SURFACE OF ACTIVATED SLUDGE PARTICLES IN RELATION TO THEIR SETTLING CHARACTERISTICS

Very little work has been reported which relates the surface properties of sewage sludges to their dewatering characteristics. The measurement of the electrophoretic mobility of activated sludge particles was therefore included in the analysis of routine samples from a Lübeck pilot-plant. These measurements were made in a rectangular cell of the type described by James (1957). In constant ionic strength buffer solutions (I = 0·2) no correlation was found between either the iso-electric points or the pK values of the sludge surfaces and the sludge volume index. Mobility measurements of the sludge particles in their own liquors however, showed that the average mobility was directly proportional to the sludge volume index, which in turn was a logarithmic function of the ratio of ammonia-nitrogen to soluble phosphate in the liquors. This would appear to indicate that the settling characteristics of activated sludges are governed by some metabolic process which can alter the nature of the surface of the sludge particles. © 1968.