• A combination of the mentioned glass vessel with a thin tube coil allows relevant biomass production rates at laboratory research scale.

  • [4] Though closed systems have better productivity compared to open systems due to the advantages mentioned, they still need to be improved to make them suitable for production
    of low price commodities as cell density remains low due to several limiting factors.

  • Since the geometry of the reactor integrates one or more down chambers that transport the culture from the top area around to the bottom area, the culture is constantly homogeneously
    supplied with the photosynthesis-relevant factors, thus achieving a high productivity.

  • Plates with different technical design are mounted to form a small layer of culture suspension, which provides an optimized light supply.

  • The rising of the air bubbles in the specially shaped plate reactor creates a homogeneous mixing of the culture and, on the one hand, a very long residence time of the CO2-air
    mixture and thus a very good CO2 input (degree of utilization) into the culture.

  • [5] All modern photobioreactors have tried to balance between a thin layer of culture suspension, optimized light application, low pumping energy consumption, capital expenditure
    and microbial purity.

  • This new procedure reduces by a factor of up to one hundred the amount of liquid needed for operation compared to the current technology, which cultivates algae in suspensions.

  • On the other hand, the homogeneous mixing ensures a very good light input of the grow-light LEDs usually installed on both sides of the system and thus a very high utilization
    of the light energy.

  • [6][5] The accumulation of photosynthetic oxygen with growth of microalgae in photobioreactors is also believed to be a significant limiting factor; however, it has been recently
    shown with the help of kinetic models that dissolved oxygen levels as high as 400% air saturation are not inhibitory when cell density is high enough to attenuate light at later stages of microalgal cultures.

  • Using open technologies also result in losses of water due to evaporation into the atmosphere.

  • The combination of turbulence and the closed concept should allow a clean operation and a high operational availability.

  • A photobioreactor (PBR) refers to any cultivation system designed for growing photoautotrophic organisms using artificial light sources or solar light to facilitate photosynthesis.

  • [9] This type is quite common in laboratory scale, but it has never been established in bigger scale, due to its limited vessel size.

  • However, they offer an insufficient control of reaction conditions due to their reliance on environmental light supply and carbon dioxide, as well as possible contamination
    from other microorganisms.

  • 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.

  • Raceway ponds are still commonly used in industry due to their low operational cost in comparison to closed PBRs.

  • Simultaneously, a larger light quantity can be exploited in order to improve photoconversion efficiency.

  • [7] Many different systems have been tested, but only a few approaches were able to perform at an industrial scale.

  • meandering flow designs or bottom gassed systems have been realized and shown good output results.

  • A dedicated location is not crucial, similar to other closed systems, and therefore non-arable land is suitable as well.

  • This has a positive impact on the necessary energy input and reduces material costs at the same time.


Works Cited

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