Steel slag filters to upgrade phosphorus removal in constructed wetlands: two years of field experiments

Environ Sci Technol. 2013 Jan 2;47(1):549-56. doi: 10.1021/es303778t. Epub 2012 Dec 18.


Electric arc furnace steel slag (EAF-slag) and basic oxygen furnace steel slag (BOF-slag) were used as filter substrates in two horizontal subsurface flow filters (6 m(3) each) designed to remove phosphorus (P) from the effluent of a constructed wetland. The influences of slag composition, void hydraulic retention time (HRTv), temperature, and wastewater quality on treatment performances were studied. Over a period of almost two years of operation, the filter filled with EAF-slag removed 37% of the inlet total P, whereas the filter filled with BOF-slag removed 62% of the inlet total P. P removal occurred predominantly via CaO-slag dissolution followed by Ca phosphate precipitation. P removal efficiencies improved with increasing temperature and HRTv, most probably because this affected the rates of CaO-slag dissolution and Ca phosphate precipitation. It was observed that long HRTv (>3 days) can cause high pH in the effluents (>9) as a result of excessive CaO-slag dissolution. However, at shorter HRTv (1-2 days), pH values were elevated only during the first five weeks and then stabilized below a pH of 9. The kinetics of P removal were investigated employing a first-order equation, and a model for filter design was proposed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Filtration / methods
  • Industrial Waste*
  • Phosphorus / chemistry*
  • Steel / chemistry*
  • Water Pollutants, Chemical / chemistry*
  • Water Purification / methods*
  • Wetlands


  • Industrial Waste
  • Water Pollutants, Chemical
  • Steel
  • Phosphorus