The growing needs for sustainable nutrient management and pollution control have motivated the development of novel technologies for nutrient recovery from wastewater. However, most of the existing technologies require extensive use of chemicals and intensive consumption of energy to achieve substantial recovery of nutrients. Herein, we present a hybrid electrochemical sequence integrating two relatively novel electrochemical processes, bipolar membrane electrodialysis (BMED) and membrane capacitive deionization (MCDI), for simultaneous removal of phosphorus and nitrogen. Specifically, the BMED process is employed to alkalify the wastewater to facilitate struvite precipitation and the MCDI process is used to further reduce the ammonia concentration in the effluent and concentrate the excess ammonia to a small stream. The electrochemical sequence is demonstrated to remove ∼89% of phosphorus and ∼77% of ammonia, recovering ∼81% of wastewater as a high-quality effluent that can be discharged or reused. This electrochemical treatment train minimizes chemical use and has competitive energy consumption as compared to electrochemical processes for nutrient recovery from wastewater.
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Prospective Life Cycle Assessment and Cost Analysis of Novel Electrochemical Struvite Recovery in a U.S. Wastewater Treatment Plant
Nutrient recovery in domestic wastewater treatment has increasingly become an important area of study as the supply of non-renewable phosphorus decreases. Recent bench-scale trials indicate that co-generation of struvite and hydrogen using electrochemical methods may offer an alternative to existing recovery options utilized by municipal wastewater treatment facilities. However, implementation has yet to be explored at plant-scale. In the development of novel nutrient recovery processes, both economic and environmental assessments are necessary to guide research and their design. The aim of this study was to conduct a prospective life cycle assessment and cost analysis of a new electrochemical struvite recovery technology that utilizes a sacrificial magnesium anode to precipitate struvite and generate hydrogen gas. This technology was modeled using process simulation software GPS-X and CapdetWorks assuming its integration in a full-scale existing wastewater treatment plant with and without anaerobic digestion. Struvite recoveries of 18–33% were achieved when anaerobic digestion was included, with a break-even price of $6.03/kg struvite and $15.58/kg of hydrogen required to offset increased costs for recovery. Struvite recovery reduced aquatic eutrophication impacts as well as terrestrial acidification impacts. Tradeoffs between benefits from struvite and burdens from electrode manufacturing were found for several impact categories.
more » « less- Award ID(s):
- 1739473
- NSF-PAR ID:
- 10471099
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Sustainability
- Volume:
- 14
- Issue:
- 20
- ISSN:
- 2071-1050
- Page Range / eLocation ID:
- 13657
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Twin Falls, Idaho wastewater treatment plant (WWTP), currently operates solely to achieve regulatory permit compliance. Research was conducted to evaluate conversion of the WWTP to a water resource recovery facility (WRRF) and to assess the WRRF environmental sustainability; process configurations were evaluated to produce five resources—reclaimed water, biosolids, struvite, biogas, and bioplastics (polyhydroxyalkanoates, PHA). PHA production occurred using fermented dairy manure. State‐of‐the‐art biokinetic modeling, performed using Dynamita's SUMO process model, was coupled with environmental life cycle assessment to quantify environmental sustainability. Results indicate that electricity production via combined heat and power (CHP) was most important in achieving environmental sustainability; energy offset ranged from 43% to 60%, thereby reducing demand for external fossil fuel‐based energy. While struvite production helps maintain a resilient enhanced biological phosphorus removal (EBPR) process, MgO2production exhibits negative environmental impacts; integration with CHP negates the adverse consequences. Integrating dairy manure to produce bioplastics diversifies the resource recovery portfolio while maintaining WRRF environmental sustainability; pilot‐scale evaluations demonstrated that WRRF effluent quality was not affected by the addition of effluent from PHA production. Collectively, results show that a WRRF integrating dairy manure can yield a diverse portfolio of products while operating in an environmentally sustainable manner.
Practitioner points Wastewater carbon recovery via anaerobic digestion with combined heat/power production significantly reduces water resource recovery facility (WRRF) environmental emissions.
Wastewater phosphorus recovery is of value; however, struvite production exhibits negative environmental impacts due to MgO2production emissions.
Bioplastics production on imported organic‐rich agri‐food waste can diversify the WRRF portfolio.
Dairy manure can be successfully integrated into a WRRF for bioplastics production without compromising WRRF performance.
Diversifying the WRRF products portfolio is a strategy to maximize resource recovery from wastewater while concurrently achieving environmental sustainability.
