Alum Floc

The key to a successful alum application is the formation of the floc and the precise placement of the floc within the lake. The floc is formed when the liquid alum and buffer mixes with lake water after application. It is a whitish-green precipitant, is denser than water and sinks through the water column at a rate of 1 foot every 2.5 minutes. The floc’s active binding sites attach to phosphorus as is it sinks, making it unavailable for the algae to use to grow.HAB’s application technology maximizes the floc formation and settling by applying the alum through drop hoses that extend into the lake. There are jet nozzles at the end of each hose and the alum is applied under the pressure created from the onboard pumps. This setup effectively injects a stream of alum and buffer that flash mixes with lake water below the surface. Floc immediately forms at a depth of 2-3 feet. Forming the floc below the lake surface bypasses any interference in settling by avoiding the surface tension of the water and algal scums on the surface. It also forms the floc at a depth where it is less susceptible to wave action. All of this results in rapid settling in the target application zone, reduces drift and ensures that the lake receives the prescribed dose without gaps in coverage.

Unlike what is observed in plastic testing containers, the floc in the lake becomes resistant to major resuspension events. The floc layer is thin (1-2 inches) and quickly consolidates and is mixed into the upper portion of the lakebed. This provides stability and holds the floc in place. The floc is no more likely to become suspended by wave activity than the lake bottom sediments and any suspended floc resettles to the bottom with the sediments. Even after the floc slightly consolidates, it doesn’t harden and remains “fluffy.” It doesn’t harm boat motors (HAB drives their application barge motors through the floc during the entire application) and it doesn’t seal the bottom of the lake, so water and aquatic organisms can easily move through it. The floc is no longer visible after a few weeks, but it still there working to bind phosphorus!

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