Issue 11, 2021

Emerging investigator series: thermodynamic and energy analysis of nitrogen and phosphorous recovery from wastewaters

Abstract

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 NH3(aq) from source-separated hydrolyzed urine can be ≈40–68% lower, whereas recovering KH2PO4(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.

Graphical abstract: Emerging investigator series: thermodynamic and energy analysis of nitrogen and phosphorous recovery from wastewaters

Supplementary files

Article information

Article type
Paper
Submitted
05 Aug. 2021
Accepted
15 Sept. 2021
First published
16 Sept. 2021

Environ. Sci.: Water Res. Technol., 2021,7, 2075-2088

Author version available

Emerging investigator series: thermodynamic and energy analysis of nitrogen and phosphorous recovery from wastewaters

S. N. McCartney, N. S. Watanabe and N. Y. Yip, Environ. Sci.: Water Res. Technol., 2021, 7, 2075 DOI: 10.1039/D1EW00554E

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