Abstract
Bioremediation is fundamentally the application of microorganisms to decontaminate or detoxify the obnoxious water, soil, sludge and hazardous materials to ensure a safe and habitable environment. As the world moves towards globalisation of resources and commodities, contamination issues in general and heavy metal contamination in particular has become an immediate global environmental concern to be addressed. Due to its economical, environment-friendly and multifarious application potentials, bioremediation has taken the centre-stage of scientific investigations in environmental management since a couple of decades. Microbial (bio)leaching that employs acidophilic microorganisms (including archaea, bacteria) and fungi to treat hazardous wastes, such as, electronic wastes, spent catalysts, steel slag and sludge containing heavy or toxic metals is one such bioremediation approach. This process involves sulphuric (H2SO4) and organic acids acidification by acidophilic bacteria and fungi respectively, and the generation of ferric iron (Fe3+) through oxidation by acidophilic microorganisms. These biochemical agents thus generated react with the hazardous wastes biotransforming them into nonhazardous forms. Successful studies on acidophilic bacteria Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, and a fungus Aspergillus niger on their role in the bioleaching process have been reported on several instances. This chapter converses on the critical aspects of microbial bioleaching of toxic metals from various sources by employing various groups of bioremediating microorganisms. The mechanism, the key operational factors, various potential microbes and their numerous promising applications have been comprehensively covered. However, the transfer of such feasible technologies from lab to the land remains a challenge for environmental technologists.