Integrated CO2 removal and NH3 recovery from wastewater using a bidirectionally productive electrochemical pH swing
Abstract
Electrochemical pH-swing processes based on proton-coupled electron transfer (PCET) offer a promising route for selective chemical separation from aqueous media. Yet in all previous systems only one half of the pH swing performs a separation, while the reverse half is expended solely to regenerate the state of charge of the active electrode or electrolyte. Using a synthetic mimic of domestic wastewater as the input feed, we demonstrate a bidirectionally productive electrochemical pH-swing generated by a phenazine-carbon nanotube PCET-active composite electrode in an aqueous flow cell, in which both the acidifying and alkalizing half-cycles perform useful chemical separation. Electrode oxidation acidifies the wastewater to convert dissolved inorganic carbon into CO 2 (aq) for removal, whereas the subsequent reduction alkalizes the feed, converting NH 4 + to NH 3 (aq) for recovery using membrane stripping. An experimentally validated reaction-transport model establishes the pH-swing sequence as a key design parameter, with oxidation before reduction enabling integrated CO 2 removal and NH 3 recovery, whereas the opposite sequence prioritizes NH 3 recovery through near-complete NH 4 + -to-NH 3 conversion. The system achieved batchwise NH 3 recovery using the reduction–oxidation sequence over 31 cycles spanning 43 h, establishing operational stability over a duration not previously demonstrated for PCET-driven nutrient recovery. The oxidation–reduction sequence achieved average energetic costs of 219.9 kJ mol -1 CO 2 removed and 12.2 kWh kg -1 N recovered, with corresponding separation rates of 4.47 μmol CO 2 h -1 cm -2 and 5.33 g N m -2 day -1 , respectively. By making both directions of an electrochemical pH swing productive, this work reframes electrode regeneration as an opportunity for a second separation, and points toward wastewater treatment plants as distributed sites for combined nutrient recovery and carbon removal.
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BibTeX
@misc{yun2026integrated,
title = {{Integrated CO2 removal and NH3 recovery from wastewater using a bidirectionally productive electrochemical pH swing}},
author = {Bin Yun and Orçun Dinçer and Marc-Antoni Goulet and David G. Kwabi},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008841/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008841/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Integrated CO2 removal and NH3 recovery from wastewater using a bidirectionally productive electrochemical pH swing
AU - Bin Yun
AU - Orçun Dinçer
AU - Marc-Antoni Goulet
AU - David G. Kwabi
PY - 2026
DA - 2026/09/15
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008841/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008841/v1
AB - Electrochemical pH-swing processes based on proton-coupled electron transfer (PCET) offer a promising route for selective chemical separation from aqueous media. Yet in all previous systems only one half of the pH swing performs a separation, while the reverse half is expended solely to regenerate the state of charge of the active electrode or electrolyte. Using a synthetic mimic of domestic wastewater as the input feed, we demonstrate a bidirectionally productive electrochemical pH-swing generated by a phenazine-carbon nanotube PCET-active composite electrode in an aqueous flow cell, in which both the acidifying and alkalizing half-cycles perform useful chemical separation. Electrode oxidation acidifies the wastewater to convert dissolved inorganic carbon into CO 2 (aq) for removal, whereas the subsequent reduction alkalizes the feed, converting NH 4 + to NH 3 (aq) for recovery using membrane stripping. An experimentally validated reaction-transport model establishes the pH-swing sequence as a key design parameter, with oxidation before reduction enabling integrated CO 2 removal and NH 3 recovery, whereas the opposite sequence prioritizes NH 3 recovery through near-complete NH 4 + -to-NH 3 conversion. The system achieved batchwise NH 3 recovery using the reduction–oxidation sequence over 31 cycles spanning 43 h, establishing operational stability over a duration not previously demonstrated for PCET-driven nutrient recovery. The oxidation–reduction sequence achieved average energetic costs of 219.9 kJ mol -1 CO 2 removed and 12.2 kWh kg -1 N recovered, with corresponding separation rates of 4.47 μmol CO 2 h -1 cm -2 and 5.33 g N m -2 day -1 , respectively. By making both directions of an electrochemical pH swing productive, this work reframes electrode regeneration as an opportunity for a second separation, and points toward wastewater treatment plants as distributed sites for combined nutrient recovery and carbon removal.
ER -