Biological Removal of Mercury and Cadmium by Iron Oxidizing Bacteria Isolated from Aqueous Media

Due to the increasing trend of industrial development and also the industrial production, the presence of heavy metals along with industrial wastewater is undeniable. Despite the various ways to remove heavy metals, choosing biological methods can be the best way to control them. Using bacteria in this field can be very useful and inexpensive with less harm.

In the present study, various aquatic environments including rivers, ponds, industrial effluents, and activated sludge were sampled. Bacteria were identified based on the growth in iron-specific culture medium in terms of shape and 16S rRNA gene. These bacteria were cultured in specific culture media for iron-oxidizing bacteria, Luria-Bertoni (LB) and PHG II, containing 2 ppm of mercury chloride and cadmium chloride. The samples were then examined for the reduction or non-change of mercury and cadmium concentrations by atomic absorption spectrometry.

The results of the present study showed that the isolated bacteria were rod-shaped and chemoorganotrophic belonging to the genus Bacillus. The average percentages of mercury and cadmium removal by the isolated bacteria were about 95% and 40%, respectively.  The highest percentage of the removal of both heavy metals was observed in the effluent sample of iron factory wastewater.

Iron oxidizing bacteria were identified as reducing agents of heavy metals in the laboratory environment. These bacteria grew in both LB medium and iron-specific culture medium. The highest percentage of the removal of both heavy metals was observed in the effluent sample of the iron processing plant. Based on the results, it can be said that the bacteria of each environment have adapted to the compounds of that place and are the best option to remove compounds such as heavy metals.