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In a circular nutrient economy, nitrogen and phosphorous are removed from waste streams and captured as valuable fertilizer products, to more sustainably reuse the resources in closed-loops and simultaneously protect receiving aquatic environments from harmful N and P emissions. For nutrient reclamation to be competitive with the existing practices of N fixation and P mining, the methods of recovery must achieve at least comparable energy consumption. This study employed the Gibbs free energy of separation to quantify the minimum energy required to recover various N and P fertilizer products from waste streams of fresh and hydrolyzed urine, greywater, domestic wastewater, and secondary treated wastewater effluent. The comparative advantages in theoretical energy intensities for N and P recovery from nutrient-dense waste streams, such as fresh and hydrolyzed urine, were assessed against the other more dilute sources. For example, compared to reclaiming the nutrients from treated wastewater effluent at centralized wastewater treatment plants, the minimum energy required to recover 1.0 M NH 3(aq) from source-separated hydrolyzed urine can be ≈40–68% lower, whereas recovering KH 2 PO 4(s) from diverted fresh urine can, in principle, be ≈13–34% less energy intensive. The study also evaluated the efficiencies required by separation techniques for the energy demand of N and P recovery to be lower than the current production approaches of the Haber–Bosch process and phosphate rock mining. For instance, the most energetically favorable ammoniacal nitrogen and orthophosphate reclamation schemes, which target hydrolyzed and fresh urine, respectively, require energy efficiencies >7% and >39%. This study highlights that strategic selection of waste stream and fertilizer product can enable the most expedient recovery of nutrients and realize a circular economy model for N and P management.
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Nested risks and responsibilities: Perspectives on fertilizer from human urine in two U.S. regions
This paper reports on social research investigating perceptions concerning the diversion of urine from the waste stream and its use as fertilizer in two study regions, New England and the Upper Midwest. We hypothesized that discomfort or disgust might affect acceptance of such a shift in human “waste” management. However, our findings suggest that a more significant concern of those potentially involved in this process may be distrust of how economic interests influence scientific and technical information. Both physical risks (to the environment and public health) and socio-political risks (to fragile farm economies and consumer communities) play out at individual, household, regional, and global scales. We describe the intersection of these complex understandings as nested risks and responsibilities that must inform the future of urine reclamation. Our respondents' shared concern about environmental risks has already galvanized communities to take responsibility for implementing closed-loop alternatives to current agricultural inputs and waste management practices in their communities. Attention to these nested understandings of both risk and responsibility should shape research priorities and foster participatory approaches to urine nutrient reclamation, including strategies for education, planning, regulation, technology design, and agricultural application.
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- Award ID(s):
- 1639244
- PAR ID:
- 10301722
- Date Published:
- Journal Name:
- Journal of Agriculture, Food Systems, and Community Development
- ISSN:
- 2152-0801
- Page Range / eLocation ID:
- 1 to 22
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5304/jafscd.2021.103.016
