Preparation and characterization of experimental oily wastewater: effect of rotor speeds and oil/water ratios in an in-line high-share mixer

Multiple oily wastewaters are necessary for scientific research and technological development. Experimental oily wastewater is prepared with an in-line high shear mixer at a constant flow rate. Rotor speeds have a significant effect on pressure drops across shear mixer, while oil/water ratios have less effect. With the increase of rotor speeds, most of the oil droplet size (D-50, D-90) show a downward trend. D-10 of oil droplets may increase at low oil/water ratios while those decrease at high ones. Oil droplet sizes (D-50 and D-90) change slowly and emulsibility values decrease with the increase of oil/water ratios, and 0.06% is most favorable for fine emulsion. Higher rotor speeds prepare the turbulent environment easily, and higher oil/water ratios are available to improve droplets coalescence. Rotor stirring changes the drop size, and in turn influences the Zeta potential and stability of the emulsion. As oil/water ratios increase, absolute Zeta potential tends to decrease and coalesce easily. The oil contents of prepared wastewater measured with polyacrylamide addition are more than those without polyacrylamide addition respectively, and all of them are lower than their theoretical counterparts respectively. The results can provide necessary parameter references for the laboratory to prepare the character-specific oily wastewater.