Effect of dilution rate and light intensity on growth of a diatom Chaetoceros calcitrans under continuous cultivation in flat-panel photobioreactor

Abstract

Batch and continuous cultures of a marine diatom Chaetoceros calcitrans were conducted in flatpanel photobioreactors. The photobioreactor was made of transparent plastic sheet filled with 5.5 L of Guillard's F/2 culture medium (prepared with 30 PSU salinity seawater). The photobioreactor was continuously illuminated at 16 µmol photon m-2 s-1 with fluorescence lamps and operated under ambient room temperature (26-38ºC). With batch cultivation, C. calcitrans had the maximum cell density of 160x104 cells ml-1 and maximum specific growth rate of 1.03 day-1. During continuous cultivation, addition of fresh medium and removal of diatom cells were conducted using a peristaltic pump. The dilution rate was varied from 0.52 to 1.97 day-1 in 12 steps. The results showed that the highest cell density of 193x104 cells ml-1 was obtained at the lowest dilution rate (0.52 day-1). When the dilution rate was increased to 1.97 day-1, cell density of the diatom at steady state was decreased to 6x104 cells ml-1. However, the highest productivity was obtained at 0.98 day-1 dilution rates which provided cell productivity of 132x104 cell ml-1 day-1. In addition, increase in light intensity from 16 to 40 µmol photon m-2 s-1 resulted in an increase of the diatom growth and productivity, especially at low dilution rate. With this study, the recommended dilution rate for continuous cultivation of C. calcitrans was approximately 0.8 day-1. At this dilution rate, cell productivity of approximately 112x104 cells ml-1 day-1 or cell dry weight productivity of 64 mg L-1 day-1 could be expected