WO2009037683A1

WO2009037683A1 - A system and apparatus for growing cultures

Info

Publication number: WO2009037683A1
Application number: PCT/IE2008/000088
Authority: WO
Inventors: Seamus Devlin; Tracey Devlin
Original assignee: Seamus Devlin; Tracey Devlin
Priority date: 2007-09-17
Filing date: 2008-09-17
Publication date: 2009-03-26

Abstract

There is described a photo-bioreactor apparatus used for the growth of algal cultures in a growth mixture. The apparatus comprises a novel bioreactor envelope construction, comprising a lower portion (64) forming a channel and an upper portion (62), wherein the lower and the upper portion form an enclosed envelope structure and at least a portion of the upper portion is light transmissive.

Description

A System and Apparatus for Growing Cultures

Field of the Invention

The present invention relates to a system and apparatus for growing cultures, more particularly a photo-bioreactor for the growing of cultures, more particularly algal cultures used in the bio-fuel, pharmaceutical or food industries.

Background to the Invention

The world's dependence upon petroleum-based products is increasing as the demand from both Western and Asian economies grows. As counterpoints to this, the discovery of new reserves of petroleum oil has reached a plateau and is predicted to decline over following decades. Also, there is increasing concern that carbon emissions from burning fossil fuels is driving climate change.

This situation has generated a boom m the demand for bio-fuels - fuel derivatives that are manufactured from biomass such as oilseed rape arid wheat. However, these fuel sources are a relatively inefficient means of producing such biomass, and require that arable laud, that was originally used for the production of food, is transferred either to the production of non-food species or for the production of edible crops that will be transferred into fuel production.

As a result, an alternative approach to the production of bio-fuel is desirable. It is found that oil-rich biomass can be produced by some types of algae. The growth rate of these forms of algae can greatly outstrip that of traditional bio-fuel crops. These forms of algae are termed Micro Algae to distinguish them from the larger forms of algae, such as seaweed, that are termed Macro Algae. The following table - Table 1 - shows oil yield comparisons for varying bio-fuel crops. Table 1 Comparison of Oil Yields

The advantages of deriving bio-fuel from algae include rapid growth rates and a high per- ^' acre yield. Also, algae bio-fuel contains no sulphur, is non-toxic, and is highly biodegradable. Some species of algae are ideally suited to bio-diesel production due to their high oil content — in some species, approaching 40% oil content.

Along with selected nutrients, algae (like numerous plant species) require three primary components to grow: sunlight, carbon dioxide and water. Photosynthesis is an important biochemical process in which plants, algae, and some bacteria convert the energy of sunlight to chemical energy. Micro Algae contain lipids and fatty acids as membrane components, storage products, metabolites and sources of energy. Algae contain anywhere between 2% and 40% of lipids/oils by weight.

The bio-fuel potential of algae has been the object of considerable research efforts in the past. One such program stands out due to its considerable comprehensiveness. This is the "Aquatic Species Program" (ASP), which ran from 1978 to 1996 under the US National Renewable Energy Laboratory (NREL), funded by the Office of Fuels Development, a division of the US Department of Energy. The focus of this program was to investigate high-oil algae that could be grown specifically for the purpose of wide scale bio-fuel production. The research began as a project looking into using quick-growing algae to sequester carbon in CO2 emissions from coal power plants. Algae had already been used in experiments to manage wastewater, and were found to make good substrates for biogas production, even though the sludge they fed on yielded more biogas. Noticing however that some algae have very high oil contents, the project shifted its focus to growing algae for another purpose - producing bio-fuel. Some species of algae were supposed to be ideally suited to bio-diesel production due to their high oil content (between 10% and 40%, depending on many different factors), and fast growth rates in laboratory situations.

The ASP programme concentrated on propagating algal biomass in open ponds and raceways that used paddle wheels to circulate the culture medium, as this was viewed as the most cost-effective method of producing the biomass on a large scale at relatively low cost. In addition, the open ponds could be sited in marginal regions where agriculture for food production would not be compromised.

The ASP programme encountered a number of technological barriers — not least of which was the fact that oil -rich forms of algae grown on open ponds were susceptible to replacement over time by more aggressive, low oil, local forms of algae. Hence the yields experienced in laboratory conditions as shown in Table 1 above could not be replicated and maintained in the field.

Similarly, the open pond and raceway systems do not lend themselves to the control and optimisation of the environment in which these oil-rich algae would flourish.

Hence, the concept and practice of growing oil-rich algae in open ponds and raceways, whilst attractive and continuing to be the subject of on-going research by a number of companies, has proven problematic.

In order to eradicate the problems associated with the open pond method of producing algal biomass, over the past few years several companies have issued press releases about technologies they have developed to produce bio-fuels from algae. Most of the projects involve the use of closed photo-bioreactors, in which the micro-organisms are grown in a controlled environment, are fed with carbon dioxide (CO₂) and nutrients.

Algal biotechnology has progressed relatively slowly in spite of its potential to produce bio-fuels and high-value products for the pharmaceutical and food industries. The principal constraint is the lack of efficient, low-cost, large-scale cultivation techniques. In addition, the production of micro-algal biomass for the downstream production of bio-fuels generally requires the propagation of oil-rich monocultures and this requirement has led to increased emphasis on the development of these closed photo-bioreactors.

With reference to Fig. 1, an example of a typical known air-lift loop photo-bioreactor is indicated generally at 10. The photo-bioreactor 10 comprises a first vertical tubular column 12 made of a transparent or translucent material. A second vertical tubular column 14 is located within the first column 12, the second column 14 being open-ended and formed of a generally opaque material, the ends of the second column 14 spaced from the respective ends of the first column 12.

The photo-bioreactor 10 contains a liquid solution 16 having a Micro Algae seed culture 18 in suspension. A light source (not shown) shines light onto the photo-bioreactor 10 as indicated by the lines 20, resulting in the creation of a photic zone 22 within the first column 12 and exterior to the second column 14 wherein the liquid solution 16 is illuminated by the light, and a dark zone 24 within the interior of the second column 14 that is shielded from the light by the opacity of the second column 14.

A sparge tube 26 having a first opening 27 is located at the base of the photo-bioreactor 10, the opening 27 being positioned directly beneath the lower open end of the second column 14. A gaseous mixture is introduced into the liquid solution 16 via the tube 26, the gaseous mixture generally comprising oxygen, nitrogen and carbon dioxide. The bubbles of the gaseous mixture rise up through the interior of the second column 14, with the motion of the bubbles causing a liquid flow from the dark zone 24 to the photic zone 22 and back to the dark zone 24 as indicated by lines 28.

The liquid flow causes the Micro Algae seed culture 18 to experience a light/dark transition, which contributes to their growth. The most common photo-bioreactors used for algae propagation are vertical, gas-sparged photo-bioreactors such as air-lift reactors, bubble column and flat panel reactors due to their relatively simple form of construction.

These systems, however, present their own sets of problems.

The cost of photo-bioreactors - and particularly large-scale photo-bioreactors - has meant that consistent, high volume productivity has to be achieved to make these potential solutions economically viable. The driving forces behind photo-bioreactor development have been the somewhat conflicting pursuits of reducing the size of cultivation systems - when compared to open pond techniques — whilst increasing biomass concentration. This has meant that photo-bioreactors have to support highly efficient light utilisation and nutrient uptake by the Micro Algae being propagated.

In such light-dependent, high-density cell cultures, a light gradient will always occur due to light absorption and mutual shading by the cells. Consequently the biomass has to be continually mixed if optimal growth is to be achieved. Similarly cells must come into contact with nutrient sources, in particular carbon dioxide, if cell and thereby lipid production volumes are to be realized.

Shearing action in gas-sparged photo-bioreactors such as bubble columns and flat panels is necessary for mixing, heat elimination and mass and light transfer - and its importance increases as the devices scale upward. However, excessive shear can lead to impaired cell growth, cell damage and eventually cell death. Cell damage due to shear stress has been referred to as the key problem in the culture of Micro Algae in photo-bioreactors (Vandanjon L., Rossignol N.,Jaouen P.,Robert J.M., Quemeneur F,. 2000. "Effects of shear on two microalgae species - contribution of pumps and valves in tangential flow filtration systems." Biotechnology & Bioengineering. Volume 23. Issue 1 Pages 1 - 9). It is a common opinion among researchers in this field that Micro Algae are intrinsically shear sensitive and that this accounts for relatively low productivity and relatively low growth rates in Micro Algae culture systems. Whilst the open pond system of algae cultivation encountered problems of contamination and the lack of adequate environmental control, the use of photo-bioreactors is similarly fraught with the difficulties of cost effectiveness and technological barriers that circumscribe the consistent production of high biomass densities. Both of these conventional techniques also require either relatively high land cost or relatively high installation cost allied with relatively high operational costs. For these reasons conventional techniques cannot be applied optimally and efficiently for the mass production of algae.

Therefore a need exists for a system that is relatively low-cost; permits open-ended scalability; and is simple to manufacture, install, operate, replace and maintain.

It is an object of the invention to provide a system that addresses some or all of the above problems.

Summary of the Invention

Accordingly, there is provided a photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion comprising a first substantially planar inclined side wall and a second substantially planar inclined side wall, the first and second side walls forming an inverted V-shaped cross-section, wherein at least a portion of said upper portion is substantially light transmissive, and wherein said upper portion and said lower portion are connected to form a substantially enclosed envelope structure.

The use of planar wall sections allows for the relative control of the level of light that is transmitted into the interior of the photo-bioreactor envelope, and the relatively simple construction results in a reduced cost. Preferably, the photo-bioreactor envelope is flexible to allow the adjustment of the angle of incline of the walls of said upper portion to control the quantity of light received to the interior of the envelope structure.

Preferably, the photo-bioreactor envelope further comprises: at least one primary attachment projection located at the upper end of said upper portion; and at least one secondary attachment projection located at the interface between the upper portion and the lower portion, and wherein when installed, the respective angles of incline of the planar side walls of said upper portion is determined by the vertical height difference between the at least one primary attachment projection and the at least one secondary attachment projection.

