Alum Application Day 1: (10/25/19)

The buffered alum application project at Shields Lake began early this morning (10/25/19). The HAB Aquatic Solutions crew worked until dark and had a very productive day. Just over half of the application was completed and they are on-schedule to finish up on Saturday. In today’s post we also discuss how HAB’s application technology ensure optimal alum floc formation and placement on the lakebed.

Precise Alum Application

An important feature of a successful alum application is the formation of the floc and the precise placement of the floc on the lakebed. The floc is formed when the liquid alum mixes with lake water immediately after application. It is a whitish-green precipitant, is more dense than water and sinks through the water column at a rate of 1 foot every 2.5 minutes. Once it reaches the bottom, the floc’s active binding sites are in place to intercept phosphorus as it leaches from the lakebed.

HAB’s application technology maximizes the floc formation and settling by applying the alum through drop hoses that extend 18-24 inches 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 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, ensures that lake sediments receive the prescribed dose without gaps in coverage and minimizes the time the floc is suspended in the water column.

Alum floc forming behind the application barge.

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