What helps in the removal of stains and impurities in water using alum?

The process of coagulation is key in the removal of stains and impurities in water when using alum. When alum (aluminum sulfate) is added to water, it dissociates into aluminum and sulfate ions. The aluminum ions interact with suspended particles and impurities in the water, causing them to clump together into larger aggregates, or flocs. This floc formation significantly enhances the settling of these particles during the subsequent treatment process.

Coagulation is particularly effective for dealing with turbidity and other contaminants, making it a crucial step in water treatment processes. As the flocs form and grow, they become larger and heavier, allowing them to settle out of the water more easily during sedimentation or enhance filtration processes. This leads to clearer and cleaner water, free from many of the stains and impurities that were present initially.

In contrast, while oxidation may help in breaking down certain organic contaminants, it does not directly involve the aggregation and settling of particles like coagulation does. Filtration is a subsequent process that may follow coagulation to remove the flocs and impurities but is not the mechanism through which alum acts. Chlorination is primarily used for disinfection and does not address impurities in the same way that coagulation does.