Exhaust gas purification using biocatalysts (fixed bacteria monocultures) — the influence of biofilm diffusion rate (O₂) on the overall reaction rate

Summary

This paper presents results of experiments on the influence of O₂ and substrate (pollutant) concentration on the overall reaction rate of a trickle-bed reactor used for biological waste gas purification. The biocatalyst was a pollutant-specific bacterial monoculture fixed on porous glass carriers. The conversion of acetone and propionaldehyde, as model pollutants that are easily soluble in water, was measured. Under constant hydrodynamic conditions (gas and liquid flow rates) the inlet pollutant concentration was varied. The O₂ partial pressure in the model gas was increased to investigate the influence of O₂ supply on pollutant conversion. At higher pollutant concentrations (>117 mg acetone.m^-3 gas and > 150 mg propionaldehyde.m^-3 gas) higher concentrations of dissolved O₂ led to a significant rise in the maximum degradation capacity of the reactor. This maximum reaction rate was independent of the pollutant mass flow. It seems that the diffusion of O₂ in the biofilm is rate-determining. The reaction rate at lower inlet concentrations was not affected by the improved O₂ supply. Here the external mass transfer through the liquid film limits the reaction rate and the maximum separation efficiency of about 80% at a residence time of 1.2s (space velocity 3000h^-1) is achieved.