Continuous flow two-stage microalgae biological carbon sequestration and product induction process based on intracellular nitrogen level regulation and control

Abstract

The invention relates to the field of sewage / wastewater treatment and biological carbon sequestration, in particular to a continuous flow two-stage microalgae biological carbon sequestration and product induction process, which comprises a culture pre-induction primary carbon sequestration stage and a product induction accumulation reinforced carbon sequestration stage. The method provided by the invention can solve the problems of long start delay period, slow biological accumulation rate, lack of directional induction regulation means and the like of traditional two-stage induction, and realizes efficient linkage of biological carbon fixation and carbon conversion. The process disclosed by the invention can be applied to deep denitrification in a water treatment process, is coupled with absorption and purification of flue gas and biogas CO2, and realizes fixed recovery and reutilization of carbon and nitrogen resources while carbon emission reduction is realized.

Description

Technical Field

[0001] The present invention belongs to the fields of sewage / wastewater treatment and biological carbon sequestration, and particularly relates to a continuous flow two-stage microalgae biological carbon sequestration and product induction process for synchronous nitrogen removal and carbon reduction by regulating the intracellular nitrogen level to control the microalgae biological reaction process. Background Art

[0002] Carbon dioxide emission control is a hot issue globally. Typical carbon dioxide capture and storage (CCU) technologies have problems such as high energy consumption in the carbon dioxide desorption process, high cost of adsorption materials, and inability to form in-situ inorganic carbon conversion. Therefore, biological carbon capture and utilization (BCCU) has gradually become a research and practical application hotspot. Reducing carbon dioxide net emissions can be achieved by fixing and storing carbon dioxide in biomass and reusing it (such as thermal utilization or biomass products). As one of the representative technologies of BCCU, microalgae biological carbon sequestration technology has received extensive attention in recent years due to its potential for carbon capture and in-situ carbon conversion and utilization. However, among the technical challenges it faces, how to improve the biological carbon sequestration efficiency and long-term effectiveness is the key to realizing large-scale application, and improving the organic product conversion rate is the key to enhancing the biological carbon sequestration efficiency and long-term effectiveness.

[0003] Typical microalgae biological carbon sequestration technologies can be divided into: carbon sequestration in the photoautotrophic process and product accumulation in the induction process. The former is limited by the theoretical value of microalgae biomass carbon sequestration of 1.83 CO 2 gg -1 biomass, resulting in limited rates of inorganic carbon conversion and organic matter accumulation in microalgae cells, and it is difficult to achieve efficient and long-term carbon sequestration; the latter requires applying conditions such as high light intensity and nitrogen starvation to form an intracellular pressure environment for organic product accumulation. However, the typical induction process technology cycle is relatively long (10 - 20 d), and it is necessary to replace the nitrogen-free / low-nitrogen culture medium. There are also technical processes that stitch together the autotrophic process and the induction process to form a two-stage induction, but the biomass between the two stages is not in a continuous state in the actual sense. The process requires waiting for the nitrogen element in the culture medium to be consumed to the limiting level or completely replacing the nitrogen-free / low-nitrogen culture medium, resulting in problems such as long induction cycles, low organic matter accumulation efficiency, and large consumption of the culture medium. How to effectively connect the photoautotrophic process and the induction process is the key to improving the microalgae biological carbon sequestration ability, and efficient and long-term microalgae biological carbon sequestration can be achieved by increasing the organic matter accumulation rate and shortening the induction cycle. Summary of the Invention

[0004] In view of the deficiencies in typical microalgae biological carbon fixation technologies, especially the low efficiency of inorganic carbon conversion and organic matter accumulation, an embodiment of the present invention provides a continuous - flow two - stage microalgae biological carbon fixation and product induction process and system based on the regulation of intracellular nitrogen levels in biomass. The process includes a cultivation pre - induction primary carbon fixation stage (R1 stage) and a product induction enhanced carbon fixation stage (R2 stage). By adjusting the ratio of extracellular nitrogen load to the specific growth rate of microalgae biomass in the continuous - flow operation mode of the R1 stage, biomass with non - saturated intracellular nitrogen levels is produced under steady - state operation conditions. The down - regulation of intracellular nitrogen levels causes microalgae biomass to enter the intracellular nitrogen stress state faster, and the transcription related to the pyruvate (PEP) - acetyl coenzyme (ACCoA) - lipid synthesis pathway is up - regulated, and the microalgae biomass rapidly accumulates organic products.

