Final Report: Phosphorus Recovery from Sewage

EPA Grant Number: SU831817
Title: Phosphorus Recovery from Sewage
Investigators: Oerther, Daniel B. , Atikovic, Emma , Carlarne, Cinnamon P , Clark, Catherine A. , Gonzalez-Fernandez, Maria C. , Hosny, Ahmed Fouad , Humringhouse, Ben , Kinkle, Brian , Kleirer, Karen , Lamendella, Regina , Lieberth, Brett , Maurer, Eric , Mouch, Daniel , Noonan, Doug , Pumphrey, Sarah , Riks, Angela , Saikaly, Pascal , Yates, Brian , deFranchi, Giovanni Battista
Institution: University of Cincinnati
EPA Project Officer: Nolt-Helms, Cynthia
Phase: I
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2004) RFA Text |  Recipients Lists
Research Category: P3 Challenge Area - Materials & Chemicals , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability


Phosphorus is a growth limiting nutrient that is mined from rock ore, refined, used in fertilizers, and discharged to the environment through municipal sewage. The impacts of phosphorus discharge include severe eutrophication of fresh water bodies as well as irreplaceable loss of a valuable nutrient. The sustainable use of phosphorus must include recovery from municipal sewage and reprocessing as a fertilizer. Although researchers in the developed world are addressing this technical challenge, research in the US lags. The innovative design pursued in Phase I of this project integrated: (a) bioprocess engineering for enhanced biological phosphorus removal, (b) phosphorus recovery through chemical precipitation of struvite, (c) experimental assessment of phosphorus bioavailability from struvite as a slow-release fertilizer, and (d) economic analysis of phosphorus recovery from sewage.

To pursue these objectives, the project team subdivided into a number of technical teams focused upon (a) bioprocess engineering, (b) chemical precipitation, (c) fertilizer evaluation, and (d) economic analysis. Each of the four technical teams was responsible for developing and executing a plan of action to collect and analyze useful scientific information. The results from each technical team were fully integrated into the final report through weekly oral and written presentations by the entire project team with input from the faculty advisors.

The bioprocess engineering technical team set-up and operated two six-liter laboratory-scale suspended growth activated sludge bioreactors using a feed-and-draw approach. Seed biomass was collected from a full-scale enhanced biological phosphorus removal facility operated by Butler County, Ohio. One bioreactor was operated as a control with a fill-and-draw cycle to encourage the removal of carbon without phosphorus accumulation. The second bioreactor was operated to encourage enhanced biological phosphorus removal (EBPR). Regular maintenance was performed daily, and the levels of carbon, oxygen, nitrogen, and phosphorus as well as biomass abundance and identity were evaluated at regular intervals during the operation of the bioreactors. Kinetic studies were performed to characterize the rate of release of phosphorus in the reactors.

The fertilizer evaluation technical team operated hydroponic (shown in the picture on the next page) and soil studies using available green house facilities at the University of Cincinnati to determine the net benefits of struvite addition for the growth of plants. Hydroponic and soil

The chemical precipitation technical team calculated the stoichiometric balances needed to recover phosphorus from typical US sewage. Experimental BERE REACTION AFTER REACT1N studies were performed to evaluate the kinetics of struvite precipitation using reagent grade chemicals as well a liquid collected from the bioreactors. Advanced analytical chemistry was used to determine the identity and relevant abundance of metals and salts in the putative struvite precipitate. As shown in the picture, when successful precipitation occurred, phosphorus was removed from the liquid phase and concentrated in - a struvite powder as measured by the loss of blue color from soluble reactive phosphorus. studies were performed with coleus and alfalfa (Medicago sativus). The benefits of struvite addition were compared to no amendments and a commercial fertilizer (e.g., Bone Meal) containing a nitrogen:phosphorus:potassium ratio of 6:12:0.

The economic analysis technical team evaluated the costs and benefits ofproducing struvite at municipal sewage treatment plants and distributing the material to farmers as a replacement for phosphorus containing fertilizer.

Phase I of this project was integrated into the curriculum at the University of Cincinnati through incorporation into CEE600 Chemistry and Microbiology of Environmental Systems (3 hrs lecture course in Autumn 04), CEE6O 1 Chemistry and Microbiology of Environmental Systems Lab (1 hr hands-on lab course in Autumn 04), and EVST 501 Environmental Capstone (3 hrs lecture project course in Winter 05 and 3 hrs lecture project course in Spring 05). This project design enabled a diverse student design team with undergraduate and graduate students enrolled in engineering and environmental studies to examine both the bioavailability of phosphorus recovered from sewage for use as a fertilizer to improve agricultural practice, and the short and long-term ecological, economic, social and political costs and benefits of recycling and reusing phosphorus. In this way, the student design team evaluated both the technical feasibility and the long-term sustainability of recovering and reusing phosphorus from sewage.

Summary/Accomplishments (Outputs/Outcomes):

Overall, the project was viewed as a success. As identified in the original proposal, our major milestones included: a) developing a microbiological bioprocess reactor to dramatically increase the mass fraction of phosphorus in wastewater biomass; b) developing a precipitator reactor to capture phosphorus from wastewater as a struvite precipitate (magnesium ammonia phosphate); c) demonstrating that the recovered phosphorus is bioavailable and capable of stimulating the growth of plants as a fertilizer; and d) developing a socio-economic analysis to demonstrate the value of recovering phosphorus from sewage as a sustainable technology to improve best agriculture practice.

