Sorption of tetracycline on biochar derived from rice straw and swine manure

Abstract

Biochar is an efficient and cost-effective sorbent for removing contaminants from aqueous environments. In this study, biochar samples derived from rice straw (R) and swine manure (M) pyrolyzed at 400 °C (R400 and M400) and 600 °C (R600 and M600) were used to adsorb tetracycline from an aqueous solution. The adsorption of tetracycline on both types of biochar included multi-step adsorption processes that were well described by the pseudo-second-order kinetics model (R² > 0.99). The adsorption equilibrium of tetracycline on rice straw and swine manure derived biochar was reached after 24 h and 36 h respectively. The solution pH affected the adsorption processes by changing the surface charges of tetracycline and biochar. Adsorption isotherms fitted both the Langmuir and Freundlich models well. The adsorption capacity was higher in biochar derived from rice straw than in biochar derived from swine manure, and increased with increasing pyrolysis temperature. Thermodynamic analysis revealed a spontaneous and endothermic tetracycline adsorption process. The values of the adsorption coefficient (K_d) were on the order of 10³ for R600 and 10²–10³ for the other three types of biochar. These experiments indicate that R600 can be used as an inexpensive adsorbent to remove tetracycline from aqueous solutions, but swine manure derived biochar needs more improvement to be a suitable adsorbent.