Biofiltration of cyclic air emissions of α-pinene at low and high frequencies

Biofiltration of periodically fluctuating concentrations of an a-pinene-laden waste gas was investigated to treat both high-frequency and low-frequency fluctuations. The effects of periodic concentration fluctuations on biofilter performance were measured. Controlled variables of periodic operation included cycle period and amplitude. The cycle period ranged from 10 min to 6 days, with the inlet a-pinene concentration fluctuating between 0 and 100 parts per million volume. At high-frequency concentration cycling (i.e., on the order of minutes), both cyclic and constant concentration biofilters maintained similar long-term performance with an average removal efficiency of 77% at an averaged loading rate of 29 g alpha-pinene/m(3) bed/hr. A first approximation suggests kinetics that are time-independent, indicating that steady-state data can be used to predict transient behavior at this time scale. Cyclic biofilter operation with a cycle period of 24 hr (with equal on/off time) was achievable for biofilters without a significant loss in performance. At longer time scales, cyclic biofilter performance decreased at the restart of the ON cycle. The recovery time to previous levels of performance increased with increasing cycle period; the recovery time was less than 1 hr for a cycle period of 24 hr and between 6 and 8 hr for a cycle period of 6 days.