ON THE ADSORPTION OF CIPROFLOXACIN BY CLINOPTILOLITE AND USE OF NON THERMAL ATMOSPHERIC PRESSURE PLASMA FOR REGENERATION OF THE SPENT ZEOLITE

Abstract

The use of antibiotics constantly increases which has a notable negative impact on water bodies. Ciprofloxacin (CIP) is widely applied antibiotic in both human and veterinary medicine, as well as in a livestock breeding. Due to its extensive use, CIP has been found in wastewater effluents in a wide concentration range from ng to mg dm^(–3). An extremely high concentration of up to 50 mg dm^(–3) has been found near drug manufacturing plants [1]. Since CIP, as well as many other pharmaceuticals, cannot be efficiently removed from wastewater streams by conventional wastewater treatments, it is of a great importance to find an acceptable method for their removal. This study reports the use of natural calcium-rich clinoptilolite (CLI) for the adsorption of CIP and regeneration of the spent adsorbent (CLI-CIP) by non-thermal atmospheric pressure plasma (NTP). The results show that the CLI possesses a high adsorption efficiency in removal of CIP at 283, 288 and 293 K in a slightly acidic medium (pH= 5) for the initial concentrations from 15 to 75 mg dm^(–3). The CIP adsorption by CLI follows the Lagergren’s pseudo-second-order kinetics and it can be described well by the Langmuir isotherm model. For all studied temperatures and initial concentrations more than 85% of the CIP is removed within the first 10 minutes. The results also indicate that the CIP adsorption mechanism includes two phenomena: 1) electrostatic interactions between negatively charged aluminosilicate lattice and cationic form of CIP species and 2) ion-exchange reaction. The use of NTP for the regeneration of CLI-CIP was based on the assumption that NTP generates highly reactive species which can induce a cleavage of the bonds formed between active sites on the CLI surface and CIP, and also induce the CIP decomposition. The NTP treatment was performed for a short time, with a low energy consumption, and without using the additional chemicals. All these make the procedure acceptable not only from economical point of view but also regarding environmental issues [2]. A surface dielectric barrier discharge plasma source was used for the treatment of CLI-CIP. The regeneration study was consisted of five successive adsorption/NTP cycles. Powder X-ray diffraction and Brunauer–Emmett–Teller surface area analyses confirmed that the plasma treatment did not influence the CLI lattice nor its textural properties. Moreover, X-ray photoelectron spectroscopy confirmed that the NTP reduces carbon content in the regenerated CLI for more than 90% and that the plasma reactive species are involved in the CLI regeneration process. The obtained results strongly support the applicability of the NTP treatment in regeneration of zeolite-based adsorbents used in pharmaceutical removal from wastewater.