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 Phae odactylum tricornutum grown semicontinuously in a helical tubular phot obioreactor 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 a nd EPA productivity were enhanced at those cell densities which suppor t 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 productivit y was greatest at the highest irradiance. This study shows that biomas s productivity and EPA productivity can be maximised by optimising cel l density and irradiance, as well as by addition of CO2.