Electron shuttles enhance phenanthrene removal in constructed wetlands filled with manganese oxides-coated sands

• Electron shuttles embedded biochar improved the catalytic oxidation of birnessite for pollutants removal in CWs. • Mn cycle was promoted by catalytic process of electron pairs formation and charge propagation. • Pollutant’s migration and functional microbial abundance were also boosted by electron shuttles. Mn oxides could realize persistent organic pollutants (POPs) removal through the cycle of Mn between Mn(II) and biogenic Mn oxides in constructed wetlands (CWs) filled with Mn oxides. However, the inefficient cycle of Mn caused by the limited oxidation ability of Mn oxides inhibited its effective degradation of POPs. Ruthenium (Ru) and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) could act as electron shuttles in catalytic Mn oxides oxidation process. In this study, phenanthrene (PHE) was selected as a typical POP and biochar (BC) supported Ru (Ru/BC) and ABTS (ABTS/BC) were induced in CWs with Mn oxides (birnessite). The removal efficiencies of PHE in CWs with Ru/BC and ABTS/BC reached 94.61% and 95.51%, higher than the control (79.91%). ABTS performed best for enhancing Mn cycle based on the results of highest oxidation removal capacity and relative abundance of Mn-oxidizing bacteria. What’s more, the addition of Ru/BC contributed to the best adsorption ability and highest relative abundance of PHE degrading bacteria.