Evaluation of Langmuir and Freundlich Isotherms for Removal of Cephalexin and Tetracycline Antibiotics By Sistan Sand from Water and Wastewater Samples

In this research, Sistan sand was used as a natural and inexpensive sorbent for removal of cephalexin and tetracycline antibiotics from water and wastewater samples. For a concentration 60.0 mg L-1 of cephalexin, optimum removal conditions were: pH of the sample 3.0, adsorbent amount 1.0 g, contact time 20.0 min, added amount of sodium chloride to adjust the ionic strength of the solution 7.0 g L-1. Langmuir isotherm was the best fitted model for this adsorption process and adsorbent capacity was calculated to be 0.26 g g-1. This adsorbent was able to remove up to 68.1% of cephalexin from wastewater. In case of tetracycline, for a 90.0 mg L-1 of the analyte, the optimum adsorption conditions were achieved at pH 8.0, 1.0 g of sorbent, contact time of 35.0 min and ionic strength of the solution as sodium chloride of 7.0 g L-1. The isotherm was best in agreement with Freundlich model. Adsorbent capacity was 0.76 g g-1 and up to 76.2% of this antibiotic could be removed from wastewater.