochemical systems, the oxygen produced by microalgae through photosynthesis can be used as an electron acceptor at the cathode to promote electrochemical reactions. In the cathode chamber, the photosynthetic oxygen production by microalgae promotes microbial activity. Combining microalgae with wetland electrochemical systems can further enhance pollutant removal capabilities.

[0013] Most of the NH4 in microalgal bioelectrowet systems + First, under aerobic conditions, ammonia-oxidizing bacteria and nitrite-oxidizing bacteria convert it into NO2. - and NO3 - This promotes the oxidative removal of ammonia nitrogen in the cathode chamber, while also partially removing NO2. - and NO3 - At the cathode, it acts as an electron acceptor and is reduced to N2. The remaining NO2...- NO3 - The ammonia nitrogen enters the anode chamber and is removed through denitrification and other processes. Organic compounds are removed by oxidation at the anode, releasing electrons that are then transferred to the cathode via an external circuit. The aforementioned ammonia nitrogen removal methods have great potential for application in the purification of wastewater and surface water.

[0014] In some embodiments, the impermeable layer includes: a clay impermeable layer and a concrete impermeable wall.

[0015] In some embodiments, the matrix layer mainly includes filler and soil.

[0016] In some embodiments, the filler is selected from at least one of fine sand, coarse sand, ceramsite, limestone, and clay.

[0017] In some implementations, the water body is sewage or a eutrophic natural water body.

[0018] In some embodiments, the cathode or anode material includes activated carbon particles, carbon felt, or carbon cloth. The cathode and anode are connected via an external circuit.

[0019] In some embodiments, the microalgae are green algae;

[0020] Preferably, the green algae include, but are not limited to, Chlorella and Scenedesmus. The algae grow near the cathode, forming an algae-bacteria system.

[0021] In some embodiments, the wetland plants are emergent plants with root growth, including but not limited to reeds, cattails, and canna lilies.

[0022] A second aspect of the present invention provides a method for removing ammonia nitrogen from the above-mentioned microalgae-coupled bioelectro-wetland system, comprising:

[0023] The aforementioned microalgae-coupled bioelectric wetland system was used to remove ammonia nitrogen from the water.

[0024] Specifically, a certain proportion of microalgae and aerobic sludge are added to the cathode of the vertical subsurface flow bioelectric wetland system. The oxygen production by microalgae photosynthesis and the nitrification by bacteria are used to oxidize the ammonia nitrogen in the influent into nitrate nitrogen. The nitrate nitrogen is first denitrified at the cathode and then enters the anode for denitrification removal.

[0025] A third aspect of the present invention provides the application of the above-described microalgae-coupled bioelectric wetland system in water treatment.

[0026] Beneficial effects of the present invention

[0027] (1) Based on the microalgae coupled bioelectric wetland system, this invention can not only absorb nitrogen through the growth of microalgae, but also fully couple the concentration and form of ammonia and the redox state of the system to complete the nitrification and denitrification process of nitrogen.

[0028] (2) This invention creates aerobic conditions in the cathode chamber using oxygen produced by microalgae photosynthesis, eliminating the need for mechanical aeration and reducing energy consumption. Compared to traditional denitrification processes, it is more energy-efficient and easier to operate.

[0029] (3) In addition to removing ammonia nitrogen, this invention also has a good removal effect on organic matter and phosphorus. Phosphorus can be removed by absorption by microalgae, and organic matter can be removed as an electron donor at the anode.

[0030] (4) In this invention, ammonia nitrogen is removed through microalgae absorption, cathode chamber nitrification, cathode denitrification and anode denitrification processes, resulting in high nitrogen removal efficiency.

[0031] (5) Compared with traditional denitrification processes, this system produces less sludge, reducing secondary pollution problems.

[0032] (6) The present invention can also generate electrical energy, which can be recycled or used for water quality testing. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 This is a schematic diagram of the microalgae-coupled bioelectric wetland system in Embodiment 1 of the present invention;

[0035] Figure 2 The nitrogen forms and concentrations in different regions of the microalgae-coupled bioelectric wetland system in Example 2 of this invention are shown.

[0036] Figure 3 The nitrogen forms and concentrations in different areas of the bioelectric wetland system in Example 3 of this invention are shown. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] Terminology Explanation:

[0039] The cathode chamber is the area above the membrane in the microalgae-coupled bioelectric wetland system;

[0040] The anode chamber is the area below the membrane in the microalgae-coupled bioelectric wetland system.

[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0042] In the following examples, all raw materials, organisms, plants, and devices are commercially available products.

[0043] Example 1

[0044] The microalgae-coupled bioelectric wetland system includes a cathode and an anode. The anode is located in the substrate layer of the constructed wetland, and the cathode is located in the near-water surface layer of the water body. The anode and cathode are connected by titanium wire and an external variable resistor. Microalgae are added to the cathode chamber, where photosynthesis produces oxygen that couples with the aerobic environment of the cathode chamber. The anode is located at the bottom layer to ensure a relatively anaerobic environment. To maintain the overall stability of the microalgae-coupled bioelectric wetland system, in this embodiment, the electrode materials of the bioelectric wetland are set as stable and low-cost materials such as carbon felt, activated carbon, and carbon cloth. The anode and cathode chambers are separated by glass wool, which is located in the middle of the wetland substrate layer.

[0045] Example 2

[0046] The microalgae-coupled bioelectric wetland system of Example 1 was used, wherein the reactor is cylindrical with a diameter of 300 mm and a height of 200 mm. From bottom to top, it consists of an impermeable layer, a matrix layer, a water layer, and wetland plants. The impermeable layer includes a clay impermeable layer and a concrete impermeable wall. The matrix layer includes filler, soil, and plant roots. The filler, from bottom to top, consists of coarse sand, fine sand, and clay, with each layer being approximately 50 mm thick. Both the anode and cathode are carbon felt, and the cathode and anode are connected to the external circuit via titanium wire.

