Oslo Airport Gardermoen (OSL) is situated over a ground water reservoir, and collection and handling of spent de-icing fluids is therefore of major importance. OSL have chosen to handle low- and medium strength spent fluids in cooperation with a nearby municipal wastewater treatment plant (WWTP). Medium strength fluid is used as a carbon source for nitrogen removal, and thus used as a resource. Low strength fluid is pre-treated in an aerobic biofilm reactor before it is routed to the plant inlet.Prior to the choice of solution for disposal of the fluids, investigations were performed in laboratory and pilot scale. The efficiency of the fluid as a carbon source for denitrification was studied in parallel with ethanol and methanol as well documented carbon sources. The achieved denitrification rates were comparable with those achieved with methanol, while the necessary addition of carbon source was slightly higher for spent de-icing fluid than for methanol. The treatment plant has been operating for almost 9 years, with operational results confirming the spent de-icing fluid to be appropriate as a carbon source.The possible toxicity and low degradability of some of the additives were particular concerns, and was studied for both aerobic and anaerobic biological processes. While the rather toxic fatty alcohol ethoxylate was easily biodegradable when sufficiently diluted, the additives benzotriazole and sodium petroleum sulphonate were hardly or not biodegradable. The latter two additives were therefore substituted. The laboratory scale results were confirmed in full scale prior to this substitution.The pre-treatment of the low strength spent deicing fluid in an aerobic biofilm reactor followed by coagulation and dissolved air flotation was tested in laboratory and pilot scale. The pre-treatment produces water suitable for discharge to the biological stage at the municipal WWTP. This technical solution is implemented, with operational results confirming that this integrated treatment of spent de-icing fluids in a WWTP is a good solution.