Nutrients and Atrazine Removal From Simulated Urban/Suburban Runoff Using Column-Scale Bi-Phasic Bioretention Rain Garden System.

Storm water runoff has been identified as a significant non-point source of pollution for surface water bodies. Rain gardens are small landscaped storm water bioretention areas that have the potential to reduce peak runoff flow and improve water quality in a natural and aesthetically pleasing manner. In this study, we examined column scale versions of two types of bioretention rain gardens—a conventional bioretention system and a new bi-phasic bioretention system. The bi-phasic bioretention system is designed to increase retention time and removal efficiency of runoff pollutants by creating a sequence of anaerobic to aerobic conditions. The objectives of this study were (1) to compare hydraulic performance of the two different bioretention designs, and (2) to evaluate the effect of carbon substrate availability on pollutant removal efficiency. A total of five simulated runoff events with various concentrations of runoff pollutants (i.e., nitrate-N, phosphate-P, and atrazine) were applied to both conventional and bi-phasic bioretention columns once every five days. Both bioretention systems showed good removal efficiency of phosphate-P (89 to 100%) and atrazine (84 to 100%). However, significantly higher removal of nitrate-N was observed in the bi-phasic bioretention columns (42 to 57%) compared to the conventional bioretention columns (27 to 29%) (P<0.001). Addition of carbon substrate in the form of glucose clearly showed that removal efficiency of nitrate-N significantly increases as C/N ratio increases, achieving up to 81% of net nitrate-N removal at a C/N ratio of 2.0. This study demonstrated the importance of retention time and environmental conditions (i.e., aerobic/anaerobic conditions and available C substrates) for bioremediation of pollutants, especially nitrates, in bioretention rain gardens.