Ethene removal from gas by recycling a water-immiscible solvent through a packed absorber and a bioreactor

Hydrophobic pollutants in waste gases are difficult to remove with the conventional biological treatment techniques because of the slow gas/water mass transfer rate. A two-stage system with a water-immiscible solvent as intermediate liquid was developed. This system consisted of a packed absorber for transfer of the model pollutant, ethene, from gas to solvent and a stirred-tank reactor (mixer) for solvent/water transfer and subsequent degradation by Mycobacterium parafortuitum. The solvent FC40, a perfluorocarbon, was recycled between these two compartments. The stability of the system was shown during a run of 10 days. The elimination efficiency was found to be a function of the solvent flow: 9% and 15% elimination were obtained at solvent flows of 6 x 10(-8) m3.s-1 and 11.3 x 10(-8) m3.s-1, respectively. Ethene removal remained constant at increasing solvent hold-ups up to 50% (v/v). In spite of the low elimination efficiencies caused by an inefficient use of the column, the feasibility of the system to remove ethene has been demonstrated. The system's performance was described by a steady-state mathematical model. Simulated ethene removal efficiencies agreed well with the experimental data. Based on this, the model was used to optimise the dimensions and operating conditions. Furthermore, the model was used to compare the performance of the combined system (PA/MS) with the performance of a similar system without solvent. It was found that the use of solvent as intermediate liquid can improve substantially the removal efficiency of hydrophobic gaseous pollutants compared with the system without solvent. This is dependent however, on the solubility of the pollutant in the solvent, on the dimensions of the system and on the operating conditions.