Enhancement of the overall volumetric oxygen transfer coefficient in a stirred tank bioreactor using ethanol

Ethanol was observed to improve the oxygen mass transfer rate into a well-m ixed bioreactor. The effects of impeller speed and ethanol concentration on the oxygen transfer from air to the water phase and on the average bubble diameter in a stirred tank bioreactor are reported and modelled. The result s show that the oxygen mass transfer coefficient (k(L)a) increases from 0.0 02 to 0.017 s(-1) (for distilled water) due to the increase of impeller spe ed from 135 to 600 rpm. With increasing ethanol concentration from 0 to 8 g /L, the oxygen mass transfer coefficients increase from 0.015 to 0.049 s(-1 ), and from 0.017 to 0.076 s(-1), for impeller speeds of 450 and 600 rpm, r espectively. The average bubble diameter decreased from 7.0 mm to 1.7 mm in pure distilled water as the impeller speed was increased from 135 to 600 r pm. When ethanol was present in the aqueous phase, the bubble diameter fell from 6.0 mm to 0.6 mm as the impeller speed was similarly increased.