Sonochemical degradation which combines destruction of the target compounds by free radical reaction and thermal cleavage is a recent advanced oxidation process (AOP) with the potential to be effective for removing low concentrations of organic pollutants from aqueous streams. AOPs typically involve the generation and use of the hydroxyl free radical as a strong oxidant to destroy compounds. The decomposition rate of pollutants by ultrasound depends on various factors. In this study, the effects of pH, initial concentration, hydrogen peroxide addition, and TSS concentration on the decomposition of organics in the secondary effluent have been investigated. COD analysis was taken as the index for organic concentration and two ultrasonic frequencies of 35 kHz and 130 kHz were used for treatment of wastewater samples. Results indicated that increases in organic concentration within the range of 20-60 mg/L would decrease organic removal efficiency from wastewater (p
