Pyrite Addition Drives Sulfur Cycling for Efficient Sulfamethoxazole Removal and Detoxification in Sulfur-based Constructed Wetlands

Sulfamethoxazole (SMX) present in tailwater from wastewater treatment plants (WWTPs) poses a significant threat to ecosystems. Sulfur-based constructed wetlands (CW-S), employed as post-treatment processes in WWTPs, exhibit inadequate removal efficiency for SMX stemming from inefficient electron transfer. Herein, we added pyrite to CW-S (CW-FeS 2 /S) to stimulate sulfur redox cycling, thereby achieving efficient electron transfer, and explored the underlying mechanisms of SMX removal and detoxification. The results revealed that CW-FeS 2 /S presented the highest total inorganic nitrogen (81.15 ± 5.64%) and SMX (79.02 ± 11.41%) removal, with a 62.77% enhancement in SMX removal relative to CW-S. Pyrite addition enhanced sulfur oxidation-reduction cycles in CW-FeS 2 /S and increased electron transport system activity by 1.94-fold compared to CW-S. Besides, the activation of sulfur-cycling in CW-FeS 2 /S significantly contributed to the breakdown of S−N and N−O bonds, along with microbial-mediated ring-opening reactions, leading to improved mineralization of SMX and a notable reduction in toxicity. Microbial analysis proved that CW-FeS 2 /S enriched Microbacterium and Nocardioides , which were capable of cross-feeding via extracellular electron transfer (EET) mediated by sulfur-cycling to facilitate SMX mineralization. The abundances of sulfur-cycling bacteria and functional genes related to sulfur oxidation and electron transport increased in CW-FeS 2 /S, providing evidence for active sulfur-cycling. Co-occurrence analysis revealed that CW-FeS 2 /S not only increased microbial network complexity and connectivity but also strengthened cooperative interactions among microorganisms. This study supplied a promising technique for simultaneous N and SMX removal from tailwater, and offered insights into microbial mediated sulfur cycle for SMX removal and detoxification mechanisms in constructed wetlands.