Final Report: Developing a Vacuum Distillation - Acid Absorption System for Recovery of Ammonia from Dairy Manure

EPA Grant Number: SU835937
Title: Developing a Vacuum Distillation - Acid Absorption System for Recovery of Ammonia from Dairy Manure
Investigators: Tao, Wendong
Institution: The State University of New York
EPA Project Officer: Hahn, Intaek
Phase: II
Project Period: October 1, 2015 through September 30, 2017
Project Amount: $74,968
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2015) Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety


The purpose of this People, Prosperity and the Planet (P3) Phase II project was to further develop this innovative ammonia recovery process for commercial applications. The specific objectives were—

  1. To evaluate the kinetics and capacity of ammonia removal in vacuum thermal stripping under temperature and vacuum combinations lower than 70°C 252 torr, using a pilot-scale vacuum thermal stripping–acid absorption system;
  2. To optimize design and operational parameters of the stripper’s demister and absorption column in order to produce ammonium sulfate crystals;
  3. To examine the synergistic effects of integrating ammonia recovery into anaerobic co-digestion of dairy manure and food waste; and
  4. To assess the economic sustainability of options for integrating ammonia recovery into anaerobic digestion of dairy manure.

Summary/Accomplishments (Outputs/Outcomes):

  • Three common types of digestate with different concentrations of total solids (23.4–50.1 g/L) were found to have similar boiling point temperature-vacuum curves. The boiling point vacuum pressure of digestate was slightly higher than that of pure water. These curves provide flexible operating parameters for commercial application and the basis to investigate ammonia stripping kinetics at specific combinations of boiling-point temperature and vacuum.
  • Seven combinations of boiling temperature and vacuum pressure were tested for batch stripping of ammonia in dairy manure digestate (i.e., 50°C 16.6 kPa, 58°C 20.0 kPa; 65°C 25.1 kPa; 70°C 33.6 kPa; 80°C 54.0 kPa; 90°C 74.2 kPa; and 100°C 101.3 kPa). The optimum boiling point temperature–vacuum pressure for ammonia recovery in a recirculation line of a mesophilic digester was 65°C and 25.1 kPa. Under the optimum combination of boiling temperature and vacuum, 95.8 percent and 99.9 percent of ammonia was stripped in 1.5 and 3 hours, respectively. The Lewis-Whitman model fitted the ammonia stripping process well, which can be used to estimate design and operational parameters for scaled-up applications, such as cycle length and stripper geometry. Under the optimum combination, the ammonia mass transfer coefficient was as high as 37.3 mm/hour, suggesting a fast process of ammonia stripping. The low ammonia saturation concentrations (0–13 mg N/L at boiling temperature 65–100°C) suggested a large driving force to strip ammonia.
  • There were two design flaws with the demister and absorption column in the original pilot system, which resulted in demister corrosion and impurity in the acid solution. To correct that, (1) we replaced copper pipe, heating tubes, and demister packing material with stainless steel pipe, tubes and scrubbers; and (2) a fine glass diffuser was replaced by a coarse plastic diffuser in the absorption column. In addition, a liquid trap was installed between the stripper and absorption column, which prevented overflow of feed and backflow of acid solution. After such corrections, it was found that a 1-ft-3-in-diameter demister works efficiently to retain water vapor and associated heat and subsequently improve crystallization of ammonium sulfate in the absorption column. An acid solution depth of 12–18 cm was adequate to absorb the stripped ammonia while preventing from temperature increase in the absorption solution.
  • Although volatile organic compounds, such as cyclohexene, were stripped along with ammonia and absorbed to the final acid solutions, no volatile organic compounds were detected in the recovered crystals. High-purity ammonium sulfate crystals (94–106%) could be produced by stripping ammonia out of dairy manure digestate, food waste digestate, sludge digestate and landfill leachate. To keep sulfuric acid attachment to the crystals minimal, it is critical to control sulfuric acid content in the final acid solution at 2–4 percent and maintain saturation of acid solution with ammonium sulfate. There is a potential that the recovered ammonium sulfate crystals be certified as analytical grade chemical and nitrogen fertilizer.
  • Dairy manure supplements nutrients and improves substrate biochemical composition for stable anaerobic co-digestion with food waste. However, overdosing results in co-substrate inhibition to biogas production due to recalcitrance of cellulose and toxicity of lignin and lignin derivatives. Batch experiments were performed to evaluate co-substrate inhibition to mesophilic co-digestion of liquid dairy manure and food waste. The semi-empirical Edwards model simulated the co-substrate limitation–inhibition kinetics best. Specific biogas yield reached the highest when co-digesting up to 86 percent food waste with 14 percent liquid dairy manure. Semi-continuous co-digestion of 30 percent liquid dairy manure and 70 percent food waste at a hydraulic retention time of 14 days attained 94 percent of the simulated maximum biogas yield.
  • Four bench-scale anaerobic digesters were operated under mesophilic conditions for co-digestion of liquid dairy manure and food waste, two without ammonia recovery and the other two with ammonia recovery. Stripping the co-digestate for 7–9 hours in three batches increased the ratio of volatile dissolved solids to total volatile solids by 33–142 percent, the ratio of soluble chemical oxygen demand to volatile solids by 9–56 percent, and the ratio of soluble protein to crude protein from 24–26 percent to 33–44 percent. The substantial increase in solids solubilization was attributed to the low-temperature thermal treatment during vacuum thermal stripping. The ratio of volatile fatty acids to volatile solids decreased by 45 percent in one batch of stripping and increased by only 16 percent in another batch, possibly due to stripping of volatile fatty acids. As organic loading rate was increased to above 3 g VS/L/d, digestate pH decreased to lower than 6.5, total ammonia nitrogen concentration increased to above 1.5 g/L and specific biogas yield began to decrease sharply, indicating anaerobic digestion suppressed by ammonia. When digestate ammonia concentration was reduced to below approximately 1.5 g/L by ammonia recovery, biogas production rate and specific yield increased significantly in one of the two digesters with recirculation of stripped digestate.
  • Approximately 8 g ammonium sulfate could be produced with per liter of digested dairy manure, making the vacuum thermal stripping–acid absorption process profitable. We performed cost-benefit analysis in four cases with interest of potentially applying the vacuum thermal stripping–acid absorption process to anaerobic digestion of food waste and rinse water, effluent of mesophilic food waste digester, effluent of thermophilic sludge and food waste co-digester, and landfill leachate. All the options we analyzed had promising economic feasibility and great potential of commercialization, having benefit/cost ratio up to 3.2–4.5 and payback period as short as 12–24 months.
  • A nonprovisional U.S. patent (utility) application entitled “Production of Ammonium Sulfate Using a Vacuum Absorption Process” was filed on April 11, 2017, and published in publication No. US-2017-0291825-A1 on October 12, 2017. The State University of New York College of Environmental Science and Forestry disseminated a technology flyer to potential patent licensees and technology users.
  • Funded ($37,000) by the New York State Center for Clean Water Technology, stripping experiments are going on to refine design and operational parameters for applying the vacuum thermal stripping–acid absorption process to ammonia recovery from source-separated human urine. A P3 student team member (Fred Agyeman) and an industry partner were awarded a $10,000 Innovation Fund award from the Syracuse Center of Excellence to characterize its rinse water and assess the feasibility of its treatment using an integrated anaerobic digestion and ammonia recovery system. In 2016, they were also funded by New Energy Xcelerator in Upstate New York to develop business models for commercializing the vacuum thermal stripping and acid absorption process.


