Evaporation is what we do.
We have a system using 55 gallon drums with the coolant from the machines going into the first one to get the tramp oil skimmed then into a drum with a wrap-around heater for evaporation. The coolant being evaporated is stirred and we have a fan blowing air over the top carry away the water vapor. The temperature of the evaporator tank is about 150 F, it is not necessary to boil it.
Initially the evaporator will loose about 10 to 15% of its volume in a day, but as the mix gets more concentrated the rate of evaporation goes down. We keep adding the skimmed waste coolant to the evaporator tank until the rate of evaporation is below about 5% per day then have this concentrated stuff picked up. Our total volume reduction is 80 to 90% I think.
We have never worried about the water vapor coming off, there is a bit of a smell but all this is done in a little shed outside the main shop and we do not have any close neighbors to complain.