Removal of phosphorus from solution using biogenic iron oxides

Phosphorus removal by biogenic iron oxides was investigated, providing an initial characterization of a potentially regenerable iron-rich sorbent. The biogenic iron oxides were collected from a wetland ecosystem and were dominated by the sheaths of Leptothrix ochracea. Sorption kinetics followed a pseudo-1st order model (R2 = 0.998) with a rate constant of 0.154 ± 0.013 h−1. The Langmuir isotherm adequately described sorption for all samples (R2 = 0.923–0.981); the Freundlich model was a better fit for only one of four samples. Maximum phosphorus sorption estimated using the Langmuir parameter ranged from 46.9 ± 2.9 to 165.0 ± 21.2 mg P/g Fe and was similar to other iron-rich substrates. Maximum sorption normalized to total solids ranged from 10.8 ± 0.7 to 39.9 ± 3.2 mg P/g, which represented the highest published values for iron-rich substrates. The high sorption capacity with respect to both iron and solids warrants further evaluation of biogenic iron oxides as a substrate for phosphorus removal.