The purpose of this research was to investigate phosphorus (P) retention capacity and rejuvenation potential of electric arc furnace (EAF) steel slag from Quebec and New Zealand (NZ) iron melter slag (IMS). Columns filled with slag materials were fed with dairy effluent and subjected to two feeding and one resting cycle(s). P retention capacities and rejuvenation potentials were determined after each feeding cycle. Elemental composition and mineralogical analysis were performed on IMS samples. Finally, chemical fractionation analysis was conducted on both NZ IMS and Quebec EAF steel slags. The results revealed that initiating a resting period in EAF steel slag filters prior to reaching their P saturation point increased the overall filter P retention capacity by 49.5 and 42.4% compared to 28% in a filter which had its resting period initiated after reaching P saturation. The rejuvenation property could play a significant role in full-scale applications by prolonging life expectancy and increasing cost efficiency. P retention and rejuvenation by NZ slag materials was negligible relative to EAF steel slag material from Quebec. Chemical fractionation analysis revealed differences between materials, indicating that the highest quantities of P were bound to Ca and Fe in EAF steel slag and to Ca and Al fractions in iron melter slag. This study also demonstrates that slag's performance is dependent on the source of the material and the steel making practices. Therefore, testing of the P adsorptive capability and, if relevant, the rejuvenation potential of individual steel mill slags, should be a prerequisite prior to their use in field applications.

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 (PFT) 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.

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