FERTILIZER-GRADE PHOSPHATE RECOVERY FROM WASTEWATER TREATMENT PLANTS, PART II

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0225859
• Project No.: WIS01573
• Project Start Date: Oct 1, 2011
• Project End Date: Sep 30, 2015

Project Director
Barak, PH, W.

Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218

Performing Department
Soil Science

Non Technical Summary
Although the local view of phosphorus research is primarily that of a water contaminant and secondarily an essential plant nutrient, a larger perspective recognizes with alarm that global supplies of phosphate rock are inherently limited and current reserves will last ~90 yrs at current production rates, and less if agricultural yields in developing countries are expected to rise. The research proposed will investigate the possibility of intervening in the poorly constructed anthropogenic phosphorus cycle currently in place with the aim of producing a high-analysis, high-value phosphorus fertilizer that can be returned from urban wastewater treatment plants to those agricultural fields for which a fertilizer phosphorus yield response is expected. Results are anticipated to be broadly scalable to other regions and nations, both developed and developing. On these grounds, the intended phosphorus recovery and recycling research addresses global food security and hunger. In order to close part of the phosphorus cycle and produce a valuable, high-analysis phosphorus fertilizer, an additional benefit will be derived: phosphorus will be diverted from biosolids that are currently land applied. In Wisconsin, the P and N concentrations in land-applied biosolids are largely correlated to the percent total solids, and P: N ratios vary from 1:3 to 1:1.5. Given the low bioavailability of biosolid-N, often estimated at ~15% in the first year, the ratio of available P to amount of available N is high, particularly when compared to plant nutrient requirements. Future application of manure and commercial fertilizers will likely be limited in order to maintain compliance with phosphorus limitations of a nutrient management plan under s. NR 151.07; biosolids applications that increase soil test P above 50 ppm would therefore prohibit application of manure to those fields, which would reduce the acceptability of biosolids by many farmers. This biosolids beneficiation aspect of the research meets the intent of funding research basic to the problems of agriculture in its broadest aspects. Likely results are a method of extracting phosphorus from the urban waste stream for return to agricultural production. Although not a new and sufficient supply of phosphorus globally, it does extend the use of the existing reserves beyond that which is possible currently, which instead build up supraoptimal P levels in soil. Removing P from biosolids will improve their acceptability as a nitrogen source, without building up soil P reserves. Removing P from the anaerobic digesters will reduce struvite precipitation potential and improve plant operations, as well as providing a new product to offset operations costs.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
403	5210	2040	33%
403	5210	2000	34%
403	5370	2000	33%

Knowledge Area
403 - Waste Disposal, Recycling, and Reuse;

Subject Of Investigation
5370 - Sewage and waste disposal facilities and systems; 5210 - Fertilizers;

Field Of Science
2040 - Mineralogy; 2000 - Chemistry;

Keywords

phosphorus recovery

phosphorus recycling

brushite

calcium phosphate

sewage treatment

anaerobic digestion

methanogenesis

acetogenesis

Goals / Objectives
Greater than 60% of total phosphorus in a modern, multiphase sewage treatment plant is solubilized in the mesophilic organic acid digestion phase and is then mostly precipitated into the biosolids, where it largely becomes a nuisance when land-applied to P-rich soils such as those of Wisconsin and the Midwest. Our current research has shown that recovery of the soluble phosphorus is greater, and potentially easier and cheaper, with calcium hydroxide added to the organic acid digest to form dicalcium phosphate than other alternatives. We therefore propose to extend our current work with synthetic solutions and lab-scale tests to small-scale studies at Madison Metropolitan Sewage District (MMSD) using a 100-L digester to produce organic acid digest and a 6-L fluidized bed reactor to produce and recover dicalcium phosphate, with varying operating conditions to optimize results. As a full-scale organic acid digester becomes available at MMSD, the experimental design will be scaled up. The recovered phosphate is suitable as-is as fertilizer in P-deficient soils or may be reprocessed as high grade ore for other purposes. Aside from recovering a natural resource in limited supply for which a global shortage is imminent, removal of P will beneficiate the biosolids and improve treatment plant operations. This project has an applied aspect but is expected to provide key new knowledge where none currently exists: * What are the environmental and operating conditions that will solubilize the greatest amount of P in the anaerobic digestion system, particularly in the organic acid digester * What are the environmental and operating conditions that will precipitate the greatest amount of P in a recoverable calcium phosphate form, after metered addition of calcium hydroxide * What is the nutrient availability of the recovered calcium phosphate compared with modern phosphate fertilizers * What is the hazard level, if any, of the recovered calcium phosphate and what limitations may be placed on its use

