Pollution and carbon reduction method for rare earth ammonia nitrogen wastewater by utilizing microalgae closed reaction

Abstract

The invention discloses a method for reducing pollution and carbon in rare earth ammonia-nitrogen wastewater by utilizing a microalgae closed reaction. The method comprises the following steps: preparing an ammonia-nitrogen wastewater culture medium, inoculating microalgae, pressurizing CO2 in a reactor, regulating and controlling culture and monitoring and harvesting. According to the invention, the waste gas CO2 discharged in the rare earth production process can be effectively utilized, a cheap carbon source is provided for an ammonia nitrogen biological removal system, meanwhile, carbon reduction and decontamination are realized, and the defect that in the current technical scheme, the biological removal of ammonia nitrogen needs to additionally provide commercial carbon nutrition for the system is overcome; the reactor runs under the micro-positive pressure condition, CO2 gas mass transfer is enhanced, a sufficient carbon source is provided for microalgae growth, system escape of ammonia nitrogen and CO2 is avoided, and the defects that in the current technical scheme, the ammonia nitrogen recycling effect is poor, and ammonia nitrogen escapes are overcome.

Description

Technical Field

[0001] The invention relates to the technical field of mining area pollution control, and in particular to a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater by utilizing a closed reaction of microalgae. Background Art

[0002] According to the Carbon Emission Database (CEADs), China's nonferrous metal industry carbon emissions have increased sharply in the past two decades and then gradually stabilized, with total emissions remaining high. Taking rare earth metals as an example, the process of extracting mixed rare earths from bastnaesite releases a large amount of CO 2 .

[0003] In addition, in-situ leaching technology is widely used in ionic rare earth mining. The leaching agent ammonium sulfate solution is directly injected into the ore body through a shallow well. As the injection time goes by, the leaching mother liquor seeps out at the bedrock position at the bottom of the mountain and is drained to the collection pool through the ditch. It can be seen that the mining of ionic rare earth mines produces a large amount of ammonia nitrogen wastewater containing rare earth elements. The ammonia nitrogen concentration in the wastewater reaches 100-5000 mg / L, far exceeding the national emission standards. If discharged directly without treatment, rare earth wastewater will cause serious pollution to the environment and ecosystem. The traditional treatment methods for rare earth ammonia nitrogen wastewater include air stripping, evaporation concentration crystallization, chemical precipitation, breakpoint chlorination, electroosmosis and ion exchange.

[0004] Those skilled in the art have conducted research and improvement on this basis, and the relevant patented technical solutions are as follows:

[0005] 1. Patent application No. 202410608265.3 is a spirulina cultivation method for treating rare earth wastewater. The key technology of this method lies in the symbiotic cultivation of spirulina and lactic acid bacteria, but its disadvantages are: ① The removed ammonia nitrogen is not effectively recycled, and the high pH (9-11) causes the ammonia nitrogen to escape without adsorption recovery; ② The wastewater is used as a culture medium for the symbiotic cultivation of spirulina and lactic acid bacteria, and a large amount of organic nutrients such as milk and soy milk need to be added to the wastewater, which not only makes the culture medium expensive, but also brings a high risk of pollution; ③ The cultivation of spirulina requires the regular addition of 0.001-0.004 g / L of sodium bicarbonate to the culture pool to maintain the pH value of the culture medium and the balance of nutrients. This operation causes the system to have CO 2 Emission risks;

[0006] 2. Patent application number 202410725504.3 is a method for degrading ammonia nitrogen in rare earth mine wastewater and recovering rare earth elements. This technology uses hydrogen oxidizing bacteria to convert ammonia nitrogen into protein and enrich rare earth elements. However, its disadvantages are: ① The system needs to be fed with mixed gas CO 2 , O 2 and H 2 , H 2The gas produced in the production process of non-rare earths is flammable, explosive and costly. 2. The basic culture medium needs to use organic carbon source glucose, which is costly and susceptible to bacterial contamination. 3. The reactor uses a blue-mouth bottle, and each gas replenishment operation consumes a lot of gas, causing CO 2 Large amounts of emissions and waste of hydrogen resources;

[0007] 3. Patent application number 201911034158.X is a method for treating rare earth wastewater by using microorganisms in large-scale outdoor pools. This technology integrates microalgae into traditional wastewater treatment processes and uses microalgae to absorb CO 2 It is converted into biomass, thus providing organic nutrition for subsequent nitrification and denitrification microorganisms. However, its disadvantages are: ① wastewater resources are not utilized as resources; ② CO in the air 2 It may not be enough to support the carbon source nutrition of microalgae, and additional lime water or bicarbonate is added to the system;

