Application of case-based reasoning to support constructed wetland management

The aim was to predict the treatment efficiencies for gully pot liquor of experimental vertical-flow constructed wetland filters containing common reed and different aggregates. Six out of twelve filters received inflow water spiked with metals. For two years, hydrated nickel and copper nitrate were added to sieved gully pot liquor to simulate contaminated primary treated storm runoff. For those six constructed filters receiving heavy metals, an obvious breakthrough of dissolved nickel was recorded after road salting during the first winter. However, a breakthrough of nickel was not observed since the inflow pH was raised to eight after the first year of operation. During the second year, reduction efficiencies of heavy metals, five-day biochemical oxygen demand (BOD) and suspended solids (SS) improved considerably. Concentrations of BOD were frequently <20 mg/l, an international threshold for secondary wastewater treatment. This is likely due to biomass maturation and the increase of pH. Case-based reasoning (CBR) incorporating fuzzy theory was applied to predict BOD and SS, and to demonstrate an alternative method of analyzing water quality performance indicators. The CBR method was successful in predicting if outflow concentrations were either above or below the water quality thresholds. Corresponding predictions of compliance were >77%.