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The dynamics of a multispecies biofilm population in a laboratory-scale trickle-bed bioreactor for the treatment of waste gas was examined. The model pollutant was a VOC-mixture of polyalkylated benzenes called Solvesso 100. Fluorescence in-situ hybridization (FISH) was applied in order to characterise the population composition. The bioreactor was operated under transient conditions by applying pollutant concentration shifts and a starvation phase. Only about 10% of the biofilm mass were cells, the rest consisted of extracellular polymeric substances (EPS). The average fraction of Solvesso 100-degrading cells during pollutant supply periods was less than 10%. About 60% of the cells were saprophytes and about 30% were inactive cells. During pollutant concentration shift experiments, the bioreactor performance adapted within a few hours. The biofilm population exhibited a dependency upon the direction of the shifts. The population reacted within days after a shift-down and within weeks after a shift-up. The pollutant-degraders reacted significantly faster compared to the other cells. During the long-term starvation phase, a shift of the population composition took place. However, this change of composition as well as the degree of metabolic activity was completely reversible. A direct correlation between the biodegradation rate of the bioreactor and the number of pollutant-degrading cells present in the biofilm could not be obtained due to insufficient experimental evidence.

The microbial composition and structure of a multispecies biofilm of a laboratory-scale tricklebed bioreactor for the treatment of waste gas was examined. The model pollutant was a volatile organic compound-mixture of polyalkylated benzenes called Solvesso 100  . Fluorescent in-situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were applied. Two new Solvesso 100  -degrading Pseudomonas sp strains were isolated from the multispecies biofilm. Corresponding isolate-specific oligonucleotide probes were designed and applied successfully. A major finding was that the fraction of Solvesso 100 -degrading bacteria in the biofilm was low (about 3-6% during long-term operation). The majority of the active cells were saprophytes which utilized intermediates and cell lysis products. The measured fraction of extracellular polymeric substances of the mature biofilm was 89-93% of the total biomass. The CLSM examinations of a 3-days-old approx 10 µm thick biofilm revealed highly heterogeneous structures with distinguished three-dimensional matrix-enclosed microcolony bodies spread across the substratum surface. The 28-days-old 80-960 µm thick biofilm exhibited voids, cellfree channels, and pores of variable sizes. In both cases, an even distribution of active cells and pollutant-degrading bacteria throughout the biofilm cross-section as well as through the biofilm depth was observed.

The biodegradation of polyalkylated benzenes (Solvesso 100®) from waste air in a trickle-bed bioreactor was studied. The immobilized mixed population was analyzed by in-situ hybridization using group-specific fluorescence labeled rRNA-target oligonucleotides. It was shown that the growth conditions of an immobilized system are not comparable to those of a submerged culture. Variations of the concentrations of the α-, β-, and γ-subclasses of the proteobacteria of the biofilm population were measured. A significant increase of the biodegradation rate and, thus, of the activity of the microbial mixed population present in the biofilm was observed by applying a forced cyclical substrate time function.

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