Adsorption of Tetracycline from Aqueous Solution by Aerobic Granular Sludge-based Biochar: Affecting Factors, Kinetics, Isotherms, and Mechanisms

L. L. Yan, W. Chen, S. Liu, Y. Zheng, J. S. Jiang and Y. Liu

Abstract
In this experiment, the influencing factors of tetracycline (TC) removal by adsorption with the aerobic granular sludge-based biochar (BC) were analyzed. In particular, the specific surface area, pore size distribution, and functional groups of the biochar were studied. In addition, the kinetics, isotherms, and diffusion models of TC removal were examined. The adsorption of TC reached a maximum (16.59 mg g–1) when the biochar carbonization temperature and time were 700 °C and 2 h, respectively. With increasing initial TC concentration, the adsorption capacity of BC to TC increased gradually. The optimal pH value of TC adsorption with BC was 7.0, and a low concentration of salt was found to promote the adsorption of TC. The pseudo second-order kinetic model and Langmuir isotherm model were found to correlate well the adsorption of TC by BC. Both the internal diffusion and liquid film diffusion were the rate-controlling steps of the adsorption process. The alkali-modified BC was found to be the best adsorbent for TC.

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Keywords
biochar, tetracycline, aerobic granular sludge, modification