*Flocculation Basic Overview*
By: KW
20 January 2013

Flocculation in its simplest terms is the gathering of suspended solids in a liquid. Once the solids gather enough mass they sink, clearing the liquid for further processing

Flocculation is used in water treatment, cheese production, and in one of my favorite subjects - brewing.

In water, flocculation is used to reduce the turbidity of the water. Turbidity is when water appears cloudy. When water is turbid it contains solids (particles) that are suspended in the water. The measurement of turbidity is a major indicator of water quality. In water there are a few different ways to get the turbidity down.

  1. Filters.
  2. Allowing settling time. This is taking the turbid water and allowing everything to settle to the bottom on its own accord. Or
  3. Flocculation

The basic systems of flocculation are not hard to achieve. Beginning with turbid water that has already been treated with chlorine or other disinfectant, you would add a clarifying agent (in brewing they are known as "Finings"). Clarifying agents can be chemical or natural and there are several different kinds; the most typical being Alum. After addition of the clarifying agent they should be flash mixed. Think of flash mixing as a hand cranked egg beater. After flash mixing you need to do a slow steady mixing or agitation. Think of this agitation as mixing the water/agent slowly by hand with a spatula. At this point the suspended solids will start to group together and produce "FLOCS". As the weight of your flocs increases, the flocs want to drop out of suspension due to gravity. As the flocs drop out of suspension, your turbidity starts to become less and less - clarifying your water. The water can then be decanted off the top of the flocs and is ready for further treatment.

In larger systems, all of the steps are completed in different chambers. Also, in larger systems a filtration occurs after the majority of flocs has dropped out of suspension. This is typically achieved by draining the water through a filter bed of Anthracite. Filtering the water and flocs through the bed captures the flocs as they pass through it due to its density. After the run of water and flocs has been completed, the bed would be violently back-flushed to push the flocs back out of the bed and to waste.


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