A Fed-Batch Strategy Integrated with Mechanical Activation Improves the Solubilization of Phosphate Rock by <i>Aspergillus niger</i>

Solubilization of phosphate rock (PR) by microorganisms is an environmentally sustainable alternative to chemical processing for production of phosphate fertilizers. The effectiveness of this PR biological solubilization process is driven by the microbial production of organic acids that chelate the cations (mainly calcium) bound to phosphate. However, the biological solubilization efficiency has been limited by the PR solids content of cultivation systems and is still low for practical applications. Here, we propose a fed-batch strategy coupled with mechanical activation to improve the biological solubilization of PR by <i>Aspergillus niger</i>. An initial systematic study of the effect of the particle size of Itafós phosphate rock (IPR), a low reactivity phosphate mineral (P₂O₅, 20%), on the biological solubilization of phosphorus revealed that the particle size played a key role in IPR solubilization. Increases of available phosphate of up to 57% under submerged cultivation and 45% for solid-state culture were observed for rocks that had been milled for only 10 min. A fed-batch procedure was proposed in order to increase the solids content while maintaining the P-solubilization efficiency, resulting in a remarkable increase of 78% in P-solubilization, compared to the conventional process. This proposed strategy could potentially contribute to the future development of biotechnological processes for the large-scale industrial production of phosphate fertilizers that are environmentally sustainable