A method for cultivating microalgae using nanofluids and a photobiological reaction device

Abstract

The present invention provides a method for culturing microalgae by using nanofluids and a photobiological reaction device. The present invention utilizes the selective light transmittance property of nanofluids to effectively accelerate the growth trend of microalgae. Nanomaterials with high light transmittance in the red and blue spectrum wavelengths are used on the photobiological reaction device for selective light transmittance. The nanofluid is coated on the outside of the photobiological reaction device, and the light source required for the growth of microalgae is outside the nanofluid. The heat absorption property of the nanofluid is used to maintain the algae liquid at a suitable temperature for the growth of algae. Due to different selections, the nanofluid has other properties such as weak magnetism in addition to selective light transmittance and heat absorption. The characteristic that microalgae are negatively charged in any pH state is utilized. The microalgae particles are agglomerated and collected by the cations carried by the nanofluid, and flocculated and harvested. After the microalgae are collected, the heat absorbed by the nanofluid is used for co-drying.

Description

Technical Field

[0001] The invention belongs to the technical field of microalgae cultivation, and in particular relates to a method for cultivating microalgae by utilizing nanofluids and a photobiological reaction device. Background Art

[0002] Entering the 21st century, the steady economic growth has led to the continuous advancement of industrialization and urbanization, which has led to a growing demand for energy. The main source of energy is fossil fuels, which are non-renewable energy sources and will eventually run out. In addition to the consumption of fossil fuels, their combustion will produce greenhouse gases, including a large amount of CO2, which is the main cause of global warming. With the rapid development of emerging economies, global energy consumption will increase significantly, which will cause more environmental damage. Therefore, while reducing carbon dioxide emissions, we strive to find cleaner renewable energy. In my country, we actively transform the energy structure and transform to a green, low-carbon, and environmentally friendly energy consumption mode.

[0003] In order to maintain the sustainable development of the world economy, the development of renewable energy is becoming increasingly important in the current situation where fossil fuels are being consumed and environmental pollution is becoming increasingly serious. The energy demand in the transportation sector ranks second in the world, and relevant departments have stated that most of the oil consumption comes from the transportation industry. Nowadays, biodiesel and bioethanol are developed as substitutes for fossil fuels such as petroleum. Sugarcane and corn are the crops that can produce the highest bioethanol, and oilseed plants such as soybeans are the crops that produce the highest biodiesel. However, the growth of these crops takes up too much land, which affects the growth of other organisms. According to research, if we rely entirely on biofuels at this stage, the growth of these raw material crops will occupy 61% of the agricultural land, which will affect the normal operation of human society and the diversity of the earth's organisms. Microalgae, as the third-generation bioenergy raw material, has the advantages of short growth cycle, no occupation of arable land, and strong photosynthesis. In terms of lipid accumulation, microalgae is nearly 80% higher than other raw materials. In addition to the high lipid content, microalgae also contains many other by-products, such as protein, carbohydrates, pigments, etc. The added value of these by-products can offset the production cost to a certain extent, so when cultivating microalgae, it is necessary to select the target product for accumulation. In addition, the yield of microalgae is increased, and the yield of biofuels is increased to enhance the competitiveness of biofuels in the market. Different growth conditions will affect the growth trend of microalgae in high-density large-scale photoautotrophic culture of microalgae, such as light intensity, temperature, metal ion concentration, pH, etc. However, excessive light produces a lot of heat energy, so excessive temperature and light intensity will inhibit the growth of microalgae. Nowadays, the focus is on how to accelerate the growth of microalgae and increase the accumulation of various organic substances in microalgae. In addition to finding the best culture environment and the best CO2 intake, light has not shown its adjustability in large-scale culture. Summary of the invention

[0004] In response to the above technical problems, the present invention provides a method for cultivating microalgae using nanofluids and a photobiological reaction device. The weak magnetism and selective light transmission characteristics of nanofluids are used to effectively accelerate the growth trend of microalgae. Microalgae grow rapidly within a certain light wavelength and effectively accumulate lipids. In addition, microalgae are stimulated by the magnetic field under a weak magnetic field to accelerate the metabolism and growth of microalgae cells, effectively promoting the growth of microalgae and the accumulation of nutrients. In the post-microalgae collection stage, the characteristic that microalgae are negatively charged at any pH state is utilized, and the cations carried by the magnetic nanofluid are used to aggregate and collect the microalgae particles. After the microalgae are collected, the nanofluid contained in the algae liquid can effectively gather heat with the help of sunlight, accelerate the drying rate of the algae liquid, and participate in subsequent utilization, reducing useless energy loss.

