Characterization of the absorption potential of atmospheric carbon dioxide by microalgae used in aquaculture to generate a clean development mechanism (CDM)
Author: Lucelia do Valle Borges (Currículo Lattes)
Supervisor: Dr Paulo Cesar Oliveira Vergne de Abreu
Co-supervisor: Dra Clarisse Odebrecht
Abstract
The increase in CO2 concentrations in the atmosphere in recent years has generated an intensification of the greenhouse effect. Due to the high rates of carbon fixation by microalgae, cultivation on a large scale and under semi-controlled conditions of these microorganisms appears as an alternative to reduce atmospheric CO2 levels. In aquaculture, the high cost of producing microalgae crops affects the profitability of producing cultured organisms. In order to increase yield and reduce costs, research is needed that results in the use of more productive microalgae species. The objective of this work was to determine which phytoplankton microalgae species used in aquaculture, which have the highest CO2 absorption rates, have some commercial value and can be cultivated on a large scale.The experiments were carried out with the species Nannochloropsis oculata (Droop) Hibberd, 1955), Chaetoceros affinis Lauder, 1864, C. muelleri Lemmermann, 1898, Phaeodactilum tricornutum Bohlin, 1897, Skeletonema costatum (Greville) Cleve, 1873, Thalassiosira, 1927, Thalassiosira , T. pseudonana (Husted) Hasle & Heimdal, 1970), Tetraselmis chuii Butcher, 1958, T. tetrathele (GS West) Butcher 1959 and Isochrysis galbana Parke, 1949. The species were kept in f/2 medium, constant temperature (optimal for each species), average brightness of 100 μmol/m2/s1 and photoperiod of 12L/12E. Primary productivity measurements at different light intensities, using the oxygen and 14C method (dissolved, particulate and total production), were carried out with culture samples that were in the logarithmic phase.The Photosynthetic Quotient (QF) and the lipid fraction of the most productive algae were also determined. N. oculata, S. costatum and C. muelleri were the species that achieved the highest cell growth yield, while C. affinis was the species with the lowest growth rate. N. oculata and I. galbana were the most productive species, in terms of O2 production, and N. oculata and T. fluviatilis obtained the highest carbon production values. Most species had QF values above 1.0. According to the results of growth and primary production, four species showed the greatest potential for large-scale production: N. oculata, S. costatum, T. fluviatilis and I. galbana. Due to their higher growth in lower light, N. oculata and S. costatum could be grown in periods of lower light,whereas T. fluviatilis and I. galbana, species adapted to light, could be cultivated in the spring/summer. In addition, the results show that N. oculata produces a large amount of lipids and fatty acids, indicating a great capacity for the production of bio-fuels.