There is further provided a photo-bioreactor for the growing of cultures, the photo- bioreactor comprising a photo-bioreactor envelope to receive a seed culture and a growth medium; a support stanchion operable to couple to the at least one primary attachment projection of said photo-bioreactor envelope; an adjustment means operable to couple to the at least one secondary attachment projection of said photo-bioreactor envelope, the adjustment means operable to adjust the respective angles of incline of the side walls of the upper portion of said photo-bioreactor envelope.

As the respective angles of incline of the side walls of the photo-bioreactor envelope can be adjusted, this allows for accurate control of the quantity of light that is reflected from the side walls, and also the quantity of light that passes into the interior of the photo- bioreactor envelope. This allows for control of the temperature of the seed culture and growth medium, to produce optimum culture growth conditions.

There is further provided a photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion, wherein at least a portion of said upper portion is substantially light transmissive, wherein said upper portion and said lower portion form a substantially enclosed envelope structure, and wherein the photo-bioreactor envelope further comprises at least one gas-permeable tube located within said channel in said lower portion such that, in use, said at least one gas-permeable tube is immersed in the seed culture and the growth medium.

The use of a gas-permeable tube within the interior of the photo-bioreactor envelope provides an alternative method of introducing gases into the seed culture and growth medium, avoiding the need to make the photo-bioreactor envelope body gas-permeable. Also, the use of a gas-permeable tube ensures that the carbon dioxide fully diffuses into the growth medium such that bubbles of gas do not escape into the headspace formed by the upper part of the envelope. It is also important to note that this diffusion of the gases through the silicone tubing does not give rise to gas bubbles, which can cause shear stresses within the culture being grown. Such bubbles, often formed by gas-sparged nozzles, can result in slower growth rates and cell death.

There is further provided a photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion wherein at least a portion of said upper portion is substantially light transmissive, wherein said upper portion and said lower portion form a substantially enclosed envelope structure, and wherein the photo-bioreactor envelope further comprises at least one mixing projection defined on the internal surface of said channel.

The use of mixing projections allows for the continued agitation and mixing of the seed culture and growth medium mixture, as the mixture passes through the photo-bioreactor envelope.

Alternatively, there is provided a photo-bioreactor for the growing of cultures, the photo- bioreactor comprising a substantially tubular main body having an upper portion and a lower portion forming a substantially enclosed envelope structure, the walls of said envelope structure having a cavity defined therebetween, said main body comprising: a transparent section; and a substantially gas-permeable section, said main body adapted to receive a seed culture and a growth medium within said cavity.

Means is provided to allow light to enter the main body through the transparent section to facilitate photosynthesis of the contained seed culture. In use, the gas-permeable section allows for the escape of water and oxygen molecules formed during the photosynthesis process and transpiration of the culture. This allows the pressure within the main body to equalise with atmospheric pressure.

In use, the gas-permeable section also allows for the ingress of carbon dioxide into the interior of the main body, which can be used by the growth medium to facilitate the growth of the seed culture.

Preferably, in use, the seed culture and the growth medium substantially cover the lower portion of said main body.

Preferably, the seed culture is an algal culture.

Preferably, said main body is formed from a plastics material.

Preferably, said main body is transparent.

Preferably, said main body is substantially gas-permeable.

Preferably, said main body comprises a substantially enclosed tube.

Preferably, said lower portion comprises a trough, said trough being adapted to retain said seed culture and said growth medium.

Preferably, said main body is provided in a substantially boustrophedonic arrangement. Preferably, said main body is formed from an upper layer portion and a lower layer portion bonded together at a first bonding location and a second bonding location, said cavity defined between said upper layer portion and said lower layer portion.

Preferably, said upper layer portion and said lower layer portion are bonded together at said first and second bonding locations using adhesive means.

Alternatively, said upper layer portion and said lower layer portion are bonded together at said first and second bonding locations using heat welding.

Alternatively, said main body is formed as a planar piece of plastics substrate material, the free ends of said substrate material being bonded together, thereby forming an enclosed envelope having said cavity defined therein.

Preferably, said photo-bioreactor comprises input valve means to allow the introduction of said seed culture and said growth medium into said cavity.

Preferably, the input valve means comprises any standard sealed valve that may be coupled to a pump or a Venturi injector device.

Preferably, said photo-bioreactor comprises output valve means to allow the extraction of said seed culture and said growth medium from the interior of said photo-bioreactor.

Preferably, said photo-bioreactor comprises a first end and a second end, said input valve means located adjacent said first end, and said output valve means located adjacent said second end.

Preferably, said seed culture and said growth medium are pumped into said photo- bioreactor through said input valve means at said first end.

Preferably, in use, said first end is located at a greater height than said second end.

Preferably, said photo-bioreactor further comprises gas introduction means. Preferably, the gas introduction means enables the introduction of gases into the photo- bioreactor and allows for the level of gases such as carbon dioxide to be more accurately regulated, as opposed to relying on the uptake of carbon dioxide from the atmosphere through the gas-permeable portion of the main body. Accurate control, of these levels allows for the rate of growth of the seed culture to be controlled also.

Preferably, said gas introduction means is located substantially within the cavity defined in the interior of said main body.

Preferably, said gas introduction means comprises a gas-permeable tube.

Preferably, said gas-permeable tube is secured to said lower layer portion.

Preferably, said gas introduction means further comprises a supply of gas, said gas- permeable tube, in use, being coupled to said gas supply to provide said gas to the interior of said main body.

Preferably, the gas supply is a container of a gas that will aid the photosynthesis process within the photo-bioreactor, e.g. carbon dioxide.

Preferably, the gas-permeable tube is located within said cavity such that the gas- permeable tube is immersed in the seed culture and the growth medium.

Preferably, said gas-introduction means comprises a control valve located between said gas-permeable tube and said gas supply, said control valve, in use, being operable to regulate the rate of gas supply to the interior of the main body.

Alternatively, the photo-bioreactor comprises a secondary layer portion secured to the exterior of the lower portion of said main body at a first securing location and a second securing location, a secondary cavity being defined between the lower portion of said main body and the secondary layer portion.

Preferably, the lower portion of said main body is gas-permeable, the photo-bioreactor further comprising a gas supply coupled with said secondary cavity. Preferably, a pump is located between said secondary cavity and said gas supply, the pump, in use, being operable to regulate the pressure of gas within said secondary cavity.

The use of a secondary cavity beneath the underside of the main body of the photo- bioreactor allows for an alternate method of introducing gas, e.g. carbon dioxide, into the interior of the main body, to facilitate the photosynthesis process.

Preferably, the photo-bioreactor further comprises a reflector, the reflector being located adjacent said main body.

The use of a reflector allows for additional light to be reflected and focused on the contained seed culture and growth medium, aiding the photosynthesis process.

Preferably, said reflector is concavely-shaped, the reflector positioned such that the focal point of said concavely-shaped reflector is located within the cavity defined within said main body.

The use of a concavely-shaped reflector will increase the concentration of light reflected into the photo-bioreactor.

Preferably, said upper portion comprises at least one primary attachment projection, said primary attachment projection being adapted to couple with primary retention means.

It will be understood that said primary attachment projection may be moulded integrally with said main body, or that said primary attachment projection may be formed by overlapping a section of said upper portion.

Preferably, said lower portion comprises at least one secondary attachment projection, said at least one secondary attachment projection adapted to couple with secondary retention means.

Preferably, the photo-bioreactor comprises at least one mixing projection defined on the internal wall of the lower portion of said main body. The use of a mixing projection acts to disturb the flow of the seed culture and the growth medium, facilitating mixing of the seed culture and the growth medium as it passes through the photo-bioreactor.

Preferably, the at least one mixing projection comprises a longitudinal baffle, the longitudinal baffle extending substantially along the longitudinal length of the photo- bioreactor.

Preferably, the at least one mixing projection comprises a wedge.

Preferably, said photo-bioreactor further comprises a light sheet, said light sheet being located substantially within said cavity.

The use of a light sheet allows the light distribution within the photo-bioreactor to be increased, through uniform dispersion of light shone upon the light sheet.

Preferably, a plurality of etches is defined on the surface of said light sheet, the etches being operable to disperse light in a uniform manner through the photo-bioreactor.

Preferably, the light sheet is formed from either an acrylite or a plexi-glass sheet.

Preferably, the light sheet extends from said upper portion towards said lower portion.

Preferably, in use, the free end of said light sheet is immersed in the culture and growth medium, the free end of said light sheet being shaped to induce mixing of the seed culture and the growth medium

Preferably, the photo-bioreactor further comprises at least one shading element, the at least one shading element being adapted to couple to the exterior of said main body, the at least one shading element being formed of an opaque material.

The use of a shading element allows for the recreation of a light/dark cycle within the photo-bioreactor as the seed culture and the growth medium pass through the photo- bioreactor. The seed culture and the growth medium move between portions of the photo- bioreactor having transparent walls (day cycle), and portions of the photo-bioreactor covered by the shading element (night cycle).

Alternatively, the main body of the photo-bioreactor may have alternating transparent sections and opaque sections integral to said main body.

Preferably, the transparent section of the photo-bioreactor main body comprises a light- filtering layer, operable to prevent passage of light of a particular wavelength into the photo-bioreactor.

Use of selective light filters in the transparent portions of the photo-bioreactor can prevent the ingress of ultra-violet or infra-red light that may inhibit the photosynthesis process happening within the photo-bioreactor.

Preferably, the photo-bioreactor further comprises a light source, the light source being located adjacent the main body.

Preferably, the photo-bioreactor further comprises a light source, the light source being located substantially within the cavity defined within said main body.

Preferably, the photo-bioreactor further comprises a heat exchanger apparatus coupled to said main body, the heat exchanger apparatus being operable to regulate the temperature of the growth medium contained within the main body.

The use of a heat exchanger allows for the accurate, efficient, and sterile regulation of the temperature of the growth medium, therefore impacting on the photosynthesis process.

