Performance Study Of Zero-valent Iron Coupling With Manganese Dioxide To Degrade Tetracycline

Due to the weakness of ZVI-based PRB system in its durability to maintain its permeability and effectiveness in groundwater contaminant removal and the feature of the transition metal oxides,we constructed the combined PRB system by zero-valent iron and manganese dioxide(ZVI-MnO2).The overall objective was to investigate degradation and removal efficiency of tetracycline(TC)in ZVI-MnO2 and the function of MnO2 in alleviating the passivation of medium.Furthermore,transformation products were identified and species of products were analyzed based on the results of liquid chromatography electrospray ionization mass spectrometry in tandem and degradation mechanisms of TC were explored in ZVI-MnO2.In our study,three different PRB columns packed with ZVI,ZVI-MnO2,and MnO2 were set up to investigate the removal effect and influence factor of different mediums on TC removal,respectively.The results show that the removal rate of three PRB columns is 65%,85%and 50%,respectively.The FTIR spectrum show that the number of-OH groups in ZVI-MnO2 increased after the reactions.It must be due to a large number of ·OH released in the ZVI and MnO2 reaction system,which have high oxidant properties to remove TC.From the results of Scanning Electron Microscope(SEM),ZVI and MnO2 fully contact together to provide further more reaction contact sites.Meanwhile,the structures of ZVI and MnO2 have an obvious change.It could be the oxidation reduction reaction between MnO2 and ZVI and other ionic forms of ZVI that destroyed the surface structure.The batch experiments prove that the TC degradation rate increased with he amount of MnO2 added.Electron transfer could be enhanced on the surface of ZVI with the presence of MnO2 to lengthen the lives of the PRB system.Actually,MnO2 could accelerate the transformation of Fe2+ into Fe3+ and combine with Fe3+ to degrade TC in different reaction sites in the ZVI-MnO2 PRB system under week acid environment(pH = 6.5).Hydroxyl radicals(·OH)were produced in this process,which contributed to about 58.3%for the TC degradation.The high performance liquid chromatography mass spectrometry(HPLC)demonstrated that,compared with only ZVI or MnO2 system,the ring structure of TC could be perfect opened and removed under ZVI-MnO2.UV-visible spectral implies that Fe3+ was likely combined with TC at the A ring and exerted a weaker effect on the BCD rings.Moreover,TC could be transformed by MnO2 and BCD rings were the crucial sites for the MnO2 mediated reactions.The UV-visible spectral also shows that both ZVI and MnO2 could exert impacts on the A ring and BCD rings of TC to achieve its degradation.