The occurrence of cyanide formation in six full-scale publicly owned treatment works.

This paper presents results from an intensive monitoring program implemented at six full-scale publicly owned treatment works (POTWs) to investigate the fate and formation of cyanide in wastewater treatment processes, with a focus on chlorination and dechlorination processes. A review of historical monitoring data for cyanide species in these POTWs was also conducted. This POTW monitoring program provided a database for the investigation of cyanide formation in wastewater secondary treatment. Data from participating POTWs showed evidence of cyanide formation in this 1-year monitoring effort, although the cyanide formation pattern varied significantly from one plant to another and among seasons. Generally, the chlorination of thiocyanate (SCN-) seems to be the most important mechanism for the formation of cyanide in wastewater treatment processes, especially in chlorination and dechlorination. This hypothesis is supported by the findings of a related laboratory study of mechanisms of cyanide formation in POTWs. It is recommended that POTWs monitor SCN in influent and secondary effluent to identify its presence and adjust chlorine dose appropriately.