(480d) A Lifecycle Assessment and Economic Analysis of Electrochemical Nutrient Recovery Technology from Municipal Wastewater Systems

Phosphorus (P) is a critical nutrient in global agriculture, essential for maintaining soil fertility and supporting plant growth. The conventional production of phosphorus fertilizers predominantly depends on finite phosphate rock reserves, which are projected to be exhausted within the next century [1]. Additionally, these production processes are energy-intensive and contribute significantly to greenhouse gas emissions, raising environmental concerns. Wastewater streams, however, present a renewable source of phosphorus and nitrogen (N) that can be recovered as struvite, thereby conserving phosphate rock resources and reducing nutrient pollution in surface waters [2], [3].

Electrochemical precipitation of struvite has emerged as a sustainable technique for recovering P and N from wastewater with minimal chemical inputs. This method involves electrochemically supplying Mg²⁺ ions from a sacrificial magnesium anode, while alkalinity is generated through an electrically driven half-cell reaction at a stainless steel cathode [4], [5]. Although conventional methods of nutrient recovery from wastewater as struvite are commercially established, the electrochemical technique offers several distinct advantages. However, comprehensive assessments of its environmental and economic performance are limited, particularly beyond the laboratory scale [6].

This study, supported by the U.S. Department of Energy (EE0009502), addresses this gap by evaluating the environmental and economic performance of electrochemical P recovery via struvite precipitation from simulated municipal wastewater on an industrial scale. The electrochemical recovery system will be modeled using OLI Flowsheet ESP software (version 12.0), simulating the integration of the technology into a full-scale wastewater treatment plant utilizing the activated sludge process. Model predictions, including P recovery efficiency and solution pH dynamics, will be validated using experimental data.

The environmental assessment will focus on estimating cumulative energy consumption (GJ/mt_P) and carbon dioxide emissions (mt_CO₂/mt_P) within the electrochemical P recovery system, comparing results with conventional nutrient recovery technologies and commercial P fertilizer production. The economic evaluation will include capital and operational expenditure analyses, profitability estimates, and sensitivity analyses to explore the influence of process variations on the technology’s sustainability.

Preliminary results indicate a strong agreement between the model predictions and experimental data for P recovery and solution pH indicating the model’s ability to predict struvite recovery from municipal wastewater sources. Moreover, benchmarking the energy and CO₂ emissions of the modeled technology to those of conventional P fertilizers showed almost similar values with less than 5% difference. However, sensitivity analysis in the study showed that specific parameters such as magnesium source, power source, etc., can lower the energy and CO₂ factors of the electrochemical struvite technology even further. In conclusion, the electrochemical struvite recovery technology presents a promising alternative to conventional P fertilizer production, especially when optimized with the appropriate Mg²⁺ source.

References

[1] J. Hallas, C. Mackowiak, A. Wilkie, and W. Harris, “Struvite Phosphorus Recovery from Aerobically Digested Municipal Wastewater,” Sustainability, vol. 11, no. 2, p. 376, Jan. 2019, doi: 10.3390/su11020376.

[2] S. A. Parsons and J. A. Smith, “Phosphorus Removal and Recovery from Municipal Wastewaters,” Elements, vol. 4, no. 2, pp. 109–112, Apr. 2008, doi: 10.2113/GSELEMENTS.4.2.109.

[3] S. R. Golroudbary, M. El Wali, and A. Kraslawski, “Environmental sustainability of phosphorus recycling from wastewater, manure and solid wastes,” Sci. Total Environ., vol. 672, pp. 515–524, Jul. 2019, doi: 10.1016/j.scitotenv.2019.03.439.

[4] Z. Belarbi and J. Trembly, “Electrochemical Processing to Capture Phosphorus from Simulated Concentrated Animal Feeding Operations Waste,” J. Electrochem. Soc., vol. 165, no. 13, pp. E685–E693, 2018, doi: 10.1149/2.0891813jes.

[5] Z. Belarbi, D. A. Daramola, and J. P. Trembly, “Bench-Scale Demonstration and Thermodynamic Simulations of Electrochemical Nutrient Reduction in Wastewater via Recovery as Struvite,” J. Electrochem. Soc., vol. 167, no. 15, p. 155524, Dec. 2020, doi: 10.1149/1945-7111/abc58f.

[6] K. G. Morrissey, L. English, G. Thoma, and J. Popp, “Prospective Life Cycle Assessment and Cost Analysis of Novel Electrochemical Struvite Recovery in a U.S. Wastewater Treatment Plant,” Sustainability, vol. 14, no. 20, p. 13657, Oct. 2022, doi: 10.3390/su142013657.