Reaction mechanism of zero-valent iron coupling with microbe to degrade tetracycline in permeable reactive barrier (PRB)

Tetracycline (TC) infiltrated in groundwater has caused potential threats to the safety of drinking water due to its persistence and high toxicity. 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 investigate the removal effect and reaction mechanism of zero-valent iron coupling with microorganisms on TC removal respectively. The results show that the removal efficiencies of three PRB are about 50%, 40% and 10% respectively. Especially, the effect of coupling ZVI and microbe on the degradation of TC is not a simple superposition. ZVI partially or fully degraded TC by adsorption and reduction. 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. 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.