An externally embedded photobioreactor and its use

Abstract

The application provides an external embedding type photobioreactor and application thereof, and belongs to the technical field of bioengineering. The external embedding type photobioreactor is used in the process of aerated culture of microalgae, so that the mixing, mass transfer, photosynthetic efficiency and CO2 fixation efficiency of the algal liquid are strengthened, and the biological yield of the microalgae is improved. In the application, the external embedding type photobioreactor comprises a center column, external elbow pipes connected to two sides of the center column, an embedded curved body and an aeration port at the bottom of the center column. The combination of the external elbow pipes and the embedded curved body ensures the general flow of the algal liquid and the circulation of the backflow, and at the same time, the vortex flow of the algal liquid flow is increased as much as possible, so that the mixing efficiency is promoted. The existence of the embedded curved body guarantees the formation of the overall upward flow and downward flow of the algal liquid, and at the same time, the residence time of CO2 in the reactor is increased, and the carbon fixation efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bioengineering technology, and particularly relates to an external embedding type photobioreactor and application thereof. BACKGROUND

[0002] Due to the widespread use of traditional fossil fuels, the emission of greenhouse gases has significantly increased, among which the emission of carbon dioxide (CO2) is the most typical, and carbon dioxide needs to be captured and utilized. Microalgae are called micro-cell factories, which have an extraordinary carbon dioxide fixation capacity, 10-50 times faster than other terrestrial organisms, and 1.83 grams of CO2 is consumed to produce 1 gram of dry microalgae biomass. Microalgae biomass can be used to extract high-protein, lipid and carbohydrate, and provides good nutritional ingredients (e.g., pigments, vitamins, polyunsaturated fatty acids and countless other nutrients). Microalgae can also be used to treat wastewater, especially sewage wastewater, pig farm wastewater, pharmaceutical wastewater and dairy wastewater. Therefore, microalgae cultivation can be used to capture CO2 emitted by large carbon emission fields (such as power plants) and convert waste into useful commodities.

[0003] In recent years, the most widely used industrial-level structure for cultivating microalgae is a circular and racetrack-shaped cultivation pond, which accounts for 90% of the global annual supply of microalgae. However, open systems have the disadvantages of poor mass transfer, high water evaporation rate, high challenge to maintain healthy crop conditions, easy pollution, need for large area construction, high power and high labor cost, while closed photobioreactors are not easily polluted, can provide optimal biological physiological conditions, and thus achieve higher biomass production rate. Closed photobioreactors (PBRs) have greater ability to adjust the growth environment in terms of nutrition, temperature, pH value and light. Therefore, a single microalgae species can be cultivated for a long time, while reducing the risk of external pollution.

[0004] At present, researchers have developed various techniques related to PBR, such as internal illumination by placing a light source in the chamber using optical fibers or light diffusers, which improves the light transmission effect to some extent, but the structure of the built-in light source also hinders the flow of algal liquid to some extent, reduces the mixing characteristics. It is also discussed in the literature that baffles or mixers are installed in the flat column or vertical column PBR to improve mixing, which is relatively ideal, but the presence of baffles can easily cause dead zones for filamentous algae flow, causing algae accumulation. A lantern-shaped pipe is installed in the vertical section of the PBR to generate multiple vortexes, which improves the biomass yield by 50% through efficient CO2 fixation and mixing; the combination of horizontal pipes and three-prism baffles reduces the mixing time (MT) of NB-PBR and traditional PBR and increases the mass transfer coefficient (MTC), thereby achieving a 70% increase in biomass yield; the Teslavalve is installed inside the vertical column PBR to improve the mixing of the solution along the baffle, thereby increasing the biomass yield by 28.1%, the above several structure PBRs are added with built-in special structures to further improve the flow and mixing of algal liquid, but the mixing effect still has room for improvement, and these PBRs do not have good carbon fixation capacity, and the CO2 residence time is short. Therefore, the photobioreactor needs to be further optimized. SUMMARY

[0005] In view of the deficiencies in the prior art, the application provides an externally embedded photobioreactor and its application, which realizes the strengthening of algal liquid mixing, mass transfer, photosynthetic efficiency and CO2 fixation efficiency during the process of aerated culture of microalgae, and further improves the biological yield of microalgae.

