Effects of redox on the phosphorus removal ability of iron-rich phophorus sorption materials

Authors: SCOTT, ISIS - Kansas State University; Penn, Chad

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2024
Publication Date: 2/14/2024
Citation: Scott, I.S., Penn, C.J. 2024. Effects of redox on the phosphorus removal ability of iron-rich phophorus sorption materials. Chemosphere. https://doi.org/10.1016/j.chemosphere.2024.141416.
DOI: https://doi.org/10.1016/j.chemosphere.2024.141416

Interpretive Summary: Phosphorus (P) leaking from tile drainage into open water, such as Lake Erie, are a major source of pollution. P removal structures are large landscape-scale filters that remove dissolved P from flowing water. Such P removal structures are buried and can be designed to flow from the bottom-upward. This depletes oxygen and may cause iron (Fe) rich filter media to unleash dissolved P. The research goal was to determine if P release occurred from three different Iron-rich filter products by lowering the soil oxygen. The filters were rusted steel metal shavings, mine drainage recovery by-products, and a commercial product. Filter materials were first treated with P before creating the lower soil oxygen levels. After the oxygen was used up, there were minor changes in P in the water, showing a lack of a potential re-release. Filter materials were also evaluated for their ability to continue to re-adsorb P after being restored to oxygenated conditions. No decrease in P sponging up potential was found. Overall, the results suggest that P removal structures that use Iron-rich filter materials can be designed to be flow from the bottom-upward.

Technical Abstract: Iron-rich phosphorus (P) sorption materials (PSMs) are often used in P removal structures, a best management practice able to sequester dissolved P from surface runoff, subsurface drainage, and wastewater. The use of bottom-upward flow in these structures is of great interest, but it creates an intrinsic complication: the presence of stagnant water between flow events may cause structures to develop anoxic conditions. It is unknown whether the redox sensitivity of iron (Fe), the predominant element in Fe-rich PSMs, will affect P binding under anoxic conditions. Understanding the potential impact of intermittent anoxic conditions on the solubility of previously adsorbed P is imperative for determining the feasibility of the bottom-up flow design. The objective of this research was to investigate the (1) development of anoxic conditions in the presence of Fe-rich PSM and tile drainage, (2) Fe-bound P mobilization and solubility, and (3) changes in P sorption capacity of Fe-rich PSMs after oxic conditions are restored. Three Fe-rich PSMs were tested in batch incubation studies: acid mine drainage residual, Fe-coated alumina, and steel metal shavings. Non-treated and P-treated PSM samples were incubated in biogeochemical reactors for as long as necessary to reach Eh=-200 mV. After incubation, dissolved P concentrations in P-treated samples and non-treated samples were similarly low, indicating stability of P retention of PSMs under anoxic conditions. The P removal ability of non-treated PSMs before and after undergoing incubation was not significantly altered, as determined in flow-through experiments. Potentially harmful trace metals were not detected in the incubated solutions. Our research shows that the development of anoxic conditions does not significantly impact PSMs Fe-bound P dissolution, and the P removal ability of PSMs persists after oxic conditions are reestablished.