Silver wastewater pollutants

Concentrations of Classical Pollutants in the Raw Wastewater of the Secondary Silver Subcategory... 

The pollutants characteristic of the industry wastewaters are summarized in Table 5.4 through Table 5.11, for both classical and toxic pollutants. The toxic pollutant data have been developed using a verification protocol established by U.S. EPA, with the exception of the following selenium, silver, thallium, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCCD). Table 5.12 presents the minimum detection limit for the toxic pollutants. Any value below the minimum limit is listed in the summary tables as below detection limit (BDL). 

Martin, M., M.D. Stephenson, D.R. Smith, E.A. Gitierrez-Galindo, and G.F. Munoz. 1988. Use of silver in mussels as a tracer of domestic wastewater discharge. Mar. Pollut. Bull. 19 512-520. 

Although the abundance of silver in the Earth s crust is comparatively low (0.07 pgg-1), it is considered an environmental contaminant and is toxic at the nanomolar level. As an environmental pollutant it is derived from mining and smelting wastes and, because of its use in the electrical and photographic industries, there are considerable discharges into the aquatic environment. Consequently, there have been studies on the geochemistry and structure of silver-sulfur compounds [31]. Silver, either bound to large molecules or adsorbed on to particles, is found in the colloidal phase in freshwater. In anoxic sediments Ag(I) can bind to amorphous FeS, but dissolved silver compounds are not uncommon. A more detailed study of silver speciation in wastewater effluent, surface and pore waters concluded that 33-35% was colloidal and ca. 15-20% was in the dissolved phases [32]. 

Most of the metals such as copper, nickel, chromium, silver, and zinc are harmful when they are discharged without treatment. The most widely used method for the treatment of metal polluted wastewater is precipitation with NaOH and coagulation with FeSCU or A12(S04)3 with subsequent time-consuming sedimentation. Other methods include adsorption, ion exchange, and reverse osmosis. Each method has... 

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