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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.

Grass and silage presscakes from various types of raw materials were hydrolyzed with dilute acid at moderate conditions to recover hemicellulose-derived sugars. Extracting the material with cold water prior to hydrolysis significantly increased the yield. The poor performance without extraction was due to the high buffer capacity of the material. The best results were obtained with extracted grass and silage from a permanent pasture and extracted clover/grass silage. The highest observed sugar yield was 16.43 g/100 g dry-matter, which represents approximately 25% of the available sugars and 60% of the hemicellulose fraction. Including the soluble sugar oligomers, the yields were even higher (up to 20 g/100 g dry-matter). A statistical experiment design with extracted clover/grass silage was performed to estimate the effects of temperature, time, and dry-matter concentration. Acid and dry-matter concentration had the highest effect on sugar yield, whereas temperature and acid concentration were mainly responsible for forming sugar degradation products. These findings agree with recent kinetic theories. Yields in this experiment were comparable to those of other lignocellulosic materials.