[0005] To achieve the above - mentioned invention purpose, the present invention is realized through the following technical solutions:

[0006] A continuous - flow two - stage microalgae biological carbon fixation and product induction process includes: a cultivation pre - induction primary carbon fixation stage and a product induction enhanced carbon fixation stage. In the cultivation pre - induction primary carbon fixation stage, CO 2 is provided as an inorganic carbon source, enabling microalgae to reach steady - state growth and enter the pre - induction state in a continuous - flow photobioreactor. The ratio of total nitrogen load to the specific growth rate of microalgae is regulated by an HRT (Hydraulic Retention Time) / SRT (Solid Retention Time) regulation tank. Utilizing the non - linear relationship between the specific growth rate of microalgae biomass growth kinetics and extracellular nitrogen concentration, the microalgae biomass is in a state of steady - state growth and non - saturated intracellular nitrogen levels. After continuous - flow algae discharge in the R1 stage, it then enters the product induction enhanced carbon fixation stage.

[0007] Preferably, the intracellular nitrogen level of microalgae biomass cells is controlled to reach a stable non - saturated state (3 - 7%) through HRT / SRT ratio regulation, and the SRT regulation range is 1 - 4d.

[0008] Preferably, the cultivation pre - induction primary carbon fixation stage includes:

[0009] R1 - 1: Batch process: Inject pre - cultured algal solution (microalgae biomass concentration < 300mgL -1 ) into the photobioreactor and operate in a batch mode;

[0010] R1 - 2: Start continuous - flow reactor (CSTR) operation: Wait until the biomass concentration is stable (400 - 700mgL -1 ), and the reactor operation switches to continuous mode;

[0011] R1 - 3: Setting of continuous - mode operation parameters:

[0012] 1: Residence time: Set the HRT and SRT for continuous flow operation, and the HRT / SRT ratio ranges from 0.25 to 2;

[0013] 2: Light setting: Natural light or artificial light can be used in the continuous flow operation mode. When using artificial light, the incident light condition is 5000 - 7000 Lux and the light path ranges from 10 to 20 cm;

[0014] 3: Aeration setting: In the continuous flow operation mode, the aeration rate ranges from 0.1 to 0.3 vvm. Flue gas / biogas / artificial mixed gas can be used, and the CO 2 concentration range should be controlled within 2 - 20%;

[0015] Preferably, the product-induced enhanced carbon fixation stage includes:

[0016] R2-1: The algal liquid discharged from the R1 stage directly enters the reactor of the R2 stage, and the product-induced enhanced carbon fixation stage is started. The induction time of microalgae biomass is 3 - 5 d;

[0017] R2-2: Light setting: The incident light intensity is 15,000 - 20,000 Lux and the light path ranges from 10 to 20 cm;

[0018] R2-3: Aeration setting: The aeration rate in the R2 stage ranges from 0.05 to 0.2 vvm. Flue gas / biogas / artificial mixed gas can be used, and the CO 2 concentration range should be controlled within 5 - 50%.

[0019] Preferably, the microalgae is any one or more of Monoraphidium, Chlorella, and Scenedesmus.

[0020] The present invention also provides a continuous flow two-stage microalgae biological carbon fixation system, including: a culture pre-induction primary carbon fixation stage component and a product-induced enhanced carbon fixation stage component, wherein the pre-induction primary carbon fixation component includes a first photobioreactor composed of a columnar aeration reactor and a tubular light absorption device and an HRT / SRT regulation tank; the product-induced enhanced carbon fixation component includes a bubble column and an aeration membrane.

[0021] Preferably, the first photobioreactor is connected to the HRT / SRT regulation tank. The liquid is drained into the HRT / SRT regulation tank by the hydrostatic pressure of the first photobioreactor. A ceramic membrane module is provided in the regulation tank to independently regulate the hydraulic retention time and the biomass retention time. A drainage pipeline is connected to the membrane cavity and the water is drained into the clear water tank through a drainage pump. Microalgae biomass is produced by draining the algal liquid from the regulation tank through a liquid drainage pump. Part of the algal liquid is returned to the first photobioreactor as algal liquid reflux through a reflux pump. The membrane cavity is also connected to a backwashing pipeline and is equipped with a ceramic membrane pipeline pressure indicator. The HRT, i.e., the total nitrogen load for supplying microalgae biomass, is controlled by the influent volume flow rate, the drainage volume flow rate, and the liquid drainage volume flow rate between the first photobioreactor and the HRT / SRT regulation tank, and the specific growth rate of microalgae biomass is controlled by the liquid drainage flow rate.

