Josue Gonzalez-Camejo

Microalgae biomass as alternative protein source from residual CO2 streams (SEMPRE-BIO project)

ANAEROBIC DIGESTION (AD) is a circular process that obtains renewable biofuels (biogas or biomethane) from organic wastes in a cost-effective way, thus promoting the energy transition. However, the production of a single product (energy source) is no longer considered sustainable in modern AD plants. During AD, residual CO2 and digestates are produced in large quantities. It is thus necessary to transform AD plants into biorefineries where all the products and by-products are exploited to maximise the economic profitability and sustainability of the process.
MICROALGAE cultivation is an emerging technology that could be a sustainable solution to recover nutrients and mitigate CO2 of AD processes, closing carbon and nutrient loops. The produced microalgae biomass has the potential to be used as a livestock feed ingredient, so that they could partially replace conventional sources of proteins such as soybean (alternative protein). Microalgae are intensive organisms that grow 10-50-fold more efficiently than terrestrial plants, being considered as “super-food”.
Preliminary results have shown that green microalgae strains (Chlorella vulgaris, Parachlorella kessleri, and Tetradesmus obliquus) can produce up to 50% dry weight (DW) of proteins, containing higher content of essential amino acid than soybean and meeting most nutritional requirements for farm animals. Even this solution is technically feasible, the origin of digestate entails legal barriers that may limit its use as a feedstock for feeding. The application of the end-of-waste criteria when the digestate comes from the digestion of food processing wastes could help to overcome this barrier.