Filter media may also be composed of particles that are rigid in structure, but are applied in bulk loose form. That is, individual particles merely contact each other. This form has the advantage of being cheap and easy to keep clean by rearrangement of the particles. When the proper size and shape of particles are selected, the section of passage may be regulated over extremely wide limits. The disadvantages of a rigid medium in simple contact are that it can be used conveniently only in a horizontal position and that it does not allow removal of thick deposits or surface cleaning except by backwashing, without disturbing the filter bed.
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