Optimization of UV/H2O2 process for integration with biological waste treatment unit was done by Taguchi ' s orthogonal design. Four factors were considered for optimization: Dosage of H2O2, pH, circulation rate and number of doses of oxidant. For each of the four factors, experiments were run at four levels. For reduction in TOC, single dosage of hydrogen peroxide was observed to be more effective than dosing the same quantity in 2, 4 or 6 equal parts. The effect of circulation rate was found to be insignificant. If AOP were to be designed as a pretreatment step before biological oxidation, 1 mole H2O2/mole TOC is the optimum level of dosage. This level of addition increased biodegradability. If AOP were to be designed as a post-treatment step after biological oxidation, then 4 mole H2O2/mole TOC would be the optimum level of dosage. At this level, decrease in TOC was high. Higher pH of the waste liquor generally favoured reduction in TOC. (c) 2005 Elsevier Ltd. All rights reserved.