High-performance and short-process sulphur autotrophic denitrification from low-C/N wastewater using novel suspended bio-S0 filters

Sulphur-based autotrophic denitrification (SAD) is a promising alternative for the elimination N from COD deficient wastewater; however, it generally produces a large quantity of SO₄²⁻ byproduct and extends process flow. Herein, novel suspended bio-S⁰ filters embedding sulphur and bacterial cells were devised and demonstrated high denitrification performance through autotrophic pathways coupled with heterotrophic pathways in the anoxic zone of low-C/N wastewater. Our results reveal that the novel suspended filters can remove 65.79%–74.09% NO₃⁻-N via SAD at a stoichiometric ratio of 5.59 mg SO₄²⁻/mg NO₃⁻-N, while heterotrophic denitrification simultaneously removes 25%–35%. A 30-d working life was indicated for the filters was based on their high removal of nitrate through fluidization in sequencing batch reactors simulating the anoxic zone of the A²/O process. An increase in the abundance of two dominant and positively correlated genera associated with SAD, Thiobacillus and Ferritrophicum (R = 0.8, P < 0.05), and the abundance of heterotrophic denitrifiers such as unclassified f PHOS-HE36 were evidenced by 16s rRNA sequencing, suggesting their key role in simultaneous autotrophic-heterotrophic denitrification. This was supported by the abundance of sulphur-carbon-and nitrogen-metabolism functional genes encoding enzymes based on KEGG annotation. Moreover, the addition of lignin improved the stability of lignin (L)-modified suspended bio-S⁰ filters compared to Glycerol (G)-modified suspended bio-S⁰ filters, as revealed by the reduced in volume (0.009 cm³ g⁻¹) and lower release of total organic carbon (TOC). The suspended filters realize high denitrification performance under anoxic condition, showing promising application prospects in fluidized bed wastewater treatment systems.