A photobioreactor operating in a large body of water

Abstract

This invention relates to a photobioreactor operating in a large body of water for cultivating microalgae in vast bodies of water such as oceans and lakes. It includes a floating work platform and a microalgae cultivation device suspended below the work platform, the cultivation device being submerged in water. The microalgae cultivation device comprises a net box with screens on all sides and bottom, and an open top. The mesh size of the screens is less than 1 micrometer, and microalgae cells are cultured in the net box. An artificial light source and a nutrient release device are installed inside the net box. A storage tank for supplying nutrients to the nutrient release device is located on the work platform. This photobioreactor does not occupy land area, has a large cultivation volume, low cost, low energy consumption, and high light energy utilization, opening up a new direction for the research and development of floating photobioreactors.

Description

Technical Field

[0001] This invention relates to the field of photobioreactor technology, and more particularly to a photobioreactor that operates in a large body of water. Background Technology

[0002] Microalgae can efficiently utilize light energy, carbon dioxide, and water for photosynthesis, producing oxygen and synthesizing a variety of bioactive substances (such as polysaccharides, proteins, oils, unsaturated fatty acids, natural pigments, vitamins, and minerals). They also have advantages such as rapid growth rate, short cultivation cycle, sustainable regeneration, and no occupation of arable land. They are considered an important source of raw materials for new biomass energy and can be widely used in food and feed, medicine and health care, cosmetics, aquatic animal and poultry and livestock farming, etc., with very broad application prospects.

[0003] Photobioreactors are the core of the entire microalgae industry chain. Currently, large-scale microalgae cultivation for commercial applications is mostly carried out in indoor and outdoor open cultivation systems and closed photobioreactors. Open ponds have become the most widely used cultivation system for large-scale microalgae cultivation due to their advantages of being more economical and easier to establish and operate. However, this type of open cultivation system is greatly affected by the environment, is easily contaminated, and has uncontrollable cultivation conditions, high water evaporation, and low effective light utilization. In contrast, closed photobioreactors offer highly controllable cultivation parameters, making microalgae cultivation less susceptible to contamination, with high light energy utilization efficiency and high biomass concentration. However, they are expensive to build and operate and maintain. Currently, microalgae photobioreactors are all terrestrial, and large-scale industrial-scale microalgae cultivation photobioreactors suitable for marine environments have not yet been developed. For terrestrial photobioreactors, the main technical problems are as follows: ① Open raceway ponds have large footprints, low cultivation density, high energy consumption for culture medium circulation, and are easily contaminated by external factors. ② Sealed, light-transmitting containers are expensive, especially glass containers. Due to the special nature and limitations of glass processing technology, they cannot be molded in one piece, resulting in very high manufacturing, installation, and maintenance costs. They also suffer from low cell culture density, insufficient space utilization, and high energy consumption. ③ Solid-state photobioreactors are highly dependent on the materials used and have low light utilization efficiency. Their applicability is also limited, and their liquid supply devices are energy-consuming, preventing further reductions in culture costs. Currently, these mainstream microalgae culture systems mainly operate on land, occupying large amounts of land. Furthermore, equipment depreciation and energy consumption increase the cost of microalgae cultivation, severely hindering the rapid development of the microalgae industry.

[0004] Although my country has a vast sea area and abundant marine resources, the cultivation of biomass energy and aquatic organisms is expanding into the ocean due to limitations in land and coastal aquaculture areas. Therefore, developing a new type of low-cost, high-efficiency, and multi-purpose marine photobioreactor has significant practical importance and enormous application prospects.

[0005] Currently, microalgae cultivation devices used in outdoor open water mainly include floating aquaculture rafts, enclosed microalgae cultivation devices, and a semi-submersible net cage with LED submersible lights. Furthermore, floating translucent film bags are easily broken by wind and waves. These devices are rudimentary in structure, have small cultivation volumes, insufficient or no underwater lighting, low light energy utilization, are easily damaged by fish, and the cultivated microalgae are easily preyed upon by zooplankton and some fish; moreover, management and maintenance are difficult. To date, there is still a lack of photobioreactors that can be stably applied to large-scale microalgae cultivation in open water, especially in the ocean. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] In view of the above-mentioned shortcomings and deficiencies of the existing technology, the present invention provides a photobioreactor that operates in a large body of water. It combines the advantages of various reactors with the characteristics of microalgae growth, and solves the problems of current terrestrial photobioreactors, such as large footprint, high cost, high energy consumption, difficulty in temperature control, low light energy utilization, slow cell proliferation rate, low biomass concentration, and easy pollution. It also opens up a new direction for the research and development of marine photobioreactors.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] The present invention provides a photobioreactor operating in a large body of water for cultivating microalgae in oceans / lakes / reservoirs, comprising a working platform floating on the water surface and a microalgae cultivation device suspended around the working platform, the microalgae cultivation device being submerged in water;

[0011] The microalgae cultivation device includes a mesh box with a screen around the sides and bottom and an open top. The mesh size of the screen is less than 1 micrometer. Microalgae cells are inoculated and cultured in the mesh box. The mesh box is equipped with an artificial light source and a nutrient release device. The working platform is equipped with a storage tank that provides nutrients to the nutrient release device.

