Thou shall not flow: assessing magnitudes and processes of dissolved reactive phosphorus (P) removal by P-sorbing materials

Berkshire, Taylor

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Description

Title

Thou shall not flow: assessing magnitudes and processes of dissolved reactive phosphorus (P) removal by P-sorbing materials

Author(s)

Berkshire, Taylor

Issue Date

2021-04-27

Director of Research (if dissertation) or Advisor (if thesis)

Margenot, Andrew J

Committee Member(s)

• Christianson, Laura E
• Christianson, Reid D

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Phosphorus
• P removal structure
• P-sorbing materials

Abstract

Agricultural phosphorus (P) losses continue to contribute to eutrophication globally. There are currently best management practices that target particulate P losses but are not specifically designed to reduce dissolved reactive phosphorus (DRP) losses. A novel practice is the use of P removal structures. Phosphorus removal structures are designed to intercept surface runoff at the edge of agricultural fields to capture DRP losses. Phosphorus-sorbing media (PSM), waste by-products with high P removal potential, are the basis of P removal structures. The ability of PSM to remove DRP depends on the physical and chemical properties of the PSM, but the estimated DRP removal potential depends on the method used for evaluation. This M.S. thesis addresses how physical and chemical traits of PSM can differ by PSM type, source, and particle size fractions, how DRP is removed by PSM, and the extent to which methodological differences challenge the comparison of DRP removal potential of PSMs. The first chapter evaluates the traits of PSM that influence DRP removal, assesses how DRP is removed by PSM using sequential fractionation, and to what extent these traits vary by PSM type, source, and particle size fraction. These traits are hydraulic conductivity, particle size, reactive metal element composition (total Ca, Mg, Fe, Al, water-soluble Ca and Mg, ammonium-oxalate extractable Fe and Al, and citrate-bicarbonate-dithionite extractable Fe and Al). The second chapter examines how the methodology used to assess DRP removal potential impacts comparability of magnitude and processes of DRP removal. The methodologies used are batch isotherms and flow-through columns. PSM type played an important role in DRP removal and the hydraulic conductivity of a PSM is a key factor to consider for feasibility in a P removal structure. A larger particle size fraction such as 4 – 6.3 mm or 6.3 – 8 mm should be used in a P removal structure to maximize DRP removal while maintaining a sufficient hydraulic conductivity. This study showed that differences in metal cation concentrations among PSM type and source are more influential in DRP removal than the difference among particle size fractions. Sequential extraction revealed that certain PSM, specifically steel slag (SS), may be removing DRP differently than commonly assumed with Al contributing to DRP removal and also the Ca removal mechanism including adsorption and not strictly precipitation. This work reveals the importance of accounting for inherent P when determining how DRP is removed by PSM. As demonstrated by sequential extraction of PSM after exposure to DRP, if inherent P is not accounted for, then the magnitude of DRP recovered is not interpretable as inherent P can account for 100% of DRP recovered for some fractions. High inherent P in PSM does not appear to impact the ability to remove P, but is important to quantify to accurately measure which metal cation is responsible for removing P. This study also highlighted the need for a standard method used for evaluating PSM to increase comparability. In batch sorption isotherms, changing the DRP concentration range and whether an electrolyte solution is used affected DRP removal potential of PSM. The use of an electrolyte solution generally decreased the DRP removal potential, as well the DRP range ≤ 20,000 mg kg-1. Evaluation of the flow-through columns showed that a retention time > 20 s and inflow solution DRP concentration > 0.5 mg L-1 would provide the most consistent DRP removal on a mass basis for both types of PSM type for a P removal structure in the field. Batch isotherms and flow-through columns provide different metrics to evaluate DRP removal potential for PSM, but the highest DRP removing PSM remained the same. Testing PSM with flow-through columns revealed that some PSM can have a net P loss as they release previously sorbed DRP as well as additional inherent P. This work also shows that the chemical and physical traits of PSM are important to their DRP removal potential and that the methods by which PSM are assessed need to be standardized to promote comparability.

Graduation Semester

2021-05

Type of Resource

Thesis

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Copyright 2021 Taylor Berkshire

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