Rheology as a tool for measurement of sludge shear

Shear intensity, shear time, and polymer dose are the main parameters that determine the dewaterability of wastewater sludge. Polymer dose required to condition the sludge increases with the increase of shear intensity (G) and shear time (t). Therefore, in order to minimize the polymer demand during conditioning and dewatering, shear should be optimized. Optimization of shear can be achieved if the total shear that the sludge network is exposed to during conditioning and dewatering can be measured and quantified. This is quite a challenge since total shear includes unintended shear introduced during piping and pumping, and currently there is no direct or indirect technique that can measure this unintended shear. Unintended shear increases the polymer demand and shifts the optimum polymer dose to a higher dose, which in turn decreases the cake solids concentration and the efficiency of the dewatering process. Thus, quantification of the unintended shear and adjustment of the polymer dose accordingly are essential for the optimization of dewatering processes. The main objective of this study was to develop a method for sludge shear measurement based on the rheological characteristics of sludge and illustrate its possible applications at treatment plants. The results of this study indicate that the rheological characteristics of sludge can be used to estimate an unknown amount of shear that sludge network is exposed to, and to match the jar-test mixing conditions to that of the full-scale mixers employed at treatment plants.