[0012] The nutrient release device can provide a nutrient solution containing carbonates or bicarbonates to provide a carbon source for algal cells, thus eliminating the need for a dedicated carbon dioxide supply device.

[0013] The mesh size of the net cage is less than 1 micrometer, which provides the necessary space for the growth and reproduction of microalgae cells, and also prevents or reduces the entry of protozoa into the net cage and their contamination of algae cells.

[0014] According to a preferred embodiment of the present invention, the working platform is equipped with a power supply device connected to the public power grid. This power supply device provides electrical energy to the artificial light source and nutrient release device. The power supply device includes transformer, rectifier, and voltage regulator circuits, and can directly utilize the mains power grid. Alternatively, more preferably, the working platform is equipped with an energy storage device and one or more of the following power generation devices: wind power generation device, photovoltaic power generation device, and wave power generation device. The electrical energy generated by these power generation devices is stored in the energy storage device, which then provides electrical energy to the artificial light source and nutrient release device. Since the working platform floats on the ocean, lake, or a wide reservoir without obstructions, it can receive sunlight and wind energy for extended periods. Therefore, it is preferable to use a combination of photovoltaic and wind power generation to produce clean electricity to provide the microalgae cultivation device below the working platform for its normal operation.

[0015] According to a preferred embodiment of the present invention, the cage is further provided with a carbon dioxide supply device, and the power supply device or the energy storage device provides electrical energy to the carbon dioxide supply device.

[0016] According to a preferred embodiment of the present invention, the artificial light source, nutrient release device, and carbon dioxide supply device are suspended below the working platform to reduce the pressure on the net cage and prevent damage to the net cage.

[0017] According to a preferred embodiment of the present invention, the carbon dioxide supply device includes a carbon dioxide distributor located at the bottom of the mesh cage; the carbon dioxide distributor is provided with a plurality of air holes, and the carbon dioxide distributor is connected to an air source above the working platform through an air supply pipe. The air source is a CO2 cylinder, an air pump, or a combination of a CO2 cylinder and an air pump.

[0018] The gas supply pipe is arranged vertically, and the carbon dioxide distributor is arranged horizontally along the bottom of the cage; wherein the gas supply pipe is a telescopic pipe, thereby adjusting the depth of the carbon dioxide distributor below the water surface.

[0019] In some embodiments, air and CO2 are fully premixed in a certain ratio and introduced from the top of the net cage, flowing downward along the gas supply pipe and distributed by the carbon dioxide distributor at the bottom of the net cage. This provides the algal cells with the CO2 required for growth and, together with the ocean waves, achieves full stirring of the algal solution and uniform distribution of algal cells.

[0020] According to a preferred embodiment of the present invention, the nutrient release device includes a liquid pump, a nutrient delivery pipe, and an opening or nozzle disposed on the nutrient delivery pipe; the nutrient delivery pipe consists of multiple pipes, dispersedly arranged in the middle of the net cage. The opening can directly release nutrient solution into the net cage, but below the deeper water surface, the water pressure is higher. In this case, a nozzle can be installed on the nutrient delivery pipe to spray the nutrient solution into the net cage at a higher pressure, which helps the diffusion and distribution of nutrients.

[0021] More preferably, the nozzle is a rotating nozzle (more preferably a 360° rotating nozzle) or a fixed nozzle to disperse the nutrients released by the nutrient release device, and the length of the nutrient delivery pipe submerged in seawater is adjustable. The nutrients are mainly nitrogen-containing nutrients or inorganic nutrients; when a carbon dioxide supply device is not installed, the nutrients also include carbonates or bicarbonates, etc.

[0022] According to a preferred embodiment of the present invention, the nutrient release device further includes a plurality of nutrient concentration detectors, which are dispersed at different positions and depths within the cage; the working platform is equipped with a controller, which starts or stops the liquid pump of the nutrient release device according to the nutrient concentration detected by the nutrient concentration detectors, so as to start or stop the release of nutrients.

