A new insight on simultaneous water purification and greenhouse gas reduction by constructing sulfur-siderite driven...

Sulfur-siderite driven autotrophic denitrification (SSAD) has received increasing attention for nutrient removal in constructed wetlands (CWs). Nevertheless, its effectiveness in simultaneous water purification and greenhouse gases (GHGs) reduction remains obscure. In this study, three vertical flow constructed wetlands (VFCWs), filled with quartz sand (CCW), sulfur (S-CW), and sulfur-siderite mixed substrates (SS-CW), were constructed to investigate the underlying mechanisms of SSAD on water purification enhancement and GHGs reduction. Results indicated that SSAD optimized the carbon, nitrogen, phosphorus, and sulfur transformation processes and enhanced the electron transfer system activity (ETSA) in CWs. Meanwhile, it resulted in the highest total nitrogen (TN) removal efficiency (91.6 ± 2.2 %) and the lowest methane (CH₄) and nitrous oxide (N₂O) emissions from SS-CW. Compared with CCW, the reduction efficiencies of CH₄ and N₂O were 76.7 ± 6.7 % and 93.4 ± 2.2 %, respectively. This was mainly ascribed to constructing ammonia oxidation coupled with iron reduction (Feammox), SSAD and multi-electron driven anaerobic oxidation of methane (AOM) pathway in SS-CW which could achieve co-emission reduction of CH₄ and N₂O. Analysis of the functional genes and microbial community structure revealed that higher abundance of genes associated with GHGs mitigation, more denitrifying bacteria and methanotrophic bacteria were enriched in SS-CW. Further analysis of metagenomic results showed that both the electron transfer pathway and the GHGs mitigation pathway were significantly enhanced in SS-CW. The results of this study provide a new insight into using SSAD as a method to improve the nutrient removal efficiency of CWs while reducing GHGs.