Impacts environmentaux, toxicité et biodégradation des dégivrants pour avions
Date de publication1996
Glycol based fluids are used to deice and anti-ice aircraft surfaces before takeoff of airplanes. It is strictly for security purposes that large volumes of aircraft deicers are used at airports. Hundreds of thousands of liters are used every year at small airports and millions of liters in the case of major airports. During deicing or anti-icing activities, an appreciable amount of deicing fluids mix with airport runoffs and finds its way into nearby streams and lakes. The objectives of this research is (1) to determine the role of temperature and initial concentration of deicers on biodegradation process, (2) to evaluate the conditions of biodegradation of deicers in a municipal biological treatment plant, and (3) to study the toxicity of deicers for different aquatic species. Results of the experiments indicate that the biodegradation rate of deicers depends on temperature and the ratio of initial concentration of deicers to microorganisms (C[subscript i]/X[subscript i]). The rate of removal of the deicing chemical follows a first-order model. Degradation rate coefficient (κ) at 20 ± 2 °C varies from 1.6 d[superscript -1] for C[subscript i]/X[subscript i] = 0.7 to 0.07 d[superscript -1] when C[subscript i]/X[subscript i] = 19.5. At a temperature of 10 ± 1°C, κ decreases to 0.72 when C[subscript i]/X[subscript i] = 0.7. No materially different k values κ values (0.05 d[superscript -1]) were recorded for the experiments at 4 ± 1 °C when C[subscript i]/X[subscript i] increased from 1.8 to 3.2. The results obtained suggest that biodegradation of deicers will take place in segments of the streams located far downward the discharge point. However, high concentrations at the discharge point could turn out to be toxic to aquatic biota. It is possible to treat deicing fluids at a municipal biological treatment plant. Biotest shows that deicers were slightly toxic to the microorganisms of activated sludge. The toxic deicer concentration responsible for a 50% reduction of the respiration rate is about 30% in volume. The addition of deicing fluids did not have any impact on the pH of the treatment plant effluent; however it exerts an additional oxygen demand. The presence of deicing fluids in the bioreactor could delay nitrification and, increases the filamentous growth. The injection of deicing fluids did not impair the treatment plant efficiency for BOD[subscript 5], COD and SS removal. Also, values of BOD[subscript 5], SS and phosphorus of the effluent were within the range usually recorded at the treatment plant. Chemical analyses demonstrate that deicing fluids did not have an impact on the dehydrated sludge. Deicers and especially anti-icers are more toxic than pure glycol. Green algae Selenastrum capricornutum turns out to be more sensitive than marine bacteria Photobacterium phosphoreum. Inhibitory concentration IC[subscript 50]-30 min of pure ethylene glycol for Photobacterium phosphoreum is estimated to 84 780 mg/L while IC[subscript 50]-30 min of de-icing fluid UCAR XL 54 and anti-icing fluid UC 5.1 are 25 752 mg/L and 5 425 mg/L respectively. In the case of Selenastrum capricornutum, IC[subscript 50]-96 h of pure ethylene glycol is estimated to 5 412 mg/L. This result is presently used by Environment Canada in the derivation of the water quality guideline on ethylene glycol. Inhibitory concentration IC[subscript 50]-96 h of de-icing fluid UCAR XL 54 and anti-icing fluids UCAR ULTRA and UC 5.1 are 2 575 mg/L, 2 785 mg/L and 41 mg/L respectively.
- Génie – Thèses