Three-Dimensional Phosphorus Sorption by Drinking Water Treatment Residuals Three-Dimensional Phosphorus Sorption by Drinking Water Treatment Residuals Konstantinos C. Makris

Need long-term solutions to reduce excess soluble P in soils and waters. Drinking water treatment residuals (WTRs) seem a potential long-term solution. Why use WTRs: –Cost-effective –Rich in P-loving metals (Fe, Al) –Non-hazardous residuals –High P sorption capacities Rationale

Synopsis Macroscopic characterization of WTRs Microscopic characterization of WTRs Long-term stability of sorbed P Spectroscopic analyses Long-term effects of WTR application to two MI soils Heat Incubations Conclusions

Macroscopic Characterization

P sorption isotherms (23C) after 80d. pH was not adjusted, no shaking.

P sorption kinetics and a initial pulse input of 10,000 mg P kg -1. 2nd order reaction rate kinetics

WTRs P desorbed (% sorbed) Tampa, FL1.8 Bradenton, FL0.2 Holland, MI0.5 Cocoa, FL0.4 Panama, FL0.8 Lowell, AR0.7 P desorption with 5mM oxalate solution in the dark of the P-treated WTRs (initial P load = 10 g P kg -1 )

Long-term Stability of Sorbed P Three approaches to “compress” and simulate long-term effects. –Study the physical nature of the adsorbent; micropores may severely restrict sorbed P mobility. –Utilize heat incubations at elevated temperatures (46, 70C) to hasten reactions that could occur in decades in the field. –Monitor longevity of a WTR effect on soil P (5.5 years after WTR application) at two sites (Holland, MI).

Physical nature of the WTRs H 0 (1): Micropores in WTRs may be responsible for slow P sorption kinetics, and even slower desorption. H 0 (2): WTRs could ultimately immobilize P.

Objectives To determine mechanisms and pathways of P sorption by WTRs. To interpret the mechanisms in terms of long-term stability of sorbed P.

r 2 = TC content (%) N 2 / CO 2 SSA ratio

Hypotheses No P With P Al-WTR, Bradenton, FL.

Mean P adsorption monolayer capacity goethites = 0.24 mg PO 4 m -2. gibbsites = mg PO 4 m -2. (Torrent et al., 1990). (van Riemsdijk and Lyklema, 1980) Total P Uptake Fe-WTR = 7.88 mg PO 4 m -2 Al-WTR = 1.23 mg PO 4 m -2 More than what the monolayer capacity can explain!!!

no P, 80dwith P, 80d Particle’s cross section Image P dot map Fe dot map ~ 20μm

P/(P+Fe) no Pwith P d 80d Fe-WTR, Tampa at the interior of the particles. LSD α=0.05 = n=15 Significant interaction, 95% confidence level.

interior edge d 80d P/(P+Fe) LSD α=0.05 = n=10 Fe-WTR, Tampa of the P-treated particles. NO significant interaction, 95% confidence level.

Micropore CO 2 -SSA based on the Dubinin Radushkevich method (DR) of WTRs treated with and without P for 80d.

8A

Long-term Stability (2 nd approach) Incubations at elevated temperatures (46, 70C). Synthetic Al and Fe hydroxides with and w/o P WTRs: with and w/o P Soils amended with WTRs: i) Holland, MI. ii) Okeechobee, FL System complexity

Hypotheses H 0 (1): Elevated temperatures will induce structural changes of particles towards more crystalline structures. H 0 (2): Transformation of the WTRs towards more crystalline phases (aging), would decrease P extractability.

200mM oxalate extractable P and Al in the Al gels with time at 70C. crystalline formation detected with XRD (pseudoboehmite)

Monitoring of P extractability in the field 5.5 years after WTR application.

Site 1 PSI = ox-P / (ox-Fe + ox-Al)

Site 2

Conclusions Multiple lines of evidence that P sorption is three-dimensional (intraparticle diffusion in micropores of WTRs):Multiple lines of evidence that P sorption is three-dimensional (intraparticle diffusion in micropores of WTRs): –minimum P desorption / maximum P sorption –2 nd order kinetics –Changes in SSA / microporosity –microprobe Micropore-bound P is stable and immobilizedMicropore-bound P is stable and immobilized.

Conclusions Heat incubations for two years showed no changes in materials crystallinity. Elevated temperatures simply increased the rate of P diffusion towards the interior of the particlesHeat incubations for two years showed no changes in materials crystallinity. Elevated temperatures simply increased the rate of P diffusion towards the interior of the particles Five and a half years following WTR application to two sites in MI, we observed no release of P with time in the WTR-amended plots.Five and a half years following WTR application to two sites in MI, we observed no release of P with time in the WTR-amended plots.

Intraparticle P diffusion in micropores Heat incubations of the WTRs Long-term WTR application field experiment Sorbed P by WTRs may be stable and immobilized in the long-term.

WTRs may be land- applied to agricultural fields, ponds, or to animal wastes to reduce soluble P levels. Sorbed P may be stable in the long-term unless acidic conditions occur (pH<4). WTRs land application may be a best management practice to reduce potential P losses in sandy soils. Practical Significance

Acknowledgements This work was funded by a U.S. E.P.A. grant. Work conducted in Univ. Florida campus:

Acknowledgements MY COMMITTIEE PROFESSORS

Acknowledgements Drs. Moudgil, Sartain, Reddy, Ma. Soil Chemistry Lab-Scott Brinton Soil Mineralogy Lab-Keith Hollien PERC Labs- Gill Brubaker Turf Science Lab- Ed Hopwood

Acknowledgements I would also like to thank: Greg Means Bill Pothier Thomas Luongo Bill Reve The Newell-Penthouse residents L. Walker N. Kabengi J. Leader T. Hanselman

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