Abstract
Microalgae are currently considered to be a promising feedstock for biodiesel production. However, significant research efforts are crucial to improve the current biomass and lipid productivities under real outdoor production conditions. In this context, batch, continuous and semi-continuous operation regimes were compared during the Spring/Summer seasons in 2.6 m3 tubular photobioreactors to select the most suitable one for the production of the oleaginous microalga Nannochloropsis oceanica. Results obtained revealed that N. oceanica grown using the semi-continuous and continuous operation regimes enabled a 1.5-fold increase in biomass volumetric productivity compared to that cultivated in batch. The lipid productivity was 1.7-fold higher under semi-continuous cultivation than that under a batch operation regime. On the other hand, the semi-continuous and continuous operation regimes spent nearly the double amount of water compared to that of the batch regime. Interestingly, the biochemical profile of produced biomass using the different operation regimes was not affected regarding the contents of proteins, lipids and fatty acids. Overall, these results show that the semi-continuous operation regime is more suitable for the outdoor production of N. oceanica, significantly improving the biomass and lipid productivities at large-scale, which is a crucial factor for biodiesel production.
Highlights
Major climate changes have been observed since 1950, and human impact, due to industrial activity, is one of the main leading causes
The outdoor work was performed at the facilities of Allmicroalgae (Pataias, Portugal) between 1 March and 8 July 2019
The microalga Nannochloropsis oceanica CCAP849/10 was obtained from the culture collection Algae and Protozoa (Oban, Scotland, UK) and is kept at Allmicroalgae culture collection
Summary
Major climate changes have been observed since 1950, and human impact, due to industrial activity, is one of the main leading causes. The emissions of greenhouse gases, including CO2 , CH4 and NO2 , have been increasing since the pre-industrial era, and those gases remain in the atmosphere, soil and oceans [1] This concern emphasizes the importance of fossil fuel replacements, like the ones based on biomass feedstocks for biofuel production [2]. Microalgae are ubiquitous microscopic photosynthetic organisms mainly found in aquatic environments (freshwater and saline), and on the surface of soil and stone, from deserts to polar sea habitats [3]. These organisms are known to efficiently fix CO2 , through photosynthesis, and convert it into organic matter with an efficiency up to 10-fold faster than terrestrial plants [4]. When compared to terrestrial plants, microalgae have the advantage of requiring less area to reach the same amount of biomass, being able
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