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The probably most important difference between alum and PACl in the point of view of stock tank mixing, is their dissolution rate; the alum takes a while to dissolve and therefore we have to design in order to implement dissolution into our experiments. The first two experiments below were done with alum coagulant and we only worried about dissolution.
Our first experiment was the "double bucket" design; the design was originally taken from Surface Water Treatment for Communities in Developing Countries by C. R. Schulz and D. A. Okun (Reflection 1). We also experimented with "moist" alum, which, in this state, is very hard to dissolve. In order to prevent this state of alum, the double bucket design always had the alum submerged. One of the assumptions we was once the alum particle becomes small enough to flow through the filter, it will be considered "disoolveddissolved" alum. However, we soon found that the filter gets clogged more consistently than not and we concluded that filters in these experiments were unreliable.
After the "double bucket" experiment, we conducted the upflow experiments, which involved mixing the alum solution through upflowvertical up flow. This gives the advantage of the up flow water being more into contact with the granular alum and dissolution of the alum.
Summer 2010
I helped run some clay experiments and learned how to use the process controller and the lab bench-scale setup. I also helped troubleshoot some mechanical errors in the lab system.
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