[0022] Preferably, the first photobioreactor is a closed photobioreactor, including a horizontal tubular photobioreactor, a vertical columnar photobioreactor, an air-lift photobioreactor, a bubble column photobioreactor, or a plate photobioreactor.

[0023] Preferably, a reactor aeration membrane is provided at the bottom of the first photobioreactor.

[0024] Preferably, the product-induced enhanced carbon fixation assembly includes a second photobioreactor, and the second photobioreactor is an air-lift photobioreactor, a bubble column photobioreactor, a vertical columnar photobioreactor, or an open raceway pond.

[0025] Compared with the prior art, the main advantages of the present invention are as follows:

[0026] 1) This technology adopts a continuous flow operation mode, with a shorter residence time and a higher operation flux than the existing similar technologies.

[0027] 2) By regulating the HRT / SRT ratio, the total intracellular nitrogen level (TN) of microalgae biomass is in a non-saturated state. Compared with the existing similar technologies, microalgae biomass is in a stable nitrogen stress state during the cultivation stage, and directly enters the organic product accumulation state after being discharged into the induction reactor, which can greatly shorten the organic product induction delay period of the traditional induction process, realize seamless connection of the two stages without delay, and the induction cycle can be shortened by more than 1 time compared with the traditional induction method.

[0028] 3) The algal liquid produced in the pre-induction primary carbon fixation stage of cultivation has the characteristic that the total nitrogen (TN) of the environmental solution is less than 1 mg / L. Compared with the existing similar technologies, nitrogen stress conditions can be directly formed when entering the product-induced enhanced carbon fixation stage, and there is no need to replace the environmental solution or remove nitrogen. -1

[0029] ​4) The process method disclosed in this invention can achieve the synergy of biological carbon sequestration and deep denitrification, realizing deep denitrification. The drained water (total nitrogen (TN) concentration is less than 1 mg / L -1 ) can be used as makeup water for landscape water to achieve reclamation of reclaimed water. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. The drawings in the following description are only used to explain some embodiments of the present invention.

[0031] Figure 1 It is a diagram of the device used in the pre-induction primary carbon sequestration stage of the embodiment of the present invention.

[0032] Figure 2 It is a diagram of the device used in the product induction and accumulation enhanced carbon sequestration stage of the embodiment of the present invention.

[0033] Figure 3 It is a diagram of the changes in microalgae biomass dry weight, TOC, and cell number.

[0034] Figure 4 It is a curve showing the change of the fluorescence intensity of intracellular oil in Nile red-stained microalgae biomass over time in the product induction and enhanced carbon sequestration stage.

[0035] Among them, 1. Feed water pump 2. Gas compressor 3. Aeration flowmeter 4. Inlet air pressure gauge 5. Feed water flowmeter 6. Reactor liquid level gauge 7. Column-type air-lift reactor 8. Reactor pressure gauge 9. Reactor aeration membrane 10. Reactor pressure relief valve 11. Reactor main drain valve 12. Tubular light absorption device 13. Main drain flowmeter 14. Ceramic membrane pipeline pressure indicator 15. HRT / SRT regulation pool 16. Three-way solenoid valve 17. Membrane module 18. Backwash flowmeter 19. Drainage three-way valve 20. Drainage flowmeter 21. Return flowmeter 22. Drainage pump 23. Return pump 24. Backwash pump 25. Drainage flowmeter 26. Water storage tank 27. Drainage pump 28. Gas compressor 29. Feed liquid pump 30. Inlet air pressure gauge 31. Inlet air flowmeter 32. Bubble column bioreactor 33. Bubble column aeration membrane 34. Reactor pressure gauge 35. Drain valve 36. Reactor pressure relief valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] An embodiment of the present invention discloses a continuous-flow two-stage microalgae biological carbon fixation and product induction process, which includes a cultivation pre-induction primary carbon fixation stage and a product induction enhanced carbon fixation stage, effectively connecting the typical photoautotrophic carbon fixation process with the induction product accumulation process, and improving the overall carbon fixation and carbon conversion efficiency. The typical induction product accumulation process has a relatively long cycle, usually 10 - 20 days. One of the main reasons is that the initiation of intracellular organic matter accumulation in microalgae requires a corresponding low intracellular nitrogen level (0.03 - 0.04 TN mg mg -1 biomass), while the intracellular nitrogen level of the biomass of typical microalgae in the photoautotrophic stage (cultivation stage) is usually in a saturated state and around 8% (0.08 TN mg mg -1 biomass), thus resulting in a start-up delay period for intracellular organic product accumulation. In the present invention, it is proposed to use a continuous-flow additional HRT / SRT regulation tank to independently regulate HRT and SRT, and stabilize the intracellular nitrogen level of microalgae biomass in the cultivation stage at a state lower than the saturated level (3 - 7%), which can shorten / eliminate the start-up delay period in the induction stage and enable microalgae cells to directly enter the state of rapid organic matter accumulation. In addition, in the continuous-flow cultivation pre-induction primary carbon fixation stage, through the independent regulation of HRT / SRT, the total nitrogen (TN) concentration in the extracellular environment of microalgae can be continuously and stably maintained at an ultra-low concentration (TN limiting level and less than 1 mg L -1 ), and directly form a nitrogen-limited stress condition when entering the product induction enhanced carbon fixation stage, avoiding the denitrification treatment of the environmental solution.