Preferably, a manifold is provided on the main body of the photo-bioreactor, the manifold extending into the cavity defined within said main body, the heat exchanger apparatus coupled to said manifold.

Preferably, said manifold comprises filter means operable to allow passage of the growth medium through said manifold while preventing passage of the culture. The use of the filter means prevents the culture from passing to the heat exchanger, meaning that only the growth medium is heated in the heat exchanger, before being returned to the interior of the photo-bioreactor main body.

There is also provided a system for the growing of cultures, the system comprising: a culture storage tank; a nutrients tank; a sterile water tank; a mixing apparatus coupled with said nutrients tank and said sterile water tank; a photo-bioreactor coupled with said culture storage tank and said mixing apparatus at a first end of said photo-bioreactor; and a harvesting station coupled with said photo-bioreactor at a second end of said photo-bioreactor, such that, in use: said mixing apparatus is operable to mix a quantity of nutrients from said nutrients tank and a quantity of sterile water from said sterile water tank to form a quantity of growth medium; said culture store tank and said mixing apparatus are operable to provide a quantity of seed culture and a quantity of growth medium to said photo-bioreactor; and said harvesting station is operable to harvest a quantity of biomass produced by said photo-bioreactor.

Preferably, the system further comprises a growth medium pump provided between said mixing apparatus and said photo-bioreactor, said growth medium pump being operable to pump growth medium from said mixing apparatus into said photo-bioreactor.

Preferably, the system further comprises a culture pump provided between said culture storage tank and said photo-bioreactor, said culture pump being operable to pump seed culture from said culture storage tank into said photo-bioreactor.

Preferably, said photo-bioreactor is arranged in a boustrophedonic configuration.

Use of a boustrophedonic arrangement allows for the maximisation of the available floor space. Preferably, said photo-bioreactor is provided on an incline, said first end of said photo- bioreactor being located at a higher altitude than said second end of said photo-bioreactor.

The difference in height between the ends of the photo-bioreactor allows for the force of gravity to act on the contained culture and growth medium, moving the culture and growth medium through the photo-bioreactor.

Preferably, the system further comprises a plurality of supporting armatures located adjacent said photo-bioreactor, said supporting armatures having retention means provided thereon, said retention means being adapted to couple to said photo-bioreactor to retain said photo-bioreactor.

Preferably, said supporting armatures project above said photo-bioreactor, said retention means comprising primary retention means, said primary retention means being adapted to couple with said primary attachment projections of said photo-bioreactor.

Preferably, said supporting armatures further comprise secondary retention means, said secondary retention means being adapted to couple with said at least one secondary attachment proj ection of said photo-bioreactor.

Preferably, said supporting armatures are adjustably mounted on a plurality of stanchions.

The adjustability of the armatures allows for the height of the photo-bioreactor above ground to be easily adjusted through manipulation of the vertical height of the armatures. The height of the photo-bioreactor can also be adjusted to set the slope of the photo- bioreactor, which may affect the speed at which the seed culture and the growth medium passes through the photo-bioreactor.

Preferably, the harvesting station comprises a filtration system operable to separate the larger cultures produced by the photo-bioreactor for harvesting from the remaining smaller cultures and the growth medium used by the photo-bioreactor. Preferably, the harvesting station is coupled to the culture storage tank, the harvesting station being operable to recycle the smaller cultures collected by the harvesting station to the culture storage tank.

The recycling stage assists in the efficient use of resources, and allows for a steady stream of fresh cultures for use at the start of the process.

Preferably, the system further comprises a compression apparatus, the compression apparatus being coupled with said harvesting station, said compression apparatus being operable to compress the larger cultures collected by said harvesting station.

The compression apparatus is operable to compress the algal cultures so that the contained oil is pressed out of the cultures, which can then be collected for further use.

Preferably, the system further comprises an enzyme converter, the enzyme converter being coupled with said harvesting station, the enzyme converter being operable to act on the larger cultures collected by said harvesting station to degrade the cell walls of the larger cultures.

As the use of an enzyme converter degrades the cell walls of the collected cultures, this makes fractionation of the oil collected from the cultures easier, and helps to maximise total oil recovered from the cultures.

Preferably, the system further comprises a gas contractor, the gas contractor being coupled to said sterile water tank, the gas contractor being operable to replace the oxygen molecules in the sterile water with carbon dioxide molecules.

As carbon dioxide is one of the main components of a photosynthesis process, the introduction of additional carbon dioxide into the sterile water, and correspondingly the growth medium, provides increased levels of stimulant for culture growth.

Preferably, the system further comprises a sulphur recovery unit and a hydrogen recovery unit, said sulphur recovery unit and said hydrogen recovery unit being coupled with said photo-bioreactor. As the sulphur recovery unit is coupled to the photo-bioreactor, sulphur can be removed from the interior of the photo-bioreactor. When sulphur is removed from the growth medium during the advanced stages of culture growth, the culture may produce large quantities of hydrogen, which can be recovered, using a hydrogen recovery unit coupled to the photo-bioreactor, for further processing.

Description of the Invention

Embodiments of the invention will now be describe, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a cross-sectional view of a prior art photo-bioreactor;

Fig. 2 is a plan view of an overall system for the growth of cultures according to the invention;

Fig. 3 is a perspective view of the system of Fig. 2 on a relatively gentle gradient;

Fig. 4 is an enlarged view of an adjustable stanchion and armature configuration;

Fig. 5 is a perspective view of the system of Fig. 2 on a relatively steep gradient;

Fig. 6 is a cross-sectional view of a photo-bioreactor according to the invention; Fig. 7 A is a perspective view of the photo-bioreactor of Fig. 6;

Fig. 7B is a perspective view of the photo-bioreactor of Fig. 6 having a diffusion tube;

Fig. 7C is a perspective view of the photo-bioreactor of Fig. 7B connected to a carbon dioxide supply; Fig. 8 is a perspective view of the photo-bioreactor of Fig. 6, showing the valves of the photo-bioreactor;

Fig. 9 is a perspective view of the photo-bioreactor of Fig. 6 having a secondary layer defining a secondary cavity;

Fig. 10 is a perspective view of the photo-bioreactor of Fig. 6 together with a solar reflector;

Fig. 11 is a perspective view of the photo-bioreactor of Fig. 6 together with a concavely-shaped solar reflector and an artificial light source;

Fig. 12 is a perspective view of a system comprising the photo-bioreactor of Fig. 6 coupled with a heat exchanger; Fig. 13 is an enlarged cross-sectional view of a heat exchanger manifold of a heat exchanger for use with the system of Fig. 12;

Fig. 14 is an enlarged perspective view of sample micro-barrier projections for use in the photo-bioreactor of Fig. 6; Fig. 15 is a perspective view of the photo-bioreactor of Fig. 6 having a plurality of vane projections;

Fig. 16 is a cross-sectional view of the photo-bioreactor of Fig. 6 having a light sheet;

Fig. 17 is a perspective view of the photo-bioreactor of Fig. 6 having a plurality of shading elements;

Fig. 18 is a perspective view of the harvesting tank of the system of Fig. 2;

Figs. 19-23 illustrate a number of different enhancements to the system of Fig. 2; and

Fig. 24 is a cross-sectional view of a photo-bioreactor envelope according to the invention coupled to support means.

With reference to Figs. 2 and 3, an overview of a system for growing cultures is indicated generally at 30. System 30 comprises an algal culture tank 32 that is fluidly coupled via a pump 36 with a sealed photo-bioreactor 34. Algal culture is formed in the algal culture tank 32 and, depending on the inoculation density required, sufficient concentration of an inoculum/algal seed culture may be periodically added to the photo-bioreactor 34 via pump 36.

The system 30 further comprises a nutrients tank 38 and a sterile water tank 40, tanks 38 and 40 being fluidly coupled to a mixing tank 42. Mixing tank 42 is fluidly coupled to a growth medium pump 44, with pump 44 being coupled to the continuous sealed photo- bioreactor 34.

Sterile water and nutrients from tanks 38 and 40 respectively are mixed in mixing tank 42 in the required ratio for optimal algal growth. The resulting mix (hereinafter termed the growth medium) can be gravity fed and/or injected via the growth medium pump 44 into the continuous sealed photo-bioreactor 34. As can be seen in Figs. 2 and 3, the photo-bioreactor 34 is in a boustrophedonic arrangement. The photo-bioreactor 34 will be described in greater detail below.

The growth medium and the algal culture pass through the photo-bioreactor 34 and the eventual algal mass is collected in a harvesting station 46, located at the end of the photo- bioreactor 34.

With reference to Fig. 3, system 30 may be installed on a relatively gentle slope 48 that faces towards a light source (not shown). The continuous sealed photo-bioreactor 34 is shown held on armatures 50 fixed on stanchions 52.

Alternatively, the stanchions 52 and armatures 50 could be height adjustable, as shown in Fig. 4. The stanchion 52 in Fig. 4 comprises a main body 54 having an end section 56 located at the upper end of said main body 54, a pair of armatures 50 being mounted on said end section 56.

The end section 56 is threaded, with said armatures 50 threadably mounted on said end section 56, such that the location of said armatures 50 on the end section 56 can be adjusted. Furthermore, said main body 54 may have a threaded aperture 58 defined thereon, the aperture 58 being adapted to receive said end section 56. Accordingly, the location of said end section 56 relative to said main body 54, and consequently the height of the armatures 50 mounted thereon, may be adjusted as desired.

The use of such adjustable armatures 50 and stanchions 52 means that the required slope of the photo-bioreactor 34 could be formed by adjustment of the stanchions 52 and armatures 50, such that a gradient is formed facing towards the light source.

In a continuous process where the mature algal biomass is harvested, say on a daily basis, the rate of flow of the growth medium, the gradient of photo-bioreactor 34 slope, and the length of the photo-bioreactor 34 can be adjusted to suit the growth cycle of the organism, such that maximum biomass density and maturity occurs at a point just before the algal mass reaches the harvesting station 46. This may best be described as a slow moving algal conveyor. It can easily be understood that the gradient aids the transport of the biomass and that forced action and impellors are not required. Alternative to this continuous process, the device can be adjusted to produce batches of biomass such that either an entire photo-bioreactor is filled at one time with a culture, or individual batches are introduced at differing time intervals until the photo-bioreactor is filled. This latter process will allow algae to pool for periods of time and this has shown to aid the propagation of some algal strains.

