Mobility of biochar-derived dissolved organic matters and their effects on sulfamerazine transport through saturated soil porous media

Abstract

Dissolved organic matter (DOM) released from biochar may impact antibiotics mobility and environmental fate in subsurface environments. Here, DOM derived from biochars (BDOMs) generated by pyrolyzing corn straw at 300, 450, and 600 °C were employed to elucidate the mobility characteristics of these organic substances and their influences on the transport of sulfamerazine (SMZ, a typical sulfonamide antibiotic) in soil porous media. The results demonstrated that BDOMs produced at a lower pyrolysis temperature exhibited greater mobility owing to the weaker hydrophobic and H-bonding interactions between BDOMs and soil particles. Additionally and importantly, BDOMs facilitated the promotion of SMZ mobility owing to the increased electrostatic repulsion between SMZ– forms and soil grains, the steric hindrance effect induced by the deposition of organic matters, and the competitive retention between SMZ molecules and BDOMs. Meanwhile, the promotion effects of BDOMs enhanced with improving pyrolysis temperature owing to the promoted deposition of organic matter on soil surfaces and the strengthened electrostatic repulsion. Moreover, the facilitated effects of BDOMs on SMZ mobility declined as the solution pH values were raised from 5.0 to 9.0 or the flow rate increased from 0.18 to 0.51 cm/min. This trend was due to decreased deposition competition and the steric effect caused by decreased retention of BDOMs on soil particles. Furthermore, the cation-bridging effect emerged as an important mechanism contributing to the promotion effects of BDOMs when the solution contained divalent cations (Cu2+ or Ca2+). Moreover, the two-site non-equilibrium model was performed to interpret the controlling mechanisms for the effects of BDOMs on the transport of SMZ. Findings from this work highlight that biochar-derived dissolved organic matter can remarkably affect the environmental behaviors of antibiotics in aquatic environments.