Sedimentation is settlement of impurities at botom whereas decantation is separation of impurities.
In sedimentation beaker is remained untouched but in decantation the water is removed from impurities.
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In the process of decantation impurities settle down at the bottom leaving the clean water above and removing the clean water from the impure water is decantation.

Filtration process is about removing clean water from impure water through filter paper.

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