[0038] An embodiment of the present invention discloses a continuous-flow two-stage microalgae biological carbon fixation and product induction process, including: a cultivation pre-induction primary carbon fixation stage (R1) and a product induction enhanced carbon fixation stage (R2), wherein the cultivation pre-induction primary carbon fixation stage is mainly carried out through a photobioreactor (composed of a columnar aeration reactor 7 and a tubular light absorption device 12) and an HRT / SRT regulation tank 15. The HRT / SRT regulation tank 15 adjusts the nitrogen load (HRT) through the influent flow rate and adjusts the sludge discharge rate (SRT) through the algae effluent flow rate, controlling the ratio of the available nitrogen concentration in the reaction system to the specific growth rate of the biomass. Since the nitrogen consumption and the specific growth rate are non-linear relationships, adjusting this ratio can maintain a stable growth state while achieving different N levels in microalgae cells; the product induction enhanced carbon fixation stage is realized through a bioreactor system composed of a bubble column 32 and an aeration membrane 33, thereby realizing biomass product induction.

[0039] Specifically, the R1 stage includes:

[0040] R1-1: Sequential batch process

[0041] The sequential batch process refers to injecting pre-cultured algal liquid (microalgae biomass concentration < 300 mg L-1 ) and operates in a batch sequence mode.

[0042] Furthermore, the microalgae have strong nitrogen absorption and carbon absorption capabilities and have certain characteristics of accumulating organic products (such as proteins and oils).

[0043] Preferably, the microalgae can be any one or more of Monoraphidium, Chlorella, and Scenedesmus.

[0044] Furthermore, the running time of the batch sequence process is preferably 3 - 5 days, the light intensity is controlled at 2000 - 3000 Lux, and the aeration rate is controlled at 0.1 - 0.3 vvm.

[0045] Furthermore, in the batch sequence process, a BG11 medium without nitrogen, phosphorus, and carbonate ions needs to be added, and nitrate and phosphate are added separately to make the N:P element concentration ratio (6:1 - 10:1).

[0046] Furthermore, the added concentration of nitrate is 30 - 50 mg / L -1 , preferably sodium nitrate; the added concentration of phosphate is 3 - 5 mg / L -1 , preferably dipotassium hydrogen phosphate.

[0047] Furthermore, the dosage of the BG11 medium added in the batch sequence process needs to ensure that the concentration of each component in it is: MgSO 4 150 - 200 g / L -1 ; CaCl 2 100 - 150 g / L -1 ; citric acid 10 - 50 g / L -1 ; ammonium ferric citrate 10 - 50 g / L -1 ; EDTA 1 - 10 g / L -1 ; A5 trace elements 1 - 3 mL / L -1 .

[0048] Furthermore, the dry weight concentration of microalgae biomass in the batch sequence process is stabilized at 400 - 700 mg / L -1 .

[0049] Furthermore, in the batch sequence process, the aeration uses CO 2 and the volume concentration should be 1 - 5%.

[0050] R1 - 2: Start the continuous flow reactor (CSTR) operation

[0051] When the biomass concentration in the batch sequence process is stabilized (400 - 700 mg / L -1 ), the operation of the reactor is switched to the continuous mode.

