Abstract

The adsorption and transport mechanisms of weakly hydrophobic antibiotics in field-aged biochar (FABC) remain unclear. This study selected sulfamethazine (SD) and florfenicol (FF), two common contaminants in purple soil, as target pollutants, and comparatively analyzed the effects of fresh biochar (FBC), 1-year aged biochar (ABC1), and 5-year aged biochar (ABC5). Through adsorption experiments, soil column leaching tests, and Hydrus-1D model simulations, the influence of biochar aging on antibiotic transport behavior was investigated.
Results showed that biochar aging significantly altered elemental composition, with a decrease in carbon content and an increase in oxygen content. ABC1 significantly enhanced the retention capacity of SD and FF in soil due to increased specific surface area (SSA) and the enrichment of oxygen-containing functional groups. Although ABC5 exhibited a reduction in SSA, it maintained long-term retention effects by enhancing the stability of the biochar–soil composite (reflected by increased dispersivity λ and higher hydrodynamic dispersion coefficient D). Hydrus-1D model simulations indicated that the proportion of equilibrium adsorption sites (f) increased with aging time, showing that aging affected the adsorption properties of biochar.
This study confirms that 1-year aged biochar exhibited the best antibiotic retention effect, while 5-year aged biochar maintained long-term retention mainly through regulation of dispersive transport. These findings provide important theoretical support for the application of biochar in controlling antibiotic pollution in soils.

图文摘要

Figure 1 Surface morphology and elemental composition analysis of fresh biochar (FBC) and aged biochar (ABC), (a) Energy Dispersive Spectroscopy (EDS); (b) Scanning Electron Microscopy (SEM).

Figure 2 Fitting results of adsorption kinetic parameters (D, α, Kd, f) during the biochar aging process.

Highlights
1.One-year aged biochar showed the best adsorption performance for antibiotics due to increased specific surface area and more functional groups.
2.After five years of aging, biochar adsorption capacity slightly decreased, but the antibiotic retention effect remained stable.
3.During aging, biochar continuously influences soil water movement, dynamically regulating the interactions between antibiotics and soil particles.
4.The migration mechanism of antibiotics in aged biochar gradually shifts from adsorption-dominated to dispersion-regulated.
Conclusions
1.After aging for one and five years in purple soil, biochar carbon content decreased while oxygen content significantly increased, resulting in more oxygen-containing functional groups on the surface.
2.One-year aged biochar performed best, with increased specific surface area and elevated f and α values, enhancing the retention capacity for weakly hydrophobic antibiotics.
3.Five-year aged biochar showed reduced Kd values, but through regulation of λ and D, it still maintained effective antibiotic retardation.
4.Aging changes the mechanism by which biochar retards the migration of weakly hydrophobic antibiotics, shifting from adsorption dominance to dispersion regulation.