The microbiology associated with glycol removal in constructed wetlands

During the winter months, the application of large quantities of glycol based anti- and de-icers to aircraft and runways poses a serious threat to receiving waters because of their toxicity and BOD effect. The orthodox approach has been to store runoff waters in aerated lagoons before discharge to receiving waters or to sewage treatment works. In the development of a pollution control strategy for Heathrow Airport Ltd. (HAL), a combination of alternative methods for treatment are being considered, and amongst these is the use of constructed wetlands on a pilot scale. Results from this study indicate that most constructed wetland plants and substrate micro-organism populations throughout the beds are not adversely affected by airport runoff or exposure to shock-loads of glycols at initial total concentrations of 1180mg/1 and 632mg/1 in the subsurface and surface flow reedbeds respectively. Apart from Typha spp, the aquatic macrophytes have adapted well to the exposure to airport runoff. Glycol removal efficiencies have improved as the beds have matured, and average removal efficiencies of 78% for the sub-surface system and 54% for the surface system have been recorded. Complimentary monitoring of substrate micro-organism populations prior to and after glycol dosings have shown that aerobic microbial groups of bacteria, fungi and actinomyctes, are present in higher numbers (105-107 CFU/g substrate dry weight) than their anaerobic counterparts (103-105 CFU/g substrate dry weight). In the laboratory, studies have shown fungi and bacteria to be most tolerant of glycol, with several strains able to utilise these compounds.