Energy-saving in fucoxanthin production by Chaetoceros gracilis in a flat-bag photobioreactor with intermittent mixing

Abstract

To save energy in the production of high-value products with antioxidant properties such as fucoxanthin by Chaetoceros gracilis, the effect of mixing frequency (once every 18 min and once every 9 min) on fucoxanthin productivity was examined using a flat bag photobioreactor. The mixing frequency of once every 9 min resulted in a significantly higher (p < 0.01) areal fucoxanthin productivity of 28.9 mg m−2 d−1 than mixing once every 18 min (13.7 mg m−2 d−1). The fucoxanthin productivity at the mixing frequency of once every 9 min was comparable to that in previous studies of diatoms cultured using continuous mixing. Moreover, intermittent mixing reduced the energy required for mixing and biomass productivity per mixing energy of 20.5-21.2 g-DW kWh−1 d−1 was achieved. The present study showed that mixing frequency affected the cell density and light intensity per dry weight of C. gracilis which means the light intensity received by individual cells. The fucoxanthin content increased exponentially with decreasing light intensity per dry weight due to the decrease of the light intensity received by individual cells. Thus, mixing frequency is an essential parameter for high fucoxanthin productivity. Light intensity per dry weight and mixing frequency should be considered in combination to achieve energy savings in fucoxanthin production by C. gracilis.