2017 Progress Report: Three-Phase Ammonia Air Scrubber Recycles WaterEPA Grant Number: SU836779
Title: Three-Phase Ammonia Air Scrubber Recycles Water
Investigators: Barsanti, Kelley
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Project Period: October 1, 2016 through September 30, 2017 (Extended to September 30, 2018)
Project Period Covered by this Report: October 1, 2016 through September 30,2017
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2016) RFA Text | Recipients Lists
Research Category: Sustainability , P3 Awards , P3 Challenge Area - Water
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 two 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.
The outputs and outcomes focused on three components: design of the biochar adsorption column, effectiveness of ammonia removal through the adsorption column, and an economic assessment of the complete system. The design for the first two-steps of the three-step air-scrubber was based on the available spacing at Scott Brothers Dairy facility in Moreno Valley, CA (location for P3 Phase II field test, see letter). The facility currently encompasses 400 acres including an onsite wastewater treatment facility. The design specifications for the adsorption column allow for an ammonia input of 25g NH3/hr to accommodate the average ammonia emissions during the months of March to September, when ambient temperatures are at a maximum. During P3 Phase I, a bench-scale prototype of the second step (adsorber) was constructed and used to conduct experiments to evaluate the ammonia removal efficiency. A one gram biochar sample was used in the prototype. The results from the bench-scale experiments demonstrate a 67% removal efficiency. This achievement surpassed the predicted 55% removal efficiency SuperPro (mathematical model). For our P3 Phase II, it was determined that a 10ft column with a bed depth of 6ft would achieve the same ammonia removal efficiency (67%) as achieved with the bench-scale prototype. The Scott Brothers Dairy currently does not have an ammonia reduction system in place, thus the reduction in ammonia emissions would provide an economic benefit to Scott Brothers Dairy (and ultimately other facilities) as listed in Table 1. The AQMD has a threshold of 200lbs 3 of ammonia per year, fees are imposed on emissions above the 200lbs per year. Based on AQMD emission factors, the 2100 cows at the Dairy emit a total of 51lb of ammonia per cow per year. At a cost of $0.03/lb, the Dairy currently pays an annual fee of $3,207. Based on design calculations and the bench-scale lab results, our three-step scrubber system will remove 70% of the gas-phase ammonia by absorption to water stream; the biochar adsorption then removes 67% of the aqueous ammonium, yielding a 53% reduction in total ammonia emitted. This 53% reduction in emissions would system save the Dairy $1504 in AQMD fees per year.
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. 4 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.