Reaction Mechanism Of Zero-valent Iron Coupling With Microbe To Degrade Tetracycline In Permeable Reactive Barrier(PRB)

Due to the production of tetracycline in industry and the widespread use of tetracycline in clinical medicine,livestock breeding and aquaculture,A large number of tetracycline enter and retention In the soil,surface water and groundwater environment.Tetracycline infiltrated in groundwater has caused potential threats to the safety of drinking water due to its persistence and high toxicity.Permeable reactive barrier as a kind of ground water pollution technology is widely used in ground water pollution treatment for its high efficiency,economy,easy installation and maintenance,etc.In this study,three permeable reactive barrier(PRB)columns packed with zero-valent iron(Fe),zero-valent iron and microorganism(M + Fe),microorganism(M)were employed to compare the removal effect of tetracycline in PRB of different reaction media.This study evaluated the performance difference of biological and non-biological zero-valent iron PRB system,and revealed the the reaction mechanism of zero-valent iron coupling with microbe to degrade tetracycline.This research studied the process of tetracycline transformation and electron transfer,and studied the change of microbial community and the role of microorganisms in the process of the reaction.The results show that the removal efficiencies of tetracycline in column M+Fe and column Fe are 51.55%and 42.83%respectively,the removal efficiencies of tetracycline in column M is only 8.72%.The removal efficiency of TOC in column M+Fe and column Fe are 38.43%and 30.78%respectively,the removal efficiency of TOC in column M is only 2.13%.Tetracycline has not been fully degradable,there is still a part of in the form of a prototype or secondary productsThe concentration of total iron and ferrous ion in column M+Fe and column Fe were analyzed in this study,and the zero-valent iron were characterized using Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)to identify the change of surface functional groups and surface morphologies of the zero-valent iron.The results show that the concentration of total iron and ferrous ion in the abiotic zero-valent iron PRB system is higher than biological zero-valent iron PRB system.There is some ferroferric oxide in the surface of zero-valent iron.In order to study the impact of zero-valent iron to microbial growth and microbial diversity,EPS of microorganism were analyzed in this study,and high-throughput sequencing analysis of microbial samples from column M+Fe and column M were carried.The results show that the content of EPS increased with the zero-valent iron,and microbial species changed obviously.It is very interesting that Comamonadaceae,Oxalobacteraceae and Chromatiaceae increased obviously in contrast to no ferric situation,and microbic removal efficiency of TC increased at the same time.The whole reaction mechanism including reduction of zero-valent iron,adsorption of zero-valent iron and flocculation coprecipitation effect,etc.In addition,tetracycline and its secondary products were transmuted and hydrolyzed by microbe.ZVI was converted into Fe2+ and Fe3+ while TC was degraded.With the presence of Fe2+ and Fe3+,EPS increased obviously and microbial community structure changed distinctly.