Novel Chitosan-FeS@biochar-added constructed wetland microcosms for NH₄⁺/NO₃^- and Pb removal: Performance and mechanism

Biochar has been proven to be efficient for enhancing purifying performance, however, studies on nitrogen (N) removal pathways and microbial community structure is far insufficient in modified-biochar-added constructed wetlands (CWs) for treating N and heavy metals co-existing wastewater. Therefore, the composite of Chitosan-FeS @ peanut shell biochar (CFP) was applied in CWs to assess its performance for treating N and Pb co-existing wastewater and investigate N removal pathways. It showed that adding CFP enhanced the nitrifica-tion and denitrification intensity and increased removal rates of NO3-, NH4+ and TN by 76.32%, 28.41% and 52.48% respectively, in CWs. CFP not only functioned as electron donor to drive denitrification but also increased the relative abundance of Thiobacillus, Sulfurimonas and Geobacter, thereby promoting N removal. Furthermore, CFP alleviated Pb stress on Acorus calamus L.Therefore, this study provides a promising and feasible strategy for treating N and Pb co-existing wastewater in CWs.