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In some AguaClara plants, a surface foam develops at the end of rapid mix. The first experiment goal was to understand the chemical conditions required for this surface foam to develop at the end of rapid mix and the first baffle. The first test trials were conducted with a constant supply of clay and varying amounts of alum but these did not exhibit any form of surface foam formation. Subsequent trials included organic matter: humic acid, but these only produced large non persistent bubbles. It was not until a stronger surfactant, liquid soap, was added to the baffle spacing that a surface foam with strong persistent bubbles developed. From these experiments it was concluded that air entrainment along with a surfactant in the raw water are the main factors behind surface foam formation. In Honduras, the raw water may contain decaying matter which decays to fatty acids acting as the surfactant while the waterfall at the LFOM creates- the perfect- condition for air entrainment (what about the waterfall does?). The process of air entrainment along with natural surfactants in the water allow for the formation of surface foam. With this in mind, the research is now focused on retrofitting AguaClara's designs so that no air entrainment occurs in the entrance tank and rapid mix chamber by eliminating waterfalls and or implementing hydraulic jumps.
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- Attempt to recreate the foam in a laboratory setting that has been forming in many of the AguaClara plants in Hoduras.
- Design a way to retrofit the current plants to eliminate the foam
- Learn about the current design for a Nonlinear Chemical Dose Controller and then update MathCAD code for the controller and hopefully be able to build a fully functional prototype by the end of the summer.
These two goals (which two?) are very important to the overall goals of AguaClara for a number of reasons. The foam that forms in the current AguaClara plants both increases the amount of work that plant operators have to spend to keep the water clean, and reduces the overall effectiveness of the plants. Although the foam cannot flow very far in the plant itself, it can be blown around by wind to the surface of the sedimentation tank. Small bubbles formed by decreased surface tension in rapid mix could persist as far as the sedimentation tank, where they would come out, possibly causing the floating floc problem. We suspect that the surfactants and natural organic matter lower the surface tension energy requirements, possibly creating these small bubbles that stay in solution long enough to reach the sedimentation tank.
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