Cultivation of green microalgae in the air

Microalgae are cultivated for a broad range of applications, from food to cosmetics, and from biofuel to biotechnology. While usually grown in suspension in bioreactors, this technique poses several challenges regarding processing, especially with respect to illumination, and harvesting. Alternatively, some microalgae can be cultivated on suitable substrates in the form of a biofilm to solve the problem of harvesting. In this case, however, a constant and sufficient light intensity on the microalgae without overheating the medium is still problematic. A previous project has thus investigated the possibility of letting green microalgae grow on a suitable substrate outside a bioreactor, i.e., in the air, under regular wetting, which would improve illumination and ease harvesting. Here, we report the growth of the green microalgae Chlorella vulgaris, which is often used as dietary supplement or for cosmetics on textile substrates outside a bioreactor. We show how the first setup was improved in terms of fixing the textile, ensuring regular watering and increasing the available light on the substrates. Our comparison between C. vulgaris grown on identical textile fabrics in a bioreactor, in a petri dish, and in the air show that the latter leads to a significantly higher microalgae growth than both the more common methods, and that cultivation of microalgae at the air should thus be optimized further in future studies.