Quantification of oxygen production and respiration rates in mixotrophic cultivation of microalgae in nonstirred photobioreactors

Online monitoring and controlling of different cellular parameters are key issues in aerobic bioprocesses. Since mixotrophic cultivation, in which we observe a mixture of cellular respiration and oxygen production has gained more popularity, there is a need for an on‐process quantification of these parameters. The presented and adapted double gassing‐out method applied to a mixotrophic cultivation of Galdieria sulphuraria , will be a tool for monitoring and further optimization of algal fermentation in nonstirred photobioreactors (PBR). We measured the highest net specific oxygen production rate (opr _net) as 5.73 · 10^?3 mol_O2 g^?1 h^?1 at the lowest oxygen uptake rate (OUR) of 1.00 · 10^?4 mol_O2 L^?1 h^?1. Due to higher cell densities, we also demonstrated the increasing shading effect by a decrease of opr _net, reaching the lowest value of 1.25 10^?5 mol_O2 g^?1 h^?1. Nevertheless, with this on process measurement, we can predict the relation between the zone in which oxygen is net produced to the area where cell respiration dominates in a PBR, which has a major impact to optimize cell growth along with the formation of different products of interest such as pigments.