With reference to Fig. 5, system 30 is shown on a relatively steep slope, having a more vertical array, which is designed to increase photo-bioreactor 34 density in a given area. A series of photo-bioreactors 34 can be arranged to optimise both area and the incidence of light (indicated by arrows 60) falling upon the algal mass. This type of arrangement is ideally suited to algal biomass grown internally in factories, warehouses and greenhouses and it is likely that artificial light sources will be required.

The structure of the photo-bioreactor 34 will now be described, with reference to Figs. 6 and 7A.

The photo-bioreactor 34 comprises a main body 34a comprising an inverted V-shaped upper layer portion 62, having an upper end 62a located at the apex of the inverted V and a pair of attachment ends 62b, 62c located at the ends of the arms of the inverted V. The inverted V-shaped portion 62 is formed from a clear or transparent gas permeable plastic.

The main body 34a of the photo-bioreactor 34 further comprises an arc-shaped lower layer portion 64 having a first end 64a and a second end 64b, formed from a second gas permeable membrane. The arc-shaped portion 64 is secured to the inverted V-shaped upper layer 62 by securing the ends 64a, 64b of the arc-shaped portion 64 to the attachment ends 62b, 62c of the upper layer 62, resulting in the main body 34a of the photo-bioreactor 34 being a sealed envelope having a cross-section shaped like a sector of a circle.

As can be seen in Figs. 6 and 7 A, a pair of shoulder projections 63b, 63c is located at the attachment ends 62b, 62c of the upper layer portion 62, generally perpendicular to the walls of the upper layer portion 62. The shoulder projections 63b, 63c aid the attachment of the lower layer portion 64 to the upper layer portion 62, by providing additional surface area for bonding the lower layer portion 64. Alternatively, it will be understood that the main body 34a of the photo-bioreactor 34 may be formed from one continuous piece of gas permeable membrane.

The envelope structure of the main body 34a is used to retain the algal culture or biomass 66 and the growth medium 68 necessary for algal growth. A cavity 70 is defined by the walls of the main body 34a above the algal biomass 66 and growth medium 68, to allow transpiration and respiration of the algae. The gas permeable membrane allows the escape of oxygen and water molecules formed during photosynthesis and transpiration by the algal biomass 66 contained within the photo-bioreactor 34.

In addition, as the temperature of the gases contained within the main body 34a rises, the gases will expand. Use of the gas permeable membrane will act as a release valve, allowing the pressure gradient between the trapped gases and atmospheric pressure to equalise. The relatively small pore sizes of the gas permeable membrane will stop other forms of contamination, most particularly undesirable forms of algae, from entering the interior of the main body of the bio-reactor 34. If required, and to aid photosynthesis, carbon dioxide could also be pumped into the main body 34a.

The gas permeable membrane allows the ingress of carbon dioxide molecules from the atmosphere. At standard temperature and pressure, the density of carbon dioxide is around 1.98 kg/m³ - about 1.5 times that of air. Carbon dioxide is soluble in water, into which it spontaneously inter-converts between CO₂ and H₂CO₃ (carbonic acid). The relative concentrations of CO₂, H₂CO₃, and the deprotonated forms HCO₃ (bicarbonate) and CO₃ (carbonate) depend on the pH of the solution.

In neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater, while in very alkaline water (pH > 10.4) the predominant (>50%) form is carbonate. The bicarbonate and carbonate forms are very soluble such that, for example, air-equilibrated ocean water (mildly alkaline with typical pH = 8.2 - 8.5) contains about 120 mg of bicarbonate per litre. Hence, by selecting an algal strain that is oil-rich and mildly alkali tolerant, the photo-bioreactor 34 can be used to leach carbon dioxide from the atmosphere, by allowing carbon dioxide molecules to pass through the gas permeable membrane whilst at the same time the relatively small pore sizes of this membrane will stop other forms of contamination from entering the bio-reactor envelope.

The depth of the contained mixture of algal biomass 66 and growth medium 68 can be varied to ensure that the amount of light incident on the algal biomass is optimised — the general rule being the shallower the growth medium the higher the light fraction incidence on individual cells of algae contained within the growth medium.

As shown in Figs. 2, 3 and 5, sterile water and nutrients from tanks 38 and 40 are mixed in mixing tank 42 in the required ratio for optimal algal growth. The resultant mix (the growth medium 68) is gravity fed or injected via growth medium pump 44 into the photo- bioreactor 34 through a valve 72, shown in Fig. 8, which is located in a wall of the main body 34a of the photo-bioreactor 34, valve 72 extending from the exterior of the main body 34a to the interior cavity 70 of the photo-bioreactor 34.

As described above, the algal cultures 66 are formed in the algae culture tank 32 and, depending upon the desired inoculation density required, sufficient concentration of the algal cultures may be periodically added to the photo-bioreactor 34 via pump 36, or by means of a Venturi injector, which are coupled to valve 74, shown in Fig. 8, located in a wall of the main body 34a of the photo-bioreactor 34, the valve 74 extending from the exterior of the main body 34a to the interior cavity 70 of the photo-bioreactor 34.

As can be seen in Figs. 6 and 7 A, a clamp projection 76 is located at the upper end 62a of the inverted V-shaped upper layer portion 62. The clamp projection 76 can be formed by folding the gas permeable plastic membrane that forms the upper layer portion 62 into an overlapping arrangement at said upper end 62a. Also, the arc-shaped lower layer portion 64 is arranged such that the ends 64a, 64b of the lower layer portion 64 project beyond the ends 62b, 62c of the upper layer portion 62.

As can be seen in Fig. 7 A, the photo-bioreactor 34 can be secured to the armature 50 of an adjacent stanchion 52 through application of retaining means 78 to said clamp projection 76, said retaining means secured to said armature. Similarly, further retaining means (only one of which is shown at 80) attached to said armature 50 may be secured to the ends 64a, 64b of said lower layer portion 64. This ensures that the photo-bioreactor 34 is thus held suspended off the ground.

It will be understood that retaining means 78, 80 may be implemented using any suitable securing mechanism, e.g. clamping means, adhesives, stapling means.

While carbon dioxide may be obtained from air distillation, this may yield only a relatively small volume of CO₂. Accordingly, the air distillation may need to be augmented to improve the growth rates of algal biomass. A relatively large variety of chemical reactions yield carbon dioxide, such as the reaction between most acids and most metal carbonates. For example, the reaction between sulphuric acid and calcium carbonate (limestone or chalk) is depicted below:

H₂SO₄ + CaCO₃ → CaSO₄ + H₂CO₃

With reference to Figs. 7B and 7C, a further enhancement to the photo-bioreactor 34 is shown. Here, a tube 86 is provided within the interior of the main body 34a, extending along the length of the photo-bioreactor 34. The tube 86 is bonded to the lower layer portion 64 of the main body 34a, locating the tube within the mixture of algal biomass 66 and growth medium 68.

The tube 86 is manufactured from a gas permeable membrane, the membrane being selected to allow the passage of carbon dioxide molecules and prevent the ingress of water molecules or molecules of the growth medium 68. Such types of tubing may be found in use in aquaria. Through control of the contained pressure, gas pumped through said tube 86 will not create bubbles in the growth medium 68.

The tube 86 is connected to an external supply 90 of carbon dioxide, via a regulator valve 88. By controlling the release of carbon dioxide gas using regulator valve 88, the level of carbon dioxide in the growth medium 68 can be augmented when required.

Continued supply of carbon dioxide from the supply 90 through tube 86 could allow the lower layer portion 64 of the main body 34a to be formed from a gas impermeable membrane, as the carbon dioxide required for growth of the algal biomass 66 could be provided artificially rather than diffusing out of the atmosphere through the gas permeable membrane and into the growth medium 68.

The tube 86 is connected to a sealed valve (not shown) incorporated into either the upper layer portion 62 or the lower layer portion 64, such that undesirable contaminants could not enter the interior of the photo-bioreactor 34. The external carbon dioxide supply 90 is connected to the inlet portion of the sealed valve.

It is important when using either the gas permeable lower layer portion 64 or the tube 86 that the rate of diffusion of carbon dioxide into the mixture of algal biomass 66 and growth medium 68 can be controlled. Similarly, it is also important to match the input of carbon dioxide to the growth rate of the algal biomass 66 to ensure that carbon dioxide depletion or oversupply do not cause algal growth to be retarded or inhibited.

With reference to Fig. 9, an alternate enhancement to the photo-bioreactor 34 is shown. In the photo-bioreactor 34 shown in Fig. 9, a secondary layer 82 of membrane is secured to arc-shaped lower layer portion 64 beneath the main body 34a of the photo-bioreactor 34. The secondary layer 82 has a first end 82a and a second end 82b, with the secondary layer 82 secured to the arc-shaped lower layer portion 64 by securing the ends 82a, 82b of the secondary layer 82 to the respective ends 64a, 64b of the lower layer portion 64.

The width of the secondary layer 82 is chosen to be greater than that of the lower layer portion 64, so that when the secondary layer 82 is secured to the lower layer portion 64, a secondary cavity 84 is defined therebetween. If required, carbon dioxide can be pumped into the secondary cavity 84, in order to provide the appropriate saturation levels required by the algal culture.

The diffusion of carbon dioxide through either a gas permeable membrane (as in the case of lower layer portion 64) or a gas permeable tube (as in the case of tube 86) may be described by Fick's Laws of Diffusion. Consider a gas permeable membrane or a gas permeable tube of surface area A(m²) and thickness B_y in contact with the growth medium 68 separating a source of carbon dioxide from the aforementioned growth medium 68. The envelope encompassed by the upper and lower layer portions 62, 64 contains the growth medium 68 having a dissolved carbon dioxide concentration C_e. On the opposite side of the gas permeable membrane or within the tube 86 the concentration of carbon dioxide C_x is greater than the concentration C_e within the envelope.