[0006] In the application, the externally embedded photobioreactor comprises a central column, external elbow pipes connected on both sides of the central column, an embedded curve body and an aeration hole at the bottom of the central column; the combination of the external elbow pipes and the embedded curve body ensures the overall flow of the algal liquid to be generally circulated and the vortex flow of the algal liquid to be increased as much as possible during the flow, thereby promoting the mixing efficiency; the presence of the embedded curve body guarantees the formation of the overall upward flow and downward flow of the algal liquid, and also improves the residence time of CO2 in the reactor and the carbon fixation efficiency.

[0007] The application first provides an externally embedded photobioreactor, which is divided into an upward pipe and a downward pipe, and specifically comprises a central column, an embedded curve body, an external elbow pipe and an aeration hole.

[0008] The central column comprises a central column body and a central column bottom plate closed connected with the bottom of the central column body, the external elbow pipe is connected to the outside of the central column body, and a plurality of embedded curve bodies are embedded in the inside of the central column body.

[0009] The external bend includes multiple external bends a and external bends b. The multiple external bends a are arranged longitudinally on both sides of the central column and are staggered on both sides of the central column. The upper end of each external bend a is connected to the embedded curved body and the lower end is connected to the central column. The external bend b is located at the top of the central column and both ends are connected to the middle column.

[0010] The aeration holes include aeration hole a and aeration hole b, which are respectively located on the outer bends a on both sides of the bottom of the central column.

[0011] Furthermore, the ratio of the height of the central column, the diameter of the central column, and the inner diameter of the outer bend is 7-10:1:0.2-0.4.

[0012] Furthermore, the externally mounted photobioreactor is provided with multiple external bends a and the same number of internal curved bodies as the external bends a, the number of which is 7 to 10.

[0013] Furthermore, the lower end of the outer bend a is connected to the central column at the following position: on the central column on the outer side below the next embedded curved body, and the lower end of the outer bend a is not connected to the next embedded curved body.

[0014] Furthermore, the height of the central column can be adjusted by changing the number of external bends a and embedded curved bodies.

[0015] Furthermore, the embedded curved body is funnel-shaped, with the upper port diameter being the same as the diameter of the central column, and the lower port diameter being the same as the inner diameter of the outer bend a.

[0016] The present invention also provides the application of the above-mentioned external photobioreactor in promoting algal liquid mixing and mass transfer and CO2 fixation.

[0017] This invention also provides a method for promoting algal solution mixing and mass transfer and CO2 fixation based on the above-mentioned external photobioreactor, specifically including the following steps:

[0018] (1) Select a good single microalgae strain under sterile conditions and inoculate it into the culture medium. Set the light intensity, pH and temperature conditions for cultivation to obtain the cultured microalgae solution.

[0019] (2) The microalgae liquid is inoculated into the external photobioreactor, and then aeration is carried out through the bottom aeration holes to make the algae liquid form a mixed flow circulation, thereby promoting the mixing and mass transfer of algae liquid and CO2 fixation.

[0020] Furthermore, in step (1), the culture conditions for the microalgae are: light intensity 12000±200lx, pH controlled at 8-10, and temperature 27±2℃.

[0021] Further, in step (2), the inoculation amount of the microalgae liquid is 0.5-1 mg / L.

[0022] Further, in step (2), the gas contains 15%-20% (v / v) CO2, and the aeration amount is controlled at 0.01-0.1 vvm.

[0023] Further, in step (2), the microalgae liquid surface is 5-10 cm away from the top of the outer-embedded photobioreactor.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] In the present application, through the combination of the external elbow pipe and the embedded curve body, the vortex flow of the algae liquid is increased as much as possible while ensuring the overall flow of the algae liquid and the circulation of the backflow, and the mixing efficiency is promoted, and the existence of the embedded curve body guarantees the overall upflow and downflow of the algae liquid, and also improves the residence time of CO2 in the reactor and the carbon fixation efficiency.

[0026] The traditional PBR is a vertical column reactor design, and the riser part is usually located in the center, and as the biomass grows, the light availability is poor. The NB-PBR described in the present application has a riser and a downcomer part, in which the algae can receive sufficient light, thereby avoiding the dark area existing in the traditional PBR. And compared with the traditional PBR, the outer-embedded photobioreactor (NB-PBR) provided in the present application converts the laminar flow into a large amount of vortex flow, and provides higher resistance to CO2 bubbles in the direction of gravity, thereby improving the carbon dioxide carbon dissolution efficiency. The NB-PBR not only increases the mixing and mass transfer, but also promotes the microalgae cells to move more frequently between the light and dark areas, further promoting the photosynthetic efficiency, thereby producing higher biomass. Through experiments, the NB-PBR reduces the mixing time by 16% compared with the traditional PBR, but increases the mass transfer coefficient by 25.9%. The results also show that the photochemical properties are improved compared with the traditional column PBR, and the biomass yield and CO2 fixation are increased by 26% and 29%, respectively.

