“Green” energy from algae

Tomorrow's energy suppliers may be microalgae under the microscope. Image credit: Florian Lehr
Date:6 August 2009 Tags:, ,

In view of the shortage of petrochemical resources and climate change, development of CO2-neutral sustainable fuels is one of the most urgent challenges of our times. Energy plants like rape or oil palm are being discussed fervently, as they may also be used for food production. Hence, cultivation of micro-algae may contribute decisively to tomorrow’s energy supply. For energy production from micro-algae, scientists from Karlsruhe Institute of Technology (KIT) are developing closed photo-bioreactors and novel cell disruption methods.

Micro-algae are monocellular, plant-like organisms engaged in photosynthesis and converting carbon dioxide into biomass. From this biomass, both potential resources and active substances as well as fuels like biodiesel may be produced. While growing, algae take up the amount of CO2 that is later released again when they are used for energy production. Hence, energy from algae can be produced in a CO2-neutral manner contrary to conventional energy carriers.

Apart from CO2-neutral closed loop management, algae have another advantage: industrial CO2 emissions may be used as a “re-source”, as algae grow faster at high carbon dioxide concentrations and, hence, produce more biomass for energy production.

However, this is not their only advantage: “Compared to land plants, algae produce five times as much biomass per hectare and contain 30 to 40 per cent oil usable for energy production”, says Professor Clemens Posten, who directs this research activity at the KIT Institute of Life Science Engineering. As the algae may also be cultivated in arid areas not suited for agriculture, there is hardly any competition with agricultural areas. There, however, closed systems are required.

Presently, algae are being produced in open ponds in southern countries of relatively small productivity. This is where Posten’s new technology starts. “In terms of process technology, our approach is completely different, as we are working with closed photo-bioreactors”, underlines the scientist. “Our plants convert solar energy into biomass, the efficiency being five times higher than that in open ponds.” The plates in usual photo-bioreactors are arranged vertically. “Every alga sees a little bit less light, but the plant is operated at increased efficiency”, emphasises the biologist and electrical engineer. Modern designs under investigation will find more intelligent ways to light distribution.

Consequently, algae production does not only work in countries with an extremely high solar irradiation. Most algae need a maximum of ten per cent of the incident sunlight intensity. According to Posten, the remaining fraction would just be wasted, if light management in the photo-bioreactor would not be optimum. Posten points out that the Sahara offers just twice as much Sun as Central Europe. But there, the reactor contents would have to be cooled. Other advantages of the closed system are drastic savings of water and fertilisers. Double use of algae for the production of food or fine chemicals and subsequent energy production from the residual-biomass may also be conceivable.

Posten’s institute hosts one of the two KIT working groups focusing on research in the field of algae biotechnology. “As far as the development of photo-bioreactors is concerned, we are among the three locations worldwide, where considerable progress is being achieved in both process technology and biology”, explains Posten.

Research conducted by the Institute for Pulsed Power and Microwave Technology on the northern campus of KIT focuses on extracting the valuable constituents of the algae biomass by an electric pulsed treatment. So far, Dr Georg Mller, head of this institute’s Pulsed Power Technology Division, has studied the decomposition of plant cells of olives, grapes, apples, sugar beets, and terrestrial energy plants in co-operation with partners from research and industry.

“It is our objective to develop new economically efficient and sustainable extraction methods to obtain a maximum amount of cell constituents from the algae that can be used for energy production”, says Mller. “The plant cells are exposed to a high electric field for a very short term. This causes a perforation of the cell membrane and the constituents are released.”

The plan is to establish a KIT “Algae Platform” for energy production from micro-algae. To make energy production from algae economically efficient, the focus will be on minimising investment and operation costs of photo-bioreactors and on developing highly-efficient processes for the harvesting and decomposition of algae.

To close the cycle for the complete use of algae biomass for energy production, KIT researchers even go another step forward. The biomass remaining after extraction (60 – 70 per cent) is planned to be converted into other energy carriers like hydrogen or methane by means of the hydrothermal gasification process developed on the northern campus.

Helmholtz Association of German Research Centres

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