"slow sand filters work through the formation of a gelatinous layer called the hypogeal layer or 'Schmutzedecke' on top of a layer of fine sand. This layer consists of bacteria, fungi, protozoa, rotifera and a range of aquatic insect larvae. As a Schmutzedecke ages more algae tend to develop and larger aquatic organisms may be present including some Endoprocta, Snails and Annelid worms.
The Schmutzedecke is the layer that provides the purification for water treatment -- the underlying sand provides the support medium for this biological layer. As water passes through the Schmutzedecke, particles of foreign matter are trapped in the mucilaginous matrix and dissolved organic material is adsorbed and absorbed and metabolised by the bacteria fungi and protozoa.
The water draining from a well managed slow sand filter can be of exceptionally good quality with no detectable bacterial content."
WorldChanging: Another World Is Here: This Week in Green Design, 1/23: See also a site of a company that makes 'em.
1 comment:
Thanks for the write up on slow sand filtration. It's good to get the word out about this low-tech, sustainable technology. Besides use for wastewater, slow sand filters are also excellent for creating drinking water from surface sources -- in fact, the filters that we make (you linked to our company website) are used mostly by people who live "off the grid" but need drinking water filtration for their surface water sources. Slow sand is excellent at making natrually clean water without chemicals or electricity! So thanks for spreading the word.
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