*** This version of Confluence is for testing only and contains a copy of content from June 29th 2026. No changes will be preserved. ***
Apparatus Description
This is the whole FReTA experimental setup to analyze floccilation.
Starting at the clay stock bucket with the clay at a concentration 10g/L in it. Below this bucket, is the clay stock control valve, which is used to control the NTU value of the raw water in the blue bucket.When the turbidity of the raw water drops below the given value in the process controller, this valve will turn on 1 second every 10 seconds to correct the turbidity. On the left of the bucket, is the influent turbidimeter, which is constantly monitoring the turbidity of raw water which pumped through it by the clay pump.
These sets of coiled tubes are the tube flocculator; it is where flocculation happens after the alum has been added to the raw water. Originally, the setup had just one length of flocculator tubing of 2796 cm. In this experiment, the other two length of tubing added, which allows to compare three results in the experiment.
Figure 1:Whole Setup
Figure 2:Bucket Setup
Figure 3:Turbidimeter
The complete experimental assembly consists of synthetic raw water (SRW) and coagulant metering system, rapid mix and tube flocculator, and flocculation residual turbidity analyzer (FReTA).
Figure 1 shows the first section of the setup. It contains the raw water, alum, and clay stock buckets, as well as the pumps and influent turbidimeter. The raw water turbidity is controlled using a feedback loop on ProCoDA Software. The influent turbidimeter is constantly monitoring the raw water stock turbidity since raw water is pumped to the influent turbidimeter by the turbidimeter pump in a loop which returns it to the stock bucket. If the turbidity drops below the desired value, the clay stock valve opens for one second every ten seconds until the desired turbidity is reached. The raw water turbidity will dilute as the plant runs.
Figure 1: Plant stock buckets for alum, clay and raw water, influent turbidimeter and pumps.
As shown in Figure 2, raw water and alum stock are pumped into the plant using peristaltic pumps. The flow rates for these pumps are set in ProCoDA Software to provide the desired plant flow rate and alum dose. The coiled, narrow diameter tubing to the left of the turbidimeter in Figure 2 serves as a rapid mix for the alum and raw water.
Figure 2: Closeup of influent turbidimeter and pumps
Flocculation actually occurs in the coiled tube flocculator section of the plant (Figure 3). We have extended the tubing so that the setup can be run at three different lengths (28 m, 56 m, and 84 m).
Figure 3: New tubing added to increase flocculator length
The final portion of FReTA is the settling column and effluent turbidity shown in Figure 4. After steady state flocs have been achieved, (we usually allow 1.5 -2 flocculator residence times to ensure a steady state floc distribution) the pumps shut gradually, ramping down the flow rate with a set deceleration rate, and the ball valve shown in Figure 4 seals off the settling column from the rest of the flocculator. The effluent turbidimeter then measures the turbidity every second for half an hour as the flocs settle out. This data is recorded by the computer, and used in the data analysis step to determine settling velocities, particle size distributions, and residual turbidity.
Figure 4: Settling column and effluent turbidimeter.
Figure 5 shows the entire setup.
Figure 5: The entire FReTA setupFigure 4:New Turbing Apparatus