Nutrients and solids removal in bioretention columns using recycled materials under intermittent and frequent flow operations

Abstract

This research investigated the fate and removal of nitrite (NO₂-N), nitrate (NO₃-N), orthophosphate (PO₄-P), and total suspended solids (TSS) in two bioretention columns, which were designed with three recycled materials. The first column was packed with Recycled Concrete Aggregate (RCA). The second column was a Layered Media (LM), which has layers of RCA with crushed glass and rice husks. The columns were tested under intermittent and frequent operations of synthetic runoff with low and high feed concentrations. The effect of inflow concentration, antecedent dry days (ADD), column age, and the anticipated number of events (EN) was also statistically analyzed on the performance of columns. Depending on column types, nutrient removal was significantly (p < 0.05) increased under frequent flow operations by 26-53% over intermittent. However, TSS removal was notably (p < 0.05) increased by 23-35% under intermittent operations over frequent. Overall, LM showed an increased NO₂-N (92 ± 2%) and NO₃-N (88% ± 2%) removal under low feed frequent operations and TSS removal (97% ± 2%) under initial intermittent operations. On the contrary, RCA showed a maximum of 99% PO₄-P removal under high feed frequent operations. Results showed that the nutrient outflow concentration was found to have a negative correlation with EN and column age and a positive correlation with ADDs throughout the experiments.

Keywords: Antecedent dry period; Green infrastructure; Layered media; Nitrogen; Phosphorus; Synthetic runoff.