Abstract
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.