[0023] The nutrient concentration detector is used to detect the concentration of one or more specific components in the nutrient solution released by the nutrient release device. When the nutrient concentration at a certain location is detected to be too low, the nutrient release device needs to be activated to release nutrients; otherwise, the nutrient release device is turned off.

[0024] According to a preferred embodiment of the present invention, the artificial light source includes a light-emitting component and a waterproof and light-transmitting sleeve, the sleeve being fitted over the light-emitting component. The artificial light source includes a plurality of light-emitting components. Seawater can dissipate heat and cool the light-emitting components; the light-emitting components are connected to an energy storage device.

[0025] Preferably, the light intensity, wavelength, and illumination period of the artificial light source are all adjustable, which greatly improves the utilization rate of light energy. An intelligent light source regulator is provided on the working platform, and light intensity sensors are installed at different depths in the cage. With the help of the light intensity sensors and the intelligent light source regulator, the luminous intensity, light quality, wavelength, luminous duration, and light-dark cycle of the light-emitting components of the artificial light source can be automatically adjusted.

[0026] The light-emitting components are fluorescent tubes and LED light strips; the waterproof and light-transmitting sleeve is one or more of PC (polystyrene), PMMA (plexiglass), AS (acrylic) or PSU (polycarbonate), which have good waterproof and corrosion-resistant properties.

[0027] According to a preferred embodiment of the present invention, the light-emitting component and the waterproof and light-transmitting sleeve as a whole can be raised and lowered relative to the working platform to adjust the depth of the artificial light source below the water surface according to the volume of the net cage and the intensity of sunlight. When the intensity of sunlight weakens, the artificial light source can be extended to a deeper position in the net cage.

[0028] According to a preferred embodiment of the present invention, the light intensity, wavelength, and illumination period of the artificial light source are all adjustable; an intelligent light source regulator is provided on the working platform, and light intensity sensors are provided at different depths in the cage. With the help of the light intensity sensors and the intelligent light source regulator, the light intensity, wavelength, light quality, light emission duration, and light-dark cycle of the light-emitting components of the artificial light source can be automatically adjusted.

[0029] According to a preferred embodiment of the present invention, a sonar device is provided below the working platform to drive away fish and prevent them from damaging the structure of the microalgae cultivation device.

[0030] According to a preferred embodiment of the present invention, several ropes are hinged below the working platform, and counterweights are suspended below the ropes. The ropes and counterweights form the skeleton structure of the net cage to maintain its volume and shape. The counterweights can be concrete blocks, iron blocks with an anti-corrosion coating, or copper blocks. The screen can be a nylon screen, a polyethylene screen, an ultrafiltration membrane, or a osmosis or reverse osmosis membrane, etc. Alternatively, several rigid vertical supports are hinged below the working platform, and horizontal supports are connected between the vertical supports to form the skeleton structure of the net cage to maintain its volume and shape.

[0031] According to a preferred embodiment of the present invention, the length of the rope is adjustable, and the screen is a flexible screen. Therefore, the volume of the net cage can be adjusted by changing the length of the rope, thus achieving volume regulation. Extending the rope can increase the effective culture volume of microalgae, while retracting the rope can reduce the volume of the net cage to achieve rapid harvesting of microalgae biomass.

[0032] According to a preferred embodiment of the present invention, a protective net cover is also provided on the outside of the net cage to prevent fish or large aquatic animals from damaging the structure of the microalgae cultivation device. The protective net cover and the sonar device work together to protect the net cage. Since the net cage is made of a flexible material with low strength, the protective net cover on its outside helps to prevent damage to the net cage.

[0033] According to a preferred embodiment of the present invention, the net cage of the photobioreactor is hexahedral in shape, and its volume is 1-100m long * 1-100m wide * 1-100m high, or an equivalent volume of a cylinder, ellipse, or other regular geometric shape, or an equivalent volume of an irregular geometric shape.

[0034] In the ocean, water temperature varies only slightly. The relationship between seawater depth and temperature is uniform between 20 and 200 meters, with temperature variations of less than 10°C at depths of 1-100 meters. To balance underwater temperature variations with cultivation scale and economic benefits, the preferred net cage size is 5-50m wide x 5-50m high, more preferably 10-30m wide x 10-30m high.

[0035] All components of the photobioreactor described above in this invention are waterproof, acid and alkali resistant, high pressure resistant, and corrosion resistant. The photobioreactor of this invention is preferably used in the ocean, where seawater contains a large amount of inorganic salts, providing natural inorganic nutrients for microalgae growth.

