GB2235210A

GB2235210A - Fluid mixing and photobioreactor apparatus

Info

Publication number: GB2235210A
Application number: GB9010371A
Authority: GB
Inventors: Howard John Fallowfield; Nicholas John Martin
Original assignee: WEST OF SCOTLAND COLLEGE
Current assignee: WEST OF SCOTLAND COLLEGE
Priority date: 1989-05-09
Filing date: 1990-05-09
Publication date: 1991-02-27
Anticipated expiration: 2010-05-09
Also published as: GB2235210B; GB9010371D0; GB8910597D0

Abstract

Photobioreactor apparatus which comprises an internally partitioned laminarium (defined) to provide a fluid pathway with even turbulent flow along channels arranged so that fluid passing from one channel to an adjacent channel undergoes a change of direction of preferably 180 degrees, together with a light source which illuminates one face of said laminarium.

Description

"Fluid Mixing and Photobioreactor Apparatus" This invention relates to fluid mixing and photobioreactor apparatus.

Many species of algae are capable of producing a wide range of valuable products, for example natural chemicals and colourants and polyunsaturated fatty acids. They may also be used in the treatment of waste. However the commercial potential has been largely ignored, mainly due to the high production costs which result from present deficiencies in suitable technology.

A photobioreactor is a system for the cultivation of photosynthetic micro-organisms such as algae. There are four basic requirements for vigorous algal growth. These are a supply of carbon dioxide and nutrients, a supply of appropriate light, a suitable temperature and agitation to ensure adequate mixing.

For the production of fine chemicals a reactor closed to the atmosphere is essential. Vertical closed photobioreactors have been designed which enable a high degree of process control to be achieved, and which minimise species diversification. At present a glass tubular loop system is used, which achieves a high surface area. The culture is recycled around the system via a pump. However the cells at the surface of the glass shade the bulk of culture behind them and prevent optimum growth, and light is therefore unevenly provided to the culture. Over-vigorous pumping to overcome this results in damage to the cells.

A further major disadvantage of such closed bioreactors is the high initial investment and production cost.

According to the present invention there is provided photobioreactor apparatus comprising a laminarium as hereinafter defined which is internally partitioned to provide a fluid pathway between an inlet and an outlet thereof, a light source for illuminating a face of the laminarium, and means for providing fluid flow from the inlet to the outlet of the laminarium.

Further according to the present invention there is provided a laminarium as described in the immediately preceding paragraph for use in photobioreactor apparatus.

Still further according to the present invention there is provided apparatus for providing fluid mixing, comprising a laminarium as hereinafter defined which is internally partitioned to provide a fluid pathway between an inlet and an outlet thereof, the partitioning defining a series of channels of which adjacent channels have an apertured common wall, the apertures being disposed at opposite end portions of the wall so that fluid passing from one channel to an adjacent channel undergoes a change of direction of substantially 180 degrees.

A laminarium is a container for fluid having generally parallel front and rear faces, the container being shallow in depth from front to rear.

Preferably, said laminarium comprises two flat transparent plates which are sealed to provide a fluid-tight container and internally partitioned to provide a non-unidirectional pathway for fluid between the inlet and the outlet.

Said pathway is preferably designed to produce an even turbulent flow by providing 180 degree turns for fluid flowing along it.

Preferably, the flow-producing means comprises a low-shear-force pump system. For example an air-lift system may be used.

Said fluid may comprise an entrained gas, for example methane or carbon dioxide, nutrients and micro-organisms such as algae in a carrier liquid.

Preferably, the light source is provided by a high pressure sodium lamp or other lamp which most preferably emits light of 400-700nm wavelength.

Preferably the laminarium is composed of a plastics sheet, for example acrylic or polycarbonate, which does not absorb radiation in the visible region of the spectrum. Acrylic sheeting such as PLEXIGLAS (Trade Mark) of Rohm Ltd may be used. This material absorbs uv light and so limits the light falling on the algae.

The apparatus may be modular, which enables units of varying capacities to be built up. The configuration of the photobioreactor is preferably one which allows instruments and monitoring controls to be inserted and samples and product to be drawn off. Facilities may be provided for the addition of substances to the photobioreactor, and a heater, a temperature sensor and pH electrode may be included.

An embodiment of the invention will now be described with reference to the drawings in which: Fig. 1 is a schematic representation of a photobioreactor of the present invention; and Fig. 2 is a cross-sectional view of a photostage forming part of the photobioreactor of Fig. 1.

A photobioreactor 1 comprises a laminarium provided as a photostage 2, a degasser 3 and a centrifugal pump 4 which together form a circuit loop 5. The photostage 2 is illuminated using a high pressure sodium lamp (400W; 10,000 lux) from which 90% of the light emitted is in the wavelength range 400-700nm. The other parts of the loop 5 are not illuminated.

If the illumination level is too high for the purposes required, a second laminarium filled with fluid such as water is placed between the lamp and the photobioreactor.

