Collectively, service stations would seem to collect tremendous amounts of old anti-freeze. Given how environmentally dangerous this substance might be (in large amounts), how do they go about disposing of it?
And how do they capture the watered-down solution that’s used to flush out a radiator?
Larger service stations can actually recycle the coolant. It’s filtered down to a pretty low micron count, checked for, I’m assuming, acidity or dissolved contaminants, then they add a refresher additive mix to it, and put it back in the car.
However, as one might expect, it’s an expensive machine and process- though for a high-volume installation, the per-gallon cost can be lower than new.
As for overall disposal, I’m not sure. I take my used stuff to the City Dump… er, Solid Waste Management Facility, and turn it in on hazmat amnesty days. Where they take it from there, I have no idea.