WO1995006111A1

WO1995006111A1 - System using tubular photobioreactors for the industrial culture of photosynthetic microorganisms

Info

Publication number: WO1995006111A1
Application number: PCT/IT1994/000140
Authority: WO
Inventors: Mario Roberto Tredici; Graziella Chini Zittelli; Silvia Biagiolini; Renato Carobbi; Francesco Favilli; Domenico Mannelli; Edoardo Pinzani
Original assignee: Consiglio Nazionale Delle Ricerche; Inalco S.P.A.
Priority date: 1993-08-27
Filing date: 1994-08-25
Publication date: 1995-03-02
Also published as: ITFI930167A0; ZA945818B; AU7508294A; TNSN94087A1; MA23313A1; IT1262502B; ITFI930167A1; IL110723A0

Abstract

The bioreactor - for the production of cultures of photosynthetic microorganisms or plant cells dispersed in nutrient-containing aqueous solutions - comprises reaction tubes (31) that are essentially transparent to solar radiation and lie at a shallow angle, generally of between 2° and 6°, to the horizontal, between two collectors (35, 43) at different levels; a nozzle (36A, 36B) is provided at the lower end of each tube (31) to blow in air (or the like) in an alternating manner as a propellant to carry the culture upwards and to remove toxic gases generated by the photoreactions; some of the tubes (31), acting alternately, return the culture from the upper collector (43) to the lower collector (35); the in-blown gas and the gas produced by the culture is removed or optionally recovered from the upper collector (43).

Description

DESCRIPTION System using tubular photobioreactors for the industrial culture of photosynthetic microorganisms Technical Field The invention relates to a bioreactor for the production of biomasses, especially of biomasses consisting of cultures of photosynthetic microorganisms or plant cells dispersed in nutrient-containing aqueous solutions, of the type that comprises at least one reaction tube or pipe that is essentially transparent to solar radiation. Background Art

The main limit on the industrial use of closed reactors for the culture of oxygenic photosynthetic microorganisms is due to the difficulties encountered in "scaling up", that is increasing their size in order to make conventional tubular photobioreactors commercially acceptable. This in turn is essentially related to the difficulty of providing suitable mixing (needed in cultures of photosynthetic organisms to prevent cells from sinking to the bottom, to break down diffusion barriers around the cells and to force the cells to experience alternating periods of light and darkness) in long tubular reactors, and to the evolution of photosynthetic oxygen, a direct consequence of the growth of an organism which uses water as an electron donor; in a closed environment, the oxygen builds up in the culture medium to toxic levels. The degree and seriousness of the phenomenon is inversely proportional to the diameter of the tubes used. With tubes having an internal diameter of 100 mm, degassing of the culture every 30-40 in is sufficient; 10-mm tubes require degassing every 3-4 min: this limits the length of tubular reactors of small diameters (20-30 mm) to a few hundred metres and significantly reduces the dimensions that can be achieved with the culture unit (module) . On the other hand, it is important to adopt small-diameter tubes for the sake of the economy of the process, as a higher culture density can be achieved with tubes of smaller diameter, and the costs of preparing and moving the medium are lower, besides which it is easier to prevent contamination by undesired microorganisms. Mixing and degassing become progressively more difficult the greater the inclination to the vertical. Moreover, it is generally preferable for a photoreactor to be horizontal in order to achieve greater ^'sizes and keep construction costs down. These and other problems are solved by the invention, which also fulfils other objects and provides other advantages which will become evident on a perusal of the following text. Disclosure of the Invention The invention relates to a bioreactor system for the production of biomasses, which system represents an improvement upon conventional systems. Basically, in the present bioreactor: means are provided for moving the biomass, that is the culture; a nozzle for gas is provided (at the starting end of said tube relative to the direction of movement) for blowing in gas (air or the like) which, as it moves through and/or with the biomass of the culture, provides mixing and removes the toxic gases generated by the photoreactions; also provided are means for returning the culture to the tube and means at the upper end of the tube for removing or optionally recovering the in- blown gas and the gas produced by the culture. Said in- blown gas may be suitable for providing certain of the nutrient gases required by the cultured organisms (for example CO2 or N₂) •

In one possible embodiment the reaction tube may actually be horizontal. In practice, and advantageously, it lies at a shallow angle to the horizontal. A reaction tube may also be helical. Advantageously, several reaction tubes are virtually straight and equidistant from each other.

