In airlift reactors transport phenomena are achieved by pneumatic agitation and circulation occurs in a defined cyclic pattern through a loop. In the present work, the effect of geometrical relations on gas holdup and liquid velocity, and consequently on the gas-liquid mass transfer coefficient, was studied in a 6-liter airlift bioreactor with A D/A R = 0.63; A D, downcomer cross-sectional area, and A R, riser cross-sectional area. Measurements of the volumetric oxygen transfer coefficient (kLa) were taken in a water-air system using a modified sulfite oxidation method. Different conditions were examined by varying parameters such as superficial air velocity in the riser (U GR), bottom clearance (d1) and top clearance (d2). It was observed from the experimental results that d1 and d2 have a remarkable effect on kLa values. The effect is due to their influence on gas holdup and liquid velocity, consequently affecting kLa. Superficial air velocity in the riser (U GR) ranged from 0.0126 to 0.0440 m.s-1 and kLa varied between 40 to 250 h-1, whereas gas holdup (e) reached values up to 0.2. The volumetric oxygen transfer coefficient (kLa), gas holdup in the riser (eR) and downcomer (eD) and superficial liquid velocity in the riser (U LR) for all the geometrical relations were successfully correlated with dimensionless numbers, namely, the Sherwood number (Sh) and the Froude number (Fr) as well as with geometrical relations such as the bottom space ratio (B = d1/D D) and top space ratio (T = (d2 + D D)/D D).

The kinetics of clavulanic acid production process by Streptomyces clavuligerus NRRL 3585 was studied. Experiments were carried out in a 4 liters bioreactor, utilizing 2 complex media containing glycerol as the carbon and energy source, and peptone or Samprosoy 90NB (soybean protein) as nitrogen source. Temperature was kept at 28°C and the dissolved oxygen was controlled automatically at 40 % saturation value. Samples were withdrawn for determination of cell mass (only peptone medium), glycerol and product concentrations. Gas analyzers allowed on line determination of CO2 and O2 contents in the exit gas. With Samprosoy, cell mass was evaluated by determining glycerol consumption and considering the cell yield, Y X/S, as being the same for both cases. Oxygen uptake and CO2 production rates were strongly related to growth and substrate consumption, allowing determination of stoichiometric constants in relation to growth, substrate, oxygen, product and carbon dioxide.