Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 57

Air flotation processes are even more effective but are relatively complex. In the dissolved air flotation cell, air is injected into the oily wastewater as fine bubbles. The oil droplets adhere to the air bubbles and rise to the surface as a froth, which is skimmed off by a motor-driven rake. Some small, suspended particulate contaminants can also be removed in the froth, and others will settle to the bottom of the cell and can be removed as sludge. A coagulant can also be added to aid removal efficiency. If lime is added, for example, it will precipitate some heavy metals and certain anions such as carbonates.

Dissolved air flotation is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter, causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.

Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, and natural gas processing plants and could find use in the oil shale industry.

See also: Settling and Flotation.