ESR scientist Dr Chris Nokes describes how adding a flocculant coagulant to muddy water causes the mud particles to group together to form larger heavier clumps that can then be filtered or settled out of the water. This flocculation-coagulation step makes it easier to treat the water to kill any microorganisms that may be present.
Dr Chris Nokes
Flocculation occurs both in natural systems, and it’s also done intentionally in water treatment. Small particles of mud or sand that are present in water carry a charge, usually a negative charge. By adding a flocculant coagulant such as an aluminium salt – and aluminium ions hold a positive charge – those positive charges help to bring the negative-charged particles together. And because the final particle you get is bigger than the original particles, it’s heavier and therefore more dense and will tend to settle out of the water faster. By adding a flocculant, you can get the particles to stick together, they settle out more rapidly, so you've got cleaner water to pass through the filters.
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