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In order to obtain conditions that better resemble those of an AguaClara plant, an alum dosing system and a rapid mix tube was were added to our experimental setup in order to dose the raw water with alum. Ideally, these slightly larger and "stickier" particles are more likely to be trapped in the foam resulting, in a lower effluent turbidity.
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Figure 1: Experimental Setup with Alum Dose
Experiments
A preliminary experiment was run to determine if better filtration performance could be achieved after dosing 5 NTU raw water with alum. A very high dose of alum was used, 25 mg/L, which is fairly unrealistic. To achieve this alum dose level, it would be necessary to install another alum doser prior to the filtration unit.
Experiment 1: 25 mg/L Alum Dose
A series of experiments were run at a constant flow rate with a low, realistic alum dose of 1.5 mg/L in order to determine whether foam filtration acted as either a function of depth, or a function surface area.
Experiment Set 2: Depth Filtration
The 5 NTU raw water turbidity level was acheived using the raw water turbidity process.