In applying Frik's First and Second Laws of Diffusion, the rate of accumulation of carbon dioxide C (hPa) within the envelope may be described as:

δt B_yV

Where K equals the permeability of CO₂ diffusion in the membrane (m²/h), and V equals the volume (m³) of the growth medium 68 within the envelope.

At time t = 0, the CO₂ concentration within the growth medium 68 is C_e and the accumulation of CO₂ within this medium may be derived by integration of the above formula such that:

iC^ C,} = AKΪ

Thus, by varying the thickness and the surface area of either the membrane or the gas permeable tube and the static or partial pressure P_c0 of the carbon dioxide outside the envelope or within the tube, the rate of CO₂ diffusion into the growth medium can be controlled.

Optimising the growth of the algal biomass also requires that the diffusion of carbon dioxide into the growth medium closely matches the algae's uptake of that carbon dioxide. Insufficient carbon dioxide in the growth medium means that growth is retarded. Elevated levels of carbon dioxide cause the growth of algae to slow due to CO₂ inhibition (Amman and Lynch 1967; Goldman et al. 1981, Silva and Pirt 1984). In a CO₂ limited algal culture, CO₂ that diffuses into the growth medium 68 is consumed and converted into biomass. Thus the increase in biomass density S (g/m³) with time t (h) can be established as:

δS = YδC δt δt

Where Y equals the biomass growth yield from CO₂ consumed (g/m³.hPa). Therefore:

δS_= AK(C, - CV)Y δt B_tV

Thus, once the rate of algal biomass growth yield (Y) has been determined for a specific strain of algae, the rate of diffusion of carbon dioxide into the growth medium 68 can be matched to the optimal growth rate of that algal biomass. Determining the biomass growth yield for varying algal species is a relatively uncomplicated laboratory process, and is simply the quantity of biomass produced per millibar of CO₂ consumer.

Accordingly, the system 30 may be tailored to match the optimal carbon dioxide requirements of a particular algal strain. This may be achieved by determining the algal biomass yield of that algal strain and responding by correlating: -

1. the surface area A (m²) of the gas permeable membrane or gas permeable tube 86 in contact with the growth medium 68; 2. the CO₂ permeability K of the gas permeable membrane or the gas permeable tube

86;

3. the differential CO₂ concentration (C_x - C_e) between that of the growth medium 68 within the membrane and that either external to this membrane or within the gas permeable tube 86; 4. the thickness B_y of the gas permeable membrane or gas permeable tube 86; and

5. the volume V of the growth medium 68,

such that these factors are combined to provide CO₂ diffusion rates that closely match CO₂ uptake rates of the algal biomass 66 at the optimal growth rate for that strain of algae. It is also understood that a number of other characteristics are regarded as important for the optimal production of algal biomass. Principal amongst these is light efficiency - optimising the amount of light energy that algal structures convert into algal biomass. Optimal cell density in normal photo-bioreactors may be achieved by the regulation of light intensity and fluid circulation where circulation mixes the algal mass exposing individual cells to light and nutrients.

In dense micro-algal structures, light intensity decreases logarithmically with distance from the irradiated surface, due to self shading and light absorption, in accordance with Beer- Lambert's Law, as described in the following equation:

I = I₀ exp(-σ p δ)

where I is the light intensity of light transmitted through a light absorbing medium; I₀ is the initial intensity from a light source; σ is the absorption coefficient; p is the concentration of a micro-organism in the light absorbing system; and δ is the thickness of the light absorbing system.

Differing species of algae require differing light energy levels to optimise vegetative growth. When the amounts of light energy are relatively high, growth of the algal biomass has been found to be inhibited, and light energy that is not used in photosynthesis is converted into heat energy. Research has shown that light levels in the range 30 W/m² and 80W/m² were optimal for the rapid growth of a range of algal species.

A number of plastics companies working in the field of horticulture have successfully manufactured films with light reflective and attenuation properties as well as plastic films that aid solarisation of crops ((l)Chen, Y., Gamliel, A., Stapleton, JJ., and Aviad, T. 1991. "Chemical, physical, and microbial changes related to plant growth in disinfested soils." Soil Solarization. J. Katan and J.E.DeVay, editors. CRC Press Pages 103-129; (2) Katan J. 1987.: "Innovative Approaches to Plant Disease Control." Soil solarisation John Wiley & Sons, New York. Pages 77 - 105; and (3) Stapleton, J.J., and DeVay, J.E. 1995. "A natural mechanism of integrated pest management.: Novel Approaches to Integrated Pest Management." Soil Solarization ; R. Reuveni, editor. Lewis Publishers. Pages 309-322).

By using photo-selective films as the outer envelope of the continuous sealed photo- bioreactor 34, the system can be tailored to meet the individual requirements of differing algal species being grown in differing climates and sun intensities. Alternatively these films could be used as separate devices to screen algal biomasses from undesirable light intensities.

It is also known that algae display high photosynthetic activity in spectral regions in which light absorption was due mainly to pigments other than chlorophyll. In addition to the chlorophyll, these pigments participate in photosynthesis. The majority of algal classes have peripheral light harvesting antennae that absorb blue light and red light due to their content of carotenoids, chlorophyll a, b and c.

Similarly, it is known that high incidence of UV light inhibits algal growth. Therefore photo-selective plastic film could be used to reduce algal attrition due to UV and allow transmission of optimal wavelengths in the red and blue light bands.

In experiments dealing with the composition of the photosynthetic process, it has been found that the spectral distribution of the incident light should favour the absorption and excitation of relevant photoreceptors. Attention also has to be given to the intensity of the light source. On one hand, the applied fluence rates must provide sufficient net photosynthesis and, on the other hand, fluence rates inducing photo-inhibition or even photo-destruction of pigment-protein complexes must be avoided. Therefore, it is recommended to apply irradiance slightly exceeding the light-saturation point of photosynthesis for the algal strain under propagation. This ensures optimum growth and saves energy.

The light-saturation point is usually determined by plotting photosynthetic oxygen evolution against irradiances. Since light-saturation points vary greatly among different algal species, it is necessary to carry out this procedure for each species of interest. In instances where artificial lights are used in algal propagation, lighting systems generating wavelengths in the red and blue bandwidths are preferred. In a further enhancement to the invention, relatively low light levels experienced due to seasonal variations or cloud cover may be augmented by the use of reflective devices and/or artificial lighting. With reference to Fig. 10, a solar reflector 92 is located adjacent the upper layer portion 62 of the photo-bioreactor 34. Use of the solar reflector 92 increases the incidence of light on the algal biomass 66 contained within the photo- bioreactor 34.

With reference to Fig. 11, a combination of one or more solar reflectors 94 and an artificial light source 96 may be installed about said photo-bioreactor 34 to aid photosynthesis during low light periods. It will be understood that the artificial light source 96 may be installed adjacent said photo-bioreactor 34, or the artificial light source 96 may be installed within the interior of said photo-bioreactor 34, e.g. within the cavity defined within said main body 34a. As can be seen in Fig. 11, the solar reflector 94 is concavely-shaped, with its focal point located within the interior of the photo-bioreactor 34, in order to focus the light intensity on the algal biomass 66 contained within the photo-bioreactor 34.

Algae are sensitive to temperature, and studies have shown that lipid production by algae declines at temperatures that are either too low or too high for a particular strain of algal culture. For example, Casadevall et al. (1985), Fernandes et al. (1989), Lupi et al. (1991) and Vladislav et al. (1994) all show that the optimal temperature for Botryococcus Braunii strains was about 25° C, whereas Oliveira et al. (1999) demonstrated that higher temperatures, in the order of 32°C, were required to reach optimal lipid production rates for Spirulena Maximus and Spirulina Platensis. Hence, the photosynthetic response of the chemical composition of algae to temperature is species specific (Thompson P. A., Guo M. Harrison P. J. 1992. "Effects of variation of temperature on the biochemical composition of eight species of marine phytoplankton." Journal of Phycology. 28. Pages 481- 488).

If the system 30 is to be used externally using sunlight as the primary source of energy, then the selection of the algal species to propagate in a specific climatic zone is important. It is not efficient to propagate a species that requires high temperature in a temperate region nor is it sensible to grow cultures that require lower temperatures for optimal growth in a tropical region. Accordingly, the temperature of the growth medium 68 and thereby the algal biomass 66 may be reduced by indirect means such as solar screening (such as discussed above), screening from wind, cooling of the CO₂ gas before it is pumped into either the second cavity 84 or the gas permeable tube 86, and spraying the main body 34a of the photo- bioreactor 34 with coolant (e.g. cold water).

Where close regulation of the temperature of the growth medium 68 has to be maintained, more direct system of cooling the growth medium 68 is required. Such a system, using ground source heat pumps and heat exchangers, is shown in Fig. 12.

The use of ground source heat pumps is particularly suited to the temperature control of the growth medium 68 (and thereby algal biomass 66) within the photo-bioreactor 34 as this is a highly efficient use of energy. Similarly, the use of heat exchangers means that there can be no cross-contamination of the growth medium 68 during heat exchange.

With reference to the structure shown in Fig. 12, a ground source heat pump 98 is coupled to a buried ground loop 100. The ground loop 100 is operable to draw heat from the earth when the external atmospheric temperature is low. The heat pump 98 is further coupled with heat exchanger 102, which is coupled with the photo-bioreactor 34 via a pair of tubes 104, 106. Tubes 104, 106 extend into the interior of the photo-bioreactor 34, to the contained mixture of algal biomass 66 and growth medium 68. Relatively cool growth medium 68 is extracted via tube 104, and heated within the heat exchanger 102. The thus warmed growth medium 68 is then returned to the photo-bio-reactor 34 via tube 106.

Conversely, when the external temperature is too high for optimum algal growth, the process can be reversed and the ground source heat pump 98 and heat exchanger 102 can be used to lower the temperature of the mixture of algal biomass 66 and growth medium 68.

