DIPHASIC ALGAL CULTURE SYSTEM

FIELD OF THE INVENTION

This invention relates to bioreactor processes, particularly photobioreactor processes for the production of biodiesel and/or hydrogen and/or methane from biomass, more particularly diphasic photobioreactor processes for the production of biodiesel and/or hydrogen and/or and methane from algae.

BACKGROUND OF THE INVENTION

The production of biodiesel and/or hydrogen gas and/or methane as well as other fermentation products from biomass, is becoming an increasingly attractive option for alternative fuel production as prices of fossil fuels and petroleum increase. As fossil fuels become depleted alternative energy sources will become a crucial area of research both in industry and in academia.

In particular hydrogen is recognized as a clean and recyclable energy carrier and there is a prominent thrust in research initiatives focusing on the sufficient, efficient, profitable and "green" production of hydrogen gas. It is believed that hydrogen gas as an alternative energy carrier is indeed one of the more promising alternatives to be considered and exploited in the future. The use of biomass in the production of hydrogen gas provides for a "green" solution for hydrogen production which is hoped will be optimized and developed to provide a means for providing an economical and profitable supply of hydrogen gas. Furthermore, biological production of hydrogen from organic wastes as well as from other recyclable resources is considered preferable to the production of hydrogen from food crops for, while the hydrogen yield of food crops such as maize and wheat is relatively high, there is a global food shortage which is in danger of becoming exacerbated by the use of food crops in biological hydrogen producing reactors.

Similarly, biodiesel is fast becoming a viable alternative to conventional fossil fuels in the production of energy needed in modern society. Biodiesel itself typically refers to diesel fuel made from a biological material comprising long- chain alkyl esters. Biodiesel usage is especially envisaged in applications including the automotive or transport industries.

Bioreactors employed in the production of biodiesel and/or hydrogen and/or methane and/or other fuels can be designed specifically for the type of biomass that is to be used in the system.

Bioreactors employing algal biomass are typically in the form of photobioreactors. Photobioreactors have a light source providing energy to the reactor system wherein algae or other phototrophic cultures are cultivated and maintained. Typically, biodiesel production from algal biomass takes place in open raceway photobioreactor systems. These systems are known to be expensive to manufacture and maintain as they require special reactor vessels, cooling means, mixing means and gas control means.

It is known that closed tubular photobioreactor systems for algal biodiesel production facilitates greater process control and higher rates of algal biomass production than the more convention open raceway systems. Typically, these photobioreactors employ only aerobic photoautotrophic algae and therefore require artificial lighting if production is envisaged during non-daylight periods.

Accordingly, there is a need for an inexpensive photobioreactor system wherein the photobioreactor system can maintain production throughout a diphasic cycle without the need of artificial light.

OBJECT OF THE INVENTION

It is the object of this invention to provide for a photobioreactor system for the production of at least biodiesel, particularly for a diphasic photobioreactor system for the production of biodiesel and/or hydrogen and/or methane wherein the biomass utilized is algae.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a diphasic photobioreactor system for the production of at least biodiesel, the diphasic photobioreactor system comprising a photobioreactor vessel compartmentalised into a first and second compartment; a connection means between the first and second compartment such that the first compartment is in fluid communication with the second compartment; and a biodiesel refinery plant in communication with the photobioreactor vessel.

The diphasic photobioreactor system further comprising a nutrient flow inlet located in the photobioreactor vessel. -A-

The diphasic photobioreactor system wherein the nutrient flow inlet is connected to the first compartment allowing for controlled flow of nutrient into the first compartment.

The diphasic photobioreactor system further comprising a second nutrient flow inlet connected to the second compartment allowing for controlled flow of nutrient into the second compartment.

The diphasic photobioreactor system wherein the nutrient comprises nitrogen and phosphorous containing compounds.

The diphasic photobioreactor system wherein the first compartment having an algal culture and utilized for algal cell proliferation and the second compartment having an algal cell culture and utilized for lipid production.

The diphasic photobioreactor system wherein the connection means facilitating movement of proliferated algal cells from the first compartment to the second compartment.

The diphasic photobioreactor system wherein the second compartment is in communication via a second connection means to biodiesel refinery plant.

The diphasic photobioreactor system wherein the biodiesel refinery plant utilizes lipids contained in algal cells from the second compartment in the production of biodiesel.

