We first began experimenting with 30ppi polyurethane foam. Our experimental setup consisted of a column with 10 layers of stacked pieces of 2.54cm thick foam. We then ran 5, 20, and 50 NTU 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. Since we also want to ensure that we would get a consistent and predictable performance from 30ppi foam, we ran repeat experiments with a 50 NTU influentand compared the results from the 3 trials.
Figure 1: 30ppi foam, 20 NTU influent
Figure 2: 30ppi foam, 5 NTU influent
Figure 3: 30ppi foam, 50 NTU influent trial comparison
These results indicate that 30ppi foam can produce a maximum pC* of 0.769 (Figure 1) 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 2). 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 50 NTU influent experiment with 30 ppi foam (Figure 3) is also of great concern since we want to be able to predict the performance of our filter.