[0052] In the pre-induced primary carbon fixation stage of cultivation, continuous-flow water inlet is achieved through the water inlet pump 1, and the influent flow rate S0 is controlled by the influent flow meter 5. Continuous-flow liquid discharge is achieved by using the liquid level difference, and the liquid discharge flow rate S1 is controlled by the main liquid discharge valve 11. The discharged liquid is introduced into the HRT / SRT regulation tank 15, and the separation of the algal liquid and water is completed through the membrane module 17 arranged in the tank: the drainage pipeline is connected to the membrane cavity of the membrane module 17 and is discharged into the water storage tank 26 through the drainage pump 22 and the drainage flow meter 20 to control the drainage flow rate S4. The microalgae biomass is retained in the regulation tank 15 to form concentrated algal liquid, and is discharged through the liquid discharge pump 27 and the liquid discharge flow meter 25 to control the liquid discharge flow rate S5.

[0053] Furthermore, the influent water during the continuous-flow operation can be the water distribution mainly composed of culture medium and the effluent from the secondary sedimentation tank of domestic sewage. The influent TN concentration range is 10 - 15 mg / L. -1 .

[0054] R1 - 3: Setting of continuous mode operation parameters

[0055] 1. Retention time: The continuous-flow operation HRT is set through the influent flow rate S0, (V is the operating volume of the photobioreactor), and the continuous-flow operation SRT is set through the liquid discharge flow rate S5, and S0 = S4 + S5 - SW. The HRT / SRT ratio needs to consider the total nitrogen (TN) concentration of the effluent S4, the dry weight concentration of microalgae biomass (D.W.), and the total nitrogen level in the microalgae biomass cells (Quota_N).

[0056] Preferably, the HRT / SRT ratio range is 0.25 - 2, where the range values of HRT and SRT are respectively 0.25 d ≤ HRT ≤ 2 d; 1 d ≤ SRT ≤ 4 d.

[0057] 2. Light setting: Natural light or artificial light can be adopted in the continuous-flow operation mode. When artificial light is adopted, the incident light condition is 5000 - 7000 Lux and the light path range is 10 - 20 cm.

[0058] 3. Aeration setting: The aeration rate range in the continuous-flow operation mode is 0.1 - 0.3 vvm. Flue gas / biogas / artificial mixed gas can be adopted, and the CO 2 concentration range should be controlled at 2 - 20%.

[0059] Furthermore, in the continuous-flow operation mode, the total nitrogen (TN) concentration of the effluent is less than 1 mg / L -1 , and the total nitrogen level in the microalgae biomass cells (Quota_N) generated under continuous-flow operation should be controlled at 3 - 7%.

[0060] Furthermore, the R1 stage also includes:

[0061] R1-4: Set up reflux:

[0062] During the continuous flow operation, a reflux SR is provided between the columnar aeration reactor 7 and the tubular light absorption device 12. Part of the algal liquid in the regulation tank 15 is pumped into the tubular light absorption device 12 through the reflux pump 23 and the reflux flowmeter 21, and a reflux SR is formed through the liquid level difference.

[0063] Preferably, according to the inner diameter of the pipeline, the reflux speed SR should be controlled at 0.2-1 m / s.

[0064] R1-5: Backwashing:

[0065] During the continuous flow operation, the membrane module 17 in the regulation tank 15 is backwashed in a periodic intermittent mode. The drainage stored in the water storage tank 26 is pumped into the membrane cavity of the membrane module 17 through the backwashing pump 24 and the backwashing flowmeter 18 to achieve backwashing and control the membrane fouling during the operation.

[0066] Preferably, the backwashing is carried out in a cycle of 10 minutes. The drainage pump 22 works for 8 minutes, then the set solenoid valve 16 rotates, the backwashing pump 24 works for 1 minute, stops for 1 minute and then the solenoid valve 16 rotates, and the drainage pump 22 continues to work.

[0067] Preferably, the backwashing flow rate SW is 3-5 times the drainage flow rate S4.

[0068] The R2 stage: Product-induced enhanced carbon fixation stage, specifically including:

[0069] R2-1: The algal liquid of R1 directly enters the product-induced enhanced carbon fixation stage;

[0070] During the continuous flow operation, the algal liquid continuously discharges S5 from the regulation tank 15 and enters the product-induced enhanced carbon fixation stage. The microalgae biomass has the characteristic of unsaturated intracellular nitrogen level (Quota_N), and the total nitrogen (TN) concentration of the drained liquid is less than 1 mg / L. -1 The drained algal liquid S5 is introduced into the bubble column bioreactor 32 through the feed pump 29, and the aeration membrane 33 in the reactor is used to achieve biomass homogenization and CO supply in the reactor. 2 In the product-induced enhanced carbon fixation stage, the algal liquid S5 supplied during the continuous flow operation directly enters the organic matter accumulation state in the bubble column bioreactor 32 by skipping the traditional induction delay period, and after a certain residence time, the microalgae biomass is discharged through the drain valve 35.

