High-reactivity biological sulfur granulation: Cross-kingdom consortium for efficient mixotrophic denitrification

The application of biological sulfur (Bio-S) in sulfur autotrophic denitrification (SAD) is hindered by its tiny size to hydraulic washout. This study innovatively upscaled the Bio-S to millimeter-scale granular biological sulfur (GBio-S) through "liquation-solidification". GBio-S exhibits chain-like sulfur surfaces with uniformly organosulfur (<1%, e.g., C-S, C-S-S-S-C, or C-S-S-S-S-C) which endowed the surface with hydrophilicity, significantly enhancing the colonization of both autotrophic (e.g., Thiobacillus: 7.5%) and heterotrophic (e.g, Stenotrophomonas: 6.3%) microorganisms based on SAD systems. The organosulfur moieties induced the rapid startup of the mixotrophic denitrification and enhanced the denitrification rate of 1.4 kg N/m³·d (2.69 times of S⁰-based systems). Therefore, this work provides new insights and a practical solution for synchronously enhancing nitrogen removal and sulfur recycling in engineered systems.