High-temperature and freeze-thaw aged biochar impacts on sulfonamide sorption and mobility in soil

Biomass-derived biochar is a carbon-rich product for soil amendment and sulfapyridine (SPY) is a typical sulfonamide of antibiotics in the soil. Amendment with biochar for soil could control SPY sorption or mobility. However, the pristine biochar inevitably goes through the long-term ageing in the environment and the information on such ageing impact on SPY sorption is not fully recognized. The simulated ageing process methods were employed for high-temperature and freeze-thraw climate to treat the biochar for two months in the present study. The batch adsorption of SPY and leaching column experiments were conducted for comparison of the fresh/aged biochar-soil system. The results showed that biochar addition could increase soil pH and saturated moisture, aged biochars own more O-containing functional groups and exhibit higher hydrophilicity and polarity. The sorption mechanism of unamended soil with SPY primarily resulted from the weak hydrophobic distribution. All fresh and aged biochar amended soil increased SPY sorption due to improvement of H-bonding interaction between SPY and biochar surface functional groups, indicating such initiative adsorption was stronger than passive partitioning. It is of importance for us to reconsider that aged biochar-amended soil, especially two-month high-temperature aged biochar-amended soil showed the highest adsorption performance and the lowest desorption capacity towards SPY. Both SPY leaching column experiments and the acid rain leaching tests suggested that the application of biochar in tropical or high-temperature climate regions for organics polluted soil remediation is favorable, but we should be aware of the uncertainty of soil amendment with biochar in cold regions.