New research published in the Journal of Soils and Sediments by Xinyu Liu, He Yang, and their colleagues reveals that subjecting biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More to wet-dry cycling, especially with organic matter or nano-silicon particles, significantly improves its ability to prevent antibiotic contamination in groundwater. The study found that organic-aged biochar enhanced the adsorption of sulfadiazine and florfenicol by up to 53.61%, drastically reducing their leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More in saturated porous media. These insights offer a promising path for more effective environmental pollution control.

Biochar has been recognized as a valuable soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More, improving soil fertility, boosting plant growth, and notably, curbing the leaching of pollutants like pesticides and antibiotics. However, its long-term effectiveness in environmental remediation is often hampered by aging in soil, which alters its physical and chemical properties. This aging process can involve various environmental factors, including wet-dry cycles, freeze-thaw cycles, and high-temperature treatments, all of which can modify biochar’s pore structure and functional groups, potentially enhancing its capacity to adsorb pollutants. Despite these observations, the precise mechanisms by which different aging conditions, such as varying moisture levels, inorganic minerals, and organic matter, influence biochar’s pollutant adsorptionBiochar has a remarkable ability to attract and hold onto pollutants, like heavy metals and organic chemicals. This makes it a valuable tool for cleaning up contaminated soil and water.   More capacity have remained largely unexplored.

The research focused on two weakly hydrophobic antibiotics, sulfadiazine (SD) and florfenicol (FLO), which pose a significant risk of groundwater contamination. The team investigated three wet-dry cycling aging (WDCA) treatments: using ultrapure water to simulate natural wet-dry cycles, nano-silicon particles (nSiO2​) for inorganic aging, and humic acid (HA) for organic aging. Through a series of batch adsorption experiments, column experiments, and Hydrus 1D modeling, they simulated real soil conditions to evaluate how these aged biochars affected antibiotic adsorption and leaching.

The findings highlight the significant impact of WDCA on biochar’s properties. All three types of aged biochar (water-aged, inorganic-aged, and organic-aged) showed changes in elemental composition, specific surface area (SSA), and surface functional groups. Notably, the carbon content increased by 4.71% to 5.26% in all aged biochars, with organic-aged biochar (OBC) showing the most pronounced increase in C content, suggesting carbon structure stabilization and organic component enrichment. The aging process also expanded the biochar’s SSA, with inorganic-aged biochar (IBC) experiencing the most significant increase at 102.65%, reaching 22.17 m2/g from an initial 10.94 m2/g, far exceeding typical field-aged biochar improvements. This enhancement in SSA, coupled with an increase in oxygen-containing functional groups, particularly in OBC, improved the biochar’s hydrophilicity and chemical reactivity, which are crucial for effective pollutant adsorption. The cation exchange capacity (CEC) of OBC also increased to 22.95 cmol/kg from FBC’s 19.54 cmol/kg.

In batch adsorption experiments, the Freundlich model provided a better fit than the Langmuir model for the adsorption data, indicating a heterogeneous surface interaction and multilayer adsorption. The superior performance of OBC and IBC is attributed to the surface modifications induced by WDCA treatments; HA in OBC increased the density of surface functional groups, and nSiO2​ in IBC enhanced the SSA and pore structure.

Column leaching experiments further confirmed these findings, demonstrating that WDCA significantly influences antibiotic migration in porous media, substantially reducing leaching under high-flow conditions (p<0.05). OBC consistently showed the most delayed breakthrough times for both SD and FLO, indicating its superior retention capabilities. For instance, at a slow flow rate (26.5 mm/h), SD and FLO breakthrough occurred at 2.0 and 3.5 PV respectively for OBC, compared to 1.5 and 2.5 PV for fresh biochar. This highlights that organic aging improves adsorption through mechanisms like surface adsorption, pore filling, hydrophobic interactions, and hydrogen bonding. While IBC also showed improved adsorption compared to fresh biochar, it demonstrated higher antibiotic mobility than OBC, likely due to its enhanced hydraulic properties and improved pore connectivity from nSiO2​ addition. The study also revealed that faster flow rates (110.0 mm/h) accelerate the appearance of peak effluent concentrations, as reduced interaction time between antibiotics and biochar surfaces leads to enhanced non-equilibrium transport.

These findings underscore the potential of WDCA treatments to optimize biochar for environmental pollution control, particularly in agricultural settings where antibiotic contamination is a concern. The research suggests that implementing organically-aged biochar, especially in high-pollution areas like livestock farms, and regulating irrigation rates to maintain slower flow can maximize antibiotic retention in soil. Future research will focus on reconciling discrepancies between laboratory aging simulations and natural aging processes, and exploring the synergistic effects between biochar and soil organic matter to assess their long-term effectiveness in mitigating antibiotic pollution.

Source: Liu, X., Yang, H., Zhang, L., Xia, L., Song, W., Zhang, J., & Ouyang, F. (2025). Experimental and modeling insights into adsorption and leaching of sulfadiazine and florfenicol in saturated porous media: Role of multiple wet-dry cycling aged biochar. Journal of Soils and Sediments.