...
THEORY AND INTRODUCTION
Tube settlers are settlers are designed to provide a low capture velocity to facilitate the removal of small flocs and hence lower the turbidity of flocculated suspensions. They are integral to the overall effectiveness and performance of the AguaClara water treatment plants, as they are involved in the final particulate settling mechanism and thus the final effluent turbidity. The experimental apparatus contains a controlled clay stock that is added to raw water and mixed to a turbidity of 100 NTU. This raw water is sent through rapid mixing with a fixed dosage of alum, which then enters a flocculator (where the floc is actually created). From this stage, the water enters a settling column where it forms a floc blanket. The tube settlers draw water from this column.
...
plate settler length
plate settler diameter
plate settler angle
capture velocity
upward velocity
turbidity of source water
coagulant dosage
natural organic matter
Dependent
velocity gradient
residence time (in plate settler and flocculation tubeflocculator and floc blanket)
EXPERIMENTAL DIRECTION
This summer the plate settler team will work on generating a controlled ideal experiment as a basis for understanding the robustness of the plate settling system. We plan to test how the settlers function under a wide variance of conditions, since changes in alum dosage and influent turbidity inevitably affect the sedimentation process in many ways. Keeping in mind that the presence of things like natural organic matter in our raw water disturbs floc blanket behavior at a molecular level, we hope to gain some physical insight into how the settling system responds to these fluctuations.
Velocity gradients within the tube settlers have proven to be very important. and we hope to continue past investigation into the nature of their formation, profiles, and physical consequences relative to our system. Why? Discuss mechanism here by which velocity gradients pull up floc particles. Particles that are supposed to settle out somehow make it into the effluent, and we would like to figure out why this is happening. Since it is likely that the density of our floc particles strongly depends on variable external parameters (like alum dosage and influent turbidity), our direction is highly geared towards a fluid dynamics anlysis.