18th October 2006 at 3:32 pm #671
Please check the link http://biosandfilter.org/biosandfilter/index.php/item/289
Here you\’ll find information on the importance of both sand size and bed depth. Personally I believe that the concrete filter is as yet not deep enough – I would prefer 50-60cm sand depth rather than only 46cm. This is because there are filtration processes that happen with increased depth. There are people that argue that shallower bed depth is fine, and bacteriologically that may be the case since the biological population is fairly mobile and within the top layers. But for sure better filtration overall (biological, chemical, physical) happens when the sand is deeper than 40cm.