Ozonation was carried out for decolorization and COD removal of raw and anaerobically treated UASB (upflow anaerobic sludge blanket) combined industrial (mainly textile) effluent in a lab-scale bubble column reactor. Ozonation of anaerobic bioprocess effluent at a dose of 300 mg/h for 10 min resulted in 81% color and 75% COD removal (100 mgO₃/80 mg COD) while for raw wastewater 25 min ozonation furnished 51% color and 67% COD removal (250 mgO₃/345 mg COD). Optimal process conditions for biotreated effluent (pH = 8 and temperature = 25°C) resulted in 100% color and 96% COD removal for 10 min ozonation (100 mgO₃/104 mg COD). Electrical energy comparison demonstrated that post ozonation required less electrical energy, 16 and 2.9 times as compared to pre ozonation.