Consequently a bioreactor according to the invention comprises at least one reaction tube that is essentially transparent to solar radiation and lies at a shallow angle, generally not more than 10°, and especially of between 2° and 6°, to the horizontal, between two points at different levels; a nozzle for gas is provided at the lower end of the tube to blow in gas (air or the like) as a propellant to carry the culture upwards and to remove toxic gases generated by the photoreactions; also provided are means for returning the culture from the upper end to the lower end of the tube and means at the upper end of the tube for removing or optionally recovering the in-blown gas and the gas produced by the biomass of the culture.

In one practical embodiment, a plurality of reaction tubes are arranged in a preferably single- layer bundle, said tubes being approximately straight and being arranged side by side parallel with each other, preferably lying on an ''inclined geometrical plane; at least one of the ends of each of said tubes is connected to a collector; and means are provided for blowing in air at the base of at least some of said tubes.

The abovementioned means may comprise at least one air distributing pipe with nozzles for blowing air or other suitable gas into all or some of the reaction tubes.

Said collector may be connected to the lower ends of the reaction tubes, or to the upper ends of the reaction tubes. Again, and alternatively, the lower ends of the reaction tubes may be connected to a first or lower collector, and the upper ends of said tubes may be connected to a second or upper collector.

In the two-collector version, one or more return pipes for returning ths culture from the upper collector to the lower collector may be provided. In one possible embodiment, the system may comprise means for distributing, and nozzles for blowing in, air or other gas that are active alternately and selectively in some of said reaction tubes, while in other of said tubes the culture is being returned from the upper collector to the lower collector; the alternating of their actions periodically reverses the movement in each reaction tube. In another embodiment, said reaction tubes are arranged in two bundles with the tubes of each bundle being approximately parallel with each other; the tubes of said two bundles are angled in opposite directions from a lower middle area; air blowing means are provided in all or some of the tubes of each bundle, optionally in alternation.

In one particular embodiment: collectors connecting together the reaction tubes at their upper ends are provided, and the tubes between the collectors form catenaries having average inclinations within the limits indicated relative to the horizontal; the air or gas is blown in at an intermediate lower point of each tube and in one of the ascending arms of at least some of the tubes, the in-blowing points active in adjacent tubes being located on opposite sides relative to the lowest point of the catenary. More particularly, in each tube there may be two opposing air-blowing nozzles on opposite sides of the lowest point of the catenary; and means are also provided for alternately supplying one or other of said blowing nozzles. Means may be provided for blowing air into one arm of one tube and into the opposing arm of the tubes oppositely adjacent thereto.

Another embodiment comprises a plurality of collectors at approximately the same level, between which run reaction tubes, all inclined- in the same direction, with joining pieces and with nozzles which blow in gas from distributing pipes; means are provided for returning the biomasses of the culture. Said means may be formed by other reaction tubes inclined in the opposite direction to said reaction tubes, and having their own joining pieces and blowing nozzles.

The reaction tubes may be of synthetic resin or glass. Alternatively the reaction tubes are made - at least in groups - from two sheets of synthetic resin welded together to define the tubes and optionally also the collectors; in the latter case temperature- regulating water may be run over said sheets. Especially in proximity to the upper ends of the reaction tubes, electrodes, probes and other sensors for monitoring the level and physical and chemical parameters of the culture may be placed in the upper collector. Advantageously, at the upper and/or lower ends of the reaction tubes and at the air inlets are devices, such as filters and the like, to keep the environment inside the reactor ^' sterile and to enable harvesting, introduction of culture medium, and other operations, to be performed in sterile conditions.

A system of the type defined above may comprise, in the collectors, shut-off members, which may be fully openable, for forcing the biomass of the culture to follow certain paths, especially in the case of a continuous-type operation.

