WO2009095688A2

WO2009095688A2 - Bioreactor

Info

Publication number: WO2009095688A2
Application number: PCT/GB2009/000269
Authority: WO
Inventors: Jamie Gerber; Colin Rice
Original assignee: Quinn Glass Limited
Priority date: 2008-01-31
Filing date: 2009-01-30
Publication date: 2009-08-06
Also published as: WO2009095688A3; GB0801809D0; GB2468625A; GB201012650D0

Abstract

A bioreactor apparatus comprising an inlet, a chamber for retaining a microorganism in an aqueous environment and an outlet characterised in that the chamber comprises one or more fixed means for creating turbulence in the bioreactor apparatus.

Description

BIOREACTOR

Field of the Invention

The present invention relates to an apparatus and method useful in the microorganism-mediated production of a useful product, such as a fuel. In particular, this invention relates to the utilisation of waste gases such as carbon dioxide, in the propagation of micro-organisms that produce a fuel. Background to the Invention

The twentieth century has been called the "hydrocarbon century" due to the abundance of fossil fuel use. Fossil fuels are currently the most economically viable source of power, for both personal and commercial uses, with more than 85 percent of total world energy consumption coming through the use of fossil fuels. However, it is now widely believed that the world is using fossil fuels at an unsustainable rate. Some experts believe that the world has already reached its peak for oil extraction and production, and that it is only a matter of time before natural gas and coal follow suit.

To release the energy stored within, fossil fuels must be burned. During this combustion process, a variety of emissions and particulates are released into the atmosphere. Primary releases are sulphur, nitrogen and carbon, which are harmful to the environment. These gases combine with water vapour in the air to form acidic compounds that result in acid rain. Further, carbon dioxide is a greenhouse gas and the release of carbon dioxide is believed to be a key factor in global climate change. Although the overall greenhouse emissions of the UK have remained constant over recent years, CO₂ emissions have risen for a third successive year, according to government figures.

With rising concern about climate change, many countries are attempting to reduce their consumption of fossil fuels and are pursuing alternative sources of energy. The Kyoto protocol has been put in place to reduce emissions of greenhouse gases, although it is not a binding measure. However, regulation of emissions alone is not sufficient and there must be continued research for the development of renewable energy technologies, in addition to an increase in conservation measures.

Biodiesel is seen as an alternative to fossil fuels. It is a biofuel that contains short chain alkyl esters, produced by transesterification of vegetable oils or animal fats. It is biodegradable, renewable and non-toxic. When burnt, biodiesel contributes no net carbon dioxide or sulphur to the atmosphere. The production of biodiesel from crops, such as rapeseed and corn, has been considered; for example, Xu et al J.Biotechnol. 2006 DeCl : 126(4) 499-507 descibes the use of heterotrophic algae to produce biodiesel from Corn Powder Hydrolysate. However, recently the focus has shifted towards producing biodiesel by converting gaseous CO₂ into biomass by harnessing photosynthesis in micro-organisms such as algae.

The use of micro-organisms to remove harmful substances such as CO₂ from the waste produced by burning fossil fuels has the dual advantages of reducing harmful gas emissions and, simultaneously, producing a useful biofuel. A review of photosynthetic biomass production in the provision of clean fuels is provided by Hankamer et al, Physiologica Plantarum 131 : 10-21.2007. In particular, the use of photosynthetic algae to convert gaseous CO₂, released by the combustion of a fossil fuel, into biomass has been proposed. Here, the photosynthetic capability of algae is harnessed to produce biodiesel.

The emissions from an industrial furnace stack are rich in CO₂. As mentioned above, algae perform the process of photosynthesis. Photosynthesis is the process by which plants, some bacteria, and certain protistans use the energy from sunlight to produce sugar. Cellular respiration converts sugar into ATP, which is the universal molecule of energy used by all living things. The conversion of unusable sunlight energy into usable chemical energy is associated with the actions of the green pigment chlorophyll. Most of the time, the photosynthetic process uses water and releases the oxygen.

6H₂O + 6CO₂ > C₆H₁₂O₆ + 6O₂

The above equation shows water and CO₂ being utilised by algae to produce a sugar and oxygen. Certain algal strains have the ability to produce high lipid content, which is known in the art. These lipids can be processed and harvested through the technology of transesterification, to produce biofuels such as biodiesel.

