The volumetric mass transfer coefficient has been determined for a system comprising air and sodium sulphite (0.8 M) in a semibatch bubble column with a diameter of 0.2 m. The superficial gas velocity was varied in the range 0.03-0.2 m/s. The measurements were made at non-isothermal conditions between 19 and 36 degrees C, and it is shown that if the mass transfer is not chemically enhanced, the absorption rate of oxygen in a sodium sulphite solution will be constant and independent of the temperature. Based on this, it is possible to determine the volumetric mass transfer coefficient without any knowledge of the kinetics of the oxidation of sulphite to sulphate. Furthermore, it is found that the parameter k(1)a/epsilon(G) in the heterogeneous regime for the system is about 0.5, which is in agreement with previous work of an air-water system. It is also shown that the mass transfer coefficient of small bubbles generated by a membrane or by a porous gas sparger is smaller compared to the mass transfer coefficient of larger bubbles formed in a gas sparger with 2 mm holes. (c) 2005 Elsevier B.V. All rights reserved.