Grantee Research Project Results
2018 Progress Report: Three- Step Scrubber for Ammonia Removal
EPA Grant Number: SV839356Title: Three- Step Scrubber for Ammonia Removal
Investigators: Barsanti, Kelley , Chen, Becky , Hanson, Samantha , Malhabour, Gabriel , Christos Stamatis, Austin Mok;
Current Investigators: Rupiper, Amanda , Barsanti, Kelley
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: II
Project Period: March 1, 2018 through February 29, 2020 (Extended to February 28, 2025)
Project Period Covered by this Report: March 1, 2018 through February 28,2019
Project Amount: $40,240
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2017) Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
Agricultural producers are primary contributors to atmospheric ammonia pollution throughout the US. Although ammonia is not a federal hazardous air pollutant or a state-identified toxic air contaminant, its acute and chronic non-cancer health effects justify its regulation. Specifically, ammonia reacts with other constituents in the air to produce fine particulate matter (PM2.5), which is a federal criteria pollutant, and causes adverse health effects. Current conventional chemical scrubbers for ammonia do not represent a sustainable solution, as they have high economic and environmental costs. Therefore, we have designed a three-step ammonia air scrubbing and filtration system for agricultural ammonia emissions that promotes sustainability by reusing water, recycling waste, and reducing costs.
Relationship to people, prosperity and the planet As noted above, ammonia is an important precursor of PM2.5, and thus reducing the release of ammonia to the atmosphere contributes to improved air quality for people. The use of the collected ammonia as an amendment for soil, rather than releasing it in waste streams as ammonium sulfate (a salt) improves water quality for people and the planet. The ability to recycle water leads to reduced waste, providing an environmental benefit; in addition, this reduces costs, providing an economic benefit and contributing to prosperity. Relevance and significance to developing or developed world The target source of ammonia emissions in this project is agriculture. Ammonia emissions will scale with the size of operation and will be affected by animal type and infrastructure, but generally, agricultural operations in both the developing and the developed world will be a source. The prototype scrubber is designed for small to medium operations with line power, but the scrubber is scalable and could be evaluated for operation on batteries or solar power, likely making it more useful in developing countries.
Implementation of the P3 Award project as an educational tool Each academic year, a team of four undergraduate students in Chemical & Environmental Engineering lead the project design, implementation, evaluation, and iteration. The team typically includes three seniors and one junior. The junior is part of the team their junior and senior year, ensuring continuity. Team members have included typically underrepresented minorities in STEM and first-generation college students. This often represents their first research experience. The students also work closely with a graduate student or postdoctoral research in the PI’s group, which provides teaching and mentoring opportunities for these graduate students and postdocs. Finally, the students participate in at least one community outreach event, in which they share their project and findings with the general public.
Progress Summary:
Modern scrubbers use significant amounts of water, as the scrubbers are flushed continuously to avoid clogging. The purpose of this project is to create a field-scale prototype of a three-step scrubber that removes ammonia emissions from agricultural sources, in part using a biochar adsorption unit; the ammonia-amended biochar can then be used as a soil amendment. This three step system is illustrated in Figure 1; the steps are briefly described here. Step one uses a water-based air-scrubbing (gas absorbing) unit. Step two uses a novel manure-based biochar adsorption column to collect ammonium from the waste stream, cleaning the water for reuse and thus eliminating the requirement for waste disposal of the water-ammonia effluent. Step three uses an air stripper to further reduce the ammonia concentration in the water. At the end of the three-steps the water can be reused and the three-step the cycle can be repeated.
Figure 1: Full-scale system flow diagram
In Phase I, this project focused on evaluation of adsorption capabilities of different biochar materials. A laboratory scale apparatus was designed and built, and removal efficiencies of ~65% were achieved, from an ammonia solution prepared to mimic effluent of the first column. In Phase II, the scope was expanded to develop a laboratory scale apparatus linking the first and second steps, and testing the efficacy of manure-based biochar as an absorbent, as well as the efficacy of the ammonia-amended manure-based biochar as a soil amendment. The objectives were to maximize the removal efficiency of the two-step process, and prepare for field-scale implementation.