Project Methods
Optimization of phosphorus solubilization: A number of experiments utilizing a 100-L organic acid digester will be conducted, varying the hydraulic retention time (2-5 days) of the digest, monitoring total and dialyzable (soluble) P concentrations, as well as pH. Our prior experience taught us that a minimum of 5 days of operation are required to drop and stabilize pH. Once monitoring pH and P shows that steady state has been likely achieved, likely 10-20 days of operation, a full set of samples will be taken for determination total and dialyzable ions and organic acids, which will then be used as input data for Minteq, a chemical speciation and equilibrium model, which will allow determination as to whether the solubility maximum had been reached based on solubility considerations. Additional measurements will be made of density (pyknometer) and viscosity (Ostwald viscometer) to permit calculations of sedimentation rates by Stokes Law for falling particles. Optimization of fluidized bed reactor performance: At each point when the small-scale organic acid digester has been determined to have reached steady state, the contents will be used as feedstock for the 6-L fluidized reactor, treated with slurried calcium hydroxide to reach pH values between 5.5 and 7. Hydraulic retention times will be altered in accordance with the particle sizes observed and the measured density and viscosity measured in order to: 1) make certain that phosphate precipitates are not swept out of the reactor with the effluent, and 2) the particles do not prematurely settle without having an adequate chance to grow in size. Determination of the Nutrient Availability of Recovered Calcium Phosphate: The recovered calcium phosphate precipitates will be characterized by x-ray diffraction for dominant crystalline minerals and by wet chemical analysis for major minerals. Standard measures such as citrate solubility to express reactive P2O5 will be undertaken. To test its chemical reactivity in soil environments, measured rates will be added to soil samples at field moisture capacity, incubated, and then extracted with heavy, immiscible liquid displacement for analysis of soil solution concentrations of P, Ca, and other constituents. Results will be input into Minteq to determine whether the material has dissolved to the full extent permitted by brushite. Bioavailability of recovered phosphorus will be determined by greenhouse experiments in which plant response curves will be determined for varying rates of diammonium phosphate and rates of the recovered phosphate. The soil (Plano silt loam) will be that of a test plot from the Arlington Research Station that has a low soil test P value and is known to produce extreme P deficiencies in corn in greenhouse tests. Hazard Level of Recovered Calcium Phosphate: Wet chemical digestion and analysis for heavy metals by ICP-OES will be undertaken. Additional elements may be analyzed by x-ray fluorescence. Samples will be submitted to the State Hygiene Lab for evaluation of the pathogen levels to obtain a measure of handling restrictions for the product if made available to agriculture or consumer.

