عنوان مقاله [English]
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<0.05). But this efficiency may be improved by increasing TSS and H2O2 concentration levels. However, the effect of H2O2 depends on its concentration such that no considerable increase was detected in organic removal efficiency with ≤5 mg/L of this chemical. Higher organic removal efficiencies can be expected only when H2O2 is added at a concentration level of 20 mg/L (p<0.01). Changes in pH level had no detectable effect on organic removal and for either methods of treatment (the ultrasound or the combined ultrasound/H2O2), the efficiency of organic treatment did not increased neither at an acidic pH (=3) nor at a basic pH (=11). This result clearly shows the independence of the treatment on pH. Finally, it is noteworthy that increased TSS level (30 mg/L) has a positive effect on ultrasound treatment so that a nearly 40 percent improvement was observed in organic removal efficiency in this experiment. It may be concluded that increased TSS and H2O2 both increase the effectiveness of the ultrasound whereas, organic removal efficiency may decrease in this method as a result of increased concentration levels of these pollutants. Furthermore, pH variation was found to have no considerable effect on the treatment process.