Using fluorochemical as oxygen carrier to enhance the growth of marine microalga Nannochloropsis oculata

The commercial value of marine Nannochloropsis oculata has been recognized due to its high content of eicosapentaenoic acid (>50 % w/w). To make it as a profitable bioresource, one of the most desirable goals is to develop a quality-controlled, cost-effective, and large-scale photobioreactor for N. oculata growth. Generally, closed culture system can offer many advantages over open system such as small space requirement, controllable process and low risk of contamination. However, oxygen accumulation is often a detrimental factor for enclosed microalgal culture that has seriously hampered the development of microalga-related industries. In this study, we proposed to use fluorochemical as oxygen carrier to overcome the challenge where four liquid fluorochemicals namely perfluorooctyl bromide, perfluorodecalin, methoxynonafluorobutane, and ethoxynonafluorobutane were investigated separately. Our results showed that the microalgal proliferation with different fluorinated liquids was similar and comparable to the culture without a fluorochemical. When cultured in the photobioreactor with 60 % oxygen atmosphere, the N. oculata can grow up in all the fluorochemical photobioreactors, but completely inhibited in the chamber without a fluorochemical. Moreover, the perfluorooctyl bromide system exhibited the most robust efficacy of oxygen removal in the culture media (perfluorooctyl bromide > perfluorodecalin > methoxynonafluorobutane > ethoxynonafluorobutane), and yielded a >3-fold increase of biomass production after 5 days. In summary, the developed fluorochemical photobioreactors offer a feasible means for N. oculata growth in closed and large-scale setting without effect of oxygen inhibition.