Ron Sheffield Memorial Student Poster Competition Winners

The Waste to Worth conference hosts a student poster competition – open to graduate and undergraduate students.

2017 – Cary, North Carolina

  • Erin Stevens University of Nebraska-Lincoln
  • Allison Deviney NC State University,
  • Linda Schott, University of Nebraska-Lincoln. 

student poster winnters 2017 waste to worth conference

L to R: Tommy Bass, Erin Stevens, Allison Deviney, Linda Schott

2015 – Seattle

  • First: Laura Kenny, Rutgers University
  • Second: George Neerackal, Washington State University
  • Third: Nicole Schuster, University of Nebraska – Lincoln

student poster winners 2015 waste to worth conference

L to R: George Neerackal, Laura Kenny, Nicole Schuster

2013 – Denver

  • First: Kira Shonkwiler, Colorado State
  • Second: Fei Sun, Washington State
  • Third: Kelsey Bruning, Iowa State

student poster winners 2013 waste to worth conference

L to R: Julianna Sheffield, Kelsey Bruning, Fei Sun, Kira Shonkwiler

Putting the Power in PowerPoint

Proceedings Home W2W Home

Presentations are an important part of our outreach. Have you ever created a powerpoint that just didn’t land with your audience? Looking to revamp your process but don’t have time to squeeze it into your busy schedule? This presentation will provide practical ways you can create more powerful powerpoints when time is of the essence. It will highlight color choice, questions to ask yourself as you develop your deck, and the assertion-evidence based approach to slide development. You’ll also hear about where you can go to find more information on creating impactful presentations. Have a slide or two you’re really struggling with? Send it to and you could be selected to collaborate on a before and after example for this session.


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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Cataloging and Evaluating Dairy Manure Treatment Technologies

Proceedings Home | W2W Home w2w17 logo


To provide a forum for the introduction and evaluation of technologies that can treat dairy manure to the dairy farming community and the vendors that provide these technologies.

What Did We Do?

Newtrient has developed an on-line catalog of technologies that includes information on over 150 technologies and the companies that produce them as well as the Newtrient 9-Point scoring system and specific comments on each technology by the Newtrient Technology Advancement Team.

What Have We Learned?

Our interaction with both dairy farmers and technology vendors has taught us that there is a need for accurate information on the technologies that exist, where they are used, where are they effective and how they can help the modern dairy farm address serious issues in an economical and environmentally sustainable way.

Future Plans

Future plans include expansion of the catalog to include the impact of the technology types on key environmental areas and expansion to make the application of the technologies on-farm easier to conceptualize.

Corresponding author name, title, affiliation  

Mark Stoermann & Newtrient Technology Advancement Team

Corresponding author email address

Other Authors 

Garth Boyd, Context

Craig Frear, Regenis

Curt Gooch, Cornell University

Danna Kirk, Michigan State University

Mark Stoermann, Newtrient

Additional Information


All of the vendors and technology providers that have worked with us to make this effort a success need to be recognized for their sincere effort to help this to be a useful and informational resource.

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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

USDA-NRCS and the National Air Quality Site Assessment Tool (NAQSAT) for Livestock and Poultry Operations

Proceedings Home | W2W Home w2w17 logo


The National Air Quality Site Assessment Tool (NAQSAT) was developed as a first-of-its-kind tool to help producers and their advisors assess the impact of management on air emissions from livestock and poultry operations and identify areas for potential improvement related to those air emissions.

What did we do?

In 2007, several land-grant universities, with leadership from Michigan State University, began developing NAQSAT under a USDA-NRCS Conservation Innovation Grant (CIG). The initial tool included beef, dairy, swine, and poultry operations. A subsequent CIG project, with leadership from Colorado State University, made several enhancements to the tool, including adding horses to the species list. In 2015, USDA-NRCS officially adopted NAQSAT as an approved tool for evaluating air quality resource concerns at livestock and poultry operations. USDA-NRCS also contracted with Florida A&M University in 2015 to provide several regional training workshops on NAQSAT to NRCS employees. Six training workshops have been completed to date (Raleigh, NC; Modesto, CA; Elizabethtown, PA; Lincoln, NE; Richmond, VA; and Yakima, WA) with assistance from multiple NAQSAT development partners. Additionally, USDA-NRCS revised its comprehensive nutrient management plan (CNMP) policy in October 2015 to make the evaluation of air quality resource concerns mandatory as part of CNMP development.

Snippet from website of the National Air Quality Site Assessment Tool

Group photo of team in field

Zwicke in class lecturing

Zwicke and group in animal housing facility

What have we learned?

