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Occupational exposure limits are the maximum allowable concentrations of hazardous elements in the air. They are defined by scientific laboratories in order to control the level of pollution in different areas. Among the main atmosphere pollutants are large-scale industry, domestic boilers and transport. The portion of each of these pollutants is different from place to place, but industrial companies are considered to be the worst pollutants. The major sources of artificial aerosol pollution of the atmosphere are thermal power plants that burn a large amount of coal with high ash content, concentrating mills, metallurgical, cement, magnesite and soot plants. |
Methods of wastewater purification
Water bodies are mainly polluted as a result of wastewater drainage from industrial enterprises and places of population. As a result of wastewater drainage the physical properties of the water are changed (the temperature, as well as turbidity are increased, different colors, smells and tastes are added); the qualitative and quantitative bacterial composition changes.
The methods used for purification of industrial and domestic wastewaters can be divided into three groups: mechanical, physical and chemical, biological. Sewage disposal plants as a rule have facilities for mechanical purification. Depending on the level of purification needed they can be supplemented by constructions of biological or physical and chemical purification. Before discharge of the purified water into a water reservoir it undergoes the process of disinfection and the sediment forming at all stages of purification is forwarded for further processing.
The purified water are then directed to circulating water supply systems of factories and plants or for agricultural needs or simply discharged into a water body. The processed sediment can be recycled, destroyed or stored.
Mechanical purification is used for separating undissolved mineral or organic admixtures from the sewage water. As a rule it is used for coarse purification and is designed for preparing the water for further biological or physical and chemical methods of purification.
