WO1999046360A1

WO1999046360A1 - Photobioreactor apparatus

Info

Publication number: WO1999046360A1
Application number: PCT/GB1999/000723
Authority: WO
Inventors: Jonathan Mortimer; Simon Thomas; Pashalis Alexandros Temekenidis
Original assignee: Applied Photosynthetics Limited
Priority date: 1998-03-11
Filing date: 1999-03-10
Publication date: 1999-09-16
Also published as: AU2739399A; GB9805028D0; GB2335199A

Abstract

The number of tubes or conduits in a fence-like configuration of photobioreactor is usually limited by hydrostatic pressure causing the flow rate to decrease successively from the upper to the lowermost tube in the array, since to function efficiently the flow rate must be maintained in a narrow range which is slow enough for algal growth but sufficiently fast to keep the tubes clean. To overcome this limitation, a plurality of fence-like arrays (16, 26, 36, 46, 56, 66, 76, 86) may be stocked one above the other, extending between elongated, common manifolds (20, 40, 60, 80). Thus, the size of the apparatus and the algal yield obtained may be greatly increased without any increase in pumping capacity.

Description

- 1 -

PHOTOBIOREACTOR APPARATUS

This invention concerns photobioreactor apparatus.

Such apparatus comprises substantially optically transparent 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 arranged in a coiled, fence-like or serpentine configuration .

For commercial scale operation of photobioreactors, e.g. production of algae for use in fish farming, it is desirable not only to maximise the yield for a given size of apparatus, but also to maximise the size of that apparatus so long as this results in a commensurate increase in yield.

Various limiting factors apply when considering the size and form of photobioreactor apparatus.

Firstly, to maximise use of the incident light a high surface area to volume ratio is desirable. This factor indicates that the tube diameter should be relatively low. - 2 - Secondly, the concentration of the organism being cultured must not become too high, nor the flow path be too long, otherwise oxygen poisoning and rapid death of the organism can result. This factor limits the reduction in tube diameter and also limits the length of any individual tubular conduit. In the case of a coiled or serpentine configuration of tubing, the overall length of the tube is thereby limited and thus the overall size of the apparatus. This is not so with a fence-like configuration where a plurality of tubes extend in generally parallel array between a pair of manifolds each in the form of larger dimensioned vessels. In other words, with a fence arrangement a number of individual, yet parallel conduits are provided. Liquid from the respective tubes/conduits mixes in the manifolds and the concentration of organisms and oxygen is thereby reduced.

A third limiting factor is the rate at which liquid medium needs to be pumped through the apparatus. The organisms being cultured generally cannot tolerate a high flow rate. In the case of algae, the maximum flow rate is about 0.5m sec^-1. On the other hand for effective operation of cleaning pigs or beads of the type disclosed in the applicants earlier GB 9621130.5 a maximum flow rate of about 0.3m sec^-1 is required. It is, of course, extremely important that the internal surfaces of the tubes are kept clean in this way otherwise the rate of photosynthesis and the resulting yield will be impaired.

In a fence configuration, where the tubes extending between the manifolds are arranged one above the other, in a substantially - 3 - vertical plane and liquid is pumped in near the bottom of one manifold and flows out near the top of the other, different rates of flow exist in each of the tubes owing to the hydrostatic pressure of the manifold at the outflow side. Thus the rate of flow in the lowest tube is slowest and the rate of flow in the top tube is highest. The existence of this pressure differential limits the number of tubes which can be employed in the arrangement all having a rate of flow falling between defined maximum and minimum levels. In practise, the maximum number of parallel tubes possible may be only, say, eight or twelve.

The applicants have found that it is possible to double the number of tubes employed in a fence arrangement photobioreactor by increasing the number of manifolds to three. A first group of tubes is arranged between a first (inflow) manifold and a second manifold, which is elongated compared to the previous arrangement, and a second group of tubes is arranged above the first group between the second manifold and a third (outflow) manifold. Generally, to maximise the number of tubes which can be employed, there will be the same number of tubes in the first and second groups. Thus the maximum possible in the overall arrangement may be increased from, say, eight to sixteen, with a resultant substantial doubling of the overall yield. The capacity of the pump connected to the inflow manifold is not affected.

