Electrochemical In Situ pH Control Enables Chemical-Free Full Urine Nitrification with Concomitant Nitrate Extraction

Urine is a valuable resource for nutrient recovery. Stabilization is, however, recommended to prevent urea hydrolysis and the associated risk for ammonia volatilization, uncontrolled precipitation, and malodor. This can be achieved by alkalinization and subsequent biological conversion of urea and a...

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Bibliographic Details
Published in:Environmental science & technology 2021-06, Vol.55 (12), p.8287-8298
Main Authors: De Paepe, Jolien, Clauwaert, Peter, Gritti, Maria Celeste, Ganigué, Ramon, Sas, Benedikt, Vlaeminck, Siegfried E, Rabaey, Korneel
Format: Article
Language:English
Subjects:
Acidification
Alkalinity
Ammonia
Bioreactors
Carbon dioxide
Dosage
Electrochemical cells
Electrochemistry
Feasibility studies
Logistics
Nitrates
Nitrification
Off odor
pH control
pH effects
Treatment and Resource Recovery
Urea
Ureas
Urine
Volatilization
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Summary:Urine is a valuable resource for nutrient recovery. Stabilization is, however, recommended to prevent urea hydrolysis and the associated risk for ammonia volatilization, uncontrolled precipitation, and malodor. This can be achieved by alkalinization and subsequent biological conversion of urea and ammonia into nitrate (nitrification) and organics into CO2. Yet, without pH control, the extent of nitrification is limited as a result of insufficient alkalinity. This study explored the feasibility of an integrated electrochemical cell to obtain on-demand hydroxide production through water reduction at the cathode, compensating for the acidification caused by nitritation, thereby enabling full nitrification. To deal with the inherent variability of the urine influent composition and bioprocess, the electrochemical cell was steered via a controller, modulating the current based on the pH in the bioreactor. This provided a reliable and innovative alternative to base addition, enabling full nitrification while avoiding the use of chemicals, the logistics associated with base storage and dosing, and the associated increase in salinity. Moreover, the electrochemical cell could be used as an in situ extraction and concentration technology, yielding an acidic concentrated nitrate-rich stream. The make-up of the end product could be tailored by tweaking the process configuration, offering versatility for applications on Earth and in space.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.1c00041