Horizontal immersion cover type carbon supplement device and carbon supplement method used for microalgae culture in open pond

Abstract

The invention relates to the field of mass cultivation of microalgae and specifically relates to a horizontal submerged cover type carbon supplement device and carbon supplement method for cultivating microalgae in an open pond. The horizontal submerged cover type carbon supplement device for cultivating microalgae in an open pond, comprises: one or more than two covers and gas distributors, wherein the gas distributor is arranged at the bottom of the open pond and the cover is arranged above the gas distributor; the cover, in form of a cylinder with openings at both ends, is arranged along the flow direction of the culture solution, the two ends of the cover being a culture solution inlet and a culture solution outlet respectively; the gas distributor is kept away from the culture solution outlet of the cover by more than 40 cm. According to the invention, when microalgae cells are cultivated in the open pond, carbon dioxide can be effectively utilized for carbon supplement, so production cost is greatly reduced.

Claims

1. A horizontal submerged cover type carbon supplement device for cultivating microalgae in an open pond, comprises: at least one cover and at least one gas distributor, wherein the at least one gas distributor is arranged at a bottom of the open pond and the at least one cover is arranged above the at least one gas distributor; the at least one cover, in a form of a cylinder with an opening at a first end and a second end thereof, is arranged along a flow direction of a culture solution, the first end of the at least one cover being a culture solution inlet and the second end of the at least one cover being a culture solution outlet and the top of the at least one cover being inundated by the culture solution; the at least one gas distributor being entirely positioned at least 40 cm from the culture solution outlet of the at least one cover.

2. The carbon supplement device according to claim 1, wherein a distance between the at least one gas distributor and the culture solution outlet of the at least one cover is between 60-750 cm.

3. The carbon supplement device according to claim 1, wherein the at least one cover is directly mounted at the bottom of the open pond or overhead arranged at the bottom of the open pond.

4. The carbon supplement device according to claim 1, wherein a bottom of the at least one cover is a closed structure.

5. The carbon supplement device according to claim 1, wherein a body of the at least one cover is one of a semi-circular cylinder, an arc-shaped cylinder, a rectangular cylinder and a trapezoidal cylinder.

6. The carbon supplement device according to claim 1, wherein the first and second ends of the at least one cover are formed with a bell mouth.

7. The carbon supplement device according to claim 1, wherein a height of the at least one cover is 2-20 cm.

8. The carbon supplement device according to claim 1, wherein a width of the at least one cover is at least 2 cm.

9. The carbon supplement device according to claim 1, wherein the carbon supplement device comprises at least two covers forming a conjoined structure.

10. A carbon supplement method for cultivating microalgae in an open pond based on the carbon supplement device of claim 1, comprises: the horizontal submerged cover type carbon supplement device is arranged at the bottom of the open pond along the direction of the channel of the open pond to enable the culture solution to inundate the top of the cover; the culture solution flows into the culture solution inlet of the cover under the driving of a stirrer of the open pond and flows out of the culture solution outlet of the cover after being in contact with CO.sub.2 released from the gas distributor in the carbon supplement device; the flow velocity of the culture solution in the open pond is 20-50 cm/s; the flow rate of the CO.sub.2 in the horizontal submerged type carbon supplement device, calculated as pure CO.sub.2 under standard condition, is 0.1-20 L/min per meter of the width of the open pond.

11. The carbon supplement method according to claim 10, wherein the depth of the culture solution in the open pond is 2-30 cm.

12. The carbon supplement method according to claim 10, wherein the blade tip of the stirrer is lower than the bottom of the open pond.

13. The carbon supplement method according to claim 10, wherein the horizontal submerged cover type carbon supplement device is arranged in a shallow groove at the bottom of the open pond.

14. The carbon supplement method according to claim 10, wherein the bottom of the shallow groove is a flat bottom, a flat bottom with round corners or a semi-circular bottom.

15. The carbon supplement method according to claim 10, wherein the CO.sub.2 is one or more of cleaned flue gas, industrial CO.sub.2 gas, pure CO.sub.2 gas or air mixed with CO.sub.2, or liquid CO.sub.2.

16. The carbon supplement method according to claim 10, wherein the medium for cultivating microalgae is Zarrouk medium, SM medium, ASP2 medium or BG-11 medium.

