Abstract Colloid removal in water treatment plants is commonly done by a sequence of processes that includes coagulation, flocculation, sedimentation, and filtration. The current study presents an innovative technique, termed grouping, for the removal of these suspended particles based on physical flow manipulation, which causes the particles to aggregate. Previous results showed that gentle oscillation in a cylindrical container facilitates simultaneous flocculation and sedimentation in the same reactor over shorter periods of time than are possible using the conventional treatment approach. This finding may confer marked improvements on the processes used today by enabling the use of both smaller reactors and less energy. Based on the findings with the cylindrical vessel, here the grouping technique is further examined in a rectangular container and over a range of different initial turbidities. The results indicate that the removal efficiency is higher in the rectangular container under the different initial turbidities tested. In addition, the removal efficiency was shown to remain robust with the decreases in initial turbidity and alum concentrations that occur during treatment. The positive results of our previous study taken together with this finding hint at the strong potential of the grouping technique to improve common flocculation processes.