Comparison of Sulfuric vs. Oxalic Sulfuric When Forming Struvite from Liquid Dairy Manure

Purpose

The purpose of this project was to demonstrate a mobile fluidized-bed cone for extraction of phosphorus in the form of struvite (magnesium-ammonium phosphate) from undigested (raw) liquid dairy manure. Since Ca binds inorganic P, a particular emphasis was placed on evaluating the effect of oxalic acid as an acidifier and Ca binder.

Dairies often have excess P in manure in relation to the need for on-farm crop production. Easily mineable reserves of phosphorus (P) worldwide are limited, with a majority residing in Morocco (USGS 2013). One approach to recycling P is to capture excess P from dairy manure in the form of struvite for off-farm export as a nutrient source for crop production.

What we did

A portable trailer-mounted fluidized-bed cone (volume of 3200 L) was used to extract phosphorus in the form of struvite (magnesium-ammonium phosphate) from undigested (raw) liquid dairy manure. Batches of 13,000 liters of manure were evaluated and the system was operated at a flow rate of ~ 32 liters per minute.  Sulfuric acid or oxalic acid-sulfuric acid were used to decrease the pH, and sodium hydroxide was used to raise the pH. Oxalic acid was chosen for evaluation due to its dual ability to decrease pH and bind calcium.

What we learned

Results of concentration of total P or ortho-P (OP) after manure treatment through the fluidized bed suggested no advantage of the combination of oxalic acid with sulfuric acid to decrease the concentration of P (see Figures 1 and 2). More detailed analyses of centrifuged post-bed samples of manure effluent indicated that the oxalic acid was binding the free calcium, but the resulting Ca compounds remained suspended in the effluent. Centrifuged manure samples had Ca contents ~23% of un-centrifuged samples when oxalic/sulfuric acid was used as a pH reducer. Centrifuged manure samples had Ca contents ~84% of un-centrifuged samples when sulfuric acid was used as a pH reducer. With raw manure, oxalate does not appear to be beneficial, unless there is a more effective step to drop Ca-oxalate out of suspension, such as centrifuging.

Figure 1. Concentration of OP or P in manure after pre-treatment with oxalic and sulfuric acid.
Figure 1. Concentration of OP or P in manure after pre-treatment with oxalic and sulfuric acid.

 

Figure 2. Concentration of OP or P in manure after pre-treatment with sulfuric acid.
Figure 2. Concentration of OP or P in manure after pre-treatment with sulfuric acid.

Future Plans

Anaerobically digested (AD) manure will be evaluated with the same set of conditions that were utilized with raw dairy manure to determine potential benefits of using oxalic acid with AD manure.

Authors

Joe Harrison1, Kevin Fullerton1, Elizabeth Whitefield1, and Keith Bowers2.

1Washington State University

2Multiform Harvest

jhharrison@wsu.edu

Citations and video links

U.S. Geological Survey, Mineral Commodity Summaries, January 2013. http://minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock/mcs-2013-phosp.pdf

The Mobile Struvite Project Overview Video: Capturing Phosphorus from Liquid Dairy Manure and Cost Efficient Nutrient Transport

Dairy Struvite Video: Capturing Phosphorus from Dairy Manure in the Form of Struvite on 30 Dairy Farms in WA state

Alfalfa Struvite Video: Struvite, a Recycled Form of Phosphorus from Dairy Manure, used as Fertilizer for Alfalfa Production

Acknowledgements

This project funded by the USDA NRCS CIG program and the Dairy Farmers of Washington.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

Comparison of Struvite to Mono-Ammonium-Phosphate as a Phosphorus Source on Commercial Alfalfa Fields

The purpose of this project was to demonstrate a regional nutrient (phosphorus (P)) recycling relationship between the dairy industry and alfalfa forage growers. Dairies often have excess P in manure in relation to the need for crop production on-farm. Easily mineable reserves of phosphorus (P) worldwide are limited, with a majority residing in Morocco (USGS 2013). One approach to recycling P is to capture excess P from dairy manure in the form of struvite for off-farm export for use as a nutrient source of crop production. Washington State produces a significant amount of alfalfa for domestic and international sales.

What did we do

Struvite (Magnesium Ammonium Phosphate – NH4MgPO4· 6H2O) and Mono Ammonium Phosphate (MAP) were applied to 33 and 30 acres (control and treatment, Farm 1); and 60 and 55 acres (control and treatment, Farm 2) sections of alfalfa fields at two commercial forage producers in Eastern Washington. Fertilizer (struvite or MAP) was applied on an equivalent P2O5 basis in August 2017 and September 2018 (Farm 1 – existing stand) and September 2017 and September 2018 (Farm 2 – new seeding).

