Post-treatment of biogenic sulfur coating enhances autotrophic denitrification

Abstract

<title>Abstract</title> Biogenic sulfur (bio-S⁰) is a promising electron donor for treating carbon-limited wastewater, yet the inherent variability of its organic coating poses an unresolved challenge for consistent denitrification performance. Here, we report that post‑treatment of bio‑S⁰ can tailor its electron donor functionality in autotrophic denitrification. Mild extraction methods (EDTA or heating) produce a thin, porous organic coating that increases nitrate removal rate by 2.4‑fold and shortens the lag phase by over 70% compared to untreated bio‑S⁰. Correlation analysis revealed that a thinner, more porous coating was associated with enhanced sulfur core exposure, preserved polysulfanes, and reduced crystallinity. Microbial analysis further reveals enrichment of the dominant genus <italic>Thiobacillus</italic> (up to 69.4%) and upregulation of energy‑conserving nitrate reduction ( <italic>narGHI</italic> ) and direct sulfur oxidation ( <italic>soxXYZAB</italic> , <italic>dsrAB</italic> ) pathways. This study provides a mechanistic basis and a practical strategy for optimizing bio‑S⁰ as a sustainable electron donor in nitrogen‑removal technologies.