In the photobioreactors made according to the invention, efficient agitation and movement of the medium is achieved, as is efficient degassing that solves the problem of the accumulation of photosynthetic oxygen (or other gas that may be generaced during growth) . This is achieved by blowing air into all or at least a large part of the reactor; the linear distance that can be achieved is at least an order of magnitude greater than is possible in conventional tubular photoreactors. In addition, by simple means with a variety of advantages, the invention does away with the need for pumps or other mechanical devices that damage the cultivated cells. The use of blown air in order simultaneously to agitate and degas can be done advantageously by having the tubes of which the module is composed lie entirely or in large part at an angle to the horizontal. The bubbles of air introduced at a slight overpressure into the lower sections also therefore exert a propulsive action as they rise to the top, moving and/or entraining the culture with them. At the top end of the tube the air that has entrained the photosynthetic O2 is separated and removed. It may be discharged or reused, for example for aerobic processes which are activated in the presence of oxygen-enriched air.

Brief Description of the Drawings

A better understanding of the invention will be obtained by examining the description and accompanying drawing. The latter shows a practical and non- restricting example of the invention. In the drawing:

Figs. 1 and 2 show in plan view and in section through the line II-II marked in Fig. 1, a schematic of an embodiment comprising two collectors; Figs. 3 and 4 show, in a similar way to Figs. 1 and 2, a modified schematic for obtaining a cyclical alternation of the movement;

Figs. 5 and 6 show, in plan view and in a section taken through the line VI-VI marked in Fig. 5, a schematic of a system having reaction tubes following a catenary path with two slopes;

Fig. 7 shows, in a similar way to Fig. 6, a schematic similar to the previous schematic but having straight or virtually straight tubes; Figs. 8 and 9 show two schematics similar to each other and suitable for systems to be installed on more or less level ground;

Figs. 10, 11 and 12 show a simplified schematic, in plan view and in vertical section, and a variant of the same in plan view;

Figs. 13, 14 and 15 show another simplified schematic, in plan view and in vertical section, and a variant of the same in plan view.

Best Way of Carrying Out the Invention In the embodiment shown in Figs. 1 and 2, a plurality of tubes of transparent material 31 is set up on, for example, slightly inclined ground, in such a way that the tubes 31 lie at an angle to the horizontal of the order of, for example, between 1° and 10°, preferably between 2° and 6°; the tubes 31 may be oriented along the lines of maximum slope, or inclined relative to the lines of maximum slope and may be installed in contact with each other or separated from each other by a distance of, for example, the same order of magnitude as the diameter of the tubes. The tubes 31 are connected to a lower collector 35; inside the lower collector 35 - or close to the collector - the ends of the tubes 31 are reached by nozzles 36 supplied with air from a distributing pipe 37 so that air is delivered to the interior of the tubes; it is possible simply to provide a pipe 37 which runs along the interior of the collector 35, passes through the lower portions of the tubes 31 that enter the collector, and has holes 36 by way of nozzles. At least one discharge 39 serves for emptying the reactor. By means of optional upper joining pieces - which may be curved - the tubes 31 are connected to an upper collector 43, in which there forms a free level of the liquid mass in an intermediate position; the upper collector 43 has outlets 43A for the air and other gases, and appropriate control systems such as probes, sensors of various kinds and thermometers. The complex is filled with culture medium. The air rises through the culture medium - in which the microorganisms or plant cells are developing - along the individual tubes 31 and creates a flow of liquid towards the upper collector 43; an equal quantity of liquid redescends down each tube 31 or preferably along return tubes or pipes 44 - arranged at intervals between the tubes 31 - which have no air-blowing nozzles and -may be of a different cross section from the tubes 31. The return tubes 44 may be positioned in i.nilluminated areas (for example underneath the surface on which the tubes 31 are laid) .

The movements of liquid set up in the tubes 31 as the bubbles of air pass through it result in the removal of the toxic gases generated by the photosynthetic reactions, and also ensure an efficient, continuous changing of position of the liquid, and hence of the microbial cells. The result is improved insolation and uniformity of the required reactions throughout the mass. The tubes 31 and optionally 44 can be laid on the ground with the slope indicated above or greater slopes, but in the latter case the tubes are set at an angle relative to the lines of maximum slope so as to maintain the desired inclination.

In the version illustrated in Figs. 3 and 4 there are at least two air distributing pipes 37A, 37B, each of which may have nozzles 36A and 36B feeding into alternate tubes 31; in the case of two distributing pipes 37A and 37B, one of them will have nozzles feeding into tubes 31 in even-numbered positions and the other will have nozzles feeding into tubes in odd- numbered positions. The nozzles and distributing pipes may be made according to the same^* principles as those illustrated in Figs. 1 and 2. In this version, air is supplied alternately and cyclically first to one, then to the other of the two distributing pipes 37A, 37B. It follows that in a cyclical manner, certain of the tubes 31 receive air and movements towards the collector 43 are set up in them, while in the other tubes 31 to which air is not fed, a return flow towards the collector 35 occurs.

