We first began be experimenting with 30ppi polyurethane foam. Our experimental setup consisted of a column consisting of 10 layers of 2.54cm foam. We then ran 5, 20, and 50NTU water with a residual alum concentration of 1.5 mg/L through the filter for 24 hours using an approach velocity of 4 mm/s.
Figure 1: 30ppi foam, 50 NTU influent
Figure 2: 30ppi foam, 50 NTU influent
Figure 3: 30ppi foam, 20 NTU influent
Figure 4: 30ppi foam, 20 NTU influent
Figure 5: 30ppi foam, 5 NTU influent
Figure 6: 30ppi foam, 5 NTU influent
We also want to ensure that we would get a consistent and predictable performance from 30ppi foam. In order to verify this, we ran the experiment with a 50 NTU influent 2 additional times and compared the results from the 3 trials.
Figure 7: 30ppi foam, 50 NTU influent experiment comparison
These results incicate that 30ppi foam can produce a maximum pC* of 0.769 (Figure 4) which is well below that of typical sand filtration units. Even at the lowest tested influent turbidity, the 30 ppi foam could only reduce the effluent turbidity of the water to 1.32 NTU(Figure 5). Since our goal is to reduce the effluent turbidity of our filtered water to below the US EPA drinking water standard of 0.3 NTU, we determined that 30ppi foam does not perform well enough to be used as a filter media for our design. The fact that we were not able to reproduce any of the results from our repeated 50 NTU experiment with 30 ppi foam is also of concern since it is important that our filter design perform consistently.