Addition of Humic Acid

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Humic acid, concentrated in soil organic matter, is a degradation byproduct of plant and animal tissues such as lipids, proteins and carbohydrates. Chemically, humic acid is a very stable compound and is not very reactive in solution. Surface waters naturally contain some humic acid, as it can leach out of soil. When dissolved in water, humic acid gives water a yellow-brown tinge. Additionally, humic acid can affect water treatment; specifically, it can react with dissolved cations such as aluminum sulfate (alum) and other aluminum species alum can dissociate to form. Because humic acid has a large negatively charged surface, it tends to adsorb much of the alum added in coagulation processes, thus competing with clay for which the alum is added. Therefore, the amount of alum needed to treat water containing humic acid will be more then what would be needed for water without it. In order to more accurately determine the optimal amount of alum to be added to treat contaminated water, humic acid should be considered in our experiment. Starting with this experiment, we will continue to use humic acid in our influent flow as it is a major competitor to clay for alum.

We conducted an experiment varying alum dose concentration and influent turbidity at a G value of 42/s. Humic acid was not mixed into our influent mixture, and therefore did not accurately determine the optimal alum dose needed to treat water at a given turbidity. Since dissolved humic acid does not naturally form colloids, its addition into the influent stream will not affect the turbidity. More specifically, the humic acid will reflect a yellow-brown wavelength but will not scatter light as does colloids like clay.

Our main objectives for adding humic acid into the experiment are to see the impact of humic acid on our previous experiment and to define a relationship between alum dosing and raw water turbidities.

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