Impact of bubble size on docosahexaenoic acid production by Crypthecodinium cohnii in bubble column bioreactor

Abstract

Cultivation conditions especially agitation and aeration have critical roles on Crypthecodinium cohnii growth and docosahexaenoic acid (DHA) formation. In this study, for the first time, different air bubble sizes were considered, in a 5-L bubble column bioreactor; and the effect of bubble size on growth and on DHA production by dinoflagellate microalgae C. cohnii was investigated. The cultivation was carried out under 0.5 vvm aeration flow rate, 28 °C, and pH ± 7. The highest yield of DHA (1.4 g DHA L−1) was achieved for 0.36-cm air bubble diameter; the corresponding biomass amount was 17.6 g. The suitable conditions during the logarithmic stage of growth were provided for 0.36-cm air bubble diameter, while oxygen limitation was observed in the culture medium afterwards. The concentration of the microalgal DHA was increased in oxygen limitation conditions. Our results indicate that the air bubble diameter is the most influencing factor on DHA production in a bubble column bioreactor. Current research indicates that optimum bubble size in bubble column bioreactor can lead to optimal conditions for growth and DHA production like two-stage oxygen supply feeding strategy.