The paper deals with the degradation of the organic pollutants in coke plant wastewater by the combination process of ultrasonic irradiation, catalytic oxidation and activated sludge. The effect factors of ultrasonic irradiation on the degradation of the organic pollutants such as saturating Vs, initial pollutant concentration, ultrasonic power density, the category and consumption of catalyst were investigated. The results indicate that putting the saturating gas into the reaction solution in the process of the ultrasonic irradiation, low COD initial concentration and high ultrasonic power density are the favorable conditions for their degradation. Compared with single activated-sludge process, co-approach of ultrasonic irradiation and activated-sludge can greatly increase the COD degradation efficiency. When the wastewater was firstly treated by ultrasonic irradiation process and then followed by activated-sludge process for 240 min, respectively, the COD degradation efficiency increased by 48.29-80.54%. Additionally, when 3.0 mmol/l of ferrous sulfate was added into the ultrasonic irradiation process, the COD degradation efficiency was as high as 95.74%, 63.49% higher than that of the activated-sludge approach alone. (C) 2004 Elsevier B.V. All rights reserved.