Nitrogen removal from domestic wastewater using core-shell anthracite/Mg-layered double hydroxides (LDHs) in constructed wetlands

To investigate the mechanism of nitrogen removal by anthracites and enhance the nitrogen removal efficiency in constructed wetland, three kinds of layered double hydroxides (MgFe-LDHs, MgCo-LDHs, MgAl-LDHs) were prepared by co-precipitation under alkaline conditions and coated in situ on the surface of anthracites to synthesize core-shell anthracites/Mg-LDHs composites. Experiments with different treatments (columns loaded with original anthracites and anthracite/Mg-LDH composites) were conducted to study the nitrogen removal efficiency of domestic wastewater in constructed wetlands. The results of nitrogen removal experiments showed that the anthracite/MgAl-LDH composite had the best performance with average removal rates of 53.69%, 72.91%, and 47.43% for TN, NH4+-N, and organic nitrogen, respectively. Modification changed the denitrification mode of the anthracites. The data of adsorption isothermal experiments were fitted better with the Freundlich model. The amount of ammonifier, nitrosobacteria, nitrobacter, and denitrifier on the surface of the Mg-LDH-modified anthracite was higher than that of the original anthracite. The performance of the anthracite in removing nitrogen was attributed to physical interception, chemical adsorption, and biological degradation. Moreover, the modified anthracites were superior to the original anthracite in the chemical adsorption and biodegradation, which indicated that coating the Mg-LDHs on the surface of common anthracite was a potential method to improve the nitrogen removal efficiency of domestic wastewater and to restore the eutrophic water body.