The diphasic photobioreactor system wherein algal cell proliferation in the first compartment is optimized by controlling independently a combination or all of the following: set point temperature, saturating irradiance levels, nitrogen and phosphorous supply, carbon dioxide supply, salinity and pH. The diphasic photobioreactor system wherein lipid production in the second compartment is stimulated by selective control of nitrogen and phosphorous into the second compartment from the first compartment.

The diphasic photobioreactor system wherein lipid production in the second compartment is further stimulated by providing high levels of irradiation and/or high levels of carbon dioxide to the second compartment.

The diphasic photobioreactor system wherein lipid production in the second compartment is stimulated by selective control of nitrogen and phosphorous into the second compartment from the second nutrient inlet.

The diphasic photobioreactor system wherein algal cell proliferation in the second compartment is minimized by controlling independently a combination or all of the following: set point temperature, saturating irradiance levels, nitrogen and phosphorous supply, carbon dioxide supply, salinity and pH.

The diphasic photobioreactor system wherein the photobioreactor vessel is tubular.

The diphasic photobiorector system wherein the photobioreactor comprise UV resistant plastics materials, preferably clear PVC or polycarbonate materials, with a preferable tube wall thickness of less than 4.0 mm.

The diphasic photobioreactor system further comprising an anaerobic fluidized granular bed reactor connected to the biodiesel plant refinery via a third connection means, the connection means facilitating the movement of algal biomass and/or glycerol from the diesel refinery plant to the anaerobic fluidized granular bed reactor wherein the algal biomass is at least partially fermented by an anaerobic bacterial consortium resulting in production of at least hydrogen.

The diphasic photobioreactor system further comprising a gas harvesting means to harvest the at least the hydrogen gas produced during dark anaerobic fermentation of algal cells inside the anaerobic fluidized granular bed reactor.

The diphasic photobioreactor system further comprising an electricity generating means, the electricity generating means utilizing hydrogen gas to generate electricity.

The diphasic photobioreactor system wherein the anaerobic fluidized granular bed reactor further produces at least one of methane, ethanol, acetate, glycerol and volatile fatty acids via anaerobic dark fermentation of waste algal biomass.

The diphasic photobioreactor system wherein the anaerobic fluidized granular bed reactor further comprises a fourth connection means facilitating the movement of acetate, glycerol and/or volatile fatty acids to a storage container.

The diphasic photobioreactor system wherein the storage container is in communication with the photobioreactor vessel, preferably the first compartment, in order to provide the algal cells with a carbon substrate in the form of acetate, glycerol and/or volatile fatty acids to support aerobic heterotrophic algal proliferation and lipid accumulation during the dark phase.

The diphasic photobioreactor system wherein the photobioreactor vessel each comprises a condenser. The diphasic photobioreactor system wherein the photobioreactor vessel comprises a gas source system, the gas source system having a gas compressor, a heat exchanger and gas spargers wherein the gas compressor provides a gas source, the heat exchanger aids to regulate the temperature inside the photobioreactor vessel and the gas spargers functioning as gas inlet means to facilitate sparging of the first and second photobioreactor vessels.

The diphasic photobioreactor system wherein the first and second compartments each comprising a gas source system, the gas source system having a gas compressor, a heat exchanger and gas spargers wherein the gas compressor provides a gas source, the heat exchanger aids to regulate the temperature inside the first and second compartments and the gas spargers functioning as gas inlet means to facilitate sparging of the first and second photobioreactor vessels.

The diphasic photobioreactor system wherein the gas source provided from the gas compressor to the first and second compartments is air enriched with carbon dioxide.

The diphasic photobioreactor system wherein the gas source provided from the gas compressor to the first and second compartments is carbon dioxide.

The diphasic photobioreactor system wherein produced hydrogen and methane can be used for the production of electricity.

According to a second aspect of the invention there is provided a diphasic photobiorector system for the production of at least biodiesel, the diphasic photobioreactor system comprising: first and second photobioreactor vessels, the first photobioreactor vessel having an algal culture and utilized for algal cell proliferation, the second photobioreactor vessel having an algal cell culture and utilized for lipid production; a first connection means connecting the first and second photobioreactor vessels in communication with each other facilitating movement of proliferated algal cells from the first photobioreactor vessel to the second photobioreactor vessel; a biodiesel refinery plant for the production of biodiesel from lipids contained in algal cells; and a second connection means connecting the second photobioreactor vessel to the biodiesel refinery plant facilitating movement of algal cells from the second photobioreactor to the biodiesel refinery plant.