[0008] 4. Patent application number 202310924489.0, a citrobacter and its application in the in-situ purification of ammonia nitrogen wastewater in rare earth mines. This technology uses a newly screened citrobacter to purify ammonia nitrogen wastewater in-situ in rare earth mines. The bacterium can tolerate high concentrations of ammonia nitrogen, has a certain ammonia nitrogen treatment capacity, has low requirements for dissolved oxygen in the environment, and has high temperature adaptability. However, its disadvantage is that this method relies on the change of microbial colonies in the mine, and long-term operation is uncertain;

[0009] 5. Patent application number 202310502865.7 is an ecological restoration method for ionic rare earth mines based on microalgae cultivation and re-injection. This technology uses the solution of ionic rare earth tailings leachate with pH value and phosphate concentration adjusted as a culture medium to cultivate microalgae, and then returns the cultured algae solution to the mine injection well for continued use. However, its disadvantage is that the system uses an open biochemical runway pool, and ammonia nitrogen escapes;

[0010] 6. Patent application number 202211525100.7 is a coupled reactor and method for treating rare earth mine tailwater using microalgae. This technology uses a racetrack photoreactor to cultivate microalgae instead of the traditional activated sludge method to treat ammonia nitrogen in rare earth mine wastewater. This patent uses a coupled reactor to treat rare earth mine tailwater with high ammonia nitrogen using microalgae, which also proves the feasibility of using microalgae to treat high ammonia nitrogen mine wastewater. However, its disadvantages are: it is unclear whether the racetrack photoreactor described in the patent document is closed. The S-type racetrack photoreactor is designed with an air inlet at the entrance and an indirect aeration device in the middle of the box. The reactor has a low recovery rate of ammonia in the wastewater and a low gas CO 2 The utilization rate is unknown.

[0011] In addition, related academic papers also involve the treatment of rare earth ammonia nitrogen wastewater:

[0012] 1. CO Fixation by Microalgae 2 In the literature, a new closed raceway pool photobioreactor was disclosed. Compared with the traditional open raceway pool, the microalgae yield was increased by 41%, with high CO 2 The reactor established in the literature is a traditional open raceway pool culture system with a "lid" added to it. The gas-liquid-lid in some areas (enclosed areas) are in direct contact with each other to change the CO 2 The path of the bubbles increases the CO 2 Residence time, the closed bioreactor designed in this document has a closed area connected to a stirred open area, and the entire reactor is connected to atmospheric pressure, CO 2 The dissolution promotion is mainly achieved by extending the gas path, increasing the gas-liquid contact time, and increasing CO 2 residence time, thereby increasing CO 2 The design principle changes the gas flow path of the traditional column reactor from vertical to horizontal along the runway, which belongs to the category of pipeline reactor. The reactor designed in the literature is suitable for CO 2 Low supply flow, if CO 2 Even with high supply, there is still obvious escape. Even with low supply flow, the system carbon fixation efficiency is less than 64%. If the gas flow rate is further reduced, CO 2 The carbon fixation efficiency will decrease with the increase of gas flow rate. In order to meet the growth needs of microalgae, the supplied CO 2 Most of it will be wasted. This reactor does not solve the problem of gas escape, ammonia nitrogen escape and CO 2 The problem of escape still exists;

[0013] 2. In the paper “Research Progress on Scale Cultivation Technology of Microalgae”, it is mentioned that “due to the low water depth of the open pool, if CO 2 When the gas is used to supplement the culture medium with carbon, the bubble stays in the water for a short time, the gas-liquid mass transfer effect is poor, and CO 2 The absorption and utilization rate of CO is very low, so currently open pool culture rarely relies on aeration with CO 2 The carbon is supplemented by gases, and more by CO in the atmosphere. 2 Natural diffusion mass transfer on the surface of the culture medium or using sodium bicarbonate as a carbon source.

[0014] In summary, the main problems of the existing technical solutions are: ① The biological removal of ammonia nitrogen requires the system to provide additional commercial carbon nutrients, such as bicarbonate, glucose, etc.; ② The ammonia nitrogen resource utilization effect is poor, and ammonia nitrogen escapes. To this end, we proposed a method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater using a closed reaction of microalgae. Summary of the invention

[0015] The purpose of the present invention is to provide a method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae, so as to overcome the technical problems existing in the prior art.

