This process is used in oils, grease and suspended solids removal and for sludge separation and concentration.
The effluent, or part of it, is pressurised in the presence of enough air to achieve saturation. When this air-liquid mixture is released at atmospheric pressure in the flotation unit, little air bubbles are formed and released from solution.
The sludge flocs,
suspended solids or oil globules are floated by these air
bubbles, which attach themselves to and enmesh in the floc
particles.
The air solids mixture rises to the surface, where it is skimmed
of. The effluent is removed from the bottom of the flotation
unit. At this time, a new portion of the effluent can be
pressurised again and reintroduced in the unit.
Based on the density difference between water and suspended solids, or other contaminants, sedimentation is a very important process in the TSS removal and occurs in tanks usually called clarifiers.
These are normally built in circular or rectangular shapes.
Most of rectangular clarifiers is equipped with scraper flights extending the with of the tank, moving the settled sludge toward the inlet end of the tank, where it is removed.
Circular clarifiers may employ either a center-feed well or a peripheral inlet. With the center-feed type, the waste is fed into a center well and the effluent is pulled off along the outside. With the peripheral-feed tank, the effluent is pulled off at the tank center.
The circular clarifier usually gives the optimal performance. Rectangular tanks may be desired where construction space is limited. In addition, a series of rectangular tanks would be cheaper to construct due to the possibility of using shared walls.
The reactor clarifier is another variation where the functions of chemical mixing, flocculation and clarification are combined in the highly efficient solids-contact unit. This combination achieves the highest overflow rate and the highest effluent quality of all clarifiers designs.