The diphasic photobioreactor system further comprising a nutrient flow inlet located in the first photobioreactor vessel allowing controlled flow of nutrient into the first photobioreactor vessel.

The diphasic photobioreactor system further comprising a second nutrient inlet located in the second photobioreactor vessel allowing controlled flow of nutrient into the second photobioreactor vessel.

The diphasic photobioreactor system wherein the nutrient comprises nitrogen and phosphorous containing compounds.

The diphasic photobioreactor system wherein algal cell proliferation in the first photobioreactor vessel is optimized by controlling independently a combination or all of the following: set point temperature, saturating irradiance levels, nitrogen and phosphorous supply, carbon dioxide supply, salinity and pH.

The diphasic photobioreactor system wherein lipid production in the second photobioreactor vessel is stimulated by selective control of nitrogen and phosphorous into the second photobioreactor vessel from the first photobioreactor vessel.

The diphasic photobioreactor system wherein lipid production in the second photobioreactor vessel is further stimulated by providing high levels of irradiation and/or high levels of carbon dioxide to the second photobioreactor vessel.

The diphasic photobioreactor system wherein lipid production in the second photobioreactor vessel is stimulated by selective control of nitrogen and phosphorous into the second photobioreactor vessel from the second nutrient inlet.

The diphasic photobioreactor system wherein algal cell proliferation in the second photobioreactor vessel is minimized by controlling independently a combination or all of the following: set point temperature, saturating irradiance levels, nitrogen and phosphorous supply, carbon dioxide supply, salinity and pH.

The diphasic photobioreactor system wherein the first and second photobioreactor vessels are tubular.

The diphasic photobiorector system wherein the photobioreactor vessels comprise UV resistant plastics materials, preferably clear PVC or polycarbonate materials, with a preferable tube wall thickness of less than 4.0 mm.

The diphasic photobioreactor system further comprising an anaerobic fluidized granular bed reactor connected to the biodiesel plant refinery via a third connection means, the third connection means facilitating the movement of algal biomass and/or glycerol from the diesel refinery plant to the anaerobic fluidized granular bed reactor wherein the algal biomass is at least partially fermented by an anaerobic bacterial consortium resulting in production of at least hydrogen.

The diphasic photobioreactor system further comprising a gas harvesting means to harvest the at least the hydrogen gas produced during dark anaerobic fermentation of algal cells inside the anaerobic fluidized granular bed reactor.

The diphasic photobioreactor system further comprising an electricity generating means, the electricity generating means utilizing hydrogen gas to generate electricity.

The diphasic photobioreactor system wherein the anaerobic fluidized granular bed reactor further produces at least one of methane, ethanol, acetate, glycerol and volatile fatty acids via anaerobic dark fermentation of waste algal biomass.

The diphasic photobioreactor system wherein the anaerobic fluidized granular bed reactor further comprises a fourth connection means facilitating the movement of acetate, glycerol and/or volatile fatty acids to a storage container.

The diphasic photobioreactor system wherein the storage container is in communication with the first and/or second photobioreactor vessel in order to provide the algal cells with a carbon substrate in the form of acetate, glycerol and/or volatile fatty acids to support aerobic heterotrophic algal proliferation and lipid accumulation during the dark phase.

The diphasic photobioreactor system wherein the first and second photobioreactor vessels each comprising a condenser. The diphasic photobioreactor system wherein the first and second photobioreactor vessels each comprising a gas source system, the gas source system having a gas compressor, a heat exchanger and gas spargers wherein the gas compressor provides a gas source, the heat exchanger aids to regulate the temperature inside the first and second photobioreactor vessels and the gas spargers functioning as gas inlet means to facilitate sparging of the first and second photobioreactor vessels.

The diphasic photobioreactor system wherein the gas source provided from the gas compressor to the first and second photobioreactor vessels is air enriched with carbon dioxide.

The diphasic photobioreactor system wherein the gas source provided from the gas compressor to the first and second photobioreactor vessels is carbon dioxide.

