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Preliminary shake-flask experiments evaluated\n                      <jats:italic>Aspergillus niger<\/jats:italic>\n                      strains (ATCC 1015 and CECT 2807), optimal carbon sources, and the influence of pH adjustment. Despite inherent biological variance across replicates,\n                      <jats:italic>A. niger<\/jats:italic>\n                      ATCC 1015 demonstrated a superior production trajectory, yielding 71.0 \u00b1 27.7 mM OA in 5 days. Intermittent pH adjustment above 4.0 significantly enhanced secretion to 90.4 \u00b1 5.8 mM, while glucose was identified as the optimal carbon source (Y\n                      <jats:sub>P\/S<\/jats:sub>\n                      <jats:inline-formula>\n                        <jats:alternatives>\n                          <jats:tex-math>$$\\approx $$<\/jats:tex-math>\n                          <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                            <mml:mo>\u2248<\/mml:mo>\n                          <\/mml:math>\n                        <\/jats:alternatives>\n                      <\/jats:inline-formula>\n                      0.4 g\/g). Building upon these preliminary findings, process intensification was conducted in a 10\u00a0L 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 \u00b1 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.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Key points<\/jats:title>\n                    <jats:p>\n                      <jats:list list-type=\"bullet\">\n                        <jats:list-item>\n                          <jats:p>\n                            <jats:italic>A.niger strain ATCC1015 was pinpointed as a suitable strain for biogenic OA production<\/jats:italic>\n                          <\/jats:p>\n                        <\/jats:list-item>\n                        <jats:list-item>\n                          <jats:p>\n                            <jats:italic>Fed-batch with pulsed feeding maximizes OA titer in scale-up.<\/jats:italic>\n                          <\/jats:p>\n                        <\/jats:list-item>\n                        <jats:list-item>\n                          <jats:p>\n                            <jats:italic>Gluconic acid and phosphate excess hinder selective OA production.<\/jats:italic>\n                          <\/jats:p>\n                        <\/jats:list-item>\n                      <\/jats:list>\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.1007\/s00253-026-14040-4","type":"journal-article","created":{"date-parts":[[2026,9,23]],"date-time":"2026-09-23T09:45:27Z","timestamp":1790156727000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Fermentation-based oxalic acid production aimed at sustainable critical metal recovery from electronic waste"],"prefix":"10.1007","volume":"110","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5984-3836","authenticated-orcid":false,"given":"Aylin Nur","family":"Erkmen","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7674-0967","authenticated-orcid":false,"given":"Roland","family":"Ulber","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9455-5044","authenticated-orcid":false,"given":"Thomas","family":"J\u00fcstel","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mirjam","family":"Altendorfner","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,9,23]]},"reference":[{"key":"14040_CR1","doi-asserted-by":"publisher","first-page":"118703","DOI":"10.1016\/j.envres.2024.118703","volume":"251","author":"AN Amenaghawon","year":"2024","unstructured":"Amenaghawon AN, Ayere JE, Amune UO et al (2024) A comprehensive review of recent advances in the applications and biosynthesis of oxalic acid from bio-derived substrates. 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