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The following week the group used humic acid in order to determine the effects of organic natural matter on surface foam formation. Varying the dosage at 1mg/L, 2mg/L, 5 mg/L and 10 mg/L, humic acid was mixed in the rapid mix chamber with alum. In the mean time the water in the first baffle was being aerated. Soon after, bubbles started forming. The formation of bubbles increased as the concentration of humic acid was increased. However, the bubbles dissipate quickly and were unable to form foam. The group observing the property of the bubbles added soap, a surfactant, to the rapid mix chamber. This resulted in a higher bubble formation, which lasted for a while forming a chain of bubbles over the surface of the water.
Results and Discussion
Our first experiment sought to determine whether or not alum was the sole factor in the formation of a foam. After dosing the water with varying alum concentrations, it was determined through photographs taken every 2 minutes and through observation that no foam was formed. Sample photos are included in Figure 1 below.
Although the foam was not formed, this data was crucial to our research. Not only did it minimize the list of potential foam formation factors, it also help build our understanding of foam formation. As a result of a foam not forming due to alum addition at the surface of the water, we also were able to rule out alum addition under the water surface as intituvely it was a solution to the form formation.
Our second experiment sought to determine whetherr or not the addition of Natural Organic Matter (NOM) contributed to the formation of surface foams. At all concentrations of humic acid, we again found there was no surface foam formed. We belived this was due to a lack of air bubbles which naturally are found in AguaClara plants so at this point we modified our experiment to include a filter to provide them.
In our next experiemnt, we varied the concentration of NOM but included a filter to provide bubble directly into what would be the (flocculation?) tank. At concentrations below XXXX we found that no foam was formed. However at higher concentrations of humic acid, we found that large bubbles would rise and then quickly pop in the center of the tank. In the meantime, smaller bubbles would form around the edges of the tank and were slightly more persitent as seen in Figure 2 below.
Bubbles form when water molecules form bonds around airpockets. A surfactant is generally an organic molecule that has both hydrophobic and hydrophilic. Due to this polality, surfactants form micelles in water which helps to stabilize air bubbles and prevent them from agregating. Humic acid is a weak surfactant, so though it did reduce the agregation of air bubbles it still occurred. This resulted in large, non persistent air bubbles that formed a foam at the surface of the water.
Although, a foam was formed at high Humic Acid concentrations, it was not the foam that is found in AguaClara plants. The foam we created in lab contained large non-persisent bubbles, however the foam we sought to create contained small persistent bubbles. At this point we began searching for a stronger surfactant to further prevent the agregation of bubbles, thus replicating the foam found in Honduran AguaClara plants.
In order to support our hypothesis, we added soap to our last experiment with lactic acid simply to see if would createthe foam we wanted. Indeed the soap caused a persistent foam, similar to that found in AguaClara plants and can be seen in Figure 3 below.