Microbial degradation of cyanide and thiocyanate

The role played by a bacterial community composed of Pseudomonas putida, st rain 21; Pseudomonas stutzeri, strain 18; and Pseudomonas sp., strain 5, an d by physical and chemical factors in the degradation of CN- and SCN- was s tudied. It was shown that the degradation of CN- is determined both by the action of bacteria and by abiotic physical and chemical factors (pH, O-2, t emperature, the medium agitation rate, etc.). The contribution of chemical degradation was found to increase drastically at pH below 9.0; when air was blown through the medium (irrespective of the pH value); under active agit ation of the medium; and when the medium surface interfacing air was increa sed. Even at elevated pH values (9.0-9.2), suboptimal for bacterial growth, the microbial degradation could account for at most 20-25 mg/l of CN-, reg ardless of its initial concentration. When CN- and SCN- were concurrently p resent in the medium, the former compound was the first to be degraded by m icroorganisms. The rate of bacterial degradation of SCN- under continuous c ultivation in a chain of reactors was found to depend on its concentration, the medium flow rate, agitation rate, and the pattern of carbon source sup ply and could exceed 1 g/(1 day). CN- and SCN- are utilized by bacteria sol ely as nitrogen sources. The mechanism of CN- and SCN- degradation by the m icrobial community is discussed.