Spatial Relationships of Suspended Solids and Phosphorus in Bioretention Cells

Abstract

Bioretention cells (BRCs) are a stormwater practice designed to infiltrate, store, and treat stormwater. These cells help to mitigate stormwater flow volume, flow rate, and remove nutrients. Suspended sediments that are commonly found in stormwater runoff decrease bioretention cell infiltration rates over time, rendering the practice less effective. Bioretention cells interact with water flow, sediment, and pollutants multi-dimensionally, thus 3-D studies are crucial for understanding their dynamics. The goal of this research was to assess how phosphorus flow is affected in non-clogged, semi-clogged and clogged BRC systems and evaluate if the current maintenance recommendations are sufficient.

Water was pumped through a 3-D flow cell (62.5 x 5 x 32.5 cm) and the spatial variability of the filtration media was analyzed. Trial 1 had no additional solids, Trial 2 was a “semi-clogged” system with 300 g of solids placed on half of the BRC media surface, and Trial 3 was a “clogged“ system with 600 g solids placed on the entire BRC media surface. For each trial, synthetic stormwater containing phosphorus fertilizer bound to iron oxides was pumped through the cell. After the stormwater flush, media samples of the cell were taken in a grid formation and analyzed for phosphorus concentration. Correlations between the amount of added solids and location of phosphorus adsorption were made by analyzing the BRC media grid. Water ponding time drastically increased with increased additions of solids, decreasing the hydraulic conductivity of the system.