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There is a growing need to develop novel technologies that reduce reactive nitrogen concentrations in wastewater streams and decrease our reliance on fossil fuel energy required to produce N-based chemicals and fertilizers. This study conducts a techno-economic analysis (TEA) and a life cycle assessment (LCA) of the electrochemical conversion of nitrate ions (NO3–) present in wastewater to hydroxylamine (NH2OH), a valuable chemical intermediate. We employ experimental data and modeling assumptions to determine NH2OH production costs and life cycle emissions for a small-scale facility (producing 1500 kg-NH2OH/day) and a large-scale facility (producing 50,000 kg-NH2OH/day) integrated into a wastewater treatment plant. The present NH2OH production costs for the small- and large-scale facilities are estimated at $6.14/kg-NH2OH and $5.37/kg-NH2OH, respectively. The parameters dominating the electrochemical reactor cost are electrolyte, separations, and fixed cost, with their values as $1.48, $0.96, and $0.53/kg. Future cost reduction projections indicate that the present NH2OH production costs for the small- and large-scale facilities can be reduced to $2.79/kg-NH2OH and $2.06/kg-NH2OH (NH2OH market price = $1.72/kg), respectively, with improvements in the sensitivity analysis parameters. LCA results indicate that the proposed electrochemical pathway to produce NH2OH has lower life cycle impacts than the conventional pathway.more » « less
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Phosphorus (P) recovery from wastewaters as struvite (MgNH4PO4·6H2O) may be a viable alternative fertilizer-P source for agriculture. The objective of this study was to evaluate the economic and environmental implications of struvite as a fertilizer-P source for flood-irrigated rice (Oryza sativa) relative to other commonly used commercially available fertilizer-P sources. A field study was conducted in 2019 and 2020 to evaluate the effects of wastewater-recovered struvite (chemically precipitated struvite (CPST) and electrochemically precipitated struvite (ECST)) on rice yield response in a P-deficient, silt–loam soil in eastern Arkansas relative to triple superphosphate, monoammonium and diammonium phosphate, and rock phosphate. A life cycle assessment methodology was used to estimate the global warming potentials associated with rice produced with the various fertilizer-P sources. Life cycle inventory data were based on the field trials conducted with and without struvite application for both years. A partial budget analysis showed that, across both years, net revenues for ECST and CPST were 1.4 to 26.8% lower than those associated with the other fertilizer-P sources. The estimated greenhouse gas emissions varied between 0.58 and 0.70 kg CO2 eq kg rice−1 from CPST and between 0.56 and 0.81 kg CO2 eq kg rice−1 from ECST in 2019 and 2020, respectively, which were numerically similar to those for the other fertilizer-P sources in 2019 and 2020. The similar rice responses compared to commercially available fertilizer-P sources suggest that wastewater-recovered struvite materials might be an alternative fertilizer-P-source option for flood-irrigated rice production if struvite can become price-competitive to other fertilizer-P sources.more » « less
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Phosphate in wastewater can be recovered in the form of struvite crystals for use as slow-release fertilizer. Currently, struvite recovery often requires supplementing magnesium ions and raising pH with chemicals, making the recovered struvite unfavorable for organic production. In an effort for cleaner production, this study developed a versatile approach employing two mineral products in variable combinations for optimal supplementation of magnesium and elevation of pH. Magnesite, a mineral of MgCO3, was ground and calcined without use of any catalysts. The magnesite calcined under the optimum conditions (800 ◦C for 30 min) can be dissolved in near-neutral filtrate of sludge digestate to supplement magnesium and raise pH for effective struvite formation. The OMRI-listed Epsom salts (MgSO4•7H2O), mineral-based water-soluble commercial products, can be used to supplement magnesium without changing pH of alkaline wastewater. Six-hour batch operation of an airlift crystallizer removed 85.7% and 94.7% of phosphate in hydrolyzed human urine when magnesium was amended to 1.2 × molar concentration of phosphate with calcined magnesite and an OMRI-listed Epsom salt, respectively. More than 98% of phosphate was removed from filtrate of sludge digestate in 3-h batch operation using calcined magnesite to raise pH to 8.5 and the Epsom salt for further magnesium supplementation. Struvite accounted for 85.7%, 90.5%, and 81.5% of the crystals recovered from urine with calcined magnesite, urine with Epsom salt, and filtrate with both mineral products, respectively. The material and energy costs of this green process were estimated to be $0.16/kg struvite from urine with calcined magnesite, $1.37/kg struvite from urine with Epsom salt, and $0.94/kg struvite from filtrate with both mineral products. This study proved the technical and economic feasibility of chemical-free magnesium supplementation and pH elevation, making the recovered struvite potentially certifiable for organic production.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/su142013657
