Optimization of outdoor cultivation of the marine microalga Nannochloropsis gaditana in flat-panel reactors using industrial exhaust flue gases

The market for microalgae is substantial and currently expanding. To meet this demand, it is necessary to demonstrate the feasibility of large-scale biomass production over long periods. This study aims to demonstrate the feasibility and sustainability of a semi-industrial process for the outdoor cultivation of the microalga Nannochloropsis gaditana in flat-panel reactors using flue gases on demand from a coal-fired power plant. To this end, four secondary objectives were defined: (i) To generate an accurate estimate of the annual average biomass production using this process; (ii) To determine how the production rate and the biochemical composition of the biomass vary with the weather conditions over the course of a year; (iii) To reduce operational costs by developing a new culture medium based on natural seawater enriched with agricultural fertilizers; and (iv) To increase the productivity yield by optimizing the air flow rate in outdoor flat-panel reactors. This research is relevant because it fills an information gap in the available literature regarding experimentation with outdoor microalgae culture, on a semi-industrial scale, using flue gases, for a period of 2 full years. Results showed that biomass production and growth rate range from 0.040 ± 0.022 g (dry weight) L −1 d −1 and 0.088 ± 0.044 d −1 to 0.078 ± 0.033 g dwt L −1 d −1 and 0.179 ± 0.079 d −1 , respectively, depending on the environmental conditions. Protein and lipid content range from 34.4 ± 8.163 to 43.5 ± 13.250% dry weight and from 12.5 ± 2.243 to 14.4 ± 0.936% dwt, respectively. The culture was maintained during a complete cycle of two years, with the stated conditions, and demonstrated the technical feasibility and sustainability of the process.