Biofilm characteristics as affected by sand size and location in fluidized bed vessels

Biofilm structure was quantitatively analyzed to detect differences in biofilm structure due to sand size (effective diameter D 10 of 0.23 and 0.60 mm) and location within a fluidized-sand filter vessel. Laser scanning confocal microscopy and 3D image analysis were used to quantify biofilm volume per unit sand area, biofilm surface area per unit sand area, and biofilm surface area per biofilm volume. Biofilms from reactor vessels using 0.60 mm sand size had thin, smoother biofilms which was attributed to higher shear environments, in contrast to the thick, rough, porous films that were measured on the 0.23 mm sand samples. The thicknesses of the biofilms in the small sand reactors were affected by their location within the reactor vessel, i.e. films from the base of the reactor in the more highly turbulent zone had thinner biofilms than films on sands that were taken from a higher less turbulent location in the reactor vessel. A major finding of this study was that biofilm surface area per biofilm volume remained fairly constant regardless of sand size and sampling location.