[0027] The controllable structure variable in the outer-embedded photobioreactor described in the present application can be adjusted individually, the algae liquid forms a mixed flow circulation at the right side of the bottom, forms a large number of different counterclockwise and clockwise liquid circulation flows, and forms a large number of vortex flows of different degrees in each area, and the uniquely designed NB-PBR can realize similar high-efficiency mixing as a static mixer in the PBR.

[0028] In the present application, the distance between the microalgae liquid surface and the top of the column pipe should not be too close, and enough space should be reserved to ensure that the algae liquid can circulate with the bubbles, and the distance between the microalgae liquid surface and the top can also ensure that the algae liquid circulating flow in the NB-PBR will not flow out of the reactor, causing pollution.

[0029] The present application has simple operation, wide application range, and can optimize the structure parameters related to NB-PBR according to different microalgae species and cultivation conditions, so as to achieve optimal mixed mass transfer, photosynthetic efficiency and CO2 fixation efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural diagram of the external embedded photobioreactor (a) and a schematic diagram of algae liquid flow when the aeration hole b is ventilated (b), wherein 1-aeration hole a, 2-aeration hole b, 3-external elbow a, 4-embedded curved body, 5-external elbow b, 6-center column, 7-center column bottom plate.

[0031] Figure 2 is a comparison diagram of the influence of aeration rate on the mixing time (MT) and mass transfer coefficient (MTC) of NB-PBR and traditional PBR in the process of microalgae cultivation.

[0032] Figure 3 is a comparison diagram of the influence of external elbow diameter on the mixing time (MT) and mass transfer coefficient (MTC) of NB-PBR in the process of microalgae cultivation.

[0033] Figure 4 is a CFD simulation diagram of NB-PBR in the process of microalgae cultivation, wherein a is a velocity vector diagram, and b is a velocity trajectory diagram.

[0034] Figure 5 is a comparison diagram of chlorophyll fluorescence induction kinetic parameters in the process of microalgae cultivation, wherein a is the content of chlorophyll-a and carotenoid, and b is the measured value of φPSII and Fv / Fm.

[0035] Figure 6 is a comparison diagram of A. platensis biomass dry weight and pH value in the process of microalgae cultivation, wherein a is A. platensis biomass dry weight and pH value, and b is the concentration of total inorganic carbon (TIC), Na2CO3 and NaHCO3.

[0036] Figure 7 is an OJIP curve diagram showing the chlorophyll a fluorescence intensity in NB-PBR and traditional BR in the process of microalgae cultivation, wherein a~b are OJIP curve diagrams of 1-4 days, and 1 is NB-PBR, and 2 is traditional PBR. DETAILED DESCRIPTION

[0037] The present application will be further described below in combination with the drawings and specific examples, but the protection scope of the present application is not limited thereto. Although only spirulina is mentioned in the examples, other non-adherent algae such as spherical and filamentous algae can also be used in the implementation or testing of the present application.

[0038] Embodiment 1:

[0039] Figure 1 The structure diagram of the outer-embedded photobioreactor (NB-PBR) described in the present application can be seen from the figure. The outer-embedded photobioreactor described in the present application comprises a central column, an inner-embedded curved body (4), an external elbow and an aeration hole.

[0040] The central column comprises a central column body (6) and a central column bottom plate (7) which is closedly connected to the bottom of the central column body (6). The outer sides of the central column body (6) are alternately and staggeringly connected with external elbows on the outside. The central column body (6) is internally embedded with a funnel-shaped inner-embedded curved body (4). The external elbows are divided into a plurality of external elbow a (3) and external elbow b (5). The upper end of each external elbow a (3) is connected with the inner-embedded curved body (4) and penetrates through it. The lower end is connected with the central column body (6) and penetrates through it. The external elbow b (5) is arranged at the top of the central column body (6) and penetrates through the central column body (6) at both ends. The lower end port is arranged at the lower side of the nearest inner-embedded curved body (4) to the top of the central column body (6).

