Effect and mechanism analysis of MnO 2 on permeable reactive barrier (PRB) system for the removal of tetracycline

Abstract Effect of manganese dioxide (MnO 2 ) on tetracycline (TC) removal/degradation in zero-valent iron (ZVI) based permeable reactive barrier (PRB) system was investigated. To analyze the role of MnO 2 , three different PRB columns packed with ZVI, ZVI and a layer of MnO 2 , and MnO 2 were set up to investigate the removal effect and reaction mechanism of ZVI coupling with MnO 2 on TC removal, respectively. The results show that the removal efficiencies of three PRB columns are 65%, 85%, and 50%, respectively. MnO 2 could accelerate the transformation of Fe 2+ into Fe 3+ and combine with Fe 3+ to degrade TC in different reaction sites in the ZVI-MnO 2 PRB system. Hydroxyl radicals (·OH) were produced in this process, which contributed to about 58.3% for the TC degradation. The UV–Vis spectrum demonstrated that A ring of TC was the main reaction site for interaction with Fe 3+ and the BCD rings were crucial for interactions with MnO 2 . On the basis of intermediates identified by LC-ESI-MS, the ring structure of TC was opened, and low-molecular-weight compounds were produced in ZVI-MnO 2 PRB system.