Key-study on plasma-induced degradation of cephalosporins in water: Process optimization, assessment of degradation mechanisms and residual toxicity

Abstract

Cephalosporins is a class of β-lactam antibiotics being widely used and often released uncontrollably in aquatic systems thus resulting in serious environmental contamination. In this work, we investigated for the first-time the degradation of cephalexin (CPX) and cefazolin (CFZ) by nanosecond-pulsed cold atmospheric plasma (NSP-CAP) using a multi-pin-to-liquid corona reactor, proposing special degradation pathways of both cephalosporins and assessing their residual toxicities. Increasing pulse voltage and frequency enhanced RONS concentration and energy input into the system both of which led to improved plasma-induced cephalosporin degradation effi- ciency, rate and energy yield, the latter being two orders of magnitude higher (0.84–1.37 g/kWh) than those reported for their photocatalytic degradation. O2- and air-plasmas displayed superior performance compared to N2-plasma due to the increased ROS concentration. The prevailing role of the short-lived ⋅OH and 1O2 in the degradation process compared to the long-lived H2O2 and plasma electrons was confirmed. Nevertheless, the identical degradation efficiencies between air and oxygen indicated the possible significant contribution of some RNS (e.g. ONOOH/ONOO–) generated due to nitrogen content in air-plasma. The plasma-induced degradants of CPX and CFZ were interrogated by UPLC/MS, comprehensive degradation maps were proposed and reduced cytotoxicity was demonstrated for both CPX and CFZ plasma-treated solutions. Given than CPX and CFZ are resistant to human (and other species) metabolism/degradation, this work supports that CAP constitutes argu- ably one of the most efficient remediation technologies to date.