Subteam Leader:

Tanya or anyone with previous knowledge of floating flocs problem

Number of team members needed:

• 3-4 members

Important team member skills:

• Process Controller (can be trained)
• MathCAD

Challenges

• Test the source of floating flocs:
  -is it air bubbles coming out of supersaturated solution?
  -is it from air bubbles already present in solution?

• If problem is caused from air bubbles already present in solution:
  -confirm that the retrofit design from the CDC team summer 09 will work
  -confirm that there are no other ways that air bubbles could be created in AguaClara plants

If air bubbles are coming out of the supersatured solution and affect performance in the AguaClara plants:
-design a few novel ways that we could get rid of air bubbles utilizing a physical means

Other challenges may include:

Details of the experiments that have been planned can be found on the Floating Flocs Fall 2009 Tentative Experiments page.

• Possibly redesign the experimental setup to better simulate the water quality at actual AC plants by adding a clay source or surfactant source.
• Confirm the cause of the floating floc problem by running experiments with the Plate Settler Team's apparatus. Two experiments have been planned in order to test whether the cause of the floating floc problem is bubbles adhering to flocs or whether bubbles form on flocs and lift them to the surface. It is also possible that both of these mechanisms are responsible for floating floc.

If the cause is confirmed to be bubble formation on or adherence to flocs due to supersaturated water the team's tentative experimental plans include:

• Run experiments using mild surfactants to witness their effects on bubble formation. Currently, the team is considering using a dilute soap solution as a surfactant. Details as to the concentration of soap solution have yet to be determined. This will likely be based on a conversion of organic matter in the water of AguaClara plants.
• Run experiments using hydrophobic surfaces with or without surfactants to see the effects on bubble formation. The details of these experiments have yet to be determined. Currently, literature searches are being performed to find cost-effective hydrophobic surfaces to test. It has been found that plant surfaces may exhibit hydrophobic properties due to their waxy coating.
• Developing a new mechanism to either remove gas, stop bubble formation, or stop floating flocs themselves. Currently, the team is looking at a mechanism that involves using lamella or something similar to trap air pockets in the water. These air pockets would be knocked around by eddies and may collect dissolved gas in the process.

One possibility to consider is whether flocs that are floating can be redirected or captured so that they are not in the effluent water. (I doubt this can be done.) Since achieving gas removal has been proven to be difficult, putting some time into considering other solutions may be worthwhile.

If the cause of floating flocs is shown to be something other than supersaturated water, the team may still focus on stopping flocs from floating; however, other approaches may be developed that are specifically tailored to actual cause of the problem.