Field studies of enhanced phosphorus removal from constructed wetland effluents

Two adsorptive media, a blast furnace slag and a cement clinker, were investigated for their capacity to remove phosphorus in a subsurface wetland. Three unplanted gravel filters, two containing a mixture of adsorptive media and one serving as a control, were installed as a polishing treatment to a constructed wetland treating wastewater at Sunny Creek Estates (SCE) mobile home park. The filters were commissioned in July 2000, and data gathering continued until July 2001, to provide a year-round data set.; The slag filter had consistently the lowest outflow dissolved phosphorus concentrations (0.27 ± 0.08 mg/L, n = 21), whereas the clinker filter had the greatest outflow dissolved phosphorus concentrations (0.72 ± 0.20 mg/L, n = 23). The clinker performed well below expectations, possibly due to lower pH conditions than observed in the lab. The filters maintained relatively constant outflow concentrations, despite varying input conditions and times of phosphorus export. Export of phosphorus occurred in the winter, although it is attributed to the decrease in input phosphorus concentrations below the maintained outflow concentrations, rather than cold temperatures or failure of the bed.; The results from these field studies provide recommendations for improving phosphorus removal at the SCE constructed wetland, in addition to valuable information for new and existing constructed wetlands in cold climate areas. For a full-scale phosphorus adsorption filter at Sunny Creek Estates, either slag or clinker could be used with greater percentages in the adsorptive media mixture. However, the hydraulic conductivity of the media needs to be increased, and the impact of an increase in the percentage of adsorptive media on phosphorus removal, media lifespan and effluent quality, particularly pH and toxicity, needs to be considered.