The effects of cyanide on the methanogenic degradation of phenolic compounds

Abstract

The effects of cyanide on the degradation of phenol, m-cresol, p-cresol, catechol and hydroquinone in acclimated methanogenic consortia were studied. Batch cultures with cyanide concentrations up to 10 mg l −1 were monitored for phenolic removal and methane production. Results showed that the methanogens were more sensitive to cyanide inhibition than the phenolic-degrading bacteria. The former group was inhibited by lower cyanide concentrations and took longer to adapt to the toxicant. Phenolic degradation was slowed to varying degrees depending upon the phenolic substrate. The addition of 400 mg l −1 acetate or 10 −2 M bromoethanesulfonic acid, a specific inhibitor of methanogenesis, also slowed the rates of phenolic degradation. Thus cyanide can affect a phenolic-degrading consortium by causing an accumulation of endproducts of the non-methanogenic fermentation (e.g. acetate) because of the inability of the methanogens to consume them. A draw and feed culture adapted to phenol degradation in the presence of 5 mg l −1 cyanide was able to produce methane from feed solutions containing 5 mg l −1 cyanide and 250 mg l −1 phenol at the same rate as a control culture receiving 250 mg l −1 phenol but no cyanide.