Direct Comparison of Fluidized and Packed Bed Bioreactors for Bioremediation of an Air Pollutant

A gas-solid fluidized bed bioreactor has been successfully used for the bioremediation of ethanol (a model volatile organic compound, VOC) contaminated air. A key objective of this fluidized bioreactor study was to compare the performance of fluid bed operation to packed bed operation. A fluid bed system increased homogeneity and improved upon operating problems such as plugging and channelling normally associated with packed bed bioreactors. The bioreactor bed was comprised of a mixture of moist sawdust particles and glass spheres. Depending on the superficial velocity of the waste gas stream, the bioreactor could be operated in either packed or fluidized mode. During fluid bed operation, the sawdust and glass sphere mixture was maintained in a bubbling/slugging regime. As expected, fluid bed operation demonstrated significantly higher mass transfer rates but the maximum elimination capacity was 75 g m-3sawdust h-1 as compared to 225 g m-3sawdust h-1 for packed bed operation. In packed bed mode, higher ethanol concentrations were used in order to have comparable ethanol loadings and this may have contributed to faster growth rates and thus faster bioremediation rates.