Comparative Study for Propranolol Adsorption on the Biochars from Different Agricultural Solid Wastes

Abstract

Currently, large amounts of agricultural solid wastes have caused serious environmental problems. Agricultural solid waste is made into biochar by pyrolysis, which is an effective means of its disposal. As the prepared biochar has a good adsorption capacity, it is often used to treat pollutants in water, such as heavy metals and pharmaceuticals. PRO is an emerging contaminant in the environment today. However, there are limited studies on the interaction between biochars with PRO. Thus, in this study, we investigate the adsorption of PRO onto the biochars derived from three different feedstocks. The order of adsorption capacity was corn stalk biochar (CS, 10.97 mg/g) > apple wood biochar (AW, 10.09 mg/g) > rice husk biochar (RH, 8.78 mg/g). When 2 < pH < 9, the adsorption capacity of all the biochars increased as the pH increased, while the adsorption decreased when pH > 9, 10 and 10.33 for AW, CS and RH, respectively. The adsorption of PRO on biochars was reduced with increasing Na+ and Ca2+ concentrations from 0 to 200 mg·L−1. The effects of pH and coexisting ions illustrated that there exist electrostatic interaction and cation exchange in the process. In addition, when HA concentration was less than 20 mg/L, it promoted the adsorption of PRO on the biochars; however, when the concentration was more than 20 mg/L, its promoting effect was weakened and gradually changed into an inhibitory effect. The adsorption isotherm data of PRO by biochars were best fitted with the Freundlich model, indicating that the adsorption process is heterogeneous adsorption. The adsorption kinetics were fitted well with the pseudo-second-order model. All the results can provide new information into the adsorption behavior of PRO and the biochars in the aquatic environment and a theoretical basis for the large-scale application of biochar from agricultural solid wastes.