Electronic waste or E-waste refers to the discarded electrical or electronic devices which have neared their useful life. Because of the toxicity and carcinogenicity of some compounds, the proper management and safe disposal of these electronic wastes have become serious challenges in recent years.

The E-waste also comprises of metals having economic value which needs to be extracted to before disposing them. Researcher across the world are working on various cost effective methods to extract the value out of the E-waste in environmentally safe manner.

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In a recent published study, bioleaching of metals from Printed Circuit Boards (PCBs) using bacterial and yeast strains (Stenotrophomonas maltophilia, Bacillus sp. and Candida tropicalis) isolated from heavily contaminated soil samples was successfully tested.

Printed Circuit Boards (PCBs) are used in almost all electronic devices which may contain up to 60 different chemical elements and have a metal content as high as 40% by weight. The PCBs are a complex mixture of materials such as plastics (13%), glass ceramics (24%), and metals (64%) including precious metals such as silver (Ag), gold (Au), and palladium (Pd), base metals such as copper (Cu), aluminium (Al), nickel (Ni), tin (Sn), silicon (Si), indium (In) and toxic metals such as cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), and bromine (Br). Hence, recovery of metals from the Printed Circuit Board is profitable, since these PCBs are used in almost every electronic gadget due to their high availability.

In the study a two-step bioleaching procedure was followed for maximum mobilization of metals. The isolated strains were able to mobilize metals from PCBs with different efficiencies depending on their ability to utilize the E-waste a carbon source when cultivated in minimal media. Bioleaching potential of isolated microbes on eight heavy metals (Cu, Ni, Mn, Pb, Fe, Cr, Zn & Co) in the sample were studied using AAS and SEM analysis before and after the two-step bioleaching process and found to be efficient.

Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cyanide. Bioleaching is one of several applications within  biohydrometallurgy and several methods are used to recover copper,  zinc, lead,  arsenic, antimony,  nickel, molybdenum, gold, silver, and cobalt.

The findings of the study revealed that microbes can play an important role in metal recovery. The metal concentrations were drastically reduced from their initial concentration because of the detoxification process and metabolic activity of microbial isolates.

According to the researchers the efficacy of leaching activity can be further improved by using a consortium of microbes which can be used as an efficient source in the removal of metals from discarded PCBs in an economic and eco-friendly way.

For the full research paper visit: 10.46488/NEPT.2022.v21i02.018

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