At present, biofuels such as ethanol and biodiesel are produced primarily from organic raw materials such as cereal starches or rapeseed oil. This means that arable land is no longer available for the production of food. Such competition for use can be circumvented by the cultivation of microalgae. These organisms also offer a wide range of other advantages compared to higher plants, including greater yields per unit area and lower water demand. A number of microalgae are able to accumulate starch as a storage product when nutrients are limited. The German Federal Ministry of Food and Agriculture (BMEL) has funded a project in which algal biomass is produced in closed photobioreactors and starch, the main component of these algae, is used for the production of ethanol.
The second major component of these starch-rich algae are proteins. To increase the value of the production chain, we are also investigating whether the algal proteins can be used as a constituent of culture media for the production of ethanol from cereal starches or as a feed ingredient. For closing loops between ethanol fermentation and algae production, two waste streams are utilizable: Fermentation off-gas can be used as a cheap, high-quality source of CO2 for photosynthetic algae production. The second loop is to use the liquid digestate of digested fermentation mash and algae residues as ammonium- and phosphate-rich nutrient source for algae production. This biorefinery concept enables utilization of the entire biomass and increases the value of the algal biomass.