Modelling recovery of ammonium from urine by electro-concentration in a 3-chamber cell

Thompson Brewster, Emma, Jermakka, Johannes, Freguia, Stefano and Batstone, Damien J. (2017) Modelling recovery of ammonium from urine by electro-concentration in a 3-chamber cell. Water Research, 124 210-218. doi:10.1016/j.watres.2017.07.043

Author Thompson Brewster, Emma
Jermakka, Johannes
Freguia, Stefano
Batstone, Damien J.
Title Modelling recovery of ammonium from urine by electro-concentration in a 3-chamber cell
Journal name Water Research   Check publisher's open access policy
ISSN 1879-2448
Publication date 2017-07-20
Year available 2017
Sub-type Article (original research)
DOI 10.1016/j.watres.2017.07.043
Open Access Status Not yet assessed
Volume 124
Start page 210
End page 218
Total pages 9
Place of publication London, United Kingdom
Publisher Elsevier
Language eng
Abstract Electro-concentration enables treatment and nutrient recovery from source-separated urine, and is a potential technology for on-site treatment using a 3 compartment configuration that has anode, cathode and middle concentrate compartments. There is a particular focus on driving concentration towards the precipitation threshold in the concentrate compartment to generate solid ammonium salts, including ammonium bicarbonate. To evaluate controlling mechanisms and the feasibility of achieving high concentrations, a dynamic mechanistic model was developed and validated using experiments with synthetic urine. It was identified that high concentrations are prevented by increased back diffusion (diffusion from the middle chamber to the anolyte and catholyte) due to large concentration gradients, and the preferential migration of protons or hydroxide ions due to a loss of buffering capacity in the anolyte and catholyte (due to pH extremes). Model-based sensitivity analysis also identified that electrolyte ion concentrations (including buffer capacity) were the main controlling mechanisms, rather than membrane or electrolyte current transfer capacity. To attain high concentrations, operation should be done using a) a high current density (however there is a maximum efficient current density); b) feed at short hydraulic retention time to ensure sufficient buffer capacity; and c) a feed high in ammonium and carbonate, not diluted, and not contaminated with other salts, such as pure ureolysed urine. Taking into account electron supply and bio-anodic buffer limitations, model testing shows at least double the aqueous concentrations observed in the experiments may be achieved by optimising simple process and operational parameters such as flow rate, current density and feed solution composition. Removal of total ammonium nitrogen (TAN) and total carbonate carbon (TCC) was between 43-57% and 39-53%, respectively. Balancing the sometimes conflicting process goals of high concentrations and removal percentage will need to be considered in further application. Future experimental work should be directed towards developing electrodes capable of higher current densities. In addition it would be desirable to use ion exchange membranes with higher resistance to water fluxes and which limit back diffusion. Future modelling work should describe osmotic and electro-osmotic water fluxes as a function of the concentration gradient across the membranes and ionic fluxes, respectively. More generalised wastewater physico-chemistry speciation models should identify best methods where relatively simple Davies activity corrections do not apply. (C) 2017 Elsevier Ltd. All rights reserved.
Keyword Ammonium bicarbonate
Electrochemical model
Nutrient recovery
Physicochemical model
Q-Index Code C1
Q-Index Status Provisional Code
Grant ID LP 150100402
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
Advanced Water Management Centre Publications
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