WO2000005337A1

WO2000005337A1 - A vessel

Info

Publication number: WO2000005337A1
Application number: PCT/GB1999/002412
Authority: WO
Inventors: Jonathan Mortimer
Original assignee: Biosynthesis Limited
Priority date: 1998-07-24
Filing date: 1999-07-26
Publication date: 2000-02-03
Also published as: GB9816177D0; AU5057699A; GB2339763A; EP1124938A1

Abstract

A flowpath is configured between an inlet (12) and an outlet (14), and includes a first chamber (22), a group of conduits (26, 28)arranged in side by side relationship in fluid parallel downstream of, and in communication with the first chamber and, a second chamber (24) downstream of, and in communication with the group of conduits (26, 28). The first and second chamber (22, 24) and the plurality of conduits (26, 28) have walls of flexible transparent (or translucent) material, a group of linear seals (16, 18, 20) formed between front and rear walls of the material define the plurality of conduits (26, 28).

Description

A Ve s se l

The present invention concerns a vessel, which is particularly suited to use as a photobioreactor, but is not limited to such use.

Typically, photobioreactors comprise substantially optically transparent (or at least translucent) tubes in which photosynthetic organisms, such as algae or the like, dispersed within a culture medium, can utilise light to undergo photosynthetic reactions, so as to grow and multiply. Hitherto, the transparent tubes, which provide conduits for throughflow of the culture medium and dispersed microorganisms, have been made of substantially rigid material, general plastics, arranged in a coiled, fence- like or serpentine configuration. Such configurations may be of considerable size, particularly for commercial scale production of algae, and are expensive to manufacture and maintain. Problems sometimes arise with contamination of the culture medium, e.g. with other microorganisms, which naturally leads to loss of production. Such problems are usually the result of inadequate sterilisation of the tubes prior to use, but since the only means of sterilisation is by flushing with a disinfecting solution, followed by rinsing, it is difficult to ensure that 100% sterility is achieved on all occasions.

Various factors apply when considering the form of a photobioreactor. On the one hand the vessel or conduit should not be too wide or too large as the ratio of the surface area for impingement of light to the volume of the vessel or conduit would be low, and the resulting concentration of algae or the like would be correspondingly low and uneconomic. On the other hand, the vessel or conduit should not be too narrow or too long as the concentration of algae or the like might become too high, resulting in death of the organisms from oxygen poisoning.

GB-A-1389412 discloses a cultivation chamber for cells and tissues formed as a closed pouch, tube or bag from a film material .

The present invention provides advantages over prior art arrangements, some of which advantages are particularly suited to the culture of microorganisms (particularly photosynthetic microorganisms) .

According to a first aspect, the invention provides a vessel comprising a flowpath configured between an inlet and an outlet, the flowpath configuration including:

a first chamber;

a plurality of conduits arranged in side by side relationship in fluid parallel downstream of, and in communication with the first chamber; and,

a second chamber downstream of, and in communication with the plurality of conduits; wherein the first and second chamber and the plurality of conduits comprise walls of flexible transparent (or translucent¹) material, a plurality of linear seals formed between front and rear walls of the material defining the plurality of conduits.

In a preferred embodiment, the vessel may include a first chamber in communication with the inlet and with one end of a first group of the conduits, a second chamber in communication with the outlet and with one end of a second group of the conduits, and a third chamber intermediate and in communication with the first and second groups of conduits .

The vessel in nature is typically in the form of a bag pouch or envelope, the flexible walls of which are expanded from a collapsed state when the culture media is present in the vessel. The volume of the chambers is typically substantially greater than the volume of the individual conduits in each group.

The vessel is particularly suitable for use as a photobioreactor. Such a vessel would however also be suitable for use for any process requiring application of electromagnetic radiation, specifically light, to a liquid or a suspension, for example a process involving a photochemical reaction other than photosynthesis.

Such a vessel could be produced from any suitable transparent (or even, less preferably, translucent) plastics, such as polyethylene, polyvinylchloride or polytetrafluoroethylene . It would be very much less^' expensive to produce and install than a vessel made up of rigid transparent plastics tubing, for example, several hundred percent less expensive. The sealing arrangement could, of course, readily be produced by heat sealing in conventional manner, and methods used for large scale heat sealing around the edges of such bags could be adapted for producing the addition seal (s) defining the conduits.

