The application of settling velocity as a parameter for characterising wastewater solids

A research programme at Aston University, the aim of which was to investigate the distribution of chemicals within the settling velocity grading curve of suspended sewage solids, has recently been completed. The pollutants investigated were COD, TKN, Phosphorous and a suite of 7 metals. Tables summarising their distributions, and the range of values observed, are presented in the paper. Although the 15 sites studied were divided into large, medium and small classes, no evidence was found to indicate that catchment size influences the distribution of chemicals significantly. However, the TKN and P loadings tended to be higher for small catchments. This is probably due to a greater proportion of their area being rural, than in the medium and large catchments. It is pointed out that when differing units are used to present the results, different conclusions can be drawn regarding the settling velocity fraction which carries the heaviest pollutant load.