[0041] The outer-embedded photobioreactor is provided with a plurality of external elbow a (3) and the same number of inner-embedded curved bodies (4) as the external elbow a (3). The number is 7-10. The lower end of the external elbow a (3) is arranged on the central column outside the lower side of the next inner-embedded curved body (4) and does not communicate with the next inner-embedded curved body (4), thereby dividing the outer-embedded photobioreactor into an ascending pipe and a descending pipe. When necessary, the height of the central column body (6) can be adjusted by adjusting the number of external elbow a (3) and inner-embedded curved body (4), so that the height of the central column body (6), the diameter of the central column body (6) and the inner diameter of the external elbow are in a ratio of 7-10:1:0.2-0.4.

[0042] Specifically, the central column body (6) is internally provided with N inner-embedded curved bodies (4) whose upper end diameter is the same as that of the central column body (6) and whose lower end interface diameter is the same as the inner diameter of the external elbow a (3). They are respectively denoted as the first inner-embedded curved body, the second inner-embedded curved body, the third inner-embedded curved body, …, the Nth inner-embedded curved body from bottom to top. N is a positive integer and 7≦N≦10. Similarly, the external elbow a (3) alternately and staggeringly arranged on the outside of the central column body (6) is also provided with N external elbow a (3) from bottom to top, which are respectively denoted as the first external elbow a, the second external elbow a, the third external elbow a, …, the Nth external elbow a. N is a positive integer and 7≦N≦10. The upper end interface of the Nth external elbow a is connected with the Nth inner-embedded curved body and penetrates through it. The lower end interface of the Nth external elbow a is located at the lower side of the N-1th inner-embedded curved body and does not directly communicate with the N-1th inner-embedded curved body. The cycle is repeated.

[0043] In addition, the aeration holes include aeration hole a (1) and aeration hole b (2), which are respectively arranged on the outer elbow pipes on both sides of the bottom of the central column (6), namely the first outer elbow pipe a and the second outer elbow pipe a, both positions can be aerated, and one of them is selected during use to realize the clockwise circulation and counterclockwise circulation of the algae liquid in the column. When the aeration hole a (1) is used for aeration, the whole algae liquid in the column circulates clockwise, and when the aeration hole b (2) is used for aeration, the whole algae liquid in the column circulates counterclockwise.

[0044] In the present embodiment, the total height of the NB-PBR main center column is 70 cm, the diameter is 10 cm, and it is divided into six height regions, each of which contains an outer elbow pipe and an embedded curve (10 cm high). The NB-PBR has an ascending pipe and a descending pipe part, both of which contain more fluid regions, each with a height of 10 cm. When the aeration hole b provides aeration, the algae liquid flow diagram is as shown in Figure 1 b, the algae liquid forms a mixed flow circulation, forms a large number of different counterclockwise and clockwise liquid circulation flows, and forms a large number of different degrees of vortex in each region.

[0045] In the present embodiment, the spirulina is also taken as an example to provide the culture of microalgae by using the above-mentioned outer-embedded type photobioreactor, to promote the mass transfer and CO2 fixation of the algae liquid, and the specific steps are as follows:

[0046] (1) In a sterile environment, select a good single spirulina strain and inoculate it into a general column reactor, and prepare BG-11 culture medium according to the literature record of Chen Xiu's "Magnetic Field Intervention on the Growth of Yellow Silk Algae and High-efficiency Cultivation Strategy Using Starch Fermentation Wastewater", and suspend the spirulina algae in the general column reactor BG-11 culture medium, the light intensity is 12000±200lx, the pH is controlled at 8-10, and the temperature is 27±2℃.

[0047] (2) The spirulina algae cultured in step (1) is inoculated into the outer-embedded type photobioreactor at an inoculation amount of 0.5-1 mg / L, the liquid surface of the algae is 5-10 cm away from the top of the outer-embedded type photobioreactor during inoculation, and then 0.01-0.1vvm of gas (containing 15% CO2) is introduced through the aeration hole at the bottom to make the algae liquid form a mixed flow circulation, so as to achieve the purpose of promoting the mass transfer and CO2 fixation of the algae liquid.

