Fermentation-based oxalic acid production aimed at sustainable critical metal recovery from electronic waste.

Electronic waste is a major environmental problem, but it also contains valuable critical metals. Conventional hydrometallurgical recovery relies on strong inorganic acids. Those acids create hazardous secondary waste and require a lot of energy. This research looks at a greener option: producing oxalic acid through fermentation and using it to bio‑leach metals from e‑waste. Acid‑producing microbes such as *Aspergillus niger* can be tuned by changing their metabolic pathways and the feedstock they grow on. The oxalic acid they make is a very selective chelating agent. It dissolves metals from ground printed‑circuit boards and then allows the metals to precipitate out as oxalate compounds. The proposed framework gives step‑by‑step guidance for:

* measuring how fast the microbes produce acid, * testing how pulp density, pH, and temperature affect leaching efficiency, * modeling the thermodynamic stability of metal‑oxalate complexes. By combining biological acid production with traditional metal recovery, the process forms a closed‑loop, low‑carbon route that reduces waste. The project support tools help researchers design, simulate, and experimentally verify bio‑based extraction methods, moving e‑waste management toward a circular‑economy model.

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