Tube Flocculator Construction History

Original Construction, Configuration and Modifications

The tube flocculator was constructed in the summer of 2008. In order to prevent flocs from settling in the tube flocculator it was arranged in a vertical figure-eight. The flocculator has the same configuration and dimensions as the lab flocculator.

The flocculator was originally made of soft flexible clear tubing. The tubing was deformed and pinched as coiled along the flocculator. Additionally, the tubing degraded at the joints (See Figure 1).

Figure 1: Deformed and pinched tubing. (12/13/08)

Air leaked into the tube at each of the bulkhead fittings. This air prevented flow through the flocculator. The plant operators advised using a thicker, more resistant tubing to solve the problem of degradation.

One attempted solution to this problem was to reconstruct the flocculator out of rigid tubing. The tubing was opaque and could not be forced into a figure eight configuration.

Finally, clear braid-reinforced tubing was used to set up the flocculator. This tubing was flexible enough to form a figure eight and very durable (Figure 2).

Figure 2: Clear braid-reinforced tubing. (12/14/08)

The flocculator was set up vertically at ground level. Elevation differences between the flocculation tank and the outlet of the tube flocculator drive flow through the tube flocculator. A tee with one end open to the atmosphere was connected to the outlet. The tee can be elevated or lowered to control the flow rate through the flocculator.

Issues

Raw water particles were settling out in the 1/4 diameter line drawing water from the flocculation tank. The incoming NTU to the line was 8.2 NTU while the effluent turbidity was 4.9 NTU. It is presumed that particles were settling because no flocs were seen in the effluent. In the future, the sampling line should be shortened to avoid this issue. The flocculator could either be set up closer to the floc tank or another option would be to measure raw water turbidity from the point which water enters the flocculator.

Data Collection

FReTA was constructed by the lab tube floc team for the plant and can be used in future semesters. FReTA measures the rate of change in turbidity as opposed to just measuring the turbidity at a specific point in the flocculator. This is advantageous because the the change in turbidity rate is comparable to the settling velocity.