[0048] Example 2:

[0049] The mass transfer coefficient evaluates the mass transfer capacity of the photobioreactor, and the mixing time reflects the mixing capacity of the photobioreactor. CO2 is one of the main limiting factors for the growth of microalgae under standard conditions, and with the improvement of the mass transfer capacity, more CO2 is dissolved. Therefore, it is necessary to improve the mass transfer capacity of the photobioreactor. The overall performance of the column PBR depends largely on the structural parameters, that is, how to design the PBR.

[0050] The determination method of mixing time (MT) and mass transfer coefficient (MTC) is shown as follows:

[0051] The test for MT is using a pH probe (InPro3253i / SG / 120 Mettler Toledo), and the steps are as follows:

[0052] First, pour 7L distilled water into the NB-PBR, then adjust the pH value of the distilled water to 3 by adding 6mol / L HCl dropwise, then add NaOH (2.5-3.5mL, 12μmol / L) dropwise into the solution, and introduce a trace of alkalinity into the solution, measure the required time for pH stability, and obtain two consecutive peaks by measuring pH, and MT is determined by two consecutive differences, and the NB-PBR is always kept aerated at the bottom (air, 0.01-0.1vvm) during the measurement.

[0053] MTC is calculated by N2 gas aeration in the solution, and the steps are as follows:

[0054] First, reduce the oxygen content to 4mg / L by aeration, then increase the dissolved oxygen content to 5mg / L by air, measured by an oxygen probe (InPro6850i / 12 / 120 Mettler Toledo), the device automatically saves data every 0.1 second, a transmitter (i-7017fc, ICP DAS, Taiwan) is connected to the two probes, and the data is collected and analyzed by system software.

[0055] (1) Effect of aeration rate on mixing time (MT) and mass transfer coefficient (MTC) of NB-PBR and traditional PBR:

[0056] In this embodiment, distilled water is used as the research object, and the rate of bottom aeration is adjusted by an air pump, and air is introduced at 0.01, 0.03, 0.05, 0.07, and 0.1vvm respectively to investigate the effect of aeration rate on mixing time (MT) and mass transfer coefficient (MTC) of NB-PBR and traditional PBR, and the determination method of mixing time (MT) and mass transfer coefficient (MTC) is referred to as shown above.

[0057] Figure 2 The comparison chart of the effect of aeration rate on mixing time (MT) and mass transfer coefficient (MTC) of NB-PBR and traditional PBR in the process of microalgae cultivation. From Figure 2 It can be seen from the chart that when the gas aeration rate increases from 0.01vvm to 0.1vvm, the mixing time in the NB-PBR decreases and the mass transfer coefficient increases, respectively (75s and 3.53h -1The main reason is that a large number of rapidly moving bubbles significantly increase the intensity of turbulence, accelerate the dissolution rate, and improve the mass transfer performance. Turbulence promotes the rotational mixing of microalgae cells, which can increase the surface area exposed to light, maintain a consistent solution temperature, and, by using the vortex generated by the structure, can improve the CO2 fixation rate. Bubble movement generated by aeration is the only way to disturb the flow of algae liquid in the NB-PBR. During the process of bubble rising, CO2 is constantly dissolved into water through the gas-liquid interface, providing a carbon source for the growth of microalgae. If the bubble stays in the water for a long enough time, it will completely dissolve in the water and disappear. Therefore, the longer the duration of the bubble in the rising phase, the more conducive to CO2 transport. In addition, a high concentration of dissolved CO2 can promote the reaction between CO2 and water, which can produce more bicarbonate ions for photosynthesis.

[0058] Therefore, increasing the gas aeration rate can shorten the mixing time and improve the mass transfer efficiency.

[0059] (2) Effect of the inner diameter of the external elbow on the mixing time (MT) and mass transfer coefficient (MTC) of the NB-PBR and the traditional PBR:

[0060] In this embodiment, by changing the inner diameter of the external elbow, the inner diameter was adjusted to 2, 2.5, 3, 3.5, 4 and 4.5 cm, respectively, and the aeration rate was maintained at 0.1 vvm. Then, the mixing time and mass transfer coefficient of the NB-PBR and the traditional PBR were measured by the method in (1), and the measurement results are shown in Table 1. Figure 3

[0061] Figure 3 The comparison chart of the effect of the diameter of the external elbow on the mixing time (MT) and mass transfer coefficient (MTC) of the NB-PBR in the process of microalgae cultivation. As can be seen from the figure, the MT is reduced from 75 seconds to 69 seconds, and the MTC of the NB-PBR is increased from 3.53 to 3.88 h -1 . It can be seen that as the diameter of the elbow arm increases, more fluid can rise because a wider tube allows enough space to increase mixing and reduce the time spent.

