Enhancement of gas-liquid mass transfer rate of apolar pollutants in the biological waste gas treatment by a dispersed organic solvent

• Published in: Enzyme and microbial technology 1997-12, Vol.21 (8), p.578-588
• Main Authors: Cesário, M.Teresa, Beverloo, Wim A., Tramper, Johannes, Beeftink, Hendrik H.
• Format: Article
• Language: English
• Subjects: apolar gaseous compounds; Biological and medical sciences; Biological treatment of gaseous effluents; Biotechnology; dispersion; emulsion; Environment and pollution; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; Mass transfer enhancement; organic solvent; waste gas treatment
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/S0141-0229(97)00069-0

Dispersed water-immiscible solvents are known to enhance oxygen transfer rates in oxygen-limited aerobic fermentations. Here, this technique is applied to improve the mass transfer rate of poorly water-soluble gaseous pollutants during the biological treatment of waste gases. In a stirred-tank reactor, the enhancement of mass transfer rates was studied as a function of the pollutant solubility in water. The solvent used was FC40 (up to 10% v/v) and the model gaseous pollutants were toluene and oxygen (moderately and poorly water-soluble, respectively). The overall volumetric mass transfer coefficient from the gas to the bulk liquid (klagl) was measured under nonsteady-state conditions in the absence of micro-organisms. It was found to be essentially constant for the solvent volume fractions tested and for both toluene and oxygen. Using the values of klagl and the partition coefficient gas/liquid (mgl), the enhancement of the mass transfer rate by solvent addition could be predicted theoretically. A good agreement between the theoretical evaluation and the experimental results from experiments in the presence of biological consumption was observed. An enhancement of the mass transfer rate by a factor of 1.1 was found for toluene using a dispersion containing 10% (v/v) FC40 while the oxygen transfer rate increased by a factor of two at the same solvent volume fraction. It was further demonstrated theoretically for other gaseous compounds that the addition of solvent has a more pronounced effect on the enhancement of the transfer rate in the case of poorly water-soluble compounds compared to moderately water-soluble ones.