The "Transesterification" process is the reaction of a triglyceride (fat/oil) with an alcohol to form esters and glycerol. A triglyceride has a glycerine molecule as its base with three long chain fatty acids attached. The characteristics of the fat are determined by the nature of the fatty acids attached to the glycerine. The nature of the fatty acids can in turn affect the characteristics of the biodiesel. During the esterification process, the triglyceride is reacted with alcohol in the presence of a catalyst, usually a strong alkaline such as sodium hydroxide. The alcohol reacts with the fatty acids to form the mono-alkyl ester, or biodiesel, and crude glycerol. In most production methanol or ethanol is the alcohol used (methanol produces methyl esters, ethanol produces ethyl esters) and is base catalysed by either potassium or sodium hydroxide. Potassium hydroxide has been found to be more suitable for the ethyl ester bio diesel production; either base can be used for the methyl ester.

"Bioreactors" are commonly used to retain micro-organisms such as algae and produce biofuels, for example by the extraction of undesirable gases from the atmosphere. Bioreactors in the art typically involve passing an undesirable gas, such as CO₂, through a tube containing a micro-organism (see, for example, WO-A-2007/011343). Tubes containing algae are commonly used as bioreactors in the art. However, to create sufficient surface area for large-scale biomass production, many tubes are often required. This has the disadvantages of requiring a large amount of space, creating difficulties in cleaning and maintenance, and has less than ideal efficiency.

For efficient algal growth, periods of light and dark are required; these periods are preferably controllable in a bioreactor, i.e. photomodulation of the bioreactor is preferred. The use of a dark cell bioreactor is therefore common in the art, wherein light is provided, when required, by internal light sources within an enclosed dark cell. However, this has the disadvantage of being a totally closed system that is difficult to monitor, clean and maintain. Both tube and dark cell bioreactors have the further disadvantage that it is difficult to provide and mix adequate nutrients and gases to the micro-organisms within. Therefore, providing a bioreactor that allows efficient conversion of gas into biomass has proven problematic due to difficulties in photo-modulation and mixing of the bioreactor contents.

There is a clear need in the art for an effective bioreactor that can be used to produce biofuels, in particular to extract unwanted gases from a gas stream and convert the unwanted gases into a useful product, such as a fuel. Summary of the Invention

The present invention is based on the surprising realisation that a bioreactor apparatus comprising one or more fixed means for creating turbulence is surprisingly effective at providing an efficient bioreactor. In particular, the bioreactor containing the fixed means is surprisingly effective at facilitating the conversion of waste gases, produced by the burning of fossil fuels, into useful products such as fuel.

The present invention is further based on the related discovery that providing a bioreactor with light that is reflected off a mirror into the bioreactor is surprisingly effective at efficiently providing light required for micro-organism growth.

The present invention is further based on the related discovery that the bioreactor can be provided with one or more rods of acrylic, or other suitable material, in which a light-emitting diode is positioned to emit light through the rod. The rod disperses the light into the bioreactor.

According to a first aspect of the invention, a bioreactor apparatus comprises an inlet, a chamber for retaining a microorganism in an aqueous environment and an outlet characterised in that the chamber comprises one or more fixed means for creating turbulence in the bioreactor apparatus. According to a second aspect of the invention, a bioreactor apparatus comprises an inlet, a chamber for retaining a micro-organism in an aqueous environment, an outlet and a light source containing at least one light and one mirror arranged so that light reflects off the mirror into the chamber.

According to a third aspect of the invention, the bioreactor according to the first or second aspect is used in the production of a biofuel.

According to a fourth aspect of the invention, a method of producing a biofuel comprises the steps of (i) providing carbon dioxide gas into the chamber of a bioreactor according to the first aspect or second aspect, (ii) allowing the microorganism to convert carbon dioxide gas into biomass; and (iii) harvesting the biomass resulting from step (ii).

According to a fifth aspect of the invention, a system for producing biodiesel comprises a bioreactor according to the first aspect or the second aspect. Brief Description of the Drawings

The invention is described with reference to the accompanying drawings, wherein:

Figure 1 is a plan view of a bioreactor apparatus according to the invention, indicating the presence of fixed baffles that create turbulence;

Figure 2 is a top view of the bioreactor, showing the cover and positions of light-emitting acrylic rods (1);

Figure 3 is a side view of the bioreactor according to the invention, showing the inlet, outlet and optional connectors to link two bioreactors together; Figure 4 is a side view of the bioreactor showing the media infeed and a dispersion tube inlet;

Figure 5 is a side view of the bioreactor showing the outlet;

