During the last decade algae biomass production increased constantly. On the one hand the elimination of carbondioxid has been tested on the other hand the production of biomass for nutrition and feeding as well as products for cosmetic industries are the most growing markets. Whereas elimination techniques for carbondioxid need no sterile and algae-monoculture conditions these are required in nutrient and healthcare productions due to the risk of infections and undesired side effects. For all algae growing techniques the use of fossil resources is state of the art. Phosphorus, potassium and micronutrients are mined while nitrogen is produced by the Haber-Bosch method consuming a lot of fossil energy during the production and distribution. The economic benefit of the carbondioxid capture or the nutrient production by algae is reduced due to the use of fossil energy.
In a new project the Department of Waste and Resource Management of the Technical University of Braunschweig is developing a sustainable and holistic concept to substitute the amount of fossil nutrients by using output material after an anaerobic digestion.
Fermentation output material for example of biowaste digestion includes all essential macro and micro nutrients for algae growth, because it contains up to 95% vegetable components of which only carbon is significantly released during the fermentation process. Carbon is released in form of methane and carbondioxid. Also a small amount of nitrogen and sulfur is released by ammoniac resp. hydrogensulfide. Good results of enhanced vegetable growth are known from applications of fermentation output material in agriculture. The innovative approach is to use this fermentation output also in algae cultivation systems. In this connection the sterile cultivation of algae for nutrients and cosmetics is a major challenge. The fermentation output material has to be separated from bacteria and other large organic compounds. If it is also necessary to eliminate the organic load is not known yet. Some algae are able to metabolize organic molecules and live mixothrophic by using photosynthetic as well as the respiratory metabolic pathway. The elimination of the organic load could depend on which algae are used in the process. But for the carbondioxid capture with algae it may be enough to filtrate the fermentation output to retard large organic and inorganic particles.
One further aim of this project is to improve the resource efficiency of fermentation facilities by optimizing in-process material flows. The heat of the CHP-plant could heat up the algae culture and carbondioxid could be used to feed the algae, while the cleaned and prepared fermentation output could maintain most of the required nutrients. Leftovers of algae proceeding treatments could be collected and reinserted in the fermentation process to close the nutrient and carbon loop. Difficulties due to unsterile conditions and nutrient composition will bind most investigation efforts to establish a sustainable algae production.