Comparative performance of dual‐ and mixed‐media filters

In an ideal filter the pore size decreases progressively with depth. It is generally believed that mixed media, which contain anthracite coal, sand, and high-density sand, is closer to an ideal filter than dual media, which contain only coal and sand. However, comparative pilotand plant-scale studies conducted under identical pretreatment conditions at Minneapolis and at other locations indicate very little difference in performance between the two types of filters.