When using lime to remove phosphorus, what is the optimal pH level?

The optimal pH level when using lime for phosphorus removal is at a pH of 10 or higher. At this elevated pH level, lime (calcium hydroxide) reacts effectively with phosphorus, forming insoluble compounds such as calcium phosphate. This reaction is crucial for efficient phosphorus precipitation, which aids in reducing phosphorus concentrations in wastewater to meet regulatory standards.

Levels of pH around or above 10 facilitate better solubility of lime and promote the necessary chemical reactions to remove phosphorus effectively. Lower pH levels, such as 7 or 8, do not optimize the conditions for this reaction, meaning that phosphorus may remain more soluble and not be adequately removed from the wastewater stream. Additionally, a pH of 12, while effective, is generally not necessary and may pose operational challenges due to its high alkalinity. Therefore, pH levels above 10 represent a balance of effectiveness while avoiding excessive alkalinity.