Flow characteristics of primary and digested sewage sludge

Summary Rheological study of sewage sludge is useful for the design, operation and control of sewage treatment plants. The rheology is highly dependent on physical, chemical and biological characteristics of the sludge. A pipeline rheometer is described in this paper for measurement of rheological properties of the sludge. Primary sewage sludge is a complex flocculated suspension having no fixed particle dimension, shape, size distribution or surface characteristics. The information available so far on rheology of sewage sludge is not suitable for application in design because of the lack of data on physico-chemical characteristics of this sludge.Primary and digested sewage sludge are non-Newtonian in character. Both exhibit yield stress and while primary sludge is shear-thinning in nature, digested sludge has been found to be shear-thickening. Parabolic and yield-power law models have been used to express the experimental data obtained for sludges at various concentrations and temperatures. Yield stress of primary sludge varies exponentially with concentration and linearly with temperature within the short temperature range studied. Primary sludge is found to be antithixotropic at low shear stress. Digested sludge does not exhibit time dependency.With 9 figures and 5 tables