Periodically or continuously, some of the culture can be discharged and the product harvested, while the volume extracted is replaced with new culture medium or with the same medium recycled. Figs. 5 and 6 show an embodiment in which two groups of tubes 51 are arranged at equal intervals and with two opposing slopes from a lower middle area; two opposing tubes can be formed by a single catenary tube, the average inclinations being approximately as described above. The tubes may be laid on natural opposing slopes or on suitably designed supports. At the two raised extremities the tubes 51 are connected up by respective collectors 59 and 61 having functions similar to those of the upper collector 43 of the previous exampl . In the lower middle area are two air distributors s-^arated by a short distance and indicated by the numerals 55 and 57, each following a zig-zag path: their task is to supply air in alternating cycles. Each of said two distributors 55 and 57, when active, blows air continuously into the ascending arm of tubes 51 in even-numbered positions and into the opposite ascending arm of tubes 51 in odd- numbered positions (or vice versa) ; it is thus possible to have reverse flows moving continuously in adjacent tubes 51.

With a single distributor {55 or 57) always active, the flow along a tube 51 is permanently in one direction, and along the tubes adjacent to it permanently in the opposite direction.

By using two distributors 55 and 57, as in the drawing, and employing an inte mittent alternating supply from the two distributors, it is possible periodically to reverse the flow in adjacent tubes 51. The system can be discharged intermittently from the lower middle part of the individual tubes using a discharge collector 63, or from either or both of the collectors 59, 61 at one end, in a continuous manner, providing a supply of new medium at a distance from the culture discharge. In particular, by supplying through one end of one collector, e.g. 59, and discharging from the opposite end of the other collector, e.g. 61, and provided the system is very large - in terms of the numbers and lengths of the tubes 51 and/or by imposing a certain path by means of shut-off members or the like - the system can be made to operate on continuous cycle.

In the alternative depicted in Fig. 7, tubes 151 sloping at opposite angles run between a lower middle collector 153 and two upper outer collectors 159 and 161. Distributors 155 and 157 can supply air to nozzles for blowing into the bottom end of the tubes 151 according to rules of cyclical selection similar to those discussed above in relation to previous examples. In the collectors used in the examples described above, suitable shut-off members, which may be fully openable or adjustable - can be provided to impose certain obligatory paths on the mass undergoing treatment, where a continuous cycle is required, with culture medium being introduced at one end and product taken off at the other end of the system.

Figs. 8 and 9 show embodiments suitable for level ground and with structures of limited vertical height. Fig. 8 shows a plurality of arrays of reaction tubes 71; the tubes 71 of each array lie with the slope already indicated between adjacent collectors 73, apart from an optional lower initial collector 731, to facilitate the return flow. The tubes 71 have a joining piece 75 with an elbow from where the actual slope of the respective tube 71 commences, and in which there fits a nozzle 77 for blowing in air from a distributor 79, or with outlet holes directly from the distributor 79 (see Fig. 1) ; from the initial collector 731 in the low position, the tubes 71 lead directly upwards. Connected to the initial collector 731 is at least one return pipe 81 arriving from the last 73X of the collectors 73. Operation is similar to that in the previous examples, with paths repeated and running over flat or approximately horizontal ground.

In the alternative shown in Fig. 9 - in which the same reference numerals denote parts and components similar to those of Fig. 8 - the one or more return pipes 81 are now replaced by further arrays of tubes 171 - more or less intimately interposed between the tubes 71, for example in groups, in order to satisfy the demands for exposure to natural light - and these tubes 171 slope in the opposite direction to the tubes 71 and have similar vertical portions 175 and nozzles 177; this approach creates a return flow which can also be used for biosynthesis. Between the groups of tubes 71 and 171 it is possible to have suitable dividing walls in the collectors 73 and 73X.

In the two versions shown in Figs. 8 and 9, the collectors 73 may also be arranged vertically to correspond to the heights of the tubes connected to them, as indicated in broken lines at 273 in Fig. 8.

