Biosorption of Metals by Microorganisms in the Bioremediation of Toxic Metals

Metal-contaminated water/wastewater is one of the most important environmental issues resulting from different industries including mining activities. Conventional water treatment techniques are not cost-effective for mine sites and are inefficient for removing elements at low concentrations. Bioremediation, using live cells, can be an alternative solution for removing metals from mine waters. The selection of resistant microbes is a prerequisite prior to designing a biotreatment system to withstand the harsh conditions of mine waters, usually acidic and containing toxic metals. The extremophile 282 indigenous mining microorganisms, particularly phototrophic eukaryotes (green microalgae), were found to be efficient metal biosorbents. These algal–microbial consortiums, as attached biofilms to drainage substrates, rely on low concentrations of available nitrate and phosphate in mine waters. The microbes are also adapted to the metal-contaminated waters, while they are able to remove and accumulate many metals actively and passively on/in their cells, through various biochemical and biological mechanisms. To immobilize the algal–microbial consortium as biofilm and achieve efficient treatment, a suitable configuration of photobioreactors is required. From the most commonly used types of biofilm reactors for water treatment, rotating biological contactors facilitate biofilm formation and provide a simple operation for potentially sustainable water treatment at mine sites. The application of bioreactors for removing metals from contaminated water and the efficiency of a biological treatment system are discussed in this chapter.