A novel closed system bubble column photobioreactor for detailed characterisation of micro- and macroalgal growth

Abstract

Growth of the marine microalga Tetraselmis striata Butcher and the macroalga Chondrus crispus Stackhouse was investigated in batch cultures in a closed system bubble column photobioreactor. A laboratory cultivation system was constructed that allowed online monitoring of pH and dissolved oxygen tension and was used for characterization of photoautotrophic growth. Carbon dioxide addition regulated pH and was used to optimise irradiance. Oxygen was removed from the system by addition of hydrogen over a palladium catalyst to quantify oxygen production. In addition, the bubble column photobioreactor was suited for cultivation of algae due to fast gas-to-liquid mass transfer (kLa) and fast mixing provided by split and dual sparging. Specific growth rates (SGRs) were measured using both offline and online measurements. The latter was possible, because rectilinear correlation was observed between carbon dioxide addition and optical density, which shows that carbon dioxide addition may be used as an indirect measurement of microalgal biomass (x). The slope of the rectilinear fit of ln (dx/dt) as a function of the time (t) then revealed the SGR. These determinations revealed detailed information about changes in growth with up to three different SGRs in the different batch cultures of both micro- and macroalgae. The maximum SGRs found by online determination were 0.13 h−1 for T. striata and 0.12 day−1 for C. crispus. We have developed and described a system and presented some data handling tools that provide new information about growth kinetics of algae.