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UBC Theses and Dissertations

Minimizing the environmental impact of urea de-icer from airport runways Ferguson, Keith Donald

Abstract

Urea finds common use at most airports in Canada where it is used as an anti-icer or de-icer. Urea contains up to 46% nitrogen which finds its way to the environment around the airport. Of the potential environmental problems, eutro-phication of lakes is of the most concern in British Columbia. Several methods for minimizing the impact of urea de-icer were considered. Urea can be hydrolyzed to ammonia by the common soil enzyme urease on an airport runway and this ammonia can volatilize to the atmosphere. The natural enzymatic activity on runway test sections was found to cause less than 0.5% of the applied urea to hydrolyze with no volatilization after 90 minutes, at room temperature. Supplemental urease was added to pyrex models to test the effect of various conditions on hydrolysis and volatilization. Thirty-two tests were performed at various temperatures (-4, 0, 4, 120C), urease additions (100, 200, 500, 750 mg/model), ice thicknesses (3, 5, 8 mm), urea applications (0.45, 0.9, 1.8 kg/70m2), urea types (Cominco Industrial and Forestry Grade, Sherritt Gordon Mines Industrial Grade) and solar radiations (50 and 100 BTU/h-ft2). An addition of 500 mg urease to the model cuased hydrolysis of 65% of the applied urea and volatilization of 1% at 12°C. Lower temperatures produced poorer results. Relative to the high costs and low efficiency, control of urea through hydrolysis and volatilization on an airport runway is impractical. Biological nitrification-dentrification, breakpoint chiorination, selective ion exchange, and air stripping have high nitrogen removal efficiencies under normal conditions, but are not suitable for winter airport operation. Passage of urea through soil can be an effective method for removal of this de-icing agent if the quantity of nitrate and urea leached to surface waters is low. Published data indicates that soil could be 75-90% efficient in controlling nitrogen loss to surface and ground waters. A reduction in the quantity of urea used on a runway would decrease the environmental impact. The yellow aura produced by the urea-Ehrlich reagent reaction, was used to monitor the movement of urea in 5 mm thick ice at -4°C. After 90 minutes from placement on the ice, the Cominco Forestry Grade aura covered the largest area. On a weight basis, however, the Sherritt Gordon Mines covered the largest area. This greater aura coverage is due to the smaller particle size of the Sherritt Gordon Mines pellets. If the size of the aura can be correlated with the ease of removal of ice from an airport runway, then the Sherritt Gordon Mines-Industrial Grade urea is more effective as a de-icer than either of the two Cominco grades under the conditions tested. Further research is recommended in optimizing the use of urea and soil treatment.

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