A further important advantage of such a vessel is that when produced of any of these readily available flexible transparent plastics material, it could be sterilised by heating in an autoclave prior to use, giving much greater reliability than sterilising by solution, which is the only method available with known photobioreactor conduits. Moreover, after use, disposal of such a vessel is a viable alternative to sterilisation for re-use, because of its low cost .

A vessel comprising a flexible bag having front and rear walls, an inlet and an outlet and a plurality of linear seals formed between the front and rear walls is disclosed in GB-A-2101966 in respect of a container in which a liquid, e.g. blood, may be stored or through which it may be passed while being heated or cooled. However, whilst having the advantages outlined above, the seals in this previous proposal are used to provide, essentially, a single serpentine conduit between the inlet and the outlet. Small gaps (of 0.24cm) which are left between the ends of some of the seals and the edges of the bag to allow secondary flow from one part of the conduit to another serve to prevent stagnation of the liquid flowing through ^• the bag. They do not provide additional pathways (conduits) through the bag. Nor do they provide chambers which allow intermingling of liquid from respective passageways .

For use in a photobioreactor, a serpentine flow pathway has considerable disadvantages. In particular, as already mentioned, for any given width it cannot be too long or else the build-up of oxygen will kill the photosynthetic algae. It is for this reason that the present invention specifies provision of plural (relatively short) conduits, and chambers adjacent the inlet, the outlet and intermediate these two in which intermixing of fluid from the several conduits can take place. A further purpose of these chambers is to reduce the pressure of flow through the bag which also could damage or kill the photosynthetic organisms if it exceeds a certain level.

In relation to the foregoing points, in preferred embodiments of the vessel of the invention each of the first, second and third chambers preferably has an internal width or diameter at least as large (preferably at least twice as large) as the width or diameter of any one of the conduits.

In most practical embodiments, the sealing arrangement will comprise a plurality of parallel seals, so as to provide plural conduits of equal length. Also, the seals will generally be straight, i.e. rectilinear. However, in principle, it would certainly be possible for the sealing arrangement to comprise non-parallel, e.g. convergent or ' divergent, seals, and/or curving seal courses. In this respect the use of the term "linear" herein is to be understood in its broadest sense, encompassing both straight (rectilinear) and curving courses, but clearly distinguishing from any arrangement of punctiliform or highly discontinuous seals.

As regards the common problem of adhesion of microorganisms to the internal surface of conduits during operation of the photobioreactor, cleaning of vessels constructed, in accordance with the invention, of flexible plastics material, can be accomplished in the same manner as described in earlier specification GB-A-2318165 , by providing mobile beads or a pig within the conduit or conduits and causing these to move to and fro by the introduction and removal of liquid from the vessel, as is normal practice in continuous culture systems.

The invention will now be further described in specific embodiments by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic side plan view of a preferred vessel according to the invention;

Figure 2 is a schematic side plan view of an alternative embodiment of a vessel according to the invention; Figure 3 is a schematic side plan view of a further embodiment of a vessel according to the invention; and,

Figure 4 is a schematic side plan view of a still further embodiment of a vessel according to the invention.

Referring to the drawings and initially to figure 1 in particular, the photobioreactor comprises a flexible bag

(10) of substantially optically transparent plastics material, such as polyethylene. The bag (10) may typically be anything from 0.5 to 50m long, and almost as wide. The dimensions will be chosen to suit the site of operation and the scale of production of algae or other photosynthetic organisms that is required.

The bag (10) may be produced in tubular form, as is conventional, then pressed flat and heat sealed at its ends (at 11 and 13) , leaving an inlet (12) and an outlet (14) at one end, conveniently adjacent respective corners of the bag (10) , as shown. In the illustrated example, additional heat seals (15 and 17) have been effected along both sides of the bag (10) .

A less common method of manufacture would involve having separate overlying webs of flexible plastics material, providing front and rear walls of the bag, which are then heat sealed right around their peripheries, again leaving an inlet and an outlet.

