Abstract
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.
Highlights
Nitrogen and phosphorus play a critical role in plant growth and supply [4]
With the current rate of extraction and consumption, these “readily exploitable” sources of phosphorus will be depleted within the 45-100 years [5]. Reserve of this resource is getting smaller and phosphate is on the EU list of critical raw material [6]
There was a slight unbalance of 1.8% over the whole system, probably due to evaporation
Summary
The increase of the world population to 8 – 10 billion by 2050 [1,2] will result in substantial pressure on food supply [3]. Nitrogen and phosphorus play a critical role in plant growth and supply [4]. Due to an increased food production the demand for nitrogen and phosphorus will grow. With the current rate of extraction and consumption, these “readily exploitable” sources of phosphorus will be depleted within the 45-100 years [5]. Reserve of this resource is getting smaller and phosphate is on the EU list of critical raw material [6]. Much research is being carried out into phosphorus removal from wastewater [8-10], and technologies are applied at full-scale [11]
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