[0005] The technical solution of the present invention is: a method for culturing microalgae using nanofluids, comprising the following steps:

[0006] Step S1, preparing nanofluid: magnetic nanofluid, and measuring the electromagnetic quantity and light transmittance of magnetic nanoparticles;

[0007] Step S2, microalgae cultivation: injecting the prepared magnetic nanofluid into the liquid film layer of the photobioreactor, and the microalgae grow in the photobioreactor under the conditions of the preset electromagnetic intensity of the magnetic nanofluid and the visible light wavelength;

[0008] Step S3, collecting microalgae: after the growth cycle of the microalgae is over, the algae liquid is collected, and part of the magnetic nanofluid in the liquid film layer is injected into the collected algae liquid, and the magnetic nanoparticles are used to flocculate the microalgae;

[0009] Step S4, drying of microalgae: placing the microalgae solution collected by using the magnetic nanoparticles under sunlight, and utilizing the photothermal efficiency of the nanofluid to dry the algae solution.

[0010] In the above scheme, the electromagnetic energy of the magnetic nanoparticles is 40 to 80 mT.

[0011] In the above scheme, the magnetic nanofluid has strong permeability at 400-700nm.

[0012] The above scheme also includes step S5, thermal conversion utilization: the nanofluid can perform thermal conversion with the microalgae.

[0013] A photobiological reaction device for realizing the method of culturing microalgae using nanofluids, wherein the photobiological reaction device is a tubular photobiological reaction device; the tubular photobiological reaction device comprises a tubular photobiological reaction device body, a connecting plate and a bottom supporting column; the bottom of the tubular photobiological reaction device body is connected by the connecting plate and the bottom supporting column; the tubular photobioreactor body has a double-layer wall surface, and a gap is left between the tube walls as a liquid film layer, and the liquid film layer is used to inject nanofluids.

[0014] A photobiological reaction device for realizing the method of culturing microalgae using nanofluids, wherein the photobiological reaction device is a racetrack photobiological reaction device; the racetrack photobiological reaction device comprises a racetrack photobioreactor body, a stirrer, a liquid film layer, a spectrometer, an embedding tank and a liquid outlet;

[0015] The stirrer is installed in the racetrack photobioreactor body, the liquid outlet is arranged at the bottom of the racetrack photobioreactor body, the liquid film layer is a plate-type liquid film, and the liquid film layer is installed on the top of the racetrack photobioreactor body.

[0016] The above scheme also includes a spectrometer, which is installed on the liquid film layer and is used to detect the transmittance of the magnetic nanofluid. If the transmittance is lower than a threshold, air is ventilated into the liquid film layer.

[0017] In the above solution, support rods are provided at the bottom of the liquid film layer, and the support rods are inserted into the embedding grooves provided around the top of the racetrack photobioreactor body. The liquid film layer can be inserted into the embedding grooves by the support legs to maintain its stability.

[0018] The above solution also includes a supporter; the supporter is installed on the outer bottom of the racetrack-type photobioreactor body.

