Q. As long as the used oil’s flash point is => 140°F, can my spent acetone (used as a degreaser) be disposed of in my onsite oily wastewater treatment facility that has two 30,000 gallon used oil tanks holding used oil sold as on-spec oil?
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A. A mixture of acetone and used oil can be managed as used oil. The federal used oil regulations set forth how mixtures of used oil and hazardous waste must be managed. Mixtures of used oil and listed hazardous waste such as acetone (considered a listed hazardous waste under 40 CFR 261.31) must be managed as hazardous waste (40 CFR 279.10(b)(1)). However, this used oil “mixture rule” exempts from hazardous waste management mixtures of used oil and “a waste which is hazardous solely because it exhibits the characteristic of ignitability (e.g., ignitable-only mineral spirits), provided that the resultant mixture does not exhibit the characteristic of ignitability” (40 CFR 279.10(b)(2)(iii)). Such mixtures may be managed as used oil.
Because acetone is listed as a hazardous waste “solely because it exhibits the characteristic of ignitability” (and exhibits no other hazardous waste characteristics) it would qualify for this exemption provided the mixture of acetone and used oil “does not exhibit the characteristic of ignitability.” For the mixture to exhibit the ignitability characteristic, it would have to have a flash point less than 60°C (140°F) (40 CFR 261.21(a)(1)). Because you have said that the flash point of your acetone/used oil mixture would exceed 140°F, your mixture would not exhibit the characteristic of hazardous waste.
Hmm. I don’t really agree with this tip. First, the question as worded states that “the used oil’s flashpoint => 140.” It doesn’t clearly indicate that the *mixture of used oil and acetone* has a flashpoint greater than 140, as the author of the answer seems to assume.
Also, for at least a couple of compelling reasons, adding acetone to used oil and managing the resulting mixture as a hazardous waste is not a great idea. While the author is correct that it’s the ignitability of the final mixture that matters, assuming that variable amounts of acetone are going to be added to the oil, the proportions of acetone and oil will vary and so will the flash point of the mixture. In the event of an inspection, the burden is on the generator to prove that *this* mixture of oil and acetone on hand at the time of the inspection actually has a flash point greater than 140. This also all assumes that the mixture is complete, and that there are not pockets of isolated/unmixed acetone that would have a lower flashpoint and represent an ignitability hazard. Aside from the regulatory question, that can be dangerous.
Also, this advice butts up against RCRA’s advice that “dilution is not the solution.” It can be argued, including by an inspector, that what a company is doing is diluting a hazardous waste stream to make it nonhazardous. RCRA’s admonition against that is based on what I stated above, but appearing to do “dilution” is a problem in its own right because they have been so forthcoming about their opposition to that. It’s a different matter if a facility produces a waste that is inherently a mixture of acetone and oil, but when an employee is consciously walking over and dumping acetone into a drum of used oil, it doesn’t look great.
It is actually a much better idea to manage the acetone as a hazardous waste, in light of considerations above.