CHAPTER 3: Removal of Dissolved Metals by Bioremediation Check Access

Rapid industrialization has been adversely affecting the environment. Industrial effluents containing toxic and heavy metals are the main source of water contamination. Heavy metal pollution poses a serious environmental threat to humans and other living creatures due to the toxic effects of these metals and their accumulation throughout the food chain. In the last few decades, the concentration of these heavy metals in river water and sediments has been increasing at an alarming rate. Build-up of these toxic metals in vegetables grown in contaminated soils is posing adverse effects on human health. Numerous research projects on metal remediation through physico-chemical methods have been explored. However, most of these methods are either expensive or unsuitable for cases of voluminous effluents containing complex organic matter and low metal concentrations. In recent years, biological techniques have been shown to be a promising approach towards metal remediation in the laboratory and on an industrial scale. Microorganisms including bacteria, algae, fungi and yeasts can efficiently accumulate heavy metals from aqueous solutions, especially when the metal concentrations in the effluent ranges from less than 1 to 20 mg L⁻¹. Biological systems employing processes such as bio-reduction, bioaccumulation or biosorption using dead/pretreated microbial biomass have been extensively studied for their roles in heavy metal removal from synthetic and industrial wastewater. However, many a times, biosorption alone may not suffice for an effective metal remediation technique when real industrial effluent is tested. Under such situations, application of living microbial cells might be a better option as they offer the ability of self-replenishment and the potential for optimization through development of resistant species and immobilization of the cell surface. These issues form the theme of the present chapter in addition to a brief overview of the various physico-chemical methods available and a detailed illustration of the bioremediation technique used for toxic metal detoxification. In addition, focus has also been given to the applicability of an enriched consortium of living metal-resistant cells for metal scavenging. This effort is directed towards the development of a green and economically viable technique for treatment of metal-rich effluents.