A method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, combining algae and bacteria.

Abstract

This invention discloses a method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, involving the field of mining wastewater treatment technology. First, alkali is added to the strongly acidic rare earth tailings wastewater with an extremely low carbon-to-nitrogen ratio to recover residual rare earth elements. After settling, the supernatant is introduced into a microalgae raceway tank A. Algae and water are mixed using a bottom mixing propeller and then introduced into a microalgae circulation pipe to increase the light-receiving area and enhance microalgae photosynthesis. The effluent is then returned to microalgae raceway tanks A and B, with the flow rate in raceway tanks A and B controlled by varying the return flow rate. If the wastewater does not meet standards, the wastewater from raceway tank B is returned to raceway tank A for continued circulation. If the wastewater meets standards, it is introduced into a vertical flow sedimentation tank for sedimentation, and then the supernatant is introduced into a denitrification tank for further treatment. Once the standards are met, the wastewater is discharged. This invention utilizes microalgae photosynthesis to achieve the recycling and reuse of pollutants in rare earth tailings wastewater, representing an economical and environmentally friendly wastewater treatment method.

Description

Technical Field

[0001] This invention relates to a method for efficiently and cost-effectively treating rare earth tailings wastewater by coupling microalgal photosynthesis with bacterial denitrification, belonging to the field of mining wastewater treatment technology. Background Technology

[0002] Rare earth elements are known as the "industrial vitamins" and are widely used in electronic equipment, automobiles, aviation, energy, and other fields. my country is rich in rare earth minerals and has a relatively complete range of rare earth elements, with reserves accounting for about 23% of the world's total reserves. Among them, ion-adsorption rare earth deposits are mainly distributed in southern regions such as Ganzhou, Jiangxi (about 36%) and Longyan, Fujian. These rare earths are mostly attached to the ore in the form of ion-adsorption rare earths. The mining of these rare earths mainly uses the in-situ leaching method, which involves injecting a high-concentration ammonium sulfate solution into the rare earth mine to displace the rare earth ions through displacement. This is a simple and easy method, but over time, a large amount of ammonium sulfate remains in the mountains. After being washed by rainwater, it accumulates in the streams and groundwater around the mine, forming a large amount of rare earth mine tailings containing high levels of ammonia nitrogen. Therefore, there is an urgent need for a fast and effective method to treat this highly hazardous wastewater.

[0003] Conventional wastewater treatment methods, such as chemical oxidation or electro-oxidation, can only rapidly remove ammonia nitrogen while leaving high concentrations of nitrate nitrogen, resulting in low total inorganic nitrogen removal efficiency. Various adsorbents, such as zeolite and bamboo charcoal, have been proven to be highly efficient and rapid for removing ammonia nitrogen and nitrate nitrogen. However, high concentrations of impurity ions (such as SO42-) remain. 2- and C1 - This will interfere with and reduce the adsorption performance of the target ions. In particular, the two physicochemical methods mentioned above are usually very expensive and difficult to apply to large-volume rare earth wastewater.

[0004] However, for algae, wastewater with a low C / N ratio and high nitrogen content provides an excellent culture medium. Algae can absorb and assimilate nitrogen from the wastewater through photosynthesis, while simultaneously producing microalgal biomass as a biological resource for biofuel or high-value byproducts. Compared to the traditional activated sludge process, microalgae can tolerate and grow rapidly in harsh wastewater environments, enabling low-cost and high-efficiency treatment of rare earth tailings wastewater. Summary of the Invention

[0005] This invention proposes a combined algae and bacteria method using a photobioreactor coupled with a denitrification tank for treating rare earth tailings wastewater. The aim is to alleviate the technical problems of difficult treatment and high operating costs associated with low C / N ratio wastewater. By avoiding the traditional linear economic model of nitrification and denitrification, this method moves towards a circular economy model, utilizing pollutants for resource recovery, thereby achieving low-cost and high-efficiency treatment of rare earth tailings wastewater.

