Nutrient Removal Performance of Advanced Bioretention Systems: Results from Three Years of Mesocosm Studies

This paper presents selected results of a 3 year study of nutrient retention responses by bioretention systems. Several amendments to the media were investigated for their long term dissolved phosphorus (P) retention performance. Advanced media containing water treatment residuals (WTRs) effectively retained dissolved P. After nearly five decades of P loads, 96% of the orthophosphate (PO4-P) and 79% of total dissolved P (TDP) was retained. An innovative outlet control device was installed to extend retention time in anticipation it would improve total dissolved nitrogen (TDN) retention. Even at very high hydraulic loading rates, retention in the outlet controlled discharge system was 60% for TDN and 63% for oxidized N (NOx-N). This was significantly better than the free discharge retention of 27% and 25%, respectively. Under more typical hydraulic loads, TDN retention was as high as 78% and NOx-N retention was as high as 94%. Under flow weighted loading concentrations approaching 9 mg-l−1, TDN retention was as high as 73%, with mass load retention of TDN as high as 3.6 g-m−2 per event. These results show the promise of deploying advanced bioretention systems to meet nutrient removal requirements.