What substance is used as a measure of filtration efficiency?

The correct answer is aluminum, used in water treatment processes, particularly in coagulation and sedimentation. Aluminum salts, such as aluminum sulfate, are commonly added to water to enhance the filtration efficiency by causing smaller particles and colloids in the water to aggregate into larger flocs. These flocs can then be more easily removed during the filtration process.

Using aluminum as a measure of filtration efficiency helps assess how effectively the filtration system can remove particulates and impurities from water. It indicates the success of coagulant application and the overall treatment process. Higher filtration efficiency suggests that more contaminants are being effectively captured and removed from the water, leading to improved water quality.

The other substances listed—silt, silica, and iron—play different roles in water treatment but are not specifically used as a metric for measuring filtration efficiency. For example, silt may contribute to water turbidity, silica is often associated with scale formation rather than filtration assessment, and iron can pose challenges in water quality but does not serve as a benchmark for filtration effectiveness like aluminum does.