Density, porosity, and pore structure of biofilms

The spatial distributions of biofilm properties have been investigated. Heterotrophic biofilms were cultured by using rotating drum biofilm reactors which were fed to a synthetic wastewater. The biofilm was first cut into 10-20 μm thick slices by use of a microtome, and then apportioned into samples representing 3 or 4 layers. By measuring total suspended solids, phospholipid concentrations and AR18 dye adsorption, and using these data with the theoretical model developed in this study, the densities, porosities, specific surface area, and mean pore radius of biofilms were determined. It was found that the densities (with units of mg-TS/cm³ total biofilm) in the bottom layers were 5-10 times higher than those in the top layers; the ratio of living cells to total biomass decreased from 72 to 91% in the top layers to 31-39% in the bottom layers; the porosities of biofilms changed from 84 to 93% in the top layers to 58-67% in the bottom layers. In contrast, the mean pore radius of biofilms decreased from approximately 1.7-2.7 μm in the top layers to 0.3-0.4 μm in the bottom layers. The results of this study are helpful in obtaining a much clearer physical description of biofilms.