Abstract: Physicochemical activities and oily sludge cleaning effect of rhamnolipids with different structure compositions were examined using crude oil and oily sludge of Daqing Oilfield. Meanwhile, the parameters of oily sludge cleaning were optimized. Results showed that there was a positive relationship between the proportion of monorhamnolipids and surface activity of rhamnolipids. The proportion of di-rhamnolipids was positively correlated with emulsifying ability of rhamnolipids to crude oil. Different ratios of mono-rhamnolipids and di-rhamnolipids affected oily sludge cleaning effect. The cleaning efficiency was the highest at a ratio of 50:50. The optimized cleaning parameters were as follows: rhamnolipids concentration of 1.0 g·L^-1, hot wash time of 1.5 h, hot wash temperature of 65 ℃, eluting power of 220 r·min^-1, and solid liquid ratio of 1:5. The cleaning efficiency was up to 81.3% under optimized conditions. After cleaning process, oil content of the ground oily sludge was reduced from 29.6% to 5.5%. The oil recovery efficiency was 87.3%. The washed crude oil has no obvious emulsification and is easy to separate. Different ratios of mono-rhamnolipids and di-rhamnolipids affect their physicochemical properties and the oily sludge cleaning effect.

Key words: fine root, soil physicochemical property, root activity., mulching, root distribution