Application of the sulfur-siderite composite filler: A case study of augmented performance and synergistic mechanism for low C/N wastewater treatment in constructed wetland

The urgent need to achieve sustainable development goals and address global climate change calls for innovative solutions in advanced low-carbon water treatment technologies. In this study, constructed wetlands (CWs), a sustainable and multifunctional wastewater treatment technology known for its low cost and energy efficiency, was focused. It was presented a novel approach that employs a sulfur-siderite composite filler in the constructed wetland (SSCF-CW), which demonstrated remarkable removal efficiencies for total phosphorus (TP) ranging from 81.14 % to 98.87 %, nitrate nitrogen (NO3−-N) ranging from 85.23 % to 99.82 %, and total nitrogen (TN) ranging from 91.65 % to 97.01 % in low C/N wastewater treatment. The electron resupply mode of the sulfur and iron cycles plays a pivotal role in enhancing denitrification efficiency. Furthermore, SSCF enhances the resilience of SSCF-CW against shock loadings, providing increased stability and performance with TN removal rate of 2.96 ∼ 3.42 g N·m−3·d−1 while HRT decreased from 48 h to 10 h. Notably, the majority of NO3−-N elimination occurs within the SSCF layer, where Thiobacillus species dominate the denitrification process in SSCF-CW. The introduction of SSCF promotes carbon fixation with the higher relative abundance of DLD gene (5.52 %) in SSCF-CW, benefiting microbial growth and accelerating electron transfer process. Co-precipitation and adsorption pathways in the SSCF layer primarily contribute to TP removal, while iron leaching from SSCF facilitates the formation of iron plaque on roots, establishing an iron reservoir and ensuring bioavailability. These findings highlight the significant potential of SSCF in constructed wetland systems, offering a cost-effective and sustainable low-carbon technology for municipal wastewater treatment.