NEW FRIENDLY TO ENVIRONMENT METHOD IN WASTEWATER TREATMENT

摘要

The present paper summarises environmental applications of conventional and unconventional methods and especially the method of flotation in order to remove pollutants from waste-waters. Due to the high throughput and efficiency of modern equipment that has been developed during the last years, flotation seems to be one of the most appropriate methods, providing efficient selective recovery of valuable ions and low sludge generation in such processes. Flotation is used to treat industrial wastewater containing substances that tend to float to the surface. These include paint, oils, grease and carbohydrates. Flotation is facilitated by the addition of chemical agents and the injection of air (dissolved air flotation). In this method bubbles are formed by a reduction in pressure of water pre-saturated with air at pressures higher than atmospheric. The supersaturated water is forced trough needle-valves or special orifices, and clouds of bubbles, 30-100 mm in diameter, are produced just down-stream of the constriction. It is concluded that this process will be soon incorporated as a technology in the minerals industry to treat the wastewaters and, when it is possible, to recycle process water and materials. The use of flotation in environmental applications is fully discussed.