Grantee Research Project Results
Final Report: Sustainable Nutrient Recovery from Urine
EPA Grant Number: SU839264Title: Sustainable Nutrient Recovery from Urine
Investigators: Blaney, Lee
Institution: University of Maryland - Baltimore County
EPA Project Officer: Page, Angela
Phase: I
Project Period: January 1, 2018 through December 31, 2018
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2017) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Safe and Sustainable Water Resources , Sustainable and Healthy Communities , P3 Awards
Objective:
1. Conduct NERD optimization studies using lab-scale reactors to maximize the rate and magnitude of nutrient recovery from synthetic and real urine
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Construct and operate laboratory-scale NERD reactors;
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Determine the effects of pH on phosphorus recovery from synthetic urine;
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Investigate the impacts of urine dilution (flushing) on nutrient recovery efficiency; Conduct experiments to recover both cationic and anionic nutrients from urine; and, Precipitate value-added fertilizers with the nutrients recovered from urine.
2. Modify a porta potty to include NERD technology and demonstrate the ability of this unit to recover nutrients from urine.
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Purchase a commercial porta potty;
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Modify the porta potty to contain a NERD reactor; and,
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Demonstrate nutrient recovery from urine to a diverse audience at the USA Science & Engineering Festival (Washington, DC).
Summary/Accomplishments (Outputs/Outcomes):
A series of NERD reactors were developed for laboratory-scale testing. The reactors were designed as shown in Figure 1. Given the relatively complex chemistry of phosphorus (as orthophosphate, P(V)), compared to cationic nutrients, such as NH4+ and K+, we focused most of the experimental studies on P(V). In this case, the waste solution was urine or synthetic urine containing P(V). The draw solution was deionized water containing a high salt (NaCl) concentration. During operation, the phosphorus (HPO42-) anions in urine exchange (across the anion exchange membrane) with chloride (Cl-) from the draw solution (see inset of membrane interface in Figure 1). The reactors worked well and allowed careful investigation of the ability of NERD technology to recover nutrients from urine-based solutions.
Figure 1. Schematic showing the two-chamber, experimental reactor with waste and draw solutions. The anion exchange membrane was AMI-7001 (Membranes International). The compartment volumes were 390 mL, and solutions were constantly stirred. Chemical conditions were changed with each experiment.
Since P(V) chemistry is pH dependent, we first investigated the impact of urine pH on P(V) recovery. The motivation behind these experiments was to see if there were potential advantages or disadvantages with changing urine pH prior to the NERD reactors. The experimental data in Figure 2 indicate better recovery of the HPO42- and PO43- species compared to the H3PO4 and H2PO4- species. These results were encouraging since the pH of fresh and hydrolyzed urine is typically in the pH 7-9 range, which is where HPO42- is the dominant P(V) species. Therefore, no modification of urine pH was needed to improve the overall performance of the recovery operation, ensuring low chemical demand and operating costs.
Figure 2. Recovery of different phosphorus species using the two-chamber NERD reactor shown in Figure 1. The phosphorus content in the waste compartment was 3.2 mM for all conditions, and the NaCl concentration in the draw compartment was set to 100 mM. The pH varied for each condition (to select for particular phosphate species).
Chemical modification of the urine solution would be costly and, based on results reported in
Figure 2, not necessary. However, we wanted to consider situations where urine may be diluted (by flushing) prior to the NERD reactor. We studied three scenarios to correspond to no dilution, moderate dilution, and high dilution. The data reported in Figure 3 show that the change in P(V) concentration in the urine solutions (labeled as waste) was similar for no, moderate, and high dilution conditions. While the P(V) concentrations varied in the recovery solution (labeled as draw), these differences stemmed from a larger fraction of P(V) remaining in the anion-exchange membrane for the high and moderate dilution scenarios. In a continuous-flow reactor, that P(V) would be recovered. Ultimately, these results suggested that the use of undiluted urine will provide optimal nutrient recovery, reducing the water demand associated with urinals.
Figure 3. Recovery of phosphorus from urine under high, moderate, and no dilution conditions. The design involved addition of 0.03, 0.32, and 3.2 mM Na2HPO4 and 0.7, 7.0, and 70 mM NaCl in the waste and recovery compartments, respectively.
Given the encouraging results from the previous experiments, we constructed a new NERD system that involved tubular anion- and cation-exchange membranes. These membranes were placed into a waste solution, containing synthetic urine, and a salt solution was continuously recirculated through the inside of the membranes. The volume of the synthetic urine waste and NaCl-based recovery solutions were 30 L and 6 L, respectively. Nutrients from the urine were expected to sorb to the outside of the tubular membranes and exchange with Na+ (for Mg2+ and K+ in this experiment) and Cl- (for P(V)). The experimental data in Figure 4 indicate successful treatment of synthetic urine solutions containing P(V), Mg2+, and K+. Over the course of the experiment, the concentrations of these three important nutrients continuously decreased, and the nutrient concentrations in the recovery solution continuously increased. The faster rate of nutrient accumulation in the draw solution (compared to the waste solution) stemmed from the volumetric differences. Mass transfer limitations may have caused the rate of nutrient recovery to slow down over the course of the experiment, and these results suggest that the reactor design can be improved to improve the rate of nutrient recovery. After 24 hours of treatment, NaOH was added to the draw solution to increase the pH to 9.0 and precipitate nutrient-enriched solids (see Figure 5). By precipitating recovered nutrients, the pH change also re-established the electrochemical potential gradient that drives Donnan equilibrium, facilitating continued recovery without additional chemical demand. This phenomenon can be observed by the increase in nutrient concentrations in the draw solution after 24 hours. Overall, these results were highly encouraging and highlighted the ability of NERD technology to recover nutrients from urine.
