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Artificial lighting may be an interesting opportunity for the cultivation of microalgae as an alternative to natural sunlight. In particular, light emitting diodes (LEDs) can be employed to tailor the lighting to the microalgal culture in a controlled mode in order to create flashing light. In order to establish the effect of the flashing frequency on growth and biochemical composition of a model microalga, a quasi‐isoactinic reactor, in which the light distribution is almost homogeneous, was set up. In this work, it was employed for the cultivation of the heterokont Nannochloropsis gaditana in two growth media with limiting and nonlimiting nutrients. The combined effect of nutrient concentration and flashing frequency on the growth, lipid content, fatty acid content, and pigment content was assessed for the first time. The results indicate that both nutrient concentration and flashing frequency influence the above‐mentioned parameters. In particular, under flashing light conditions, an increase of lipid content and a decrease of polyunsaturated fatty acids (PUFAs) and chlorophyll are observed when nutrients are deficient, while the opposite effects are shown when nutrients are abundant. [ABSTRACT FROM AUTHOR]

One of the main parameters affecting autotrophic algae cultures is photon absorption distribution inside the photobioreactor. This clearly depends on the geometry of both the radiation source and the photobioreactor, as well as on algae suspension optical properties. In this work the local volumetric rate of photon absorption LVRPA in a cross-section of a horizontal-pipe photobioreactor was investigated by means of simplified Monte Carlo simulations. In particular, the fate of a number of photons perpendicularly hitting the photobioreactor circular section was simulated in relation to different values of algae concentration. The model takes into account refraction/reflection phenomena at the air/photobioreactor-wall interface. Simulation results show that radiation distribution inside the photobioreactor is quite strongly affected by reflection/refraction at the air-reactor interface. In particular, dark zones (not revealed when neglecting reflection/refraction phenomena) are observed in conjunction with unexpected radiation intensification in other zones. These phenomena are bound to affect photobioreactor performance and should therefore be considered if effective photobioreactor models are sought. [ABSTRACT FROM AUTHOR]

Bubble formation at variously inclined submerged nozzles, fed with a continuous gas flow rate, is investigated. The average liquid velocity induced by bubble motion is determined, leading to a simple correlation for estimation of the liquid velocities induced by the repeated passage of bubbles. An effective model for the prediction of bubble sizes at their detachment from vertical nozzle orifices is presented which encompasses a bound expansion stage, followed by an accelerated expansion phase, and ends by an original bubble detachment criterion. The existence of a liquid-phase effective entrainment velocity, generated by the continuous passage of the bubble stream, is quantified and included in the model. Model predictions are found to correlate well with experimental and literature data. [ABSTRACT FROM AUTHOR]