Removal, partitioning, and fate of silver and other metals in wastewater treatment plants and effluent-receiving streams

We investigated the removal of silver in five publicly owned treatment works (POTWs) and the fate of Ag in effluent receiving streams. Comparisons were made to several other metals. Silver was removed efficiently (>94%) in all POTWs. The percentage of total Ag removed was independent of the influent Ag concentration, while the concentration of Ag in effluents was directly related to influent concentration. A good correlation (r(2) = 0.77) between metal removal (%) and partition coefficient (K-d) indicated that differences among metals in removal efficiency were controlled mainly by metal partitioning (sorption) to particles removed by settling and/or filtration. A large fraction (19-53%) of Ag in the filterable (<1.0-mu m) fraction of POTW effluents was associated with submicron particles or colloids (>0.05 mu m), and the percentage filterable Ag was directly related to DOC concentration (r(2) = 0.96). Effluent Ag concentrations (0.06-2.6 mu g/L) were several orders of magnitude higher that typical "background" stream levels (1-2 ng/L), but Ag discharged to streams was rapidly dissipated by dilution and incorporation into stream sediments.