Innovative process for total petroleum hydrocarbons reduction on oil refinery sludge through microbubble ozonation

Abstract

Oil refinery sludge is a complex mixture of hydrocarbons, water and sediments produced in the refining process, which is classified as a hazardous waste. The source reduction of sludge is inhibited by the combination of total petroleum hydrocarbons (TPH) and solid particles, and the decomposition of TPH is a critical step for oily sludge (OS) disposal. Microbubble ozonation was introduced to improve the efficiency for TPH removal in this work. 70.9% of TPH was found to be decomposed from OS with the initial pH of 3, ozone dosage of 0.27 gO3/gTS and total solid of 2% in 120 min. The corresponding reaction rate constant k for the rapid stage reached 0.0269 min−1, two times higher than the control system of macrobubble ozonation. The synergistic effect of oxidation and flotation was observed in the microbubble system by destroying the chemical bonds between petroleum hydrocarbons and particle surface and improving the adhesion probability between microbubbles and oily flocs. A broad-spectrum removal rate of 71.7–79.5% was observed for the middle or long chain hydrocarbons fractions (nC7-C10, nC11-C20, nC21-C30 and nC31-C40) in TPH. Most of heavy hydrocarbons (nC21-C40) in OS were oxidized and decomposed to the low boiling point hydrocarbons according to thermogravimetric results. The principal intermediates included 42.6% carboxylic acids, 18.8% phenolics and 13.9% alcohols and other gaseous byproducts. Microbubble ozonation is expected to be the first step for detoxification and decomposition of OS, thus reducing the generation of hazardous wastes.