Five times per year, my county’s recycling centers accept old coolant, along with used motor oil, oil filters, trans fluid, brake fluid, car batteries, scrap metal, pesticides, and other stuff that can’t go into the garbage. Isn’t it possible that you could locate something similar in your county?
Note: I edited this after referring to the list of acceptable items at the recycling centers. They classify all of this stuff as Household Hazardous Waste.