Efficacy and mechanistic insights into dielectric barrier discharge plasma degradation of antiretroviral drug efavirenz

Antiretroviral drugs (ARVDs), used in the treatment of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) have been recognised as emerging contaminants (ECs). Various ARVDs have been identified and quantified in surface waters worldwide. This research presents the first degradation of efavirenz using dielectric barrier discharge (DBD) plasma. Efavirenz was successfully degraded with 93 % removal efficiency at discharge power of 59.3 W and pH 9. Incorporating free radical promoters (Fe2+/H2O2) significantly improved the rate constants from 0.134 min−1 to 0.269 min−1 resulting in a 40 % increment in energy yield, from 235 mg/kWh to 330.5 mg/kWh. The presence of free radical promoters also eliminated the need for upward pH adjustments. The optimal gas flow rate of 0.6 L/min enabled maximized production of reactive species that resulted to highest efavirenz removal efficiency (93 %). Electron paramagnetic resonance (EPR) confirmed the presence of •OH and ONOO- radical species during plasma discharge. Subsequent chemical probes confirmed the dominance of e-aq and •OH in efavirenz degradation. Coexisting inorganic ions largely retarded efavirenz degradation. Six degradation by-products were identified, and possible degradation pathway was proposed. Electron transfer and hydrogen abstraction were the primary mechanisms through which the radicals attacked the efavirenz contaminant. DBD demonstrated adaptability to actual water matrices contaminated with efavirenz, signifying its practical feasibility as a treatment option for ARVD-contaminated waters in the environment. This study provides an invaluable reference for understanding the degradation of ARVDs in the environment using DBD plasma, contributing to the collective endeavours aimed at preserving the integrity of terrestrial and aquatic ecosystems.