A simple heat exchanger manifold 108 for use with the above-described system is shown in Fig. 13. In Fig. 13, the mixture of algal biomass 66 and growth medium 68 is understood to be moving from left to right as viewed in the drawing. The manifold 108 comprises a container body 110 that is secured to the underside of the lower layer portion 64 of the photo-bioreactor 34 main body 34a, for example using heat welding. A section of the lower layer portion 64 of the main body is cut out corresponding to the outline of the manifold container body 110, allowing the manifold 108 to fluidly couple to the contained mixture of algal biomass 66 and growth medium 68 within the photo-bioreactor 34.

A divider projection 112 extends across the width of the manifold 108, interior to the container body 110 and transverse to the main body of the photo-bioreactor 34. The divider projection 112 defines a first pocket 114 and a second pocket 116 within the container body 110. Pockets 114, 116 are capped by a micro-fine fibre mesh 118. The micro-fine fibre mesh 118 is configured such that the mesh size is too narrow for the algal biomass 66 to pass through, but is wide enough to allow passage of the growth medium 68.

A first tube 104 is fluidly connected with the pocket 114 via outlet valve 120, while second tube 106 is fluidly connected with the pocket 116 via inlet valve 122. The growth medium 68 is drawn through the outlet valve 120 and passes to the heat exchanger 102 through tube 104 for heating or cooling as required. The growth medium 68 is then returned from the heat exchanger 102 via tube 106 and passes back into the photo-bioreactor 34 through the inlet valve 122.

Greater control of temperature is achievable if the photo-bioreactor 34 is used internally, e.g. inside a building. However, this may require expenditure on secondary heating and cooling systems to keep the algal biomass 66 at optimum temperature.

Both the gas permeable membrane of the lower layer portion 64 and the gas permeable tube 86 that allow the passage of carbon dioxide molecules helps alleviate one of the major problems associated with normal photo-bioreactors. The small pore sizes of the gas permeable membrane eradicate the problem of shearing action in gas-sparged photo- bioreactors as gases diffuse though the entire surface of this membrane, and bubble formation is dramatically reduced and pressure gradients from the nozzles of gas sparging tubes are eliminated. Similarly, the numbers of pores in the gas permeable membranes can be varied to match the oxygen generation rates during photosynthesis, the transpiration rate and the carbon dioxide saturation level required by the algal biomass 66. Efficient and yet non-destructive mixing of the algal biomass 66 is an important component in underpinning efficient photosynthesis by algae. With reference to Figs. 14 and 15, further enhancements to the photo-bioreactor 34 are shown to aid the mixing of the algal biomass 66.

Fig. 14 shows a sample series of micro-barriers 124, 126, 128 that have been designed to be introduced or incorporated onto the lower layer portion 64 of the main body 34a of the photo-bioreactor 34. The micro-barrier 124 comprises a substantially bulb-tee projection, the second micro-barrier 126 comprises an undulating sloped projection, and the third micro-barrier 128 comprises a transverse wedge projection. The micro-barriers 124, 126, 128 divert the flow of the algal mass 66 to induce low-level turbulence sufficient to cause algal mix.

Fig. 15 illustrates a plurality of substantially parallel shaped vane projections 130 provided on said lower layer portion 64. Said vane projections 130 may extend along the length of the photo-bioreactor 34 to aid mixing of the contained algal biomass 66 and growth medium 68.

It will be understood that the micro-barriers displayed in Fig. 14 and the vanes shown in Fig. 15 are indicative and are non-limiting examples of mixing devices that could be used for algal mixing.

An alternative and/or complementary process to increase the light distribution within the photo-bioreactor is shown in Fig. 16. The photo-bioreactor 34 shown in Fig. 16 further comprises a light sheet 132 to distribute sunlight within the photo-bioreactor 34. The light sheet 132 may also be used to induce mixing of the contained algal biomass 66.

The light sheet 132 extends from the upper end 62a of the upper layer portion 62 towards the lower layer portion 64, such that a portion of the light sheet 132 towards the free end 132a of the light sheet 132 is immersed within the mixture of algal biomass 66 and growth medium 68. The light sheet 132 comprises a hook-shaped end portion to induce mixing, but it will be understood that other shapes of light sheet may be used and the design shown in Fig. 16 is an example. The light sheet 132 comprises an acrylite or a plexi -glass sheet that has micro-etches on the back of the sheet 132 to disperse the sunlight in a uniform and controlled manner. The light sheet 132 could be shaped to allow the sunlight to be dispersed throughout the growth medium 68, allowing for maximum algae illumination and production of biomass.

Light/dark cycles have been shown to determine the light efficiency, and thereby the productivity of photo-bioreactors (see references listed below). Very fast alterations between high light intensities and darkness — typically between 40 microseconds and 1 second - can greatly enhance photosynthetic efficiency. Light intermittence is associated with two basic parameters; firstly, the light fraction (which is a ratio between the light period and the cycle time) and secondly, the length of the light/dark cycle.

In normal photo-bioreactors, the reactor design, length of the light path, culture concentration, extent of culture turbulence and the light intensity will determine the frequency and light fraction of the cycles. The degree of mixing is known to significantly affect reactor productivity.

By their design, normal photo-bioreactors cannot accommodate the very fast light/dark cycles of less than 1 second that are required to enhance photosynthetic efficiency.

Typically, photo-bioreactors exhibit liquid circulation times in the range 10 to 100 seconds.

With reference to Fig. 17, the photo-bioreactor 34 is adapted to introduce light/dark cycles. A plurality of shading elements 134 is provided, the shading elements 134 being spaced along the length of the photo-bioreactor 34. The shading elements 134 comprise a main body 134a adapted to couple with the main body 34a of the photo-bioreactor 34. The main body 134a of the shading elements 134 comprise a first portion 136 adjacent the upper layer portion 62 of the photo-bioreactor 34. The main body 134a of the shading elements 134 further comprises first and second engagement portions 138, 140 that are adapted to couple with the clamp projection 76 of the upper layer portion 62 and the first end 64a of the lower layer portion 64 respectively, securing the shading elements 134 in position relative to the main body 34a of the photo-bioreactor 34. The shading elements may also be supported by legs 142, projecting from the underside of said shading elements 134. It will be understood that other designs of shading elements 134 may be employed, for example a shading element that completely envelops a portion of the main body of the photo-bioreactor 34. Shading elements 134 are formed from any suitable light- impenetrable material, that prevents light passing through the elements 134 into the interior of the photo-bioreactor 34.

Using this configuration, various light/dark cycle times may be achieved. Consider a section of continuous sealed photo-bioreactor 100 metres long with a growth medium liquid flow-rate of 0.5 metres per second and sunlight or an artificial light source. By introducing independent shading elements held on supports where each shading element is 0.25 metres long installed at 0.25 metre intervals along the length of the photo-bioreactor, such as shown in Fig. 17, a light/dark cycle time of 0.5 seconds is achieved. As will be understood, cycle time can be varied by introducing shorter or longer shading elements 134 at closer intervals.

Alternatively, independent shading elements 134 may be replaced by the use of light reflective or light impenetrable plastics sheeting sections that have been incorporated into the largely clear or transparent gas permeable membrane of the upper layer portion 62. In this instance, control of light and shading intervals may be established for a given flow rate of the algal biomass 66 and its growth medium 68 along the photo-bioreactor 34. The light/dark cycle may thus be maintained by controlling the rate of flow of the contained seed culture and growth medium.

With reference to Figs. 3 and 5, the harvesting stage is generally performed at the lower end of the slope. When a segment of algal biomass 66 is ready for harvesting, the main body 34a of the photo-bioreactor 34 may be double heat welded above the area of algal biomass 66 to be harvested. The section containing the harvested biomass 66 can then be removed for processing. The act of heat welding the upper layer portion 62 of the main body 34a serves to reseal the system and prevent the ingress of contaminants. If the algal biomass 66 is harvested using the heat welding technique, up-stream sections of the main body 34a can be added to the system at the pump level, thereby keeping the overall length of the photo-bioreactor 34 at the optimum length for algal biomass production. Alternatively, the harvested algal biomass 66 may be allowed to flow into a sterile harvesting station or harvesting tank 46, as shown in Fig. 18. The harvesting tank 46 comprises has an inlet pipe 144 of the same shape as the main body 34a of the photo- bioreactor 34, such that the photo-bioreactor 34 fits securely over the inlet pipe 144, and thereby stops the passage of contaminants into both the harvesting tank 46 and the photo- bioreactor 34.

The harvesting tank 46 further comprises a fine micro-mesh 146, that acts to filter the larger algal cultures, such that the growth medium 68 and relatively smaller algal cultures pass into the bottom portion 148 of the harvesting tank 146. The growth medium 68 and the relatively small algae cultures are recycled via pipe 150 back to the algae culture tank 32 shown in Fig. 2 as an inoculum/seed culture of the next batch of algae. This configuration ensures efficient use of resources.

With reference to Figs. 19-23, a number of different enhancements to the system of Fig. 2 is illustrated.

Fig. 19 shows the photo-bioreactor system that could be typically used for small-scale seasonal production of oil from algal biomass. It details the process components including:

A. Algae Culture tank

B. Sterile Water tank

C. Micro-nutrients tank

D. Mixing tank

E. Reactor Inlet

F. Algae Harvesting Station

G. Oil Recovery Station

H. Oil Storage Station

I. Algal Biomass Storage

Oil can be recovered from the produced algal biomass using a variety of different procedures. Smaller scale oil recovery will generally use the expression or expeller press process whereby when the algal biomass is dried it retains its oil content, which then can be "pressed" out with an oil press. The remaining algal biomass can be sold on to the pharmaceutical and nutrients industries, used as animal feedstuff or use by burning it as a fuel for power generation.

Fig. 20 shows the same basic arrangement as detailed in Fig. 19, the only addition being:

J. the use of a ground source heat pump.

The ground source heat pump serves two functions:

1. maintains the temperature of the growth medium at optimum temperature for algal growth; and

2. extends the growing season.

