Hydrologic characteristics and nitrogen removal performance by different formulated soil medium of bioretention system

Bioretention systems have been widely used to reduce stormwater runoff pollution. However, there are few researches on how to ensure the nitrogen removal performance while meeting the requirements of the hydrologic performance of the bioretention systems. Formulated soil medium is a key factor affecting hydrologic characteristics and nitrogen removal performance. Therefore, seven bioretention systems have been constructed with different formulated soil medium, including three regional guidelines groups, three different modifier addition groups, and one control group. The effects of different formulated soil medium on hydrological performance and nitrogen removal performance of bioretention systems were evaluated. The results showed that the infiltration rate, water retention volume rate and nitrogen leaching risk could be significantly reduced with the silt content increasing and the addition of modifiers, while the moderate silt content (10%) had excellent NO3–N removal efficiency (71.6% ± 19.8%). AC as a high-efficiency soil improver can be reasonably used in practical projects. Additionally, it was found that the capillary/non-capillary hydrophobicity of formulated soil might be an important indicator for assessing the nitrogen removal performance through the correlation analysis between the physical and chemical properties of the formulated soil medium, hydrological performance, and nitrogen removal performance. It is difficult to achieve the best hydrological performance and nitrogen removal performance in the bioretention system simultaneously, thus it is necessary to find a more suitable soil medium formula to balance the two performance. This study may contribute to a greater understanding of the influence of formulated soil medium on hydrological performance and nitrogen removal performance in bioretention systems. [Display omitted] •The hydrological characteristics of bioretention system is affected by soil medium.•Activated carbon is recommended as a high-efficiency soil improver.•The percentage of silt is a key factor that affects the performance of system.•Capillary/non-capillary porosity can evaluate and predict NO3–N removal property.