Faculty Publications

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Process engineering aspects in bioleaching of metals from electronic waste
(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Minimol, M.; Shetty K, V.; Saidutta, M.B.
Obsolete electronic devices and their components majorly contributed by the computer and mobile phone printed circuit boards (PCBs) constitute the electronic waste (e-waste). The e-wastes pose an environmental threat due to their eco-toxicological characteristics, thus making its management a mandate through an ecologically sustainable process. Further, the high concentration of metals in the e-waste makes it a secondary ore for metal recovery. Bioleaching is a bio-hydrometallurgical process, which is microbe-mediated dissolution of metals. Different nutritional classes of microorganisms like autotrophs and heterotrophs are active bioleaching agents of e-wastes. The mode of action of microbes for bioleaching of metals is obscure and is believed to ensue through redox reactions, protonic attack, or chelation. The process of bioleaching is influenced by biotic factors like the group and class of microorganism, growth rate, metabolic activity, etc. However, there are several abiotic factors that strongly affect the bioleaching efficiency. Development of a bioleaching process would need the study of various biological, nutritional, and engineering factors that influence the process. This chapter presents the critical analysis of various process engineering aspects in the bioleaching of metals from e-waste. To engineer a bioleaching process, (1) various biological, nutritional, and physicochemical factors, such as media composition, pH, e-waste loading, particle size, oxygen requirement, inoculum size, etc., should be optimized and (2) suitable bioreactor choice considering the microbial type, phases to be contacted, and the pattern of contacting followed by optimization of bioreactor operational parameters. This paper brings out a critical review of these bioprocess engineering aspects in bioleaching of metals from e-waste, directing the reader to the future scope of research on bioleaching, a bioremediation strategy to save and conserve environment for sustainable development. © 2020, Springer Nature Switzerland AG.
Bioleaching of zinc from e-waste by A. aquatilis in fluidised bed bioreactor
(Taylor and Francis Ltd., 2023) Minimol, M.; Shetty K, V.; Saidutta, M.B.
Technological advancements with the use of new-generation electronic devices and accumulated electronic wastes (e-wastes) raise environmental concerns. E-waste, especially mobile phone Printed Circuit Boards (PCBs) is a rich source of metals. Bioleaching, a microbe-mediated metal dissolution process is employed for the recovery of metals. The operational parameters like particle size, inoculum percentage (v/v) and e-waste load (w/v) were optimised for Zn bioleaching by Alcaligenes aquatilis in shake flasks and fluidised bed bioreactor (FBR). The e-waste feed particle size of 0.175 mm and 5% inoculum was found to be the optimum for Zn bioleaching in both the shake flask and FBR. The optimum e-waste load was 5% in the shake flask and 2% in FBR. The maximum recovery of Zn was 0.6 mg/g (13.73%) in the shake flask and 0.57 mg/g (13%) in FBR, implying that FBR exhibits similar efficiency of Zn bioleaching as in the shake flask. Further three sequential batch runs increased the recovery to a maximum of 1.66 mg/g from 4.37 mg/g Zn present in the PCBs ie., 38% Zn recovery. This shows that efficient bioleaching of Zn on a larger scale can be achieved with sequential batches and applied for the simultaneous recovery of metals from PCBs. © 2023 Indian Institute of Chemical Engineers.
Performance of Fluidized-Bed Bioreactor in Copper Bioleaching from Printed Circuit Boards using Alcaligenes aquatilis
(Springer Science and Business Media B.V., 2024) Madhavan, M.; Shetty K, V.; Saidutta, M.B.
Technological advancements have led to a demand for modern electronic gadgets and outdated ones discarded as electronic waste (e-waste). The printed circuit boards (PCBs) constitute a significant portion of these wastes that contain hazardous substances that mandate e-waste management. The rich source of precious and base metals makes it a resource for urban mining. Bioleaching, a process of biohydrometallurgy, an alternative to conventional heat and chemical-based metal recovery processes, can be efficiently applied for metal recovery from these wastes in an environmentally safe manner. The process parameters like particle size, inoculum size (v/v), and e-waste load (w/v) for bioleaching of Cu from PCBs in a Fluidized-Bed bioreactor (FBR) and shake flask using Alcaligenes aquatilis as bioleaching agent were optimized. The bioleaching of 47.99% and 37.54% of Cu from PCBs were achieved in shake flask and FBR, respectively. The optimal conditions of Cu bioleaching were 0.175 mm particle size, 5% (v/v) inoculum, and 2% (w/v) e-waste load with 169.45 mg/g and 132.55 mg/g of Cu recovery in shake flask and FBR at 84 and 96 h, respectively. Further, the Cu bioleaching was carried out in sequential batches to improve the recovery with the optimized conditions. There was a prominent increase in the cumulative %Cu bioleaching of about 80.02% after three sequential batch experiments from PCBs with an initial Cu concentration of 353.09 mg/g. The present study proves that sustainable heterotrophic bioleaching of Cu can be efficiently achieved in a Fluidized-bed bioreactor operated in sequential batch mode by Alcaligenes aquatilis. Graphical Abstract: (Figure presented.) © The Author(s), under exclusive licence to Springer Nature B.V. 2023. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

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