Cyanide, which is inhibitory to methanogenesis, is a common toxic contaminant in a variety of industrial wastewaters. Among these are coal conversion and coking wastewaters which contain phenolics which are amenable to biodegradation by methanogenic consortia.

Semicontinuous anaerobic phenol-degrading cultures were exposed to a range of total cyanide concentrations from 5 to 30 mg/l (free cyanide from 0 to 18 mg/l) for a 140-day period. The higher cyanide concentrations gave longer lag periods before the onset of methane production. After methanogenesis became established, the rate of methane production in cyanide-fed cultures matched that of the cyanide-free controls. In batch cultures, free cyanide was substantially removed before the onset of methanogenesis.

Addition of 14CN to a semicontinuous culture demonstrated that the majority of the label was transformed to a product that remained in the liguid phase. Although the product has not been identified, thin layer chromatography analysis has shown that it is not one of the following detoxification products reported for aerobic biological systems: thiocyanate, β-cyanoalanine, valine, alanine, aspartate or asparagine; nor is the product ferrocyanide or a cobalt complex.

These studies have shown that methanogenic consortia can detoxify cyanide while they continue to degrade phenol.

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