I've seen about six people go through this journey. Burning waste veggie oil, or even biodiesel, is considerably more annoying and labor intensive than merely filling a car. Unless this changes, it's unlikely to scale in the way you indicate.

The real threat is actually blends that use a small amount of biodiesel mixed with rock diesel. These can be burned in any engine, and there is so little food oil (animal and vegetable) compared to the demand for liquid fuel, that this practice can easily lead to the kind of effects you describe.

To add to this, has anyone actually tested the diesel engine to make sure it meet all emission standards?

How safe are the fumes to be burned around cities? Remember when we found out lead in gas was unsafe to be inhaled from exhaust pipes?

From Wikipedia: "Biodiesel is the only alternative fuel to have successfully completed the Health Effects Testing requirements (Tier I and Tier II) of the Clean Air Act (1990)." https://en.wikipedia.org/wiki/Environmental_impact_of_biodie...

Either way the tetraethyl lead situation was completely different. It was very clear early on that the stuff was extremely toxic. Lead was already known to be toxic, and workers at the refineries were dying left and right due to exposure.

Slow down there.

Biodiesel is meant to be used in standard diesel engines and is thus distinct from the vegetable and waste oils...

I have no idea - but my anecdata point relates to a school friend who converted a van. It smelt like a fish and chip shop from a fair distance. It ran great until the home-brew water injection failed. It was parked on a slope and the water filled the cylinders. Turning it on was a rather violent attempt at compressing water.

Unfun fact, the person who invented tetraethyl lead gasoline additive also invented chlorofluorocarbons.

https://en.wikipedia.org/wiki/Thomas_Midgley,_Jr.

Why is it unfun? Is he evil for inventing things that later turned out to be harmful?

Apparently he indeed was evil: "On October 30, 1924, Midgley participated in a press conference to demonstrate the apparent safety of TEL. In this demonstration, he poured TEL over his hands, then placed a bottle of the chemical under his nose and inhaled its vapor for sixty seconds, declaring that he could do this every day without succumbing to any problems whatsoever. Midgley himself was careful to avoid mentioning to the press that he required nearly a year to recover from the lead poisoning brought on by his demonstration at the press conference."

I believe the grandparent was merely stating a piece of possibly interesting but not particularly useful knowledge that might normally be labelled a "fun fact", but didn't want to use the word "fun" when mentioning inventions that caused thousands of deaths.

In Poland it's already taxed. If you burn oil in your engine that was not intended for that purpose (and not taxed for that purpose) you should go to your tax office and pay the missing tax. Of course this is met with silent "piss off" from all the people who are doing it.

Not to mention the simple fact that it's hardly a waste product in most places as-is.