Coating Modification of Anthracite Substrates in Vertical-flow Constructed Wetlands by LDHs Synthesized from Different Metal Compounds and the Nitrogen Removal Efficiencies

As one kind of vertical-flow constructed wetlands substrates,anthracite was selected in this experiment. LDHs(layered double hydroxides) were synthesized in alkaline conditions by co-precipitation of different kinds of metal compounds,such as CaCl2,ZnCl2,MgCl2,FeCl3,AlCl3,CoCl3. The synthesized LDHs were in-situ coated onto the surface of anthracite substrate to achieve the aim of modification. Simulated test columns were constructed to study the nitrogen removal efficiency of the urban sewage using the original anthracite substrates and 9 kinds of modified anthracite substrates. The results showed that: LDHs synthesized by all the 9different kinds of methods could effectively modify the anthracite substrate by in-situ coating. With Mg2 +involved in the synthesis of modified substrates,good TN and ammonia nitrogen removal efficiencies were observed. The modified anthracite substrates coated with MgCo-LDHs had the optimal performance with average TN and ammonia nitrogen removal efficiencies of higher than 80% and 85%,respectively. The ammonia nitrogen removal efficiencies by the modified anthracite substrates coated by LDHs reacted with Mg2 +and Fe3 +were also high. The ammonia nitrogen removal efficiencies by modified anthracite substrates coated with CaFe-LDHs and MgFeLDHs were higher than 85%.