Most impoant layer of a slow sand filter is -
The most impoant layer of a slow sand filter is the vital layer or zoogleal layer or the biological layer. It is composed of thread like algae and other forms of life. It is called so because it removes organic matter, holds back bacteria and oxidises ammoniacal nitrogen and helps in yielding bacteria-free water. (PARK TB 25th edition pg 772)
Zoological layer
Sand bed
Filter system
Raw water
Environment and health