1. Introduction
Since the early 1970s there has been growing concern over the diverse effects of heavy metals on humans and aquatic ecosystems. Many heavy metals and their compounds have been found that are toxic, while some are also subjected to biomagnification (Viessman and Hammer, 1993; Gardea-Torresday et al., 1996). Environmental impact by heavy metals was earlier mostly connected to industrial sources. In recent years, metal production emissions have decreased in many countries
due to legislation, improved cleaning technology and altered industrial activities. Today and in the future, dissipate losses from consumption of various metal containing goods are of most concern (Bergback et al.,2001). Therefore, regulations for heavy metal containing
waste disposal have been tightened (European Commission,2002).A significant part of the anthropogenic emissions of heavy metals ends up in wastewater. Major industrial sources include surface treatment processes with elements such as Cu, Zn, Ni and Cr, as well as industrial
products that, at the end of their life, are discharged in wastes (Sun and Shi, 1998). Major urban inputs to sewage water include household effluents, drainage water,