Simpler versions than those discussed thus far may adopt a single collector, lower or upper, with air blowing means for the purposes already indicated, and with tubes sloping at a shallow angle to the horizontal.

Figs. 10 and 11 show an arrangement with a single upper collector 201, from which run tubes 203 closed at the lower end and traversed by a distributing pipe 205 with nozzles 207 for blowing air into the tubes 203. Though rather slowly, the biomass does still move along the tubes 203 and the toxic gases generated inside them are still removed. In the variant shown in Fig. 12 there are pairs of tubes 203A joined and connected together at the bottom* to form a U; using twin distributing pipes 205A with corresponding alternating holes or nozzles 207A, it is possible to ir^ect air alternately into first one then the other of the tubes of each pair; if only a single distributing pipe 205A is used, one of the two tubes will always carry a rising current and the other a descending current. Similar arrangements to the above are shown in

Figs. 13-15, in which from a single lower collector 301 run individual tubes 303 or pairs of tubes 303A sloping gently upwards and having gas vents 309 at the upper end of the individual tubes 303 or at the upper joining piece between the tubes 303A of each pair, an air distributing pipe 305 or a pair of' alternately operating air distributing pipes 305A have the same function as 207 and 207A.

At the outlets communicating with the exterior for venting gas and air, and/or in other positions, protective filters and other means for ensuring sterility and/or avoiding contamination of the interior and/or exterior can be provided.

By way of illustration, 125 tubes having an external diameter of 40 mm, an internal diameter of 30 mm and lengths of 200 m may be laid out parallel on an inclined surface with an interval of one diameter from one to the next. The tubes are connected at the upper and/or lower ends. Compressed air is blown into the bottom ends of alternate tubes (or tube sections) in order to get the culture moving and mixing, with a cyclical return of the mass to the lower end. In this way a culture unit having a surface area of 2000 m² (10 200 m) and approximately 18,000 litres of useful volume is constructed. Tubes made of PVC, polyethylene, glass, polymethyl methacrylate, polycarbonate or other transparent material can be used. The diameter of the tubes may vary between 15 and 50 mm, but other diameters are possible, as also are structures made of polyethylene or PVC films welded to form tubes connected together on the same principles.

It will be understood that the drawing shows only an illustrative embodiment which is provided purely as a practical demonstration of the invention, it being possible for the invention to be varied as regards forms and arrangements without however departing from the scope of the concept underlying said invention. The purpose of any reference numerals in the accompanying claims is to facilitate the reading of the claims with reference to the description and to the drawing, and does not limit the scope of protection represented by the claims.

To assist comprehension, the inclinations shown in the drawings are generally not to proportion.

Claims

1. Bioreactor for the production of biomasses, especially of biomasses consisting of cultures of photosynthetic microorganisms or plant cells dispersed in nutrient-containing aqueous solutions, comprising at least one reaction tube or pipe that is essentially transparent to solar radiation, characterized in that means are provided for moving the biomass, that is the culture; in that a nozzle for gas is provided in said tube for blowing in gas (air or the like) which, as it moves, mixes the culture and removes the toxic gases generated by the photoreactions; and in that means are provided for returning the culture to the tube and means at the upper end of the tube for removing or optionally recovering the in-blown gas and the gas produced by the culture; which in-blown gas can also provide certain of the nutrient gases required by the cultured organisms (for example CO2 or N2 .

2. Bioreactor for the production of biomasses, especially of biomasses consisting of cultures of photosynthetic microorganisms or plant cells dispersed in nutrient-containing aqueous solutions, comprising at li, st one reaction tube or pipe that is essentially transparent to solar radiation, characterized in that said tube lies at a shallow angle, generally not more than 10°, and especially of between 2° and 6°, to the horizontal, between two points at different levels; in that a nozzle for gas is provided at the lower end of the tube to blow in gas (air or the like) as a propellant to carry the culture upwards and to remove toxic gases generated by the photoreactions; and in that means are provided for returning the culture from the upper end to the lower end of the tube and means at the upper end of the tube for removing or optionally recovering the in-blown gas and the gas produced by the biomass of the culture; which in-blown gas can also provide nutrient gases required by the cultured organisms.