[0006] A method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, characterized by the following three steps in the wastewater treatment process:

[0007] Step 1: After the initial mixing of algae and water is completed in microalgae raceway pool A using a propeller, the mixture is introduced into the microalgae circulation pipe to increase the light-receiving area of ​​the microalgae and thus improve their photosynthetic efficiency. The effluent then flows to microalgae raceway pool A and microalgae raceway pool B respectively.

[0008] Step 2: Control the wastewater flow rate in microalgae raceway tanks A and B by varying the return flow rate. If the wastewater does not meet the standards, control the flow rate at 0.6 m / s to 1.2 m / s to improve the algae-water mixing rate; if the wastewater meets the standards, control the flow rate in microalgae raceway tank B to 0.2 m / s to 0.5 m / s to facilitate microalgae sedimentation, and discharge the supernatant into a vertical flow sedimentation tank.

[0009] Step 3: Utilizing the deep, light-proof characteristics of the vertical flow sedimentation tank, planktonic microalgae undergo a dark reaction, consuming a large amount of oxygen in the water and forming an anaerobic environment. Some microalgae decompose and release a large amount of COD, creating favorable conditions for subsequent denitrification until the effluent meets the standards.

[0010] The influent is alkaline rare earth tailings wastewater with a carbon-to-nitrogen ratio ranging from 0.18 to 0.58 and a pH range from 8.53 to 10.21.

[0011] The microalgae mentioned is a highly tolerant Chlorococcum robustum, which has the following characteristics: high activity in wastewater with low carbon-to-nitrogen ratio; significant photosynthesis during photoperiod, rapidly assimilating nutrients; and good sedimentation performance.

[0012] The microalgae circulation tube is composed of explosion-proof glass tubes with an inner diameter of 100mm, a left-right spacing of 400mm, and a top-bottom spacing of 300mm, which can maximize the efficiency of microalgae photosynthesis.

[0013] The flow rate control is achieved by controlling the amount of water entering and leaving the raceway pool per unit time.

[0014] In the vertical flow sedimentation tank, microalgae consume large amounts of oxygen and synthesize lipids intracellularly during the dark reaction. They gradually sink to the bottom of the tank and decompose under gravity, creating an anaerobic and carbon-containing environment.

[0015] The experiment was conducted outdoors under natural light conditions.

[0016] Compared with the prior art, the main features and beneficial effects of this invention are as follows:

[0017] (1) Effectively utilize microalgae photosynthesis to absorb nitrogen in rare earth tailings wastewater, avoid the traditional linear economic model of nitrification and denitrification, and move towards a circular economy by turning pollutants into resources, thereby achieving low-cost wastewater treatment.

[0018] (2) Microalgae treatment of low carbon-to-nitrogen ratio wastewater avoids aeration costs and carbon source addition costs, and during its growth process, it secretes a large amount of extracellular polymers (proteins, polysaccharides) that can be utilized by denitrifying bacteria.

[0019] (3) Microalgae respire in the dark, which can rapidly consume oxygen in the water and accumulate intracellular lipids. After lysis, they can increase the COD concentration in wastewater, providing a good environment for denitrifying bacteria. Attached Figure Description

[0020] Figure 1 Nitrogen removal efficiency of microalgae in the runway pool

[0021] Figure 2 The amount of microalgae growth in the runway pool (measured in chlorophyll content).

[0022] Figure 3 Changes in dissolved oxygen concentration in the raceway pool and vertical flow sedimentation tank

[0023] Figure 4 COD concentration in a vertical flow sedimentation tank

[0024] Figure 5 Flowchart of combined bacterial and algal treatment Detailed Implementation

[0025] This invention is based on the following idea: without adding additional agents or aeration, all ammonia nitrogen and some nitrate nitrogen in rare earth tailings wastewater are assimilated by the photosynthesis of highly tolerant microalgae, and then all nitrogen in the wastewater is removed by denitrification.

