Effect of elemental sulfur on anaerobic ammonia oxidation: Performance and mechanism

Biological nitrogen removal processes provide effective means to mitigate nitrogen-related issues in wastewater treatment. Previous studies have highlighted the collaborative efficiency between sulfur autotrophic denitrification and Anammox processes. However, the trigger point induced the combination of nitrogen and sulfur metabolism is unclear. In this study, elemental sulfur (S⁰) was introduced to Anammox system to figure out the performance and mechanism of S⁰-mediated autotrophic denitrification and Anammox (S⁰SAD-A) systems. The results showed that the nitrogen removal performance of the Anammox reactor decreased with the increasing concentrations of NH₄⁺-N and NO₂^--N in influent, denitrification occurred when NH₄⁺-N concentration reached 100 mg/L. At stage ⅳ (150 mg/L NH₄⁺-N), the total nitrogen removal efficiency in S⁰SAD-A system (95.99%) was significantly higher than that in the Anammox system (77.22%). Throughout a hydraulic retention time, the consumption rate of NH₄⁺-N in S⁰SAD-A was faster than that in Anammox reactor. And there existed a nitrate-concentration peak in S⁰SAD-A system. Metagenomic sequencing was performed to reveal functional microbes as well as key genes involved in sulfur and nitrogen metabolism. The results showed that the introduction of S⁰ elevated the abundance of Ca. Brocadia. Moreover, the relative abundance of Anammox genes, such as hao, hzsA and hzsC were also stimulated by sulfur. Notably, unclassified members in Rhodocyclaceae acted as the primary contributor to key genes involved in the sulfur metabolism. Overall, the interactions between Anammox and denitrification were stimulated by sulfur metabolism. Our study shed light on the potential significance of Rhodocyclaceae members in the S⁰SAD-A process and disclosed the relationship between anammox and denitrification.