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The adsorption of roxarsone by iron (hydr)oxide-modified multiwalled carbon nanotubes (MWCNTs) from aqueous solution and its mechanism were investigated. The amount of roxarsone adsorbed by modified MWCNTs is higher than MWCNTs at the same condition. The results show that the sorption isotherms are nonlinear, and can be well fitted according to the Freundlich and Polanyi-Manes models. The adsorption kinetics could be well described by pseudo-second-order model. Thermodynamic analysis shows that the adsorption of roxarsone on the adsorbents is an exothermic and spontaneous process. Desorption process had no obvious desorption hysteresis phenomenon. The FT-IR and XPS analysis confirmed the loading of iron ions on the MWCNTs, and revealed the involvement of carboxyl groups and iron ions on the adsorption of roxarsone.

High concentration animal wastewater is often contaminated by tetracycline and an upflow anaerobic sludge bioreactor (UASB) with granular sludge is often used to treat the wastewater. The investigation of the adsorption process of tetracycline on anaerobic granular sludge during anaerobic digestion of animal wastewater will increase the understanding of antibiotics behavior in the UASB reactor. In this study, the effects of initial pH, humic acid concentration, and temperature on the removal of tetracycline by anaerobic granular sludge from aqueous solution were investigated using the batch adsorption technique in 100 mL flasks with 75 mL of work volume. The results show that the highest removal efficiency of 93.0% was achieved around pH 3.0 and the removal efficiency at the neutral pH range (pH 6.0-8.0) is about 91.5%. The thermodynamic analysis indicates that the adsorption is a spontaneous and endothermic process. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms analysis indicates that the Langmuir model is better than the Freundlich model for the description of the adsorption process and confirms the result of thermodynamics analysis. The maximum adsorption capacities were 2.984, 4.108 and 4.618 mg/g at 25, 35 and 45 °C, respectively. These results provide useful information for understanding the fate and transformation of tetracycline in a UASB digestion system and improving the management of tetracycline contaminated animal wastewater.

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