Dual sparging laboratory-scale photobioreactor for continuous production of microalgae

A description is given of a reliable 1.7-L photobioreactor with a minimum m aintenance requirement for continuous production of photosynthetic microorg anisms. The reactor is without moving parts and equipped with two different spargers operated in dual sparging mode: sufficient mixing to keep the cel ls in suspension is obtained by sparging with air through two single orific e spargers which deliver large bubbles, and pure CO2 is supplied, controlle d by pH, through a perforated membrane sparger which delivers small bubbles that give an efficient mass transfer of CO2 from gas to liquid. Separation of CO2 supply from air for mixing by dual sparging increased the transfer of CO2 from gas phase to liquid phase five fold relative to conventional sp arging. The photoautotrophic microalga Rhodomonas sp. has been produced con tinuously for up to 415 d with a dilution rate of 0.6 d(-1) and a steady st ate cell number of 10(7) cells mL(-1). The productivity of Rhodomonas cultu re in the dual sparging photobioreactor was identical to the productivity o f cultures grown with mechanical mixing.