Grantee Research Project Results
Final Report: Struvite Recovery from Anaerobically Digested Dairy Manure
EPA Grant Number: SU835331Title: Struvite Recovery from Anaerobically Digested Dairy Manure
Investigators: Tao, Wendong , Mayer, Douglas , Mazinani, Ehsan , Ukwuani, Anayo , Agyeman, Fred , Abdulai, Hamidu , Austin, Scott , Das, Jonathan Masih , Robinson, Jesse , Stephan, Emily , White, Krystal , Wolcott, Scott , Elniski, Autumn
Institution: The State University of New York
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2012 through August 14, 2014 (Extended to November 14, 2014)
Project Amount: $89,943
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2012) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities
Objective:
Struvite recovery has been demonstrated at pilot and full scales mainly with municipal sludge digester effluent. However, phosphorus removal from dairy manure via struvite recovery has been low. This P3 project was to explore low-cost methods to overcome the hindrances to struvite recovery from anaerobically digested dairy manure. This project in Phase I developed a passive pebble-sand filtration system to reduce solids concentration to non-inhibitory level (<1 g/L) and found that calcium carbonate precipitation could be employed to minimize calcium hindrance to struvite formation. The major objectives of this project in Phase II were 1) to develop the solid-liquid separation system at a larger scale in order to provide manure filtrate for struvite recovery; 2) to explore cost-effective methods to eliminate the other hindrances to struvite formation in the filtrate of anaerobically digested dairy manure; and 3) to improve the design of an air-lift crystallizer for struvite crystallization in manure filtrate.
Summary/Accomplishments (Outputs/Outcomes):
Pebble filters separate solids from liquid in anaerobically digested dairy manure by surface filtration because a cake is formed on a bed of pebbles. After one batch of filtration, pebble filters produced manure filtrate with total suspended solids below 1 g/L. Therefore, the 2nd stage sand filtration is not necessary. We compared two modes for loading digested dairy manure to six pebble filters for solid-liquid separation. It was found that weekly small doses resulted in significantly faster filtration relative to one-time loading to 2-3 months of cycles. It was also found that pre-filtration of anaerobically digested dairy manure using a screw press significantly decreased surface filtration in the pebble filters. Three scaled-up pebble filters were set up in October 2013 and operated until August 2014. With the improved operation of larger pebble filters, manure filtrate with higher ammonia concentrations (1.2-1.7 g N/L) was produced and stored for struvite tests. A farm waste (shredded corncobs) could be mixed with anaerobically digested dairy manure for enhancement of manure filtration. Electric arc furnace slag was found to effectively increase manure filtrate pH to the levels for struvite recovery and Ca precipitation.
Struvite production with Ca-removed manure filtrate and diluted filtrate still posed challenges to significantly increase recovery efficiency. One possible reason was dissolution of calcium hydroxide accompanied with dilution of manure filtrate, which resulted in elevated Ca2+:Mg2+ and Ca2+:PO43- ratios as well as too high pH (>9.5). Rather than using air-lift crystallizers, we performed flask tests to quickly identify the effects of stirring speed and pH on struvite precipitation with different dilution ratios of manure filtrate. Moreover, we tested solids formed at different sizes and changes of phosphorus forms (soluble reactive, acid hydrolyzable, and total) along with struvite precipitation. No significant differences were found between these dilutions. Ionic strength, one of the potential hindrances to struvite recovery from dairy manure, could be decreased by ammonia recovery via a thermal stripping – acid absorption process. It was found that ammonia recovery could produce another value-added product and may improve struvite recovery due to adjusted pH and dissolution of particulate phosphates via thermal treatment.
Air-lift crystallizers are different from fluidized bed reactors and agitated reactors. An air-lift crystallizer is a bubble column with an additional draft tube, which divides the column into an air-sparged riser and a downcomer. Pressure gradient drives liquid circulation in the crystallizer. In addition to velocity gradient (G value), gas holdup and liquid velocity are important factors affecting crystallization. Further experiments with the high-viscosity manure filtrate are needed to optimize the design of air-lift crystallizer for struvite nucleation and crystal growth.
Conclusions:
Pebble filtration is a low-cost, effective method for solid-liquid separation of anaerobically digested dairy manure. Manure filtrate has low concentrations of suspended solids without interference with struvite recovery. Manure cake could be composted and reused as bedding material. Diluting manure filtrate with sludge digestion liquor appeared not to increase removal efficiency of orthophosphates despite more precipitates could be formed. Struvite recovery from dairy manure still has a limited efficiency as the other research groups have found recently. Ammonia recovery is more promising, which could produce another value-added product and overcome hindrance to struvite recovery from anaerobically digested dairy manure. Dairy farms have a great interest in integrating nutrient recovery into their farm nutrient management plans. The fertilizers recovered from dairy manure have the potential of organic labelling
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 8 publications | 3 publications in selected types | All 3 journal articles |
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Agyeman F, Tao W. Anaerobic co-digestion of food waste and dairy manure: Effects of food waste particle size and organic loading rate. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2014;133:268-274 |
SU835331 (Final) |
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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. |
SU835331 (2014) SU835331 (Final) SU835723 (Final) |
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Supplemental Keywords:
agricultural wastewater treatment, bio-based feedstocks, biofiltration technology, phosphorus recovery, sustainable design, waste to valueRelevant Websites:
Dr. Wendong Tao's Website Exit
Progress and Final Reports:
Original AbstractP3 Phase I:
Sustainably Overcoming Hindrance to Struvite Recovery from Anaerobically Digested Dairy Manure | 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.