According to a variant of this embodiment, it can also be advantageous, to improve the life of {TAIL ~ the beds}, to insert between the activated carbon bed and sand bed a layer of {HEAD ~ a third granular material} with a density between that of activated carbon and sand, for example, anthracite 
According to a variant of this embodiment , it can also be advantageous , to improve the life of { TAIL ~ the beds } , to insert between the activated carbon bed and sand bed a layer of { HEAD ~ a third granular material } with a density between that of activated carbon and sand , for example , anthracite
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH