Influence of modified biochar supported Fe-Cu/polyvinylpyrrolidone on nitrate removal and high selectivity towards nitrogen in constructed wetlands.

In this study, the biochar (BC) supported Fe-Cu bimetallic stabilized by PVP (Fe-Cu/PVP/BC) were prepared and utilized to enhance the nitrate (NO3-) removal and the selectivity toward nitrogen (N2). Results showed the optimum Fe:Cu:BC ratio and the dosage of the BC (pyrolysis at 700 °C) supported Fe-Cu bimetallic stabilized by polyvinylpyrrolidone (PVP) (Fe-Cu/PVP/BC700) were respectively 1:2:3 and 1 mg L-1 with the selectivity toward N2 of 31 %. This was mainly due to the synergy among Fe0, Cu0 and BC in the Fe-Cu/PVP/BC. The addition of Fe0 could reduce the NO3- through providing electron. The Cu0 and BC improved the selectivity of NO3- to N2 through forming [Cu-NO2-ads] and adjusting redox potential. The addition of Fe-Cu/PVP/BC could supply electrons for denitrification and enhance the relative abundances of Azospira and Thauera related to denitrification to improve NO3- removal. This result was further confirmed by the variations of denitrifying functional genes (narG, nirK, nirS and nosZ). This research provided an effective method to improve NO3- removal during surface water treatment in constructed wetlands (CWs) by adding Fe-Cu/PVP/BC.