Development and validation of a minimal growth medium for recycling Chlorella vulgaris culture.

When microalgae culture medium is recycled, ions (e.g. Na(+), K(+), Ca(2+)) that were not assimilated by the microalgae accumulate in the medium. Therefore, a growth medium (HAMGM) was developed that included ions that were more easily assimilated by Chlorella vulgaris, such as ammonium one (NH(4)(+)). Recycling performance was studied by carrying out 8-week continuous cultivation of C. vulgaris with recycled HAMGM medium. No loss of biomass productivity was observed compared to culture in a conventional medium, and accumulation of ions over time was negligible.

Investigation of fatty acids accumulation in Nannochloropsis oculata for biodiesel application.

Lipids production of the marine microalga species Nannochloropsis oculata was deeply investigated by studying under continuous light the effects of different nitrogen starvation strategies in photobioreactors of various thicknesses. Operating parameters like incident photons flux density (PFD), initial nitrogen (progressive starvation strategy) or biomass concentrations (sudden starvation strategy) were examined, with a detailed analysis of their effects on the quality and production kinetics of total (TL) and triglycerides (TG). In addition to the already known effect of nitrogen starvation to trigger reserve lipids accumulation (mainly TG), it was demonstrated the relevance of the light received per cell affecting TG content and productivities, as well as fatty acids (FA) profiles. With appropriate optimization, N. oculata was confirmed as an interesting candidate for biodiesel application, with high FA accumulation (up to around 50%DW with 43%DW in TG-FA), high productivity (maximum 3.6×10(-3)kg(TG-FA)m(-2)d(-1)) and a TG-FA profile close to palm oil.

Systematic investigation of biomass and lipid productivity by microalgae in photobioreactors for biodiesel application.

We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the "light-limited" regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25-37% of DW), while the highest TAG content was found in C. vulgaris (11-14% of DW). These two species showed similar TAG productivities.

Investigation of biomass and lipids production with Neochloris oleoabundans in photobioreactor.

The fresh water microalga Neochloris oleoabundans was investigated for its ability to accumulate lipids and especially triacylglycerols (TAG). A systematic study was conducted, from the determination of the growth medium to its characterization in an airlift photobioreactor. Without nutrient limitation, a maximal biomass areal productivity of 16.5 g m(-2) day(-1) was found. Effects of nitrogen starvation to induce lipids accumulation was next investigated. Due to initial N. oleoabundans total lipids high content (23% of dry weight), highest productivity was obtained without mineral limitation with a maximal total lipids productivity of 3.8 g m(-2) day(-1). Regarding TAG, an almost similar productivity was found whatever the protocol was: continuous production without mineral limitation (0.5 g m(-2) day(-1)) or batch production with either sudden or progressive nitrogen deprivation (0.7 g m(-2) day(-1)). The decrease in growth rate reduces the benefit of the important lipids and TAG accumulation as obtained in nitrogen starvation (37% and 18% of dry weight, respectively).