Performance of a membrane diffuser bioreactor for the removal of gaseous toluene

Hollow fiber membrane bioreactors have emerged as a promising technology for use in the treatment of volatile organic compounds (VOCs), due to their high surface area for VOC mass transfer and significant biodegradation capacity. In this study, a bioreactor operated in a diffuser mode using a submerged, hollow fiber membrane module (referred to as membrane diffuser bioreactor, MDBR) was employed in order to investigate its performance for the treatment of gaseous toluene. MDBR experiments were performed at different inlet toluene concentrations of 54, 160, and 750 ppm_v, respectively. Overall, toluene removal efficiencies were maintained in the range of 60-70% at each operating condition. The biomass density in the liquid phase was changed according to the inlet loading rate, but the toluene concentrations in the liquid phase were always extremely low, indicating that the overall reaction was controlled by the mass transfer rate of toluene, rather than by the biodegradation rate. Additionally, elimination capacity (EC) tests showed that the bioreactor system could biodegrade toluene at up to 415 g/m³/h, which was substantially higher than the maximum ECs for toluene reported in the bioreactor literature. However, a carbon balance calculation and images taken by a scanning electron microscope showed the development of the biofilm layer on the outer surface of the membrane, resulted in the increase of the pressure drop. As a result, methods to effectively remove the biofilm from the membrane need to be implanted to obtain stable MDBR operation.