Continuous high-purity bioelectrochemical nitrogen recovery from high N-loaded wastewaters

Microbial electrolysis cells (MEC) have been identified as an energy efficient system for ammonium recovery from wastewater. However, high ammonium concentrations at the anode can have inhibitory effects. This work aims to determine the effects on current generation performance and active ammonia nitrogen recovery in wastewater containing 0.5 to 2.5 g N-NH₄⁺/L. The study also evaluates the effect of two cathode materials, stainless steel (SS-MEC) and nickel foam (NF-MEC). When the concentration of ammonium in the feed was increased from 0.5 to 1.5 g N-NH₄⁺/L the maximum current density increased from 3.2 to 3.9 A/m², but a further increase to 2.5 g N-NH₄⁺/L inhibited the biofilm activity, decreasing the current density to 0.5 A/m². The maximum ammonium removal and recovery efficiencies were 71 % and 33 % at 0.5 g N-NH₄⁺/L. The SS-MEC exhibited more energy efficient ammonium recovery compared to the NF-MEC, requiring 3.6 kWh/kg_N,recovered at 0.5 gN-NH₄+/L. The highest ammonium recovery rate of 33 g_N/m²/d (1.5 gN-NH₄⁺/L) was obtained with an energy consumption of 4.5 kWh/kg_N,recovered. Conversely, a lower recovery rate (10 g_N/m₂/d for 2.5 gN-NH₄⁺/L) resulted in reduced energy consumption at 2.1 kWh/kg_N,recovered. This highlights the inherent trade-off between energy consumption and efficient ammonium recovery in the process.