Performance of downpipe treatment system for removal of dissolved metals from roof runoff

Abstract

Untreated metal roof runoff can contribute elevated zinc and copper to receiving waterways, with associated ecotoxic impacts on the aquatic ecosystem. The majority of the metals in roof runoff are in dissolved form, which can be difficult to remove with conventional stormwater treatment systems. Treatment materials such as limestone and zeolite are capable of removing dissolved metals, but most research to date has only assessed the performance of such materials using synthetic runoff and long contact times. This study assessed the performance of limestone, zeolite and waste mussel shells in a vertical downpipe configuration with short contact time using actual metal roof runoff. Metal removal was compared under flowrates of 1 L/min and 3 L/min, material compaction level (less/more), and material depth (1 m and 0.5 m). A 93-99% reduction was achieved in dissolved zinc by all treatment materials for all flowrates, compaction levels and depths. Higher variance in dissolved Cu removal rates were observed, with material depth found to have the greatest influence on performance: 84-99% removal rates were achieved by the three materials at 1 m depth, but for 0.5 m depths, 44-99%, 34-92%, and 47-93% removal were achieved by zeolite, limestone, and waste mussel shells respectively. The mussel shell removal performance was comparable to zeolite and limestone, yet it provides the added benefit of using a waste resource that would otherwise be disposed of to landfill. While this study demonstrates the potential of waste mussel shells for dissolved metal treatment, long term field trials and experimental analysis of the removal mechanisms of waste mussel shells would enable optimisation of this treatment technology.