[0019] A photobiological reaction device for realizing the method of culturing microalgae using nanofluids, wherein the photobiological reaction device is a flat-plate photobiological reaction device; the flat-plate photobiological reaction device comprises a flat-plate photobioreactor body, aeration holes and a liquid film layer; the flat-plate photobioreactor body has a double-layer wall structure, and a gap between the two walls is the liquid film layer; the flat-plate photobioreactor body is provided with an aeration hole at the bottom, which is opened during the aeration and microalgae growth period to provide necessary air for the microalgae growth.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The selective light transmission of nanofluids can effectively promote the growth of microalgae. Due to the weak magnetism carried by the nanofluids, a stable static magnetic field is formed. The growth rate of microalgae is accelerated under a weak magnetic field of 40 to 80 mT and the accumulation of nutrients is promoted. Due to its own heat absorption characteristics, the nanofluids can absorb most of the useless heat of the invisible light part to maintain the stability of the temperature of the microalgae growth environment. The heat absorbed by the nanofluids can be used for microalgae drying. Magnetic nanomaterials are cheap, and the liquid film thickness is thin, and the solution particle density is low, which reduces the upstream economy and improves the overall economic benefits. Nanofluids can be used for multiple purposes, and can be used for microalgae cultivation, microalgae collection, and even for subsequent coordinated drying of microalgae. Under the irradiation of the light source, the temperature of the nanofluid gradually rises due to its own thermal conductivity. In the microalgae collection stage, the algae liquid is collected and dried using the heat contained in the nanofluid and the weak magnetic field. The present invention comprehensively considers the effects of light, temperature and magnetic field on the growth of microalgae, and uses magnetic nanoparticles to prepare magnetic nanofluids. In view of the selective light transmission, thermal conductivity and weak magnetism of the nanofluids, the three directions of increasing the yield of microalgae can be met under the current research status. Nanofluids are easy to prepare, inexpensive, and have a wide range of applications. During the microalgae collection stage, magnetic nanofluids are used for efficient recovery, and after recovery, they can be quickly dried by sunlight. After the collection is completed, the remaining nanoparticles are used for subsequent thermal utilization along with the dried microalgae particles, which can effectively improve operating efficiency and reduce useless losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Growth trend diagram of Microsphagnum microalgae in an embodiment of the present invention under a magnetic field of 80 mT;

[0023] Figure 2 Growth trend diagram of Chlorella in 80mT magnetic field according to one embodiment of the present invention;

[0024] Figure 3 The tubular photobioreactor of the present invention with an added external interlayer;

[0025] Figure 4 A top view of a tubular photobioreactor of the present invention;

[0026] Figure 5 The racetrack photobioreactor of the present invention;

[0027] Figure 6 The racetrack photobioreactor of the present invention;

[0028] Figure 7 The racetrack photobioreactor of the present invention;

[0029] Figure 8 The flat-plate photobioreactor of the present invention;

[0030] Fig. 9 The present invention relates to a flat-plate photobioreactor.

[0031] In the figure, 1-tubular photobioreactor body, 2-connecting plate, 3-bottom support column, 4-agitator, 5-liquid film layer, 6-spectrometer, 7-support, 8-embedded groove, 9-liquid outlet, 10-racetrack photobioreactor body, 11-gas aeration hole, 13-flat plate photobioreactor body. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] A method for culturing microalgae using nanofluids comprises the following steps:

[0036] Step S1, preparing a magnetic nanofluid, and measuring the electromagnetic quantity and light transmittance of the magnetic nanoparticles;

[0037] Step S2, microalgae cultivation: injecting the prepared magnetic nanofluid into the liquid film layer 5 of the photobioreactor, and the microalgae grow in the photobioreactor under the conditions of the preset electromagnetic intensity of the magnetic nanofluid and visible light with a wavelength of 400-700nm;

[0038] Step S3, collecting microalgae: after the growth cycle of the microalgae is over, the algae liquid is collected, and part of the magnetic nanofluid in the liquid film layer 5 is injected into the collected algae liquid, and the microalgae are flocculated by the magnetic nanoparticles; the nanofluid is coated between the photobiological reaction device and the light source, and the nanofluid in the liquid film layer 5 needs to be ventilated regularly to prevent the nanoparticles from sinking to the bottom;

[0039] Step S4, drying of microalgae: placing the microalgae solution collected by using the magnetic nanoparticles under sunlight, and utilizing the photothermal efficiency of the nanofluid to dry the algae solution.

[0040] Step S5, thermal conversion utilization: the nanofluid can be thermally converted with the microalgae without separation.

[0041] Preferably, the electromagnetic energy of the magnetic nanoparticles is 40-80 mT.

[0042] like Figure 1 and 2 As shown in the figure, the growth trend of Microalgae and Chlorella under 80mT magnetic field, OD is the value of spectrophotometer, the growth rate of microalgae is significantly improved under weak magnetic field, which promotes the growth of both Microalgae and Chlorella.

[0043] As shown in Tables 1-3, under the action of an 80mT magnetic field, the lipid content of Chlorella and Microcystis increased, the dry weight of Chlorella and Microcystis increased significantly, and the total biomass increased.

[0044] Table 1 Accumulation of non-magnetic nutrients

[0045]

[0046] Table 2 Accumulation of magnetic nutrients

[0047]

[0048] Table 3 Drying comparison with and without magnetism

[0049]

[0050] Preferably, the magnetic nanofluid has strong permeability at 400-700 nm. The nanofluid has heat absorption properties, absorbs light of additional wavelengths, and blocks heat in the invisible light range, so that the temperature of the algae liquid is suitable.

