Intensification of non-thermal plasma for aqueous Ciprofloxacin degradation: Optimization study, mechanisms, and combined plasma with photocatalysis

Abstract

As it is well known that wastewater treatment is becoming a global concern, the search for advanced intensive oxidation processes with minimal waste generation for wastewater treatment remains a major challenge. In the present work, the photodegradation of Ciprofloxacin (CIP) was studied using the Dielectric-Barrier-Discharge (DBD) process. The effect of some operating parameters such as CIP initial concentration (from 1 to 6 mg/L), air flow rate (from 0 to 240 L/h) and frequency (from 350 to 600 Hz) on DBD performance in term of CIP degradation efficiency (%D) has been investigated. Here, as a major result, the CIP degradation efficiency and the mineralization yield (%M) reached >99 % and >49 %, respectively, during 60 min, under the obtained optimum experimental conditions (an initial concentration of 1 mg/L, an air flow rate of 100 L/h, a voltage of 18 kV, and a frequency of 350 Hz). It can be concluded that the DBD process exhibits an eco-friendly and great potential for aqueous CIP degradation. Moreover, the mechanisms involved in the degradation process by DBD were explained. The scavengers study revealed that °OH, HO2°and O2−° radicals were the basic reactive oxygen species (ROS) in CIP degradation process. Results show that in addition to ROS, the reactive nitrogen species (RNS) also play a key role in the CIP removal process. In order to get closer to the real conditions, DBD experiments were also carried out in other water matrices, tap water (TW) and synthetic pharmaceutical water (SW). Significant inhibition of CIP degradation (%D) and mineralization (%M) was observed in TW (%D = 76, %M = 33) and SW (%D = 60, %M = 10) with reference to the CIP degradation and mineralization in ultra-pure water (UPW) (%D ≥99, %M = 54), after 90 min irradiation. It showed that the presence of organic and inorganic molecules in TW and SW lowered the CIP degradation efficiency. Thus, the combined plasma-photocatalysis system, using luminous textile as photocatalyst, was performed for the CIP degradation in SW, in order to get closer to the real conditions, leading to >99 of %D and 64 of %M. Moreover, the use of combined DBD plasma-photocatalysis process significantly enhanced the CIP degradation performance if compared to each process considered separately. Overall, the combination of DBD and photocatalysis may be a promising technology for economical, efficient and environmentally friendly removal of pollutants in wastewater.