"dc" wrote in message
...
Dick wrote in
:

No filter, I can imagine, would be classified as "biological
filtration." Why would one want to filter out bacteria?

Your semantics are very limited.

Biological filtration is a widely used term to describe the natural
process
of the nitrogen cycle. It has nothing to do with the "filtering out of
bacteria", which doesn't even make sense. Bacteria will adhere to any
surface where it is able to obtains the means for it to survive--it exists
in every part of your filter.

Biological filtration describes the action of biological organisms
(bacteria) on organic chemicals (nitrogenous wastes) as they convert them
into various, and progressively less toxic forms.

DC for calm under fire I hereby award a distinguised service medal.
Well done man.