CDC SU2009 RP

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.

In addition to this information, it is commonly known that surfactants aid in the formation of foam by stabilizing the bubbles. This in turn prevents small bubbles from combining and forming larger bubbles which are easily popped. As a result, many small persistent bubbles, or a foam, form.

List of Parameters

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

• Alum Dosage
• Concentration of Natural Organic Matter (NOM)
• The Location of the alum addition
• The aeration of water
• Addition of a surfactant

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 concentration of NOM increases, so will the amount of foam formed.

• 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

• We suspect that bubbles may be forming due to aeration in the water. We hypothesize that aerated water will generate a surface foam.

• Surfactants help to stabilize bubbles in water. We believe that the addition of surfactants will cause small persistent bubbles, to form surface foam.

• 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.