Figure 6 illustrates a preferred light source for use in a bioreactor, wherein light from LEDs is reflected off a polarised mirror into a bioreactor (not shown); and

Figure 7 is a drawing of a light-emitting acrylic rod, having a light-emitting diode as a light source positioned at one end. Detailed Description of the Invention

It has been found, surprisingly, that an improved bioreactor can be provided by creating turbulence within the bioreactor; the turbulence alone is sufficient to mix the bioreactor contents and improve the growth of the microorganism within the bioreactor, thereby improving efficiency. Therefore, the present invention relates to a bioreactor apparatus comprising one or more fixed means for creating turbulence. It has further been found that an improved apparatus for providing light to a bioreactor comprises at least one light source and one mirror, arranged such that light from the light source reflects off the mirror and into the bioreactor.

It has also been found that an improved apparatus for providing light to a bioreactor comprises providing one or more rods of acrylic or other suitably transparent material, in which a light-emitting diode (LED) emits a light source which is dispersed within the reactor cell. Preferably there is a plurality of LEDs used per rod.

As used herein, the "bioreactor" refers to a device that contains live microorganisms and converts one or more substrates into biomass. Preferably, the substrate is a gas. For the avoidance of doubt, a "bioreactor" contains live, viable micro-organisms at a level sufficient to convert a substrate, preferably a gas, into biomass. The micro-organisms exist in an aqueous medium sufficient to propagate the micro-organism. The substrate that can be converted into biomass by the bioreactor, and therefore the biomass that is produced, is dependant on the micro-organism(s) present in the bioreactor, as detailed below. However, for the avoidance of doubt, the bioreactor preferably converts a gas, more preferably carbon dioxide, into a biofuel or biofuel precursor. The preferred biofuel is biodiesel. The substrate is any chemical substance that can be converted into biomass by a micro-organism. The substrate can be solid, liquid or gas and can be organic or inorganic. In one embodiment, the substrate is an organic carbon source such as glucose or corn powder hydrolysate. In an alternative embodiment, the substrate is a gas such as Sulphur Oxides (SOx) or Nitrogen Oxides (NOx). The preferred gas is Carbon Dioxide.

The "bioreactor apparatus" is the apparatus of the bioreactor without the presence of micro-organisms in media, i.e. it is the components of the bioreactor before the addition of a micro-organism. The bioreactor apparatus must contain an inlet for the substrate, an outlet and a chamber for retaining micro-organisms in an aqueous environment. The inlet is preferably controlled by a valve that allows regulation of the flow through the inlet. The chamber is a receptacle that is water-tight and can therefore retain a fluid medium containing a microorganism. In one embodiment, the sides of the bioreactor are not transparent, but the top and bottom, or the top only, is transparent, allowing light to pass into the bioreactor. The chamber is preferably translucent or, more preferably, transparent. The chamber may be any shape, such as a cube or cylinder. Preferably, the chamber is recognisable as a rectangular box shape. The bioreactor is preferably constructed an acrylic plastic, more preferably from transparent acrylic plastic. The chamber preferably contains grooves on one or more internal surfaces, more preferably microgrooves. The term "microgroove" refers to a groove that is less than 1μm wide. The depth of a microgroove is in the micron range, preferably 1-50μm, for example 8-12μm. Microgrooves can be manufactured using the process of laser microgrooving, which is known in the art. These grooves are useful in preventing micro-organisms in the chamber from attaching themselves to the internal surfaces and forming a biofilm, which reduces bioreactor efficiency. The grooves also aid in the creation of turbulence, further increasing the effective mixing of bioreactor contents. Preferably the microgrooves are coated with a nanoparticulate polymer, e.g. zetag (manufactured by GlaxoSmithkline), which prevents algae or other microorgansims attaching to the walls of the bioreactor.

An advantage of a transparent chamber is the availability of daylight to micro-organisms in the chamber; this is a clear advantage when the micro- organisms are photosynthetic. However, to improve efficiency further, an artificial light source can be used to provide light to a bioreactor of the invention, regardless of whether the chamber is transparent or not.

The bioreactor contains an inlet and an outlet, through which the substrate can be added, and also through which micro-organisms and suitable media (such as water and nutrients) can be added (inlet) and removed (outlet). A single opening that acts as both inlet and outlet may be present, or there may be a separate inlet and outlet as shown in Figures 3 to 5. Multiple inlets and outlets are possible. In the embodiment shown in Figure 3, an inlet valve for water, media and micro-organisms is indicated by and the separate outlet valve is on the far right of the Figure. Figure 4 shows the inlet and Figure 5 shows the outlet. Preferably, the inlet(s) and outlet(s) are each controlled by a valve that allows regulation of the fluid flow through the inlet/outlet.

