of sludge in the aeration tank and/or the final clarifier will result in
the formation of a scum layer on the surface of the tank. In extreme
cases, this scum layer can be 50-100 cms thick and the solids
concentration can increase to about 50 g/l.
usually arise through small, stabilised gas bubbles attaching to the
sludge flocs. The bubbles can be filled with air, or also with nitrogen
gas that arises through denitrification processes.
of a persistent scum layer in domestic treatment plants is nearly always
caused by certain Gram positive, filamentous bacteria such as Microthrix
parvicella and Nocardioforms species. Together with detergents (always
present in domestic waste water) these filamentous bacteria are
responsible for the extreme stabilisation of the interface around the gas
bubbles. Controlling the filamentous bacteria responsible is the only
adequate solution for this problem.
The aeration tank is completely covered with scum
|scum on the final clarifyer||scum on the aeration tank|
|A real catastrophe||Actinomycetes frequently causes scum|