'Green' energy from algae6 August 2009

Tomorrow's energy suppliers may be microalgae underthe microscope. Credit: Photo by: Florian Lehr

In view of the shortage of petrochemical resourcesand climate change, development of CO2-neutralsustainable fuels is one of the most urgentchallenges of our times. Energy plants like rape oroil palm are being discussed fervently, as they mayalso be used for food production. Hence,cultivation of microalgae may contribute decisivelyto tomorrow's energy supply. For energyproduction from microalgae, Karlsruhe Institute ofTechnology scientists (Germany) are developingclosed photo-bioreactors and novel cell disruptionmethods.

Microalgae are monocellular, plant-like organismsengaged in photosynthesis and converting carbondioxide (CO2) into biomass. From this biomass,both potential resources and active substances aswell as fuels like biodiesel may be produced. Whilegrowing, algae take up the amount of CO2 that islater released again when they are used for energyproduction. Hence, energy from algae can beproduced in a CO2-neutral manner contrary toconventional energy carriers.

Apart from CO2-neutral closed loop management,algae have an-other advantage: Industrial CO2

emissions may be used as a "re-source", as algaegrow faster at high carbon dioxide concentrations

and, hence, produce more biomass for energyproduction.

However, this is not their only advantage:"Compared to land plants, algae produce five timesas much biomass per hectare and contain 30 to40% oil usable for energy production", saysProfessor Cle-mens Posten, who directs thisresearch activity at the KIT Institute of Life ScienceEngineering. As the algae may also be cultivated inarid i.e. dry, areas not suited for agriculture, there ishardly any competition with agricultural areas.There, however, closed systems are required.

This is a newly developed plate reactor for an optimumlight management in the cultivation of microalgae as asource of energy at the Karlsruhe Institute of Technology.Credit: Photo by: Florian Lehr

Presently, algae are being produced in open pondsin southern countries of relatively small productivity.This is where Posten's new technology starts. "Interms of process technology, our approach is

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completely different, as we are working with closedphotobioreactors", underlines the scientist. "Ourplants convert solar energy into biomass, theefficiency being five times higher than that in openponds." The plates in usual photo-bioreactors arearranged verti-cally. "Every alga sees a little bit lesslight, but the plant is operated at increasedefficiency", emphasizes the biologist and electricalengineer. Modern designs under investigation willfind more intelligent ways to light distribution.

Consequently, algae production does not only workin countries with an extremely high solar irradiation.Most algae need a maximum of ten percent of theincident sunlight intensity. According to Posten, theremaining fraction would just be wasted, if lightmanagement in the photobioreactor would not beoptimum. Posten points out that the Sahara offersjust twice as much sun as Central Europe. Butthere, the reactor contents would have to becooled. Other advantages of the closed system aredrastic savings of water and fertilizers. Double useof algae for the production of food or fine chemicalsand subsequent energy production from theresidualbiomass may also be conceivable.

Posten's institute hosts one of the two KIT workinggroups focusing on research in the field of algaebiotechnology. "As far as the development ofphotobioreactors is concerned, we are among thethree locations worldwide, where considerableprogress is being achieved in both processtechnology and biology", explains Posten.

The stop of his research area on the southern KITcampus marks the starting point of researchconducted by the Institute for Pulsed Power andMicrowave Technology on the northern campus ofthe KIT. Here, it is focused on extracting thevaluable constituents of the algae biomass by anelectric pulsed treatment. So far, Dr. Georg Müller,head of this institute's Pulsed Power TechnologyDivision, has studied the decomposition of plantcells of olives, grapes, apples, sugar beets, andterrestrial energy plants in cooperation withpartners from research and industry. Partly, large-scale facilities were constructed. "It is our objectiveto develop new economically efficient andsustainable extraction methods to obtain amaximum amount of cell constituents from the

algae that can be used for energy production", saysMüller. "The plant cells are exposed to a highelectric field for a very short term. This causes aperforation of the cell membrane and theconstituents are released."

Cooperation of both working groups now aims atbundling the existing know-how, with starting fundsbeing provided by the KIT Energy Center. It isplanned to establish a KIT "Algae Platform" forenergy production from microalgae. In the mediumterm, pilot-scale and demonstration plants shall bebuilt on the northern KIT campus, with the favorableconditions in terms of space and infrastructurebeing made use of. "This will represent a majornode in the presently rather rapid networking ofalgae biotechnology", emphasizes Posten. Tomake energy production from algae economicallyefficient, it will be focused on minimizing investmentand operation costs of photobioreactors and ondeveloping highly efficient processes for theharvesting and decomposition of algae.

To close the cycle for the complete use of algaebiomass for energy production, KIT researcherseven go another step forwards. The biomassremaining after extraction (60 - 70%) is planned tobe con-verted into other energy carriers likehydrogen or methane by means of thehydrothermal gasification process developed on thenorthern campus.

Source: Helmholtz Association of GermanResearch Centres

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APA citation: 'Green' energy from algae (2009, August 6) retrieved 9 June 2018 from https://phys.org/news/2009-08-green-energy-algae.html

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