[0047] The microalgae-coupled bioelectric wetland system was first acclimatized until a stable voltage was generated before experimentation. During the experimental phase, the reactor was shaded and the cathode and anode chambers were separated by a membrane. This process prevented the microalgae from disrupting the anaerobic environment in the anode chamber of the bioelectric wetland system, which could lead to unstable pollutant removal and consequently affect the removal of ammonia nitrogen by the microalgae in the bioelectric wetland system. Furthermore, microalgae (Chlorella vulgaris) and aerobic sludge were added to the cathode of the system, with a microalgae concentration of 0.2 g / L and an aerobic sludge concentration of 2 g / L. The microalgae and aerobic bacteria were added to the cathode at a volume ratio of 5:1. The constructed continuous subsurface flow microalgae-coupled bioelectric wetland system had a top-down water flow direction. Sweet flag (Acorus calamus) was selected as the wetland plant, with a plant density of 3 plants / m². 2 The hydraulic retention time is 24 hours, the light-to-dark ratio is 12 hours:12 hours, and the operating temperature is 25-30°C. The electrode material is set to carbon felt.

[0048] Figure 2This embodiment illustrates the nitrogen forms and concentrations in different areas of the microalgae-coupled bioelectromechanical wetland system. Test results show that after ammonia nitrogen enters the system, it is rapidly reduced from nearly 50 mg / L to approximately 22 mg / L through algal absorption and bacterial oxidation. Subsequent ammonia nitrogen is further removed at the anode, ultimately reducing the effluent ammonia nitrogen concentration to approximately 14 mg / L. In the cathode area, some nitrate nitrogen accumulates due to ammonia nitrogen oxidation. This nitrate nitrogen then enters the anode for denitrification, ultimately reducing the nitrate nitrogen level to less than 1 mg / L. Furthermore, this system also demonstrates good removal efficiency for phosphorus and organic matter.

[0049] Comparative Example 1

[0050] The difference from Example 2 is that no microalgae and aerobic sludge were added.

[0051] Figure 3 To illustrate the nitrogen forms and concentrations in different areas of this comparative microalgae-coupled bioelectric wetland system, in the control case of the bioelectric wetland system, due to the low dissolved oxygen concentration in the cathode area and the low ammonia nitrogen oxidation rate, the anode could not generate enough nitrate nitrogen for denitrification in the anode area. Therefore, the ammonia nitrogen removal efficiency of the bioelectric wetland system was low, and the effluent ammonia nitrogen concentration exceeded 30 mg / L.

[0052] Comparative Example 2

[0053] The difference from Example 2 is that no bioelectric wetland system was set up, and a pure algae and bacteria system (microalgae concentration of 0.2 g / L, aerobic sludge concentration of 2 g / L, and microalgae and aerobic bacteria added in a volume ratio of 5:1) was used for ammonia nitrogen removal.

[0054] Test results show that in a pure algae-bacteria system, due to algal photosynthesis, the dissolved oxygen concentration is high, the denitrification rate is low, nitrate nitrogen accumulates, and nitrogen cannot be removed quickly.

[0055] As can be seen from the comparison of Example 2, Comparative Examples 1 and 2, this application effectively improves the ammonia nitrogen removal rate by coupling microalgae with a bioelectric wetland system, and the microalgae and the bioelectric wetland system play a synergistic role in removing ammonia nitrogen.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microalgae-coupled bioelectric wetland system, characterized in that, include: Vertical subsurface flow bioelectric wetland system; The vertical subsurface flow bioelectric wetland system is a continuous subsurface flow constructed wetland system. The water flow direction is from top to bottom, and the wetland structure from bottom to top consists of an impermeable layer, a matrix layer, a water body layer, and wetland plants. The anode is located in the matrix layer, and the cathode is located in the near-water surface layer of the water body layer. A diaphragm is installed between the cathode chamber and the anode chamber, and the cathode and anode are electrically connected. The cathode chamber is equipped with microalgae and aerobic sludge; the microalgae are green algae. In microalgae-coupled bioelectric wetland systems, most NH4 + First, under aerobic conditions, ammonia-oxidizing bacteria and nitrite-oxidizing bacteria convert it into NO2. and NO3 This promotes the oxidative removal of ammonia nitrogen in the cathode chamber, while also partially removing NO2. and NO3 At the cathode, acting as an electron acceptor, it is reduced to N2; the remaining NO2... NO3 It enters the anode chamber and is removed by denitrification.

2. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The impermeable layer includes: a clay impermeable layer and a concrete impermeable wall.

3. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The matrix layer mainly includes filler and soil.

4. The microalgae-coupled bioelectric wetland system as described in claim 3, characterized in that, The filler is selected from at least one of fine sand, coarse sand, ceramsite, limestone, and clay.

5. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The water body is either sewage or a eutrophic natural water body.

6. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The cathode or anode materials include: activated carbon particles, carbon felt, and carbon cloth.

7. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The green algae include Chlorella and Scenedesmus.

8. The microalgae-coupled bioelectric wetland system as described in claim 1, characterized in that, The wetland plants are emergent plants with root growth, including reeds, cattails, and canna lilies.

9. A method for removing ammonia nitrogen, characterized in that, include: The ammonia nitrogen in the water body is removed by using the microalgae-coupled bioelectric wetland system as described in any one of claims 1-8.

10. The application of the microalgae-coupled bioelectric wetland system according to any one of claims 1-8 in water treatment.

Images