What have we learned

Accumulative yield of alfalfa in 2018 for Farm 1 was struvite = 7.14 tons, MAP = 7.51 tons. Accumulative yield (2 of 3 cuttings) of alfalfa in 2018 for Farm 2 was struvite = 3.08 tons, MAP = 2.95 tons. Average P concentration of alfalfa in 2018 for Farm 1 was struvite = 0.27, MAP = 0.27 (% DM).  Average P concentration in alfalfa in 2017 for Farm 1 was struvite = 0.31, MAP = 0.32 (% DM). Average P concentration of alfalfa in 2018 for Farm 2 for struvite and MAP was 0.27 and 0.28 % DM, respectively. Average accumulative P uptake of alfalfa in 2018 for Farm 1 was 38 and 39 lbs P/acre for struvite and MAP, respectively. Average accumulative P uptake (2 of 3 cuttings) of alfalfa in 2018 for Farm 2 was struvite = 15 lbs, MAP = 16 lbs P/acre. Results indicate that struvite is equivalent to MAP as a P source for commercial production of alfalfa.

Future Plans

The nutrient recycling project will continue through 2019. In addition, companion replicated plots studies are underway to evaluate the effects of ratio of MAP:Struvite and amount of P application for yield and quality of alfalfa.

Authors

Joe Harrison1, Steve Norberg1, Kevin Fullerton1, Elizabeth Whitefield1, Erin Mackey1, and Keith Bowers2.

1Washington State University, jhharrison@wsu.edu

2Multiform Harvest

Citations and video links

U.S. Geological Survey, Mineral Commodity Summaries, January 2013. http://minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock/mcs-2013-phosp.pdf

    The Mobile Struvite Project Overview Video: Capturing Phosphorus from Liquid Dairy Manure and Cost Efficient Nutrient Transport

    Dairy Struvite Video: Capturing Phosphorus from Dairy Manure in the Form of Struvite on 30 Dairy Farms in WA state

    Alfalfa Struvite Video: Struvite, a Recycled Form of Phosphorus from Dairy Manure, used as Fertilizer for Alfalfa Production

Acknowledgements

This project funded by the USDA NRCS CIG program and the Dairy Farmers of Washington.

 

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

Mobile Struvite System for Nutrient Extraction from Dairy Manure


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Purpose            

Use of dairy manure as the sole source of nitrogen can lead to increased amounts of P in soil. In addition, P reserves around the world are finite and technologies are needed to effectively capture excess P in manure for the purpose of recycling to areas and crops in need of P.

What did we do?          

During the past decade we have adapted a fluidized bed technology to effectively recover P from liquid dairy manure in the form of struvite (magnesium mono-ammonium phosphate). A starter amount of struvite is placed at the bottom of an inverted cone that forms the fluidized bed for producing additional struvite. Manure that has been pre-treated is pumped up through the bottom of the cone to create the swirling action of the fluidized bed. To effectively form struvite, P in manure has to be dissociated from Ca, before subsequently binding with Mg and NH3. The fluidized bed technology was originally demonstrated with swine manure which is relatively lower in Ca compared to dairy manure. Due to the greater content of Ca in dairy manure we determined that it was necessary to lower the pH in dairy manure so that P could be free of Ca and available to form struvite. The pH has been most successfully lowered with use of sulfuric acid. As the low-pH manure is pumped up through the cone, ammonia is injected into the bottom of the cone to raise the pH and promote formation of struvite. The struvite we produced has been used as an effective fertilizer for growth of triticale, oats, corn silage and alfalfa. 

Picture of fluidized bed technology

What have we learned?            

Agriculture and human waste water industries have shown interest in this technology for the capture of P. The technology has been demonstrated as stationary units at three dairies, and has also been adopted by the human waste water plants. Phosphorus removal from dairy manure has been greater than 50%. Greenhouse and field plot studies compared struvite to mon-ammonium phosphate (MAP) and results indicated that struvite was comparable or superior compared to MAP in acidic soils and inferior to MAP in alkaline soils.

Future Plans    

Our current project will involve the demonstration of a mobile system that can be easily transported from dairy to dairy on a 24 foot trailer. Struvite that is captured from each dairy will be used in agronomic studies to promote a nutrient recycling relationship.

Corresponding author, title, and affiliation        

Joe Harrison, Professor, Washington State University

Corresponding author email    

jhharrison@wsu.edu

Other authors   

Keith Bowers and Elizabeth Whitefield

Additional information              

http://www.puyallup.wsu.edu/dairy/nutrient-management/default.asp

Acknowledgements       

This project is funded USDA NRCS CIG #69-3A75-17-51.

Separation Technologies for Capturing Nutrients from Manure

Exporting phosphorus and possibly nitrogen from larger livestock operations as well as regions of large livestock populations is often essential for protecting water quality. Solids (and nutrient) separation technologies are an option for concentrating nutrients for export. This webinar introduces three approaches to solids separation that are being applied in commercial settings. This presentation was originally broadcast on January 18, 2019. More… Continue reading “Separation Technologies for Capturing Nutrients from Manure”