Method for quantitative analysis of flocculation performance

The sedimentation rate and the post-sedimentation residual turbidity of flocculated suspensions are properties central to the design and operation of unit processes following flocculation in a water treatment plant. A method for comparing flocculation performance based on these two properties is described. The flocculation residual turbidity analyzer (FReTA) records the turbidity of flocculent suspensions undergoing quiescent settling. The fixed distance across which flocs must travel to clear the measurement volume allows sedimentation velocity distributions of the flocculent suspension to be calculated from the raw turbidity data. By fitting the transformed turbidity data with a modified gamma distribution, the mean and variance of sedimentation velocity can be obtained along with the residual turbidity after a period of settling. This new analysis method can be used to quantitatively compare how differences in flocculator operating conditions affect the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity.

► A method for comparing flocculation performance based on sedimentation rate and the post-sedimentation residual turbidity is described.
► The effects of flocculator operating conditions on the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity are reproducibly quantified.
► Experiments using this method are currently being carried out to evaluate the contribution of velocity gradients, residence time, and coagulant dose on flocculator performance.