12 August 2009

Fueling the future with algae

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 time.

One of the catches, though, is to find an energy source that does not take away from the food supply. That is where the cultivation of microalgae may come in. By developing closed photo-bioreactors and novel cell disruption methods energy production from microalgae may be close at hand, researchers said.

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

Who needs oil? Tomorrow’s energy supply may come from microalgae.

Apart from CO₂-neutral closed loop management, algae have another advantage: Industrial CO₂ emissions may be a “resource,” as algae grow faster at high CO₂ 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% oil usable for energy production,” said Professor Clemens Posten, who directs this research activity at the Karlsruhe Institute of Technology (KIT) Institute of Life Science Engineering in Germany. As the algae may also exist in arid, dry areas not suited for agriculture, there is hardly any competition with agricultural areas.

Presently, algae production occurs 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 photobioreactors,” he said. “Our plants convert solar energy into biomass, the efficiency being five times higher than that in open ponds.” In the usual photo-bioreactors, researchers arrange the plates vertically. “Every alga sees a little bit less light, but the plant is operated at increased efficiency,” he said. Designs now 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 10% of the incident sunlight intensity. Posten said the remaining fraction would just be a waste, if light management in the photobioreactor would not be optimum. Posten said the Sahara offers just twice as much sun as Central Europe. But there, the reactor contents would have to undergo cooling. Other advantages of the closed system are drastic savings of water and fertilizers. Double use of algae for the production of food or fine chemicals and subsequent energy production from the residual biomass may also be conceivable.

While Posten does his research, Dr. Georg Müller, head of KIT’s Pulsed Power Technology Division, studies the decomposition of plant cells of olives, grapes, apples, sugar beets, and terrestrial energy plants.

“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,” Müller said. “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.”

Cooperation of both working groups now aims at bundling the existing know-how, with starting funds provided by the KIT Energy Center. The goal is to establish a KIT “Algae Platform” for energy production from microalgae. In the medium term, the researchers will build pilot-scale plants on the northern KIT campus. “This will represent a major node in the presently rather rapid networking of algae biotechnology,” Posten said. To make energy production from algae economically efficient, it needs to focus on minimizing investment and operation costs of photobioreactors 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%) could convert into other energy carriers like hydrogen or methane by means of the hydrothermal gasification process under development at KIT.

For related information, go to www.isa.org/manufacturing_automation.