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This article in JEQ

  1. Vol. 40 No. 6, p. 1955-1962
     
    Received: July 21, 2009


    * Corresponding author(s): wroberts@sciborg.uwaterloo.ca
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doi:10.2134/jeq2009.0274

Treatment of Wastewater Phosphate by Reductive Dissolution of Iron: Use of Ferric Oxyhydroxide Media

  1. W. D. Robertson *a and
  2. P. S. Lombardob
  1. a Dep. of Earth and Environmental Sciences, Univ. of Waterloo, Waterloo, ON, N2L 3G1, Canada
    b Lombardo Associates Ltd., Newton, MA. Assigned to Associate Editor Robert Hubbard

Abstract

In smaller wastewater treatment systems such as septic systems, there is an interest in the development of passive phosphorus (P) removal methods. This study tested fixed-bed filters containing ferric oxyhydroxide media for wastewater P removal in a laboratory column test and in a full-scale domestic septic system. In the column test, during 30 mo of dosing with domestic wastewater, reductive iron dissolution reactions delivered consistent moderate concentrations of Fe into solution (2.9 ± 1.6 mg L−1), and influent PO4–P of 3.7 ± 1.0 mg L−1 was attenuated to 0.09 + 0.04 mg L−1 in the column effluent (98% removal). Phosphorus breakthrough at successive locations along the column indicated that in addition to sorption, mineral precipitation reactions probably also played an important role in the observed P attenuation. This was supported by electron microprobe analyses, which showed the presence of thick (20 μm) secondary Fe-rich coatings containing P on the primary ferric media grains. Assays of NaHCO3–leachable and acid-extractable P on the column solids showed accumulation of up to 5.4 mg g−1 acid-extractable P near the column inlet, but <5% of this amount was easily desorbable, further indicating P attenuation from processes other than sorption. Over 19 mo of operation, the domestic septic system also showed generally consistent increased Fe in the filter effluent (2.6 ± 1.7 mg L−1) and achieved 99% P removal to 0.03 ± 0.02 mg L−1 when the effluent was subsequently oxidized in a sand filter. Ferric iron filters could be attractive options for P removal in smaller wastewater systems because of their passive nature.

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