How are colloidal particles removed from waste water

How are colloidal particles removed from waste water  

Waste water from a drain or rain-overflow usually contains sediment, including sand, dust and solid particles such as grit. But smaller, colloidal particles also pollute the water. Water purification requires the removal of such particulate matter, generally before disinfecting the water and subsequent removal of any water-soluble effluent. 

Larger particles of grit and dust settle relatively fast, but colloidal solids can require weeks for complete sedimentation (i.e. colloid breaking) to occur completely. Such sedimentation occurs when microscopic colloid particles approach, touch and stay together because of an attractive interaction, and thereby form larger particles, and sink under the influence of gravity. We call this process aggregation. 

But time is money. The waste industry, therefore, breaks the colloid artificially to remove the particulate solid from the water. They employ one of two methods. Firstly, they add to the water an inorganic polymer such as silicate. The colloid s thermodynamic stability depends on the surface of its particles, each of which has a slight excess charge. As like charges repel (in consequence of Coulomb s law  

The word flocculate comes from the Latin floccus, meaning an aggregate (originally of sheep, hence their collective noun of flock ). 

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