No abstract

An experimental study on the removal of xylene vapours from an air stream was conducted on three identical upflow laboratory-scale wood-chips-based bed biofilters. Three different inoculums were used: fungi (Phanerochaete chrysosporium and Cladosporium sphaerospermum), a bacterial consortium (EVB110), and a mixed culture of fungi and EVB 110. The empty bed gas residence time was 59 s, and various inlet concentrations of the contaminant were tested. The results obtained revealed a strong correlation between the average temperature of the biofilter and the intensity of the microbial activity in the filter bed. In addition, the mass of carbon dioxide produced per mass of xylene removed was equal to 3.03, indicating elimination of the pollutant by aerobic biodegradation. The removal rates of xylene in both fungal and bacterial systems were similar up to an inlet load of 100 g m(-3) h(-1). However, a better performance was achieved in the fungal system at higher inlet loads of the pollutant. The maximum elimination capacity achieved in the fungal and bacterial systems was 77 and 58 g m(-3) h(-1), respectively; and an early set-off of the inhibition effects was observed in the latter. The bioreactor inoculated with the mixed culture was the least effective, with a maximum elimination capacity of only 38 g m(-3) h(-1). Problems with microbial population survival and competition among different types of microorganisms could be responsible of this lower performance. The fungal system was also tested for the removal of toluene vapour and achieved a maximum elimination capacity of 110 g m(-3) h(-1).

In industrial activities, operation of air biofilters may be interrupted for a long period of time. In order to examine the effect of shut-down on the performance of biofilters, a pilot scale biofiltration unit was restarted up after a non-use duration of eight months. After a reacclimation period of eight days, the biofilter reached an elimination capacity of 35 g x m(-3) x h(-1) compared to 38 g x m(-3) x h(-1) before shut-down, for the same operating conditions. The results obtained indicate that the microorganism activity was completely restored and this was confirmed by the microbial count tests performed on filter bed material samples. The impact of varying the inlet concentration of toluene on biofilter performance was also investigated. A maximum elimination capacity of 120 g x m(-3) x h(-1) was achieved, compared to 135 g x m(-3) x h(-1) before shut-down. The biofilter removal efficiency exceeded 96% for inlet concentrations up to 1.8 g x m(-3). Temperature measurements revealed that the filter bed temperature depends strongly on the intensity of microbial activity and the biofilter effectiveness in eliminating toluene. Experimental data were compared with the calculations of a mathematical model. Comparison showed that the theoretical model was successful in predicting the performance of the biofiltration unit.