Investigation of the carbon footprint of the cultivation of the heterotrophic microalga Galdieria sulphuraria on hydrolyzed straw and digestate

The purpose of this study was to assess the carbon footprint of a production process for 1 kg of dry algal biomass powder (Galdieria sulphuraria) cultivated on straw and digestate as carbon and nitrogen sources, respectively, for further optimization. It was examined whether and to what extent the use of straw and digestate can reduce the environmental impact (global warming and resource efficiency) and how this can result in a more sustainable use of resources. The investigated process was compared to a process where conventional glucose serves as a carbon source. The findings demonstrate that the hydrolysis of straw results in a worst environmental impact compared to the conventional process. Hydrolysis alone releases approx. 8 kg CO2-eq., which is predominantly caused by the energy demand. The results of this study therefore clearly revealed that the hydrolysis of straw needs to be optimized to foster a sustainable use of agriculture residues.