1.

How the performance of rapid sand filter can be improved?

A. Replacing the top 15 cm layer of sand with Anthracite
B. Replacing the bottom15 cm layer of sand with Anthracite
C. Increasing the thickness of a layer of sand
D. Replacing 15 cm layer of Anthracite with sand
Answer» B. Replacing the bottom15 cm layer of sand with Anthracite


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