[0036] (III) Beneficial Effects

[0037] To address the problems of existing technologies, this invention has developed a novel photosynthetic bioreactor that is low-cost, energy-efficient, highly light-utilizing, rapidly proliferating, and has a high biomass concentration. It is also less prone to pollution and suitable for large-scale industrial-scale microalgae cultivation in large bodies of water such as oceans and lakes. This invention can reduce the overall cost of microalgae cultivation while also providing significant economic and environmental benefits. This novel reactor not only overcomes the design flaws commonly found in existing terrestrial photobioreactors, but also does not occupy land (avoiding competition with farmland) and can broaden the future research and development of photobioreactors. Specifically, the technical effects of this invention are also reflected in the following aspects:

[0038] (1) The photobioreactor consists of a floating working platform and a submerged microalgae cultivation device. This invention can reduce the overall cost of microalgae cultivation while bringing good economic and environmental benefits. This novel reactor not only overcomes the design defects of existing terrestrial photobioreactors, but also does not occupy land (does not compete with farmland) and can broaden the new field of future photobioreactor research and development. Compared with traditional floating photobioreactors, the photobioreactor of this invention has a very small specific surface area and a huge cultivation volume. The small specific surface area results in a small amount of high-cost materials used, and the cost is relatively low. The net cage extends underwater (the net cage volume can be fixed or adjusted according to the ropes), and the underwater waves are very small, making it practically feasible to operate. The working platform is equipped with at least one of several solar / wind power generation devices / wave power generation devices and an underwater sonar device for energy supply to the microalgae photobioreactor and for driving away fish.

[0039] (2) For photobioreactors used in the ocean, the net cages for microalgae cultivation devices come in various shapes, such as cylinders, cubes, and cuboids (rounded corners, right angles). The outer wall of the net cage is surrounded by a sieve with a pore size of less than 1 micrometer, which ensures that microalgae cells can grow and reproduce within the net cage and prevents or reduces contamination from protozoa, etc. The sieve can be nylon sieve, polyethylene sieve, ultrafiltration membrane, osmosis membrane, or reverse osmosis membrane, etc. The ropes and the counterweights connected to the lower ends of the ropes serve to stretch and reinforce the net cage frame. The counterweights can be iron blocks, copper blocks, stone blocks, or concrete blocks coated with anti-corrosion coatings. The volume of the net cage can be adjusted by the length of the ropes, making it easy to expand the cultivation volume and harvest algae cells.

[0040] (3) The light source of the microalgae cultivation device adopts sunlight and artificial light source immersed in water, or a combination of both, which can realize the adjustment of light intensity, wavelength and light cycle, and greatly improve the light energy utilization rate. The artificial light source consists of light-emitting components and a waterproof and light-transmitting sleeve. The artificial light source can be cooled by absorbing heat from seawater. The artificial light source can be a fluorescent tube, LED light strip or light-emitting material; the transparent tube material can be PC (polystyrene), PMMA (plexiglass), AS (acrylic) or PSU (polycarbonate), etc.

[0041] (4) The carbon dioxide supply device distributes the carbon dioxide through a carbon dioxide distributor located at the bottom of the net cage. On the one hand, it provides the carbon source required for the growth and photosynthesis of algal cells. On the other hand, it combines with wave agitation to achieve full agitation of the culture solution and uniform distribution of algal cells. The supplied gas can be pure carbon dioxide or a mixture of air and carbon dioxide in a certain proportion. The gas distributor has various shapes, such as porous discs, meandering S-shaped pipes with vents, and parallel porous pipes, etc.

[0042] (5) The nutrient release device is located near the center inside the reactor and includes a liquid pump, a nutrient delivery pipe, and nozzles mounted on the nutrient delivery pipe. Preferably, the nutrient delivery pipe is located near the center of the mesh cage to maximize the release path of nutrients, ensuring more uniform distribution of nutrients within the mesh cage. This allows the nutrient solution to be consumed just as it reaches the edge of the mesh cage, preventing nutrients from escaping to the outside. Nutrient salts are sprayed out through 360° rotating nozzles, and the utilization of nutrient salts is maximized by adjusting the pressure. The nutrient delivery pipe's central location maximizes the release path of nutrients and ensures more uniform distribution within the mesh cage. Furthermore, the nutrient release device includes multiple nutrient concentration detectors, and a controller is installed on the working platform. The controller starts or stops the liquid pump of the nutrient release device based on the detected nutrient concentration, thereby saving energy and nutrients and avoiding waste.

