Heavy Metal Removal Processes by Sulfate-Reducing Bacteria

Abstract

Actually, natural phenomena and anthropogenic activities have led to large environmental pollution in all kinds of ecosystems. From the above exist the needed to implement technological actions in order to diminish the pollution problems. Among these technological actions, the biotechnology processes have the great advantage of high specificity for the removal of chemical compounds as heavy metals with low energy consumption. The microorganisms are the biological agents most used in the treatments of polluting compounds, due to their degradation capacities of organic and inorganic pollutants, but the metals are not degraded but only can be modified in their redox state, converting them to less toxic forms. Precipitation and biosorption are the most employed process for metal ion removal from water. Microalgae, fungi and bacteria have been used successfully in the removal of metals, but in the last decade, sulfate-reducing bacteria (SRB) have taken great relevance in the processes of metal removal from wastewater. The removal of heavy metals is promoted when hydrogen sulfide is produced; it reacts with metal ion and forms metal sulfides, which are insoluble and tend to precipitate; it is not the only mechanism by which metal ions are removed, biosorption mechanisms can also be carried out (with biomass and production of exo-polysaccharides), immobilization and enzymatic reduction of the metal ion to less toxic and insoluble forms, but this will depend on the type of bacteria and their tolerance to metals.