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

Abstract

Ammonia (NH₃) recovery from used water (previously wastewater) is highly desirable to depart from fossil fuel-dependent NH₃ production and curb nitrogen emission to the environment. Electrochemical NH₃ recovery is promising since it can simply convert aqueous NH₄⁺ to gaseous NH₃ using cathodic reactions (OH^- generation). However, the use of a separated electrode and membrane imposes high resistances to the cathodic reaction and NH₃ transfer. This study examined an activated carbon (AC)-based membrane electrode functionalized with nickel to electrochemically recover NH₃ 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 NH₃-N recovery flux of 50.3 ± 0.4 gNH₃-N/m²/d was produced at 17.1 A/m² with a recovery solution at pH 7, and NH₃-N fluxes and energy consumptions were improved as the recovery solution became acidic (62.2 ± 2.1 gNH₃-N/m²/d with 16.0 ± 1.6 kWh/kgNH₃-N at pH 2). Increasing PVDF loadings did not impact the electrochemical performances of the Ni/AC-PVDF electrode, but slightly lower (7%) NH₃-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.