The effects of a lower irrigation system on pollutant removal and on the microflora of a biofilter.

Moisture control is one the most important parameters in biofilters for air pollution control. Biofilters tend to experience drying at the air inlet port, which causes decreased pollutant removal over time. In this study, the installation of an irrigation system within the lower part of the biofilter bed was proposed, and its effect was quantified in a laboratory scale biofilter operated side by side with a control biofilter. The removal of toluene vapours at short gas residence time (13.5 s) served as a model system. The results showed that the rate of toluene elimination in the biofilter with the lower irrigation system was 1.2-1.7 times greater than the rate of toluene elimination in the control biofilter. At the completion of the two-month experiment, a detailed examination was conducted of the packing materials with the immobilized pollutant-degrading culture. The results highlighted the effects of bed drying on cell viability in the control biofilter. They also revealed that the bottom segment of the biofilter with the lower irrigation system had a higher moisture content, a higher biomass density and a larger fraction of active biomass than the corresponding segment in the conventional biofilter. These detailed examinations explained why an increased toluene removal was observed in the system equipped with a lower irrigation system. Overall, this study demonstrates enhanced pollutant removal in biofilters equipped with a lower irrigation system through a better control of moisture.