A series of parallel heat seals (16, 18, 20) are provided between the front and rear walls of the bag (10) . These are typically formed concurrently with the heat sealed edges of the bag. In this embodiment there are seven seals, and they are provided at substantially equal spacings and parallel with the larger sides of the bag (and with the side seals 15, 17) . The central seal (20) connects to the seal (11) which extends between the inlet (12) and the outlet (14) , but stops short of the seal (13) at the other end of the bag (10) . The ends of the other seals (16 and 18) stop short of, i.e. are spaced from, the seals (11, 13) at the respective ends of the bag (10) .

Thus, in effect, the seals (16, 18, 20) define a first chamber (22) leading from the inlet (12) , a second chamber

(24) leading to outlet (14) , four conduits (26) , of substantially equal dimensions, in the upper half of the bag, four conduits (28) , also of substantially equal dimension, in the lower half of the bag, and an intermediate chamber (30), where all the conduits (26, 28) are in communication, adjacent the end of the bag remote from the inlet (12) and the outlet (14) . These chambers (22, 24, 30) have a function corresponding to that of manifolds in an equivalent fence-like arrangement of conduits made of separate tubes. The chamber (30) is, of course, half way along the flow path between the inlet (12) and the outlet (14) .

In this specific illustrated example, the chambers (22, 24, 30) may each have a diameter, when filled, of about 5cm. In other words, the gaps between the ends of the seals (16, 18) and the edge seals (11, 13) and also the gap between the end of the seal (20) and the edge seal (13) is about 5cm. The distance between the adjacent seals (16, 18, 20) is only about 2.2cm, which is therefore the approximate width or diameter of the conduits (26, 28) . Thus the chambers (22, 24, 30) are more than twice the width/diameter of the conduits (26, 28).

In a somewhat larger version of photobioreactor, the width of the chambers (22, 24, 30) may be about 7cm, and that of the conduits (26, 28) about 2.8cm, giving a ratio of 2.25:1.

When the bag (10) is used as a photobioreactor, it may advantageously be supported in a vertical disposition, just as illustrated, as this minimises floor space requirements and will usually maximise the area in receipt of incident sunlight. Liquid culture medium with a chosen strain of algae suspended therein will be circulated through the bag. Preferably the inlet (12) will be at the bottom, the outlet (14) at the top, so that the liquid flows to the right along the conduits (28) in the bottom half of the bag (10) , as shown in the drawing, and then to the left along the conduits (26) in the top half of the bag (10) . The rate of flow will generally be of the order of 0.5 to l.Om/s or less, and this will typically be maintained by a pump located in a pipe leading to the inlet (12) . In the culture system downstream of the the outlet (14) , the liquid will pass into a collection vessel (not shown) such as a holding/separation tank, from where a certain proportion of the algae may be harvested, e.g. by filtration and/or sedimentation, with the extracted volume replenished by fresh culture medium. With the outlet (14) at the top, the liquid may be allowed to drop or splash into the collection vessel, which results in bubble formation and aids the purging of oxygen therefrom. The system includes a pump for inducing the flow of the culture medium.

The dimensions of the conduits (26, 28), i.e. the arrangement of the seals (16, 18, 20) will be chosen depending on the strain of micro-organism being cultured, and other factors, such as the flow rate, light intensity, etc.

The provision of the chambers (22, 24, 30) is important in countering build-up of a high oxygen concentration in any one of the conduits (26, 28) which could lead to failure of the whole system by poisoning, and also in minimising the pressure head. The overall arrangement provides a large surface area/volume ratio for incident light, and a short residence time, as the culture medium passes relatively quickly from the inlet to the outlet.

The flexible plastics bag (10) provides the required conduit system of the photobioreactor in a particularly compact and cost effective manner, and has the advantage of being able to withstand autoclaving, so that it can be reliably sterilised prior to use.

Numerous variations in the sealing arrangements, the number and arrangement of the conduits and other details are, of course, possible within the scope of the invention. The illustrated arrangement of conduits in the embodiment of figure 1 includes a chamber for communication provided at -lithe opposite end to the inlet and outlet is particularly favourable because it is relatively compact.

In the embodiment shown in figure 2, a larger bag (110) is provided with an inlet chamber (122) and an outlet chamber (124) at opposite ends and a communication chamber (130) midway between these .

In the embodiment shown in figure 3, the arrangement of sealing lines (218) defining the conduits is provided in a single group communicating directly between an inlet chamber (222) and an outlet chamber (224) .

