Assessing the environmental and economic efficacy of two integrated constructed wetlands at mitigating eutrophication risk from sewage effluent

The nutrient removal efficiency of two integrated constructed wetlands (ICWs) installed at commercial wastewater treatment plants (WWTPs) in Norfolk, UK, is assessed – the River Ingol ICW (1 year old) and the River Mun ICW (5 years old). Analysing water samples collected across the ICWs between February and September 2019, significant reductions in both effluent nutrient concentration and load were recorded. At the River Mun ICW, mean nitrate and phosphate concentrations were reduced by ~63% across the wetland, whilst nutrient loadings were reduced by ~57%. At the River Ingol ICW, mean nitrate and phosphate concentrations were reduced by ~30%, whilst nutrient loadings were reduced by ~70%. Economically, the total capital cost of both ICWs was comparable at £31-39 per person served. Overall, this study demonstrates ICWs can significantly reduce the eutrophication risk associated with WWTP discharges and can do so whilst providing a cost-effective alternative to conventional tertiary wastewater treatment.