Two liquid-phase bubble column bioreactors for the removal of volatile organic compounds from air streams

Two equal-sized bubble column bioreactors were used to investigate the effect of silicone oil on the removal efficiency (RE) of a bubble column bioreactor for hydrophobic volatile organic compounds (VOCs). In the first stage, the performance of the two liquid-phase bubble column bioreactors (in terms of hexane removal) containing 4 L mineral medium and 400 mL of silicone oil was compared to a control bioreactor (without silicone oil). With the airflow rate of 1.5 L min-1 and n-hexane concentration of 1.6 g m-3, the hexane RE of oil-added bioreactor was 27% compared to 16.3% for the control bioreactor. To obtain better removal efficiencies, in the second stage of the experiments, the airflow rate and the inlet n-hexane concentration were reduced to 0.9 L min-1 and 1 g m-3, respectively. In this stage, 150 mL of fermentation medium was replaced with fresh medium daily to avoid possible nutrient limitation and build up of toxicants. As a result of this replacement, the hexane RE of the oil-added bioreactor was 76% compared to 37% for the control bioreactor. In the third stage, the effect of silicone oil percentage on the bioreactor's hexane RE was investigated. The results showed that increasing silicone oil percentage from 5 to 15% had a significant positive effect on the hexane RE (for the hexane inlet concentration of 1.6 g m-3, the RE approximately doubled). However, the effect of oil percentage on the VOC RE was seen insignificant when silicone oil was above 15%. In the final stage of this work, the effect of adding expanded perlite particles to the liquid medium of two liquid-phase bubble column bioreactors was investigated. The results showed that perlite had a significant positive effect on the hexane RE of the bioreactor. (C) 2011 Curtin University of Technology and John Wiley & Sons, Ltd.