Biofilm characteristics as affected by sand size and location in fluidizedbed vessels

Biofilm structure was quantitatively analyzed to detect differences in biof ilm 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 confoc al microscopy and 3D image analysis were used to quantify biofilm volume pe r unit sand area, biofilm surface area per unit sand area, and biofilm surf ace area per biofilm volume. Biofilms from reactor vessels using 0.60 mm sa nd size had thin, smoother biofilms which was attributed to higher shear en vironments, in contrast to the thick, rough, porous films that were measure d 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 ha d thinner biofilms than films on sands that were taken from a higher less t urbulent location in the reactor vessel. A major finding of this study was that biofilm surface area per biofilm volume remained fairly constant regar dless of sand size and sampling location. (C) 2000 Elsevier Science B.V. Al l rights reserved.