columns and airlift photobioreactors can be useful for culturing phototrophic organisms requiring light as a nutrient. Light a®ailability in bubble columns and airlift ( de®ices is influenced by aeration rate, gas holdup, and the liquid ®elocity mixing and ) turbulence . The photosynthetically generated oxygen also needs to be remo®ed, as ex-cessi®e dissol®ed oxygen suppresses photosynthesis. Oxygen remo®al capacity is go®erned by the magnitude of the o®erall gas ᎐ liquid mass-transfer coefficient, k a . This work L L characterizes the rele®ant hydrodynamic and mass-transfer parameters in three airagitated reactors: bubble column, split-cylinder airlift de®ice and concentric draft-tube sparged airlift ®essel. The reactors are then e®aluated for culture of the microalga Phaeodactylum tricornutum. All reactors were about 0.06 m 3 in working ®olume, and the working aspect ratio was about 10. Data were obtained in tap water for a base-line comparison and in Mediterranean seawater, as a potential medium for algal culture. A theoretical relationship was de®eloped and pro®ed between k a and the aeration rate.
L L In addition, a method based on mechanistic relationships was pro®ed for predicting the liquid circulation ®elocity and k a in airlift reactors. Existing correlations applied sat-L L isfactorily to gas holdup and k a data obtained in the bubble column. Aqueous solu-L L ( ) tion of sodium chloride 0.15 M closely resembled seawater in terms of its hydrodynamics and oxygen transfer beha®ior. Under the conditions tested, all three reactors attained a biomass concentration of about 4 kg ؒ m y 3 after ; 260 h. The mean maximum specific growth rate was 0.022 h y 1 in all cases at a power input of 109 W ؒ m y 3 .