Abstract
Due to increased food production, the demand for nitrogen and phosphorus as fertilizers grows. Nitrogen-based fertilizers are produced with the Haber–Bosch process through the 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 interactions of nitrogen recovery with biogas production, phosphorus recovery, and cellulose recovery were examined. The mutual interference of the several nitrogen recovery technologies was studied using adaptive policy making. The most promising mature technologies that can be incorporated into existing wastewater treatment plants include struvite precipitation, the treatment of digester reject water by air stripping, vacuum membrane filtration, 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 the 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
The increase of the world population to eight to 10 billion by 2050 [1,2] will result in substantial pressure on food supply [3]
To avoid the eutrophication of water, in the current wastewater treatment technology based on the conventional activated sludge process, the reduced reactive nitrogen is biologically converted to its nonreactive N2 gas form through the nitrification/denitrification or deammonification process [14], and released back into the atmosphere
The wastewater treatment plant (WWTP) Amsterdam-West was used as a specific case in this studTyh.eTwhiasstpelwanatteisr otrpeeartamteedntbpylathnetilAitmy Wsteartdearnme-tW, weshticwhaiss uthseedpuasblaicspweactiefircscearsveicienotfhtishe stCuidtyy
Summary
The increase of the world population to eight to 10 billion by 2050 [1,2] will result in substantial pressure on food supply [3]. To avoid the eutrophication of water, in the current wastewater treatment technology based on the conventional activated sludge process, the reduced reactive nitrogen is biologically converted to its nonreactive N2 gas form through the nitrification/denitrification or deammonification (anammox) process [14], and released back into the atmosphere. The biological removal of nitrogen from the wastewater results in nitrous oxide (N2O) gas emissions representing an intermediate of increasing concern in terms of greenhouse gas emissions from wastewater treatment plants: the emission is relatively small (3% of the estimated total anthropogenic N2O emission), but is a significant factor (26%) in the greenhouse gas footprint of the total water chain [15] For these reasons, it is relevant to examine more sustainable pathways for nitrogen, which consist of interventions in the present (anthropogenic) nitrogen cycle, such as the direct recovery of nitrogen from wastewater and reuse. Saescteowndaltye,rtthoejsuedlegcetethdeaeltxecrlnuastiiovnesor arseynpelargceydwbietshidtheeostehoerthaelrterrensaotuivreces froercorveseoryuracleterrencaotviveerys (fSroemctiownas3t.e3w). aTtheirrdtolyju, dthgeeatlhterenxactliuvesisofnor ornsityrnoegregnyrweciothvethryesaenodthrerusresaoruercceomrepcoavreedrywailtherneactihveosth(Serecttoioinde3n.3t)if.yThloircdkl-yin, sth, ewainlt–ewrniant,ivaensdfonronirtergorgeetnmreecaosvuerreys a(Snedctrieounse3.a3r)e. compared with each other to identify lock-ins, win–win, and no-regret measures (Section 3.3)
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