[0051] From Table 4, we can see that the growth, dry weight, and total biomass of microalgae under 1600lux, 2400lux, and 3200lux light intensities, and the light intensity for optimal growth are selected. It can be seen that 2400lux has a significant improvement on the growth of microalgae, while 3200lux inhibits the growth of microalgae. It can be seen that the appropriate light intensity effectively accelerates the growth of microalgae, and excessive light intensity inhibits the growth of microalgae. Not only does the light intensity affect the growth of microalgae, but different colors of light have a significant effect on the lipid accumulation of microalgae growth. Red and blue light can effectively promote the growth of microalgae and the accumulation of lipid substances. The main wavelength band of light required for the growth of microalgae is between 400 and 700nm. Nanofluids have selective light transmittance, including nanomagnetic fluids, which also have special magneto-optical effects and weak magnetism, which significantly promote the growth of microalgae and the accumulation of nutrients.

[0052] Table 4 Effect of light intensity on the growth of Microalgae

[0053]

[0054] During the growth stage of microalgae, nanofluids are prepared using nanoparticles. Appropriate nanoparticles are selected, and substances with poor light transmittance between 400 and 700 nm are preferred. In addition, the thermal conductivity of nanofluids is taken into consideration. The higher thermal conductivity can effectively utilize the heat of the light source through subsequent steps. If metal particles are selected, the particles can be magnetized to carry weak magnetism, and the nanofluid forms a weak magnetic field to promote the growth of microalgae. During the microalgae collection stage, magnetic nanofluids are used to flocculate and collect negatively charged microalgae particles. Microalgae and nanofluids are recycled together, with no energy consumption, no pollution, multiple uses of one material, reduced material loss, and high collection efficiency. After the microalgae are collected, the flocculated product is exposed to sunlight, and the heat absorption properties of the nanofluid are used to accelerate the drying rate. The nanofluid temperature can reach up to 120°C, and the nanofluid can then be thermally converted with the microalgae.

[0055] like Figure 3 and 4 As shown, a photobiological reaction device for realizing the method of culturing microalgae using nanofluids is a tubular photobiological reaction device; the tubular photobiological reaction device comprises a tubular photobiological reaction device body 1, a connecting plate 2 and a bottom support column 3; the bottom of the tubular photobiological reaction device body 1 is connected to the bottom support column 3 through the connecting plate 2; the tubular photobiological reaction device body 1 has a double-layer wall surface, and a gap is left between the tube walls as a liquid film layer 5, and the liquid film layer 5 is used to inject nanofluids. Support columns are added to the bottom of the tubular photobiological reaction device, and the four sides are connected to maintain stability. The nanofluid flows into the middle liquid film layer 5 and surrounds the tubular photobiological reaction device.

[0056] like Figure 5-7As shown, a photobiological reaction device for realizing the method of culturing microalgae using nanofluids is a racetrack photobiological reaction device; the racetrack photobiological reaction device comprises a racetrack photobioreactor body 10, a stirrer 4, a liquid film layer 5, a spectrometer 6, a support 7, an embedding groove 8 and a liquid outlet 9; the stirrer 4 is installed in the racetrack photobioreactor body 10, the liquid outlet 9 is arranged at the bottom of the racetrack photobioreactor body 10, the liquid film layer 5 is a plate-type liquid film, and the liquid film layer 5 is installed at the top of the racetrack photobioreactor body 10. The spectrometer 6 is installed on the liquid film layer 5, and is used to detect the transmittance of the magnetic nanofluid, and if the transmittance is lower than the threshold, the liquid film layer 5 is ventilated. A support rod is provided at the bottom of the liquid film layer 5, and the support rod is inserted into the embedding groove 8 provided around the top of the racetrack photobioreactor body 10, and the liquid film layer 5 can be inserted into the embedding groove 8 by means of support legs to keep it stable. The support 7 is installed on the outer bottom of the racetrack photobioreactor body 10. The support 7 is opened at the end of the microalgae culture to tilt the racetrack photobioreactor, and then the liquid outlet 9 is opened to collect the algae liquid. The racetrack photobioreactor device is designed with an embedded plate layer liquid film layer 5, which leaves a gap with the racetrack photobioreactor body 10. The plate layer is detachable, and the internal nanofluid can pass through the spectrometer 6 placed inside the plate layer, set a threshold to determine whether to replace the nanofluid, or ventilate the inside to reduce the deposition of the nanofluid to keep the nanofluid uniform. There is a support 7 at the bottom of the racetrack photobioreactor. In the microalgae collection stage, the support 7 is started to tilt the runway. A liquid outlet 9 is provided at the bottom of the racetrack photobioreactor, which is closed in the microalgae growth stage and opened in the microalgae collection stage, and the algae liquid is effectively collected through the angle supported by the support 7.

