ARTICLE Assessment of the Impact of Salinity and Irradiance on the Combined CO 2 Sequestration and Carotenoids Production by Dunaliella salina: A Mathematical Model O.Q.F. Arau ´ jo, 1 C.N. Gobbi, 1 R.M. Chaloub, 2 M.A.Z. Coelho 1 1 Escola de Quı´mica, Universidade Federal do Rio de Janeiro, Av. Hora ´cio Macedo, 2030, Edifı´cio do Centro de Tecnologia Bloco E sala/209, Cidade Universita ´ria, CEP: 21941-909Rio de Janeiro, RJ, Brazil; telephone: þ55-21-25627535; fax: þ55-21-25627637; e-mail: ofelia@eq.ufrj.br 2 Departamento de Bioquı´mica, Instituto de Quı´mica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil Received 8 March 2008; revision received 11 June 2008; accepted 30 July 2008 Published online ? ? ? ? in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bit.22079 ABSTRACT: Current anthropogenic activities have been causing a significant increase in the atmospheric concentra- tion of CO 2 over the past 60 years. To mitigate the con- sequent global warming problem, efficient technological solutions, based on economical and technical grounds, are required. In this work, microalgae are studied as impor- tant biological systems of CO 2 fixation into organic com- pounds through photosynthesis. These microorganisms are potential sources of a wide variety of interesting chemical compounds, which can be used for commercial purposes, reducing the cost of CO 2 capture and sequestration. Speci- fically, Dunaliella salina culture was studied aiming at the impact evaluation of operational conditions over cellular growth and carotenoid production associated with the CO 2 sequestration on focus. The main experimental parameters investigated were salinity and irradiance conditions. The experimental results supported the development of a descriptive mathematical model of the process. Based on the proposed model, a sensitivity analysis was carried out to investigate the operational conditions that maximize CO 2 consumption and carotenoid production, in order to guide further development of technological routes for CO 2 capture through microalgae. A preliminary cost estimation of CO 2 sequestration combined to carotenoids production for a 200 MW power plant is presented, based on the growth rates achieved in this study. Biotechnol. Bioeng. 2008;9999: 1–12. ß 2008 Wiley Periodicals, Inc. KEYWORDS: Dunaliella salina; CO2 mitigation; modeling; irradiance; carotenoids Introduction Q1 Recent aggravation of global warming, due to increased levels of greenhouse gases (GHG) in the atmosphere, results in sensible environmental consequences observed around the world (Tomkiewicz, 2006): about 85% of GHG are related to CO 2 (Jean-Baptiste and Ducroux, 2003). The average concentration of anthropogenic CO 2 in the atmo- sphere has increased from 278 ppmv in the pre-industrial era to 358 ppmv in 1996 (Simeonova and Diaz-Bone, 2004 Q2 ). Simulation of carbon cycle predict that if CO 2 emissions are maintained at the present levels, by 2,100 CO 2 atmospheric concentration will reach 500 ppmv (Johnston et al., 2003). To restrain this expansion, Kyoto Protocol established the goal of reducing GHG emissions in 5.2% during the period from 2008 to 2012, based on 1990 data (Simeonova and Diaz-Bone, 2005). Given the fossil fuels burning is the major contributor to anthropogenic CO 2 (6 Gt C/year) (Johnston et al., 2003), a reduction of the level of burned fossil fuels would contribute to limiting atmospheric CO 2 . However, it was predicted that, until year 2020, energy demand will still be supplied by fossil fuels (Ametistova et al., 2002). Hence, a need is imposed for removing CO 2 from stationary sources, by already existing and still to be developed sequestration technologies. The ‘‘natural’’ sequestration of CO 2 by plants and also by its dissolution in the oceans account for 50% of the emis- sions, while the remaining CO 2 accumulates in the atmos- phere (Ametistova et al., 2002; Johnston et al., 2003). CO 2 sequestration by algae, to mitigate GHG, shows promising perspectives due to their photosynthetic capacity and growth rates larger than those observed for higher plants. Correspondence to: O.Q.F. Arau ´jo Contract grant sponsor: CNPq Contract grant number: 504358/2004-9 ß 2008 Wiley Periodicals, Inc. Biotechnology and Bioengineering, Vol. 9999, No. 9999, 2008 1 BIT08-233.R1(22079)