Effects of Thiocyanate on the Formation of Free Cyanide during Chlorination and Ultraviolet Disinfection of Publicly Owned Treatment Works Secondary Effluent

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 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.

Uptake, assimilation and toxicity of cyanogenic compounds in plants: facts and fiction

“…It can also be used directly in a variety of processes, including electroplating and hydrometallurgical gold or silver extraction (Boening and Chew 1999;Srivastava and Duvvuru Muni 2010). The extensive use of cyanide-containing chemicals results in a significant release of cyanide into the environment on a continuous basis (Zheng et al 2004;Donato et al 2007). For example, the open tailing ponds stored effluents generated from extraction process of gold mining operation contain up to 120 mg/L free cyanide to 400 mg/L total cyanide, including various iron cyanides with heavy metals (Ebel et al 2007).…”

Factors Affecting Cyanide Generation in Chlorinated Wastewater Effluent Matrix

“…The mechanism of cyanide and CNCl formation from glycine in water under free chlorine conditions has been reported by Na and Olson (2006). Monochloramine has been shown to react with formaldehyde and eventually yield HCN (Pedersen et al, 1999); organocyanide compounds (cyanocobalamin and coenzyme vitamin B12) release free or metal-complexed cyanide upon chlorination (Yi et al, 2002); solutions of L-serine that were chlorinated and subsequently dechlorinated were shown to produce cyanide (Zheng et al, 2004a); reaction of nitrite with aromatic compounds can produce cyanide (Zheng et al, 2004b); microorganisms have been shown to be capable of producing cyanide (Brandl, 2005); less than stoichiometric chlorination of thiocyanate can liberate free cyanide (Zheng et al, 2004c); and, it was found that phenol reacts with nitrous acid to produce cyanide ions (Adachi et al, 2003). The potential for chloramination to yield cyanide from organic compounds was demonstrated in earlier experiments using synthetic solutions spiked with select precursor organics such as ascorbic acid, humic acid, D-ribose, and 2-furaldehyde (Carr et al, 1997).…”

Toxins and Their Phytoremediation

“…For example, thiocyanate is discharged in a variety of industrial wastewater discharges, while cyanogen halides are released upon chlorination or bromination of water containing free cyanides (Zheng et al 2004). For example, thiocyanate is discharged in a variety of industrial wastewater discharges, while cyanogen halides are released upon chlorination or bromination of water containing free cyanides (Zheng et al 2004).…”