Ammonium recovery and energy production from urine by a microbial fuel cell

Nitrogen recovery through NH₃ stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid-gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 g_N d⁻¹ m⁻² (vs. membrane surface area) was achieved at a current density of 0.50 A m⁻² (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ g_N⁻¹, which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.