Abstract
The continuous discharge of cyanide-containing effluents to the environment has necessitated for the development of environmentally benign treatment processes that would result in complete detoxification of the cyanide-containing wastewaters, without producing additional environmental toxicants. Since biological detoxification of hazardous chemical compounds has been renowned for its robustness and environmental-friendliness, the ability of the Exiguobacterium acetylicum (GenBank accession number KT282229) and Bacillus marisflavi (GenBank accession number KR016603) to co-metabolise thiocyanate (SCN−) and free cyanide (CN−) under alkaline conditions was evaluated. E. acetylicum had an SCN− degradation efficiency of 99.9 % from an initial SCN− concentration of 150 mg SCN−/L, but the organism was unable to degrade CN−. Consequently, B. marisflavi had a CN− degradation efficiency of 99 % from an initial concentration of 200 mg CN−/L. Similarly, the organism was unable to degrade SCN−; hence, this resulted in the evaluation of co-metabolism of SCN− and CN− by the two microbial species. Optimisation of operational conditions was evaluated using response surface methodology (RSM). A numeric optimisation technique was used to evaluate the optimisation of the input variables i.e. pH, temperature, SCN− and CN− concentrations. The optimum conditions were found to be as follows: pH 9.0, temperature 34 °C, 140 mg SCN−/L and 205 mg CN−/L under which complete SCN− and CN− degradation would be achieved over a 168-h period. Using the optimised data, co-metabolism of SCN− and CN− by both E. acetylicum and B. marisflavi was evaluated, achieving a combined degradation efficiency of ≥99.9 %. The high degradative capacity of these organisms has resulted in their supplementation on an active continuous biological degradation system that is treating both SCN− and CN−.Electronic supplementary materialThe online version of this article (doi:10.1007/s13205-016-0491-x) contains supplementary material, which is available to authorized users.
Highlights
Cyanide is a naturally occurring compound which is produced by a variety of living organisms, such as fungi, plants, bacteria and algae (Luque-Almagro et al 2005), and is existent in the stratosphere and non-urban troposphere as a result of natural activities such as gases from volcanoes and burning of biomass
When minimal media (MM) was utilised as the growth media, E. acetylicum achieved complete degradation of SCN- over a period of 98 h (Fig. 2a), while B. marisflavi achieved complete CNdegradation over a 98-h period (Fig. 2b)
This study focused on the co-metabolism of the free cyanide and thiocyanate by the isolated B. marisflavi and E. acetylicum
Summary
Cyanide is a naturally occurring compound which is produced by a variety of living organisms, such as fungi, plants, bacteria and algae (Luque-Almagro et al 2005), and is existent in the stratosphere and non-urban troposphere as a result of natural activities such as gases from volcanoes and burning of biomass. The contribution of these natural activities to cyanide contamination in the environment is insignificant as compared to anthropogenic activities. The co-existence of CN- and SCN- in wastewaters is detrimental to both the environmental and living organisms, including humans
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