The bioreactor may also contain one or more ports which can be used when connecting two or more bioreactors together. These ports are shown as "cell interconnectors" in Figure 3. The ports allow the media etc to flow from one bioreactor to the next. Alternatively they may be "close" so that media cannot flow from one bioreactor to the other. Alternatively the cell interconnectors may only be used to connect bioreactors, and may not be configured as ports.

Preferably, the substrate that is converted into biomass by the micro- organism in the bioreactor is a gas. In this embodiment, the bioreactor apparatus preferably contains a sparge unit functionally connected to the (gas) inlet, such that the gas passes from the (gas) inlet, through the sparge unit and subsequently into the chamber. The gas is therefore preferably "sparged" into the chamber. The terms "sparging", "sparge" and "sparged" are to be given their usual meaning in the art, i.e. relating to the introduction of a gas into a fluid. In this embodiment, the sparging gas inlet is preferably separate to the inlet for water, media and micro-organisms. Figure 1 shows a dispersion tube which allows the sparging gas to be introduced into the bioreactor. The dispersion tube is preferably located at the bottom of the bioreactor and extends throughout the bioreactor. The tube contains holes which release the gases into the bioreactor. In a further embodiment, some or all of the gas substrate can be sparged into a separate vessel, referred to as a feeding vessel, containing water. A preferred feeding vessel has a 50,000 litre capacity. The gas that is sparged into the feeding vessel will dissolve into the water, which can then be introduced into the bioreactor chamber through an inlet, preferably through the inlet for water, media and micro-organisms.

In a first aspect of the invention, the bioreactor apparatus comprises one or more fixed means for creating turbulence in the apparatus. The purpose of this means is to enhance mixing of the contents of the bioreactor by creating turbulent eddies in the micro-organism-containing media within the bioreactor. It has been found that creating turbulence alone is sufficient to mix the contents of the bioreactor. Previous attempts at creating bioreactors have relied upon the use of moving parts, such as an impeller, to mix the bioreactor contents. However, moving parts can be detrimental to the microorganisms present in the bioreactor. Therefore, in a preferred embodiment, the fixed means for creating turbulence is the only physical means in the bioreactor apparatus that cause significant mixing, i.e. an impeller or other mixing apparatus is not present. The movement of the liquid caused by the inlet of substrate, combined with the turbulence caused by the fixed means for creating turbulence, is sufficient to mix the bioreactor contents. The inlet flow of substrate can be adjusted to achieve a sufficient level of mixing, as will be apparent to one skilled in the art. Particularly effective mixing can be achieved by sparging a gas substrate through the inlet. An example of a suitable pressure for sparging gas through the inlet is between 1 and 5 bar, more preferably 2-3 bar.

The fixed means for creating turbulence according to the invention can be any structure, within the apparatus, that causes turbulent eddies and therefore mixing. Turbulent eddies are formed when the substrate is introduced through the inlet and causes movement of the liquid within the bioreactor, which subsequently creates turbulence as it interacts with the means for creating turbulence. The means is therefore an obstacle to fluid flow in the chamber. One or more means may be present; preferably, between 1 and 20 means are present, more preferably between 6 and 10. The fixed means for creating turbulence is preferably attached to an internal surface, i.e. wall, of the chamber and extends inwardly. It is therefore "fixed" and cannot move from its position of attachment on an internal surface nor does it turn on its own axis, rotate or translate to an alternative position.

The fixed means provides turbulence and facilitates overall mixing of the bioreactor contents. Preferably, the fixed means extends less than halfway across the chamber, as illustrated in Figure 1. More preferably the fixed means extends less than 1/3 of the distance across the chamber, for example 1/4 of the chamber width. One or more internal surfaces of the chamber can contain fixed means, for example 2, 3, 4 or more internal surfaces. Preferably, opposing walls of the chamber each contain at least one fixed means.

The fixed means can be of any shape or configuration, as will be apparent to the skilled man. The means is preferably impermeable to water and is made of a resilient material such as rubber, more preferably a rigid material such as glass or acrylic plastic. The means is preferably flat or substantially flat, i.e. it preferably has a planar configuration. The means is more preferably sheet-like.