The diphasic photobioreactor system wherein produced hydrogen and methane can be used for the production of electricity.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention will be described below by way of example only and with reference to the accompanying drawing which shows a diagrammatic representation of one embodiment of a diphasic photobioreactor according to the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION: The diphasic photobioreactor system 10 comprises a first 12 and second 14 tubular transparent photobioreactor vessels connected to each other in series.

The first tubular transparent photobioreactor vessel 12 operatively containing an algal culture and utilized for the growth and proliferation of the algal culture. The second tubular transparent photobioreactor vessel 14 containing an algal cell culture utilized for lipid production. A first connection means in the form of a first effluent overflow pipe 16 connects the first and second tubular transparent photobioreactor vessels 12, 14 in so doing facilitating the displacement of proliferated grown algal cells from the first to the second tubular transparent photobioreactor vessels 12, 14. The first and second tubular transparent photobioreactor vessels 12, 14 each contain a nutrient flow inlet 18 allowing for controlled flow of nutrient from a nutrient tank 15 into the photobioreactor vessels 12, 14 by making use of a flow meter (not shown) or a variable pump (not shown).

The first photobioreactor vessel 12 is supplied with nutrient medium enriched with concentration levels of nitrogen and phosphorous that promotes cell proliferation and growth rates. Algal cell proliferation and growth therefore takes place in the first photobioreactor vessel 12 where the majority of the nitrogen and phosphorous supplied to this photobioreactor vessel 12 is consumed by the algal culture. Consequently, only residual quantities of nitrogen and phosphorous are transferred via first effluent overflow pipe 16 to the second photobioreactor 14. The low concentrations of nitrogen and phosphorous received into the second photobioreactor vessel provide insufficient support to sustain algal cell division resulting in relatively low levels of proliferation and growth when compared to that occurring in the first photobioreactor vessel 12. However, the second photobioreactor 14 experiences high rates of algal lipid production compared to that of the first photobioreactor vessel 12. Lipid production and consequently lipid accumulation takes place in the second photobioreactor 14 in response to low nitrogen and phosphorous concentrations under conditions of unlimited irradiance and a non-limiting carbon dioxide supply from a gas source system 20 allowing for selected gas to be introduced into either one or both of the first and second photobioreactor vessels 12, 14.

The gas source system 20 comprises a gas compressor 22 for the compression of gas, a heat exchanger 24 for the operative temperature regulation of the gas, and gas spargers 26 facilitating the sparging of gas into and through the first and second photobioreactor vessels 12, 14. Upon complete depletion of nitrogen and phosphorous in the second photobioreactor vessel 14 the lipids in the algal chloroplasts are converted into storage lipids and oils. The chloroplast undergoes a reduction in size and photosynthetic rates decline to cell maintenance levels. Lipid and oil storage bodies are maintained and not depleted once the chloroplasts have undergone size reduction. The algal cells can be maintained in this state at high densities for several days. The temperatures of both the first and second photobioreactor vessels 12, 14 can, with respect to the similar radiation loads, be differentially controlled by the temperatures and flow rates of the gas stream supplied to the individual photobioreactors via the spargers. The gas stream consists of air preferably enriched with CO ₂ .

The set point temperature of the first photobioreactor vessel 12 that promotes optimum rates of cell proliferation under conditions of photosynthetic saturating irradiance levels, unlimited nitrogen and unlimited phosphorous supply and elevated CO ₂ supply, can be controlled by the gas source system 20. Similarly, the set point temperature of the second photobioreactor vessel 14 that promotes optimum rates lipid production and lipid accumulation under conditions of photosynthetic saturating irradiance levels, low nitrogen and low phosphorous concentrations, and elevated CO ₂ supply, can also be controlled by the gas delivery system. In addition to the positive effects of photosynthetic saturating irradiance levels, elevated temperatures, elevated CO ₂ levels, low nitrogen and low phosphorous concentrations on lipid production and lipid accumulation in algal cells, other factors such as salinity and pH also can be used to induce lipid production and lipid accumulation in algal cells. Therefore, in the second photobioreactor vessel 14 the following combination of treatment factors can be simultaneously and independently controlled to enhance algal lipid production and lipid accumulation under photosynthetic saturating irradiance levels: CO ₂ concentration, nitrogen and phosphorous concentration, temperature, salinity and pH. Similarly, for the first photobioreactor vessel 12, the positive effects of the following combination of factors can be used to further induce or positively augment high rates of algal cell production: photosynthetic saturating irradiance levels, elevated temperatures, elevated CO ₂ levels, N and P concentrations, on algal cell production, control of factors such as salinity and pH. Therefore, in the first photobioreactor the following combination of treatment factors can be simultaneous and independently controlled to enhance algal cell production under photosynthetic saturating irradiance levels: CO ₂ concentration, N and P concentration, temperature, salinity and pH. Algal cells are recovered from the first effluent overflow pipe 16 connecting to the second photobioreactor 14 vessel by collection through gravity flow into a biodiesel refinery plant 25. The biodiesel refinery plant 25 includes raceway ponds (not shown) which function as temporary storage facilities for the algal cells before being processed into biodiesel. Produced biodiesel may be conveyed from the biodiesel refinery plant via a biodiesel conduit 27 to a desired location.

