Upgrading constructed wetlands phosphorus reduction from a dairy effluent using electric arc furnace steel slag filters

In 2003, a subsurface flow constructed wetlands (SSF-CW) system was built at the University of Vermont (UVM) Paul Miller Dairy Farm as an alternative nutrient management approach for treating barnyard runoff and milk parlour waste. Given the increasing problem of phosphorus (P) pollution in the Lake Champlain region, a slag based P-removal filter technology (PFr) was established (2004) at the CW with two objectives: (i) to test the filters' efficiency as an upgrade unit for improving P removal performance via SSF-CW (ii) to investigate the capacity of filters technology to remove P as a "stand alone" unit. Six individual filters (F1-F6) were filled with electric arc furnace (EAF) steel slag, each containing 112.5 kg of material with a pore volume of 21 L. F1-F4, fed with CW treated water, received approximately 2.17 g DRP kg^-1 EAF steel slag (0.25 kg DRP total) during the 259 day feeding period. F1-F4 retained 1.7 g DRP kg^-1 EAF steel slag, resulting in an average P removal efficiency of 75%. The addition of filters improved CW DRP removal efficiency by 74%. F5 and F6, fed non-treated water, received 1.9 g DRP kg^-1 EAF steel slag (0.22 kg DRP in total) and retained 1.5 g DRP kg^-1 resulting in a P removal efficiency of 72%. The establishment of the EAF slag based PFT is the first in-field evaluation of this technology to reduce P from dairy farm effluent in Vermont.