Effect of switching gas inlet position on the performance of a polyurethane biofilter under transient loading for the removal of benzene, toluene and xylene mixtures.

The performance of a polyurethane (PU) biofilter was evaluated using different operating modes (unidirectional flow (UF) and flow-directional switching (FDS) operations) under transient loading conditions (intermittent and shutdown). Gas mixtures containing benzene, toluene and xylene (BTX) were employed as model gases. Quantitative real-time PCR methods were used for targeting the tmoA gene responsible for BTX degradation and estimating density of the BTX-degraders in the PU filter bed. Although the overall BTX Removal efficiencies at the outlet (50 h(-1) of space velocity) were similar between the UF and FDS biofilters, the removability of BTX in the FDS biofilter was higher than that in the UF biofilter until the 3rd sampling position (68 h(-1) of space velocity). The BTX removal potentials and tmoA gene copy numbers of the FDS biofilter remained constant, irrespective of the distances from the inlet, but those of the UF biofilter increased with increasing distance from the inlet position. These results indicate that an even distribution of BTX degraders in the FDS filter bed contributed to better BTX removal performance. After a 10 day-shutdown, the performances of the UF and SDF biofilters were rapidly restored within 1 day.