Figure 4. Co-recovery of P(V), Mg2+, and K+ from urine using the tubular anion and cation exchange membranes from the NERD-modified porta potty unit.
Figure 5. A scanning electron microscopy image of the solids recovered from the experiment shown in Figure 4. Characterization of the solids indicated that the recovered particles were magnesium phosphate (Mg3(PO4)2) and magnesium potassium phosphate (MgKPO4).
Given the positive results from the laboratory-based studies included under Objective R.1, we moved forward with Objective R.2 activities. First, we designed the nutrient recovery-enabled porta potty (see Figure 6). The strategy involved purchasing a commercial porta potty, removing the original waste container (under the toilet seat), and installing the NERD reactor. For this project, we focused on incorporating the NERD reactor with the urinal for simplicity; however, future efforts can incorporate the NERD technology into urine-diverting toilets to recover nutrients in urine from both men and women. The original porta potty and the NERD-modified porta potty are shown in Figure 7.
Figure 6. Illustration of the NERD-modified porta potty.
Figure 7. Photographs of the (a) outside of the original porta potty and (b) inside of the modified porta potty, showing the waste collection basin, containing ion exchange membrane units, and the draw solution / precipitation reactor.
We exhibited the NERD-modified porta potty at the 2018 USA Science & Engineering Festival in Washington, DC. Over the course of the two-day festival, we interacted with elementary school students, high school students, college students, parents, entrepreneurs, government scientists, other researchers, and a wide variety of interested citizens. Our team stood out with our bright yellow shirts, bright yellow porta potty, and porta potty-shaped information cards. While we did not specifically count the number of visitors, we estimated that almost 1000 people stopped by our booth to learn about nutrient pollution, hear how we plan to address this issue through innovative nutrient recovery technologies, and use the NERD-modified porta potty (see Figure 8).
Figure 8. Photograph of the inside of the NERD -modified porta potty with P3 messaging about how nutrient recovery will positively affect people, prosperity, and the planet.
Young kids, their parents, and everyone else were excited to hear about our research, see our demonstrations, and pee into the urinal (see Figure 9). In the NERD-modified porta potty, visitors pulled water containing yellow food coloring into a plastic syringe and then shot it into the urinal. The water went down into the NERD reactor, where nutrients (the food coloring in this case) was removed by the ion-exchange membranes. Colorless water passed into the recovery solution and was pumped back through the ion-exchange membranes to recover more nutrients. Our demonstration was a major success – we had a number of visitors who had heard about the porta potty team and wanted to see the NERD-modified unit for themselves.
Figure 9. Photographs from the USA Science & Engineering Festival. Our booth included the NERDmodified porta potty, a nutrient recovery game for kids, a demonstration of how the NERD technology works, posters with our results from Objective R.1, and handouts with information about nutrient recovery and our P3 project.
Our goal was for all visitors to walk away with the take-home message shown in Figure 10.
Active recovery of nutrients from source-seperated urine will reduce (i) nutrient pollution of drinking water supplies and (ii) occurrence of harmful algal blooms, while simultaneously improving resource integrity and furthering green technologies. | |
Nutrient recovery from source-separated urine will protect water quality and ecosystem services by reducing stressor presence in sensitive ecosystems; furthermore, these results will reduce the intensity and occurrence of dead zones. | |
The production of new fertilizer supplies from source-separated urine will create jobs, generate incentives for improved waste management, and protect full security; furthermore, the protection of water bodies will generate revenue from fisheries and tourism. |
Conclusions:
Our research showed that the NERD technology was able to recover nutrients from urine and produce valuable fertilizer products. The chemistry of urine facilitates the recovery of important nutrients, like phosphorus, nitrogen, and potassium. In the laboratory, we were able to recover more than 90% of these nutrients using NaCl. Experimental results indicated that concentrated urine with no chemical/pH modification provided the best recovery rate. These results are encouraging since they minimize the operating costs. To demonstrate the ability of this innovative technology, we constructed a NERD-modified porta potty. The demonstration reactor used solar power to continuously pump a salt solution through the tubular cation- and anionexchange membranes, enabling nutrients to transfer across the membranes into a recovery solution. Over time, the nutrients in the recovery solution can be precipitated as valuable fertilizer products. As a result, we were able to (i) treat nutrient pollutants in urine and decrease the amount of nutrients going into the wastewater system, (ii) recover the nutrients as valuable fertilizers, and (iii) generate a potential source of new, green jobs.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Chen H, Shashvatt U, Amurrio F, Stewart K, Blaney Lee. Sustainable nutrient recovery from synthetic urine by Donnan dialysis with tubular ion-exchange membranes. Chemical Engineering Journal 2023;460(141625). |
SU839264 (Final) |
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Supplemental Keywords:
nutrients; resource recovery; water quality; resource integrity; environmental education; resource security; sustainable communitiesThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.