[0043] (6) All components of the photobioreactor are waterproof, acid and alkali resistant, high pressure resistant, and corrosion resistant; the depth of the artificial light source submerged below the water surface is adjustable, the length of the gas delivery pipe is adjustable, the length of the nutrient delivery pipe is adjustable, and the volume of the net cage is adjustable, allowing for the adjustment of the microalgae cultivation scale according to needs and natural environment and climate. The photobioreactor of this invention provides cultivation facilities for marine algae, such as *Phaeodactylum tricornutum*, *Isochophyton chinensis*, and *Hygrophytes spp.* Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the overall structure of the photobioreactor for cultivating microalgae in the ocean according to Embodiment 1 of the present invention.

[0045] Figure 2 This is a schematic diagram of the structure of the cultivation device (net cage and auxiliary facilities) of the photobioreactor for cultivating microalgae in the ocean according to Embodiment 2 of the present invention. Detailed Implementation

[0046] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Example 1

[0048] This invention proposes a photobioreactor operating in a large body of water for cultivating microalgae in the ocean. It includes a floating work platform and microalgae cultivation devices suspended around the platform, submerged in seawater. The microalgae cultivation devices are suspended below the work platform, providing space for microalgae inoculation and cultivation. The work platform mainly houses wind / photovoltaic / wave power generation devices and energy storage devices, a control box, carbon dioxide tanks, air pumps, liquid pumps, a drive circuit board for an artificial light source, an artificial light source controller, a walking path for workers, nutrient solution storage tanks, staff dormitories, offices / monitoring rooms, and a laboratory. The microalgae cultivation device mainly consists of a net cage, an artificial light source, a carbon dioxide supply device, a nutrient release device, a sonar device, and a rigid protective net (or a flexible protective net made of strong and tough material) located within the net cage. The electrical energy storage device on the work platform provides the necessary electrical energy to the artificial light source, carbon dioxide supply device, and nutrient release device.

[0049] To better understand the above technical solution, the following will refer to... Figure 1 Exemplary embodiments of the present invention will be described in more detail below.

[0050] like Figure 1The diagram shows a schematic of a photobioreactor according to a preferred embodiment of the present invention. It includes a working platform 10, which floats on the water surface. A microalgae cultivation device 20 is symmetrically fixed around the working platform 10, comprising a net cage 21, an artificial light source 22, a carbon dioxide supply device 23, a nutrient release device 24, a sonar device 25, and a protective net cover 26. Except according to... Figure 1 In addition to the square working platform 10 shown, the working platform 10 can also be arranged in a long straight line structure, with several microalgae cultivation devices 20 symmetrically distributed on both sides of the straight line.

[0051] The working platform 10 is equipped with wind / solar / wave power generation devices (the wave power generation device is partially submerged in shallow water to receive wave impact energy and convert it into electricity) 11, energy storage devices 12, nutrient solution storage tanks 13, etc. These power generation and storage devices provide all the energy for the operation of the microalgae cultivation device 20. The loads on the working platform 10, such as the power generation equipment and energy storage devices, should be distributed as evenly as possible to avoid tilting the working platform 10.

[0052] The microalgae cultivation device 20 includes a mesh cage 21 comprising a frame 210, a screen 213, and other components. The mesh cage 21 has a screen 213 around its sides and bottom, and an opening 214 at the top (a steel frame structure or steel beam 2141 is provided above the working platform 10 corresponding to this opening 214, allowing artificial light sources 22, carbon dioxide supply devices 23, and nutrient release devices 24 to be suspended below the steel frame structure or steel beam 2141, extending into the mesh cage 21 from the opening 214), allowing direct sunlight exposure. The mesh 213 has a pore size of less than 1 micrometer, providing the necessary growth and reproduction space for microalgae cells while preventing or reducing contamination from protozoa and other organisms. The frame 210 of the mesh cage 21 consists of ropes 211 hinged below the working platform 10 and counterweights 212 connected to the lower ends of the ropes 211. The number of ropes 211 can be 4, 6, 8… up to 20, etc., with no specific limit. Screens 213 are fixed to the bottom and all four sides of the frame 210, with an open top 214, allowing the net box 21 to be shaped into a cuboid, hexagonal prism, octagonal prism, cylinder, elliptical cylinder, etc. The screens 213 are tied to ropes 211, with the lower edge of the screen 213 fixed to the lower end of the ropes 211 and the upper edge fixed to the upper end of the ropes 211, further reinforced in the middle. The screens 213 are made of flexible materials, such as nylon screens, polyethylene screens, ultrafiltration membranes, or osmosis and reverse osmosis membranes, allowing water molecules and gases to pass through, but not allowing microalgae cells and protozoa to pass through. The ropes 211 are retractable steel or nylon ropes, with adjustable length submerged in seawater. The counterweight 212 can be a concrete block, an iron block with an anti-corrosion coating, or a copper block. The frame 210 can maintain the volume and shape of the net cage 21. At the same time, since the screen 213 is a flexible screen and the rope 211 is a retractable rope (the steel frame structure or steel frame beam 2141 is equipped with a retractor), the effective volume of the net cage 21 and the scale of aquaculture can be expanded by extending the rope 211, or the volume of the net cage 21 can be reduced by retracting the rope 211, thereby quickly harvesting microalgae cells.

