BACKGROUND Degradation of glucocorticoids (GCs), including fluocinolone acetonide (FA), triamcinolone acetonide (TA) and clobetasol propionate (CP), in water by dielectric barrier discharge (DBD) and DBD combined with calcium peroxide treatment (DBD/CaO2) were investigated. Effects of discharge power, pH, plasma-working gas and CaO2 dosage were examined during DBD and DBD/CaO2 treatments. The synergistic output from the combination of CaO2 with DBD on center dot OH concentration, pH, conductivity, CaO2 adsorption and the overall influence on GC removal were assessed. Toxicity variations and feasibility to various water matrices by DBD and DBD/CaO2 treatments also were analyzed and compared. RESULTS The removal efficiencies of FA, TA and CP achieved were 74%, 70% and 75%, respectively, at 36.68 W over 120 min in air with unadjusted pH (energy yield of 7.47 mg kW(-1) h(-1)). Significant synergistic effects were observed in combining CaO2 with DBD with a CaO2-concentration-dependent mechanism. The removal efficiency of FA, TA and CP increased by 7%, 32% and 31%, respectively, by DBD/CaO2 in comparison with DBD alone after 60 min treatments at CaO2 dosage of 0.4 g L-1. In addition, DBD/CaO2 treatment was more effective in controlling toxicity and had better efficacy in various water matrices than DBD alone. CONCLUSION This study provides a reference point for the application of DBD and DBD/CaO2 treatments to effectively remove GCs from water. (c) 2019 Society of Chemical Industry