[0026] This invention provides a method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, involving the following three steps:

[0027] Step 1: After the initial mixing of algae and water is completed in microalgae raceway pool A using a propeller, the mixture is introduced into the microalgae circulation pipe to increase the light-receiving area of ​​the microalgae and thus improve their photosynthetic efficiency. The effluent then flows to microalgae raceway pool A and microalgae raceway pool B respectively.

[0028] Step 2: Control the wastewater flow rate in microalgae raceway tanks A and B by varying the return flow rate. If the wastewater does not meet the standards, control the flow rate at 0.6 m / s to 1.2 m / s to improve the algae-water mixing rate; if the wastewater meets the standards, control the flow rate in microalgae raceway tank B to 0.2 m / s to 0.5 m / s to facilitate microalgae sedimentation, and discharge the supernatant into a vertical flow sedimentation tank.

[0029] Step 3: Utilizing the deep, light-proof characteristics of the vertical flow sedimentation tank, planktonic microalgae undergo a dark reaction, consuming a large amount of oxygen in the water and forming an anaerobic environment. Some microalgae decompose and release a large amount of COD, creating favorable conditions for subsequent denitrification until the effluent meets the standards.

[0030] The type of microalgae raceway pool described in this invention is not specifically limited; it is an open raceway pool commonly used in microalgae cultivation processes.

[0031] The source of the rare earth tailings wastewater described in this invention is not specifically limited; any high-ammonia-nitrogen rare earth tailings wastewater requiring treatment can be used. In this example, the low carbon-to-nitrogen ratio wastewater used comes from the Ganzhou rare earth tailings wastewater treatment plant in Jiangxi Province (C / N=0.53, pH=8.53~10.21).

[0032] The algal strain described in this invention is a highly tolerant Chlorella vulgaris ( Chlorococcum robustum AY122332.1) has the following characteristics: it has high activity in wastewater with low carbon-to-nitrogen ratio; it exhibits significant photoperiodic photosynthesis and rapidly assimilates nutrients; and it has good sedimentation performance.

[0033] The microalgae circulation tube of this invention is composed of explosion-proof glass tubes with an inner diameter of 100mm, a left-right spacing of 400mm, and a top-bottom spacing of 300mm, which can maximize the photosynthetic efficiency of microalgae.

[0034] The flow rate control described in this invention is achieved by controlling the amount of water entering and leaving the raceway pool per unit time.

[0035] In the vertical flow sedimentation tank described in this invention, microalgae consume a large amount of oxygen and synthesize lipids intracellularly during the dark reaction, and gradually sink to the bottom of the tank. Under the action of gravity, they decompose, forming an anaerobic and carbon-containing environment.

[0036] The experiment described in this invention was conducted outdoors under natural light conditions.

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] The following results were obtained after implementing this embodiment:

[0039] Figure 1 This represents the nitrogen removal efficiency of microalgae in the raceway pool over two cycles. For example... Figure 1As shown, under ambient temperatures of 16.5℃ ~ 23.5℃ and pH of 8.2 ~ 10.75, the ammonia nitrogen (92.6 mg / L) removal rate from the influent to the standard (<15 mg / L) took 4.5 ~ 5.5 days, with an average ammonia nitrogen removal rate as high as 92.5%. The average denitrification rate of the reactor was 15.55 ± 1.43 mg / L, and the volumetric loading rate reached 3 g N / m³. 3 d.

[0040] Figure 2 This represents the growth rate of microalgae in the runway pool (expressed as chlorophyll). For example... Figure 2 As shown, the chlorophyll concentration can be divided into three stages during the 100-day experiment. Due to the good settling properties of the microalgae used in this experiment, the microalgae and wastewater were clearly separated in the early stage of reactor operation (1-25 days), making it impossible to measure the chlorophyll in the wastewater. As the reactor continued to operate, algal blooms gradually appeared in the reaction tank. In the next 45 days, the chlorophyll concentration in the tank increased from the initial 0.51 mg / L to 15.13 mg / L, and finally soared to 25.61 mg / L (25-70 days). However, due to the sudden drop in temperature, the suspended microalgae in the reactor rapidly decreased to 0 mg / L.