3. Bioreactor according to Claim 2, characterized in that a plurality of reaction tubes (31, 51, 71, 171) are arranged in a preferably single-layer bundle, said tubes being approximately straight and being arranged side by side parallel with each other, preferably lying on an inclined geometrical plane; in that at least one of the ends of each of said tubes is connected to a collector; and in that means are provided for blowing in air at the base of at least some of said tubes.

4. Bioreactor according to Claim 3, characterized in that said means comprise at least one air distributing pipe (37, 55, 57, 79, 205, 205A, 305) with nozzles for blowing air or other suitable gas into all or some of the reaction tubes.

5. Bioreactor according to Claim 3, characterized in that said collector is connected to the lower ends of the reaction tubes.

6. Bioreactor according to Claim 3, characterized in that said collector is connected to the upper ends of the reaction tubes.

7. Bioreactor according to Claim 3, characterized in that the lower ends of the reaction tubes are connected to a first or lower collector, and in that the upper ends of said tubes are connected to a second or upper collector.

8. Bioreactor according to at least Claim 7, characterized in that it comprises return pipes (44; 81) for returning the culture from the upper collector to the lower collector.

9. Bioreactor according to at least one of Claims 1-7, characterized in that it comprises means for distributing, and nozzles for blowing in," air or other gas that are active alternately and selectively in some of said reaction tubes, while in other of said tubes the culture is being returned from the upper collector to the lower collector; the alternating of their actions periodically reversing the movement in each reaction tube.

10. Bioreactor according to one or more of the previous claims, characterized in that said reaction tubes (51; 151) are arranged in two bundles with the tubes of each bundle being approximately parallel with each other; in that the tubes of said two bundles are angled in opposite directions from a lower middle area; air blowing means being provided in all or some of the tubes of each bundle, optionally in alternation.

11. Bioreactor according to Claim 10, characterized in that collectors (59, 61) connecting together the reaction tubes (51) at their upper ends are provided; in that the tubes (51) between the collectors (55, 57) form catenaries having average inclinations within the limits indicated relative to the horizontal; and in that the air or gas is blown in at an intermediate lower point of each tube and in one of the ascending arms of at least some of the tubes (51) , the in-blowing points active in adjacent tubes being located on opposite sides relative to the lowest point of the catenary.

12. Bioreactor according to Claim 11, characterized in that in each tube (51) there are two opposing air- blowing nozzles on opposite sides of the lowest point of the catenary; means being provided for alternately supplying one or other of said blowing nozzles.

13. Bioreactor according to Claim 11 or 12, characterized in that it comprises means for blowing air into one arm of one tube and into the opposing arm of the tubes oppositely adjacent thereto.

14. Bioreactor according to at least one of the previous claims, characterized in that it comprises a plurality of collectors (73) at approximately the same level, between which run reaction tubes (71) , all inclined in the same direction, with joining pieces (75) and with nozzles (77) which blow in gas from distributing pipes (79) ; means (81; 171) being provided for returning the biomasses of the culture.

15. Bioreactor according to Claim 14, characterized in that said means are formed by other reaction tubes (171) inclined in the opposite direction to said reaction tubes (71) , and having their own joining pieces (175) and blowing nozzles (177) .

16. Bioreactor according to one of the previous claims, characterized in that the reaction tubes are of synthetic resin or glass.

17. Bioreactor according to one of Claims 1-15, characterized in that the reaction tubes are made - at least in groups - from two sheets of synthetic resin welded together to define the tubes and optionally also the collectors; it being possible for temperature- regulating water to be run over said sheets.

18. Bioreactor according to one of the previous claims, characterized in. that, especially in proximity to the upper ends of the reaction tubes, electrodes, probes and other sensors for monitoring the level and physical and chemical parameters of the culture are placed in the upper collector.

19. Bioreactor according to at least one of the previous claims, characterized in that at the upper and/or lower ends of the reaction tubes and at the air inlets are devices, such as filters and the like, to keep the environment inside the reactor sterile and to enable harvesting, introduction of culture medium, and other operations, to be performed in sterile conditions.

20. Bioreactor according to at least one of the previous claims, characterized in that it comprises, in the collectors, shut-off members, which may be fully openable, for forcing the biomass of the culture to follow certain paths, especially in the case of a lcontinuous-type operation.