What is the optimal pH range for removal of particulate with alum?

The optimal pH range for the removal of particulates using alum is 5.8 to 6.5. This range is crucial because the effectiveness of alum, which is aluminum sulfate, as a coagulant is highly dependent on the pH of the water being treated. At this pH range, the solubility of aluminum hydroxide, the floc that forms when alum is added, is maximized, allowing for optimal particle aggregation and settling. This improves the removal efficiency of suspended solids and turbidity from the water.

In pH conditions below this optimal range, such as in the acidic ranges, aluminum solubility increases, which can hinder effective coagulation and lead to insufficient floc formation. Likewise, pH levels above this range can lead to reduced effectiveness of the alum as the precipitation of aluminum hydroxide may not occur as readily, impacting the removal of particulates negatively.

Understanding the chemistry behind the process and maintaining the pH within this optimal range helps ensure that water treatment processes are effective and efficient in providing clean, safe water.