Similar to stfoulks above, in Pittsburgh, about twice a year there is a organized disposal center that sets up at a local park where you can drop off all kinds of hazardous liquids (Paints, fuel, oil, etc.). I would check for something similar in your area, as they would be less discriminating with a water oily mix. The one here charges on a per gallon rate.
Another suggestion to try: Perhaps fill the oily/water mix you have into old 1 gallon milk containers. It is my understanding that eventually, all the oil will separate from the water and lay on top. Once this occurs, poke a hole in the bottom of the milk container and let the water flow out, plug the hole when you get to the oil and drain that into a separate container. Eventually, you would be left with almost all oil. Then, you may be able to take it to a oil change center or, if your area has it, an organized recycling event.
Good luck with it.