Applying biochar coupled with pyrite substrates simultaneously enhanced nutrient and heavy metal removal in constructed wetland: Performance and mechanism

Wastewater polluted by heavy metals with low C/N ratio posed a big challenge to constructed wetlands (CWs) for sustainable advanced wastewater purification. In this study, biochar coupled with pyrite was successfully applied in CWs to simultaneously remove organics, total nitrogen (TN), total phosphorus (TP) and heavy metals, with the highest removal efficiency of 95.78%, 98.78%, 96.22% and 99.91%, respectively. Batch tests proved that the complexation of ferric hydroxide from pyrite oxidation played an important role in TP and heavy metals removal. Meanwhile, fluorescence excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) further manifested that protein-like substances contributed a lot to heavy metals stabilization. Moreover, the multiplication of Proteobacteria, Chloroflexi at phylum level and Dechloromonas at genus level, which were capable of heterotrophic or autotrophic nitrate reducing process indicated that the denitrification capacity of CWs was significantly enhanced by biochar and pyrite. This study provided a feasible insight into the application of CWs with biochar and pyrite addition to enhance the treatment of low C/N wastewater.