A preferred means for creating turbulence is a baffle. As used herein, the term "baffle" is to be given its usual meaning in the art, namely a deflector plate that affects fluid flow.

The fixed means for creating turbulence is advantageous as it forces the aqueous fluid, containing the microorganism, to mix, thereby improving the efficiency of the conversion of the gas into useful biomass. In a preferred embodiment, the fixed means has a second role, that of ensuring that a portion of the fluid containing a micro-organism is retained in the chamber when the chamber is drained to harvest (the majority of) the micro-organisms. The chamber is preferably drained by actuating the outlet valve. For the avoidance of doubt, once the micro-organisms in the chamber have grown to a level suitable for harvest (to obtain the biomass), the outlet is actuated to allow the contents of the bioreactor to flow, or be pumped, out of the chamber. The fixed means therefore has a preferred second role of preventing some of the contents of the bioreactor (including micro-organisms) from flowing out of the chamber.

A large number of configurations will be apparent to the skilled person that are capable of retaining a proportion of micro-organism in the chamber and the invention is not limited to a particular arrangement. The precise configuration of the means to facilitate the retention of microorganism will be apparent to one skilled in the art. A variety of configurations will be able to prevent some of the micro-organisms from exiting the chamber through the outlet when it is actuated. The configuration will depend on the position of the outlet relative to the fixed means; the skilled person will realise that any configuration wherein a physical barrier is placed between the micro-organism and the outlet will retain some micro-organisms. In a preferred embodiment, the physical barrier forms a pocket or trap in which some of the contents of the chamber is retained. Preferably, the means is configured such that a proportion of the micro-organism is retained in an area created between the means and an internal surface, preferably a wall, of the chamber. This "retaining area" can, in one embodiment, be created by ensuring that the fixed means is not perpendicular to the surface to which it is attached, i.e. by angling the fixed means relative to the wall of the chamber such that a substantially v-shaped trap is formed between the wall and fixed means. In this embodiment, the fixed means forms the physical barrier to exit. A preferred angle for forming this substantially v-shaped trap is 45° between the fixed means and the surface to which it is attached. Figure 1 illustrates baffles angled at 45° to the wall of the chamber. The skilled person will realise that 45° is not a limiting requirement and that a range of angles are possible in this embodiment, preferably between 1° and 89°.

In a preferred embodiment, the inlet and outlet are situated on opposite surfaces of the chamber. In this embodiment, it is preferred that the fixed means for creating turbulence is angled towards the inlet, so that it acts against the substrate inlet flow, creating turbulence, while also forming a retaining area that will retain micro-organism when the outlet valve is actuated.

Figure 1 illustrates one embodiment, wherein baffles are angled at 45° relative to the wall of the chamber such that when the aqueous fluid containing micro-organisms is released out of the outlet (on the right of the figure), some of the fluid (and therefore micro-organisms) will be retained between the baffle and the side wall of the chamber, due to the physical barrier formed by the baffle.

The advantage of retaining some of the microorganism is that there is no need to "re-seed" the bioreactor, with new microorganisms, after each harvest. The microorganisms that are retained can simply be supplied with fresh media

(through the inlet) in which to grow and proliferate. This reduces the steps required, and time, between harvesting and re-starting the bioreactor.

According to a second aspect of the invention, a bioreactor apparatus comprises an apparatus for providing light to the bioreactor wherein the apparatus contains at least one artificial light source and at least one reflective material. As used herein the term "artificial light source" refers to any man-made means for producing light and includes chemical, electro-chemical, electrical and electronic means. Preferred artificial light sources include light bulbs, fluorescent lighting and light-emitting diodes (LEDs). LEDs are preferred. As used herein, the term "reflective material" is to be given its usual meaning in the art and refers to any material that bounces back some or preferably substantially all of the wavelengths of light that strike the material. A preferred reflective material is a mirrored surface. The preferred reflective material is a mirror.

In the apparatus for providing light, the artificial light source and reflective material are configured so that light from the artificial light source reflects off the reflective material and into the bioreactor to which the apparatus is attached. Any arrangement that allows reflected light to enter the bioreactor is within the scope of the invention. In a preferred embodiment, light enters the bioreactor both directly from the artificial light source and indirectly, reflected off the reflective material. A preferred arrangement is where the light source and reflective material are angled with respect to one another so that both light directly and indirectly originating from the light source enters the bioreactor.

