CYANIDE FORMATION DUE TO WASTEWATER DISINFECTION: LABORATORY ISSUES AND COMPLIANCE STRATEGIES

Numerous wastewater plants across the United States have detected cyanide in chlorinated effluents at levels exceeding those in influent waters, and in some cases, exceeding NPDES (National Pollutant Discharge Elimination System) discharge limits. Previous studies have suggested that cyanide may be formed during wastewater chlorination. In addition, studies conducted by a number of POTWs (Publicly Owned Treatment Works) have indicated that false positives are possible due to artifacts of sample handling and analytical techniques, and that the management of cyanide at many wastewater plants is complicated by method shortcomings and the lack of species-specific analytical techniques. Due to these and other cyanide water-related issues, the Water Environment Research Foundation (WERF) funded a three-year research project titled “Cyanide Formation and Fate in Complex Effluents and Its Relation to Water Quality Criteria.” Malcolm Pirnie, Inc. and a multi-organization team (Carnegie Mellon University, Clarkson University, three industrial organizations, and thirteen utilities managing POTWs) were selected to perform this research.The project team's research approach involved first the identification and evaluation of analytical methods for measuring cyanide species at detection limits appropriate for water quality management, and the testing of these methods at a number of POTWs to determine the fate of cyanide during wastewater treatment. Second, the approach involved an assessment of the apparent sources and/or causes of cyanide formation and disappearance in POTWs based on plant monitoring programs, compilation and analysis of historical data, and laboratory tests of cyanide formation. Third, the approach involved a compilation of water quality criteria currently used for water quality management as well as a summary of existing aquatic toxicity data for cyanide species in receiving waters. Finally, the approach involved an assessment of the relative magnitude of processes influencing the fate of cyanide in receiving waters with the support of industrial participants.Specific to laboratory issues, this study compared and evaluated seven methods for the analysis of cyanide in reagent water and different contaminated water matrices. The methods compared were weak acid dissociable (WAD) cyanide (APHA, 1995, 4500-CN-I), free cyanide by microdiffusion (ASTM D4282-95), available cyanide [Federal Register: December 30, 1999 (Volume 64, Number 250)], metal cyanides by ion chromatography (Dionex Application Note No.55), automated total cyanide by thin film distillation (ASTM D4374-93), automated weak acid dissociable by thin film distillation (ASTM D4374-93), and automated total cyanide by low power UV digestion (USEPA Method 335.3). Five different contaminated water samples, including groundwater from a manufactured gas plant site, POTW influent and effluent, aluminum smelting plant groundwater, and reagent waters prepared in the laboratory, were used in the study. Analysis of each contaminated water with the methods selected involved replications and spiking with sodium cyanide (NaCN), nickel cyanide (K2Ni(CN)4) and ferrocyanide (K4Fe(CN)6) to evaluate matrix-dependent method detection limits (MDLs), precision, and bias. This phase of the WERF study demonstrated that various species-specific cyanide analytical techniques can be employed reliably for low-concentration analysis with a range of contaminated water types, with the exception of the available cyanide method, which, when applied to raw municipal wastewater, resulted in significant interference problems. Also, there was recovery of some diffusible cyanide in microdiffusion tests with nickel-cyanide-spiked samples, apparently reflecting dissociation of this weak metal-cyanide complex during the test. These analytical method performance data can be used to assess the potential for routine application of the particular methods with different types of waters.Because the key objectives and findings of the WERF study are thoroughly documented in a study report co-published by WERF and the International Water Association (IWA) in 2003, this paper presents only a brief overview of the WERF-funded study, with a focus on analytical laboratory issues related to cyanide as well as compliance strategies for municipal and industrial discharges of cyanide-impacted wastewater to consider and customize for their particular situations.