[0016] In order to achieve the above technical objectives and the above technical effects, the present invention provides the following technical solutions:

[0017] A method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae, comprising the following steps:

[0018] Step 1: Preparation of ammonia nitrogen wastewater culture medium,

[0019] a. Wastewater concentration detection: First, detect and confirm the ammonia nitrogen concentration of rare earth ammonia nitrogen wastewater. If the ammonia nitrogen concentration does not exceed the set value, it can be used directly without dilution. If the ammonia nitrogen concentration exceeds the set value, it needs to be diluted before use.

[0020] b. Sterilization treatment: transfer the wastewater to a closed photobioreactor for sterilization treatment.

[0021] c. pH value adjustment: Use caustic soda to adjust the pH value of the wastewater to a neutral range of 6-8;

[0022] Step 2: Microalgae inoculation,

[0023] a. Select algae species, choose the microalgae species suitable for treating ammonia nitrogen wastewater,

[0024] b. Inoculate in proportion: inoculate the microalgae seed liquid into the prepared ammonia nitrogen wastewater culture medium at a ratio of 5%-20%;

[0025] Step 3: Reactor CO 2 Pressurization,

[0026] a. Close the reactor to ensure that the photobioreactor is in a closed state.

[0027] b. Injection of CO 2 Tail gas, CO generated during the production of rare earth metals 2 The tail gas is injected into the reactor to replace the headspace air.

[0028] c. Pressurized treatment, using CO 2 The tail gas pressurizes the reactor to adjust the headspace pressure to the set value, providing sufficient CO for the growth of microalgae.2 supply;

[0029] Step 4: Regulate the culture.

[0030] a. Set the culture conditions. Set appropriate culture conditions, including temperature control at 25-30°C, light conditions of natural light or artificial light, and speed control at 80-160rpm.

[0031] b. Monitor the pH value. During the culture process, continuously monitor the pH value of the culture medium and ensure that the pH value remains within a reasonable range by adjusting it;

[0032] Step 5: Monitor the harvest.

[0033] a. End the cultivation process. When the microalgae biomass reaches a stable state, end the cultivation process.

[0034] b. Release pressure and sedimentation: Release the headspace pressure in the reactor to allow the microalgae biomass to settle naturally.

[0035] c. Separation and treatment: separate the supernatant for further treatment to remove residual ammonia nitrogen and other pollutants, and harvest the microalgae mud for subsequent utilization and treatment.

[0036] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the set value of the ammonia nitrogen concentration in step one is 2000 mg / L.

[0037] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the sterilization method in step one adopts a high temperature and high pressure sterilization method at 121°C for 20 minutes.

[0038] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the concentration of the caustic soda solution used for pH adjustment in step one is 1 mol / L.

[0039] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the types of microalgae selected in step 2 include but are not limited to green algae and blue algae.

[0040] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the headspace pressure setting value in step three is 1-1.7 atm.

[0041] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the intensity of the artificial light source in step 4 is 100-180 μmol / m 2 ·s.

[0042] Preferably, in a method for reducing pollution and carbon emissions from rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, the pH value in step four is adjusted in the range of 6-8.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The present invention can convert waste gas CO emitted during the rare earth production process into 2 Effective utilization provides a cheap carbon source for the biological removal system of ammonia nitrogen, while achieving carbon reduction and pollution removal, solving the shortcoming of the current technical solution that the biological removal of ammonia nitrogen requires additional commercial carbon nutrition for the system;

[0045] 2. The present invention innovates the microalgae culture reactor, reforms the traditional open pool and column reactor, draws on the anaerobic fermentation system, adopts a closed bioreactor, and the reactor operates under a slightly positive pressure condition to strengthen CO 2 Gas mass transfer provides sufficient carbon source for the growth of microalgae and avoids ammonia nitrogen and CO 2 In this enhanced bioconversion system, ammonia nitrogen is more effectively converted into biomass organic nitrogen and stored in the form of high value-added products such as protein, which solves the shortcomings of poor ammonia nitrogen resource utilization and ammonia nitrogen escape in the current technical solution.

[0046] In summary, the present invention can achieve the purpose of carbon reduction and pollution removal, enhance gas mass transfer, and avoid gas escape. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the description of the specific implementation methods will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 It is a working schematic diagram of the present invention. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Embodiment 1

[0051] In this embodiment, the nitrogen content of wastewater is 620 mg / L, the wastewater is sterilized at 121°C for 30 min, and the pH value is adjusted to 7.1;

[0052] Inoculate with Chlorella sorokinensis at a ratio of 10%;

[0053] Exhaust gas CO 2 Concentration 30%, pressure controlled at 1.7 atm after replacing headspace;

[0054] The culture was cultured at 140 μmol / m2·s and 25°C with 120 rpm rotational shaking for 12 days;

[0055] The microalgae cells experienced a significant growth lag period, and the microalgae biomass yield was greatly increased in the later period. The biomass yield reached 3.14±0.07g / L, that is, the ammonia nitrogen resource biological nitrogen fixation was about 293mg / L.

