Characterizing the mechanism and rate of calcium phosphate precipitation in aerobic granular sludge

With increasingly stringent standards for wastewater treatment plant effluent, the demand for technologies that are able to increase phosphorus removal while also recovering a valuable and marketable fertilizer product is growing. Aerobic granular sludge (AGS) is a promising technology that has demonstrated the ability to increase phosphorus removal while enhancing recovery through the precipitation of calcium phosphate minerals within the granule1–3. A rigorous understanding of precipitation mechanism and rate has been limited by simultaneous biological uptake and release of phosphate and cations. As a result, more work is needed to better understand how to control and enhance mineral precipitation within the polymeric matrix of the granule as well as how the pre-existing mineral phases within the granule influence recovery. To address this issue we performed precipitation experiments using AGS and solutions supersaturated with respect to hydroxyapatite and CaHPO4. We monitored the solution characteristics (pH, and [P]) in order to quantify the impact of calcium pre-enrichment on the extent and rate of phosphate removal with aerobic granular sludge. Our results showed that the use of calcium enriched granules significantly enhances the extent and rate of phosphorus removal. The final phosphorus concentration decreased from 1.64 mM of P to 1.06 mM of P when comparing calcium enriched granules to the abiotic control. The rate also increased from 1.9 to 11.2 day-1 with the presence of calcium enriched granules. Additionally, a lack of fines production indicated that precipitation was promoted within the granule EPS matrix. Results have also indicated that calcium pre-enrichment increases the transition from amorphous calcium phosphate to more stable forms. XRD analysis resulted in a solids spectra that contained peaks characteristic of hydroxyapatite, suggesting that more crystalline forms of calcium phosphate were deposited within the granules over time. SEM imaging showed an increase in phosphorus and calcium within the granules. Overall, this work identifies conditions under which aerobic granules enhance mineral phosphate precipitation and suggests that calcium treated granular sludge can be used to recover phosphorus as a stable calcium phosphate mineral. Future work will identify the solubilities of the minerals recovered via this process as well as their value as a phosphorous product for agriculture.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Environ Engr in Civil Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Kitt, Dianna Breanna

Contributors dc:contributor

• Cusick, Roland D.

• Aerobic Granular Sludge Calcium Phosphate Phosphorus Recovery

Statement dc:rights

• Copyright 2019 Dianna Kitt

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/105252

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/105252