The laboratory-scale bioreactors achieved approximately 90% phosphorus recovery from a synthetic municipal sewage with a dynamic phosphorus profile that included an initial phosphorus level of 10 mg/liter at the start of the anaerobic phase, increasing to more than 50 mg/liter at the start of the aerobic phase, and concluding at less than 1 mg/liter at the start of the decant phase. Novel molecular biology-based techniques (shown in the picture) were used to assess the abundance of putative phosphorus accumulating organisms in the bioreactors, and the results demonstrated that the system was highly enriched for beta-subclass Proteobacteria that have been implicated as an important biocatalysts for enhanced biological phosphorus removal. Although the bioreactor successfully removed phosphorus, future work should examine the long term, stable operation of the bioreactor when phosphorus is removed from the system for struvite precipitation. Also, we need to explore the use of low tech options to recover phosphorus as developing countries may not have the financial nor technological resources for bioreactor operation as performed routinely in the US and western Europe.

Attempts to use liquid collected from the bioreactors as a starting material for struvite precipitation were unsuccessful. This was due to an unacceptably low concentration of phosphorus in the liquid waste which hindered our ability to create favorable stoichiometric conditions for struvite precipitation. To produce struvite for the fertilizer studies, reagent grade chemicals were substituted. The composition of our precipitates was evaluated using Hach test- n-tube reagents and Ion Chromatography. Dried struvite powder was created and subsequently analyzed as a fertilizer. Future work should re-examine alternative bioreactor design strategies to increase the levels of phosphorus in the precipitator reactor to allow struvite precipitation from liquid collected from the bioreactors. As mentioned above, we also need to explore low tech options for struvite precipitation to be used in developing countries.

The growth of representative plants, namely coleus and alfalfa, with struvite as a source of phosphorus provided encouraging results. Struvite significantly increased the height of alfalfa plants, and the extent, color, and density of foliage on coleus was significant enhanced with the addition of struvite. As shown in the picture, run-off studies indicated that phosphorus from struvite can be lost from soil during saturating rainfall. Therefore, future work should examine how struvite can be used as a long term, slow release source of phosphorus. Furthermore, additional plants should be examined to document the wide-spread benefits of struvite as a fertilizer including cash crops relevant to developing countries such as vegetables for community gardens.

The economic analysis for phosphorus recovery from wastewater is complex. The cost of eutrophication is difficult to assess, but estimates of the ecological impact of the nearly 8,000 square mile zone of hypoxia that occurs each summer in the Gulf of Mexico can be used as a conservative estimate of the tremendous environmental value that could be recovered with phosphorus recycling. Fishing alone in the Gulf generates nearly $3 billion of annual revenues which are severely threatened because Gulf hypoxia is most severe on the coastal shelf where it negatively impacts fish hatcheries and crustaceans. In the US, approximately twenty thousand publicly owned treatment plants process more than thirty five billion gallons of sewage each day. The current cost of treatment is approximately twenty billion dollars per year. With an average phosphorus content of nearly 10 mg/liter, assuming phosphorus recovery of ninety percent and a retail value of struvite of $400 per ton, phosphorus recovery from wastewater represents an annual gross revenue of nearly $3.5 billion dollars. Another difficult cost to assess is the displacement of workers in the existing phosphorus mining industry. If phosphorus is recycled from sewage, phosphorus mining would presumably decrease negatively impacting employment in local economies dependent upon phosphorus mining (e.g., Florida and South Africa). Future work should examine the social hurdles involved in accepting phosphorus from sewage as a fertilizer as well as quantifying the overall economic benefits versus costs in developed and less developed countries.

Each of our four major milestones was addressed in a significant way with a positive outcome. Our positive experience with the Phase I project provides definite objectives that we have incorporated into our Phase II proposal.

Proposed Phase II Objectives and Strategies:

Phase II will build upon our successful results from Phase I where we met our four major milestones. The overall objectives of Phase II can be divided into two major thrusts. The first thrust is focused upon phosphorus recovery from sewage in developed countries where our objective is to demonstrate that existing technology can provide stable, long term phosphorus recovery and precipitation as struvite. One of the major goals for developed countries is to cross the threshold of acceptance for farmers and gardeners to accept a fertilizer that originated from sewage. The second thrust is focused upon phosphorus recovery from sewage in less developed countries where our objective is to evaluate low tech alternatives for bioreactor operation and struvite precipitation. One of the major goals for developing countries is to address the technical challenge where low costs alternatives are needed.

To address issues in developed countries, we propose to purchase and operate pilot-scale bioreactor systems designed for automated process control and high throughput. This will address the technical challenge of stable, long term phosphorus recovery. We propose to collaborate with The Ohio State University agricultural extension service to host workshops for local farmers and community gardeners to assess their resistance to phosphorus fertilizers originating from sewage. We will visit successful programs established by the city of Milwaukee where Milorganite ( is marketed as a commercially viable soil amendment derived from sewage sludge.

To address issues in developing countries, we propose to take advantage of the Fulbright Scholar’s program of the US Department of State. The P1 has been selected to visit the Indian Institute of Science (IISc) in Bangalore from January — June, 2006 as a Fulbright Scholar. As a developing country and an emerging economic power, India provides an opportunity for field- based research on phosphorus recovery with a balance between technologically savvy institutions for high learning within major metropolitan areas and technologically challenged less developed agricultural regions. The P1 will work with researchers at IISc to develop and test low tech alternatives for phosphorus recovery. By significantly expanding the P3 project at the University of Cincinnati to include India as a partner, the educational benefits to the students participating in the program is expected to be significant: This global collaboration between a developed and developing country meets the broad objectives of the P3 program.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

agriculture, analytical, bacteria, bioavailabi I ity, engineering, innovative technology, precipitation, renewable, sustainable development, water,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Sustainable Industry/Business, Chemical Engineering, Sustainable Environment, Environmental Chemistry, Technology for Sustainable Environment, Ecology and Ecosystems, Chemicals Management, biofertilizer, phosphorus recovery, euthrophication, chemcial synthesis, pollution prevention, municipal sewage, application of agricultural chemicals

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