[0053] Methods for harvesting microalgae include centrifugation, filtration, flocculation and sedimentation of algal solutions. Preliminary harvesting facilities such as centrifuges, filters or flocculation tanks can be set up on the work platform to perform preliminary concentration treatment on the harvested algal solutions before transporting them to the processing plant for further processing.

[0054] When the cage 21 is a cuboid, its volume is 1-100m long * 1-100m wide * 1-100m high. When it is in other shapes, it can be a regular geometric shape such as a cylinder or ellipse with an equivalent volume to the cuboid, or an irregular geometric shape with an equivalent volume to the hexahedron.

[0055] The artificial light source 22 includes a light-emitting component 220 and a waterproof and light-transmitting sleeve 221. The waterproof and light-transmitting sleeve 221 is fitted over the light-emitting component 220. The artificial light source 22 includes several light-emitting components, which are distributed and spaced apart in the net cage 21. The artificial light source 22 is mainly located at a depth of 2 meters below seawater to supplement the insufficient intensity of natural light below seawater. Seawater can dissipate heat and cool the light-emitting components. The light-emitting components 220 are connected to the power storage device 12 on the working platform 10. The light intensity, wavelength, light quality, and light-dark cycle of the artificial light source 220 can all be adjusted to maximize the utilization of light energy. An intelligent light source regulator is provided on the working platform 10, and light intensity sensors are installed at different depths in the net cage 21. With the help of the light intensity sensors and the intelligent light source regulator, the light intensity, wavelength, and light duration of the light-emitting component 220 of the artificial light source can be automatically adjusted. The light-emitting component 220 is one or a combination of fluorescent tubes, LED light strips, etc., while the waterproof and light-transmitting sleeve 221 is one or more of PC (polystyrene), PMMA (plexiglass), AS (acrylic), or PSU (polycarbonate). The light column structure, composed of the light-emitting component 220 and the waterproof and light-transmitting sleeve 221, can be adjusted vertically relative to the working platform 10 to adjust the depth of the artificial light source below the water surface according to the volume of the net cage 21 and the intensity of sunlight. When the sunlight intensity weakens, the artificial light source 22 can be extended deeper into the net cage 21.

[0056] In some embodiments, the light-emitting component 220 can be configured as a flexible and retractable light-emitting strip, while the waterproof and light-transmitting sleeve 221 is made of a flexible and retractable material. This allows the light-emitting length of the component 220 within the net cage 21 and its depth below the water surface to be adjusted according to the volume of the net cage 21 and the intensity of sunlight. During cloudy weather, more light-emitting strip can be released into the net cage 21 to increase light intensity.

[0057] The carbon dioxide supply device 23 includes a carbon dioxide distributor 230, located at the bottom of the net cage 21. The carbon dioxide distributor 230 has several air holes and is connected to a gas delivery pipe 231, which in turn connects to a gas source above the working platform 10. The gas source is a CO2 cylinder, an air pump, or a combination of both. The gas distributor 230 can have various shapes, such as a perforated disc, a meandering S-shaped pipe with air holes, or parallel perforated pipes. The gas delivery pipe 231 is arranged vertically within the net cage 21, and the carbon dioxide distributor 230 is positioned nearly horizontally at the bottom of the net cage 21. Preferably, the gas delivery pipe 231 is a telescopic pipe, thereby adjusting the depth of the carbon dioxide distributor 230 below the water surface. In some embodiments, air and CO2 are fully premixed in a certain ratio and introduced from the top of the net cage 21, flowing downward along the air supply pipe 231 and distributed by the carbon dioxide distributor 230 at the bottom of the net cage 21. This provides the algal cells with the CO2 required for growth and, together with the ocean waves, achieves full stirring of the algal solution and uniform distribution of algal cells.

