Which of the following coagulants is most commonly used for low to medium turbidity?

Aluminium sulphate, commonly known as alum, is frequently used as a coagulant for treating water with low to medium turbidity levels. It functions by forming a gelatinous precipitate when it reacts with water, which effectively traps and removes suspended particles. This sedimentation process helps clarify the water by allowing the particulates to aggregate and settle out, making alum especially effective in a wide range of municipal water treatment applications.

The popularity of aluminium sulphate stems from its reliability, ease of use, and effectiveness in various water qualities. It also has the advantage of being relatively cost-effective and widely available compared to some other coagulants. The optimal pH range for alum's coagulation chemistry typically falls between 6 and 8, which aligns well with most drinking water standards.

In comparison, while other coagulants like ferric chloride and ferrous sulphate are also effective, alum tends to be the go-to choice primarily due to its established history and performance across diverse water conditions, particularly in treating low to medium turbidity. Lime, on the other hand, is generally used to adjust pH levels and for softening water rather than primarily for coagulation.