Ultrasonic treatment for sludge reduction in wastewater treatment plants (WWTPs) can substantiallyaffect the fate of trace pollutants. However, their fates in the different phases of sludge and mass balanceshave rarely been reported. In this study, wastewater sludge samples were ultrasonicated at 600 W for 0–30 min. Then, the leaching of the 16 priority polycyclic aromatic hydrocarbons (PAHs) from the sludgesolids (sediment) to the liquid phase (supernatant) was investigated. The total concentration of PAHs(P16 PAHs) in the sludge sediment (2.10 lg/g) was comparable with those of previous worldwide studies.Among the 16 PAHs, naphthalene and acenaphthylene were dominant. The total concentrations ofPAHs in the supernatant generally increased with sonication time, indicating that PAHs associated withsludge materials, such as microorganisms, were released into the supernatant. Lighter and more watersoluble PAHs were released preferentially into the supernatant in dissolved form, whereas heavier andmore hydrophobic PAHs were strongly bound to particles. According to mass balance calculations, 21%of the PAHs in the sludge sediment moved to the supernatant without discernible sonodegradation. Anadditional experiment for degradation of PAHs supported this interpretation, and several reasons forthe no significant sonodegradation were discussed. This result suggests that leaching trace pollutantsmay significantly contaminate the sludge filtrate after ultrasonic treatment, and therefore their fatesshould be investigated.
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