The design of the individual tubular transparent photobioreactor vessels 12, 14 are preferably based on, but not limited to, the following dimensions: height 5.1 m, diameter 0.1 m, bioreaction volume 40 L. The tubular transparent photobioreactor vessels 12, 14 are constructed from UV resistant low cost plastic materials such as clear PVC or polycarbonate materials, with tube wall thickness less than 4.0 mm.

Extending from an upper end 30 of the first and second photobioreactors 12, 14 are condensers 32.

A second connection means in the form of a second effluent overflow pipe 34 connects the second photobioreactor vessel 14 to the biodiesel refinery plant 25 facilitating movement of algal cells from the second photobioreactor 14 to the biodiesel refinery plant 25. The diphasic photobioreactor system 10 further comprises an anaerobic fluidized granular bed reactor 28 connected to the biodiesel plant refinery 25 via a third connection means 38 in the form of a third effluent overflow pipe 38, the third connection means 38 facilitating the movement of algal biomass and/or glycerol from the biodiesel refinery plant 25 to the anaerobic fluidized granular bed reactor 28 wherein the algal biomass is at least partially fermented by an anaerobic bacterial consortium resulting in production of hydrogen, methane, ethanol, acetate, glycerol and volatile fatty acids via anaerobic dark fermentation of waste algal biomass.

The diphasic photobioreactor system 10 wherein the anaerobic fluidized granular bed reactor 28 further comprises a fourth connection means in the form of a fourth effluent overflow pipe 40 facilitating the movement of acetate, glycerol and/or volatile fatty acids to a storage container 42, the storage container 42 is in communication with the first and/or second photobioreactor vessel 12,14 via a second connection means 44 in order to provide the algal cells with a carbon substrate in the form of acetate, glycerol and/or volatile fatty acids to support aerobic heterotrophic algal proliferation and lipid accumulation during the dark phase.

In a further embodiment of the invention, the individual diphasic bioreactors 10, where one diphasic bioreactor 10 consists of two serially connected photobioreactors vessels, can be assembled into a system consisting of 500 individual units per 100 m corresponding to individual diphasic photobioreactor densities of 100 000 units per ha. In this further embodiment a space of about 0.5 m separates each row of bioreactors.

Solar radiation re-distribution via reflection within the arrays of diphasic photobioreactors 10 and photon re-capture by the diphasic photobioreactors 10 is promoted by covering the surface underlying the bioreactors with a high reflective material.

A preferred density of 100 000 units per ha corresponds to a total photobioreactor volume of 8000 m ³ per ha. 4000 m ³ per ha for algal cell production and 4000 m ³ per ha for lipid production and accumulation. After extraction of the lipids, the processed algal biomass together with the glycerol is used as a feed stock for an anaerobic fluidized granular bed bioreactor 28 for biohydrogen, methane, ethanol and volatile fatty acid (VFA) production, acetate being the primary VFA.

Biohydrogen and methane are used as a fuel for electricity generation and are connected to an electricity generation means (not shown)

VFAs produced by the anaerobic bioreactor are used as substrates to support algal growth and lipid production in the bioreactor units during dark periods, thus allowing for a non-stop 24 h cycle of algal cell growth and lipid production. The mode of operation of the anaerobic bioreactor in point facilitates conversion of all CO ₂ into acetate. Thus the combined system consisting of diphasic photobioreactors 10 and anaerobic fluidized granular bed bioreactor together operates as net CO ₂ sink. With the majority of carbon leaving the system as algal biodiesel.

Accordingly, there is provided an inexpensive diphasic photobioreactor system.