Electrochemical Ammonia Recovery from Anaerobic Centrate Using a Nickel-Functionalized Activated Carbon Membrane Electrode

Ammonia (NH 3 ) recovery from used water (previously wastewater) is highly desirable to depart from fossil fuel-dependent NH 3 production and curb nitrogen emission to the environment. Electrochemical NH 3 recovery is promising since it can simply convert aqueous NH 4 + to gaseous NH 3 using cathodic reactions (OH – generation). However, the use of a separated electrode and membrane imposes high resistances to the cathodic reaction and NH 3 transfer. This study examined an activated carbon (AC)-based membrane electrode functionalized with nickel to electrochemically recover NH 3 from synthetic anaerobic centrate. The membrane electrode was fabricated using nickel-adsorbed AC powder and a polyvinylidene fluoride (PVDF) binder, and the PVDF membrane layer was formed at the electrode surface by phase inversion. The NH 3 -N recovery flux of 50.3 ± 0.4 gNH 3 -N/m 2 /d was produced at 17.1 A/m 2 with a recovery solution at pH 7, and NH 3 -N fluxes and energy consumptions were improved as the recovery solution became acidic (62.2 ± 2.1 gNH 3 -N/m 2 /d with 16.0 ± 1.6 kWh/kgNH 3 -N at pH 2). Increasing PVDF loadings did not impact the electrochemical performances of the Ni/AC-PVDF electrode, but slightly lower (7%) NH 3 -N fluxes were obtained with higher PVDF loadings. Ni dissolution (3.7–6.0% loss) was affected by the recovery solution pH, but it did not impact the performances over the cycles.