The effect of impellers configuration on the gas dispersion in a given raw material is investigated using a stainless steel and transparent agitated column with narrow annular gap (NAGU) equipped with right-angle cross paddle impellers or cylinder. Using right-angle cross paddle impeller in NAGU, several configurations are considered by changing: the angle (theta=0 degrees-30 degrees-45 degrees) and the gap (delta=0 or 5 mm) between two successive elements. It is shown that the compact shifted geometry (delta=0 mm; theta=30 degrees) is much more efficient to achieve total gas incorporation than the others. Conversely, the impeller configuration does not seem to influence bubble mean diameter. The mean diameter decreases slightly from 19 mu m to 15 mu m when the rotation speed increases from 200 rpm to 1600 rpm, whatever the configuration. Qualitative and quantitative aspects of the bubble breakup are investigated using a transparent NAGU. Tip breakup appears to be the predominant dispersion phenomenon in the system. (C) 2012 Elsevier Ltd. All rights reserved.