ABSTRACT
Colloidal gas aphrons (CGAs) are applied in pollutant removal due to their large specific surface area and high surface activity. The structure and properties of the prepared CGAs were investigated in the process of oil removal from oily sludge. The prepared CGAs had a liquid film thickness was 5-10 µm with high stability. CGA interfacial tension was as low as 3.157 mN/m. Then it was found that the oil removal rate of CGAs was higher than that of chemical treatments, showing that CGAs could increase the mass transfer surface area and provide additional attachment sites for pollutants, enhancing the oil removal. The treatment conditions of the oil removal were optimized through response surfaces, showing that under optimal treatment conditions, the oil removal rate of oily sludge reached 96.07%. Additionally, the interaction between surfactant concentration and temperature was the most significant of all of the influencing factors. The behavior and mechanism of CGAs in the cleaning process of oily sludge were further investigated using an inverted fluorescence microscope, SEM, FTIR, and two-dimensional fluorescence spectrometer, showing that pollutants transferred from the liquid film surface of CGAs to the inside the film, and CGAs could specifically adsorb negatively charged organic compounds and aromatic hydrocarbons. The results show that CGAs achieved liquid membrane solubilization. Many negatively charged organic compounds and aromatic hydrocarbons are adsorbed onto the CGAs liquid membrane surface via electrostatic and hydrophobic interactions and then migrated to the hydrophobic layer of the CGAs liquid membrane due to the distribution effect, thus enabling rapid pollutant migration between solid and liquid phases.
ABSTRACT
Currently, research on oily sludge treatment mainly focuses on optimizing the deoiling effect and research on the deoiling mechanism, and the influence of petroleum components on the properties and treatment of oily sludge is rarely considered. Therefore, in this study, petroleum substances in three types of oil sludge were eluted using the biosurfactant cleaning technology, and the influence of petroleum components on the cleaning process was explored. The results showed that the biosurfactants rhamnolipid and sophorolipid had a synergistic effect, and the oil-removal rate was as high as 92.2% when the SL mass fraction was 0.4 in the compound biosurfactant. Three types of oily sludge, wellsite-landing sludge, pipeline-landing sludge, and tank-bottom sludge, were cleaned by the compound biosurfactant; the results showed that the residual petroleum substance in liquid and solid phases, the turbidity value, and the zeta-potential value of the supernatant of oil sludge samples after cleaning increased with the increase in the heavy components of the oily sludge, and the oil-removal rate decreased gradually. After cleaning, the average relative molecular weight of the three oil phases increased with the heavy components, which was increased by 1.83, 4.83, and 10.72%, respectively, and the increase in molecular weight increased the difficulty of cleaning. After cleaning, the retention time and peak intensity of the oil sample changed significantly, and it had a stronger elution effect on low-molecular-weight alkanes. It was found that the compound biosurfactant had a good elution effect on polycyclic aromatic hydrocarbons, but the increase in the content of heavy components and the increase in aromatic rings increased the difficulty of cleaning. Moreover, it was found that the compound biosurfactant could not completely elute the petroleum substances on the surface of solid particles, and the asphaltene components in the oil phase were more difficult to elute than other components.
