Contaminants in the used oil
many contaminants such as PAHs, PCBs, and chlorinated compounds were not found in any of the four used oil samples as predicted. BTEX compounds and heavy metals did present in these four used oil samples, however, the levels of concentrations were mostly much lower than typical values (Refer to Table 2-2). The reason for why such deviated and not-so-representative samples were acquired probably was due to the fact that these samples were taken from some upper levels of the holding towers. Thus, they were already cleaner than the average condition. Contaminants tend to settle at the bottom of the big holding tower with particulates or colloids after a period of holding time. It is possible that the water was already separated out and stayed at the bottom of the holding tower, so very low water content was found in original four used oil samples. The lack of PAHs, PCBs, and chlorinated compounds is hard to explain. It may be because the cross contamination did not occur in the sources of the four used oil samples. It is obvious that these samples may not be representative enough for the feasibility studies about ultrasound’s ability to decompose every potential contaminant in used oil. On the other hand, it could also be the fact that it is just too difficult to acquire used oil samples containing all potential contaminants within; if this is the case, then the current four used oil samples may still tell us some stories. In the first few test runs 112 applying ultrasonic irradiation on the four used oil samples, only heavy metals and BTEX compounds could be investigated. For future studies, synthetic used oil samples with known constituents will be prepared in order to systematically control the consistency of the experimental samples.