Reduction of [Co(iii)–EDTA]− complex by a novel process using phototrophic granules: a step towards sustainable bioremediation

Abstract

Microbial granules are more effective than monoculture bacteria in the bioremediation process of environmental contaminants. Among various types of microbial granules phototrophic granules are relatively advantageous in bioremediation than heterotrophic granules since they are self-sustaining. [Co(III)–EDTA]⁻ generated during nuclear waste management is difficult to remove from the radioactive waste due to its high solubility and stability. In this study, phototrophic granules generated from a freshwater source were used for the reduction of [Co(III)–EDTA]⁻ under anoxic conditions. The results of the study showed that the phototrophic granules efficiently reduced the highly soluble [Co(III)–EDTA]⁻ to a lesser soluble form, [Co(II)–EDTA]^2– up to a concentration of 20 mM. The rate of [Co(III)–EDTA]⁻ reduction was found to be relatively high when the process was performed with acclimatized phototrophic granules when compared to non-acclimatized granules. Specific studies using antibiotics to kill the heterotrophic bacterial population of the phototrophic granules showed that [Co(III)–EDTA]⁻ reduction was carried out predominantly by the phototrophs. Investigations were also carried out to test the robustness of phototrophic granules to perform [Co(III)–EDTA]⁻ reduction after gamma irradiation. The phototrophic granules showed substantial radio-tolerance and could reduce [Co(III)–EDTA]⁻ without any significant loss in the activity, when irradiated up to 2 kGy. The study suggests that phototrophic granules have potential application in bioremediation of moderate level nuclear waste.