Publication: Fermentation-Based Oxalic Acid Production Aimed At Sustainable Critical Metal Recovery from Electronic Waste

This study systematically investigates the biogenic production of oxalic acid via submerged fermentation to establish a sustainable reagent for critical metal recovery applications. Preliminary shake-flask experiments evaluated Aspergillus niger strains (ATCC 1015 and CECT 2807), optimal carbon sources, and influence of pH adjustment. Despite inherent biological variance across replicates, A. niger ATCC 1015 demonstrated a superior production trajectory, yielding 71.0 ± 27.7 mM OA in 5 days. Intermittent pH adjustment above 4.0 significantly enhanced secretion to 90.4 ± 5.8 mM, while glucose was identified as the optimal carbon source (YP/S ≈ 0.4 g/g). Building upon these preliminary findings, process intensification was conducted in a 10 L stirred-tank bioreactor. Transitioning to a fed-batch strategy with pulsed feeding and continuous pH control effectively contributed to substantially higher OA titers, achieving a peak OA titer of 260.1 ± 4.8 mM over 14 days. Co-production of gluconic acid and acidogenesis inhibition posed a challenge in attaining higher product yields. Collectively, these findings establish a robust, scalable bioprocess for sustainable OA generation, directly supporting its emerging application as a highly selective leaching agent for critical metal recovery from electronic waste streams.

A.N. Erkmen, R. Ulber, T. Juestel, M. Altendorfner; Fermentation-Based Oxalic Acid Production Aimed At Sustainable Critical Metal Recovery from Electronic Waste; Applied Microbiology and Biotechnology (2026) in press