Factors Affecting Cyanide Generation in Chlorinated Wastewater Effluent Matrix
Abstract:False positives for cyanide analysis in wastewaters have been reported. We examined the effects of storage time at high pH and of pH adjustments on the cyanide levels. Cyanide levels changed within the holding time allowed by Standard Methods. We also studied the difference in cyanide levels using two disinfection conditions -- breakpoint chlorination and chloramination. Glycine was used as the precursor to study the cyanide formation pathways. Under breakpoint chlorination conditions, cyanide formation is complete relatively quickly and detectable cyanogen chloride is produced. On the other hand, chloramination yields cyanide through a relatively slow, base-catalyzed reaction. Chloramination followed by dechlorination with sodium arsenite and addition of NaOH results in cyanide levels that increase significantly upon reanalysis in the first 24 hours and then remain relatively constant after that time. Cyanogen chloride (CNCl) was <5 ppb in samples disinfected with chloramination. Mechanisms are proposed that explain the very different cyanide results that are obtained when disinfection is carried out under breakpoint chlorination conditions versus chloramination conditions.
Document Type: Research Article
Publication date: January 1, 2006
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