Which chemical helps to remove phosphorus and encourages sludge settlement in clarifiers?

Alum, or aluminum sulfate, is a coagulant commonly used in wastewater treatment processes, particularly for the removal of phosphorus and the enhancement of sludge settlement in clarifiers. When alum is added to wastewater, it reacts with alkalinity and forms a gelatinous precipitate of aluminum hydroxide. This precipitate adsorbs phosphorus, thereby reducing its concentration in the treated effluent. Additionally, as this floc develops, it helps to agglomerate smaller particles and promotes the formation of larger, denser flocs, which settle more easily in clarifiers. This improved settlement leads to more effective separation of solids from the liquid phase and enhances the overall efficiency of the treatment process.

While ferric chloride is also a coagulant used for phosphorus removal, alum is often favored in certain applications due to its lower cost and effectiveness in specific water chemistry conditions. Calcium carbonate mainly acts as a buffering agent and does not have the same coagulating properties to directly remove phosphorus. Cationic polymers can aid in flocculation as well but are utilized primarily for enhancing the settling of sludge rather than directly removing phosphorus. Therefore, alum is the most effective choice for this particular function in wastewater treatment.