Progress 10/01/11 to 09/30/15

Outputs
Target Audience:The target audience reached during this project consisted in wastewater treatment plant directors, policy makers and operators and those with specialized interest in nutrient recovery through the Water Environment Research Foundation at the national and regional (Central States Water Environment Association) level. Also those involved in soil fertility, fertilizers and crops research and practice at ASA-CSSA-SSSA annual meetings. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided the scientific material for graduate research assistant Tyler Anderson to conduct master's level research at the UW-Madison, culminating in a master's thesis and a Master of Science degree from the UW-Madison in August 2015. Anderson also was afforded opportunities to present his research at the 2014 annual meetings of ASA-CSSA-SSSA and the 2015 annual meeting of the Central States Water and Environment Assoc. Additionally, this project provide Tyler Anderson, undergraduate Carolyn Barker, and research scientist Christy Davidson the opportunity to participate in a National Collegiate Inventors and Innovators Association, NCIIA, (now VentureWell) workshop to develop entrepreneurial skills to market this idea to industry. An undergraduate student, Connor Todd, used the research data as the subject of an undergraduate research project, culminating in a Poster presented in partial fulfillment of Biology 152 at the UW-Madison. How have the results been disseminated to communities of interest?Two distinct communities of interest were identified: the water and wastewater treatment industry and the soil fertility/fertilizers community, as well as the local academic unit. Presentations were made by Barak to the director and senior staff of the wastewater treatment plants of Milwaukee (11 Mar 2015), Madison, WI, and Woodridge, IL (24 Jul 2014). Presentations were made at annual meetings of the Central States Water and Environment Assoc. on 16 May 2013 ('Nutrient Recovery and Upcycling: Finding Value in Wastewater', Madison, WI), 13 May 2014 ('Nutrient Recovery and Upcycling: Phosphorus recovery in the form of brushite from municipal wastewater', St. Paul, MN) and 19 May 2015 ('A Greenhouse Study Comparing Brushite and Struvite, both Wastewater Recoverable Fertilizers, to standard Phosphorus fertilizers' and 'Phosphate Fertilizer Recovery from Anaerobic Acid Digesters in Sewage Treatment Plants: From Batch Process to Continuous Pilot', 19 May 2015, Oakbrook Terrace, IL). Results were disseminated to the soil fertility/fertilizer community through presentations at ASA-CSSA-SSSA meetings as a poster presentation ('A Greenhouse Study Comparing Brushite, MAP, DAP, TSP, and Struvite Using a Phosphorus Deficient Prairie Soil', 3 Nov 2014, Long Beach CA) and an oral presentation ('Recycling Post-consumer NPK Back into Agriculture', 16 Nov 2015, Minneapolis, MN). Results were disseminated to the academic unit by Tyler Anderson as a public thesis defense ('Production and Evaluation of Wastewater-Derived Brushite as Fertilizer', Dept of Soil Science, UW-Madison) on 13 Aug 2015 and by Barak as a public seminar ('The Public and Private Sides of Nutrient Recovery from Wastewater in the Barak lab', Dept of Soil Science, UW-Madison, 1 Oct 2014). What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Five runs to produce calcium phosphate at Madison Metropolitan Sewerage District's Nine Spring treatment plant from the organic acid digest were performed. We learned that successful operating conditions required addition of a flocculating polymer and use of a centrifuge to produce centrate suitable for recovering brushite. Chemical analysis of the initial and final digest for soluble phosphorus showed that 60 to 99% of soluble P was precipitated. The second goal, determining the environmental and operating conditions that precipitate the greatest amount of calcium phosphate, revealed the requirement of near-colloidal calcium hydroxide to have maximum effect; in the alternative, a mixture of struvite and unreactive granules of calcium hydroxide was found to be present together with brushite in the recovered product. A greenhouse experiment conducted with synthetic brushite found that brushite performance was nearly identical to those of mono- and di-ammonium phosphate (MAP and DAP). Greenhouse experiments showed that the MMSD product performed like MAP and DAP at low and moderate rates but underperformed compared to synthetic brushite at higher dosages, likely due to the presence of the small amount of unreacted calcium hydroxide present. Nonetheless, the MMSD product were very low in heavy metals and easily met the California standards for heavy metals in P fertilizers. In the course of this work, we observed the very high concentrations of ammoniacal nitrogen in the anaerobic digests, which is largely regarded as a nuisance since it must be removed before discharge, often removed by nitrification and denitrification. We experimented with removal of ammonium nitrogen by electrodialysis, filed an invention disclosure report with WARF, the intellectual property holder for the UW-Madison, which chose not to pursue patent protection; the PI petitioned return of title to the invention from the USDA, which was granted. The PI filed for preliminary US patent protection and then patent protection, which is currently pending.

Publications

• Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Anderson, T.J., Production and Evaluation of Wastewater-Derived Brushite as Fertilizer. Masters thesis, University of Wisconsin-Madison. 2015.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Target audiences include wastewater treatment plant operators who may use this process for removing phosphate from wastewater treatment plants and agronomists/soil scientists who may recommend the use the derived brushite as a phosphorus fertilizer to agricultural producers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Valuable graduate training opportunities have been provided to Mr. Tyler Anderson, in pursuit of his MSc in Soil Science from the Univ of Wisconsin-Madison. Undergraduate research opportunities have been provided to three undergraduates. An undergraduate mentored research opportunity was provided to a student of Bio 152 in the Barak lab. How have the results been disseminated to communities of interest? Results have been disseminated as oral presentations (Madison Metropolitan Sewage District, 24 Jun 2014; DuPage Co. Sewerage District, 24 Jul 2014; Strand Associates, Inc.; 13 Aug 2014) and posters (CSWEA, 12 May 2014; WARF Discovery Challenge, 21 May 2014). What do you plan to do during the next reporting period to accomplish the goals? Remaining work is to improve the value of the recovered brushite by identifying the limiting component that interfered with plant P uptake, perhaps residual base occluded in the product, and removing it by altering the recovery process or post-recovery processing. Also, beginning in the spring of 2015, a pilot plant using this technology will be set up by Nutrient Recovery and Upcycling, LLC, a spin-off company from this lab funded by USDA SBIR Phase II grant, at the DuPage County (IL) wastewater treatment plant, with the goal of capturing 5-10% of their organic acid digest on a continuous basis. Additional tweaking of methodology to add both calcium salts and calcium hydroxide will be considered.

Impacts
What was accomplished under these goals? Maximum soluble phosphorus at MMSD was to be found in the organic acid digest, ranging from 1000 to 1600 mg P/L. Maximum phosphorus precipitation was at pH 6.5 and reduced soluble P to between 2 to 200 mg P/L, amounting to phosphate reduction from 61 to 99%. The nutrient availability of the recovered phosphate products contained from 20 to 38% P2O5 by wt, of which 68 to 87% was 'available P' as judged by citrate-solubility. A separate greenhouse study agreed that brushite was very nearly as available as monoammonium phosphate and diammonium phosphate; the recovered phosphate products underperformed at higher P rates. The recovered phosphate products were analyzed for arsenic, cadmium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium and zinc and were far below AAPFCO limits (set as ppm per %P2O5).

