Biodegradability assessment of ozonated raw and biotreated pharmaceutical wastewater

The activated sludge specific oxygen uptake rate (SOUR) and BOD₅/COD ratios of biologically pretreated pharmaceutical wastewater were analyzed and compared to assess relative changes in biotreatability during ozonation at a rate of 7.4 g/(L × h) for 4 h. An appreciable COD removal (41%) was achieved by the initial biological treatment process, whereas ozonation was more effective in reducing the UV-sensitive aromatic compounds present in the pretreated effluent. Sequential treatment using activated sludge + ozonation processes resulted in an average COD removal efficiency of 48%, and a proceeding biotreatment stage increased the overall COD removal to 53%. An optimum ozone dose in the range of 1,8543,708 mg/L corresponding to a specific ozone input rate of 0.23-0.46 mg O₃/mg COD_o existed where SOUR (3.7 × 10^-3 mg O₂/[mg MLSS × min] for ozonation at pH 8) and BOD₅/ COD (0.57) as well as the proceeding biological COD removal yield Y_COD (average 8 mg COD/mg MLSS) exerted maximum values.