FILTRATION FOR METALS REMOVAL FROM STORMWATER

Filtration as a method of stormwater treatment was investigated in a 3-year study. Equilibrium and kinetic studies of metals’ capture were performed initially on twelve media. The three best performing media: peat-sand mix, compost, and zeolite were then selected for in-depth study. Upflow filters did not clog as easi ly as downflow, and longer-term performance was better in the upflow column. Metals were retained on the filters during anaerobiosis. Metal retention by the filters was no t different from what was observed in oxygenated environments. Tests also indicated that the heavy metals of concern remain strongly bound to the particulates during long expo sures at the extreme pH conditions likely to occur in receiving water sediments. Several medi a were tested in a pilot-scale device using water from a detention pond that drains a medium-density residential area. In this series of tests, the metals concentrations in the influent we re extremely low (near the detection limit of the analysis). When the influent metals concentrati on was higher, such as shortly after a rain storm, the filters proved effective at removing inf luent concentrations down to a level of approximately 10 ‐ 15 �g/L. Removals to concentrations lower than that wer e not possible on a consistent basis.