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Spirulina platensis was cultivated at small scale in photobioreactors for CO 2 sequestration experiments carried out at different CO 2 concentrations within the range 0.5 to 10%, temperatures 10 to 40 o C and light intensities 60 to 200 μmol s -1 m -2. CO 2 sequestration effi ciency of achieved 99.9 %, specifi c growth rate, doubling time, rate of CO 2 sequestered into the algal cells and small changes of pH found for each batch experiment. Spirulina Platensis adapted to a novel nutrient solution was cultivated to explore its capacity to sequester CO 2 . The impacts CO 2 concentration, light intensity and temperature, on specifi c growth rate of Spirulina platensis and the adapted algae strain were described using empirical microbial growth kinetic models, Monod, Andrews and Mayo. The fi rst two models described properly the effects of CO 2 concentration and light intensity whereas the third the impact of temperature. Kinetic parameters from each model estimated optimum growth conditions of Spirulina platensis (2.5% CO 2 , 25 o C, 60 to 100 μmol s -1 m -2 ) and Spirulina platensis adapted (2.5% CO 2 , 25 o C, 100 μmol s -1 m -2 ) photoinhibition pedicted for extreme growth conditions (10% CO 2 , 40 o C, 200 μmol s -1 m -2 ) with both algal culture. Given comparable productivity between Spirulina Platensis and its adopted it would be worthwhile to select the algae strain adopted to specie to be used for CO 2 sequestration using photobioreactors at commercial scale and the production of value-added products.

In this research, the physiological response of the microalgae Spirulina platensis to salinity stress (1 and 100 g L-1 ) was investigated. Spirulina platensis and Spirulina platensis (adapted to high salt concentration) were operated at laboratory scale in a semi-continuous photobioreactors. The responses examined were within 0.5 to 10% CO2 concentration, temperatures from 10 to 40 oC, light intensities from 60 to 200 μmol m-2 s -1 and presented better results in terms of all kinetic parameters. The highest rate of CO2 biofixation for Spirulina platensis was 25.1 gCO2 m-3 h -1 , and the maximum specific growth (μmax) achieved was 0.44 d-1 - 0.67 d-1 at 2.5% CO2, 150 µmol m-2 s -1 at 25 oC. Corresponding determined values of Spirulina platensis adapted were 18.2 gCO2 m-3 h -1 , 0.31 d-1 - 0.58 d-1 at 2.5% CO2, 60 µmol s-1 m-2 and 28 oC. However, both microalgae exhibited experimental limiting growth factors, CO2 10%, 40 oC and 200 µmol m-2 s -1 , conditions under which photosynthetic CO2 biofixation may be inhibited and photoinhibition of photosynthesis may be enhanced by salinity. The efficiency of 2.5% CO2 removal by Spirulina platensis achieved 99%, whereas Spirulina platensis adapted to 96%, respectively. The kinetic parameters estimated for Spirulina platensis can be used to improve photobioreactor design for reducing of atmospheric carbon dioxide.

SENSITIZED SOLAR CELLS WITH PHOTOSENSITIVE DYES OBTAINED FROM PLANTS OF THE SOUTHERN REGION OF ECUADOR.Four vegetal species of the southern of Ecuador were used as sensitizers for making dye-sensitized solar cells (DSSCs). The effect of type and amount of material, type and time of maceration were tested in order to determine the best conditions of extraction. The extraction of the natural dye was made with acidified ethanol. The sensitizing agents were adsorbed on TiO 2 nanoparticles in small solar cells. The DSSCs made with natural dyes from extracts of blackberry (Rubus glaucus B), mortiño (Solanum americanum Mill), escancel (Iresine herbstii Hook) and beet (Beta vulgaris L) developed an open-circuit tension (Voc) 0.65, 0.5, 0.45 and 0.19 V, respectively. The short-circuit currents (Isc) varies from 2.05 to 19.68 mA cm -2 and the fill factor ranging from 0.61 to 0.69. The DSSCs sensitized with the extract of Rubus glaucus B offered the highest maximum power of 8.83 mW. Thus, the natural dyes used showed great potential as sensitizers in DSSCs, besides being environmentally friendly and their low cost.Keywords: Dye-sensitized solar cell; natural dyes; nanoparticles TiO 2 . INTRODUCCIÓNEn el siglo XXI la humanidad se enfrenta al reto del incremento global de la demanda de energía y el control del nivel de emisiones de CO 2 para reducir el efecto invernadero. Por lo cual surge la necesidad en el desarrollo de fuentes de energías alternativas por medio del desarrollo de energías renovables, asegurando protección y armonía con el medio ambiente. 1 Una de estas fuentes de energía alternativa y renovable es el aprovechamiento de la energía solar, mediante la aplicación en celdas solares. Hoy en día, las celdas solares convencionales son basadas en silicio. Sin embargo, su desventaja son los altos costos de fabricación. 2 Otra fuente de energía son los combustibles fósiles, más económicos pero con las desventajas de ser un recurso no renovable y de alta contaminación. 3 Las celdas solares sensibilizadas con colorantes (DSSCs), han despertado un gran interés desde la publicación de O'regan y Grätzel, 4 debido a que representan una alternativa potencial y relativamente económica en comparación con el silicio que son actualmente los más utilizados.Las DSSCs consisten en un electrodo o ánodo, un contra--electrodo o cátodo, electrolito redox (reducción y oxidación) y un agente sensibilizador. 5 En estas celdas, el colorante sensibilizador juega un papel clave en la absorción de la luz solar y la conversión de energía solar en energía eléctrica. Hoy en día, algunos complejos metálicos y colorantes orgánicos se han sintetizado y usado como sensibilizadores. Por el momento, la mayor eficiencia en DSSCs se da por Ru que contienen compuestos absorbidos en TiO 2 nanocristalino alcanzando un 11.1% y una potencia máxima de 2.429 mW. 6 Aunque tales DSSCs han proporcionado un rendimiento relativamente alto, hay varias desventajas de la utilización de metales nobles, debido a su limitada disponibilidad; por lo tanto su producción es...