Energetic use of microalgae biomass

Microalgae offer a high protein, carbohydrate or lipid content, depending on growth conditions. Fast growing microalgae have a high protein content with a favorable distribution of essential amino acids. Many microalgae have the ability to produce substantial amounts (e.g. 20 – 70 percent dry cell weight) of triacylglycerols (TAGs) or starch as a storage product when under stress and growing slowly, and simultaneously high light intensities are available.

In screening tests at the Fraunhofer IGB various algae were tested for their ability to produce storage lipids under the conditions of a flat panel airlift (FPA) reactor. Lipid content increased up to 70 percent of dry cell weight and starch contents up to 60 percent are achievable. Under these conditions mainly monounsaturated fatty acids with 16 and 18 carbons were synthesized. Lipid productivity was not specific for a certain strain but depended largely on the light intensity per cell.

Starch can be used as sugar feedstock for miscellaneous biotechnological processes for biofuels or biobased chemicals. The Fraunhofer IGB has developed a two-stage process for production of starch-rich microalgae, which has been established under outdoor conditions as well as scaled up to pilot scale in the range of 100 kg dry biomass.

© Fraunhofer IGB

Closing cycles of CO2 and nutrients between algae production and anaerobic digestion

Sustainability by recycling of nutrients

Fraunhofer IGB is developing sustainable, resource-efficient and ecologically friendly production processes for the production of valuable products and the energetic use of microalgae combining the use of flue gas from combustion processes or offgas from biotechnological fermentations like bioethanol as the carbon source (combined heat and power stations with biogas or natural gas). Our intention first is to recover valuable products from microalgae followed by digestion of the residual biomass to biogas. Carbon dioxide is recycled to the algal cultivation process. For a positive net energy balance the use of waste gas as the carbon source is a basic requirement for photoautotrophic microalgae biomass production. Additionally, recycling of nitrogen and phosphorous from anaerobic digestion effluents is possible.

Reference projects

 

 

Algal starch biorefinery

Duration: December 2012 – November 2015

Biofuels such as ethanol and biodiesel are produced primarily from crops. The competition for arable land can however be circumvented by using microalgal biomass for the production of biofuels. In this project, algal biomass is therefore produced in closed photobioreactors and starch, the main component of these algae, is used for the production of ethanol.

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Lipid-rich algae biomass as a regenerative energy-source

Currently, biofuels are mainly produced from plant-based raw materials, for example biodiesel from rapeseed or palm oil. Biodiesel from microalgae represents an alternative to present-day biofuels. Fraunhofer IGB has operated an outdoor pilot plant to characterize the lipid production process with the microalgae Chlorella vulgaris. Making use of the results generated under outdoor conditions, the high lipid content of the biomass can be selectively adjusted by means of process management. A defined, consistent quality of the biomass with high lipid content provides the ideal basis for the development of a downstream process to obtain biodiesel from algae.

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DeDeBio – Development and validation of design tools for design of decentralized biomass power plant concepts for combined heat and power generation

Mathematical models for the design of decentralized biomass power plant concepts are being developed as part of the research project DeDeBio. To generate biogas, both a thermal wood gasification process (DLR) and also a biological process, with algae as the source material, are to be examined. Besides the development of tools for CFD-based (computational fluid dynamics) combustor design, the focus is on the modeling of the biogas reactor and the wood gasifier. 

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