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Alum Dosing Theory

Alum, or aluminum hydroxide, is added to raw water in order to coagulate the particles suspended in the water. Before alum is added, the particles have a slight negative surface charge and therefore repel one another. Dosing the water with alum neutralizes the charge on these particles so they are more likely to stick together. The particles are allowed to grow in a flocculator, where the dosed water is thoroughly mixed in order to disperse the alum and promote the flocculation of the particles. These conglomerates are referred to as flocs.

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