Measurement method for in situ particle settling velocity

The most meaningful parameter to determine the treatment efficiency of large scale sedimentation tanks is the settling velocity of suspended solids. However it is difficult to measured representative settling velocity because of the instability of suspended solids. A water elutriation system was tested to assess the treatment efficiency of sedimentation tanks. In laboratory tests the flow conditions in the water elutriation system were investigated which are important for the separation process of different settleable particles. Furthermore particle tracer tests were carried out in the water elutriation system to examine the separation efficiency of the system. An investigation made on the performance of sedimentation tanks proves the applicability of the system under real operation conditions. The field investigations indicate that high over-all efficiency must not be the result of a well constructed and working tank if it results on a great amount of well settleable particles in the inflow. Furthermore real time particle size distributions of suspended particles were carried out with a submersible field instrument developed for in-situ observation. These results confirm the function of the water elutriation system measurement which was carried out parallel.