2. The secondary treatment is mainly to remove biodegradable organic dissolved substances and part of colloidal substances, and reduce biochemical oxygen demand and part of chemical oxygen demand in wastewater. Usually, biological treatment is adopted. After biological treatment, there is still a considerable amount of COD in wastewater, sometimes with high color, fragrance and taste, or because of the high requirements of environmental hygiene standards, it is necessary to adopt the three-stage treatment method for further purification.
3. The tertiary treatment is mainly to remove organic pollutants and dissolved inorganic pollutants that are difficult to biodegrade in wastewater. Commonly used methods include activated carbon adsorption and ozone oxidation, and ion exchange and membrane separation techniques can also be used. Various chemical wastewater can be treated by different methods according to different water quality and quantity and the requirements of treated effluent quality.
Extended data
The history of human using cutting fluid can be traced back to ancient times. It is known that watering can improve efficiency and quality when polishing stone tools, bronzes and ironware. In ancient Rome, olive oil was used when turning piston pump castings, and butter and water solvent were used to polish metal armor in16th century.
Since 1775, John J.Wilkinson of England has successfully developed a boring machine for processing the cylinder of Watt steam engine, accompanied by the application of water and oil in metal cutting. 1860 After a long development, various machine tools such as turning, milling, planing, grinding, gear processing and thread processing have appeared one after another, which also marks the large-scale application of cutting fluid.
19 In the 1980s, American scientists first evaluated the cutting fluid. Taylor discovered and expounded the phenomenon and mechanism that supplying sodium carbonate aqueous solution by pump can increase cutting speed by 30% ~ 40%. The tool material used at that time was carbon tool steel, and the main function of cutting fluid was cooling, so the word "cooling fluid" was put forward. From then on, people called cutting fluid cooling lubricant.
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