Dynamic responses of biofilters to changes in the operating conditions in the process of removing toluene and xylene from air

The dynamic behaviour of biofilters intended to remove toluene and xylene f rom air was studied during transient states. Laboratory scale biofilters we re filled with a mixture of peat, bark and wood and inoculated with a mixed microbial population. Toluene and xylene were applied both as single pollu tants and as mixtures. Attention was focused on the evaluation of the follo wing transients: the response of biofilters to step changes and peaks in po llutant concentrations, the effect of changes between single and multiple p ollutant loadings and the response to shutdown periods. The biofilters demo nstrated a good dynamic stability during transient states induced by change s in inlet pollutant concentrations. Their time periods did not exceed thre e hours. No interaction between xylene and toluene degradation was observed during changes in loading with single pollutants or their mixture. The per formance interruptions lasting less than 24 hours were found to have no sig nificant influence on the removal efficiency of biofilters. When the biofil ters were reacclimated after longer starvation periods, a short temporary d ecrease in efficiency whose minimum and duration were proportional to the l ength of a preceding shutdown period was observed. The longest starvation p eriod (7 days) resulted in a reacclimation lasting 7 hours only. Adaptation s of a microbial population to new operating conditions as well as sorption /desorption processes were suggested as the main factors influencing the dy namic response characteristics.