Point-Of-Use Foam Filtration Unit Design
Materials and Construction Components
At the moment, our design consists of the following parts:
- five gallon bucket that holds all of the components of the filter, as well as the filtered water
- 12 inch foam column, with 10 inch depth of foam media
- alum doser
- chlorine doser
- PVC tubing
General Description
Influent water from a stock tank first mixes with alum that is stored in an alum doser. It then enters the filtration column, where the water is filtered through the depth of foam media. The effluent water is then chlorinated and sent through a series of spiral tubing which serves as a rapid mix system. The filtered water is stored in the same bucket that holds the components of the filter. This acts as the distribution system for providing water to the community.
Fabrication of the filtration unit will utilize parts that are relatively inexpensive. The parts will also be locally available so that the operator can find and purchase newer parts for the filter when needed. Additionally, over-designing is better than under-designing: it is better to meet and exceed the needs of the users than to fail to meet the design requirements.
Design of Alum-Doser
Much of the focus of our design work has been on the alum doser. Originally, we planned to use the alum doser to dose untreated water at an appropriate level using a mere "hole-in-the-bucket" situation with a float valve to maintain a constant water level and thus maintain constant head. Yet we discovered that this design required a bottom orifice with a diameter of less than 3 mm. These calculations can be seen in the original Alum Doser MathCAD file. The problem with small orifices (with diameters below 3 mm) is that clogging occurs very easily. Thus, we needed designs that incorporated large amounts of head loss in the system to allow for the use of a larger orifice size.
Hence, we proposed three alternative designs for incorporating this alum doser into our system:
Unfortunately, we realized that both the "Series of Orifices" and "PVC Cap as Orifice" designs do not generate enough head loss to dose with small amounts. Also, in order for the the "Spiral Tubing" design to successfully work, a extra tubing length of around 3.5 meters is needed; this is not feasible considering our desire to have a small overall filtration unit. Therefore, we need to look into other viable options for the design of the alum doser (which will be a model for the required chlorine doser as well).
As of currently, we are re-considerig the use of a float value to monitor the surface level of the alum solution. This should make dosing less variable and may help find a better solution to the orifice problem. Originally, we eliminated this design because we did not want to include small, hard-to-fabricate components into the design. Yet, this seems like the only potentially successful option at the moment. Also, we are looking into the addition of a flocculation component.