Enhancing tetracycline adsorption by riverbank soils by application of biochar-based composite materials

To explore the effect of adding biochar (C)-based composite materials on tetracycline (TC) adsorption by bank soils, bentonite (B) and dodecyl dimethyl betaine (BS)-modified B (BS-B) were separately supported on the pores and surface of C (prepared by xeromorphic (XAp-C) and hydrophytic (HAp-C) Alternanthera philoxeroides) to form C-based composite materials. Then, 1% (mass ratio) composite materials were used to amend the bank soil obtained from Mianyang (MY), Suining (SN), and Hechuan (HC) along Fu River. The effects of pH, temperature, and ionic strength on TC adsorption were studied, and the isothermal adsorption characteristics of TC on different amended soils were compared under the best environmental conditions. The results showed the following: (1) at the pH range of 3-6, the adsorption of TC on amended bank soils decreased with the increase in pH. In the range of 10 degrees C-40 degrees C, TC adsorption amount of each amended soil increased with the increase in temperature. With the increase in ionic strength, the adsorption amount of TC by amended soils increased first and then decreased, (2) the adsorption isotherms of TC on each sample were L-shaped and accorded with the Langmuir model. The maximum adsorption capacity (q(m)) of TC was 9.33-21.29 mmol/kg. At the same conditions, q(m) of TC on different amended soils showed the trend of SN > HC > MY when using XAp-C and with BS-B loading presenting best soil improvement effect, (3) TC adsorption of each amended soil was a spontaneous, endothermic, and entropy-adding process. Cation exchange capacity and total organic carbon of bank soil are the key factors to determining the adsorption effect of TC.