NAQSAT has proven to be a useful tool for bench-marking the air emissions impacts of current management on confinement-based livestock and poultry operations. In the training sessions, students have been able to complete NAQSAT runs on-site with the producer or producer representative via tablet or smartphone technologies. Further classroom discussion has helped to better understand the questions and answers and how the NAQSAT results can feed into the USDA-NRCS conservation planning process. Several needed enhancements and upgrades to the tool have been identified in order to more closely align the output of the tool to USDA-NRCS conservation planning needs. NAQSAT has also proven to be useful for evaluating the air quality resource concern status of an operation in relation to the CNMP development process.

Future Plans

It is anticipated that the identified needed enhancements and upgrades will be completed as funding for further NAQSAT development becomes available. Additionally, as use of NAQSAT by USDA-NRCS and our conservation planning and CNMP development partners expands, additional training and experience-building opportunities will be needed. The NAQSAT development team has great geographic coverage to assist in these additional opportunities.

Corresponding author, title, and affiliation

Greg Zwicke, Air Quality Engineer – Air Quality and Atmospheric Change Team, USDA-NRCS

Corresponding author email

Other authors

Greg Johnson, Air Quality and Atmospheric Change Team Leader, USDA-NRCS; Jeff Porter, Animal Nutrient and Manure Management Team Leader, USDA-NRCS; Sandy Means, Agricultural Engineer – Animal Nutrient and Manure Management Team, USDA-NRCS

Additional information


C.E. Meadows Endowment, Michigan State University

Colorado Livestock Association

Colorado State University

Florida A&M University

Iowa Turkey Federation

Iowa Pork Producers

Iowa Pork Industry Center

Iowa State University

Iowa State University Experiment Station

Kansas State University

Michigan Milk Producers Association

Michigan Pork Producers Association

Michigan State University

Michigan State University Extension

National Pork Board

Nebraska Environmental Trust

Oregon State University

Penn State University

Purdue University

Texas A&M University

University of California, Davis

University of Georgia

University of Georgia Department of Poultry Science

University of Idaho

University of Maryland

University of Maryland Department of Animal and Avian Sciences

University of Minnesota

University of Missouri

University of Nebraska


Virginia Tech University

Washington State University

Western United Dairymen

Whatcom County (WA) Conservation District

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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Nitrogen and Phosphorus Cycling Efficiency in US Food Supply Chains – A National Mass-Balance Approach

Proceedings Home | W2W Home w2w17 logo


Assessing and improving the sustainability of livestock production systems is essential to secure future food production. Crop-livestock production systems continue to impact nitrogen (N) and phosphorus (P) cycles with repercussions for human health (e.g. secondary particle formation due to ammonia emission and drinking water contamination by nitrate) and the environment (e.g. eutrophication of lakes and coastal waters and exacerbation of hypoxic zones). Additionally, P is a limited resource, and sustaining an adequate P supply is a major emerging challenge. To develop strategies for a more sustainable use of N and P, it is essential to have a quantitative understanding of the flows and stocks of N and P within the society. In this study, we developed detailed national N and P budgets to assess nutrient cycling efficiency in US (livestock) food supply chains, to identify hotspots of nutrient loss and to indicate opportunities for improvement!

What did we do? 

1. National nutrient mass-balance

A mass-balance framework was developed to quantify nutrient flows within the US. In this framework, the national US system is represented by 9 major sectors are relevant in terms of nutrient flows: mining (relevant for P only), industrial production, agriculture, food & feed processing industry, retail, households and other consumers, energy and transport, humans, and waste treatment. These sectors can exist of several sub-sectors. For example, the agricultural sector consists of several secondary sub-systems including pasture, agricultural soil, livestock and manure management (WMS – waste management system).

Different livestock categories can have distinct environmental impacts and nutrient use efficiencies (e.g. (Hou et al. 2016), (Eshel et al. 2014), (Herrero et al. 2013)), we therefore distinguish six livestock categories (dairy cattle, beef cattle, poultry (meat), poultry (layers), sheep, hogs) and

 their associated food commodities (dairy products, beef from dairy cattle, beef, poultry, eggs, lamb, pork).

For each sub-system, we identify and quantify major flows to and from this compartment. All flows are expressed in a common unit, i.e. metric kiloton N per year (kt N/yr) for nitrogen and metric kiloton P per year (kt P/yr) for phosphorus. Quantified flows include nutrient related emissions to the environment and waste flows.

At present, the waste sectors and environmental compartment are outside the system boundaries, that is, we quantify flows to these compartments, but we do not attempt to balance these sectors. We do, however, keep track of the exact chemical species (e.g. emission of N2O-N to air instead of N to air) emitted as far as possible. The municipal waste treatment (MSW) and municipal waste water treatment (WWTP) are treated in more detail: major flows from and to these compartments are quantified. These sub-sectors are treated in more detail because of their role in nutrient recycling through e.g. sewage sludge application on agricultural soils.

Data were collected in priority from national statistics (e.g. USDA NASS for livestock population) and peer-reviewed literature, and were supplemented with information from industrial reports and extension files if needed. If available, data were collected for the years 2009 to 2012 and averaged, when unavailable, we collected data for the closest year.