[0058] The nutrient release device 24 includes a liquid pump (not shown), a nutrient delivery pipe 240, and nozzles 241 mounted on the nutrient delivery pipe 240. Preferably, the nutrient delivery pipe 240 is vertically positioned near the center of the net cage 21. More preferably, the nutrient delivery pipe 240 is located on the central axis of the net cage 21, with multiple branch pipes arranged radially along the pipe, and the nozzles 241 are mounted on these branch pipes. The nozzles 241 are 360° rotating nozzles, dispersing the nutrients released by the nutrient release device at a certain pressure. The length of the nutrient delivery pipe 240 submerged in seawater is adjustable to regulate the nutrient release depth. The nutrients are mainly nitrogen-containing nutrients or inorganic nutrients. Setting the nutrient delivery pipe 240 near the center of the net cage 21 has two advantages. First, it allows the nutrients to have the maximum release path, so that the nutrients are consumed before they diffuse to the edge of the net cage 21 after being released, thus avoiding the waste caused by the nutrients escaping to the outside of the net cage 21 too quickly. Second, it can make the nutrients in the net cage 21 as uniform as possible.

[0059] Preferably, the nutrient release device 24 further includes multiple nutrient concentration detectors, dispersed at different positions and depths within the net cage 21. A controller is provided on the working platform 10. The controller starts or stops the liquid pump of the nutrient release device 24 based on the nutrient concentration detected by the nutrient concentration detectors, thereby starting or stopping the release of nutrients. Therefore, in some embodiments, the nutrient release device 24 operates intermittently; whether to start nutrient release is determined by the detection results of the nutrient concentration detectors, thus avoiding nutrient waste. The nutrient concentration detectors detect the concentration of one or more specific components in the nutrient solution released by the nutrient release device. When the nutrient concentration at a certain location is detected to be too low, the nutrient release device needs to be started to release nutrients; otherwise, the nutrient release device is turned off.

[0060] The sonar device 25 can be located at the bottom of the net cage 21 or inside the net cage 21. It is used to emit sound waves to drive away fish and prevent them from damaging the structure of the microalgae cultivation device.

[0061] A protective net cover 26 is installed on the outside of the net cage 21 to prevent fish or large aquatic animals (especially whales, sharks, and large zooplankton in the ocean) from colliding with or becoming entangled in seaweed and damaging the structure of the net cage 21. The protective net cover 26 can be made of welded stainless steel and is fixed below the working platform 10, with hinged joints to withstand a certain amount of impact. The protective net cover 26 and the sonar device 25 work together to protect the net cage 21.

[0062] All components of the photobioreactor in the above scheme are waterproof, acid and alkali resistant, high pressure resistant, and corrosion resistant. Furthermore, the above photobioreactor has the following advantages:

[0063] (1) The net cage 21 used for cultivating microalgae is suspended on the seawater and does not occupy land resources; the net cage 21 has a very small specific surface area and low cost per unit volume; the net cage 21 can flexibly increase or decrease the algae cultivation volume in the vertical direction by adjusting the length of the rope 211 (from thousands of tons to millions of tons), so as to expand the cultivation scale according to the needs and facilitate the harvesting of microalgae cells; the net cage (pore size less than 1 micrometer) can prevent or reduce pollution from protozoa, etc.

[0064] (2) The photobioreactor of the present invention is particularly suitable for use at sea, where the water surface is wide and the wind is strong. It can generate electricity using renewable natural energy sources such as solar / wind energy and ocean current energy. It can also utilize the natural nutrients in the sea, such as inorganic salts, organic matter and trace elements. The solar / wind / wave power generation device 11 installed on the working platform on the water surface can provide electricity for the microalgae cultivation device, thereby achieving "zero" energy consumption. Natural seawater can provide a stable temperature for the cultivation system and can also cool and absorb the heat of the artificial light source components. After absorbing heat, the water can maintain a suitable growth temperature for microalgae in the microalgae cultivation device. The natural ocean current can also be used to stir the algae solution, so that the algae cells are evenly distributed. The inorganic salts, organic matter and trace elements in the seawater can provide the nutrients required for the growth of microalgae.

[0065] (3) The light source of the microalgae cultivation device is sunlight, with an artificial light source 22 built in, or a combination of both. It can adjust the light intensity, wavelength, light quality and light cycle, greatly improve the light energy utilization rate, and provide light for algal cell growth and proliferation 24 hours a day. It can efficiently increase algal cell yield and shorten the production cycle.

[0066] (4) The carbon dioxide supply device 23 not only provides carbon dioxide needed for microalgal photosynthesis, but also couples with the ocean current to achieve full stirring of the algal liquid and uniform distribution of algal cells.

[0067] (5) Based on the needs of different growth stages of microalgae cells, the concentration of nutrients in the culture solution can be controlled by adjusting the pressure of the nutrient release device 24, thereby maximizing the utilization of nutrients.

