Nitrogen Recovery from Wastewater: Possibilities, Competition with Other Resources and Adaptation Pathways

Due to an increased food production the demand for nitrogen and phosphorus as fertilizers grows. Nitrogen based fertilizers are produced with the Haber-Bosch process through industrial fixation of N2 into ammonia. Through wastewater treatment the nitrogen is finally released back to the atmosphere as N2 gas. This nitrogen cycle is characterized by drawbacks. The energy requirement is high, and in the wastewater treatment nitrogen is mainly converted to N2 gas and lost to the atmosphere. In this study technologies for nitrogen recovery from wastewater were selected based on four criteria: sustainability (energy use and N2O emissions), the potential to recover nitrogen in an applicable form, the maturity of the technology and the nitrogen concentration that can be handled by the technology. As in wastewater treatment the focus is also on the recovery of other resources, the interaction of nitrogen recovery with biogas production, phosphorus recovery and cellulose recovery was examined. The mutual interference of the several nitrogen recovery technologies was studied using adaptive policymaking. Most promising mature technologies that can be incorporated in existing wastewater treatment plants were struvite precipitation, treatment of digester reject water by air stripping, vacuum membrane filtration and hydrophobic membrane filtration, and treatment of air from thermal sludge drying, resulting respectively in 1.1%, 24%, 75%, 75% and 2.1% nitrogen recovery for the specific case wastewater treatment plant Amsterdam-West. The effects on sustainability were limited. Higher nitrogen recovery (60%) could be realized by separate urine collection, but this requires a completely new infrastructure for wastewater collection and treatment. It was concluded that different technologies in parallel are required to reach sustainable solutions. Nitrogen recovery does not interfere with recovery of the other resources. An adaptation pathways map is a good tool to take into account new developments, uncertainties and different ambitions when choosing technologies for nitrogen recovery.