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Urban flooding is of growing concern due to increasing densification of urban areas, changes in land use, and climate change. The traditional engineering approach to flooding is designing single-purpose drainage systems, dams, and levees. These methods, however, are known to increase the long-term flood risk and harm the riverine ecosystems in urban as well as rural areas. In the present paper, we depart from resilience theory and suggest a concept to improve urban flood resilience. We identify areas where contemporary challenges call for improved collaborative urban flood management. The concept emphasizes resiliency and achieved synergy between increased capacity to handle stormwater runoff and improved experiential and functional quality of the urban environments. We identify research needs as well as experiments for improved sustainable and resilient stormwater management namely, flexibility of stormwater systems, energy use reduction, efficient land use, priority of transport and socioeconomic nexus, climate change impact, securing critical infrastructure, and resolving questions regarding responsibilities.

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Methanol and ethanol have been used for three years as external carbon sources in a nutrient removal system based on pre-precipitation and post-denitrification in a single sludge activated sludge plant. Based on these long-term experiences it has been shown that the nitrogen standards of 8 mg N/l in the effluent wastewater can be met with both carbon sources. The process entails operational flexibility and the possibility to optimize the nitrogen removal due to seasonal variations in influent wastewater characteristics. Very high specific nitrate utilization rates were measured in the system with the use of external carbon sources. Rates of around 10 mg N/g VSS.h were reached with ethanol and around 3 mg N/g VSS.h with methanol. These rates were much higher than experienced in a pre-denitrification system with the use of the influent organic material as carbon source for denitrification. A start-up with the addition of ethanol led to a direct response of the system while a start-up with methanol resulted in a much longer adaptation period before full effect of the carbon source added was reached.