No untreated rainwater shall be discharged in Copenhagen. In the “Straussvej” Courtyard Pilot Project in the center of Copenhagen, rainwater is collected from rooftops and stored in a system of wetlands, gutters and a central swimming pond, the centerpiece of the new Straussvej courtyard. Sponge City with temporary water surfaces.
Water is experienced in the wet seasons and disappears during long dry periods. Rainwater from the roof and walkways is collected and pre-cleaned through natural ground passages. The water then flows into a soil filter located under the green area. This cleans the water and directs it into the swimming pond. The overflow skimmer of the swimming pond drains the surface water. This is fed again to the soil filter to achieve a steady dilution in the swimming pond.
We used our numerical simulation tools to design the water treatment system and positioned it in close coordination with the open space planners and the client. According to model calculations, phosphorus concentrations of 5 to 31 µg/l Ptot-P occur. So far, the measured concentrations were 5 – 15 µg/l.
Is the water suitable for bathing?
Yes, despite the high E.coli entries coming from the rainwater through the roofs, biological water treatment maintains the E.coli concentrations under 50 CFU/100 ml. The removal efficiency per soil filter passage is 1-3 log levels.