Improving Floc Formation for Cleaner Water

The Laminar Tube Flocculator’s current goals are based on a floc breakup theory by one of our former graduate students, Karen Swetland. Flocs are formed by unwanted particles sticking to each other to create unwanted masses in the water. These undesirable masses are then separated from the water later. Swetland's theory basically hypothesizes that when larger flocs are broken up during the flocculation process, they are given the opportunity to regrow and collect more particles, thereby resulting in a lower residual turbidity. 

The setup of the laminar tube flocculator team. The machines attached are called turbidimeters, and
measure the influent and effluent turbidity.

To test this theory, Vicki and Yining are conducting a series of experiments using clamps with openings measuring 4 millimeters and 5 millimeters, something that was decided this past summer to break up flocs and most effectively achieve the desired residual turbidity levels. Coagulant dose is varied along with clamp size, and each configuration of the two is tested multiple times in order to make sure that experiment results are consistent with themselves. As a control for the clamp test, they collected data on the effect that having no clamps had on the residual turbidity.

So far, they have found that having one clamp in the middle arrangement of the tubing does not reduce residual turbidity when compared to the base case data. Their next steps are to test with multiple clamps to see if breaking up flocs more frequently throughout the process will reduce residual turbidity.

Lab-scale turbulent tube flocculator. Newly built!

Laminar tube flocculation is useful primarily at the scale of laboratory experiments because the movement of the particles through the water is very orderly, resulting in more straightforward analyses. Compare this with turbulent tube flocculation, where the movement of particles in water is erratic and difficult to analyze.

However, turbulent tube flocculation best describes the process of the actual plants in Honduras. This semester, the turbulent tube flocculator team was primarily concerned with building a scaled version of the flocculator based off of designs by the Summer 2013 team. However, they hope to, like the laminar tube floc team, test Karen Swetland’s floc breakup research. While Karen’s research was done with the laminar system in mind, turbulence may have some effects on flocculation that aren’t reflected in testing with its laminar counterpart.

Both research teams’ efforts are centered on achieving lower residual turbidity. Regardless of whether floc breakup will help them better achieve this end, the results of their research will have implications for how the full-scale flocculator will be designed.