Performance evaluation of representative Wildfowl & Wetlands Trust constructed wetlands treating sewage

Data collected from five Wildfowl & Wetlands Trust constructed wetland systems offering a range of styles and inflow water types between 2005 and 2009 were examined and compared to identify long-term trends in nutrient removal. Ammonia-nitrogen concentrations were reduced between 31.9 and 96.8%. In contrast, the concentrations of nitrate-nitrogen and total oxidised nitrogen in the effluent exceeded the influent in many of the systems. Reduction in ortho-phosphate-phosphorus and total phosphorous were between -10.5 and 87.6%, and between 6.9 and 92.5%, respectively. Removal efficiencies of biochemical oxygen demand were between 0.0 and 87.3%, and reductions of total suspended solids ranged from -249.3 to 57.6%. Ammonia-nitrogen reduction was effective during summer. Long-term nitrogen removal has been efficient and consistent. However, phosphorous reduction was only sufficient during the early stages of operation, and generally declined as the wetland aged.