In a preferred embodiment, more than one light and/or more than one mirror is comprised within the lighting apparatus. Preferably, a plurality of lights and mirrors exists, more preferably arranged so that each light has its own mirror. Yet more preferably, the light and mirrors alternate in series in the apparatus, i.e. in the order: {light-mirror}_n wherein n is any number, preferably between 1 and 100, more preferably between 1 and 50, yet more preferably between 2 and 20, i.e. 3, 4, 5, 6, 7, 8, 9 or 10. Each light and corresponding, adjacent mirror is preferably angled towards one another, so that the combination of multiple lights and mirrors form a zig-zag, as depicted in Figure 7.

The apparatus for providing light can be positioned anywhere in or on the bioreactor, provided that the light can enter the chamber of the bioreactor. Preferably, the apparatus is situated alongside an outer wall of the chamber.

The skilled person will realise that if the apparatus for providing light is positioned inside the chamber the reflective material will reflect light from the light source around the chamber, i.e. light is reflected further into the chamber.

In a separate embodiment, the bioreactor contains one or more rods made of a transparent acrylic or other suitable material, and comprises a light source at one end. The light source emits light which travels along the rod and is dispersed in the bioreactor. A suitable rod is shown in Figure 7. This shows an LED light source positioned at one end of an acrylic rod. The rod is lathe turned to aid the dispersal of the light from the LED. The rods may be positioned in the bioreactor such that they extend vertically from the top of the bioreactor. The light source is positioned on top of the rod.

The rod may be fixed in the vertical position. One way of achieving this is to construct the rods with a screw end, which can be inserted into an appropriate hole in the bioreactor. The rod may also be lathe-turned to produce a screw-type end with variable pitch, which allows the light to be dispersed to different extents into the bioreactor. For example, Figure 7 shows a rod with a screw-type end having three different levels of pitch. When the pitch is narrow (that shown closest to the LED source) light is emitted to a lower extent than when the pitch is wide (shown furthest away from the LED source). The rods may be used in the bioreactor with or without the mirrors.

For the avoidance of doubt, the present invention improves bioreactor efficiency and contains two aspects, a first aspect relating to fixed means for creating turbulence and a second aspect relating to an apparatus for providing light. The two aspects of the invention can be combined, providing a bioreactor comprising a means for creating turbulence and an apparatus for providing light, according to the invention.

A bioreactor according to the invention will, when working to convert a substrate into biomass, contain a microorganism. Any microorganism that is capable of converting a substrate into biomass and/or removing a harmful substance from the substrate may be used. One or more micro-organisms can be used. Preferably, a mixture of two or more different micro-organisms with different purposes, are used. More preferably, the two or more organisms work synergistically, to improve the bioreactor efficiency. Preferably, the microorganism is a photosynthetic microorganism, more preferably autrotophic, that is capable of converting CO2 gas into biomass by the process of photosynthesis. Examples of preferred photosynthetic microorganisms include photosynthetic cyanobacteria and algae. The term "algae" as used herein refers to the subset of photosynthetic eukaryotes that excludes the Charales (land plants). Preferred algal species include Botryococcus braunii, Dunaliella primolecta, Dunaliella tertiolecta, Chlorella stigmatophora, Chlorella salina, Chrysotila stipitata, Skeletonema costatum.

Preferably, organisms that convert SO_x and/or NO_x are included in the bioreactor. Sulphur compounds can be utilised by organisms such as Purple Sulphur bacteria, which utilise sulphurous compounds to produce water and nutrients, which further encourage the algal production. An example of these organisms is Desulfovibrio, which work in symbiosis with algae (Vladar P et a/, 2007 Microb. Ecol. Dec 8), thereby reducing overall SO_x emissions.

