Sulfur-based electron donor driven autotrophic denitrification for nitrate removal: Mechanisms, performance, and nitrous oxide emission

Sulfur-driven autotrophic denitrification (SAD), an organic-free biological nitrogen removal process driven by sulfur-based electron donors (SEDs), offered advantages including low energy consumption, low sludge yield, and reduced greenhouse gas emissions. The sulfur-based compounds, with their abundant global reserves and cost-effectiveness, serve as utilizable electron donors for advanced nitrogen removal in wastewater treatment and polluted water remediation. Research on a variety of SEDs and SAD processes had expanded significantly, yet documentation of their large-scale implementation remained scarce in industrial practice. This paper presented a comprehensive review of the research and application of SADs over the past two decades. It summarized and compared the physicochemical properties and nitrogen removal performance of various SEDs, and evaluated their economic and environmental impacts. Moreover, the key factors affecting SAD efficiency were identified, along with feasible solutions to support its large-scale applications. Nitrous oxide (N₂O) emissions were considered a critical indicator for evaluating the sustainability of future wastewater treatment technologies. Therefore, this study also examined the N₂O emission characteristics from SAD processes, highlighting their potential for low-carbon applications, and further proposed strategies to mitigate N₂O emissions. Finally, the review outlined future research directions and prospects of SAD, providing insights to filter material development and guide process design in engineering applications. This study systematically evaluated the merits and constraints of SAD, delineating critical application bottlenecks while identifying potential unresolved scientific challenges demanding further investigation.