Bioretention Media for Enhanced Permeability and Phosphorus Sorption from Synthetic Urban Stormwater

A high-flow medium (HFM), modified with two aluminum-based amendments, alum and partially hydrolyzed aluminum (PHA), is used to achieve enhanced dissolved P removal and promote high infiltration of runoff in urban stormwater control measures (SCMs). Compared with unmodified HFM, the sorption of adenosine monophosphate (AMP), myo-inositol hexakisphosphate (IHP), and inorganic phosphate using PHA-modified HFM is increased by factors of 80, 8, and 163, respectively. Column-scale kinetics studies show that P removal using modified HFM is markedly faster than that using unmodified HFM; PHA-modified HFM reduces P concentrations to <0.01mgP/L within a contact time of <1min. Alum-modified and PHA-modified HFM exhibit different sorption preferences for the three different P species investigated. Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area analyses support the underlying sorption mechanisms for the enhanced P removal by the amended HFM. Compared with alum, PHA modification is easier to implement because it requires a lower liquid:medium ratio, less consumption of alkalinity, and no required mixing. Therefore PHA-modified HFM is recommended for use in high-flow bioretention systems to provide effective and efficient P removal.