Ammonia Recovery from Domestic Wastewater Using a Proton-Mediated Redox Couple

Ammonia in wastewater can be a valuable resource if recovered sustainably and with sufficient purity to compete with commercial ammonia products. A new electrochemical method employing a proton-mediated redox couple was developed to selectively recover ammonia from domestic wastewater by simultaneous separation of NH4+ and conversion into NH3 at an elevated pH. Using hydroquinone (HQ) and benzoquinone (BQ), solution pH increased by H+ uptake (BQ + 2H(+) + 2e -> HQ) or decreased by H+ release (HQ -> BQ+ 2H(+) + 2e(-)). This redox reaction facilitated the separation of ammonium from synthetic wastewater (5 mM NH4+ + 20 mM Na+) at a nitrogen flux of 33.8 g N m(-2) day(-1) while increasing the solution pH to 9.6. A low voltage of 0.47 V at 9.6 A m(-2) resulted in a 3.2 kWh kg(-1) N energy consumption. The separated ammonia was recovered in a membrane contactor at a nitrogen flux of 12.0 g N m(-2) day(-1) (9.1 kWh kg(-1) N). This proof-of-concept demonstrated the use of a proton-mediated redox couple as a new platform to enable ammonia recovery from wastewater.