Nutrients adsorption characteristics and water retention capacity of polyurethane–biochar crosslinked material modified filler soil in stormwater treatment

Bioretention systems are frequently used practice in stormwater treatment to remove pollutants from runoff and reduce waterlogging. The additive materials of filler soil in bioretention facilities play a key role in function realization, while the traditional additives have some problems of unstable removal efficiency on nutrients and decreasing hydrologic performance. Polyurethane–biochar crosslinked material (PCB) is a new polyurethane composite material, having low nutrients leaching quantities and strong adsorption capacity. To evaluate the feasibility of PCB as an additive material of filler soil, physicochemical properties tests, adsorption experiments, column experiments and soil water characteristic curve tests were conducted. With the addition of PCB, the particle grading and physicochemical properties of filler soil were optimized, increasing the specific surface area and cation exchange capacity. Through electrostatic attraction and chemisorption, PCB improved the adsorption quantities and further prolonged the lifespan of the filler soil owing to high cation exchange capacity and hydrophilicity of the PCB. Due to its porosity, the matric suction of the PCB modified filler soil increased significantly, as well as the permeability coefficient and saturated water content. The application of PCB expanded the contact area and time between stormwater and filler soil, and increased the infiltration channels, providing better conditions for adsorption reaction. The results suggest the addition of PCB optimized adsorption and hydrologic performance of the filler soil in bioretention facilities, showing promising potential for stormwater treatment.