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Microalgae are promising feedstocks for the production of biofuels thanks to their high biomass yield and the lack of competition with food crops for arable land. Algal industrial exploitation, however, still needs to address several technological challenges to reach energetic and economic sustainability. Genetic improvement of microalgae strains is seminal to fully exploit the potential of these organisms. In this work, we investigated how key environmental parameters affected productivity of a promising genetically modified algal strain cultivated in industrially relevant conditions. We observed that intensive growth conditions strongly influenced algae biology as evidenced by molecular and functional analyses. We also showed that specific operational conditions significantly affected performances, enhancing or reducing the advantages of the strains genetic modification, such as the chlorophyll content per cell and the abundance of photosynthetic apparatus components. This work demonstrates the presence of a strong influence of cultivation environment on the phenotype of improved strains, suggesting that operational parameters have a seminal influence on algae performances and must be taken into full account during strains development efforts. [ABSTRACT FROM AUTHOR]

Microalgae-based biorefinery processes are gaining particular importance as a biotechnological tool for direct carbon dioxide fixation and production of high-quality biomass and energy feedstock for different industrial markets. However, despite the many technological advances in photobioreactor designs and operations, microalgae cultivation is still limited due to the low yields achieved in open systems and to the high investment and operation costs of closed photobioreactors. In this work, a new alveolar flat panel photobioreactor was designed and characterized with the aim of achieving high microalgae productivities and CO 2 bio-fixation rates. Moreover, the energy efficiency of the employed pump-assisted hydraulic circuit was evaluated. The 1.3 cm thick alveolar flat-panels enhance the light utilization, whereas the hydraulic design of the photobioreactor aims to improve the global CO 2 gas-liquid mass transfer coefficient (k L aCO 2). The mixing time, liquid flow velocity, and k L aCO 2 as well as the uniformity matrix of the artificial lighting source were experimentally calculated. The performance of the system was tested by cultivating the green microalga Acutodesmus obliquus. A volumetric biomass concentration equal to 1.9 g L−1 was achieved after 7 days under controlled indoor cultivation conditions with a CO 2 bio-fixation efficiency of 64% of total injected CO 2. The (gross) energy consumption related to substrate handling was estimated to be between 27 and 46 Wh m−3, without any cost associated to CO 2 injection and O 2 degassing. The data suggest that this pilot-scale cultivation system may constitute a relevant technology in the development of microalgae-based industrial scenario for CO 2 mitigation and biomass production. [Display omitted] • New alveolar flat panel photobioreactor with positive pressure-serpentine circulation. • CO 2 supply strategy enhancing the global CO 2 mass transfer coefficient (k L aCO 2). • Low energy demand for liquid culture circulation and mixing. • Acutodesmus obliquus mean daily volumetric productivity of 0.21 g L−1 d−1. • CO 2 bio-fixation efficiency equal to 64% of total injected CO 2. [ABSTRACT FROM AUTHOR]