Two adsorptive media, a blast furnace slag and a cement clinker are investigated for their capacity to remove phosphorus in a subsurface wetland. The field studies are being conducted at Sunny Creek Estates (SCE) mobile home park near Trenton, Ontario (100 km west of Kingston), which currently treats its wastewater with two aerated lagoons followed by a constructed wetland. The results from this study will 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. Three unplanted gravel filters, two containing adsorptive media and one serving as a control (using the same medium present in the wetland), have been installed as a post wetland polishing treatment prior to final effluent discharge. The adsorptive media are present as a fixed percentage in a mixture of fine stone and the adsorptive media. All filters are 3 m long, 0.6 m wide and 0.7 m deep, and each receives a portion of the constructed wetland effluent. Three monitoring wells have been installed along the transect of each filter. Samples are taken from a number of points in each filter, and are analyzed for phosphorus, pH and temperature. 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. In addition to providing recommendations for retrofitting the constructed wetland at SCE, the field studies provide regional information for new constructed wetlands and retrofits for existing wetlands experiencing similar performance limitations.
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