VERBAL - The Vertical Flow Reed Bed at Leidsche Rijn. A natural way to filter urban water

This project aimed to demonstrate a successful system for improving the quality of relatively clean surface water for a complete urban area that could last at least 30 years. It sought to test a 1 ha filter to define the optimal set up of a future 6 ha vertical reed bed filter in the residential area Leidsche Rijn. It also sought to design a general applicable model for the design, maintenance and control of vertical flow reed beds in other settings. Results proved that vertical flow reed bed filter is effective at cleaning low polluted surface water in a closed system in a large-scale urban area, making minimal use of chemicals and energy and blending naturally into the landscape. To monitor the quality of the different water flows, a number of continuous measurements were taken, as well as regular water samples to measure the levels of nitrate and phosphate. Removal rate was very high and the collected data provided sufficient information to construct an optimal full-scale filter and fit it in to the water system at Leidsche Rijn.