Amer Ican City Types

Abstract

in Wiley InterScience (www.interscience.wiley.com).The ability to cultivate the cyanobacterium Arhtrospira platensis in artificially lightened photobioreactors using high energetic efficiency (quasi-monochromatic) red LED was investigated. To reach the same maximal productivities as with the polychromatic lightening control conditions (red þ blue, P/2e À ¼ 1.275), the need to work with an optimal range of wavelength around 620 nm was first established on batch and continuous cultures. The longterm physiological and kinetic behavior was then verified in a continuous photobioreactor illuminated only with red (620 nm) LED, showing that the maximum productivities can be maintained over 30 residence times with only minor changes in the pigment content of the cells corresponding to a well-known adaptation mechanism of the photosystems, but without any effect on growth and stoichiometry. For both poly and monochromatic incident light inputs, a predictive spectral knowledge model was proposed and validated for the first time, allowing the calculation of the kinetics and stoichiometry observed in any photobioreactor cultivating A. platensis, or other cyanobacteria if the parameters were updated. It is shown that the photon flux (with a specified wavelength) must be used instead of light energy flux as a relevant control variable for the growth. The experimental and theoretical results obtained in this study demonstrate that it is possible to save the energy consumed by the lightening device of photobioreactors using red LED, the spectral range of which is defined according to the action spectrum of photosynthesis. This appears to be crucial information for applications in which the energy must be rationalized, as it is the case for life support systems in closed environments like a permanent spatial base or a submarine. V V C 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 151-162, 2009 Keywords: photobioreactor, Arthrospira platensis, cyanobacteria, spectral kinetic knowledge model, LED, monochromatic light Introduction and ObjectivesThe use of artificially lightening controlled photobioreactors (PBR) seems a very promising technology if the production of high valuable compounds from photosynthetic microorganisms is to be envisaged. PBR are also of major interest as main operation in biological life support systems. Such complex artificial ecosystems as the MELiSSA project of ESA (http://www.esa.int/SPECIALS/Melissa/) aim at recycling CO 2 gas, liquid, and solid wastes produced by a crew in water, food, and oxygen inside a thermodynamically closed system (a lunar or Martian base for example). In these systems, the two critical points are the size (or mass) of unit operations and their energy consumption. This is also the case if a previous subsystem and small scale demonstrator is envisaged for a flight onboard the International Space Station such as the Biorat project, 1 in which the atmosphere revitalization of a consumer compartment (two mice) is ensured by a fully controlled PBR artificially li...