The liquid nutrient medium in which the algae is suspended travels from the first manifold along any one of the first group - 4 - of tubes to the second manifold and then back along any one of the second group of tubes to the third manifold, and thence to a container, from which the algae may be harvested.

The applicants have now found that it is practical to further develop this arrangement so as effectively to stack a large number of such fence-like arrangements on top of each other, and interlink them, and thereby increase the overall yield correspondingly, without requiring any increase in pumping capacity.

More generally, the present invention provides photobioreactor apparatus comprising a plurality of transparent conduits and a plurality of larger dimensioned transparent manifolds, the conduits and the manifolds being interconnected in such a way that a first group of the conduits extend between a first and a second of the manifolds to provide a first series of parallel passageways for throughflow of a liquid medium and a second group of the conduits extend between the second manifold and a third of the manifolds to provide a second series of parallel passageways for throughflow of liquid medium, characterised in that at least a third group of the conduits extend between the third manifold and a fourth of the manifolds to provide a third series of parallel passageways for throughflow of a liquid medium.

Of course, in practical embodiments, in order to minimise the floor space requirements of such apparatus, the conduits in all the groups will preferably be substantially parallel to each - 5 - other, and the groups of conduits will preferably be stacked above each other.

In many practical embodiments of the invention, the conduits will take the form of tubes of substantially rigid material, usually plastics, but possibly glass, with the manifolds also in the form of tubes or similar vessels of substantially rigid transparent material, but of larger diameter or dimension than the conduits. However, in some embodiments the conduits and manifolds may be provided as passageways and larger lacunae defined by liner seals between front and rear walls of one or more bags of flexible transparent material, as disclosed in the applicants' earlier specification GB 9715762.2.

In the case of apparatus formed of rigid material, the tubes providing the conduits may all lie in the same plane, which will usually be a substantially vertical plane. However it may be advantageous, to reduce the overall height of the apparatus and make it more compact, if adjacent tubes within each group are offset relative to each other so that there is a staggered arrangement with alternate tubes lying in a common plane.

The overall arrangement of any embodiment in accordance with the invention effectively combines the advantages of the known apparatus having a serpentine flow path and the known apparatus of fence-like configuration, i.e. having plural parallel flow paths extending between larger volume manifolds. - 6 - The invention will be described further, by way of example, with reference to the accompanying drawings in which the single figure is a diagrammatic representation of a practical embodiment of the photobioreactor apparatus of the invention.

The illustrated embodiment comprises an interlinked series of nine manifolds, 10-90. Each manifold comprises a relatively large diameter tube of substantially rigid plastics material. As shown, manifolds 10, 30, 50, 70 and 90 are arranged substantially vertically one above each other at one side of the apparatus, while manifolds 20, 40, 60 and 80 are similarly arranged substantially vertically one above the other at the other side of the apparatus .

The lowest manifold 10 is connected to an inflow pipe 12 and may be termed the inflow manifold. A pump (not shown) is connected to this pipe 12. It may conveniently be a diaphragm pump or an air lift pump capable of maintaining a maximum flow rate of 0.5m sec^-1 within the apparatus. The highest manifold 90 is connected to an outflow pipe 14 which leads to a collection vessel (not shown) from where algae grown in the apparatus may be harvested. A proportion of the culture medium pumped through the apparatus to the collection vessel is recirculated, but some fresh medium is introduced. As the culture medium falls into the collection vessel oxygen and other gaseous products, which have accumulated within the medium by virtue of algal photosynthesis, are dispersed and these are exhausted through a valve. - 7 - It will be noted that the inflow and outflow manifolds 10, 90 are smaller than the others, and that the manifolds 20, 40, 60, 80 at one side are staggered in their vertical position relative to the manifolds 10, 30, 50, 70, 90 at the other side.

