A method for measuring sludge settling characteristics in turbulent flows

Abstract

A method for the determination of the settling velocity for sludge as a function of turbulence intensity and sludge concentration has been developed. The principle of the method is to continuously feed the top of a settling column with sludge so that a steady state and uniform concentration distribution occurs in the middle of the column. This eliminates time scale effects such as flocculation from the measurements, as the resulting settling velocity only can be found at steady state and uniform conditions. The method assumes that flocculated sludge settles faster than disintegrated sludge to make a mass balance involving concentration at the top and at the middle of the column as well as the inlet sludge flow. The resulting mass balance is used to calculate a local settling velocity. The turbulence is introduced by an oscillating grid in the whole depth of the settling column. Settling velocities can be measured at arbitrarily selected combinations of turbulence and concentration. The foremost advantage of the method is that settling characteristics measured in this way can be utilized directly in numerical models of sedimentation tanks, process tanks, etc.