Publications

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: The target audience reached during this reporting period consisted in wastewater treatment plant operators and those with specialized interest in nutrient recovery through the Water Environment Research Foundation at the national and regional level. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? This project has provided the scientific material for graduate research assistant Tyler Anderson, undergraduate Carolyn Barker, and research scientist Christy Davidson to participate in a National Collegiate Inventors and Innovators Association, NCIIA, workshop to develop entrepeneurial skills to market this idea to industry. How have the results been disseminated to communities of interest? Oral presentation to Central States Water Environment Association, 86th Annual meeting, Madison, WI, 16 May 2013, "Bringing Modern Water Treatment to the Developing World through Resource Recovery from Wastewater" What do you plan to do during the next reporting period to accomplish the goals? Plan to report to Central States Water Environment Association annual meeting and perhaps to national Water Environment Research Federation conference.

Impacts
What was accomplished under these goals? Five runs to produce calcium phosphate from the organic acid digest have been performed. Chemical analysis of the initial and final digest for soluble phosphorus is pending, but is expected to address the second goal, environmental and operating conditions that will precipitate the greatest amount of calcium phosphate. A greenhouse experiment has been conducted with brushite to determine the available phosphate from product, and the recovery five brushite samples are on their way for analysis of citrate-soluble ("available") P2O5; chemical analysis will also show whether the materials meet the California standards for heavy metals in fertilizers. We have observed the very high concentrations of ammoniacal nitrogen in the wastewater, which is largely regarded as a nuisance since it must be removed before discharge, often removed by nitrification and denitrification. We have begun experimentation with removal of ammonium nitrogen by electrodialysis

Publications

• Type: Conference Papers and Presentations Status: Accepted Year Published: 2013 Citation: "Bringing Modern Water Treatment to the Developing World through Resource Recovery from Wastewater", Carolyn Barker, Menachem Tabanpour and Phillip Barak. Oral Presentation. Central States Water Environment Association 86th Annual Meeting, 16 May 2013, Madison, WI.

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: In the past year, a graduate research assistant, Mr. Tyler Anderson, a BS (major: chemistry) from Arizona State University, was engaged for this project, beginning in September 2012. The digester for the project is 55-gal in capacity, has stainless-steel walls, aluminum internal heating coils, and variable speed direct drive motor with propeller for mixing the digest. The digester was tested in a 10-day run at Madison Metropolitan Sewage District Nine Springs waste water treatment plant; pH, percent solids, and other run parameters were monitored. The resulting digest was sent for testing to determine rheological properties and to confirm suspicions that this digest behaved as a non-Newtonian fluid. Field trips were taken to other waste water treatment plants not related to municipal sewage, including the Dane County manure digester in Vienna, WI, in partnership with Clear Horizons, and the Montchevre cheese waste digester designed and operated by Procorp. Grab samples were taken and analyzed at both of these facilities, as well as from the manure lagoon at the Swine Research Facility at the UW-Madison Agricultural Research Station in Arlington, WI. PARTICIPANTS: Ms. Christy Davidson, research scientist, BSc in Soil Science; Mr. Menachem Tabanapour, research scientist, BSc UW-Madison; Mr. Tyler Anderson, graduate research assistant, BSc (Chemistry) Arizona State University; Professor Phillip Barak, PI. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The motor for mixing in the digester was found to be underpowered at 1 amp and mixing was continued on a temporary basis by pumping the digest continuously from out-port to in-port for the duration of the run. Rheological measurements showed that the digest had properties of non-Newtonian solutions, with shear-thinning at low sheer rates and sheer-thickening at higher rates. These results will permit better selection of a motor to drive the mixing shaft and guide the separation techniques for removal of solids when producing phosphates from the digest. Analysis and chemical modeling revealed that slurries were saturated with struvite at the cow manure digester and the swine facility, whereas at the cheese waste digester, three-quarters of soluble phosphate dropped out of solution as brushite and the digest was significantly undersaturated with regard to struvite.

Publications

• No publications reported this period

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: In the first three months of this project, there are no outputs to report and no results have been disseminated. PARTICIPANTS: Individuals working on this project are the PI, Dr. Phillip Barak, and Research Specialist Menachem Tabanpour. Cooperating organization is Madison Metropolitan Sewage District, with Mr. Steve Reusser as liaison. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
In the first three months of this project, there are no outcomes to report.

Publications

• No publications reported this period