Problems with Contaminants from the used oil

 When the chemical-aided ultrasonic irradiation method was proposed as the pretreatment process for biochemical process, we looked into the possibility to adopt this method as the pretreatment step for other used oil recycling/reusing processes if it proves to be economically feasible. Since the undesirable toxic contaminants in used oil that cause problems in other reclaiming, reprocessing or re-refining operations are the same. 

For reclaiming operation, since only a minimum simple step is applied on the used oil, the remaining fuel dilution and cracked hydrocarbon molecules often limit lubricant performance. Acids and metals that are not completely removed may act as catalysts and may further degrade or shorten the useful life of oil. Additional costs and long-term liability of the water, fuels, sludges, and residues generated by the drying and filtering process must be considered. These new wastes may need to be further treated onsite or sent to landfills or incineration plants. 
For reprocessing operation, as mentioned earlier, odor produced from nitrogen and sulfur species is the greatest concern. Severe corrosion may occur in the equipment when acidic gases from additive elements and water vapors combine during the process. These problems can be avoided and eliminated if the trouble-making components removed from the process as early as possible. Wastes generated from each step also need further handling. 
For re-refining operation, less problems are presented. Heavy metals are removed from the dewatered oil components at the distillation step and then ended in asphalt flux, while higher-boiling-point halogenates and polar compounds are expected to be removed in the hydrotreating step. Refer to Table 2-4, it is obvious that chlorinated and sulfur compounds are not removed until the last hydrotreating step. Unfortunately, data on how other organic toxins are removed during each step or the concentrations in the final products are not publicly available. It was claimed by Evergreen Oil that all those organic contaminants are removed from the distillation step, however, it is really hard to make believe. Refer to Appendix B, it is obvious that many contaminants have very high boiling points, which make them end up either in the asphalt flux or gas oil to become the problem for the byproducts or possibly still stay in the lube oil distillates and go through the process. According to data compiled from  analyses on many re-refined oils from different sources/countries, are found in re-refined oil samples at a higher level than those found in  filtering process must be considered. These new wastes may need to be further treated onsite or sent to landfills or incineration plants.