17. The carbon supplement method according to claim 10, wherein the microalgae are spirulina, scenedesmus, haematococcus pluvialis,Dunaliella salina, chlorella, or chlamydomonas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a horizontal submerged cover type carbon supplement device for cultivating microalgae in an open pond of the invention.

(2) FIG. 2 is a schematic diagram of the location of the horizontal submerged cover type carbon supplement device in the channel of an open pond for cultivating microalgae in an open pond of the invention

(3) FIG. 3 is a view of the horizontal submerged cover type carbon supplement device in use along the flow direction of culture solution for cultivating microalgae in an open pond of the invention.

(4) FIG. 4 is a side view of the horizontal submerged cover type carbon supplement device in use for cultivating microalgae in an open pond of the invention.

(5) FIG. 5 is a schematic diagram of different cross section shapes of the main body of a cover 1 of the carbon supplement device of the invention (showing the covers which are directly located at the bottom of the open pond, showing one or more gas distributors below each cover and showing the section shapes of the covers).

(6) FIG. 6 is a schematic diagram of different arrangement ways of the carbon supplement device of the invention (showing overhead covers, showing covers with open or closed bottoms, showing conjoined covers and showing grounded or overhead gas distributors).

(7) FIG. 7 is a schematic diagram of the carbon supplement device of the invention, the cover of which is in a structure with a bell mouth.

(8) FIG. 8 is a schematic diagram of the carbon supplement device of the invention, which is used together with a stirrer of which the blade tip is lower than the bottom of the open pond when the depth of the culture solution is relatively small.

(9) FIG. 9 is a view of the carbon supplement device of the invention, which is mounted in a position lower than the bottom of the open pond, along the flow direction of the culture solution.

(10) FIG. 10 is a side view of the carbon supplement device of the invention, which is mounted in a position lower than the bottom of the open pond.

(11) FIG. 11 is a schematic diagram of overall layout of the carbon supplement device for cultivating microalgae in an open pond of the invention (top view).

(12) FIG. 12 is a schematic diagram of a system utilizing the carbon supplement device of the invention for automatic carbon supplement.

DESCRIPTION OF THE REFERENCE NUMERALS

(13) TABLE-US-00001 1. Cover 2. Gas distributor 3. Culture solution inlet 4. Culture solution outlet 5. Flow direction of culture solution 6. Bottom of an open pond 7. Wall of an open pond 8. Surface of microalgae culture solution 9. Stirrer 10. Arc-shaped groove 11. Shallow groove 12. pH sensor 13. Control device 14. CO.sub.2 gas source 15. Execution mechanism 16. Flow meter 17. Pressure gauge

DETAILED DESCRIPTION OF THE INVENTION

(14) A horizontal submerged cover type carbon supplement device for cultivating microalgae in an open pond of the invention comprises one or more than two covers 1 and gas distributors 2 (FIG. 1 and FIG. 6), wherein the gas distributor 2 is arranged at the bottom 6 of the open pond, the cover 1, covering the gas distributor 2, takes the form of a cylinder with openings at both ends and is arranged along the flow direction 5 of the culture solution, with the two ends being a culture solution inlet 3 and a culture solution outlet 4 (FIG. 2 and FIG. 3) respectively; moreover, the gas distributor 2 is kept away from the culture solution outlet 4 of the cover 1 by more than 40 cm. Preferably, the gas distributor 2 is kept away from the culture solution outlet 4 of the cover 1 by 60-750 cm. The cover 1 can be directly mounted at the bottom of the open pond (FIG. 5) or overhead arranged at the bottom of the open pond (FIG. 6, a supporting device is omitted), with the bottom of the cover 1 being open or closed (FIG. 6). The main body of the cover 1 can be a semi-circular cylinder, an arc-shaped cylinder, a rectangular cylinder or a trapezoidal cylinder (FIG. 5). In order to reduce the flow resistance of the fluid in the cover, the culture solution inlet 3 and/or the culture solution outlet 4 of the cover 1 can be in a structure with a bell mouth (FIG. 7). The height of the cover 1 is 2-20 cm, which is determined so as for the cover 1 to be submerged by the liquid surface 8 of the microalgae culture solution. The width of the cover 1 can be as small as 2 cm (i.e. covering one gas distribution pipe), and be as large as the width of the open pond channel (namely the distance between the walls 7 of the open pond on the two sides of the flow channel) (i.e. covering a plurality of gas distribution pipes or gas distributors). Two or more covers 1 can be formed into a conjoined structure by conjoining processing (FIG. 6).