The arrangement shown in figure 4 is more complex and represents a sealed bag system permitting recirculating culture. The arrangement includes a reverse pass conduit arrangement (generally similar to the arrangement of figure 1) , including an inlet chamber (322) , and conduits (328) defined by seal lines (318) divided into two groups by a seal wall (320). Seal wall (320) separates inlet chamber (322) from outlet chamber (324) . Additionally however, the configuration of seal lines impressed onto the bag includes a seal line (311) spaced from the edge seal (310) of the bag defining an additional chamber (350) communicating with the inlet (312) and the outlet (314) . The additional chamber acts as a holding/storage/settling chamber and enables the bag to function as a stand alone recirculating system for organism culture. A pugged port (351) permits the introduction of culture media (including any nutrients required) . The plugged port (351) also permits culture harvesting. A magnetic pump (352) sealed into the bag induces re-circulation of the culture media along the flowpath.

Claims

Claims :

1. A vessel comprising a flowpath configured between an inlet and an outlet, the flowpath configuration including:

a first chamber;

a second chamber downstream of, and in communication with the plurality of conduits;

wherein the first and second chamber and the plurality of conduits comprise walls of flexible transparent (or translucent) material, a plurality of linear seals formed between front and rear walls of the material defining the plurality of conduits.

2. A vessel according to claim 1, wherein the chambers and the plurality of conduits are formed integrally.

3. A vessel according to any preceding claim, wherein each of the first, second and third chambers has an internal width or diameter at least as large as the width or diameter of any one of the conduits.

. A vessel according to any preceding claim, wherein the first and second chambers are defined adjacent respective ends of conduit defining linear seals, the seal ends defining the respective chambers being substantially in-line.

5. A vessel according to any preceding claim, wherein the arrangement of linear sealing between the front and rear walls of the vessel consists of or includes a plurality of substantially parallel seals.

6. A vessel according to any preceding claim, wherein the linear course of the or each seal between the front and rear walls is substantially straight.

7. A vessel according to any preceding claim, wherein the inlet and outlet are defined by seals formed between the front and rear walls of the vessel.

8. A vessel according to any preceding claim, wherein the first chamber is in communication with the inlet and adjacently in communication with one end of a first group of the conduits, the second chamber is in communication with the outlet and adjacently in communication with one end of a second group of the conduits, and a third chamber is intermediate and in communication with the first and second groups of conduits .

9. A vessel according to claim 8, wherein the third ^ΓÇó chamber is defined adjacently intermediate ends of seals defining two groups of conduits, the seal ends defining the conduit groups being substantially in- line.

10. A vessel according to any preceding claim, wherein fluid communication between the first and second chamber, other than via the first and second groups of conduits is substantially inhibited.

11. A vessel according to any of claims 8 to 10, wherein the inlet and the outlet and the respective first and second chambers are disposed at one end of the vessel and the third chamber is disposed at the opposed end of the vessel.

12. A vessel according to any of claims 8 to 10, wherein the inlet and the outlet and the respective first and second chambers are disposed at opposed ends of the vessel and the third chamber is disposed intermediate the opposed ends of the vessel .

13. A vessel according to any preceding claim, wherein a dividing wall, comprising a seal formed between the front and rear walls of the vessel, separates the first and second chambers.

14. A vessel according to any preceding claim, wherein perimiter seal or seam lines define the outer extent of the vessel .

15. A vessel according to any preceding claim including a further chamber communicating with both the inlet and the outlet.

16. A microorganism culture system having a culture flowpath including a vessel according to any preceding claim.

17. A method of microorganism culture comprising directing the culture through a system according to claim 16.

18. A method of manufacturing a vessel, comprising sealing first and second portions of translucent or transparent flexible sheet material along a predetermined arrangement of seal lines so as to define a vessel including:

a first chamber;

a plurality of conduits arranged in side by side relationship in fluid parallel communication with the first chamber; and,

a second chamber spaced from the first chamber and in communication with the plurality of conduits .

19. A method according to claim 18, wherein the seal lines are formed by a heat sealing process.

0. A method according to claim 18, or claim 19, wherein the heat sealing to the required configuration is implemented in a single heat sealing operation.