Removal of tetracycline by biochar-supported biogenetic sulfidated zero valent iron: Kinetics, pathways and mechanism

The application of zero-valent iron (ZVI) is limited due to passivation and agglomeration. Therefore, biochar loading (MB) and biogenetic sulfidation via sulfate-reducing bacteria (SRB) were used to improve the reactivity of ZVI (BS-ZVI@MB) towards tetracycline (TC) degradation. Biochar provided more attachment sites for ZVI and SRB, thus alleviating the agglomeration. Additionally, quinone groups on biochar enhanced the electrons transfer through the measurement of electron donating/accepting capacities, and biogenetic sulfidation could inhibit the surface passivation of ZVI. Fe(II/III) produced after the addition of BS-ZVI@MB could complex with the A ring in TC to form Fe(II/III)-TC, which brought the oxidation of TC by complexed Fe(III). Reactive oxygen species (ROS) (primarily circle OH) were generated during the oxidation of Fe(II), so as to promote the TC degradation. Extracellular polymeric substances (EPS) secreted from SRB had a slight quenching effect on ROS. Meanwhile, EPS formed a protective layer with Fe(II/III) on BS-ZVI@MB, reducing its reactivity with TC. Overall, this study showed an efficient modification technology of ZVI by biogenetic sulfidation and biochar loading for TC degradation.