Niccolò Bassi

Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor.

Thirty microalgal strains were screened in the laboratory for their biomass productivity and lipid content. Four strains (two marine and two freshwater), selected because robust, highly productive and with a relatively high lipid content, were cultivated under nitrogen deprivation in 0.6‐L bubbled tubes. Only the two marine microalgae accumulated lipid under such conditions. One of them, the eustigmatophyte Nannochloropsis sp. F&M‐M24, which attained 60% lipid content after nitrogen starvation, was grown in a 20‐L Flat Alveolar Panel photobioreactor to study the influence of irradiance and nutrient (nitrogen or phosphorus) deprivation on fatty acid accumulation. Fatty acid content increased with high irradiances (up to 32.5% of dry biomass) and following both nitrogen and phosphorus deprivation (up to about 50%). To evaluate its lipid production potential under natural sunlight, the strain was grown outdoors in 110‐L Green Wall Panel photobioreactors under nutrient sufficient and deficient conditions. Lipid productivity increased from 117 mg/L/day in nutrient sufficient media (with an average biomass productivity of 0.36 g/L/day and 32% lipid content) to 204 mg/L/day (with an average biomass productivity of 0.30 g/L/day and more than 60% final lipid content) in nitrogen deprived media. In a two‐phase cultivation process (a nutrient sufficient phase to produce the inoculum followed by a nitrogen deprived phase to boost lipid synthesis) the oil production potential could be projected to be more than 90 kg per hectare per day. This is the first report of an increase of both lipid content and areal lipid productivity attained through nutrient deprivation in an outdoor algal culture. The experiments showed that this marine eustigmatophyte has the potential for an annual production of 20 tons of lipid per hectare in the Mediterranean climate and of more than 30 tons of lipid per hectare in sunny tropical areas. Biotechnol. Bioeng. 2009;102: 100–112.

Oil production by the marine microalgae Nannochloropsis sp. F&M-M24 and Tetraselmis suecica F&M-M33.

Nannochloropsis sp. F&M-M24 and Tetraselmis suecica F&M-M33 were cultivated outdoors in Green Wall Panels under nutrient deficiency to stimulate oil synthesis. Under nitrogen deprivation, Nannochloropsis attained average biomass and lipid productivities of 9.9 and 6.5 g m(-2) day(-1), respectively. Starved Tetraselmis cultures achieved a biomass productivity of about 7.6 g m(-2) day(-1) and a lipid productivity of 1.7 g m(-2) day(-1). Lipids represented 39.1% and 68.5% of non-starved and starved Nannochloropsis biomass, respectively. Starvation did not increase lipid content in Tetraselmis biomass. Important differences in lipid classes and in fatty acid composition were observed under the different cultivation conditions for both microalgae.

Photobioreactors for Microalgal Biofuel Production

Many different PBR designs have been proposed for biofuel production, few of them have been tested at pilot-scale, none developed at the (large) scale necessary for a complete and correct evaluation. Thus the main issues that impact on the reactor’s performance (i.e., suitable construction materials, efficient mixing, heating/cooling, CO2 supply and oxygen removal), although explored at pilot level, still await evaluation at real scale. Although the main limitations of PBR are the high cost and the reduced scalability, with few exceptions, R&D on photobioreactor design is aimed at achieving high photosynthetic efficiencies and at pushing productivity beyond that currently attainable. The main strategies explored to this end are intensive mixing, light dilution via large external surfaces or internal light conducting structures. This chapter reviews and examined recent advances and innovations in photobioreactor design and operation.

Oil and eicosapentaenoic acid production by the diatom Phaeodactylum tricornutum cultivated outdoors in Green Wall Panel (GWP®) reactors

Phaeodactylum tricornutum is a widely studied diatom and has been proposed as a source of oil and polyunsaturated fatty acids (PUFA), particularly eicosapentaenoic acid (EPA). Recent studies indicate that lipid accumulation occurs under nutritional stress. Aim of this research was to determine how changes in nitrogen availability affect productivity, oil yield, and fatty acid (FA) composition of P. tricornutum UTEX 640. After preliminary laboratory trials, outdoor experiments were carried out in 40‐L GWP® reactors under different nitrogen regimes in batch. Nitrogen replete cultures achieved the highest productivity of biomass (about 18 g m−2 d−1) and EPA (about 0.35 g m−2 d−1), whereas nitrogen‐starved cultures achieved the highest FA productivity (about 2.6 g m−2 d−1). The annual potential yield of P. tricornutum grown outdoors in GWP® reactors is 730 kg of EPA per hectare under nutrient‐replete conditions and 5,800 kg of FA per hectare under nitrogen starvation. Biotechnol. Bioeng. 2017;114: 2204–2210.