Impacts of filter media, temperature and nutrient conditions on treatment of airport runoff

Airports in cold climatic conditions represent a stormwater management challenge due to the large amounts of impervious surfaces and the unique chemicals used to minimize the unfavourable effects of icy conditions on safety. These chemicals are highly mobile and pose severe risks to receiving surface and ground waters. To tackle the water quality problems at airports, subsurface flow wetlands (SSFW) have been proposed as treatment solutions due to their relatively low construction and maintenance costs. However, these systems e.g., in Paris, London, and Edmonton, have had a large footprint; in addition to large reserved land areas and long hydraulic retention times, the artificial addition of nutrients is commonly needed. In this study, laboratory-scale experiments were carried out with the aim to understand the influence of different filter media (gravel, expanded clay, biochar) on the performance of these systems under unfavourable cold conditions. The investigation of both nutrient and organic load removal, as well as the factors influencing filter performance, is required to develop optimal solutions for the treatment of urban runoff. All materials showed promising results, yet aeration was needed for optimal filter performance. The results can be used to increase the overall performance of the treatment systems and reduce the environmental footprint of airports. The results of the study are utilised in the planning of the SSFW at the Helsinki Airport, Finland.