Evaluation and Optimization of Bioretention Media for Treatment of Urban Storm Water Runoff

Bioretention is a relatively new urban storm water best management practice. The objective of this study is to provide insight on media characteristics that control bioretention water management behavior. Eighteen bioretention columns and six existing bioretention facilities were evaluated employing synthetic runoff. In columns, the runoff infiltration rate through different media mixtures ranged from 0.28 to 8.15  cm/min at a fixed 15 cm head. For pollutant removals, the results showed excellent removal for oil/grease (>96%). Total lead removal (from 66 to >98%) decreased when the total suspended solids level in the effluent increased (removed from 29 to >96%). The removal efficiency of total phosphorus ranged widely (4-99%), apparently due to preferential flow patterns, and both nitrate and ammonium were moderate to poorly removed, with removals ranging from 1 to 43% and from 2 to 49%, respectively. Two more on-site experiments were conducted during a rainfall event to compare with laboratory investigation. For bioretention design, two media design profiles are proposed; >96%  TSS, >96%  O/G, >98%  lead, >70%  TP, >9%  nitrate, and >20%  ammonium removals are expected with these designs