An improved approach to design bioretention system media

Bioretention modified media consists of modifier, soil, sand, and organic matter (OM), which was applied to clean rainfall runoff pollutants and control flood. These should support plant growth, cost-effectiveness, local availability besides rainwater runoff and its pollution control. A modified bioretention media design approach was developed, to determine whether the modified media could compensate the deficiency of infiltration and/or purification ability for traditional bioretention soil mixing (BSM) and undisturbed soil. Taking the soil conditions of a typical area in northwest China as an example, we defined the BSM as the mixture of river sand, soil and wood chips, and the ratio was 65:30:5 by mass, and modified media are a mixture of BSM with modifiers. The characteristics of ten modifiers were tested, and the proportions of BSM and modifiers were determined though Langmuir adsorption isotherm mainly. The infiltration capacities of modified media were over 220 mm/h, and they were more than 3.4 times that of undisturbed soil. We also got the maximum adsorption capacity and longest lifespan media which were BSM + 10% water treatment residuals (WTR) for soluble reactive phosphorus (SRP), and BSM + 10% green zeolite (GZ) for ammonia though batch and mini-column experiments. Based on analytic hierarchy process (AHP), considering infiltration, water-holding adsorption, lifespan, and cost, the comprehensive performance of modified media is as follows: BSM + 10% flyash (0.2683) > BSM + 10% GZ (0.2589) > BSM + 10% WTR (0.2443) > BSM + 10% medical (0.1553) > BSM (0.0731). The results of this study will contribute to a greater understanding of adsorption mechanism of bioretention system media, contributing to the design and evaluation of bioretention efficient media.