[0057] like Figure 8-9 As shown, a photobiological reaction device for realizing the method of culturing microalgae using nanofluids is a flat-plate photobiological reaction device; the flat-plate photobiological reaction device includes a flat-plate photobioreactor body 13, an aeration hole 11 and a liquid film layer 5; the flat-plate photobioreactor body 13 has a double-layer wall structure, and a gap between the two walls is a liquid film layer 5; the flat-plate photobioreactor body 13 is provided with an aeration hole 11 at the bottom, and the aeration hole 11 is opened during the growth of microalgae to provide necessary air for the growth of microalgae. An aeration strip is arranged at the bottom of the flat-plate photobioreactor body 13, and the double-layer side wall design leaves a 3-4 mm liquid film layer 5 in the middle, into which a suitable nanofluid can be added. The side walls are all made of transparent materials, and nanofluids can be used to selectively transmit light to culture microalgae.

[0058] Embodiment 1:

[0059] The nanofluid is Fe3O4 magnetic nanofluid,

[0060] A method for culturing, collecting and drying microalgae using nanofluids comprises the following steps:

[0061] Step 1: Prepare magnetic nanofluids and measure the electromagnetic properties and light transmittance of the particles;

[0062] Step 2: Cultivating microalgae: injecting the prepared magnetic nanofluid into the liquid film layer of the photobioreactor, and cultivating the microalgae to grow in the photobioreactor under the conditions of a certain electromagnetic intensity of the magnetic nanofluid and visible light with a wavelength of 400 to 700 nm;

[0063] Step 3: Collecting microalgae: After the growth cycle of Chlorella is over, collect the algae liquid, and inject part of the Fe3O4 magnetic nanofluid in the liquid film layer into the collected algae liquid, and use the Fe3O4 magnetic nanoparticles to flocculate the microalgae;

[0064] Step 4: Drying of microalgae: The microalgae solution collected by Fe3O4 magnetic nanoparticles is placed under sunlight and the photothermal efficiency of the nanofluid is utilized to dry the algae solution;

[0065] Step 5: Thermal conversion utilization: The nanofluid can be used for thermal conversion with microalgae, such as co-hydrothermal, co-pyrolysis and other thermal conversion experiments.

[0066] The step S1 of preparing Fe3O4 magnetic nanofluid is specifically as follows: polyvinyl pyrrolidone PVP and ferric nitrate are dissolved in water, Fe3O4 magnetic nanoparticles are obtained by ultrasonic spray pyrolysis, and the hysteresis loop of Fe3O4 magnetic nanoparticles is measured at room temperature by using a vibrating sample magnetometer, so that the electromagnetic quantity attached to Fe3O4 magnetic nanoparticles can be known. Fe3O4 magnetic nanoparticles are mixed with water to prepare 0.05wt% Fe3O4 magnetic nanofluid, and then the transmittance and thermal conductivity are tested. Fe3O4 magnetic nanofluid is injected into the glass interlayer liquid film layer 5 on a runway-type photobiological reaction device, and microalgae are cultured with sunlight as the light source. The magnetic field of the prepared Fe3O4 magnetic nanofluid is 40-80mT. Since light transmission is selected instead of opacity, the nanofluid concentration is selected to be an intermediate concentration of 0.05wt%, and the mixing ratio of PVP / Fe in the nanoparticles is nit=0.33, that is, the mixing ratio of PVP and ferric nitrate.

[0067] The prepared Fe3O4 nanofluid solvent is injected into the glass interlayer of the tubular photobioreactor. During the growth of the microalgae, the LED lamp is continuously irradiated, and the chlorella culture solution is injected into the tubular photobioreactor 1. During the microalgae cultivation period, the nanofluid will naturally settle due to its own weight, and it is necessary to regularly ventilate the liquid film to keep the nanofluid uniform.

