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Effects of Thiocyanate on the Formation of Free Cyanide during Chlorination and Ultraviolet Disinfection of Publicly Owned Treatment Works Secondary Effluent
Author(s) -
Zheng Anping,
Dzombak David A.,
Luthy Richard G.
Publication year - 2004
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143004x141744
Subject(s) - cyanide , thiocyanate , effluent , chemistry , chlorine , nitrate , nuclear chemistry , environmental chemistry , inorganic chemistry , environmental engineering , organic chemistry , environmental science
Cyanide has been detected in effluent of some publicly owned treatment works (POTWs) at levels exceeding influent concentration. Thiocyanate (SCN − ) is a cyanide‐related compoundencountered 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.