Degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge with ultrasound and Fenton processes: Effect of system parameters and synergistic effect study

To establish an efficient oxidation process for the degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge, the effects of various operating parameters were optimized during the ultrasound process, Fenton process and the combined ultrasound–Fenton process. The results showed that the ultrasonic density of 1.80   w/cm 3 , both H 2 O 2 and Fe 2+ dosages of 140   mmol/L and pH 3 were favorable conditions for the degradation of PAHs. The degradation efficiency of high molecular weight PAHs was close to or even higher than that of light molecular weight PAHs. The highest degradation efficiencies of Σ16 PAHs were obtained within 30   min in the order of: Fenton (83.5%) >ultrasound–Fenton (75.5%) >ultrasound (45.5%), then the efficiencies were decreased in the other of: ultrasound–Fenton (73.0%) >Fenton (70.3%) >ultrasound (41.4%) in 60   min. The extra PAHs were released from the intracellular substances and the cavities of sludge due to the disruption of sludge during the oxidation process. Also, the degradation of PAHs could be inhibited by the other organic matter in the sludge. The combined ultrasound–Fenton process showed more efficient than both ultrasound process and Fenton process not only in the surface of sludge but also in the sludge interior.