Effects of surface active agents on hydrodynamics and mass transfer characteristics in a split-cylinder airlift bioreactor with packed bed

The effects of three types of surface active agents (containing SDS, HCTBr and Tween 40) with various concentrations (0–5 ppm) on the hydrodynamic and oxygen mass transfer characteristics in a split-cylinder airlift bioreactor with and without packing were investigated. It was observed that in the surfactant solutions, surface tension of the liquid decreased and smaller bubbles were produced in comparison with pure water. So, surfactants presence strongly enhanced mixing time and gas hold-up although oxygen mass transfer coefficient and the liquid circulation velocity reduced. Furthermore, the packing installation enhanced the overall gas–liquid volumetric mass transfer coefficient by increasing flow turbulency and Reynolds number compared to an unpacked column. The packing increased gas hold-up and decreased bubbles size and liquid circulation velocity.

► Surface active agent addition and its concentration effects on gas hold-up, liquid circulation velocity and mixing time and the volumetric mass transfer coefficient in a split-cylinder airlift reactor with packing installed in the riser section have been experimentally investigated.
► Surfactants addition increased mixing time and overall gas hold-up. Overall gas hold-up was increased in the presence of surfactants about 30% (at UG = 0.6 cm/s and at highest surfactant concentration).
► In the packed bed airlift bioreactor, HCTBr as a cationic surfactant (with the highest surface tension) considerably increased gas hold-up.
► Further, the surfactants presence decreased the liquid circulation velocity, bubbles diameter and volumetric mass transfer coefficient compared to the pure water.
► Two simple correlations were developed to predict the overall gas hold-up and volumetric mass transfer coefficient in the bioreactor with surfactant solutions.