EFFECT OF CELL-DENSITY AND IRRADIANCE ON GROWTH, PROXIMATE COMPOSITION AND EICOSAPENTAENOIC ACID PRODUCTION OF PHAEODACTYLUM-TRICORNUTUM GROWN IN A TUBULAR PHOTOBIOREACTOR

Growth and eicosapentaenoic acid (EPA) productivity of the diatom Phaeodactylum tricornutum grown semicontinuously in a helical tubular photobioreactor were examined under a range of irradiances (approximately 56 to 1712 mumol photons m-2 s-1) and cell densities (almost-equal-to 3 X 10(6) to 18 x 10(6) cells mL-1). Self shading sets the upper limit of operational maximum cell density. Higher irradiance increases this upper limit and also increase the growth rate. Biomass productivity and EPA productivity were enhanced at those cell densities which support the fastest growth rate irrespective of irradiance. The cell protein content increased with increasing irradiance and the carbohydrate and lipid content increased with increasing cell density. EPA productivity was greatest at the highest irradiance. This study shows that biomass productivity and EPA productivity can be maximised by optimising cell density and irradiance, as well as by addition of CO2.