[0071] Preferably, during the product-induced enhanced carbon fixation process, the residence time of the microalgae biomass is 3-5 days.

[0072] R2-2: Light setting;

[0073] Preferably, in the product-induced enhanced carbon fixation stage, the incident light intensity is 15,000 - 20,000 Lux and the optical path range is 10 - 20 cm.

[0074] R2-3: Aeration setting;

[0075] Preferably, during the product-induced enhanced carbon fixation process, the aeration rate is controlled at 0.05 - 0.2 vvm, and the CO 2 supply concentration is 5 - 50%.

[0076] The embodiment of the present invention also provides a continuous flow two-stage microalgae biological carbon fixation system, as Figure 1 and 2 shown. The system includes: a culture pre-induction primary carbon fixation stage component ( Figure 1 ) and a product-induced enhanced carbon fixation component ( Figure 2 ).

[0077] Furthermore, the culture pre-induction primary carbon fixation stage component mainly includes a photobioreactor and an HRT / SRT regulation tank 15; among them, the photobioreactor is composed of a columnar aeration reactor 7 and a tubular light absorption device 12. The product-induced enhanced carbon fixation stage component is mainly composed of a bubble column 32 and an aeration membrane 33 to form a bioreactor system.

[0078] Even further, the culture pre-induction primary carbon fixation stage component further includes a feed water pump 1 and a feed water flow meter 5 for realizing continuous flow water inlet and controlling the water inlet flow rate; a main drain valve 11, a drain pump 22 and a drain flow meter 20, a liquid discharge pump 27 and a liquid discharge flow meter 25 for discharging the liquid into the next unit; a membrane module 17 for separating the algae liquid from water; a reflux pump 23 and a reflux flow meter 21 for pumping part of the algae liquid in the HRT / SRT regulation tank 15 into the tubular light absorption device 12 and forming a reflux SR through the liquid level difference; a backwash pump 24 and a backwash flow meter 18 for pumping the drainage stored in the water storage tank 26 into the membrane cavity of the membrane module 17 to realize backwashing to control the membrane pollution during the operation process. The product-induced enhanced carbon fixation stage component further includes a feed liquid pump 29 for feeding the discharged algae liquid S5 into the bubble column bioreactor 32; a bubble column aeration membrane 33 for realizing biomass homogenization in the reactor and CO 2 supply; a drain valve 35 for discharging the microalgae biomass.

[0079] The technical solutions and advantages of the present invention will be described in detail below in combination with specific embodiments.

[0080] Example 1

[0081] A 1×20 L continuous flow photobioreactor is used for the culture pre-induction primary carbon fixation stage, and a 4×10 L bubble column bioreactor is used for the product-induced enhanced carbon fixation stage.

[0082] The specific operation process of the technical method in this embodiment is as follows:

[0083] R1: Cultivate the pre-induced primary carbon fixation stage

[0084] R1-1: Inject the pre-cultured Monoraphidium sp. algal solution with a concentration of 100 - 200 mg / L into the photobioreactor (composed of a columnar aeration reactor 7 and a tubular light absorption device 12), -1 , add the BG11 medium without nitrogen, phosphorus, and carbonate (after purchase, it is subjected to nitrogen and phosphorus removal treatment, which is an operation well-known to those skilled in the art), and separately add sodium nitrate with a concentration of 30 mg / L - 1 NO 3 - -N and potassium hydrogen phosphate with a concentration of 5 mg / L -1 PO 4 - -P. The concentrations of each component in the finally prepared medium are shown in Table 1. Operate in a batch sequence for 3 days. During this process, the light intensity is controlled at 3000 Lux, and the aeration rate is controlled at 0.1 vvm (1% CO 2 ), and finally, the microalgae biomass concentration in the photobioreactor reaches 400 - 600 mg / L -1 .