A bioreactor according to the invention is preferably used in a setting where waste gases are released into the atmosphere. Two or more bioreactors can be used together, e.g. in a "stack" or series, preferably utilising the same substrate source, i.e. attached to the same chimney or flue. In a preferred embodiment, a stack or series of bioreactors contains a number of bioreactors each directed to a different purpose, i.e. containing a different micro-organism. For example, one bioreactor could convert CO2 and another could convert NOx and/or SOx. A first bioreactor can contain a photosynthetic micro-organism, such as an algae, to convert CO₂ into biodiesel. A second bioreactor could be installed to process SO_x and/or NOx gases, for example as produced from flue emissions. Sulphanomides and cyanobacter can be utilized in a bioreactor of the invention to process SO_x to water and oxygen. The cyanobacter will process NOx to give pure nitrogen, oxygen and water. All these products are useful and can be further used on site. A bioreactor system according to this embodiment therefore has the potential to completely recycle all flue gas emissions via biological processes. The bioreactor can be used in both domestic and industrial settings. Preferably, the bioreactor is attached to a chimney, waste outlet or flue. In a particularly preferred embodiment, a bioreactor is attached to an industrial chimney, waste outlet or flue, for example a furnace flue. This will provide a rich source of waste gases, in particular CO₂, SOx and NOx. In the embodiment where a flue furnace is used, the flue gas emissions from the furnaces can be extracted, from which they may need to be cooled via the use of a heat exchanger, in which this energy may be used to drive a turbine to generate energy to further feed the process further down stream (i.e. lighting and heating). The cooled gases then can be piped, preferably sparged, into the bioreactor of the invention, through the (gas) inlet, under sufficient pressure to create turbulence. In a preferred bioreactor there are baffles composed of simple rigid structures of acrylic plastic which will create turbulent eddies; this allows ample mixing of the gas with the solution found in the reactor. The solution contains preferably water, a selection of nutrients targeting the growth of the selected micro-organism, preferably algae, and the flue gases which are sparged into the system. Algae will process the CO₂ via photosynthesis.

Algae will respire to produce their own CO₂; this pure clean CO₂ can be further used in other processes on site. As micro-organisms grow in the bioreactor they will eventually saturate the solution preferably on a daily basis. Once this stage is reached, the microorganism needs to be harvested.

The micro-organisms can be harvested by simply draining or pumping out the majority, for example 3/4, of the bioreactor contents, leaving the remaining amount, i.e. 1/4, to be used to re-seed the bioreactor.

After harvest, it is necessary to separate the culture medium into a liquid phase and into a solid phase which contains the microorganisms (biomass). The means for performing this separation is preferably included as part of a system with the bioreactor. The biomass can be separated from the liquid phase by a filter unit.

Once separated, the biomass is next dried. This is very simple to do and will be apparent to the skilled person. For example, drying can occur in the sun or, if in a cold country, dry within a greenhouse or drum filter (with vacuum) system, or hot air oven, all of which can be powered by the energy produced from cooling the flue gases.

Once dry, the cells now can be further processed to give oils and solids. The process of extracting the oils can vary as follows:

a. Expeller/Press

When the algae is dried, it retains its oil content, which then can be

"pressed" out with an oil press. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil. While more efficient processes are emerging, a simple process is to use a press to extract a large percentage (70-75%) of the oils out of algae.

b. Hexane Solvent Method

Algal oil can be extracted using chemicals. Benzene and ether have been used, but a popular chemical for solvent extraction is hexane, which is relatively inexpensive. The downside to using solvents for oil extraction is the inherent dangers involved in working with the chemicals. Benzene is classified as a carcinogen. Chemical solvents also present the problem of being an explosion hazard. Hexane solvent extraction can be used in isolation or it can be used along with the oil press/expeller method. After the oil has been extracted using an expeller, the remaining pulp can be mixed with cyclo-hexane to extract the remaining oil content. The oil dissolves in the cyclohexane, and the pulp is filtered out from the solution. The oil and cyclohexane are separated by means of distillation. These two stages (cold press & hexane solvent) together will be able to derive more than 95% of the total oil present in the algae.

c. Supercritical Fluid Extraction

This can extract almost 100% of the oils. This method however needs special equipment for containment and pressure in the supercritical fluid/CU2 extraction; CO₂ is liquefied under pressure and heated to the point that it has the properties of both a liquid and gas. This liquefied fluid then acts as the solvent in extracting the oil. The water from the cell does not need to be treated in any form it can simply be recycled as it is a continuous flowing system, and it will have some algae growth with it.

From the process described above, three main products are produced:

Biodiesel, which depending on the strain can yield up to 93% oil of the cell weight. This can be used to fuel processes on site and subsequently reduce the use of fossil fuels on site. It is estimated that the reactor will be able to process and reduce CO2 emissions by 50-85% depending on system efficiency.

Dry cake, this being the dry solids of the remaining micro-organisms. This can be processed into pellets and sold as animal feed, or processed back into the furnace and used as a fuel, similar to that of peat moss. Alternatively, this dry cake, which contains sugars, can be combined with water and yeast and fermented to produce bioethanol.

Pure CO₂ used in further onsite processes.

