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Alum, or aluminum hydroxide precipitate, 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.
Following the flocculation, the stream water enters a sedimentation tank, where the flocs begin to settle. This settling creates a "blanket" of flocs, which serves to trap more flocs and provide effective filtration as it grows. The floc blanket is an integral part of the AguaClara technology and enables the system to acheive achieve much lower effluent turbidity.
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