(359a) Adsorption of Tetracycline Antibiotics in Wastewater Onto Biochar-Based Adsorbents 

Tetracycline (TC) is one of the most widely used antibiotics for both human and animal diseases. TC has been detected at the level of ng L^-1 to mg L^-1 in domestic wastewater, but 10-100 mg L^-1 in dairy manure, hospital, and pharmaceutical manufacturing wastewater. Like other antibiotic compounds, release of TC to aquatic ecosystem can significantly cause acute and chronic toxicity and propagation of antibiotic resistance in microbial community. Current treatment methods such as biodegradation, advanced oxidation and membrane filtration have not shown effective elimination of TC in wastewater and water due to low concentration and biorecalcitrant nature of TC.

Compared with other methods, adsorption is a simple and cost effective process without generating any toxic byproducts. Recently biochar is generated as a byproduct from gasification of solid wastes such as sludges, biosolids, agricultural residues and animal manure. Owing to beneficial physical and chemical properties of biochar, it is considered as an emerging adsorbent for eliminating various contaminants.

In this study the dairy manure-derived biochar (BC) was modified by the wet impregnation technique to immobilize MgO to the biochar for enhancing TC adsorption capacities and reducing the inherent functional groups interfering interaction between TC and the biochar. The physical and chemical properties (i.e., surface area, porosity, surface chemistry) of the BC and MgO-BC were characterized.

The adsorption efficiencies of TC were investigated using both the BC and the MgO-BC at the selected conditions. The results showed that the MgO-BC showed higher adsorption capacity of TC (70-95 %) than that that by the BC (59-71%) at the selected conditions. The higher adsorption using the MgO-BC was thought to be due to possible π–π electron donor–acceptor interactions and hydrogen bonding between the MgO-BC and TC. Rather the BC would rely on mainly hydrophobic interaction. The adsorption isotherm study suggested Freundlich isotherm to be a representative model for adsorption of TC onto the MgO-BC. It would indicate monolayer adsorption of TC on the MgO-BC. The adsorption capacities of TC onto the MgO-BC were found to be 2 – 10 mg TC per g biochar from the adsorption isotherm. The adsorption capacities were higher than those by the biochar made from agricultural residues and other surface modification techniques. The adsorption kinetic analysis revealed that the pseudo-second order kinetic model fitted to the experimental results (R²>0.98) better than the pseudo-first order kinetic model. It also indicated that the adsorption of TC on the MgO-BC would include several mechanisms including diffusion, adsorption, and desorption which are also often found in other carbon-based adsorbents such as activated carbon, graphene and carbon nanotube. Further works will include the detailed mechanisms for adsorption and desorption, the column tests for practical application and the mathematical modeling for engineering design.