Purification Efficiency of Bioretention with Modified Media under Varied Rain Intensity and Drying Conditions

Abstract

Bioretention media plays a vital role in bioretention systems for controlling rainfall runoff volume and removing pollutants. In this work, three different types of modified media used in bioretention including a mixture of river sand, soil, biochar, and volcanic (BV), and BVS (BV + iron-coated sand) were assessed. To evaluate the purification efficiency, the removal of total nitrogen (TN), total phosphorus (TP), ammonium (NH4+–N), and chemical oxygen demand (COD) in rainfall runoff were measured under different rainfall intensities and antecedent dry times (ADTs). As a result, the bioretention system with BVS was more beneficial to the removal of TP under variable ADT and rainfall intensity. The bioretention system with BVZ possessed much better performance in TN removal, which was more than 2.2 times that of BV and BVS, and lower nitrogen leaching during long ADT due to its great affinity for nitrogen. All three bioretention systems have better removal efficiency of NH4+–N during a longer ADT for the occurrence of nitrification. The three bioretention systems also exhibited excellent COD removal that could even reach over 95% after the microorganisms multiplied. Based on the analytic hierarchy process (AHP) with cost, purification, and infiltration, the comprehensive performances of modified media were as follows: BVZ (0.926)>BV (0.723) > BVS (0.696).