Fate and speciation of silver in publicly owned treatment works

Abstract

AbstractThe fate and speciation of silver in three categories of publicly owned treatment works and their receiving waters were studied. The plants included those that treated (a) municipal sewage and commercial photoprocessing effluents, (b) municipal sewage and nonphotographic silver effluents and (c) municipal sewage with no known silver effluents. Specific objectives were to determine if the source of silver affects silver removal and how secondary treatment affects the speciation of silver.The average removal efficiency for total silver at the six treatment plants studied was 75%. The two plants receiving silver from photoprocessing operations achieved 95% removal. The two plants receiving silver from industrial sources achieved 83% removal. The plants with no known silver contributors achieved 48% removal. There was no significant increase in silver in any of the sediments downstream of the treatment plant discharges.The highest influent free silver ion concentrations were associated with the treatment plants that had no known photoprocessing or industrial silver sources. The concentrations of silver ion in the effluents from all treatment plants ranged from 0.001 to 0.07 μg/L. Downstream silver ion concentrations were always ≤ 0.05 μg/L. With the chronic toxicity value to freshwater aquatic life for silver ion being stated as 0.12 μg/L, the relatively small quantities of silver ion and total silver that were discharged should have little, if any, impact on receiving water quality.