(15) In a carbon supplement method for cultivating microalgae in an open pond of the invention, one or more groups of horizontal submerged cover type carbon supplement devices are arranged in the open pond along the direction of the flow channel, each group comprises one or more horizontal submerged cover type carbon supplement devices, and each horizontal submerged cover type carbon supplement device comprises one cover along the flow direction of the culture solution and one or more gas distributors shrouded by the cover. Preferably, the gas distributors are positioned at the culture solution inlet 3 of the cover. The overall layout is shown in FIG. 11, wherein the number of groups of the horizontal submerged cover type carbon supplement devices, the number of the horizontal submerged cover type carbon supplement devices in each group and the number of the gas distributors below each cover are determined according to the carbon supplementing flow rate of a single horizontal submerged cover type carbon supplement device, the size of the open pond, the growth rate of objective microalgae to be cultured and the requirements of culture conditions. When the culture solution flows in the open pond under the driving action of a stirrer (conventional stirrer in the art is a paddle wheel), part of the culture solution flows into the horizontal submerged cover type carbon supplement device from the culture solution inlet 3 so as to be in contact with the gas containing carbon dioxide, which is released from the gas distributor and sealed below the cover, then the culture solution flows through the space below the cover and flows out of the horizontal submerged cover type carbon supplement device from the culture solution outlet 4, so that the gas-liquid contact time is greatly prolonged; and on the other hand, after the gas containing carbon dioxide passes through the gas distributor, the gas becomes into very small bubbles, which makes the gas-liquid contact interfacial area is drastically increased, thereby the absorption efficiency of the carbon dioxide is greatly improved.

(16) The flow of the culture solution can be implemented by the driving of a stirrer of the open pond, such as a paddle wheel or a rotating arm, and the stirrer can be made of bamboo chips, plastics, stainless steel, other metal materials and the like.

(17) When the horizontal submerged cover type carbon supplement device is used, the flow velocity of the culture solution in the open pond is 20-50 cm/s generally, and the flow rate of CO.sub.2 (calculated as pure CO.sub.2 under standard conditions) is 0.1-20 L/min per meter of the width of the open pond.

(18) The depth of the culture solution in the open pond can be 2-30 cm.

(19) When the depth of the culture solution in the open pond is relatively small, the stirrer 9 of the open pond can be arranged above an arc-shaped groove 10, and the blade tip of the stirrer is lower than the bottom of the open pond (FIG. 8); and a shallow groove 11 can be dug out in the region at the bottom of the open pond where the carbon supplement device is to be placed so as to install the carbon supplement device, namely the carbon supplement device is installed at a position lower than the bottom of the open pond (FIG. 9 and FIG. 10). The bottom of the shallow groove 11 for installing the carbon supplement device can be a flat bottom, a flat bottom with round corners or a semi-circular bottom (FIG. 9); and the material of the groove 11 can be cement, a plastic plate, a stainless steel plate, bricks, the same material as that of the bottom of the open pond or the like.

(20) Embodiment 1

(21) As shown in FIG. 11, spirulina is cultivated in a raceway type culture pond (a most common open pond, referred as a raceway pond), wherein the flow channel of the raceway pond has a perimeter of 70 m and a width of 3 m. A stirrer 9 comprises four groups of steel paddle wheels driven by a rotating shaft, each paddle wheel comprising four blades spaced by 90-degree, the blades of two adjacent paddle wheels are staggered by 45-degree, the rotating shaft being driven by an alternating current motor through variable gearing, and the radius of the stirrer 9 in rotating being 50 cm.

