Thalia Aoki's Individual Contribution Page

Spring 2012 Contributions

To date, I have worked with Sahana Balaji on redesigning the demo plant's sedimentation tank. We have based our design on the ENGRI 1131 class work from the Fall 2011 semester, and using that design, I constructed a sedimentation tank that successfully creates a floc blanket when connected to the demo plant flocculator. We encountered several flaws in the initial floc blanket and sedimentation tank, however:

1. As the floc blanket built up, it quickly expanded into the tube settler, overwhelming it and preventing it from being able to capture smaller, post-floc blanket particles.
2. Large, non-standard alum and clay doses were used, making it difficult to reproduce the results.
3. The flow rate of the plant was both very high, and unknown, meaning that the design criteria for the sedimentation tank (and the SRSF) were potentially not being met.
4. The sedimentation tank was much larger than needed for demonstration purposes.
5. The demo plant as a whole had problematic hydraulics: the height differences between different parts of the plant, in combination with build up of air bubbles in the system required constant adjustments during operation.

Thus far, I have addressed those problems in the following ways:

1. I have installed a floc drain into the sedimentation tank, allowing for drainage of excess flocs, helping to modulate the height of the floc blanket.
2. I have begun recording the alum and clay dosages I use, and their effectiveness, in order to better determine necessary operating dosages.
3. I have adjusted the flow rate to its lowest setting (using the chemical doser), and begun recording flow rates into the flocculator, in order to get a sense of the consistency and accuracy of the flow rate, and its relation to the formation of a floc blanket.
4. Sahana and I cut down the sedimentation tank, to about half its previous size, resulting in a floc blanket builder about 40 cm tall, and a tube settler about 20 cm long. This has made the sedimentation tank much easier to fit onto the demo plant, and will ultimately make for a cleaner product.
5. As we begin work on an 80/20 metal frame, in which we can adjust the height differences more easily than with the current set-up, I hope to adjust those values, and eliminate the problems with them. I am still unsure about what to do about the air bubbles entering the system.

My main goal in advancing the sedimentation tank portion of the demo plant is to determine optimal alum and clay dosages in order to easily build a floc blanket. For the plant as a whole, I would like to fabricate the 80/20 frame, and eliminate the air bubble issues.