The progressive steps for TPH stripping and the decomposition of oil refinery sludge using microbubble ozonation

Total petroleum hydrocarbons (TPH) in activated petroleum waste sludge (PWS) hindered the disintegration of sludge, and microbubble ozonation (MB-O₃) was explored to separate the TPH and solids particle, enhance the decomposition of PWS, and improve the efficiency of ozonation. The maximum solubilization of PWS reached to approximately 41.9% at an ozone dose of 5.40 gO₃/gTS, two times higher than the control one. The ozone mass transfer coefficient of k_La increased from 0.1101 min^-1 to 0.2293 min^-1 in MB-O₃, resulting in the formation of a higher concentration of 1.29 μg/L hydroxyl radicals. The medium diameter sharply declined from 38.6 μm to 17.5 μm, and more porous surface of sludge flocs was observed, indicating that MB-O₃ destroyed the water-oil-gel structure and contributed to the stripping of TPH. The soluble chemical oxygen demand was released by 390% with respect to initial value (from 764 to 3740 mg/L) and acetic acid was the predominant component with yield of 590 ± 7.1 mg/L, which could be served as an additional carbon source. This study provides an efficient approach to achieve sludge disposal and simultaneous enhance the stripping of total petroleum hydrocarbons from oil refinery sludge.