Data, outputs, outcomes, findings
To analyze how adsorbent particle size affects design parameters of the biochar column, we conducted two different experiments. The first experiment examined how the particle size of biochar affected the flow rate out of the biochar column. Over three trials, the average flow rate for a particle size of <1/20” was 10% of the initial flow rate into the biochar column. The second experiment examined the ammonia removal efficiency using the bench-scale system with 100 mL of biochar. The absorption column was expected operate at a 99% efficiency based on the Chemglass product description. To ensure that there is no volatilization of ammonia in the reservoir, the temperature of the system was kept below the boiling point of ammonium (38°C). The biochar particle size in the column is expected to be <1/20”. The results of this experiment are shown in Figure 2. The highest fractional removal of ammonia occurs in the 1st pass through the adsorbent, ~ 48%. The average ammonia removal rate reaches 60% with a maximum of 78%. The removal efficiencies are at a flow rate of 4.77 ± 0.73 mL/s, and a retention time of 152 ± 30 seconds in the biochar column. With lower flow rates, higher retention times, and multiple passes through the biochar column, the ammonia removal percentage is likely to increase.
Figure 2: Ammonia removal percentage with three passes through a biochar column
In addition to the laboratory-scale experiments in which the efficiency of the biochar adsorbent was measured, we was also investigated the ability of the ammonia-saturated biochar to serve as an effective soil amendment. We rented space in a greenhouse to run various trials under controlled conditions. A total of 16 romaine lettuce plants were grown across four garden planters with four plants in each of four soil types. This allowed the comparison between ammonia-saturate biochar and a control group, commercial fertilizer, and biochar alone. In the first phase, the ideal growing conditions for the plants were optimized. They were determined to be one square foot of soil per plant, 50-70°F ambient temperature, shade, and watering once every other day. Since transplants were used and not seedlings, it took approximately three weeks for the romaine lettuce to reach maturity. In the second phase (repeated twice), all of the leaves, except the two smallest on each plant, were peeled before the next trial began. Every week, the number of leaves on each plant were counted and recorded, as shown in Figure 3.
Figure 3: Average number of leaves per plant by week
During the final week of each trial in the second phase, the total weight of all the leaves were taken to determine the average leaf weight as shown in Figure 4. After conducting two trials of romaine lettuce growth between the four soils, we determined biochar to be an excellent soil amendment. Among all soils, ammonia-saturated biochar had the highest number of leaves each week. It also had the second highest leaf weight, but only behind the highest average leaf weight by 0.06 grams. These results suggest that ammonia-saturated biochar can be a viable soil amendment.
Figure 4: Average leaf weight at the end of the trials
Future Activities:
Currently, there are various methods available for the removal of ammonia in air and water. These mechanisms include a variety of scrubber systems and air strippers that have both strengths and limitations in the reduction of ammonia emissions from various sources. The initial unit costs, annual unit operation costs, and ammonia removal percentages are summarized in Table 1.
Table 1: Technology costs and ammonia removal percentages [1,2,3]
Technology | NH3 Removal (%) | Initial Cost | Unit Operation Cost/Year |
Acid Scrubber | 90% | $10,000 | $3,200 |
Bioscrubber | 70% | $15,000 | $3,200 |
Air Stripper | 50% | $25,000 | $2,000 |
This Design | 70% | $18,472 | $1,381 |
First, wet scrubbers reduce ammonia from the air by injecting liquid into a gas stream in order to collect gaseous ammonia from the air.[4] These scrubbers use wet surfaces, spray systems, or wet material beds to absorb ammonia from the air.[5] Although wet scrubbers are fairly efficient, they produce liquid effluent that has to be treated as a waste product.[4,5] Second, acid scrubbers, are used to trap gaseous ammonia in a sulfuric acid solution that is circulated over a packed acidic bed with a low pH.[5] The initial unit cost is approximately $10,000, while the annual operating cost is $3,200.[6] Although this technology has been proven to remove 90% of ammonia in the air and 30% of the existing odor, it produces toxic salts, causes corrosion of the scrubber unit, and has a specific disposal protocol.