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Background and Purpose: Recently, release of pollutants such as pharmaceuticals to the environment becomes one of the most important problems for soil and water. The present study was conducted to introduce walnut shell-based activated carbon (AC) as a new low-cost adsorbent for the removal of cephalexin (CFX) antibiotic from aqueous solutions. Materials and Methods: This study was conducted in laboratory scale. To investigation of the morphology of the prepared walnut shell AC and nanoparticles, scanning electron microscopy analysis was applied. The effect of the presence of Fe 2 O 3 and SiO 2 nanoparticles on the adsorption of CFX on the walnut shell AC is also studied. Results: The maximum removal efficiency (RE) was obtained 98.4% at 100 mg/L initial CFX concentration and decreased to 72.9% with increasing in the initial CFX concentration to 200 mg/L. The results showed that the presence of nanoparticles in the optimum increased the RE of CFX by about 2.1 and 6.5% for Fe 2 O 3 and SiO 2 nanoparticles, respectively. Conclusion: Results suggest the potential of using the walnut shell AC as an adsorbent for effective treatment of pharmaceutical-contaminated wastewaters.

Abstract. The adsorption of cephalexin (CFX) onto walnut shell-based activated carbon (AC) was investigated. The mass transfer coefficients were calculated by employing constant wave propagation theory. The effect of different conditions on the mass transfer coefficient was also studied. In addition, three models to predict the mass transfer coefficient were developed.

Abstract.1 In this work activated carbon (AC) was used for the removal of cephalexin (CFX) from aqueous solution in a fixed-bed column. The breakthrough curves of the adsorption process of CFX on the walnut shell AC at different mass of the adsorbent, flow rate and initial CFX concentration were determined.