Micro-pollutant removal in stormwater biofilters : A preliminary understanding from 3 challenge tests

Biofilters are often used as treatment systems for urban stormwater runoff and have been shown to efficiently reduce nutrient loads. However, there is limited knowledge on how biofilters perform reduction of micro-pollutants in stormwater. This topic is of high importance if we are to harvest stormwater for human uses and in particular treat it to potable standards. This study investigated the micro-pollutant removal efficiency of two field-scale stormwater biofilters dosed with seminature stormwater, which included some key stormwater micro-pollutants (THMs, PAHs, TPHs, phthalates, halogenated phenols, glyphosate, and triazines). The results show excellent removal of PAHs, TPHs, phthalates and halogenated phenols, while there are variable levels of removal of glyphosate, triazines and chloroform. The outflow concentrations varied with the total pore volume over three tests, with the two cells having very different removal efficiencies. This preliminary study confirmed that in-situ challenge tests could be carried out to validate stormwater harvesting biofilters. It also suggests that design characteristics have a large impact on micropollutant removal, and a targeted lab study is needed to optimise biofilter design for this important function.