Session C10 -  New materials to improve SCM performance

The LIFE ADSORB project (LIFE17 ENV/FR/000398) assessed the performance of vertical flow constructed wetlands, with or without adsorbing materials, for the treatment of urban stormwater runoff, particularly from road infrastructures. Implemented in a dense urban and environmentally sensitive area, the system achieved high removal efficiencies for suspended solids, COD, hydrocarbons, and several trace metals, while ensuring good ecological and landscape integration. Full-scale results indicate that the added value of the Rainclean® adsorbent layer is limited under the filter's operating conditions, suggesting that conventional constructed wetlands may offer a cost-effective alternative for the specific case studied here. However, laboratory studies of various adsorbent materials (activated carbon, biochar, zeolite) have shown that their performance varies depending on the pollutants targeted, opening the way to choices adapted to local conditions. The project also led to the development of a micropollutant module within the ORAGE software, providing a unique decision-making tool for designing and assessing the sustainability of this type of structure. Environmental monitoring revealed no adverse effects on biodiversity or the receiving water body.

Rapid urbanization has increased impervious surface cover, disrupting natural hydrologic processes and intensifying stormwater runoff volumes and peak flow rates, with climate change further heightening urban flood risk. Bioretention systems, a key Low Impact Development (LID) strategy, help mitigate these impacts by restoring hydrologic functions, yet their performance depends on engineered soil media that must balance filtration capacity with hydraulic efficiency. This study evaluates three engineered soil mixes composed of a 50:50 sand–soil base amended with increasing proportions of carbonized rice husk (CRH) through controlled column experiments assessing hydraulic performance (peak flow attenuation and volume reduction) and water quality performance based on total suspended solids (TSS) removal. Preliminary results indicate that the unamended control media provided the most consistent and balanced hydraulic detention performance, achieving >90% peak flow attenuation, up to 47 minutes lag time, and 120 minutes of hydraulic detention time that enhances TSS removal. However, simulation experiments are currently underway to evaluate runoff retention behavior and further validate the retention performance of the filter media, particularly under varying flow conditions and pollutant concentrations. These ongoing investigations will help clarify the role of CRH amendments in enhancing or diminishing overall bioretention functionality.

By using the potential energy of rooftop rainfall, stormwater can be gravity-conveyed into aboveground, non-invasive NBSsw. This enables space-efficient, no-dig management of even extreme events. Since 2019, the approach, which is known as pressurized stormwater-NBS, has been demonstrated in Copenhagen’s Green Climate Screen, which manages a 240 m² roof while doubling as a noise barrier. This paper describes the design, construction, and early performance of three novel elements for pressurized stormwater-NBS: the Rain Dyke, the Rain Mound, and the Raised Rainbed, implemented in a residential courtyard and receiving runoff from three roofs (≈190 m²). A three-point sizing method balances daily storage with evapotranspiration, infiltration up to the service level, and temporary aboveground storage for 100-year events. All elements are soil-based, maintaining a positive or even zero soil balance. The conveyance system uses frost-tolerant PE tubing and a mineral-wool filter. Observations confirm soil’s suitability as a sponge and construction material in evaporation-based-NBS and show seamless integration into residents’ recreational areas. Continued monitoring will document water balance and maintenance. The demonstration highlights pressurized stormwater-NBS as a scalable, low-carbon, low-cost solution for dense cities.

Stipes of the brown seaweed Laminaria digitata were used to fabricate a lightweight porous material for use in stormwater management e.g. as a compliment to nature-based solutions in space-limited environments. Sections of L. digitata were fibrillated, freeze-cast, and CaCl₂ crosslinked to produce structurally stable porous foams. The optimized sample showed ~90% porosity, good wet mechanical stability (~4 kPa), and high absorption capacities of ~2800% (deionized water) and ~3000% (stormwater). Microtomography confirmed an interconnected pore structure, and cyclic absorption tests demonstrated reusability. Seed germination on the material further supported its potential as a plant-compatible, biodegradable absorbent layer. Overall, the seaweed-based porous foam offers a promising nature-based solution for enhancing stormwater retention in e.g. green roof applications.