Negative-pressure gas-diffusion electrode for effective ammonia recovery in bioelectrochemical systems

Recovery of ammonia from wastewater attracts increasing attentions as a sustainable way of nitrogen treatment. Here a novel gas-diffusion electrode membrane with negative-pressure extraction was developed in bioelectrochemical systems, achieving the highest ammonia recovery rate of 178 gNH(3)-N/(m(2).d) with a low energy consumption (2.41 kW h kgNH(3)-N-1). The conjugate acid-base conversion of ammonium consumed OH near the cathode, enhanced current density by decreasing overpotential which in turn facilitated the ammonia recovery. With an optimized thickness of 0.5 mm, the membrane electrode achieved ammonia removal and recovery efficiencies of 83% and 77% at 0.03 MPa, and the performance was highly repeatable after 20 recovery cycles. Modeling prediction exhibited a better performance under a higher vacuum, where the back-diffusion effect can be effectively mitigated. The membrane electrode can be fabricated at a low cost of 13.5 $ m(-2), showing a potential usage in ammonia recovery from wastewater.