Exploring the valorisation potential of urban wastewater in Flanders by the application of a 2-stage technology

Nitrogen (N) fixation and production of N-based fertilizers by the application of the Haber-Bosch process is associated to 1-2% of the global energy consumption. Additionally, the biological N-removal during urban wastewater (WW) treatment by application of both nitrification (conversion of NH4+ to NO3-) and denitrification (conversion of NO3- to N2) is an energy demanding process and is moreover linked to additional N2O emissions. This study aims to close nutrient cycles by exploring the potential of a 2-stage technology connecting WW treatment and agriculture needs by treatment of real domestic WW by high-rate activated sludge (HRAS) and subsequent recovery of N from the effluent using natural zeolites as adsorption material. The process demonstrated N and C-removal efficiencies, ranging from 74% to 82% and 76% to 89%, respectively. An adsorption capacity of 1.4-8.4 mg N/g of zeolites was achieved. The N-content of the regeneration liquid ranged between 25-845 mg NH4+-N/L.