[0085] Table 1 Medium components and concentrations

[0086] Component Concentration Component Concentration Sodium nitrate <![CDATA[30mgL -1 > <![CDATA[MgSO 4 > <![CDATA[183gL -1 > Dipotassium hydrogen phosphate <![CDATA[5mgL -1 > <![CDATA[CaCl 2 > <![CDATA[136gL -1 > Citric acid <![CDATA[30gL -1 > Ammonium ferric citrate <![CDATA[30gL -1 > EDTA <![CDATA[5gL -1 > Trace element A5 <![CDATA[1mLL -1 >

[0087] R1-2: Start the continuous flow mode of operation and start the cultivation of the pre-induced primary carbon fixation stage. Achieve continuous flow of water through the water inlet pump 1 and control the influent flow rate S0 = 27 L / d through the influent flow meter 5 -1 , and the influent water used is simulated secondary sedimentation tank effluent (TN = 10 - 15 mg / L -1 ). Use the liquid level difference to achieve continuous drainage and control the drainage flow rate S1 through the main drainage valve 11 to be 0.8 - 1.2 m 3 h -1 , discharge the drainage into the HRT / SRT regulation tank 15 and complete the separation of the algal solution and water through the membrane module 17 set in the tank: the drainage pipeline is connected to the membrane cavity of the membrane module 17, discharged into the storage tank 26 through the drainage pump 22 and the drainage flow meter 20, and control the drainage flow rate S4. The microalgae biomass is retained in the regulation tank 15 to form a concentrated algal solution and is discharged through the drainage pump 27 and the drainage flow meter 25, and control the drainage flow rate S5 = 10 L / d -1 .

[0088] R1-3: Set the continuous mode operation parameters. Set the continuous flow operation HRT = 0.75 d through the influent flow rate S0, (V = 20 L), set the continuous flow operation SRT = 2 d and HRT / SRT = 0.375 through the drainage flow rate S5. The incident light intensity during the continuous flow operation is 5500 - 6000 Lux, the aeration rate is controlled at 0.2 vvm, and the CO 2 concentration is 2%.

[0089] R1-4: During the continuous flow operation, there is a reflux SR between the columnar aeration reactor 7 and the tubular light absorption device 12. Through the reflux pump 23 and the reflux flowmeter 21, part of the algal liquid in the regulation tank 15 is pumped into the tubular light absorption device 12 and forms a reflux SR through the liquid level difference. Effectively controlling the reflux ratio can improve the light energy utilization efficiency of the microalgae biomass in the photobioreactor and reduce the deposition and wall adhesion of the microalgae biomass in the tubular absorption pipeline. In this embodiment, SR = 0.5 m / s -1 .

[0090] R1-5: During the continuous flow operation, the membrane module 17 in the regulation tank 15 is backwashed in a periodic intermittent mode. Through the backwash pump 24 and the backwash flowmeter 18, the drainage stored in the water storage tank 26 is pumped into the membrane cavity of the membrane module 17 to achieve backwashing to control the membrane fouling during the operation. The drainage pump 22 works for 8 minutes, then the set solenoid valve 16 rotates, the backwash pump 24 works for 1 minute, the pump stops for 1 minute and then the solenoid valve 16 rotates, and the drainage pump 22 continues to work. The backwash flow rate SW can be 3 times the drainage flow rate S4 to control the membrane fouling. In this embodiment, S4 = 27.2 L / d and SW = 10.2 L / d.

[0091] R2: During the continuous flow operation, the algal liquid continuously drains out of the regulation tank 15 at S5 and enters the product-induced enhanced carbon fixation stage. Through the feed pump 29, the drained algal liquid S5 is introduced into the bubble column bioreactor 32, and the biomass homogenization and CO 2 supply in the reactor are achieved by using the aeration membrane 33 in the reactor. Each bubble column bioreactor 32 is set with an incident light intensity of 15,000 Lux, the aeration rate is controlled at 0.1 vvm, and the CO 2 concentration is 5%. The residence time of the microalgae biomass in a single bubble column bioreactor is 4 d. The microalgae biomass is discharged through the drain valve 35.

[0092] The effects of the culture pre-induced primary carbon fixation stage, the product-induced enhanced carbon fixation stage, and the intracellular lipid accumulation of the microalgae biomass are shown in Table 2, Table 3, and Figure 3 , Figure 4 as shown. The data shows that the culture pre-induced primary carbon fixation stage can achieve ultra-low TN concentration in the continuous effluent and the microalgae biomass in the reactor can stably maintain an unsaturated intracellular nitrogen content (6%). The biological carbon fixation efficiency can be obtained according to the continuously discharged biomass. Figure 3 and4 Data shows that after entering the product-induced enhanced carbon fixation stage, the number of microalgae cells stops increasing. The dry weight of microalgae biomass and total organic carbon complete the maximum rate of accumulation within 3 days, accompanied by an increase in the fluorescence intensity of oil staining, indicating that within a 5-day induction period, microalgae biomass achieves efficient CO 2 fixation and conversion into intracellular organic carbon products to form oil accumulation.

