Rotating-disk mechanical foam-breakers (MFRDs) were applied to the control of foaming in bubble column (BC) reactors containing complex solutions and biological media. The foaming behaviour of BCs and the foam-breaking behaviour of MFRDs fitted to BCs were evaluated respectively from the changes in the liquid hold-up in ascending foam, phi(b), and the required critical disk rotational speed, N(c), for foam-breaking. The differences in phi(b) and N(c), reflecting the difficulty or ease of foam-breaking among the liquids, correlated well with differences in the foaming characteristic term, F(CT), of respective liquids, which could be determined on the basis of the results measured in the experimental small foaming apparatus which were different from those measured in the gas-bubbling apparatus employed in practice. The usefulness of the empirical correlations for the prediction of phi(b) and N(c), which can be applied independently of the type and concentration of foaming liquid or their physical properties, was also demonstrated.