Comparison of urban stormwater plant biofilter designs for nutrient and metal removal in South Africa

This paper presents a comparison of six plant biofilter designs for urban stormwater quality improvement and reports on their performances. Thirty-six columns were populated with the endemic South African plant Prionium serratum, representing plant biofilter designs which incorporate different pollutant removal mechanisms in the biofiltration process. The experimental biofilter columns were subjected to low, typically observed and high urban nutrient and metal synthetic stormwater pollution for five months. Significant loads of NH3-N and dissolved Cd, Pb and Zn were removed, whereas removal of NO3--N, PO43- -P and dissolved Cu was more variable. The most efficient design was found to include standard plant biofiltration techniques with upflow filtration, plenum aeration and a saturated zone supporting anaerobic microbial activity. It was found that the most efficient design removed on average 96% of urban stormwater nutrient and metal loads.