Synergistic effect of high-efficiency shear and hydraulic cavitation to efficiently clean oily sludge at room temperature: process optimization and mechanism

Oily sludge contains a variety of toxic and harmful substances, which not only seriously pollutes the environment, but also is difficult to deal with. In this study, a new multi-layer stirring rotor was designed for cleaning oily sludge by high-speed stirring (HSS). The study determines the optimal conditions for cleaning oily sludge through single-factor experiments. The results showed that the stirring speed of 6000 r/min, the cleaning time of 15 min, the amount of sodium silicate of 5 %, and the solid to liquid ratio of 1:7 g/mL were the optimal conditions for cleaning oily sludge by the HSS method. It can reduce the residual oil rate from 13.81 % to 0.74 % with the oil removal rate of 94.64 %. Additionally, the effect of HSS process on oil removal in oily sludge was verified by scanning electron microscope, fourier transform infrared spectroscopy, and four-component analysis. Ultimately, the mechanism of oily sludge cleaning was analyzed by simulation. The simulation results indicated that the rotor generated strong shear force and released heat in the process of HSS cleaning, which not only broke the sludge, but also facilitated the reduction of slurry viscosity. Furthermore, hydraulic cavitation occurred within the rotor due to pressure changes. The combined effects of these phenomena synergistically enhanced the elution of petroleum hydrocarbons. This study significantly improved the cleaning effect, and the treated sludge met the discharge standard. This work is of great significance for the future management of oily sludge and the sustainable development of petrochemical industry.