Biological treatment of benzene in a controlled trickle bed air biofilter.

Trickle bed air biofilters (TBABs) are suitable for treatment of relatively high volumes of volatile organic compounds due to their controlled environment. A laboratory-scale TBAB was used for the treatment of an air stream contaminated with benzene under different loading rates (LRs) ranging from 7.2 to 76.8 gm(-3)h(-1). The TBAB was operated at pH 7 and 25 degrees C. Consistent long-term performance of the benzene TBAB depends on various factors one of which is the excess amount of biomass accumulated within the bed. Three experimental strategies for biomass control were employed in the study: weekly backwashing for 1h, starvation (no benzene feed for a period of 2d/week) and stagnation (no benzene, air and nutrient flow for a period of 2d/week). The experimental plan was designed to investigate the long-term performance of the TBAB with emphasis on the empty bed resident time (EBRT), different benzene LRs, removal efficiency with TBAB depth, volatile suspended solids and carbon mass balance closure. For benzene loading up to 34.1gm(-3)h(-1), removal efficiency consistently over 98% was achieved. At the maximum LR 76.8 gm(-3)h(-1) the removal efficiency was still above 80% by utilizing stagnation strategy for 2d and gas flow switching once per week as means of biomass control. Backwashing once per week provided less efficient performance as compared to stagnation while starvation showed the worst performance. EBRT at 120 s provided the best performance while EBRT at 90 s showed slightly lower performance.