Nedbrytning av propylenglykol i uppsamlingssystem för avisningsvätskor : En studie utförd vid Stockholm Arlanda flygplats

Sammanfattning: Deicing fluids based on Propylene glycol are used at Stockholm Arlanda airport to remove or prevent ice on aircrafts. The high oxygen demand of propylene glycol can cause oxygen depletion in rivers downstream from the airport if not collected. Mass balance calculations made by Swedavia indicate that the actual amount of gathered propylene glycol is underestimated. Suspicions that propylene glycol is degraded in the stormwatersystem designed to collect deicingfluids, called the B-glycolsystem, have to be investigated in order to establish with certainty that no propylene glycol in other ways leaves the B-glycol system. The purpose of this study was to determine if degradation of propylene glycol is present in the B-glycol system and also to estimate the extent of the degradation. Propylene glycols high biological oxygen demand can cause oxygen depletion in waters downstream from Stockholm Arlanda airport if not collected. To investigate if degradation is present, three collection tanks in the B-glycolsystem were studied. Temperature and oxygen measurements were performed and samples were collected for analysis of degradation products. A degradation experiment was performed in laboratory and the accumulation times for water in the collection tanks were compiled from surface level data. These accumulation times were later used in a computational model to estimate the extent of the degradation. The results from the analysis showed that the degradation product n-propanol was present in the B-glycolsystem even in the coldest months which indicates that degradation of propylene glycol occurs in the system. Low oxygen levels were measured and a number of visual indicators were observed such as biological growth on the walls of the wells. The results from the degradation experiment showed decreasing TOC- and oxygen levels. The total degradation of propylene glycol was estimated by the computational model to be 1 – 2.5 parts per thousand of the total usage of propylene glycol at Stockholm Arlanda airport. It can be concluded that aerobic degradation of propylene glycol occurs in the B-glycolsystem even during the coldest months of the deicing period. The computational model gives an indication of the magnitude of the degradation in the parts of the B-glycolsystem that was studied. However, no concrete conclusions regarding the extent of the degradation can be drawn due to the many assumptions made in the calculations with the model.