The discharge of effluent from the pharmaceutical industries is a major source of environmental pollution due to the toxic and at times carcinogenic nature of contaminants. The current work investigates the treatment of pharmaceutical industry effluent (PIE) using ultrasonic horn, operated individually and in combination with oxidants. Under controlled operating conditions, the effect of addition of hydrogen peroxide (ratio of COD of PIE: H2O2 varied over the range from 1:1 to 1:10), ozone (flow rate of 400 mg/h) and Fenton's reagent (FeSO4:H2O2 ratio of 3:5) was investigated as a possible process intensification strategy. The combined approach of ultrasound, ozone and CuO catalyst (0.3 g/L) as well as US + H2O2 + Ozone was also studied. The combined operation of US with H2O2 and Ozone resulted in a 73 % COD reduction, whereas the combination of the US, ozone and CuO catalyst gave maximum COD reduction of 92 %. The study also focused on identification of intermediate products formed during the PIE treatment. The component analysis of PIE before and after treatment was carried out by high-resolution liquid chromatography-mass spectroscopy (HR-LCMS). The research work has clearly established that cavitation in combination with other AOPs can be effectively used for the treatment of PIE with a significant increase in the extent of COD reduction for the combination approach. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.