Biofiltration systems for optimised stormwater management in urban areas

Decrease in permeable areas due to urbanisation and increased frequency of extreme event due to climate change are putting more pressure on conventional drainage systems. This is leading to more frequent urban floods and water receptor deterioration. Sustainable drainage systems are green infrastructure that aim to achieve multiple benefits while managing stormwater runoff. Among these infrastructures, biofiltration systems are a promising retrofit option for site-constrained urban areas due to the vertical arrangement of treatment stages that leads to a relatively compact footprint. Existing knowledge about the influence of their design and configuration on hydrological, stormwater pollutant removal and long-term performance is limited and this has been identified as a barrier to their widespread uptake. Laboratory test were used to study the influence that high hydraulic conductivity amended biofilters have on removal performance and plant fitness.
Media were tested in laboratory and selected based on their physical-chemical and hydraulic characteristics to build a biofilter designed to treat dissolved pollutants. Non-vegetated test with control biofilters and configuration amended with Zeolite, GAC, and a mix of both, were dosed with the equivalent of an average annual runoff volume of Leeds (650 L) with synthetic stormwater simulating typical pollutants concentration of urban runoff areas. Results for this test informed the design that underwent a second phase were mesocosms in greenhouse were dosed with semi-synthetic runoff and monitored for 6 months for nutrients, heavy metals, and hydraulic conductivity. Biofilters were planted with two plant species characterised by different root system, Carex flacca and Deschampsia Cespitosa. At the end of the experiment biofilters were disassembled to investigate the fate of pollutants in media and vegetation. Results suggests that high hydraulic conductivity amended biofilters increase the removal performance of dissolved pollutants without compromising plant fitness possibly reducing the footprint of this system.