Integrated CO2 removal and NH3 recovery from wastewater using a bidirectionally productive electrochemical pH swing
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Language: English
Subfield: Environmental Engineering
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213322203