Experimental studies and theoretical modelling of an unsteady state biofilter used to treat fluctuating concentrations of an alpha-pinene air emission

This research describes the biofiltration of a transient, α-pinene laden air emission and compares experimental results to a dynamic diffusion-reaction model for a plug flow reactor. Three parallel biofilters, two biofilters (replicates) treating a cyclically fluctuating concentration and the third biofilter treating a constant concentration, were used to study the effect of periodic concentration fluctuations on biofilter performance. The cycle period ranged from 10 minutes to 6 days, with maximum α-pinene concentration fluctuations between 0 to 100 ppmv.; Both cyclic (cycle period of 10 minutes) and constant concentration biofilters maintained similar long-term performance (averaging removal efficiencies of 77%) at an averaged loading rate of 29 g α-pinene/m3 bed/h.; The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclically operated biofilters operating at short cycle periods (i.e., on the order of minutes and hours). As a first approximation, steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 hour cycle period, the dynamic model compares well with experimental results. At longer times scales the model does not effectively predict transient behaviour as adsorption and changes in kinetic parameters are not accounted for.; For long cycle periods (i.e., hours and days), removal efficiency decreased after periods of non-loading; the longer the period of non-loading, the poorer the biofilter's performance at the re-commencement of pollutant loading. The recovery time for a cycle period of 24 hours was less than one hour. The recovery time for a cycle period of 6 days was between 6–8 hours.; Modelling results showed that similar biofiltration performance for cyclic and constant concentration biofiltration of α-pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, C_g,max/C_g, relative value of the half saturation constant in the Monod expression, K _s, and effective diffusivity of α-pinene in the biofilm, D _e.