A gas supply is connected to the loop 5 via an inlet tube 6, and an outlet tube 7 is provided from the degasser 3. Gas is supplied from air at a rate of 600ml/min, or carbon dioxide is drawn from a cylinder and mixed with air to provide a 5 carbon dioxide mixture.

The degasser 3 contains inlet and outlet tubes 8 for liquid and gas and accommodates various sensors. An overflow pipe 9 is connected to the degasser to enable collection of output.

A temperature controller, which is activated by a resistance thermometer, switches on or off an electric heating element in the degasser 3 to maintain the ambient temperature at 30 degrees + 2 degrees. A pH electrode is also sited in the degasser 3 and the pH of the culture is maintained between 6.5 and 7.75 through automatic addition of sodium hydroxide and HCl via the tubes 8. Foam formation is suppressed by addition of the antifoam agent polypropylene glycol.

The photostage 2 is formed by spaced parallel acrylic sheets 10 bounding a laminar volume which is partitioned to form channels 11 with a bore of approximately 1.5 x 1.3 cm. The partitioning is staggered to form a serpentine flow path with a continuous path length in the photostage of 29m, occupying an area of 0.49m . The acrylic material used absorbs radiation in the uv region of the spectrum.

Thus the desired algal culture is introduced via the degasser 3, together with any nutrients or liquid necessary, and is pumped around the system to be joined by the gas supply. The whole mixture is then channelled through the illuminated photostage in a turbulent manner, as the channels changed direction abruptly. It is regulated as many times as required and samples may be drawn off via the degasser.

A polycarbonate material which does not absorb radiation in the visible region of the spectrum may be substituted for the acrylic material. This may be sterilised using an autoclave unit whereas acrylic can be sterilised in situ by passing a sterilising agent around the loop.

Algae are not the only organisms which can be used in this system - yeast or bacterial cultures may also be introduced to the system. Non-photosynthetic micro-organisms, particularly for growth on gaseous substrates where long gas/liquid contact times are desirable, may also be used.

The flat surface of the photostage allows uniform irradiation of the culture which together with the regular changes in direction of the channels produces uniform conditions throughout. It incorporates controlled flow, long light residence times and efficient mixing. The photobioreactor is a self-contained, inexpensive unit which could be used singly or in a multi-unit configuration. The novel design does not rely upon the interconnection of many lengths of glass or silicone tubes.

This low cost reactor offers several advantages over conventional culture systems; 1) Novel construction from low cost materials.

2) The light climate is defined and easily measured.

3) Maximises light utilisation since all the light is normally incident on the algal culture.

4) Combines the high surface area to volume ratio of tubular systems with compact and simple construction.

5) Reduces the number of light sources required to achieve high surface irradiance due to (4).

6) Excellent gas exchange characteristics.

7) Facilitates the measurement of time-dependent parameters at points along the channel length.

Possible applications for the multi-pass fermenter under development are: 1) The continuous or batch culture of photosynthetic microorganisms.

2) The continuous or batch culture of organisms on gaseous substrates.

3) Biological gas stripping e.g. carbon dioxide 4) Life support systems for prolonged space flight.

5) As an educational or research and development apparatus or tool in schools and universities.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1. Photobioreactor apparatus comprising a laminarium which is internally partitioned to provide a fluid pathway between an inlet and an outlet thereof, a light source for illuminating a face of the laminarium, and means for providing fluid flow from the inlet to the outlet of the laminarium.

2. Apparatus for providing fluid mixing, comprising a laminarium which is internally partitioned to provide a fluid pathway between an inlet and an outlet thereof, the partitioning defining a series of channels of which adjacent channels have an apertured common wall, the apertures being disposed at opposite end portions of the wall so that fluid passing from one channel to an adjacent channel undergoes a change of direction of substantially 180 degrees.

3. Apparatus as defined in any one of the preceding Claims, in which the laminarium comprises two flat transparent plates which are sealed to provide a fluid-tight container and internally partitioned to provide a non-unidirectional pathway for fluid between the inlet and the outlet.

4. Apparatus as defined in any one of the preceding Claims wherein said pathway is designed to produce an even turbulent flow by providing 180 degree turns for fluid flowing along it.

5. Photobioreactor apparatus as defined in Claim 1, wherein the flow-producing means comprises a low-shear-force pump system.

6. Apparatus as defined in any one of the preceding Claims, wherein said fluid comprises an entrained gas, nutrients and micro-organisms in a carrier liquid.

7. Apparatus as defined in Claim 1, wherein the light source is a high pressure sodium lamp or other lamp which emits light of 400-700nm wavelength.

8. Apparatus as defined in any one of the preceding Claims, wherein the laminarium is composed of plastics sheet which does not absorb radiation in the visible region of the spectrum.

9. Apparatus as defined in any one of the preceding Claims, wherein the apparatus is modular to enable units of varying capacities to be built up.

10. Apparatus as defined in any one of the preceding Claims, further comprising instruments and monitoring controls and facilities for the addition of substances to the apparatus.

11. Apparatus as defined in any one of the preceding Claims wherein a heater, a temperature sensor and pH electrode are included.

12. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.