[4] Third, bioscrubbers use bacterial growth on biomass to convert gaseous ammonia into nitrate and nitrite. The initial unit cost for a bioscrubber is approximately $15,000, while the annual operating cost is $3,200.[6] Although the ammonia removal is 70% and the odor reduction is 50%, bioscrubbers use eight to ten times as much water as wet scrubbers. This leads to the production of nitrogen-saturated wastewater which must be kept within regulated parameters.[4] While these technologies reduce gaseous ammonia, they each produce some variant of contaminated wastewater that is required by regulations to be treated before being discharged into the environment. Treatment of wastewater adds additional costs to the overall ammonia removal systems while producing excess, unused waste. Additionally, scrubbers use an excess amount of water which can cause a strain in water-limited areas.[4] Furthermore, measures need to be taken to ensure a functional ventilation system feeds into the scrubber. While scrubbers do their primary job of removing ammonia from air, they produce a new set of environmental problems such as producing toxic waste that needs to be regulated by the Environmental Protection Agency and using excess resources such as water, acid, and electricity.[4]
Second, air stripping removes ammonia from wastewater streams through gas-liquid interaction by lowering the pH and temperature of air.[7] This method, however, has not been traditionally used in the agricultural industry, because of certain limitations like the need for freshwater to be pumped into the system. This causes a high initial unit cost of approximately $25,000, higher power costs, and increased maintenance for farm operators.[8] This is also an unreliable technique because of the additional atmospheric based ammonia emissions which are released into the environment. While both we scrubbers and air stripping have been used historically for ammonia removal, new methods are continually emerging. The method developed and applied in this project, which includes the combination of a gas absorption column and a biochar adsorption column, has been specifically intriguing due to its ability to not only mitigate ammonia emissions, but also to be recycled as a fertilizer. The initial cost of a full-scale unit is projected $18,475 and the annual operating cost at $1,381.[8]
At the conclusion of year one, the team has done substantial research, calculations, and experimentation in the context of the laboratory-scale system. In the next year, the focus will be linking the three steps (if needed, it may be that the first two are sufficient). Once this is complete, we will optimize the absorption column, filtration column, and flow rates for operation in the field. In addition, we will continue to optimize the biochar adsorbent step. The team in on track to build and test a field-scale system in this second year. The system design continues to evolve, but overall, the objectives and deliverables remain the same.
References:
[1] Huang, Jianyin. “Removing Ammonium from Water and Wastewater Using Cost-Effective Adsorbents: A Review.” Journal of Environmental Sciences, Elsevier, 30 Sept. 2017, www.sciencedirect.com/science/article/pii/S1001074217315565#f0060.
[2] EPA, 1996. U.S. EPA, Office of Air Quality Planning and Standards, “Stationary Source Control Techniques Document for Fine Particulate Matter, “EPA-452/R-97-001, REsearch Triangle Park, NC, October 1998.
[3] Fischer, Dave. Lowering Operating Costs Lowering Operating Costs For Water and Wastewater Treatment with Tray Air Strippers. QEN Environmental Systems Inc, 2012.
[4] Harmon, Jay D., et al. Animal Housing -- Wet Scrubbers. Iowa State University Extension & Outreach, 2014, www.agronext.iastate.edu/ampat/animalhousing/scrubber/homepage.html. Accessed 31 Oct. 2018.
[5] Clark, Chad. Ammonia Removal Utilizing an Ammonia Scrubber. Gulf Coast Environmental Systems, 2017, www.gcesystems.com/ammoniascrubber/. Accessed 6 Nov. 2018.
[6] Behera, Sailesh N., et al. “Ammonia in the Atmosphere: a Review on Emission Sources, Atmospheric Chemistry and Deposition on Terrestrial Bodies.” Environmental Science and Pollution Research, vol. 20, no. 11, 28 Aug. 2013, pp. 1–8., doi:10.1007/s11356-013-2051-9
[7] Osha.gov. (2018). Chemical Sampling Information | Ammonia | Occupational Safety and Health Administration. [online] Available at: https://www.osha.gov/dts/chemicalsampling/data/CH_218300.html (Accessed Nov. 5 2018).
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectProgress and Final Reports:
Original AbstractP3 Phase I:
Three-Phase Ammonia Air Scrubber Recycles Water | 2017 Progress Report | Final ReportThe 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.
Project Research Results
- 2023
- 2022 Progress Report
- 2021 Progress Report
- 2020 Progress Report
- 2019 Progress Report
- Original Abstract
- P3 Phase I | 2017 Progress Report | Final Report