(22) One group containing six horizontal submerged cover type carbon supplement devices is arranged in the raceway pond along the direction of the flow channel, and each horizontal submerged cover type carbon supplement device comprises a cover 1 along the flow direction of the culture solution and a gas distributor 2 shrouded by the cover 1. Each cover 1 is made of a stainless steel sheet with a thickness of 1 mm; the shape of cross-section of the main body of the cover 1 is semi-circular; and each cover 1 has a length of 400 cm, a width of 10 cm and a height of 5 cm. The gas distributor 2, a micro-porous rubber film aeration pipe with a length of 50 cm, an outer diameter of 16 mm, an inner diameter of 10 mm and a pore size of about 30-60 m, is positioned in the region apart from the culture solution inlet 3 by 0-50 cm under the cover 1 along the flow direction of the culture solution and positioned centrally in the radial direction. The culture solution is driven by the stirrer 9 to flow along the raceway pond channel, such that part of the culture solution flows into the carbon supplement device from the culture solution inlet 3 so as to be in contact with the bubbles released from the gas distributor 2, then the culture solution flows through the space below the cover 1 till flows out of the culture solution outlet 4 of the carbon supplement device. Then, the culture solution out of the outlet 4 of the carbon supplement device is mixed with the culture solution which does not enter the carbon supplement device to flow in the flow channel.

(23) The carbon supplementing procedure is controlled in an automatic mode, such as the method disclosed in application with No. CN200410009360.4, and a system for implementing the control is shown in FIG. 12, wherein, a pH sensor 12 is a commercially available pH sensor, a control device 13 is a pH meter with a switch controller, a CO.sub.2 gas source 14 is pure carbon dioxide gas from a steel cylinder, and an execution mechanism 15 is a two-position normally-closed solenoid valve (the flow diameter of the valve is 8 mm). The carbon dioxide delivering valve (the execution mechanism 15) is controlled to be open or closed according to the pH value of the culture solution. The flow rate and the pressure of CO.sub.2 gas are monitored by a flow meter 16 and a pressure gauge 17.

(24) The algae species is Spirulina Platensis, numbered 439, which is from the Freshwater Algae Culture Collection of the Institute of Hydrobiology, Chinese Academy of Sciences. The medium is Zarrouk medium, wherein the initial concentration of sodium bicarbonate is 0.05 mol/L. The average depth of the culture solution in the raceway pond is 15 cm, and the inoculation density of algae cells is 0.40 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 9.6-9.7, and when the pH value of the culture solution rises to 9.6, automatic carbon supplementing procedure is initiated. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 1 L/min (pure carbon dioxide, standard conditions). The rotational speed of the motor is regulated to enable the flow velocity of the culture solution in the raceway pond to be about 25 cm/s.

(25) The concentration of other nutrient salts is detected and supplemented timely if necessary every day, and a small amount of water is also supplemented to make up for the loss of water caused by evaporation. After the culture procedure is continuously carried on for 6 days, the density of the algae cells reaches 0.70 g (dry cell weight)/L, and the production of the algae cells per unit area reaches 13.3 g (dry cell weight)/m.sup.2.Math.d. The composition and the content of conventional components, amino acids, fatty acids and carotenoids of the obtained spirulina algae powder are basically consistent with those reported in prior art documents. From calculation according to material balance the utilization efficiency of the carbon dioxide from the steel cylinder reaches 92%.

(26) Embodiment 2

(27) The features that are the same as those of embodiment 1 are omitted. Chlorella sp. is cultivated in the open pond, and the medium is BG-11 medium with NaNO.sub.3 as nitrogen source. The average depth of the culture solution in the raceway pond is 12 cm. The inoculation density of the algae cells is 0.5 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 7.5-7.6. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 0.5 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 30 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 90%.

(28) Embodiment 3

(29) The features that are the same as those of embodiment 1 are omitted. In this embodiment, each cover has a length of 800 cm, a width of 6 cm and a height of 3 cm. The average depth of the culture solution in the raceway pond is 10 cm. The inoculation density of the algae cells is 0.6 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 9.5-9.6. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 1 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 50 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 98%.

(30) Embodiment 4

(31) The features that are the same as those of embodiment 1 are omitted. One group containing three horizontal submerged cover type carbon supplement devices is arranged, each horizontal submerged cover type carbon supplement device comprises a cover along the flow direction of the culture solution and four gas distributors shrouded by the cover. The shape of cross-section of the main body of the cover is arc-shaped, with each cover having a length of 200 cm, a width of 40 cm and a height of 10 cm. Chlorella sp. is cultured in the open pond, wherein the medium is BG-11 medium with NaNO.sub.3 as nitrogen source. The average depth of the culture solution in the raceway pond is 20 cm. The inoculation density of the algae cells is 0.3 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 7.5-7.6. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 0.5 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 25 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 86%.

