Effects of thiocyanate on the formation of free cyanide during chlorination and ultraviolet disinfection of publicly owned treatment works secondary effluent. |
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Authors: | Anping Zheng David A Dzombak Richard G Luthy |
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Institution: | Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA. |
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Abstract: | Cyanide has been detected in effluent of some publicly owned treatment works (POTWs) at levels exceeding influent concentration. Thiocyanate (SCN-) is a cyanide-related compound encountered in most POTW influents and may be decomposed to free cyanide (CN-) under some circumstances. Effects of SCN- on the formation of cyanide during chlorination and UV disinfection were studied through a laboratory study with synthetic solutions and POTW secondary effluent. Results indicated that CN- was detected in SCN- solutions after chlorination in which the chlorine dose or reaction time was not sufficient to destroy SCN-completely, thus ensuring no residual chlorine to destroy any CN-produced. It was also found that SCN can be broken down to yield cyanide by UV irradiation. In addition, SCN- was observed to cause significant positive error in the conventional total cyanide analysis technique involving acidic distillation and colorimetric measurement when nitrate was present in the sample. |
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