Performance and economy of antibiotic adsorption by the composite of plant decomposed liquid, chemical modifier, and clay

Antibiotics is one of the four types of new pollutants which are widely concerned in the world. To investigate the performance and economy of antibiotic adsorption by a composite made of clay, plant decomposed liquid (DL), and chemical modifier, bentonite (B) and kaolin (K) were modified by the DL of Alternanthera philoxeroides to prepare biological clays. Then, dodecyl dimethyl betaine (BS), polyacrylamide (PAM), and ethylenediaminetetraacetic acid (EA) were compositely modified on the biological clay to prepare different chemical–biological clays. The thermodynamic and kinetic characteristics of oxytetracycline (OTC) and chlortetracycline (CTC) adsorption were investigated by batch treatment. The adsorption changes in antibiotics on the modified clays under various pH levels, ionic strengths, and temperatures were compared, and the economy of antibiotic adsorption by different modified clays was analyzed. The maximal adsorption capacity ( q m ) values for OTC and CTC were 82.48–301.08 and 63.00–258.26 mmol/kg, respectively, ranking in the order of PAM- > BS- > EA-modified biological clays. The q m values of antibiotics by different modified Bs were higher than those by different modified Ks. In the pH range of 3–7 and temperature range of 10 °C–30 °C, high temperature and pH were conducive to antibiotic adsorption, which was determined as a spontaneous, endothermic, and entropy-increasing process. The amount of antibiotic adsorption initially increased and then decreased with the increase in ionic strength, with the maximum adsorption observed at 0.1 mol/L ionic strength. The adsorption of antibiotics by different modified clays conformed to the pseudo-first-order kinetic equation. The economy ( q m /price) of different m odified clays for antibiotic adsorption ranged between 29.55 and 169.66 mg/¥, and the PAM-modified biological clays showed the highest economy. The modified Bs had higher economy in antibiotic adsorption than the modified Ks.