[0062] Therefore, the uniform mixing of nutrients in PBR and CO2 dissolution is increased, which increases the conversion of HCO 3- ions consumed during the effective growth of A. platensis (CO2+H2O→HCO 3- +H + ).

[0063] ​In summary, the aeration rate and the inner diameter of the external elbow have a greater influence on the mixing time and mass transfer coefficient of the NB-PBR. When the gas aeration rate increases from 0.01 vvm to 0.1 vvm, the mixing time in the NB-PBR decreases by about 75 s, and the mass transfer coefficient increases by about 3.53 h -1 The mixing characteristics are improved. Under the condition of ensuring the aeration amount, with the increase of the inner diameter of the external elbow, the NB-PBR compared with the traditional PBR, the MT decreases from 75 seconds to 69 seconds, and the MTC increases from 3.53 to 3.88 h -1 The increase of the inner diameter of the external elbow can better improve the mixing characteristics of the fluid.

[0064] Example 3

[0065] The flow of the algal liquid is maintained only by the kinetic energy generated from the bottom aeration, and then the whole forward and reverse circulation and the vortex circulation in the partial area are formed, and the simulation process is time-consuming, so in this embodiment, the speed and vortex of the algal liquid are confirmed by simulating the culture conditions in the NB-PBR by changing the aeration rate (0.01-0.05 m / s) by CFD.

[0066] Figure 4 The NB-PBR in the process of microalgae cultivation is simulated by CFD, wherein a is a velocity vector diagram, and b is a velocity trajectory diagram. The simulation results show that the vortex occurs in the curved arm and the main column area, and the NB-PBR rising section and the falling section are the same, thereby supporting the formation of the vortex in each section. The speed reaches between 0.04 to 0.05 m / s, and the radial velocity is 1.9 times higher than that in the traditional PBR solution when the input gas rate is 0.12 vvm, and the speed is as low as 0.01 m / s. It can be seen that the improved radial flow enhances the movement of microalgae between the dark and light areas, thereby enhancing the flashing effect of microalgae, and thus having a positive influence on the photosynthesis and biomass accumulation of microalgae. The unique design of 6 sections (3 sections of the rising pipe and the falling pipe) in the NB-PBR described in the application is used to generate a widely distributed flow state, so that the microalgae at different depths of the photobioreactor can obtain a good light / dark cycle.

[0067] Example 4

[0068] Chlorophyll is an important pigment in photosynthesis, more than 60% of which is combined with the light-harvesting antenna complex to absorb light energy and transfer excitation energy to the photosynthetic reaction center. Carotenoids are an important part of the antenna system and chlorophyll-binding protein, which can help capture light energy and remove excess free radicals in microalgae cells. The chlorophyll in spirulina is mainly chlorophyll a. The higher the content of chlorophyll a in Arthrospira sp., the higher the photosynthetic efficiency of the cell.

[0069] Therefore, in the present embodiment, the kinetics parameters of chlorophyll fluorescence induction in the process of microalgae cultivation and the chlorophyll a fluorescence intensity in the process of microalgae cultivation in the NB-PBR and the traditional PBR are investigated, and the specific investigation steps are as follows:

[0070] The measurement is performed by using the AquaPen portable chlorophyll fluorescence instrument, and in the process of microalgae cultivation, 5 mL of algal liquid is taken every 12 h, diluted 5 times by distilled water, dark reacted for 15 min under dark conditions, and then the QA, OJIP, NPQ1 and other values are measured by using the fluorescence instrument, and the data is exported and analyzed by connecting the computer analysis software.

[0071] Figure 5 is a comparison result graph of the kinetics parameters of chlorophyll fluorescence induction in the process of microalgae cultivation, wherein a is the chlorophyll a and carotenoid parameters, and b is the φPSII and Fv / Fm parameters. As can be seen from the graph a, the average chlorophyll a content and the average carotenoid content of the cells in the traditional PBR are 7.45 mg / g and 0.66 mg / g, respectively. The average chlorophyll a content and the average carotenoid content of the cells in the NB-PBR are 8.21 mg / g and 0.75 mg / g, respectively, which are increased by 10.3% and 13.9%, respectively. The increase of the chlorophyll a and carotenoid content in the cells of the NB-PBR promotes the photosynthesis and CO2 fixation of the spirulina.

