Visualisation of the establishment of a heterotrophic biofilm within the schmutzdecke of a slow sand filter using scanning electronic microscopy

The unique feature of slow sand filters is the schmutzdecke, a biofilm formed at the sand - water interface. Scanning electron microscopy was used to observe the surface of sand obtained from the schmutzdecke of a newly seeded and a mature slow sand filter. The complex nature of the biofilm formed on the sand was observed. A distinct difference was seen between the freshly seeded schmutzdecke compared to the schmutzdecke from a mature filter. It was found that a larger amount of extracellular matrix was present within the schmutzdecke removed from a mature filter. The images obtained show that sand, at the sand-water interface of slow sand filters, offers an attractive environment for the colonisation of a variety of micro-organisms including diatoms, algae, bacteria and their extracellular products.

Keywords
biofilm, schmutzdecke, slow sand filtration, scanning electron microscopy, SEM