In 2003, a subsurface flow constructed wetland (SSF-CW) system was built adjacent to the University of Vermont Paul Miller Research Center. The aim of the SSF-CW is to test the efficiency of this technology in organic matter, bacteria, suspended solids and nutrient removal under regional climatic conditions. The SSF-CW is designed to treat barn yard runoff and milk house wash water generated during milking. Given the increasing importance of phosphorus (P) pollution in the Lake Champlain region, a new filter based experiment was designed with two major objectives: i) to test filters technology as an upgrade unit for improving P removal performance via constructed wetlands; ii) to investigate the capacity of filters technology to remove P as a “stand alone” unit.

Column experiments previously conducted under laboratory conditions using synthetic P solution have demonstrated that electric arc furnace (EAF) slag has extremely high P retention capacity (3.65 g kg-1) over extended periods of time. Therefore, this material was chosen as the preferred media for the UVM phosphorus filter technology. This research represents the first in-field evaluation of the EAF slag filters for P removal from dairy farm effluent in Vermont. The influent for all filters had a range of 7.6 - 59.9 mg L-1of P (avg. 36.25 mg L-1) during the first 265 days of testing. P adsorption by the EAF slag in four filters recieving SSF-CW treated influent has averaged 75% total remediation of dissolved reactive phosphorus(DRP) from the filter influent over the same period of time. There have been no significant differences in the adsorption capacity of the slag related to direction of flow through the filter (upwards & downwards). Comparisons between filters receiving SSF-CW treated water and non-treated water have shown no signifcant difference in performace, demonstrating the filters efficiency to treat dairy effluent as “stand alone units."