Simulation of pollutant deep transport characteristics in a partially infiltrated bioretention system

Insufficient research on improving filler characteristics and deep transport of pollutants in infiltration type bioretention systems. It is more important for loose media, high elemental background content, heavy pollution, long term operation and shallow groundwater areas. Modified bioretention systems were constructed, which take water treatment residues (WTR) and recycled aggregate of construction waste (RACW) as the modifiers. The results showed that the bioretention were effective in NH4+-N, TP, Cu and Zn purifying(average removal >= 69 %), but NO3--N leaching was the most obvious (-14 % to -268.9 % removal). High influent pollutants and low rainfall intensities achieved superior results. The contents of TN, TP and heavy metals in the media showed a general trend of upper > middle > lower vertically. A reliable HYDRUS soil physical model with different bottom boundaries was established (R-2 > 0.61). The simulation results showed that the increase in rainfall intensity and antecedent dry periods (ADPs) strengthened the driving force of downward water movement, and the deep infiltration capacity was enhanced. The results showed that the recharge rate for two partially infiltrated systems was 90.33 % (1#) and 72.5 % (2#), respectively, during the simulation period, which due to the differences in infiltration capacity (K-WTR = 1.20 cm/min, K-RACW = 1.84 cm/min). TN has a deeper transport depth than TP attribute to NO3--N leaching.