Determination of local elimination capacities and moisture contents in different biofilters treating toluene and xylene

The removal of toluene and xylene from an artificial waste gas was investigated in two laboratory scale biofilters filled with mixtures of peat, bark and wood. The packed beds differed in the mixture of materials used, so that peat and then bark was the dominant constituent. The biofilters were operated in an upflow mode. Both biofilters showed relatively high removal efficiencies for both pollutants (74-98%). The evaluation of the local elimination capacities in the peat-loaded biofilter revealed that the major part of pollutants was degraded in the middle layer. In this biofilter, larger differences in the removal rates along the bed height were also observed. In the biofilter with bark as dominant material, the major part of pollutants was degraded at the inlet of the bed and also at a relative height of 0.7. Moisture contents of 71-80% and 65-78% were found for the biofilter with peat and bark respectively. When the regular pouring of nutrient solution through the bed was interrupted for 1 month, a decrease in efficiency was observed in the biofilter with bark, whilst the efficiency in the biofilter with peat remained the same.