Cyanide Formation and Fate in Complex Effluents and Its Relation to Water Quality Criteria: Results From a Three-Year Werf Study

Abstract

Numerous wastewater plants across the United States have detected cyanide levels in their effluents that exceed influent concentrations. Researchers have found that these low concentrations of cyanide, generally less than 25 µg/L as free cyanide, can be formed during disinfection. Because discharge limits for total cyanide are very low, the cyanide generated during disinfection may exceed National Pollutant Discharge Elimination System (NPDES) permit limits. Complicating the situation, analytical interferences in monitoring samples can lead to cyanide false positives, and current methods for analyzing cyanide species have method detection limits that are very close to the discharge limits.In an effort to address research gaps associated with cyanide formation, fate in complex effluents and its relation to water quality criteria, a three-year research project was initiated by the Water Environment Research Foundation (WERF) in 1998. First, seven analytical methods for cyanide species were evaluated and tested in municipal and industrial wastewaters. Second, the sources, transport and fate of cyanide species in POTWs and receiving waters were evaluated using laboratory, modeling and field studies. Third, information on the toxicity of cyanide species to aquatic organisms was compiled and synthesized. Finally, current U.S. and state cyanide water quality criteria were evaluated. This manuscript will summarize key findings of the WERF study (Deeb et al., 2003a). In addition, based on the findings of this study, strategies that can be pursued by municipal and industrial dischargers in order to comply with cyanide standards will be presented.