Microbial cell factories in the remediation of e-wastes: an insight

Electronic waste, also known as e-waste, is the discarded or by-products of electronic appliances, constituting a major percentage of the total solid waste produced globally. Such e-waste is mostly composed of plastics, various heavy metals, azo dyes, and xenobiotic components, which are mostly non-biodegradable or less degradable in nature. As a result, they increase environmental toxicity, preventing the growth of crops and causing health issues for humans and other animals. On the other hand, recycling e-waste may also lead to the consumption of heavy metals through water or the inhalation of polluted air after combustion, which may cause various health issues such as asthma, nerve, respiratory, kidney, liver disease, and even cancer. Hence, microbial degradation of e-waste has become a new trend in managing such solid wastes. However, their mode of action is somewhat less explored. Microbes degrade various components of e-waste through a number of mechanisms such as bioleaching, biosorption, biotransformation bioaccumulation, and biomineralization. Some microorganisms release enzymes such as reductases, laccases, esterases, carboxylesterases, catalases, and dioxygenases for the bioconversion of various components of e-waste into their less toxic forms. This review provides insight into the role of microbes in the conversion of various components of e-wastes such as polyaromatic hydrocarbons (PAHs), azo dyes, and heavy metals and their mode of action.