Biofiltration for the treatment of complex mixtures of VOC - Influence of the packing material

Currently air biofiltration is largely considered for the removal of Volatile Organic Compounds (VOC) from polluted airstreams. In order to select a suitable packing material for the treatment of VOC polluted air and better understand the influence of the packing material properties upon the removal efficiency, a mixture of eleven VOC was treated in two down-flow biofilter units packed with either peat or Granular Activated Carbon (GAC) and functioned under similar operating conditions for 92 days. Using the peat biofilter under steady-state conditions achieved a removal efficiency of 90% greater than the 80% achieved using the GAC filter. Moreover, in both cases, a stratification of the abatement along the column was observed but it differed according to the type of the packing material used. For the peat biofilter, elimination of oxygenated compounds occurred in the first 50 cm of the column, whereas aromatic and halogenated compounds were treated in the segments closer to the outlet. In contrast, with GAC, the removal of oxygenated and aromatic compounds took place along the height of the column. For the removal of microorganisms fixed on peat and activated carbon particles, the crushing with an ultar-turrax was the most efficient dispersing method, compared to agitation with a vortex and ultrasound. The counting of microorganisms using three culture media [Luria Bertoni (LB); Plate Count Agar (PCA); Tryptic Soy Agar, tenfold diluted (TSA 1/10)] demonstrated that the TSA 1/10 was likely most suitable for the recovery of the peat biofilter microflora (TSA 1/10: 5.6 x 10(9) CFU/g of dry peat, PCA: 1.5 x 10(9) CFU/g of dry peat, LB: 0.3 x 10(9) CFU/g of dry peat) probably due to the dominance of oligotrophic bacteria, whereas for the activated carbon biofilter there was no significant difference (PCA: 4.4 x 10(9); LB: 4.2 x 10(9); TSA 1/10: 4.5 x 10(9) CFU/g of dry activated carbon) between these media suggesting that oligotrophic and zymogeneous bacteria are likely in the same proportion. The results illustrated that even the removal efficiency is associated with the pollutant properties; it was assumed that the sorptive properties of GAC could modify the VOC degradation mechanisms and then entail a real reduction of the removal efficiency.