Outdoor production of Phaeodactylum tricornutum biomass in a helical reactor.

The production of microalga Phaeodactylum tricornutum in an outdoor helical reactor was analysed. The influence of temperature, solar irradiance and air flow rate on the yield of the culture was evaluated. Biomass productivities up to 1.5 g l(-1) per day and photosynthetic efficiency up to 14% were obtained by maintaining the cultures below 30 degrees C, dissolved oxygen levels less than 400% Sat. (with respect to air saturated culture) and controlling the cell density in order to achieve an average irradiance within the culture below 250 microE m(-2) s(-1). Under these conditions, the fluorescence parameter, Fv/Fm, which reflects the maximal efficiency of PSII photochemistry, remained roughly 0.6-0.7 and growth rates up to 0.050 h(-1) were achieved. The average irradiance and the light/dark cycle frequency, were the variables determining the behaviour of the cultures. A hyperbolic relationship between growth rate and biomass productivity with the average irradiance was observed, whereas both biomass productivity and photosynthetic efficiency linearly increased with the light/dark cycle frequencies. Optimum design and operational conditions which maximise the production of P. tricornutum biomass in outdoor helical reactors were determined.