Modified Approach to Evaluate Column Test Data

In the conventional method of calculating the fractional removal of flocculent particles, it is assumed that the average settling velocity for different particle sizes in the lower depths in settling basins is the same as in the upper depths. This assumption is not quite correct, because the particles continuously flocculate or shear during the entire settling depth, and hence the average settling velocity changes both with depth and time. In the modified method, a different approach for calculating the fractional removal of particles is proposed to overcome the deficiency in the conventional method. Instead of considering a vertical constant time line, a horizontal constant depth line for that particular time is used. This approach is more reasonable because the settling velocities of different flocculating particles are all averaged over the same depth.