The Algotron: microalgae cultivation coupled to biogas production

Microalgae constitute an interesting alternative to 1st or 2nd generation biofuels, notably because of their high photosynthetic yield potential and because they compete less for the use of cultivated land. In the context of the ANR SYMBIOSE project, scientists in the INRA Laboratory for Environmental Biotechnology (LBE) in Narbonne, and from SupAgro in Montpellier, have been working with INRIA, IFREMER, CNRS and Naskeo Environnement to develop a process for microalgae cultivation coupled to biogas production.

Algotron. © inra
Updated on 01/17/2013
Published on 10/04/2012

Microalgae cultivation and methane production

The use of agri-resources to produce bio-ethanol and biodiesel gives rise to new environmental constraints (eutrophication, scarcity of resources, ecotoxicity, damage to biodiversity) and competes with food production. The idea of recycling the CO2 generated by industry as a source of carbon for the cultivation of microalgae, and then anaerobic digestion to produce biogas, is a novel alternative that could circumvent the constraints imposed by other biomass transformation processes.

The Algotron, a new pilot installation

This research project is based both on recent advances in the cultivation of microalgae and on mastery of the anaerobic digestion process, and has given rise to a pilot plant, the Algotron.

The algae are cultivated in an open tank where they concentrate by natural decantation and are centrifuged if necessary. The flux of concentrated algae is then injected into an anaerobic digester. The methane production thus achieved can then be used as a biofuel for combustion engines.

 Environmental and energy analyses within the methodological framework of life cycle assessment

From an environmental standpoint, the scientists evaluated the use of methane produced by the anaerobic digestion of microalgae as a biofuel, and compared it with fossil fuel and first-generation biofuels. According to the principles of life cycle assessment, the system was considered as a whole. Thus the process included the production, harvest and concentration of algae, their transformation into methane and combustion of the latter. The construction and disassembly of installations was taken into account at all these stages. Based on this system, all resource consumption and emissions of pollutants into the environment were quantified for the production of a megajoule of energy (MJ) through combustion in an engine. Using this inventory, the life cycle assessment approach was able to evaluate both resource consumption and environmental damage (global warming, environmental eutrophication, toxicities, etc.).

In the context of this research, the results suggested that the impacts generated by methane production from microalgae were strongly correlated to the electricity consumption of the plant. Improvements could be made by optimising the cultivation systems (agitation, circuit of fluxes, etc.) and their associated energy requirements. Notable gains could be achieved by improving the efficiency of the anaerobic process under controlled conditions.

But the value of this research was the conclusion that this new-generation process for bioenergy production can strongly rival that of other biofuels. If a clearer understanding can be gained of the phenomena involved, and an optimal design of the algae cultivation/anaerobic digestion couple can be achieved, it may be possible to envisage alternatives to fossil fuels which perform well from an environmental point of view.

The LBE-INRA Algotron, an entirely instrumented pilot plant resulting from the Symbiose project and coupling microalgae cultivation and anaerobic digestion.

Scientific contact(s):

For further information

  • Pierre Collet, Arnaud Hélias, Laurent Lardon, Monique Ras, Romy-Alice Goy, Jean-Philippe Steyer, « Life-cycle assessment of microalgae culture coupled to biogas production », Bioresource Technology 102 (2011) 207-214.