Vacuum thermal stripping coupled with acid absorption is an innovative process to efficiently remove ammonia from digestate and ammonia-rich wastewater. The best practical boiling point for ammonia recovery is at temperature 65°C and vacuum pressure 25–28 kPa. By controlling sulfuric acid concentration in the absorption solution at 2–4 percent and optimizing the demister design, high-purity ammonium sulfate crystals can be produced. Recovering ammonia in high-purity ammonium sulfate crystals makes this process profitable. In addition, it is promising to use this process as a biomass pretreatment method for downstream anaerobic digestion and other beneficial uses of bio-residues, such as dairy and swine manure.

Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 11 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Anwar SW, Tao W. Cost benefit assessment of a novel thermal stripping – acid absorption process for ammonia recovery from anaerobically digested dairy manure. Water Practice and Technology 2016;11(2):355-364.
abstract available  
SU835937 (Final)
  • Abstract: IWA-Abstract
  • Journal Article Tao W, Ukwuani AT. Coupling thermal stripping and acid absorption for ammonia recovery from dairy manure: ammonia volatilization kinetics and effects of temperature, pH and dissolved solids content. Chemical Engineering Journal 2015;280:188-196.
    abstract available   full text available
    SU835937 (Final)
    SU835331 (2014)
    SU835331 (Final)
    SU835723 (Final)
  • Full-text: Science Direct-Full Text HTML
  • Abstract: Science Direct-Abstract
  • Other: Science Direct-Full Text PDF
  • Journal Article Ukwuani AT, Tao W. Developing a vacuum thermal stripping–acid absorption process for ammonia recovery from anaerobic digester effluent. Water Research 2016;106:108-115.
    abstract available   full text available
    SU835937 (Final)
  • Abstract from PubMed
  • Full-text: Science Direct-Full Text HTML
  • Abstract: Science Direct-Abstract
  • Other: Science Direct-Full Text PDF
  • Supplemental Keywords:

    Bio-based feedstock, resource recovery, waste to value, concentrated animal feeding operations

    Relevant Websites:

    Faculty advisor's website covering this P3 project and P3 team students:

    Sustainable Wastewater Treatment & Resource Recovery Exit


    Progress and Final Reports:

    Original Abstract
  • 2016 Progress Report

  • P3 Phase I:

    Developing a Vacuum Distillation – Acid Absorption System for Recovery of Ammonia from Dairy Manure  | Final Report