Attached microbial growths-II. Frictional resistance due to microbial slimes

Abstract

A number of cases have been reported in which water-carrying conduits have suffered from remarkable losses in delivery capacity within relatively short operation periods. In one instance (SEI~RT et al., 1950), the maximum capacity of a 24-in. (nominal diameter), 50 mile long water supply line was reduced to about 55 per cent of its original value within a few years. The loss was due to a thin, slimy layer that consisted largely of organic material imbedded with fine clay particles and was not caused by a substantial decrease in effective internal diameter. The layer was characterized by a "ripple-like" surface having an average height of 0.025 in. The results indicate that this type of roughness could not be explained in terms of equivalent sand roughness common to friction factor relationships.The rippled surface structure seems to be an essential, but not the only, factor involved in the unusual frictional behavior caused by microbial slimes. Experiments using solid surfaces of similar pattern have shown a high frictional resistance, but not nearly as high as those occurring in water mains.