Fluid shear influences on flocculation

Introduction

The tube flocculator was used to study how fluid shear levels affect the settling properties of a flocculated alum-kaolin suspension. FReTA was employed to quantitatively compare the effects of varying fluid shear and hydraulic residence time on the sedimentation velocity distributions and the post-sedimentation residual turbidities of flocculated suspensions formed in the tube flocculator. Results showed that shear induced floc break up occurred at all velocity gradients evaluated. There was a correlation between high floc settling velocities and low residual turbidities, both of which were optimized at low fluid shear levels and long fluid residence times. This study showed that, for hydraulic flocculation systems, low turbidity water was produced when fluid shear was kept at a minimum.

Results and discussion

All the results and discussion for these experiments can be found in Ian Tse's M.S. thesis: Fluid shear influences on hydraulic flocculation systems characterized using a newly developed method for quantitative analysis of flocculation performance

During fall 2009, two challenges were tested with the completion of one. For the first challenge, the study of the effect of shear rate on tube flocculator performance, our goal was to replicate an experiment from spring 2009 for the team to familiarize itself to the experimental apparatus and analysis techniques. Though this challenge did not provide new data, it showed the overall functions of the tube floc experimental setup and the computer programs used for data analysis.