The mechanism and influencing factors of sludge de-oiling process collected from the Tahe oil field, a thickened oil field in China, were investigated using biosurfactant. The oily sludge was collected from ground sludge near the oil-well blowout and pipeline perforation, and the storage time about 3 similar to 5 years, resulting in high content of heavy components in the sludge. The viscosity of the recovered oil at 50 degrees C was approximately 2.5 x 10<^>4 mPa.s. The contents of saturated fraction, aromatic fraction, colloid, and asphaltene of the oil in the oily sludge were 24.37%, 29.35%, 15.55% and 30.37%, respectively. When the solid-liquid ratio was 1:2.5, the stirring strength was 350 r/min, the cleaning agent concentration was 15 g/L, the cleaning time was 100 min, and the temperature was 65 degrees C, the oil content of the cleaned sludge was less than 0.5 wt%. The surface of the solid particles of sludge was rough and exhibited a porous structure, which were beneficial to the adsorption of crude oil and other pollutants. Interface analysis showed that the interfacial tension decreased from 25 mN/m to 5 mN/m, whereas the contact angle increased from 7.88 degrees to 36.02 degrees. Biosurfatcant could markedly lower the interfacial tension and change the wettability of the surface of solid particles. As a result, the oil-water interface film on the surface was destroyed, the contact angle between the crude oil and the solid surface increased, and the crude oil was peeled off.