Claims

1. A bioreactor apparatus comprising an inlet, a chamber for retaining a microorganism in an aqueous environment and an outlet characterised in that the chamber comprises one or more fixed means for creating turbulence in the bioreactor apparatus.

2. A bioreactor according to claim 1 , wherein the fixed means for creating turbulence in the bioreactor apparatus is a baffle extending inwardly from a wall of the chamber.

3. A bioreactor according to claim 1 or claim 2, wherein the fixed means for creating turbulence in the bioreactor apparatus retains a portion of the microorganism in the chamber when the outlet valve is actuated.

4. A bioreactor according to any preceding claim, wherein the chamber comprises between 1 and 20 fixed means for creating turbulence in the bioreactor apparatus.

5. A bioreactor according to any preceding claim, wherein the chamber comprises between 6 and 10 fixed means for creating turbulence in the bioreactor apparatus.

6. A bioreactor according to any preceding claim, wherein the fixed means for creating turbulence in the bioreactor apparatus is fixed to an internal surface of the chamber and extends inwardly.

7. A bioreactor according to claim 6, wherein the fixed means for creating turbulence in the bioreactor apparatus extends less than half way across the chamber.

8. A bioreactor according to claim 7, wherein opposing internal surfaces of the chamber each have a fixed means for creating turbulence extending less than half way across the chamber.

9. A bioreactor according to any preceding claim, wherein the fixed means for creating turbulence is impermeable to water.

10. A bioreactor according to any preceding claim, wherein the fixed means for creating turbulence in the bioreactor apparatus is rigid.

11. A bioreactor according to any preceding claim, wherein the fixed means for creating turbulence in the bioreactor apparatus is acrylic or polypropylene plastic.

12. A bioreactor according to any preceding claim, wherein the chamber is acrylic or polypropylene plastic.

13. A bioreactor according to any preceding claim, which is transparent.

14. A bioreactor according to any preceding claim, wherein the fixed means for creating turbulence in the bioreactor apparatus is not perpendicular to the surface to which it is attached.

15. A bioreactor according to claim 10, wherein the fixed means for creating turbulence in the bioreactor apparatus is angled against the direction of inlet flow.

16. A bioreactor according to any preceding claim, comprising microgrooves on one or more internal surfaces.

17. A bioreactor according to any preceding claim, comprising an artificial light source.

18. A bioreactor according to claim 17, wherein light from the light source is reflected off a reflective material into, or further into, the chamber of the bioreactor.

19. A bioreactor according to claim 17 or claim 18, wherein the light source is a light-emitting acrylic rod.

20. A bioreactor according to any preceding claim, comprising a microorganism in an aqueous environment.

21. A bioreactor according to claim 20, wherein the microorganism is a cyanobacter or an algae.

22. A bioreactor according to any preceding claim, that is a box, cube or other geometric shape.

23. A bioreactor apparatus substantially as described in the figures.

24. Use of a bioreactor according to any preceding claim, in the production of a biofuel.

25. Use according to claim 24, wherein the biofuel is biodiesel.

26. A system for producing biodiesel comprising a bioreactor according to any of claims 1 to 23.

27. A system according to claim 26, comprising a plurality of bioreactors according to any of claims 1 to 23, preferably in a stack.

28. A system according to claim 26 or 27, comprising a heat exchanger between a gas source and the gas inlet.

29. A system according to claim 28, wherein heat obtained from the heat exchanger is used to power a turbine.

30. A bioreactor apparatus comprising an inlet, a chamber for retaining a micro-organism in an aqueous environment, an outlet and a light source containing at least one light and one mirror arranged so that light reflects off the mirror into the chamber.

31. A bioreactor apparatus comprising an inlet, a chamber for retaining a micro-organism in an aqueous environment, an outlet and a light source, wherein the light source is a light-emitting acrylic rod.

32. A bioreactor apparatus according to claim 30 or claim 31 , wherein the light source is substantially as described in Figure 6 or Figure 7.

33. A bioreactor apparatus according to claim 30 to 32, additionally comprising the features of any of claims 1 to 23.

34. A bioreactor apparatus according to any of claims 30 to 33, comprising a micro-organism in an aqueous environment.

35. A method of producing a biofuel, comprising the steps of: (i) providing carbon dioxide gas into the chamber of a bioreactor according to claim 20, 21 or 34;

(ii) allowing the microorganism to convert carbon dioxide gas into biomass; and (iii) harvesting the biomass resulting from step (ii).