• Created by user-5ca95, last updated on Jun 29, 2009 3 minute read

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Introduction and Theory

In multiple AguaClara plants in Honduras, it is has been noted that there is foam formation in the first baffles of the flocculator. However to date it is unknown how or why the foam is formed. During the summer of 2009, our team will run experiments in order to replicate the foam formed in these plants while also identifying the cause of the foam formation.

We will first vary the alum dosage because research supports that surface foam can be attributed to the overdosing of aluminum sulfate. Additionally, the presence of natural organic matter (NOM) has been proven to lower surface tension in water, thus creating a surface foam. The location of the alum addition is also thought to effect the foam formation. This is because in small quantities, aluminum sulfate dissolves in water and the aluminum begins to precipitate as aluminum hydroxide. Air is then entrained in the aluminum hydroxide, forming bubbles which are less dense than water and are persistent on the water surface.

List of Parameters

In our rapid mix experiment we plan to vary the following independent variables:

  • Alum Dosage
  • Turbidity
  • The Location of the alum addition

Experimental Design

  • We are first testing the alum dosage to determine whether it is the cause of the foam formation. We will use the following dosages of alum (35 mg/L, 45 mg/L, 55 mg/L, 65 mg/L).
  • We hypothesize that as the alum dosage increases there will be an increase in the formation of the surface foam.
  • We also are testing to the effect of natural organic matter (NOM) on foam formation. We hypothesize that as the turbidity of the water increases so will the foam formation.

You are mixing two concepts here. Turbidity is an optical property that is correlated with the volume of suspended solids. Natural organic matter can be either dissolved or particulate and thus may or may not contribute to turbidity. Increasing the turbidity by adding more clay is not expected to affect the foam formation.

  • The foam formation may not be due to the alum dosage or the turbidity, it may in fact be due to the location that the alum is added to the system; above water surface vs below water surface. We hypothesize that the foam formation will be greater when the alum is applied to the surface of the water
  • For all of the experiments conducted we will take pictures at 10 minute intervals of the surface of the water to determine if there is foam formation.

There is substantial evidence from the plant at Cuatro comunidades that the foam is generated from air bubbles that are entrained in the rapid mix and transported to the first chamber of the flocculator. I suggest that you investigate the effect of aeration after rapid mix to see if that causes foam formation. Your goal is to generate foam, so do a quick series of experiments where you add natural organic matter (you can use humic acid that we have in the lab) and alum to water that is aerated. If that doesn't form foam in 5 minutes, then we may need to find a different source of natural organic matter such as Fall Creek. At this stage there is no need to take pictures or to conduct long experiments. The first goal is simply to see what is required to reproduce the foam problem.

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