[0072] As can be seen from the graph b, the φPSII and ETR gradually decrease from the 12th hour of the growth of the spirulina, and with the increase of the algal density, the φPSII and ETR decrease more rapidly. Increase in algal biomass, Figure 7 The algal density rapidly increases. Since the calculation formula of φPSII is φPSII=(Fm'Fs) / Fm', wherein Fm' is the maximum fluorescence in light adaptation, and Fs is the fluorescence under stable state; therefore, when the photosynthesis of the algae is in a stable state, higher fluorescence is required.

[0073] The OJIP transient can also be converted into biophysical parameters, and the F0 and FM between them are considered to be variable fluorescence (FV), and the ratios FV / F0 and FV / FM are used to evaluate the photosynthetic efficiency. The chlorophyll fluorescence parameters can be used to quantify the changes on the donor and acceptor sides of the PSII reaction center, and the analysis of the chlorophyll fluorescence parameters provides rich information about the absorption, utilization and transmission of energy and the state of electron transfer in the photosynthetic electron transport chain. Therefore, in the present embodiment, the photochemical reaction of PSII is also investigated by the four-day rapid induction kinetics curve of chlorophyll fluorescence (from the OJIP test).

[0074] Figure 6For the microalgae cultivation process, the OJIP curve graphs of the chlorophyll a fluorescence intensity in NB-PBR and traditional BR are shown in Figures 1-4. As can be seen from the graphs, when the measurement aperture of the chlorophyll fluorometer is increased from 0.1 to 2.0 mm, φPo and ABS / RC are increased from 0.48 to 0.52 and 5.5 to 6.3, respectively, which indicates that the maximum photochemical efficiency and the light energy absorbed per reaction center are both increased. The sufficient HCO3- promotes the Calvin cycle reaction, thereby increasing the demand for ATP and NADPH, which in turn promotes the pigment to absorb more light energy. Since the higher absorption of light energy enhances the maximum light energy conversion efficiency of the PSII reaction center, φPo gradually increases. In addition, φEo, ETo / RC and TRo / RC are increased from 0.19, 1.1 and 2.68 to 0.342, 0.983 and 0.787, respectively, which indicates that the electron transfer chain is accelerated. φDo and DIo / RC are decreased from 0.54 and 3.3 to 0.48 and 2.6, respectively, which indicates that the light energy used for heat dissipation is reduced, and the reduction of heat dissipation indicates that a higher proportion of light energy is used for photosynthesis.

[0075] Therefore, the OJIP curve of the four consecutive days reflects the gradual increase in photosynthetic rate with the increase in the NF aperture.

[0076] Example 5:

[0077] In this example, the biomass dry weight and pH value of A. platensis in the NB-PBR and traditional PBR during the microalgae cultivation process were investigated, and the investigation method is shown as follows:

[0078] The algal cells were collected by filtration, the dry weight of the microalgae cells was measured by weighing, and the pH value was measured by a pH meter.

[0079] Figure 6 is a comparison graph of the biomass dry weight and pH value of A. platensis in the NB-PBR and traditional PBR during the microalgae cultivation process, wherein a is a biomass dry weight graph of A. platensis, and b is a pH value parameter graph. As can be seen from the graph, during the 144-hour cultivation of A. platensis, the biomass yield of the NB-PBR increased by 23% (g / L) compared with the traditional PBR (shown in Figure a). ​ Subsequently, the NB-PBR structure produced improved flow in the elbow tube section, resulting in uniformity in the maintenance of nutrient and CO2 dissolution.

[0080] In addition, due to the low density of A. platensis, the pH value of the solution decreased rapidly within the first 24 hours, because the chemical conversion of CO2 and H2O resulted in HCO 3-, while excess CO2supply results in conversion of H+ions, followed by conversion of Na2CO3to NaHCO3ions in solution, i.e.:

[0081] (CO2+ H2O → HCO 3- + H + ) and (CO2+ Na2CO3+ H2O → 2NaHCO3, HCO 3- → CO2+ OH - ).

