2016 Progress Report: Developing a Vacuum Distillation - Acid Absorption System for Recovery of Ammonia from Dairy ManureEPA Grant Number: SU835937
Title: Developing a Vacuum Distillation - Acid Absorption System for Recovery of Ammonia from Dairy Manure
Investigators: Tao, Wendong , Abrams, Neal
Current Investigators: Tao, Wendong
Institution: The State University of New York
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 2015 through September 30, 2017
Project Period Covered by this Report: October 1, 2015 through September 30,2016
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
Confined animal feeding operations generate significant amounts of liquid manure, which is rich in ammonia. Ammonia is further accumulated through anaerobic digestion of liquid manure. Liquid manure that exceeds the agronomic nutrient needs must be treated on site or transported offsite. This P3 project developed a vacuum thermal stripping – acid absorption process for recovery of ammonia from digested dairy manure. Ammonia is stripped out of digestate at boiling and reacts with sulfuric acid to produce ammonium sulfate crystals as a marketable chemical product. Vacuum lowers the boiling point temperature. When vacuum thermal stripping is installed in a recirculation line of digesters, digester heating could be eliminated or reduced when ammonia-recovered hot manure is returned to the digesters. With ammonia recovery, anaerobic digesters could produce more biogas or be loaded at a higher rate.
In Phase II, this P3 project is to further develop this innovative ammonia recovery process for commercial applications. The specific objectives are:
1. To evaluate the kinetics and capacity of ammonia volatilization in vacuum thermal stripping at seven combinations of boiling-point temperature and vacuum;
2. To optimize design and operational parameters of the stripper's demister and absorption column in order to produce granular ammonium sulfate;
3. To examine the synergies from integrating ammonia recovery into anaerobic co-digestion of dairy manure and foodwaste; and
4. To assess economic sustainability of options for integrating ammonia recovery into anaerobic digestion of dairy manure.
Major results and significant findings attained during Project Year 1 are as follows:
- Three common types of digestate (municipal sludge, food waste, dairy manure) with different concentrations of total solids (23.4-50.1 g/L) were found to have similar boiling point temperature-vacuum curves, which are slightly higher than that of pure water. These curves provide flexible operating parameters for commercial application.
- The optimum boiling point temperature – vacuum pressure for ammonia recovery in a recirculation line of a mesophilic digester was 65 oC and 25 kPa. Under the optimum combination of boiling temperature and vacuum, 95.8% and 99.9% of ammonia was stripped out of digested dairy manure in 1.5 and 3 h, respectively. The Lewis-Whitman model fitted ammonia stripping process well, which can be used to estimate design and operational parameters for scaled-up applications. Approximately 8 g ammonium sulfate could be produced with per liter of digested dairy manure, making the vacuum thermal stripping – acid absorption process profitable.
- A short demister works efficiently to retain water vapor while avoiding an adverse vacuum loss.
- High-purity ammonium sulfate crystals (94-106%) could be produced by stripping ammonia out of digested dairy manure, digested food waste, sludge digestate, and landfill leachate. To keep impurity at minimal, it is critical to control sulfuric acid content in the final acid solution and maintain saturation of acid solution with ammonium sulfate. There is a potential that the recovered crystals be certified as analytical grade chemical and nitrogen fertilizer.
Vacuum thermal stripping coupled with acid absorption is an innovative process to efficiently remove ammonia from digestate. Recovering ammonia in high-purity ammonium sulfate crystals makes this process highly profitable. The optimum boiling point temperature was 65oC as a vacuum is maintained. By controlling sulfuric acid concentration in the absorption solution, high-purity ammonium sulfate crystals can be produced.
In Year 2, there will be the following activities:
- More tests with the pilot system will be carried out to optimize the absorption column.
- Semi-continuous anaerobic co-digestion of dairy manure and foodwaste will be conducted to evaluate the synergistic effects of ammonia recovery on anaerobic digestion.
- Cost-benefit analysis will be performed to evaluate economic sustainability of integrating ammonia recovery into anaerobic digestion, including the synergies from integrating ammonia recovery into anaerobic digestion.