60 ppi Foam Sheet Experiments

Experiment 1.1: 60 ppi foam with a flow rate of 100 m/day.

In the first experiment, a flow rate of 100 m/day was used simply to get an estimate of what level of removal the filter foam material could acheive. 100 m/day was chosen as the flow rate since it is a typical upflow velocity for an AguaClara sedimentation tank. We used an influent raw water turbidity of 5 NTU, which is the typical turbidity of effluent water from an AguaClara sedimentation tank. Alum was not added to the system as we wanted to test the filtering capacity of the foam using the smallest level of particles that would be sent through the filter.

Figure 1: Raw Water and Effluent Turbidity vs time for a flow rate of 100 m/day
A few things to note about the graph above:

• When 5 NTU raw water is sent through the filtering device, the effluent water turbidity is about 2 NTU for the first 6 hours and slightly improves to about 1.5 NTU.
• The clay stock ran out after 14 hours, as evidenced by the drop in turbidity in the raw water.
• It is interesting to note that despite the drop in raw water turbidity, the filter is still effective. Raw water of about .6 NTU was filtered to about .12 NTU.

Figure 2: pC* vs time for a flow rate of 100 m/day

The graph above is a plot of pC*, which is the percent of colloide removal.
A few things to note:

• The percent removal is approximately constant with time, though it does show some improvement in the first several hours.
• Even when the raw water turbidity dropped after 14 hours, the percent removal of colloides remained constant. This indicates that the percent colloide removal is independent of influent raw water turbidity, within this range of values.
• While this indicates that the filter material does indeed acheive a significant level of colloidal removal, we would like this value to be higher (around .9).

Experiment 1.2: 60 ppi foam with a flow rate of 200 m/day.

Ultimately, we would like the filtration unit to take up the smallest amount of planned area possible. Therefore, we decided to increase the flow rate through the filter to 200 m/day, which is equivalent of reducing the top view area of the filter to half the original size. The influent raw water was kept as above, at 5 NTU with no alum dosage.

Figure 3: Raw Water and Effluent Turbidity vs time for a flow rate of 200 m/day
This graph indicates that the higher flow rate of 200 m/day increased the effluent turbidity to about 2 NTU. However, given the amount of planned space saved by this increase, this level of loss may be acceptable.

Figure 4: PC* vs time for a flow rate of 200 m/day

As expected, the percent colloide removal decreased with the increase in flow rate. At 200 m/day, only about 40% of colloides are removed. Again, we would optimally like to acheive a percent colloide removal of about 90%, therefore, we will investigate foam with a higher ppi (smaller pore sizes).

See Experiment set 2: 90 ppi Foam.