On the stability and settling of suspended solids in settling ponds. Part II. Diffusion analysis of initial settling of suspended solids

The initial settling behaviour of the low solids concentration suspensions is examined and analyzed to provide information on sedimentation characteristics and distribution of solids concentration profiles with time. The presence of surface-active forces, which participate in development of the suspended solids settling characteristics, does not always permit easy application of standard sedimentation models for calculating settling rates of the suspended solids. A simplified diffusion–convection model using the relative flux approach has been developed to predict the initial settling performance of the suspended solids. Experimentally determined fluid diffusion coefficients relative to diffused volumetric fluid contents are obtained to provide input to the calculations for prediction of actual test cases. Comparisons using laboratory settling test data, together with information from a field settling pond, are made with predictions obtained using the model. The comparative results show that the analyses obtained using the theoretical model can predict initial settling of the suspended solids. Key words: suspended solids, settling, sedimentation, diffusion, solids concentration, fines thickening.