Biomass feedstocks and carbonization methods affect antibiotic adsorption on biochar

Biochar has been reported as a useful adsorbent of organic contaminants. Here, reed, cotton stalk, and bamboo willow were selected as feedstocks to produce biochars via oxygen-limited or aerobic methods for carbonization. The obtained biochars were first characterized for their physical and chemical properties and then investigated for their performance in adsorbing oxytetracycline（OTC） and sulfamethoxazole（SMX）. It was found that both feedstocks and carbonization methods affected OTC and SMX adsorption. Reed and cotton stalks were better carbonized under oxygen-limited conditions to produce biochars（O2-limited biochars）, whereas bamboo willow was suitable to produce biochars via aerobic carbonization（aerobic biochar）. The aerobic biochar adsorbed 11.98 and 10.12 mg/g of OTC and SMX, respectively, from a solution with an initial concentration of 50 mg/L of the biotics. Batch adsorption experiments and the Fourier transform infrared spectroscopic analysis indicated that π-π electron donor-acceptor interaction was the primary mechanisms for OTC and SMX adsorption on the aerobic biochar. Electrostatic attraction further promoted OTC adsorption on aerobic biochar at high pHs, whereas pore filling could contribute to SMX adsorption. This work showed that aerobic biochar were better adsorbents of OTC and SMX than O2-limited biochars, and suggested that biochar adsorbents can be tailor-made for different contaminants by judicious selection of feedstocks and carbonization processes