Treatment of gully pot liquor containing heavy metals with constructed wetlands in Scotlands

The aim of this investigation was to assess the treatment efficiencies for gully pot liquor of 12 experimental vertical-flow constructed wet and filters containing Phragmites australis (Cav.) Trin. ex Steud. (Common Reed) and filter media of different adsorption capacities in a cold climate. Seven of the twelve filters received inflow water spiked with heavy metals. For one year, hydrated copper nitrate and hydrated nickel nitrate were added to sieved gully pot liquor to simulate contaminated primary treated storm water runoff. The inflow concentrations for dissolved copper, nickel and nitrate-nitrogen were approximately 1.0, 1.0 and 1.45 mg/l, respectively, which represent mean loading rates of 0.063 g/m²/d for Filters 2 and 7 to 11, and 0.115 g/m²/d for Filter 12. For these filters receiving metals, an obvious breakthrough of dissolved nickel was recorded after road gritting and salting during winter. Sodium chloride was responsible for nickel leaching. Reductions of copper, nickel, biochemical oxygen demand and suspended solids were frequently insufficient compared to international secondary wastewater treatments standards. Moreover, the overall filtration performance for all filters was similar.