[0068] After the growth cycle of Chlorella, the algae liquid is collected and the Fe3O4 magnetic nanofluid in the glass interlayer is injected into the collected algae liquid. The Fe3O4 magnetic nanoparticles can effectively flocculate the microalgae. The microalgae particles are negatively charged at all pH values, while the cationic Fe3O4 magnetic nanoparticles can effectively agglomerate the microalgae particles.

[0069] The algae solution collected by Fe3O4 magnetic nanoparticle fluid is placed in the sun, and the algae solution is dried using the photothermal efficiency of the nanofluid. The temperature of the nanofluid can reach up to 120°C. The nanofluid can then undergo thermal conversion with the microalgae.

[0070] Embodiment 2:

[0071] The difference between this embodiment 2 and embodiment 1 is that the prepared Fe3O4 nanofluid solvent (0.05wt%, PVP / Fenit=0.33) is injected into the liquid film layer 5 of the racetrack photobiological reaction device, and a gap is left between the liquid film and the racetrack. During the growth of the microalgae, sunlight is continuously irradiated. During the cultivation of microalgae, the nanofluid will naturally settle due to its own weight. A spectrometer 6 is set in the liquid film layer to detect the uniformity of the liquid film. A threshold is set. When the reading of the spectrometer 6 is less than the threshold, the liquid film is ventilated to ensure the uniformity of the nanofluid. The racetrack photobiological reaction device is equipped with a stirrer 4, which stirs the algae liquid slowly to make it uniform. Air pumps are set on the four sides to ensure the stable growth of the microalgae.

[0072] At the end of the growth of microalgae, the support 7 is opened to make the runway tilted at 30 degrees, and the liquid outlet is opened to drain the algae liquid inside the runway. The nanofluid in the liquid film is collected and mixed with it for flocculation collection. Since the concentration of the nanofluid in the liquid film is relatively low, and the total amount of microalgae cultured in the runway-type photobiological reaction device is large, additional nanoparticles need to be added to ensure the flocculation efficiency of the microalgae.

[0073] Since there are many magnetic nanoparticles, too many nanoparticles will affect the subsequent thermal conversion, so a separation step is required first. By taking advantage of the difference in hydrophilicity between nanoparticles and microalgae particles, liquid membranes are used for effective separation to separate sufficient nanoparticles, which are then dried together.

[0074] Embodiment 3:

[0075] The difference between Example 3 and Example 1 is that Fe3O4 magnetic nanofluid (0.05wt%, PVP / Fenit=0.33) is configured, and the nanofluid is injected into the liquid film layer 5 of the flat-plate photobiological reaction device, and the nanofluid exhibits weak light absorption at a wavelength of 500-700nm. The microalgae are cultured using strong light irradiation (light intensity greater than 3200lux), with a light-dark ratio of 12:12. Air is introduced into the bottom aeration hole at 0.2vv / m to perform pseudo-culture.

[0076] After the growth cycle is over, the magnetic nanofluid is mixed with the algae solution, and the magnetic nanoparticles absorb and aggregate the negatively charged microalgae particles due to the cations they carry.

[0077] After the microalgae are collected, 0.06g / L of nanofluid made of ethylene glycol and carbon powder is reconfigured. The nanofluid is stable at 150°C, and its properties can be used to perform heat conversion and other operations with the collected microalgae mixture under sunlight. Ethylene glycol is soluble in water but insoluble in oils and hydrocarbons, and its properties are active, and it can undergo esterification, alcoholization and other reactions, which can promote the generation of the target product of heat conversion.

[0078] The present invention utilizes the selective light transmittance property of nanofluids to effectively accelerate the growth trend of microalgae. Nanomaterials with high light transmittance in the red and blue spectrum wavelengths are used in a photobiological reaction device for selective light transmittance. The nanofluid is coated on the outside of the photobiological reaction device, and the light source required for the growth of microalgae is outside it. The heat absorption property of the nanofluid is used to maintain the algae liquid at a suitable temperature for algae growth. Due to different selections, the nanofluid has other properties such as weak magnetism in addition to selective light transmittance and heat absorption. The characteristic that microalgae are negatively charged in any pH state is utilized. The cations carried by the nanofluid are used to aggregate and collect the microalgae particles, and the flocculation is harvested. After the microalgae are collected, the heat absorbed by the nanofluid is used for co-drying.

