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In our next experiment, we varied the concentration of NOM but included an aerator to provide bubble directly into what would be the (flocculation?) tankfirst baffle spacing. At concentrations below 2 g/mL 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 persistent as seen in Figure 2 below.
Bubbles form when water molecules form bonds around air pockets. A surfactant is generally an organic molecule that has both hydrophobic and hydrophilic. Due to this polarity, surfactants form micelles in water which helps to stabilize air bubbles and prevent them from aggregating. Humic acid is a weak surfactant, so though it did reduce the aggregation of air bubbles it still occurred. This resulted in large, non persistent air bubbles that formed a foam at the surface of the water.
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