A slow sand filter is a filter used to purify water. The original design is composed of a layer of gravel, then a layer of fine sand. Sometimes, however, there is an extra layer of bacteria on the top doing most of the purification.
This layer of bacteria is called the Schmutzdecke (German for dirt covering).
- How do slow sand filters work (I'm referring to ones without the Schmutzdecke)?
- Are there any other materials that have the same "water purification" abilities as sand and gravel?
- Is the gravel base optional? Does it help with any of the actual purification?
- How do you grow the Schmutzdecke?
I do see that in the picture, the gravel is used as support. But I'm wondering if it'll affect the clarity of the water if removed.
I've seen that to grow the Schmutzdecke, you just have it sit in water for a week, and it should grow. But I'm not sure that's correct, because
- Where will the bacteria come from?
- The bacteria won't have any food to grow!
And also, setting a bottle with dirty water in it for a week did nothing to the top layer of sand.