[0082] As the biomass increases with the increase in the cultivation time and the algal culture density, the effective H+ions are gradually utilized by A. platensis through active transport, while releasing OH-ions in the solution, and the pH value gradually increases. Therefore, the gradual increase in the biomass production after 24 hours results in an increase in the consumption of dissolved CO2. The high pH value indicates that the microalgal cells achieve a higher CO2fixation rate, and thus the NB-PBR exhibits a higher pH value relative to the conventional PBR.

[0083] In summary, the NB-PBR of the present application promotes mixing and mass transfer throughout the culture and frequent movement of A. platensis cells, thereby improving photochemical efficiency. The novel NB-PBR significantly increases the biomass production of A. platensis by 26%.

[0084] The above-described embodiments are preferred embodiments of the present application, but the present application is not limited to the above-described embodiments, and any obvious modifications, replacements, or variations that can be made by those skilled in the art without departing from the essential content of the present application fall within the scope of the present application.

Claims

1. An externally mounted photobioreactor, characterized in that, The externally embedded photobioreactor is divided into an ascending pipe and a descending pipe, specifically including a central column, an embedded curved body (4), an external curved pipe, and aeration holes; The central column includes a central column body (6) and a central column base plate (7) which is closedly connected to the bottom of the central column body (6). An external curved pipe is connected to the outside of the central column body (6), and multiple embedded curved bodies (4) are embedded inside the central column body (6). The external bends include multiple external bends a (3) and external bends b (5). The multiple external bends a (3) are arranged longitudinally on both sides of the central column and are staggered on both sides of the central column (6). The upper end of each external bend a (3) is connected to the embedded curved body (4), and the lower end is connected to the central column (6). The external bend b (5) is located at the top of the central column (6), and both ends are connected to the middle column (6). The upper end of each external bend a (3) is connected to the embedded curved body (4), and the lower end is connected to the central column (6). The lower end of the external bend b (5) is located on the lower side of the embedded curved body (4) closest to the top of the central column (6). The aeration holes include aeration hole a (1) and aeration hole b (2), which are respectively located on the outer bends a (3) on both sides of the bottom of the central column (6).

2. The externally mounted photobioreactor according to claim 1, characterized in that, The ratio of the height of the central column (6), the diameter of the central column (6), and the inner diameter of the outer bend is 7~10:1:0.2~0.

4.

3. The externally mounted photobioreactor according to claim 1, characterized in that, The externally mounted photobioreactor is provided with multiple external bends a (3) and the same number of internal curved bodies (4) as the external bends a (3), the number of which is 7 to 10.

4. The externally mounted photobioreactor according to claim 1, characterized in that, The lower end of the outer bend a (3) is connected to the central column (6) at the position on the central column (6) below and outside the next embedded curved body (4), and the lower end of the outer bend a (3) is not connected to the next embedded curved body (4).

5. The externally mounted photobioreactor according to claim 1, characterized in that, The height of the central column (6) is adjusted by adjusting the number of external bends a (3) and embedded curved bodies (4).

6. The externally mounted photobioreactor according to claim 1, characterized in that, The embedded curved body (4) is funnel-shaped, with the upper port diameter being the same as the diameter of the central column (6), and the lower port diameter being the same as the inner diameter of the outer bend a (3).

7. The application of the external photobioreactor according to any one of claims 1 to 6 in promoting algal liquid mixing and mass transfer and CO2 fixation.

8. A method for promoting algal solution mixing and mass transfer and CO2 fixation based on the externally mounted photobioreactor according to any one of claims 1 to 5, characterized in that, Specifically, the steps include the following: (1) Select a good single microalgae strain under sterile conditions and inoculate it into the culture medium. Set the light intensity, pH and temperature conditions for cultivation to obtain the cultured microalgae solution. (2) The microalgae liquid is inoculated into the external photobioreactor, and then aeration is carried out through the bottom aeration port to form a mixed flow circulation of the algae liquid, thereby promoting the mixing and mass transfer of the algae liquid and CO2 fixation.

9. The method according to claim 8, characterized in that, In step (1), the culture conditions for the microalgae are: light intensity 12000±200lx, pH controlled at 8-10, and temperature 27±2℃.

10. The method according to claim 8, characterized in that, In step (2), the inoculum concentration of the microalgae solution is 0.5~1 mg / L; The gas being introduced contains 15%~20% (v / v) CO2, and the gas flow rate is controlled at 0.01-0.1vvm; The surface of the microalgae solution is 5-10 cm from the top of the externally embedded photobioreactor.

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