[0041] Figure 3 This shows the changes in dissolved oxygen concentration in the raceway pool and vertical flow sedimentation tank. For example... Figure 3 As shown, during one treatment cycle, the dissolved oxygen concentration in the wastewater gradually increased from 5.25 mg / L at the time of influent to 16.52 mg / L (0~4 days), indicating a supersaturated state. Within 1.5 days after being introduced into the vertical flow sedimentation tank, the dissolved oxygen in the wastewater was rapidly consumed until it approached zero.

[0042] Figure 4 Changes in COD concentration in a vertical flow sedimentation tank, such as Figure 4 As shown, during one treatment cycle, due to the extracellular polymers secreted by microalgae, the COD concentration in the wastewater gradually increased from 18.54 mg / L at the influent to 42.87 mg / L, and continued to increase after being introduced into the vertical flow sedimentation tank. Under the influence of the dark environment and water pressure, the microalgae gradually lysed. With the outflow of intracellular lipids and proteins, the COD concentration in the wastewater increased to 68.22 mg / L, a year-on-year increase of 59.1%.

[0043] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for treating rare earth tailing wastewater by algae-bacteria combination of photobioreactor coupled denitrification tank, characterized in that, The method comprises the following three steps: Step 1: After the initial mixing of algae and water is completed in microalgae raceway pool A using a propeller, the mixture is introduced into the microalgae circulation pipe to increase the light-receiving area of ​​the microalgae and thus improve their photosynthetic efficiency. The effluent then flows to microalgae raceway pool A and microalgae raceway pool B respectively. Step 2: Control the wastewater flow rate in microalgae raceway tanks A and B by varying the return flow rate. If the wastewater does not meet the standards, control the flow rate between 0.6 m / s and 1.2 m / s to improve the algae-water mixing rate. If the wastewater meets the standards, control the flow rate in microalgae raceway tank B to 0.2 m / s to 0.5 m / s to facilitate microalgae sedimentation. The supernatant is then discharged into a vertical flow sedimentation tank. Step 3: Utilizing the deep, light-proof characteristics of the vertical flow sedimentation tank, planktonic microalgae undergo a dark reaction, consuming a large amount of oxygen in the water and forming an anaerobic environment. Some microalgae decompose and release a large amount of COD, creating favorable conditions for subsequent denitrification until the effluent meets the standards. The influent in step one is alkaline rare earth tailings wastewater with a carbon-to-nitrogen ratio ranging from 0.18 to 0.58 and a pH range of 8.53 to 10.

21. The microalgae selected in step one is highly tolerant Chlorella vulgaris, which has the following characteristics: high activity in wastewater with low carbon-to-nitrogen ratio; significant photosynthesis during photoperiod, rapidly assimilating nutrients; and good sedimentation performance.

2. The algal-bacterial combined method of processing rare earth tailing wastewater by using a photobioreactor-coupled denitrification tank according to claim 1, characterized in that, The microalgae circulation tube in step one is composed of explosion-proof glass tubes with an inner diameter of 100mm, a left-right spacing of 400mm, and a top-bottom spacing of 300mm, which can maximize the efficiency of microalgae photosynthesis.

3. The method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, as described in claim 1, is characterized in that... In step two, the flow rate control is achieved by controlling the amount of water entering and leaving the raceway pool per unit time.

4. The method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, as described in claim 1, is characterized in that... In step three, the microalgae consume a large amount of oxygen and synthesize lipids intracellularly during the dark reaction, and gradually sink to the bottom of the pool. Under the action of gravity, they decompose, creating an anaerobic and carbon-containing environment.

5. The method for treating rare earth tailings wastewater using a photobioreactor coupled with a denitrification tank, as described in claim 1, is characterized in that... The method is performed outdoors under natural light conditions.

Images