Fig. 21 shows all of the process elements displayed in Fig. 20, but it also incorporates:

K. an Algal Enzyme Converter.

This process uses enzymatic extraction to degrade the cell walls of the remaining algal biomass remaining after use of the expression/expeller process. This makes fractionation of the recovered oil much easier, and maximizes the oil recovered from the algal biomass.

This process is both complementary to, and offers a replacement for, the expression/expeller process, and decisions whether to use both processes of the enzyme conversion process on its own may depend upon the cost of these processes.

Fig. 22 shows the same process arrangements as displayed in Fig. 21. However, an extra process element has been added:

L. a Gas Contractor.

A gas contractor is a device that can extract one gas from a liquid and replace it with another alternate gas. As free oxygen molecules in the sterile water will tend to inhibit algal growth, this oxygen is replaced with carbon dioxide using the gas contractor. As carbon dioxide is one of the essential components of algal photosynthesis, the gas contractor removes an inhibitor and provides a stimulant to algal growth.

Fig. 23 shows the same process arrangement as shown in Fig. 22. However, two extra process elements have been added:

M. a Sulphur Recovery Unit; and N. a Hydrogen Recovery Unit.

It has been found that, if all trace elements of sulphur are removed from the growth medium at a relatively advanced stage of algal growth, the effect of this is to change the photosynthetic processes of the algal biomass. In effect, under the stress of a sulphur free environment, the algal biomass begins to produce economic quantities of hydrogen as the by-product of photosynthesis rather than oxygen which is normally produced.

This hydrogen would be recovered by the Hydrogen Recovery Unit, and compressed to a liquid state for transport and future use.

Turning to Fig. 24, another embodiment of the photo-bioreactor system of the invention is indicated generally at 200. The photo-bioreactor comprises an envelope main body 202 having an inverted V-shape upper portion 204 and a lower portion 206. The lower portion 206 acts as a trough to receive a mixture 208 of growth medium and a seed culture.

A pair of gas-permeable tubes 210 are bonded to the internal surface of the lower portion 206, immersed in the mixture 208. The gas-permeable tubes 210 are used to allow for the introduction of CO₂ into the growth medium and seed culture mixture 208. The use of two gas-permeable tubes 210 as opposed to a single tube (as in Figs. 7B and 7C) improves the diffusion Of CO₂ into the mixture 208.

The gas-permeable tubes are preferably made from silicone. However, other suitable gas- permeable materials may be used, for example Tygon® and Pharmed-BPT tubing from Saint Gobain, if lesser gas permeability is required. It will be understood that the envelope structure may be formed from a gas-impermeable material, preventing the ingress or the egress of any gases or contaminants to the interior of the envelope structure. The use of the gas-permeable tubes allows for the introduction of carbon dioxide into the interior of the envelope structure, and suitable valve means may be used to allow for the extraction of any by-product gases produced during transpiration.

A primary attachment projection 212 is located at the apex of the upper portion 204. The primary attachment projection 212 is coupled to support rod 214, which is provided on horizontal support stanchion 216. A pair of secondary attachment projections 218 are located at the interface between the upper portion 204 and the lower portion 206.

A support cable 220 is threaded through a first of said secondary attachment projections 218, through the upper end of the support rod 214, and then through the second of said secondary attachment projections 218. This connection configuration is repeated for any adjacent photo-bioreactor envelope bodies 202, resulting in the support cable being treaded through each envelope body present in an array.

As the main body of the envelope 202 is suspended from the support rod 214 and the stanchion 216, the length of cable provided across the array of envelopes 202 determines the dimensions of the theoretical triangle formed between the primary attachment projection 212 of the envelope body 202, the upper end of the support rod 214, and the secondary attachment projection 218. As additional length of support cable 220 is provided, the length of the cable 220 between the upper end of the support rod 214 and the secondary attachment projection 218 increases accordingly. Thus, the appropriate side wall 204a of the upper portion 204 (having a set length) experiences a change in the angle of incline of the side wall 204a. This results in a change in the angle between the side wall 204a and the surface of the contained mixture 208 of growth medium and seed culture.

The effect of Photosynthetically Active Radiation (PAR light) upon the bioreactor structure is twofold in that it provides the energy for photosynthesis, but it, along with UV and IR radiation, also causes the growth medium to heat up. If the temperature of this growth medium is too high (or too low) the growth rate of the algae tends to be affected. The angles of the side walls 204a are varied to either maximise the light received or to minimise the light received. Maximum light is transmitted into the bioreactor envelope 202 when such light is perpendicular to said walls 204a. As the incident light angle changes or the wall angles change, an increasing amount of light is reflected by the side walls and less enters the bioreactor chamber.

The effect of this is to allow tailoring of the system to suit the latitude of the installation in question such that, for example, for installations in temperate zones the side wall angles may be 20 to 30 degrees, such that even when the sun is vertically overhead a large portion of the light incident upon the walls will pass into the bioreactor envelope.

Conversely, in tropical regions it is desirable to reflect much of the sunlight at midday. In this instance the bioreactor walls 204a would be angled at steeper angles, of up to 60 to 80 degrees, to increase the amount of light reflected during this period.

The control of the length of support cable 220 may be linked into a central computer control system, which would allow for continuous adjustment of the angle of incline of the bioreactor side walls to ensure optimum performance.

It will be understood that the gas permeable membranes may be formed through spiral wound, hollow fibre, tube-in-fill or plate-in-frame processes. Alternatively, the gas- permeable membranes may be formed by punching an array of holes in a sheet of plastic using a heated ultra-fine needle. This method is sufficient in cases where it is desired to prevent ingress of any contaminants that are large in size relative to the size of the ultra- fine holes.

It will be understood that, for the structures employing gas permeable portions of the envelope structure, the gas permeable membrane may be made of a material that is capable of being inflated without undue stress being exerted upon the material. As the temperature within the bioreactor envelope increases during the day, the gases in the headspace above the growth medium will expand. Similarly, the level of evaporation of the water constituent of the growth medium will increase. This will increase positive pressure within the bioreactor envelope. The upper gas permeable membrane will have to expand to accommodate this pressure increase whilst at the same time the gas permeable "holes" in this membrane will dilate to increase the rate of passage of these gases and water vapour through the membrane. The positive pressure inside the membrane means that the penetration of contaminants through these dilated holes is avoided.

Further details regarding the background processes and the underlying principles can be found in:

1. Casadevall, E. Bailliez, C. Largeau, C.1985. "Growth and hydrocarbon production of Botryococcus braunii immobilized in calcium alginate gel". Journal of Applied Microbiology and Biotechnology. December 1985. Pages 99-105. 2. Fernandes, H.L., Tome, M.M., Lupi, F., Fialho, A.M., Sa-Correia, L, Novais, J.M.

1989. "Biosynthesis of high concentrations of an exopolysaccharides during the cultivation of the microalga Botryococcus braunii". Biotechnology Letters.11: Pages 433-436.

3. Lupi, F.M, Fernandes, H.M.L, Sa-Correia, I. Novais, J.M. 1991. "Temperature profiles of cellular growth and exopolysaccharide synthesis by Botryococcus braunii" Kutz. UC 58. Journal of Applied Phycology. 3, Pages 35-42.

4. Oliveira, M. A. S., Monteiro, M, P., Robbs, P. G., Leite, S. G. 1999. "Growth and chemical composition of Spirulena maxima and Spirulena platensis biomass at different temperatures". Aquaculture. International 7, Pages 261-275. 5. Vladislay C, Jaromir L. 1994. "The effect of high irradiances on growth, biosynthetic activities and the ultrastructure of the green alga Botryococcus braunii strain" Droop 1950/807-1. Archiv fur hydrobiologie, Pages 115-131

The invention is not limited to the embodiments described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. A photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion comprising a first substantially planar inclined side wall and a second substantially planar inclined side wall, the first and second side walls forming an inverted V-shaped cross-section, wherein at least a portion of said upper portion is substantially light transmissive, and wherein said upper portion and said lower portion are connected to form a substantially enclosed envelope structure.

2. The photo-bioreactor envelope of claim 1, wherein said photo-bioreactor envelope is flexible to allow the adjustment of the angle of incline of the walls of said upper portion to control the quantity of light received to the interior of the envelope structure.

3. The photo-bioreactor envelope of claim 2, wherein the photo-bioreactor envelope further comprises: at least one primary attachment projection located at the upper end of said upper portion; and at least one secondary attachment projection located at an interface between the upper portion and the lower portion, and wherein when installed, the respective angles of incline of the planar side walls of said upper portion is determined by the vertical height difference between the at least one primary attachment projection and the at least one secondary attachment projection.

4. The photo-bioreactor envelope of any preceding claim, wherein said photo-bioreactor envelope is formed from an upper layer portion and a lower layer portion bonded together at a first interface between the upper portion and the lower portion and a second interface between the upper portion and the lower portion, said envelope structure defined by said upper layer portion and said lower layer portion.

5. The photo-bioreactor envelope of claim 4, wherein said upper layer portion and said lower layer portion are bonded together at said first and second interfaces, the bond comprising one of an adhesive bond or a welding bond.

6. The photo-bioreactor envelope of any of claims 1-3, wherein said photo-bioreactor envelope comprises a single sheet of plastics substrate material bent along a ridgeline, the free ends of said substrate material being bonded together at a first bonding location, thereby forming an enclosed envelope structure.

7. A photo-bioreactor for the growing of cultures, the photo-bioreactor comprising a photo-bioreactor envelope as claimed in claim 3 to receive a seed culture and a growth medium; a support stanchion operable to couple to the at least one primary attachment projection of said photo-bioreactor envelope; an adjustment means operable to couple to the at least one secondary attachment projection of said photo-bioreactor envelope, the adjustment means operable to adjust the respective angles of incline of the side walls of the upper portion of said photo-bioreactor envelope.

8. The photo-bioreactor as claimed in claim 7, wherein said photo-bioreactor envelope is provided in a substantially boustrophedonic arrangement.

