Removal of tetracycline via the synergistic effect of biochar adsorption and enhanced activation of persulfate

Abstract

We developed a simple in-situ system to remove model antibiotic tetracycline (TC) using biochar (BC) adsorption and persulfate (PS) oxidation (Cu/BC/PS). The biochar produced by pyrolysis of corn stalks at 700 °C exhibited a much higher Brunauer-Emmett-Teller (BET) surface area (431 m2/g), absorption capacity of Cu2+ (8.37 mg/g) and tetracycline (18.80 mg/g) than that of other temperature-prepared biochar. The removal efficiency of TC with the Cu/BC700/PS system reached 55.4%–72.6% with solution conditions of pH 4–9, 120 mg/L TC, 300 mg/L PS and 0.5 g/L BC. Under 619 ± 5 mg/L chemical oxygen demand (COD) condition, the TC removal efficiency of the Cu/BC700/PS system was about 5 times more than that of the Cu/PS system. The results of characterization methods such as Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and radical quenching experiments suggested that the reduced Cu(I) on biochar was a catalytic center in the degradation process and the SO4·- and [rad]OH were the dominant radicals. The reaction kinetics showed that the BC adsorption of Cu2+ and TC were the limiting steps of the entire reaction. A proposed system mechanism is that Cu is absorbed by the biochar and helps further enhance the activation of PS. In the practical application to biogas slurry (2383 ± 47 mg/L COD), the total removal efficiencies of 5 heavy metals and 15 antibiotics were 57.4% and 42.3%, respectively. Moreover, the germination index (GI) of the biogas slurry increased from 8.50% to 43.48% after treatment. Thus, the Cu/BC/PS system has a great prospect in the harmless treatment and recycling of livestock wastewater.