Process development for the economically feasible production of medium value products from microalgae

In this project we aimed to adapt algae biotechnology for the production of food and feed components by specific process optimization. We succeeded to steer the macromolecular cell composition of photoautotrophic microorganisms by using different process strategies from lab to pilot scale.

Specifically, we investigated how the macromolecular composition of the microalgae Chlorella vulgaris can be changed by varying cultivation parameters, such as light intensity and substrate concentrations. In these experiments, total protein contents between 20 % and 60 % and fatty acid contents between 20 % and 40 % could be achieved.

To translate insights from lab scale experiments to pilot scale, outdoor cultivation was performed using a 230 L plate photobioreactor in repeated batch cultivation mode. Changing conditions during day and night cycles, which result in changes of photosynthetic and respiratory activities of the microalgae cells, could be overcome by using an automated controller.

In a second series of experiments in continuous reactor systems, nitrogen-saturated and nitrogen-limited growth was studied in the microalgae Nannochloropsis limnetica , the diatom Phaeodactylum tricornutum as well as the cyanobacterium Synechocystis sp.. Nitrogen deprivation led to an accumulation of storage compounds in all tested strains, whereas sufficient nitrogen supply resulted in accumulation of proteins. Furthermore, the yield of essential amino acids or saturated fatty acids could be shifted within the range of stoichiometric minima and maxima. Hence, the objective of a targeted production of physiologically valuable substances for the food and feed industry is getting closer.

Tailor-made process strategies can help to realize economically feasible production of microalgae products. Local production of microalgae proteins could in future substitute the import of conventional protein sources, for instance soybean.