Turning in waste oil is a good thing for sure because some of it is reconstituted into the very synthetic oil that saves gas by lowering friction in the engine. It also saves wear, and the longer a car lasts, then more energy is saved from not having to build a new car. I would like to also mention that a large percentage of used oil ends up going into blast furnaces. Especially when the fuel prices are up. The modern blast furnace is set up to inject any oil from heavy to light, as well as steam and natural gas. While this is probably good as it saves other fossil fuel use, it certainly gets burned no cleaner than in say the babbington burner.
The heavy metals end up in the pig iron which again is often good because they add most of those metals to modern steel alloys anyway. Other uses for the used oil are large industrial burners which mix it with the heavy bunker oils. It is most likely filtered, but again, I’d like to look at their emission results when burning used oil. Most small ones are not regularly monitored. It is still better than dumping oil on the ground or in a sewer which was done for years. Even putting it in a landfill it will eventually burst it’s container adding to the sludge that oozes out into filtering basins or the groundwater.
Cars and trucks regularly emit a small amount of badly combusted motor oil, or you wouldn’t ever need to add any unless it leaked. Rebuild your motor to save fuel, oil, and clean the air. My point is that if a guy can save a buck on kerosine, number 2 heating oil, propane, or natural gas. He’s probably also burning used oil in a non-point source of pollution where the environment can better handle it. This is also a good saving of fossil fuel. Yes, cooking oil can probably burn cleaner but it also has other uses.
In this area companies process it into animal feeds and other uses, so it holds value. Not every community has recycling centers for oil, especially in remote areas. Generally, if you don’t want to breathe the diluted smoke coming from your combustion devise, your neighbors don’t want to either. Take a look at what you are doing and use the talent on this list to clean it up. Choose your best, cleanest alternative source of BTU’s. Use your cleanest available combustion devise, and take pride in helping the whole of humanity.