Removal of heavy metals by microbial communities

A scarcity for clean water has drawn global attention and thus various technologies for heavy metal removal from water are being explored and designed to ensure water recovery/recycle/reuse. Effective and successful water treatment processes have been aimed toward exploiting alternative sources of water (apart from freshwater) such as seawater, stormwater, wastewater, and industrial effluents. Conventional technologies like adsorption, filtration, chemical precipitation, reverse osmosis, ion exchange, and membrane separations are expensive and have several limitations. Thus various microbial communities that include especially bacteria, yeasts, and fungi have received increasing attention for heavy metal removal and recovery due to their efficient biosorption capacity. Moreover, biological processes for heavy metal removal involve low costs and are environment-friendly, reusable, and easy to scale up. The surface of microbial biosorbents provide metal-binding functional sites that include carboxyl, imidazole, sulfydryl, amino, phosphate, sulfate, thioether, phenol, carbonyl, amide, and hydroxyl moieties. In this chapter, we present an elaborate account of several bacterial communities from genus Geospirillum, Geospirillum, Desulfutomaculum, Bacillus, Crysiogenes, Pseudomonas, Rhodopseudomonas, Ralstonia, Thiomonas, etc., for the effective removal of toxic metal ions like arsenic, cadmium, chromium, cobalt, copper, iron, lead, and manganese. Similarly, applications of fungus and yeasts from the genera Penicillium, Rhodosporidium, Schizosaccharomyces, Torulopsis, Aspergillus, Saccharophagus, Saccharomyces, etc, are also discussed. Further, various cellular mechanisms, genes, and enzymes involved in microbial metal removal technology are presented that can be used for designing genetically engineered microbes. Lastly, commercial biosorbents which may be inexpensive and more efficient alternatives for the removal of toxic metals from aqueous solutions are discussed.