[0093] Table 2. Operating effect of the pre-induction primary carbon fixation stage in cultivation

[0094]

[0095] Table 3. Operating effect of the product-induced enhanced carbon fixation stage

[0096]

[0097] Example 2

[0098] The concentration of CO in the R2 stage is 20%, and the rest is the same as in Example 1. 2 The concentration of CO in the R2 stage is 20%, and the rest is the same as in Example 1.

[0099] Example 3

[0100] The concentration of CO in the R2 stage is 2 50%, and the rest is the same as in Example 1.

[0101] It should be understood that the detailed description of the technical solutions of the present invention with the aid of the preferred embodiments is illustrative rather than restrictive. Those of ordinary skill in the art can modify the technical solutions recorded in each embodiment based on reading the specification of the present invention, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A continuous flow two-stage microalgae biocarbon fixation and product induction process, comprising: S1: Cultivation pre-induction primary carbon fixation stage, in which CO2 is provided as an inorganic carbon source, so that the microalgae grow and pre-induce in the photobioreactor, and the total nitrogen load and the microalgae specific growth rate are adjusted by the HRT / SRT control pool, so that the microalgae biomass is stably in a state of unsaturated intracellular nitrogen level; and S2: Product-induced enhanced carbon fixation stage.

2. The process according to claim 1, characterized in that In the step S1, the intracellular nitrogen level of the microalgae biomass is controlled below 7% by adjusting the HRT / SRT ratio, and the SRT regulation time is 1-4 days.

3. The process according to claim 1, characterized in that The step S1 comprises: R1-1: Batch process: The photobioreactor is injected with pre-cultured microalgae biomass at a concentration of <300 mg L -1 of algae solution, run in batch mode; R1-2: Start the continuous flow reactor operation; R1-3: Continuous mode operation parameter setting: Set the continuous flow operation HRT and SRT, and the HRT / SRT ratio range is 0.25-2.

4. The process according to claim 1, characterized in that In step S2, the incident light intensity is 15,000-20,000 Lux, the aeration rate is 0.05-0.2 vvm, the CO2 supply concentration is 5-50%, and the residence time of the microalgae biomass is 3-5 days.

5. The process according to any one of claims 1 to 4, characterized in that The microalgae is any one or more of Mononeurium, Chlorella and Scenedesmus.

6. A continuous flow two-stage microalgae biocarbon fixation and product induction system, comprising: Pre-induced primary carbon fixation component and product-induced enhanced carbon fixation component, Among them, the pre-induced primary carbon fixation component includes a first photobioreactor composed of a column aeration reactor and a tubular light absorption device and an HRT / SRT control tank; the product induced enhanced carbon fixation component includes a bubbling tower and an aeration membrane.

7. The system according to claim 6, characterized in that The first photobioreactor is connected to the HRT / SRT control tank, and liquid is discharged into the HRT / SRT control tank by hydraulic static pressure. A ceramic membrane assembly is provided in the control tank to achieve algae-water separation. Part of the algae liquid is returned to the first photobioreactor as algae liquid reflux through a reflux pump. A backwash pipeline is also connected to the membrane cavity of the ceramic membrane assembly and a ceramic membrane pipeline pressure indicator is provided. The first photobioreactor and the HRT / SRT control tank control the total nitrogen load of HRT, i.e., the supply of microalgae biomass, through the inlet volume flow rate, the outlet volume flow rate, and the drainage volume flow rate, and control the specific growth rate of the microalgae biomass through the drainage flow rate.

8. The system according to claim 6, characterized in that The first photobioreactor is a closed photobioreactor, including a horizontal tube photobioreactor, a vertical column photobioreactor, an airlift photobioreactor, a bubble tower photobioreactor or a plate photobioreactor.

9. The system according to claim 6, characterized in that A reactor aeration membrane is arranged at the bottom of the first photobioreactor.

10. The system according to any one of claims 6 to 9, characterized in that: The product-induced enhanced carbon fixation component comprises a second photobioreactor, and the second photobioreactor is an airlift photobioreactor, a bubble tower photobioreactor, a vertical column photobioreactor or an open running pool.

Images