Aspergillus niger Enhances the Efficiency of Sewage Sludge Biochar as a Sustainable Phosphorus Source

Abstract

Phosphorus-rich biochar derived from sewage sludge (SS) could be a sustainable alternative P source for agriculture. However, most of biochar P is not readily available to plants. We evaluated the potential of P release from SS biochar into soil solution by Aspergillus niger. Additionally, we assessed the effect of SS biochar on the solubilization of phosphate minerals by the fungus. An incubation study was performed for 7 days in shaken flasks containing culture medium supplemented, or not, with a P-fixing soil. Biochar showed a dual role in phosphate solubilization by A. niger: (i) improved solubilization of AlPO4 and rock phosphate; and (ii) acted as a P source. Aspergillus niger solubilized up to 50% of the P contained in the biochar. A combined application of SS biochar and A. niger increased P availability by 500 times in a solution containing P-fixing soil. These results suggest that P-use efficiency from SS biochar could be improved by A. niger, allowing for the use of lower doses of this soil amendment. These findings contribute to a better understanding of the role of phosphate-solubilizing microorganisms in the interaction between soil and biochar. Furthermore, the results underpin the potential P fertilizer value of the SS biochar. Finally, our results present a win–win environmental benefit as it reduces SS accumulation and improves P-use efficiency.