Carbon dioxide sequestration in photobioreactors

Author(s)

Eduardo Jacob Lopes

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2007-03-12

Examining board members

Telma Teixeira Franco; Gustavo Paim Valença; Maria Almerinda Vieira Fernandes Ribeiro Alves; Maria Isabel Queiroz; Gustavo Paim Valença; Ranulfo Monte Alegre; Edson Tomaz

• Advisor: Telma Teixeira Franco

Abstract

The photosynthetic conversion of carbon dioxide in photobioreactors was investigated with the objective of developing a biological carbon sequestering system. The process used consisted of transferring gaseous carbon dioxide to the liquid phase of a reactor, in which this compound was converted into photosynthetic metabolism products by the activity of microalgae. Considering this, the objectives of the present work were: (1) evaluate the photosynthetic culture of the microalgae $SKDQRWKHFH_PLFURVFRSLFD_1lJHOL under different conditions of temperature, light intensity and carbon dioxide concentration; (2) evaluate the absorption/desorption kinetics of carbon dioxide in photobioreactors; (3) define the appropriate operational conditions for the biological removal of carbon; (4) evaluate the effects of light cycles on the fixation of carbon dioxide and (5) study different configurations and operational modes of photobioreactors for the removal of CO2. The carbon sequestering capacity of the system was considered from an analysis of the free CO2 profiles in the liquid phase of the system, measurements of the gas phase concentration and the stoichiometric conversion into biomass. The results obtained demonstrated the importance of the operational parameters evaluated in the fixation of carbon in biomass, as also in the overall removal of CO2. The use of response surface methodology was adequate to optimise the process, and resulted in an increase greater than 58% in the maximum cell density. The effect of the duration of the light cycle was determinant in process performance, resulting in reductions in maximum efficiency of up to 99.69%. The configurations of the reactors studied demonstrated the superior performance of airlift systems, as compared to bubble-column reactors. With respect to operational mode, the systems involving the recirculation of contaminated air were shown to be efficient in decreasing reduced amounts of carbon dioxide, although two reactors connected in series were more efficient and showed greater capacity in eliminating carbon dioxide. The current stage of development of this work is evidence of the potential for the application of this type of reactor in carbon sequestering processes, due to the elevated elimination rates. However, only the partial characterisation of the photosynthetic CO2 conversion routes was considered. (AU)