The main source of zinc in wastewater of electroplating and metal processing industry is the towing liquid of electroplating or pickling. Pollutants are transferred to rinsing water again through metal rinsing process. Pickling process includes first immersing metal (zinc or copper) in strong acid to remove the oxide on the surface, and then immersing in the brightener containing strong chromic acid for light enhancement. The waste water contains a large amount of heavy metal ions such as hydrochloric acid, zinc, copper and organic brighteners, etc., which are highly toxic, and some of them also contain highly toxic substances that are carcinogenic, teratogenic and mutative, which do great harm to human beings. Therefore, the electroplating wastewater must be carefully recycled to eliminate or reduce its pollution to the environment.