[0056] Embodiment 2

[0057] In this embodiment, the nitrogen content of wastewater is 620 mg / L, the wastewater is sterilized at 121°C for 30 min, and the pH value is adjusted to 7.0;

[0058] Inoculate with Chlorella sorokinensis at a ratio of 10%;

[0059] Exhaust gas CO 2 The concentration is 30%, and the pressure is controlled at 1.3 atm after replacing the headspace.

[0060] At a light intensity of 140 μmol / m 2 ·s and 25°C in an environment with a rotational shaking of 120 rpm for 7 days;

[0061] The microalgae cells maintained a high biomass production rate, with a biomass yield of 0.36 g / L / day, that is, the cell biological ammonia fixation rate was about 34 mg / L / day, and the headspace CO 2 The residual concentration is about 7.5%.

[0062] Embodiment 3

[0063] In this embodiment, the wastewater ammonia nitrogen concentration is 602 mg / L, the wastewater is sterilized at 121°C for 30 min, and the pH value is adjusted to 7.1;

[0064] Inoculate with Chlorella vulgaris at a ratio of 10%;

[0065] Exhaust gas CO 2 Concentration 30%, pressure controlled at 1.3atm after replacing headspace;

[0066] At a light intensity of 140 μmol / m 2 ·s and 25°C in an environment with a rotational shaking of 120 rpm for 7 days;

[0067] Biomass yield 1.73g / L, cell biological nitrogen fixation rate about 23mg / L / day, headspace CO 2 The residual concentration is about 10%.

[0068] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0069] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater using a closed reaction of microalgae, characterized in that: The following steps are involved: Step 1: Preparation of ammonia nitrogen wastewater culture medium, a. Wastewater concentration detection: First, detect and confirm the ammonia nitrogen concentration of rare earth ammonia nitrogen wastewater. If the ammonia nitrogen concentration does not exceed the set value, it can be used directly without dilution. If the ammonia nitrogen concentration exceeds the set value, it needs to be diluted before use. b. Sterilization treatment: transfer the wastewater to a closed photobioreactor for sterilization treatment. c. pH value adjustment: Use caustic soda to adjust the pH value of the wastewater to a neutral range of 6-8; Step 2: Microalgae inoculation, a. Select algae species, choose the microalgae species suitable for treating ammonia nitrogen wastewater, b. Inoculate in proportion: inoculate the microalgae seed liquid into the prepared ammonia nitrogen wastewater culture medium at a ratio of 5%-20%; Step 3: Reactor CO2 pressurization, a. Close the reactor to ensure that the photobioreactor is in a closed state. b. Inject CO2 tail gas: Inject the CO2 tail gas generated during the rare earth metal production process into the reactor to replace the headspace air. c. Pressurization treatment: Use CO2 tail gas to pressurize the reactor so that the headspace pressure is adjusted to the set value to provide sufficient CO2 supply for the growth of microalgae; Step 4: Regulate the culture. a. Set the culture conditions. Set appropriate culture conditions, including temperature control at 25-30°C, light conditions of natural light or artificial light, and speed control at 80-160rpm. b. Monitor pH value. Continuously monitor the pH value of the culture medium during the culture process and ensure that the pH value remains within the set range by adjusting it; Step 5: Monitor the harvest. a. End the cultivation process. When the microalgae biomass reaches a stable state, end the cultivation process. b. Release pressure and sedimentation: Release the headspace pressure in the reactor to allow the microalgae biomass to settle naturally. c. Separation and treatment: separate the supernatant for further treatment to remove residual ammonia nitrogen and other pollutants, and harvest the microalgae mud for subsequent utilization and treatment.

2. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: The set value of ammonia nitrogen concentration in step 1 is 2000 mg / L.

3. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: In step 1, the sterilization treatment method is to use high temperature and high pressure sterilization at 121° C. for 20 minutes.

4. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: The concentration of the caustic soda solution used for pH adjustment in step 1 is 1 mol / L.

5. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: The microalgae species selected in step 2 include but are not limited to green algae and blue algae.

6. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: In step 3, the headspace pressure setting value is 1-1.7 atm.

7. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: The light intensity of the artificial light source in step 4 is 100-180 μmol / m 2 ·s.

8. The method for reducing pollution and carbon in rare earth ammonia nitrogen wastewater by using a closed reaction of microalgae according to claim 1, characterized in that: In step 4, the pH value is adjusted in the range of 6-8.

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