Mechanistic study of cefixime degradation with an atmospheric air dielectric barrier discharge – Influence of radical scavengers and metal ion catalyst

The ineffective removal of antibiotic residues and their metabolites by conventional wastewater treatment setups lead to their continuous discharge into the environment, causing risks to both aquatic life and human health. This study explored the use of a non-thermal plasma (NTP) generated by atmospheric air for the degradation of cefixime (CFX), a widely consumed and recalcitrant antibiotic. This study achieved a complete degradation of CFX using an NTP technology in 8 min treatment time at 6 kV and 20 kHz applied AC voltage and frequency, respectively using a high voltage alternating current power supply unit. An energy yield of 0.42 g/kWh was estimated. The degradation of the pollutant was influenced by solution flow rate, applied voltage and the solution characteristics. Five degradation by-products were identified based on quadrupole time-of-flight (q-TOF) mass spectrum analysis and a possible degradation pathway for the pollutant was proposed. Also, radical scavenger experiments were set up to understand the specific chemical species facilitating CFX degradation. The effect of Fe2+ catalyst on the degradation of CFX was investigated in the aqueous solution. This low-cost metal ion catalyst has been known to improve the degradation of organic compounds by facilitating the oxidizing power of H2O2. Considering this, a new idea was examined in this study which was the degradation of the antibiotic in the presence of both Fe2+ catalyst and some radical scavengers (iso-propyl alcohol – IPA, tert-butyl alcohol – TBA, and sodium hydrogen carbonate – NaHCO3). When Fe2+ was introduced into CFX solutions containing TBA, IPA and NaHCO3, respectively, the degradation and kinetics increased by at least 33 %. In these mixed additives, the degradation of the pollutant was enhanced by the consumption of H2O2.