ENVE 420Industrial Pollution Control.ppt

ENVE 420Industrial Pollution Control FLOTATION (Ref: 1- WPCF – Wastewater Treatment Plant Design 2- Eckenfelder) Dr. Asl?han Ker? Objective of Using Flotation Used for the removal of: - Suspended Solids - Oil and Grease from wastewater the seperation and concentration of sludges Mechanism of Flotation If density of particle density of water ? can be separated by flotation e.g. ? Petroleum industry Edible oil industry Fiber recycling in paper industry Flotation Types Simple flotation Flotation with aeration Dissolved air flotation Electroflotation Vacuum flotation Mechanism of Dissolved Air Flotation (DAF) Solid particles in liquid suspension become attached to microscopic air bubbles. Waste flow or a portion of clarified effluent is pressurized to 3.4 – 4.8 atm in the presence of sufficient air to approach saturation. When pressurized air-liquid mixture is released to atmospheric pressure, minute air bubbles are released from the solution. Mechanism of Dissolved Air Flotation (DAF) Agglomerate rise to the surface to join other particles and form a blanket that can be removed mechanically. Flotation is used primarily to remove light SS. Sludge flocs, suspended solids, oil globules are floated by the air bubbles which: Attach to floc particles Become enmeshed in floc particles Mechanism of Dissolved Air Flotation (DAF) Air-solids mixture ? skimmed off from the surface Clarified liquid ? removed from the bottom A portion of the effluent ? recycled back to the pressure chamber Primary variables for flotation design Pressure Recycle ratio Feed solids concentration Retention period For clarification, retention time: 20 – 30 min loading rate: 0.06 – 0.16 m3/min-m2 For thickening: longer tR Principal components of flotation system Pressurized pump ? elevated pressure to increase solubility Air-injection facilities Retention tank (saturation tank) ? 1-3 min Back pressure regulation device ? constant head on pressurizing pump Flotation unit ?