What pH range is considered optimal for coagulation?

The optimal pH range for coagulation in water treatment processes is typically around 5 to 7. Within this range, the conditions are most favorable for the aggregation of suspended particles and the formation of larger flocs that can be more easily removed during the subsequent filtration stages.

At this pH range, commonly used coagulants, such as aluminum sulfate, work effectively, as they tend to be more soluble and reactive. When the pH is lower than 5, coagulation may not be as effective due to the increased solubility of the coagulants, leading to a reduced chance of particle aggregation. Conversely, when the pH exceeds 7, the performance of coagulants may decrease because increased alkalinity can lead to a lower positive charge on the coagulant and negatively charged particles in the water, hindering effective coagulation.

Hence, the 5 to 7 range is optimal because it balances the reactions needed for effective coagulation, ensuring that impurities are removed efficiently while maintaining the stability of the resulting floc.