The treatment of a synthetically prepared wastewater containing ethylbenzene and p-nitrophenol has been investigated using combined treatment schemes based on the advanced oxidation process followed by the conventional aerobic oxidation process (using primary activated sludge (PAS), modified prepared activated sludge (MPAS) based on the use of combined sludge from different treatment sources and activated sludge (AS)). The operating conditions for the pretreatment scheme have been optimized and it has been observed that initial pH of 3-3.5, a Fe2+ dosage of 2.0 g L-1 and a H2O2 dosage of 1.5 g L-1 in combination with ultrasound gives the best performance. Approximately, 55-70% reduction in the chemical oxygen demand (COD) was obtained at optimum conditions after pretreatment from initial conditions of COD as 3642 and 3417 mg L-1 and BOD as 881 and 533 mg L-1 for the wastewater containing ethylbenzene and p-nitrophenol respectively. From an initial BOD5/COD (BI) value of around 0.15-0.2, the ratio was found to increase to about 0.30-0.35 after pretreatment, which is considered good for the aerobic treatment. In the case of aerobic oxidation, promising results were obtained for the modified prepared activated sludge giving better conversion ability of intermediates into solid residue and higher biomass yield that could be separated by simple filtration as compared to the primary activated or the activated sludge treatment. The best treatment approach as established in the work was ultrasound assisted Fenton process as the pretreatment followed by biological oxidation using MPAS. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.