The Power of Microalgae – A Trip to a Biobased Micro-World

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Gerhard Schubert GmbH - Verpackungsmaschinen

Elementar Analysensysteme GmbH

EDL Anlagenbau Gesellschaft mbH

All open pond systems are prone to contamination. Although unwanted organisms can be excluded by operating at high salinities or adjusting pH, this in turn limits the range of microalgae species to be cultivated.

For more sensitive applications, closed photobioreactors are the method of choice. As incoming light cannot be dispersed by mixing and steep light gradients occur between the surface and the deeper layers of the suspension, a high surface-volume ratio is one of the important design criteria for photobio­reactors.

Light Makes the Difference

Simply turning up the light is not feasible as the light uptake by algae is limited and higher intensity might even have negative effects on metabolic performance. Materials for photobioreactors need to be translucent without losing transparency over time, robust and UV-resistant, allow for the construction of long tubes or large plates by thermoforming, should preferably prevent the build-up of biofilms on the inner surface, and as a lot of material is required, cost is a major issue.

Schott offers a broad range of borosilicate glass equipment including U-bends and couplings to allow for the construction of large reactor systems. Plastics typically used are low density and high density polyethylene, rigid acrylic, and polyvinyl chloride. Gicon emphasizes that its “Christmas tree” bioreactors are made of a new material blocking UV radiation while preventing biofouling.

Two Reactor Designs, One Common Goal

Both plate and tubular reactors, the main types currently in use, provide thin layers of algae suspension, thus minimizing the light gradients. A further “dilution” is accomplished by keeping the suspension in constant motion either by pumping or the “air-lift” principle. As CO₂ needs to be supplied anyway, mixing the suspension by introducing gas bubbles sounds very logical. However, bubble size and dispersion need to be controlled and closely monitored, because the gas-liquid mass transfer otherwise may limit the productivity.

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