Study of the biodegradability of basic oils used in the manufacture of lubricants

The primary biodegradability of different base oils hers been evaluated by the CEC L-33A-93 test to correlate this biodegradability with physical-chemical properties and manufacturing processes of base oils. Preliminary experiments showed no significant variations in the biodegradability data according to the nature and origin of microbial inoculum although the inoculum size varied between 10(4) and 10(7) CFU/ml. Therefore, ail biodegradability tests were performed with the same inoculum (secondary effluent) whose reproducibility was systematically checked by the analysis of two reference oils. ii has been demonstrated that the biodegradability of an oil increases with its viscosity index but decreases when its viscosity and refractive index increase. It also appears that hydro-cracked oils ore the most biodegradable mineral oils with biodegradabilities ranging from 66 to 75 %. The biodegradability of vegetable oils (rapeseed oils, polymerised or not) is higher than 95%.