Photobioreactor

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Photobioreactor in general

A bioreactor is an installation for the production of microorganisms outside their natural but inside an artificial environment. The prefix “photo” particularly describes the bio-reactor's property to cultivate phototrophic microorganisms, or organisms which grow on by utilizing light energy. These organisms use the process of photosynthesis to build their own biomass from light and CO2. Members of this group are Plants, Mosses, Macroalgae, Microalgae, Cyanobacteria and Purple Bacteria. Key objective of a photobioreactor, or PBR, is the controlled supply of specific environmental conditions for respective species. Thus, a photobioreactor allows much higher growth rates and purity levels than anywhere in natural or habitats similar to nature. Basically, photobioreactors can grow phototropic biomass even from nutrient polluted waste water and from flue gas carbon dioxide.

Moss photobioreactor to cultivate mosses like Physcomitrella patens at laboratory scales

Open versus closed systems

Open raceway pond

First approach for the controlled production of phototropic organisms was and still is a natural open pond or artificial raceway pond. Therein, the culture suspension, which contains all necessary nutrients and CO2, is pumped around in a cycle, being directly illuminated from sunlight via the liquid’s surface. This construction principle is the simplest way of production for phototrophic organisms. But due to their depth up to 0,3m and the related reduced average light supply, open systems only reach limited areal productivity rates. In addition, the consumption of pumping energy is relatively high, as high amounts of water containing low product concentration have to be processed.

Grounds in Areas on earth with a dense population are expensive, while water is rare in others. Using open technologies causes high losses of water due to evaporation into the atmosphere. Hence, since the 1950's several approaches have been conducted to develop closed systems, which theoretically provide higher cell densities of phototrophic organisms and therefore a lower demand of water to be pumped. In addition, closed construction avoids system-related water losses and the risk of contaminations trough landing water birds or dust is minimized.[1]

Photobioreactor types

All modern photobioreactors have tried to balance between a thin layer of culture suspension, optimized light application, low pumping energy consumption, CAPEX and microbial purity. Many different systems have been tested, but only a few approaches were able to perform at an industrial scale.[2]

Redesigned laboratory fermenters

The simplest approach is the redesign of the well-known glass fermenters, which are state of the art in many biotechnological research and production facilities worldwide. The moss reactor for example shows a standard glass vessel, which is externally supplied with light. The existing head nozzles are used for sensor installation and for gas exchange.[3] This type is quite common in laboratory scale, but it has never been established in bigger scale, due to its limited vessel size.

Tubular photobioreactors

Tubular glass photobioreactor

Made from glass or plastic tubes, this photobioreactor type has succeeded within production scale. The tubes are oriented horizontally or vertically and are supplied from a central utilities installation with pump, sensors, nutrients and CO2. Tubular photobioreactors are established worldwide from laboratory up to production scale, e.g. for the production of the carotenoid Astaxanthine form the green algae Haematococcus pluvialis or for the production of food supplement from the green algae Chlorella vulgaris. These photobioreactors take advantage from the high purity levels and their efficient outputs. The biomass production can be done at a high quality level and the high biomass concentration at the end of the production allows energy efficient downstream processing. Due to the recent prices of the photobioreactors, economically feasible concepts today can only be found within high-value markets, e.g. food supplement or cosmetics.[4]

The advantages of tubular photobioreactors at production scale are also transferred to laboratory scale. A combination of the mentioned glass vessel with a thin tube coil allows relevant biomass production rates a laboratory research scale. Being controlled by a complex process control system the regulation of the environmental conditions reaches a high level.[5]

Christmas tree photobioreactor

Christmas tree reactor

An alternative approach is shown by a photobioreactor, which is built in a tapered geometry and which carries a helically attached, translucent double hose circuit system.[6] The result is a layout similar to a Christmas tree. The tubular system is constructed in modules and can theoretically be scaled outdoors up to agricultural scale. A dedicated location is not crucial, similar to other closed systems, and therefore non-arable land is suitable as well. The material choice shall prevent biofouling and ensure high final biomass concentrations. The combination of turbulences and the closed concept are ought to reach a clean operation and a high operational availability.[7]

Plate photobioreactor

Plastic plate photobioreactor

Another development approach can be seen with the construction based on plastic or glass plates. Plates with different technical design are mounted to form a small layer of culture suspension, which provides an optimized light supply. In addition, the more simple construction when compared to tubular reactors allows the application of cheap plastic materials. From the pool of different concepts e.g. meandering flow designs or bottom gassed systems have been realized and shown good output results. Some unsolved issues are material life time stability or the biofilm forming. Applications at industrial scale are bordered by the limited scalability of plate systems, additionally.[8]

In April 2013, the IBA in Hamburg, Germany, a building with an integrated glass plate photobioreactor facade has been commissioned.[9]

Foil photobioreactor

The pressure of marked prices has led the development of foil-based photobioreactor types. The cheap PVC or PE foils are mounted to form bags or vessels which cover the algae suspension and expose it to the light. The pricing ranges of photobioreactor types have been enlarged with the foil systems. It has to be kept in mind, that these systems have a limited sustainability as the foils have to be replaced from time to time. For full balances, the investment for required support systems has to be calculated as well.

Outlook of photobioreactor development

The discussion around Microalgae and their potentials in CO2 sequestration and biofuel production has caused high pressure on developers and manufacturers of photobioreactors.[10] Today, none of the mentioned systems is able to produce phototrophic microalgae biomass on a price level, which is able to compete on the crude oil market. New approaches test e.g. dripping methods to produce ultra-thin layers for maximal growth with application of flue gas and waste water. Further on, much research is done worldwide on genetically modified and optimized microalgae. The expected influence of increasing crude oil price on a successful microalgae breakthrough is still to come.

See also

External links

References

  1. ↑ Lane. G. (2013). Up To Speed On: Algae Biofuels 1. Smashwords. pp. 1–9. ISBN 9781301351961. 
  2. ↑ Submariner Project: Photobioreactor design principles
  3. ↑ Eva Decker, Ralf Reski (2008): Current achievements in the production of complex biopharmaceuticals with moss bioreactors. Bioprocess and Biosystems Engineering 31(1), 3-9 term=Current+achievements+in+the+production+of+complex+biopharmaceuticals+with+moss+bioreactors
  4. ↑ Pulz. O. (2001). Photobioreactors: production systems for phototrophic microorganisms 57. pp. 287–293. 
  5. ↑ Algae Observer: IGV Biotech Presents Novel Algae Screening System
  6. ↑ F. Cotta, M. Matschke, J. Großmann, C. Griehl und S. Matthes; “Verfahrenstechnische Aspekte eines flexiblen, tubulären Systems zur Algenproduktion” (Process-related aspects of a flexible, tubular system for algae production); DECHEMA 2011
  7. ↑ Großmann Ingenieur Consult GmbH: [http://www.gicon.de/news-and-jobs/aktuelles/nachrichtendetails/article/aufbau-eines-biosolarzentrums-in-koethen.html?tx_ttnews[backPid]=143&cHash=8ed808ad8ed97c41db87cb397bd1a625 Aufbau eines Biosolarzentrums in Köthen], 6. März 2011.
  8. ↑ Handbook of microalgal culture 2nd edition 1. Blackwell Science Ltd. 2013. ISBN 978-0-470-67389-8. 
  9. ↑ art-magazin.de: IBA Hamburg - Opening, Algaehouse, Worldquartier
  10. ↑ Spolaore. P. et al. (2006). "Commercial Applications of Microalgae". Journal of Bioscience and Bioengineering 102: 87–96. 
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