9. The photo-bioreactor as claimed in claim 7, wherein said photo-bioreactor comprises an input valve located at a first end of said envelope to allow the introduction of said seed culture and said growth medium into said envelope.

10. The photo-bioreactor as claimed in claim 9, wherein the input valve means comprises a sealed valve arranged to couple to a pump or a Venturi injector device.

11. The photo-bioreactor as claimed in claim 9, wherein said photo-bioreactor further comprises an output valve located at a second end of said envelope to allow the extraction of said seed culture and said growth medium from the interior of said photo-bioreactor envelope.

12. The photo-bioreactor as claimed in claim 11, wherein said first end is located at a greater height than said second end.

13. The photo-bioreactor as claimed in any one of claims 7-12, wherein the adjustment means comprises a support cable.

14. The photo-bioreactor as claimed in any one of claims 7-13, wherein the photo- bioreactor further comprises a gas inlet to enable the introduction of gases into the interior of the photo-bioreactor envelope.

15. The photo-bioreactor as claimed in any one of claims 7-14, wherein the photo- bioreactor further comprises a gas-permeable tube located within said channel in said lower portion such that, in use, said at least one gas-permeable tube is immersed in the seed culture and the growth medium.

16. The photo-bioreactor as claimed in any one of claims 7-15, wherein the photo- bioreactor further comprises a reflector, the reflector being located adjacent said photo- bioreactor envelope.

17. The photo-bioreactor as claimed in claim 16, wherein said reflector is concavely- shaped, the reflector positioned such that the focal point of said concavely-shaped reflector is located within the interior of said envelope structure.

18. The photo-bioreactor as claimed in any one of claims 7-17, wherein said photo- bioreactor further comprises a light diffuser, the light diffuser comprising a sheet, said sheet being located substantially within the interior of said envelope structure.

19. The photo-bioreactor as claimed claim 18, wherein a plurality of etches is defined on the surface of said sheet, the etches operable to disperse light in a uniform manner through the photo-bioreactor.

20. The photo-bioreactor as claimed in claim 18, wherein the sheet is formed from either an acrylite or a plexi-glass sheet.

21. The photo-bioreactor as claimed in claim 18, wherein the sheet extends from said upper portion towards said lower portion, and such that, in use, the free end of said sheet is immersed in the seed culture and growth medium, the free end of said sheet being shaped to induce mixing of the seed culture and the growth medium as they are channelled through said bioreactor.

22. The photo-bioreactor as claimed in any one of claims 17-21, wherein the photo- bioreactor envelope further comprises at least one mixing projection defined on the internal surface of said channel.

23. The photo-bioreactor as claimed in any one of claims 17-22, wherein the photo- bioreactor further comprises at least one shading element, the at least one shading element being adapted to couple to the exterior of said envelope structure, the at least one shading element being formed of an opaque material.

24. The photo-bioreactor as claimed in any one of claims 17-23, wherein the envelope structure of the photo-bioreactor comprises alternating light transmissive portions and opaque sections integral to said envelope structure.

25. The photo-bioreactor as claimed in any one of claims 17-24, wherein said light transmissive portion of the envelope structure comprises a light-filtering layer, said light- filtering layer operable to prevent passage of light of a particular wavelength into the interior of the envelope structure.

26. The photo-bioreactor as claimed in any one of claims 17-25, wherein the photo- bioreactor further comprises a light source, the light source being located adjacent the photo-bioreactor envelope.

27. The photo-bioreactor as claimed in any one of claims 17-26, wherein the photo- bioreactor further comprises a heat exchanger coupled to said envelope structure, the heat exchanger being operable to regulate the temperature of the growth medium contained within the envelope structure.

28. The photo-bioreactor as claimed in claim 27, further comprising a manifold provided on the envelope structure of the photo-bioreactor, the manifold extending into the interior of the envelope structure, the heat exchanger coupled to said manifold.

29. The photo-bioreactor as claimed in claim 28, wherein said manifold comprises filter means operable to allow passage of the growth medium through said manifold while preventing passage of the seed culture.

30. The photo-bioreactor as claimed in any one of claims 7-29, wherein the envelope structure comprises a substantially gas-permeable section.

31. A photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion, wherein at least a portion of said upper portion is substantially light transmissive, wherein said upper portion and said lower portion form a substantially enclosed envelope structure, and wherein the photo-bioreactor envelope further comprises at least one gas-permeable tube located within said channel in said lower portion such that, in use, said at least one gas-permeable tube is immersed in the seed culture and the growth medium.

32. The photo-bioreactor envelope of claim 31, wherein said at least one gas-permeable tube is secured to said lower portion.

33. The photo-bioreactor envelope of claim 31, wherein said at least one gas-permeable tube is formed from a material operable to allow passage of carbon dioxide.

34. The photo-bioreactor envelope of claim 33, wherein said gas-permeable material is silicone.

35. The photo-bioreactor envelope of claim 31, wherein said photo-bioreactor envelope further comprises a connector operable to couple said gas-permeable tube to a supply of gas to provide said gas to the interior of said photo-bioreactor envelope.

36. A photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising a substantially tubular main body having an upper portion and a lower portion forming a substantially enclosed envelope structure, the walls of said envelope structure having a cavity defined therebetween, said main body comprising: a substantially light-transmissive section; and a substantially gas-permeable section, said main body adapted to receive a seed culture and a growth medium within said cavity.

37. The photo-bioreactor envelope as claimed in claim 36, wherein the substantially gas- permeable section is formed by a spiral wound, hollow fibre, tube-in-fill or plate in frame processes.

38. The photo-bioreactor envelope as claimed in claim 36, wherein the substantially gas- permeable section comprises a sheet of plastic having an array of ultra-fine holes defined thereon.

39. The photo-bioreactor envelope as claimed in any one of claims 36-38, wherein said main body is formed from a flexible plastics material, such that the walls of said envelope structure can expand during a build-up of gases within the envelope structure.

40. A photo-bioreactor envelope for the growing of cultures, the photo-bioreactor envelope comprising: a lower portion forming a channel to receive a seed culture and a growth medium; and an upper portion wherein at least a portion of said upper portion is substantially light transmissive, wherein said upper portion and said lower portion form a substantially enclosed envelope structure, and wherein the photo-bioreactor envelope further comprises at least one mixing projection defined on the internal surface of said channel.

41. The photo-bioreactor envelope as claimed in claim 40, wherein the at least one mixing projection comprises a longitudinal baffle, the longitudinal baffle extending substantially along the longitudinal length of the photo-bioreactor envelope.

42. The photo-bioreactor envelope as claimed in claim 40, wherein the at least one mixing projection comprises a wedge.

43. A system for the growing of cultures, the system comprising: a culture storage tank; a nutrients tank; a sterile water tank; a mixing apparatus coupled with said nutrients tank and said sterile water tank; a photo-bioreactor according to any one of claims 7-29 coupled with said culture storage tank and said mixing apparatus at a first end of said photo-bioreactor; and a harvesting station coupled with said photo-bioreactor at a second end of said photo-bioreactor, such that, in use: said mixing apparatus is operable to mix a quantity of nutrients from said nutrients tank and a quantity of sterile water from said sterile water tank to form a quantity of growth medium; said culture store tank and said mixing apparatus are operable to provide a quantity of seed culture and a quantity of growth medium to said photo-bioreactor; and said harvesting station is operable to harvest a quantity of biomass produced by said photo-bioreactor.

44. The system as claimed in claim 43, wherein the system further comprises a growth medium pump provided between said mixing apparatus and said photo-bioreactor, said growth medium pump being operable to pump growth medium from said mixing apparatus into said photo-bioreactor.

45. The system as claimed in claim 43, wherein the system further comprises a culture pump provided between said culture storage tank and said photo-bioreactor, said culture pump being operable to pump seed culture from said culture storage tank into said photo- bioreactor.

46. The system as claimed in claim 43, wherein said photo-bioreactor is arranged in a boustrophedonic configuration.

47. The system as claimed in claim 43, wherein said photo-bioreactor is provided on an incline, said first end of said photo-bioreactor being located at a higher altitude than said second end of said photo-bioreactor.

48. The system as claimed in claim 43, wherein the system further comprises a plurality of supporting armatures located adjacent said photo-bioreactor, said supporting armatures having retention means provided thereon, said retention means being adapted to couple to said photo-bioreactor to retain said photo-bioreactor.

49. The system as claimed in claim 48, wherein said supporting armatures project above said photo-bioreactor, said retention means comprising primary retention means, said primary retention means being adapted to couple with said primary attachment projections of said photo-bioreactor.

50. The system as claimed in claim 49, wherein said supporting armatures further comprise secondary retention means, said secondary retention means being adapted to couple with said at least one secondary attachment projection of said photo-bioreactor.

51. The system as claimed in claim 48, wherein said supporting armatures are adjustably mounted on a plurality of stanchions.

52. The system as claimed in claim 43, wherein the harvesting station comprises a filtration system operable to separate the larger cultures produced by the photo-bioreactor for harvesting from the remaining smaller cultures and the growth medium used by the photo- bioreactor.

53. The system as claimed in claim 43, wherein the harvesting station is coupled to the culture storage tank, the harvesting station being operable to recycle the smaller cultures collected by the harvesting station to the culture storage tank.

54. The system as claimed in claim 43, wherein the system further comprises a compression apparatus, the compression apparatus being coupled with said harvesting station, said compression apparatus being operable to compress the larger cultures collected by said harvesting station.

55. The system as claimed in claim 43, wherein the system further comprises an enzyme converter, the enzyme converter being coupled with said harvesting station, the enzyme converter being operable to act on the larger cultures collected by said harvesting station to degrade the cell walls of the larger cultures.

56. The system as claimed in claim 43, wherein the system further comprises a gas contractor, the gas contractor being coupled to said sterile water tank, the gas contractor being operable to replace the oxygen molecules in the sterile water with carbon dioxide molecules.

57. The system as claimed in claim 43, wherein the system further comprises a sulphur recovery unit and a hydrogen recovery unit, said sulphur recovery unit and said hydrogen recovery unit being coupled with said photo-bioreactor.