Research progress of constructed wetland based on sulfur autotrophic denitrification

In response to growing concerns over water pollution and eutrophication, primarily caused by excessive nitrogen and phosphorus discharges, the integration of sulfur-based autotrophic denitrification (SAD) with constructed wetlands (CWs) has emerged as a promising, eco-friendly and cost-effective alternative for advanced wastewater treatment. This study conducts a comprehensive review and bibliometric analysis to evaluate the research progress, current status and future trends of SAD-CWs technology. Utilizing the Web of Science and CNKI databases, relevant literature from 2010 to 2024 was analyzed using tools such as Citespace and VOSviewer to map the knowledge structure and evolution in this field. The analysis reveals that the innovative SAD-CWs technology significantly enhances the nitrogen and phosphorus removal performance of traditional CWs, particularly for treating wastewaters with a low Carbon-to-Nitrogen (C/N) ratios, such as municipal secondary effluent and rural domestic sewage. By replacing organic carbons with inorganic sulfur compounds (e.g., elemental sulfur, pyrite) as electron donors, the process promotes the activity of autotrophic denitrifiers like Thiobacillus and Sulfurimonas, leading to efficient nitrate reduction with lower sludge production, reduced operational costs and minimal secondary pollution risks compared to conventional heterotrophic denitrification. The review also summarizes key factors influencing system performance, including the type and bioavailability of sulfur sources, dissolved oxygen levels, temperature, hydraulic retention time (HRT) and influent C/N ratios. It highlights the technology’s advantages in optimizing microbial community structures and improving treatment stability under specific conditions. However, the study also identifies several critical challenges hindering widespread application. These included an insufficient understanding of the complex microbial interactions and metabolic mechanisms governing the SAD process within the CWs ecosystem, a lack of standardized and optimized design and operational parameters, concerns regarding the long-term stability and durability of sulfur-based materials and performance inhibition under low-temperature conditions. Furthermore, potential issues such as sulfide toxicity and nitrous oxide emissions require careful management. As such, future research directions are proposed to address these gaps. Priorities include in-depth investigations into microbial ecology and functional genomics to elucidate key mechanisms, the development and evaluation of novel, efficient, and environmentally benign composite sulfur materials, the optimization of system design and operational strategies (especially for cold climates), and holistic assessments of long-term performance, economic feasibility, and environmental sustainability. By addressing these research fronts, SAD-CWs technology can be further refined and effectively implemented, offering a robust and sustainable solution for water quality restoration and significantly contributing to the advancement of ecological engineering in water pollution control.