(32) Embodiment 5

(33) The features that are the same as those of embodiment 1 are omitted. A semi-circular arc-shaped groove with a radius of 52 cm and a depth of 10 cm is dug out below the stirrer to lower the blade tip of the stirrer to be 8 cm lower than the bottom of the raceway pond. Each horizontal submerged cover type carbon supplement device comprises a cover along the flow direction of the culture solution and two gas distributors shrouded by the cover. The shape of the cross-section of the main body of the cover is arc-shaped, with each cover having a length of 200 cm, a width of 15 cm and a height of 3 cm. A shallow groove with a depth of 2 cm and with a flat bottom and two slope sides is dug out at the bottom of the raceway pond in the region below each carbon supplement device, each of the cover and the gas distributors is mounted on the flat bottom of the shallow groove (FIG. 9 and FIG. 10). Scenedesmus sp. is cultivated in the open pond, wherein the medium is BG-11 medium with NaNO.sub.3 as nitrogen source. The average depth of the culture solution in the raceway pond is 5 cm. The inoculation density of the algae cells is 1.2 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 7.4-7.5. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 0.5 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 25 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 85%.

(34) Embodiment 6

(35) The features that are the same as those of embodiment 1 are omitted. A semi-circular arc-shaped groove with a radius of 52 cm and a depth of 10 cm is dug out below the stirrer to lower the blade tip of the stirrer to be 8 cm lower than the bottom of the raceway pond. Each horizontal submerged cover type carbon supplement device comprises a cover along the flow direction of the culture solution and two gas distributors shrouded by the cover. The shape of the cross-section of the main body of the cover is arc-shaped, with each cover having a length of 200 cm, a width of 10 cm and a height of 2 cm. A shallow groove with a depth of 3 cm and with a flat bottom and two slope sides, is dug out at the bottom of the raceway pond in the region below each carbon supplement device, and each of the cover and the gas distributors is mounted overhead by 1 cm over the flat bottom of the shallow groove (FIG. 9, FIG. 10 and FIG. 6). The average depth of the culture solution in the raceway pond is 3 cm. The inoculation density of the algae cells is 2 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 9.7-9.8. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 0.5 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 25 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 88%.

(36) Embodiment 7

(37) The features that are the same as those of embodiment 1 are omitted. The shape of the cross-section of the main body of the cover is trapezoidal, with each cover having a length of 100 cm, a width of 15 cm and a height of 15 cm. The gas distributor, a variable-pore aeration hose with a diameter of 65 mm and a length of 40 cm, is positioned in the region apart from the culture solution inlet by 0-40 cm under the cover along the flow direction of the culture solution. The average depth of the culture solution in the raceway pond is 25 cm. The inoculation density of the algae cells is 0.24 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 9.8-9.9. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 1 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 20 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 79%.

(38) Embodiment 8

(39) The features that are the same as those of embodiment 1 are omitted. Each horizontal submerged cover type carbon supplement device comprises a cover along the flow direction of the culture solution and two gas distributors shrouded by the cover. The shape of the cross-section of the main body of the cover is rectangular, with each cover having a length of 50 cm, a width of 20 cm and a height of 20 cm. The gas distributors are sand cores with a diameter of 30 mm and a height of 70 mm, which are arranged side by side vertically to the flow direction of the culture solution and apart from the culture solution inlet by 5-10 cm under the cover. The average depth of the culture solution in the raceway pond is 30 cm. The inoculation density of the algae cells is 0.2 g (dry cell weight)/L. The range of the pH value of the culture solution is controlled within 9.9-10.0. The flow rate of the carbon dioxide gas of each gas distributor (while the execution mechanism 15 is open) is 0.5 L/min (pure carbon dioxide, standard conditions). The flow velocity of the culture solution in the raceway pond is about 15 cm/s. After the culture procedure is continuously carried on for 6 days, the utilization efficiency of the carbon dioxide from the steel cylinder reaches 75%.