They are a kind of a symbol of wastewater treatment. Description Weir plates are attached to the outer wall of the launder. Scam baffles retain solids floating on water surface inside the clarifier and prevent their escaping over the weir plate. Types of floating solids Sludge doughnuts Most frequently, especially at old-fashioned clarifiers, scraping is not perfect at all places of the clarifier bottom. Those doughnuts have frequently a non uniform color.
Some parts are darker while other lighter.
Most common reason for rising sludge is denitrification in the sludge blanket. For details on rising sludge, see Henze et al. Biological foam Many treatment plants suffer by biological foaming. Layers of biological foam can be extremely high, up to 1 m if retained in a tank or a tank compartment for time long enough. In winter, if ambient temperature drops below freezing point, the foam freezes and can cause mechanical damages to the equipment.