<unk>  (German, “dirt cover” or dirty skin, sometimes wrongly spelled<unk>  is a hypogeal biological layer formed on the surface of a slow sand filter. The<unk>  is the layer that provides the effective purification in potable water treatment, the underlying sand providing the support medium for this biological treatment layer. The composition of any particular<unk>  varies, but will typically consist of a gelatinous biofilm matrix of bacteria, fungi, protozoa, rotifera and a range of aquatic insect larvae. As a<unk>  ages, more algae tend to develop, and larger aquatic organisms may be present including some bryozoa, snails and annelid worms.
Schmutzdecke
Mittelschmerz
Witzelsucht
Viktor von Weizsäcker
Studierfenster
Zellballen
Muʽassel
Pendelluft