In metal industry, almost all processes produce wastewater in sync, including mining, smelting, and down-stream processing like electroplating, which usually contains various contaminants and large quantity. According to the main pollutant components, it could be divided into heavy metal wastewater (mining, smelting, electrolysis, electroplating, etc.), acid & alkali wastewater (metal processing, etc.), oil-bearing wastewater (mining, mechanical processing, etc.), that if these kinds of wastewater are discharged directly without treatment, it will cause serious pollution to the natural environment.

Taking electroplating industry as an example, electroplating is an important process in metal products, which is a technology that makes use of the principle of electrolysis to attach film to the surface of metal so as to improve the wear resistance, electrical conductivity, reflectivity, corrosion resistance, and improve the appearance of products. The wastewater from electroplating treatment includes rinsing water, waste plating solution, washing water, which contains various metal ions, acids and alkalis, grease and oil, and highly toxic substances. Due to the complexity of water quality and some heavy metal ions or cyanide may have the risk of carcinogenesis and teratogenesis, electroplating wastewater treatment is a great challenge in the industry.