Cultivation of heterotrophic algae on enzymatically hydrolyzed municipal food waste

Municipal food waste is a unique source of biomass but with great variances in occurrence and properties. Economic, cultural and biophysical factors influence its composition. Therefore, investigation of novel applications requires experiments with real materials obtained from industrial processings, rather than tests with self-composed waste samples having a highly controlled composition. In this study, cultivation of the heterotrophic algae Chlorella sorokiniana on enzymatically hydrolyzed food waste was investigated. Municipal food waste of industrial origin hydrolyzed in a 1000-l stirred tank reactor led to an increase in glucose content from approximately 10 g l−1 to 50 g l−1 within 6 h. Chlorella sorokiniana grown on this medium exhibited an optical density of 32 corresponding to algae biomass concentration of approx. 9.5 g l−1 at a glucose concentration of 20 g l−1. The maximum biomass concentration was reached within four days under significant consumption of carbon and nitrogen. Approximately 30% of the carbon and 25% of the nitrogen were used, whereby glucose and acetic acid were the main carbon compounds consumed by C. sorokiniana in a diauxic manner. Other molecules like lactic acid were not metabolized, suggesting their conversion to biogas in a cascade approach. Nutrients present in the cultivation medium of C. sorokiniana are beneficial for subsequent anaerobic digestion. With a protein content of 37.8% and a lipid content of 26.4%, the composition of algae biomass was comparable to biomass grown on synthetic and other waste derived media.