#filtration.natural_process  the process of filtering
  supertype:  #natural_process__naturalproces__natural_action__naturalaction__action__activity  a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity"
  subtype:  #percolation.filtration  the slow passage of a liquid through a filtering medium; "the percolation of rainwater through the soil"

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