Dual sparging laboratory-scale photobioreactor for continuous production of microalgae

A description is given of a reliable 1.7-L photobioreactor with a minimum maintenance requirement for continuous production of photosynthetic microorganisms. The reactor is without moving parts and equipped with two different spargers operated in dual sparging mode: sufficient mixing to keep the cells in suspension is obtained by sparging with air through two single orifice spargers which deliver large bubbles, and pure CO2 is supplied, controlled 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 sparging. The photoautotrophic microalga Rhodomonas sp. has been produced continuously for up to 415 d with a dilution rate of 0.6 d(-1) and a steady state cell number of 10(7) cells mL(-1). The productivity of Rhodomonas culture in the dual sparging photobioreactor was identical to the productivity of cultures grown with mechanical mixing.