Author: AguaClara Pilot Plant Spring '08 Sub-Team

Sections on Testing of the Tapered Flocculator were written by:
* Rebecca Thompson: rnt3@cornell.edu
* Narayana Pappu: nvp4@cornell.edu

h2. Developing Turbidity Profiles along the Flocculator

This testing procedure has two parts: finding the optimal alum dose on the day of testing and running the Profile Test. This procedure was developed and implemented in the Spring '08 semester.

h4. Optimal Alum Dose Testing

Because the pilot plant takes water directly from the stream, environmental conditions change all the time and affect the incoming turbidity to the plant as well as the chemical composition of the particles causing turbidity. It is therefore necessary to determine the best alum dose for each day of testing to ensure the formation of good flocs. This requirement was implemented in the following way:
The Process Controller was used under the "Increment Alum" setting, which starts the Alum Dose at 0 mg/L, and increments at 5 mg/L until it reaches a maximum of 40 mg/L. Each of the alum doses ran for a 30-minute period, or for about 3 times the residence time of the tank. After the completion of the test, data processing was performed to select the data from the last 10 minutes of each individual alum increment. The first 20 minutes of data were rejected because the residence time in the flocculator was 10 minutes, and the residence time in the tube settler was also about 10 minutes. Therefore, in order to get readings from the final turbidimeter that were representative of the alum dose that we were testing, we discarded the first 20 minutes of data at each alum dose. The outgoing turbidity (from turbidimeter 4) was then analyzed for each increment, and the alum dose achieving the lowest turbidity was selected for the second part of the experiment.

h4. Profile Test Procedure

\\
{float}
{anchor:flow path top view}[!Pilot Plant^3.jpg|width=200px!|Pilot Plant^3.jpg]
h5. Picture of the Flocculator set-up.
{float}
\\
\\
\\
\\
 
\\
{float}
{anchor:flow path top view}[!Pilot Plant^picture1.jpg|width=200px!|Pilot Plant^picture1.jpg]
h5. Experimental Set-up of the Tube Settler Placement.
{float}
The purpose of this experiment was to develop a profile of flocculation at different places along the flocculator. In order to do this, we moved the tube settlers to different points along the length of the flocculator and tested the turbidities of the water after it passed through the tube settler and reached the turbidimeter. In Experimental Set-up of the Tube Settler Placement above, you can see a schematic of the experimental set-up. A photograph of the same set-up is also shown. The experiment has three parts, A, B, and C, each lasting for 45 minutes. During the experiment, the location of tube settlers 2 and 3 were moved to different places along the flocculator as shown above. Turbidimeter 1 was always testing the incoming water, and turbidimeter 4 was always testing the turbidity of the water at the end of the flocculator (location 4 above). Along with moving tube settlers 2 and 3, we emptied tube settler 4 of water between parts A, B, and C of the experiment. This is because when the tube settler is filling with water, plug-flow conditions exist in which velocity gradients cannot develop, and flow up the tube settler is more even. So, by emptying tube settler 4 of water, we ensured that the potential effects of this condition in the tube settler were even across all the tube settlers.
Likewise, when performing the data analysis after the experiment, we found an increase in the turbidity to unreasonably high levels (on the order of 100 NTU) for about 10 minutes after moving the tube settlers. This was because the air in the tube settlers which was being pumped through the turbidimeters. Therefore, only the data at the end of each part of the experiment was used (approximately after 10 minutes of running). The removal of the air can be easily observed in the data when the system appears to have reached a steady-state.