Simultaneous bio-clogging mitigation and nutrient removal enhancement via sulfide addition in constructed wetlands

Bio-clogging, primarily driven by excessive biofilm growth, significantly hampers the efficiency and longevity of constructed wetlands (CWs). This study introduces an innovative sulfide addition strategy to mitigate bio-clogging and enhance nitrogen and phosphorus removal in CWs. Experimental results indicate sulfide addition notably slows bio-clogging by up to 3.72-fold, primarily through targeted disruption of extracellular polymeric substances, particularly polysaccharides. Scanning electron microscopy confirmed that biofilms in sulfide-treated CWs developed porous, network-like structures, significantly improving substrate permeability. Three-dimensional fluorescence excitation-emission matrix analyses revealed substantial production of tryptophan-like proteins and microbial byproducts under anaerobic conditions in sulfide-treated CWs, which were subsequently fermented into short-chain fatty acids. Under carbon-limited conditions (COD/N = 3), sulfide-enhanced CWs achieved approximately 78.19 % and 84.23 % removal efficiencies for nitrogen and phosphorus, respectively—roughly 20 % higher than conventional CWs. Mechanistically, enhanced nitrogen and phosphorus removal in SCW primarily resulted from short-cut nitrification, increased carbon source availability promoting denitrification, sulfur-driven autotrophic denitrification and sulfur related denitrifying dephosphatation. Overall, these findings propose sulfide addition as a viable approach for sustainable CW operation.