The manifolds 10-90 are interlinked, in series, in a generally serpentine manner by eight groups of relatively small diameter tubes 16, 26, 36, 46, 56, 66, 76, 86. In this particular embodiment there are eight individual tubes 18 in each group. Only the three lowest groups 16, 26, 36 are shown fully, the remainder being depicted by a single broken line representing each tube 18. All of the tubes 18 run substantially parallel to each other and are stacked above each other in a substantially vertical plane.

The first group of tubes 16 extend between and provide parallel flow paths or conduits between the first and second manifolds 10, 20. The second group of tubes 26 extend between and provide parallel flow paths or conduits between the second and third manifolds 20, 30. The third group of tubes 36 extend between and provide parallel flow paths or conduits between the third and fourth manifolds 30, 40, and so on, as is apparent from the drawing. The direction of flow of liquid medium being shown by arrows in each group of tubes 16-86.

The first and second manifolds 10, 20, interconnected by the first group of tubes 16 may be considered to correspond to a known fence-like arrangement of photobioreactor. The same - 8 - applies to each consecutive par of manifolds and their interconnecting group of tubes, but each such "fence" arrangement is itself interlinked via the manifolds at each end to a further such arrangement, until the outflow manifold 90 is reached.

In use, liquid culture medium, including algae and nutrients for their growth/reproduction is pumped around the circuit, algae being harvested from the collection vessel and nutrient medium being replenished, as necessary.

As mentioned, in experiments up to eleven manifolds have been connected in this manner by ten groups of tubes without any increase in pumping capacity being necessary and without any deterioration in the relative yield of algae, which increases commensurate with the increase in size of the apparatus. An arrangement including a greater number of manifolds may well be possible, the only practical limit apparently being the space required to house the apparatus.

The invention is not, of course, limited to the details of the illustrated embodiment and many design variants are possible. Vertical stacking is usually to be preferred as it usually maximises the amount of incident light available to the algae within the apparatus. However, each group of tubes may lie in a vertical plane while respective groups of tubes may be offset relative to each other. Also, within each group a more compact arrangement may be achieved by offsetting alternate tubes without any reduction in the light available to each. In some cases, - 9 - also, it may be of advantage to arrange the tubes in a group, or the groups of tubes in an inclined plane.

As mentioned in the introduction further embodiments of the photobioreactor of the invention may be constructed from one or more flexible bags of transparent material, the conduits and manifolds then being provided as passageways and larger lacunae defined by linear seals between front and rear walls of the or each bag.

Claims

- 10CLAIMS

1. Photobioreactor apparatus comprising a plurality of transparent conduits and a plurality of larger dimensioned transparent manifolds, the conduits and the manifolds being interconnected in such a way that a first group of the conduits extend between a first and a second of the manifolds to provide a first series of parallel passageways for throughflow of a liquid medium and a second group of the conduits extend between the second manifold and a third of the manifolds to provide a second series of parallel passageways for throughflow of liquid medium, characterised in that at least a third group of the conduits extend between the third manifold and a fourth of the manifolds to provide a third series of parallel passageways for throughflow of a liquid medium.

2. Apparatus according to claim 1 wherein the conduits in all the groups are substantially parallel to each other.

3. Apparatus according to claim 1 or 2 wherein the groups of conduits are stacked above each other.

4. Apparatus according to any preceding claim including up to ten groups of conduits extending between eleven manifolds, the conduits and manifolds being interconnected in the manner defined in claim 1. - 11 -

5. Apparatus according to any preceding claim having eight conduits in each group.

6. Apparatus according to any preceding claim wherein the conduits take the form of tubes of substantially rigid transparent material and the manifolds take the form of tubes or similar vessels of substantially rigid transparent material, but of larger diameter or dimension than the conduits.

7. Apparatus according to any of claims 1 to 5 wherein the conduits and manifolds are provided as passageways and larger lacunae defined by linear seals between front and rear walls of one of more bags of flexible transparent material.

8. Apparatus according to any preceding claim wherein the conduits in all the groups lie in substantially the same plane.

9. Apparatus according to any preceding claim wherein the conduits in each of the groups lie in a substantially vertical plane.

10. Apparatus according to claim 6 wherein adjacent tubes within each group are offset relative to each other so that there is a staggered arrangement with alternate tubes lying in a common plane.