Electrochemical and bioelectrochemical ammonium recovery from N-loaded streams using a hydrophobic membrane

Bioelectrochemical systems enable the recovery of ammonium from wastewater with low energy requirements and as a concentrated nitrogen-rich stream. This work aims to thoroughly investigate different cathodic electrode configurations and to optimize the operational conditions for active ammonium recovery from synthetic wastewater as concentrated ammonium sulphate. Different applied current intensities (50 mA, corresponding to 5 A m⁻², and 75 mA, corresponding to 7.5 A m⁻²) and initial ammonium concentrations (between 0.3 and 3 g L⁻¹ N-NH₄⁺) were tested in an abiotic electrochemical system to understand the upper threshold of the used three-chamber configuration with hydrophobic membrane in terms of ammonium recovery rate (R_rec). With an external current of 75 mA, the highest value was 55 gN-NH₄⁺ m⁻² d⁻¹ when removing 97 % from an initial ammonium concentration of 3 g L⁻¹. Bioelectrochemical ammonium removal/recovery was evaluated under different applied potentials (0.8, 1.0, 1.2, and 1.4 V) using two configurations: a Nickel-based gas diffusion electrode (GDE) and a configuration with the cathode (stainless steel or nickel foam) physically separated from the hydrophobic membrane. The highest removal rate (R_rem) (21 gN-NH₄⁺ m⁻² d⁻¹) was exhibited for stainless steel cathode at 1.4 V mainly due to its higher current density, which increased the cations migration. This higher R_rem also led to a higher R_rec (17 gN-NH₄⁺ m⁻² d⁻¹).