Three- Step Scrubber for Ammonia RemovalEPA Grant Number: SV839356
Title: Three- Step Scrubber for Ammonia Removal
Investigators: Barsanti, Kelley
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Project Period: March 1, 2018 through February 29, 2020
Project Amount: $40,240
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2017)
Research Category: Sustainability , P3 Awards , P3 Challenge Area - Water
Agricultural producers are primary contributors to atmospheric ammonia pollution throughout the United States. California in particular, as the leading state in cash farm receipts, contributes significantly more ammonia emissions than any other U.S. state; with the largest contribution coming from dairy facilities. In 2000, the Air Quality Management District (AQMD) reported, “Most of the potentially significant sources of ammonia are area-wide sources such as livestock, fertilizer application, and soils.” 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 under the AQMD's risk management programs. The risk of ammonia pollution is attributed to its ability to react with other contaminants in the air to produce fine particulate matter (PM2.5), which enters the human respiratory system and can cause significant health issues.
A complete installation of our design, which includes the initial absorber unit, complete biochar adsorption column, the water-based air stripper, and relevant input and output systems will be constructed and tested at the Scott Brothers Dairy facility over the span of two years. The adsorption column will be constructed using the design dimensions established in P3 Phase I. Scott Brothers Dairy will provide an allotted area for installation of our proposed system. The team will continue to examine the effectiveness of biochar as an adsorbent in this system and address any concerns that arise. Additionally, further laboratory research will be conducted in P3 Phase II to examine and improve the adsorption capacity of the biochar through advanced particle sieving techniques to achieve finer material for more adsorption. More accurate instrumentation, an advanced ammonia analyzer, will be used in the laboratory and in the field.
Upon the implementation of our design at the Dairy, on-site emissions will be reduced and the facility will be supporting and demonstrating a sustainable approach to treating ammonia emissions while also achieving water savings and effluent reduction. We will monitor the ammonia emissions produced by the facility throughout the year to ensure the productivity of the design. We will also monitor any potential "unintended" effluent (spent biochar, non-recyclable water, etc.). Moreover, we will meet with the dairy facility employees and surrounding community members to address any concerns they may have or suggestions for improvement.
Modern agricultural producers use chemical scrubbers to reduce ammonia emissions. These scrubbers use significant amounts of water, as the scrubbers are flushed continuously to avoid clogging. Our primary sustainability challenge is to reduce the calculated water consumption of 158,900 gpd (gallons per day) without compromising performance. Our secondary sustainability challenge is to maximize the separation efficiency of ammonia from both the initial air (feed gas) and flushing water stream. We have designed a three-step ammonia air scrubbing and filtration system that promotes sustainability by reusing water, recycling waste, and reducing costs. While ammonia emissions from agricultural sources remain a significant concern for air quality, the current conventional chemical scrubbers do not represent a sustainable solution, as they have high economic and environmental costs. "Non-chemical" water scrubbers do exist, but they are not sustainable with respect to ammonia removal because a continual stream of water is required, adding economic and environmental costs. Our innovative three-step design builds on these current systems to facilitate eventual large-scale adoption. 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. This second step eliminates the requirement for waste disposal of the water-ammonium effluent. Step three uses an air stripper to further reduce the ammonia concentration from the water. At the end of the three-step system the water can be reused to complete the cycle again. In P3 Phase I of this project we tested the biochar adsorbent; in P3 Phase II of this project we will build and test a field-scale version of our three- step system, which has great potential for reducing economic and environmental costs.
Overall, we achieved an ammonia removal efficiency of 67%, surpassing the modeled 55% based on the average ammonia concentration using the minimum amount of water required. While the efficiency was reasonable, the results were obtained in a laboratory environment with a single biochar sample with limited variations in particle size and can be improved upon. We hypothesize that biochar samples with smaller particle sizes will allow for higher removal efficiency due to an increase in surface contact area. Nonetheless, the relatively high removal efficiency achieved demonstrates that the second step design is an effective and environmentally contributive method for removing ammonia from dairy operations. This is the most important of the three steps for achieving sustainability goals and the success of this step supports moving on to a field-scale version of the our three-step air-scrubber system. Our innovative design will satisfy the overarching goal of preventing large emissions of ammonia into the atmosphere which contribute to pollution-induced health risks; while also significantly reducing the water consumption of agricultural operations in comparison to existing ammonia removal methods.