[0068] (6) The microalgae cultivation device utilizes in-situ seawater, and the photobioreactor is permeable to water but not to algae. The cultured algal solution can exchange water with the natural water body in real time, eliminating problems such as wastewater collection and treatment. When harvesting the cultured algal cells, the algal solution can be concentrated by adjusting the volume of the photobioreactor. Combined with ultrafiltration technology and centrifugation, rapid and efficient algal cell separation and collection can be achieved.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photobioreactor operating in a large body of water for cultivating microalgae in oceans / lakes / reservoirs, characterized in that, It includes a working platform floating on the water surface and a microalgae cultivation device suspended around the working platform, the microalgae cultivation device being submerged in water; The microalgae cultivation device includes a mesh box with a screen on all sides and bottom and an open top. The screen can be any type of nylon screen or polyethylene screen, and the mesh size of the screen is less than 1 micrometer. Microalgae cells are inoculated and cultured in the mesh box. The mesh box is equipped with an artificial light source and a nutrient release device. The working platform is equipped with a storage tank to provide nutrients to the nutrient release device. The work platform is equipped with a power supply device connected to the public power grid, which provides power to the artificial light source and nutrient release device; or the work platform is equipped with an energy storage device and one or more of the following power generation devices: wind power generation device, photovoltaic power generation device, and wave power generation device; the energy storage device provides power to the artificial light source and nutrient release device; the artificial light source and nutrient release device are suspended and connected below the work platform. The nutrient release device also includes multiple nutrient concentration detectors, which are distributed at different positions and depths within the cage; the working platform is equipped with a controller, which starts or stops the liquid pump of the nutrient release device according to the nutrient concentration detected by the nutrient concentration detectors, so as to start or stop the release of nutrients. Several ropes are hinged below the working platform, and counterweights are suspended below the ropes. The ropes and counterweights form the skeleton structure of the net cage to maintain its volume and shape. The length of the ropes is adjustable, and the screen is a flexible screen. The volume of the net cage is adjusted by the length of the ropes, and the rapid harvesting of microalgae biomass is achieved by winding up the ropes. The cage is also equipped with a carbon dioxide supply device, which includes a carbon dioxide distributor located at the bottom of the cage. The carbon dioxide distributor is connected to a gas source above the working platform through a gas pipeline. The gas pipeline is a telescopic pipeline, thereby adjusting the depth of the carbon dioxide distributor below the water surface. The nutrient release device includes a liquid pump, a nutrient delivery pipe, and an opening or nozzle on the nutrient delivery pipe; the length of the nutrient delivery pipe submerged in seawater is adjustable, and there are multiple nutrient delivery pipes, which are distributed in the middle of the net cage; the nozzle is a rotating nozzle / fixed nozzle to disperse the nutrients released by the nutrient release device. The artificial light source includes a light-emitting component and a waterproof and light-transmitting sleeve, which is fitted over the light-emitting component. The light-emitting component and the waterproof and light-transmitting sleeve as a whole can be raised and lowered relative to the working platform to adjust the depth of the artificial light source below the water surface according to the volume of the net cage and the intensity of sunlight.

2. The photobioreactor of claim 1, wherein, The power supply device or the energy storage device provides electrical energy to the carbon dioxide supply device; the carbon dioxide supply device is suspended below the working platform; the carbon dioxide distributor is provided with several air holes.

3. The photobioreactor of claim 2, wherein, The gas pipeline is arranged vertically, and the carbon dioxide distributor is arranged horizontally along the bottom of the cage.

4. The photobioreactor of claim 1, wherein, The artificial light source includes several light-emitting components, which are connected to an energy storage device. The light intensity, wavelength, and illumination period of the artificial light source are all adjustable. An intelligent light source regulator is provided on the working platform, and light intensity sensors are provided at different depths in the cage. With the help of the light intensity sensors and the intelligent light source regulator, the light intensity, wavelength, light quality, light emission duration, and light-dark cycle of the light-emitting components of the artificial light source can be automatically adjusted.

5. The photobioreactor of claim 1, wherein, A sonar device is installed below the working platform. The sonar device is submerged in seawater and is used to drive away fish and prevent them from damaging the structure of the microalgae cultivation device.

6. The photobioreactor of claim 1, wherein, A protective net cover is also provided on the outside of the net cage to prevent fish or large aquatic animals from damaging the structure of the microalgae cultivation device; the net cage of the photobioreactor is hexahedral in shape, with a volume of 1-100m long * 1-100m wide * 1-100m high, or an equivalent volume of a cylinder, ellipse, or an irregular geometric shape with an equivalent volume of the hexahedron.

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