Location: National Soil Erosion ResearchTitle: Mechanisms of phosphorus removal by phosphorus sorbing materials
|ZIXUAN, QIN - University Of Delaware|
|SHOBER, A - University Of Delaware|
|SCHECKEL, K - Environmental Protection Agency (EPA)|
|TURNER, K - University Of Delaware|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2018
Publication Date: 8/2/2018
Citation: Zixuan, Q., Shober, A.L., Scheckel, K.G., Penn, C.J., Turner, K.C. 2018. Mechanisms of phosphorus removal by phosphorus sorbing materials. Journal of Environmental Quality. 47:1232-1241. https://doi.org/10.2134/jeq2018.02.0064.
Interpretive Summary: Excessive dissolved phosphorus (P) pollution to surface waters can be reduced through the use of landscape-scale filters known as P removal structures. These structures utilize various by-products as P sorption materials (PSMs) that have a high affinity for dissolved P. The mechanisms by which these materials are able to remove P somewhat dictates the conditions in which they are utilized most efficiently. The objective of this study was to characterize P sorption mechanisms of PSMs previously used in P removal structures, using solid-state spectroscopy. PSMs were found to generally remove P by formation of either calcium (Ca), aluminum (Al), or iron (Fe) phosphate minerals. Some PSMs were able to remove P through formation of all three minerals. The preference is for PSMs that form Al and Fe phosphates since they tend to remove dissolved P faster than Ca is able to. This research directly impacts agricultural producers and those interested in improving water quality.
Technical Abstract: Stormwater filtration units are a structural best management practice designed to reduce dissolved phosphorus (P) losses from runoff. Various industrial by-products are suitable for use as P sorbing materials (PSMs) for treatment of drainage water; P sorption by PSMs varies with material physical and chemical properties. Previously, P removal by PSMs was estimated using chemical extractions. We determined speciation of P when reacted with various PSMs using X-ray absorption near edge structure (XANES) spectroscopy. Twelve PSMs were reacted with P solution in the laboratory under batch or flow-through conditions. In addition, three slag materials were collected from working stormwater filtration structures. Phosphorus K-edge XANES spectra were collected on each reacted PSM and compared with spectra of 19 known P standards using linear combination fitting (LCF) in Athena. We found evidence of formation of a variety of calcium (Ca)-, aluminum (Al)-, and/or iron (Fe)-phosphate minerals and sorbed phases on the reacted PSMs, with exact speciation influenced by the chemical properties of the original un-reacted PSM. We grouped PSMs into three general categories based on the dominant P removal mechanism: 1) Fe and Al mediated removal (i.e., adsorption of P to Fe/Al-(hydro-)oxide minerals and/or precipitation of Fe-/Al-phosphate minerals); 2) Ca mediated removal (i.e., precipitation of Ca-phosphate mineral); and 3) both mechanisms. We prefer the use of Fe/Al sorbing PSMs for use in stormwater filtration structures where stormwater retention time is limited because reaction of P with Fe or Al generally occurs more quickly than Ca-P precipitation.