Rapid sand filtration, Slow sand filtration - How does it work

[@johnbolton3711]

In a slow sand filtration scenario it IS NOT the sand that does the filtration. It is the Schmutzdecke. The sand is simply the media that the biological component of the filtration grows on

[@halforab588]

Dear John, Very good point indeed. Thanks for the clarification. Some short comments in regard to your point. The sand will be the media for a natural forming biofilm, that will reduce dissolved substances which can create odour problem in the water. So a slow sandfilter can not be backflushed thus it is very important that particulate material is removed before the SSF. Cleaning of a SSF is done from time to time by removing the top layer and replacing it with new sand. As John notes in his comment it is the biofilm/bacteria that is the purpose of SSF and it will take some time for a new or a cleaned filter to reach its expected capacity until the biofilm is fully formed. 😃