[0079] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0080] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for culturing microalgae using nanofluids, characterized in that: The following steps are involved: Step S1, preparing nanofluid: magnetic nanofluid, and measuring the electromagnetic quantity and light transmittance of the magnetic nanofluid; the nanofluid is Fe3O4 magnetic nanofluid, and the Fe3O4 magnetic nanofluid is prepared by dissolving polyvinyl pyrrolidone PVP and ferric nitrate in water, and then ultrasonically spraying and pyrolyzing Fe3O4 magnetic nanoparticles, and mixing with water to prepare 0.05 wt% Fe3O4 magnetic nanofluid; Step S2, microalgae cultivation: injecting the prepared Fe3O4 magnetic nanofluid into the liquid film layer (5) of the photobioreactor, and growing the microalgae in the photobioreactor under the conditions of the preset electromagnetic intensity of the magnetic nanofluid and the visible light wavelength; the electromagnetic intensity of the magnetic nanofluid is 40-80 mT; the magnetic nanofluid has strong permeability at 400-700 nm; Step S3, collecting microalgae: after the microalgae growth cycle is over, the algae liquid is collected, and part of the magnetic nanofluid in the liquid film layer (5) is injected into the collected algae liquid, and the magnetic nanofluid is used to flocculate the microalgae; Step S4, drying of microalgae: placing the microalgae solution collected by the magnetic nanofluid under sunlight, and utilizing the photothermal efficiency of the nanofluid to dry the algae solution.

2. The method for culturing microalgae using nanofluids according to claim 1, characterized in that: The method further comprises step S5, heat conversion utilization: the nanofluid can perform heat conversion with the microalgae.

3. A photobiological reaction device for realizing the method of culturing microalgae using nanofluids as described in any one of claims 1 to 2, characterized in that: The photobiological reaction device is a tubular photobiological reaction device; the tubular photobiological reaction device comprises a tubular photobiological reaction device body (1), a connecting plate (2) and a bottom support column (3); the bottom of the tubular photobiological reaction device body (1) is connected to the bottom support column (3) via the connecting plate (2); the tubular photobiological reaction device body (1) has a double-layer wall surface, a gap is left between the tube walls to form a liquid film layer (5), and the Fe3O4 magnetic nanofluid is contained in the liquid film layer (5).

4. A photobiological reaction device for realizing the method of culturing microalgae using nanofluids as described in any one of claims 1 to 2, characterized in that: The photobiological reaction device is a racetrack-type photobiological reaction device; the racetrack-type photobiological reaction device comprises a racetrack-type photobiological reactor body (10), a stirrer (4), a liquid film layer (5), an embedding groove (8) and a liquid outlet (9); The stirrer (4) is installed in a racetrack photobioreactor body (10); the liquid outlet (9) is arranged at the bottom of the racetrack photobioreactor body (10); the liquid film layer (5) is a plate-type liquid film; the liquid film layer (5) is installed at the top of the racetrack photobioreactor body (10); and the Fe3O4 magnetic nanofluid is contained in the liquid film layer (5).

5. The photobiological reaction device for cultivating microalgae using nanofluids according to claim 4, characterized in that: It also includes a spectrometer (6), which is mounted on the liquid film layer (5) and is used to detect the light transmittance of the magnetic nanofluid. If the light transmittance is lower than a threshold, air is ventilated into the liquid film layer (5).

6. The photobiological reaction device for cultivating microalgae using nanofluids according to claim 4, characterized in that: A support rod is provided at the bottom of the liquid film layer (5), and the support rod is inserted into an embedding groove (8) provided around the top of the racetrack-type photobioreactor body (10).

7. The photobiological reaction device for cultivating microalgae using nanofluids according to claim 4, characterized in that: It also includes a support (7); the support (7) is installed on the outer bottom of the racetrack-type photobioreactor body (10).

8. A photobiological reaction device for implementing the method of culturing microalgae using nanofluids as described in any one of claims 1 to 2, characterized in that: The photobiological reaction device is a flat-plate photobiological reaction device; the flat-plate photobiological reaction device comprises a flat-plate photobiological reactor body (13), an air aeration hole (11) and a liquid film layer (5); the flat-plate photobiological reactor body (13) has a double-layer wall structure, a gap between the two walls is the liquid film layer (5), and the liquid film layer (5) contains the Fe3O4 magnetic nanofluid; the flat-plate photobiological reactor body (13) is provided with an air aeration hole (11) at the bottom.

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