2. Scenario analysis

In the scenario analysis, we test the opportunity for dairy livestock production systems to contribute to a more efficient nutrient use through anaerobic co-digestion of dairy manure and organic food waste. Recently, Informa Economics assessed the national

 market potential of anaerobic digester products for the dairy industry (Informa Economics 2013). Next to a reduction in greenhouse gas emissions, anaerobic co-digestion of dairy manure and organic food waste can contribute to improve nutrient cycling efficiency (Informa Economics 2013). Dairy manure contains high levels of nitrogen and phosphorus, which can be used as a natural crop fertilizer, if recuperated from manure. Presently, non-farm organic substrates such as food waste are typically disposed of in landfills, which causes greenhouse gas (GHG) emissions and also results in a permanent removal of valuable nutrients from the food supply chain (Informa Economics 2013). By anaerobic co-digestion, a part of the nutrien! ts contai ned in dairy manure and food waste can be recovered. These nutrients can be used to fertilize crops and substitute synthetic fertilizer application. In the scenario analysis, we test to what extent anaerobic co-digestion of dairy manure and food waste can contribute to improve nutrient cycling efficiency, particularly by substituting synthetic fertilizers. We develop the scenario based on data provided in the InformaEconomics report.

What have we learned? 

In general, our results show that livestock production is the least efficient part of the total food supply chain with large losses associated with manure management and manure and fertilizer application to crops. In absolute terms, the contribution of the household stage to total and N and P losses from the system is small, approximately 5 and 7% for N and P, respectively. However, households ‘waste’ a relatively large percentage of purchased products, (e.g. 16% and 18% of N and P in dairy products end up as food waste), which presents an opportunity for improvement. A scenario was developed to test to what extent anaerobic co-digestion of dairy manure and food waste can contribute to improving nutrient cycling efficiency on a national scale. Results suggest that 22% and 63% of N and P applied as synthetic fertilizer could potentially be avoided in dairy food supply chains by large scale implementation of anaerobic co-digestion o! f manure and food waste.

Future Plans     

Future research plans include a further development of scenarios that are known to reduce nutrient losses at the farm scale and to assess the impact of these scenarios on national nutrient flows and losses.

Corresponding author, title, and affiliation        

Karin Veltman, PhD, University of Michigan, Ann Arbor

Corresponding author email

Other authors    

Carolyn Mattick, Phd, Olivier Jolliet, Prof., Andrew Henderson, PhD.

Additional information                

Additional information can be obtained from the corresponding author: Karin Veltman,


The authors wish to thank Ying Wang for her scientific support, particularly for her contribution in developing the anaerobic co-digestion scenario.

This work was financially supported by the US Dairy Research Institute.


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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Planning for Resilience: Using Scenarios to Address Potential Impacts of Climate Change for the Northern Plains Beef System

Proceedings Home W2W Home w2w17 logo


Resiliency to weather extremes is a topic that Northern Plains farmers and ranchers are already familiar with, but now climate change is adding new uncertainties that make it difficult to know the best practices for the future. Scenario planning is a method of needs assessment that will allow Extension and beef system stakeholders to come together using the latest climate science to discover robust management options, highlight key uncertainties, prioritize Extension programming needs, and provide an open forum for discussion for this sometimes controversial topic.

Overall objectives:

1. Determine a suite of key future scenarios based on climate science that are plausible, divergent, relevant, and challenging to the beef industry.

2. Determine robust management options that address the key scenario drivers.

3. Develop a plan for Extension programming to address determined educational needs.

What did we do?

A team of researchers, Extension specialists, and educators was formed with members from University of Nebraska and South Dakota State University. They gathered the current research information on historical climate trends, projections in future climate for the region, and anticipated impacts to the beef industry. These were summarized in a series of white papers.

Three locations were selected to host two half day focus groups, representing the major production regions. A diverse group representing the beef industry of each region including feedlot managers, cow calf ranchers, diversified producers, veterinarians, bankers, NRCS personnel, and other allied industries. The first focus group started with a discussion of the participants past experiences with weather impacts. The team then provided short presentations starting with historic climate trends and projection, anticipated impacts, and uncertainties. The participants then combined critical climate drivers as axis in a 2×2 grids, each generating a set of four scenarios. They then listed impacts for each combination. The impacts boundaries were feed production through transporting finished cattle off-farm.

Project personnel then combined the results of all three locations to prioritize the top scenarios, which were turned into a series of graphics and narratives. The participants were then brought together for a second focus group to brainstorm management and technology options that producers were already implementing or might consider implementing. These were then sorted based on their effectiveness across multiple climate scenarios, or robustness. The options where also sorted by the readiness of the known information: Extension materials already available, research data available but few Extension materials, and research needed.

Graphic depicting warm/dry, warm/wet, cold/dry, cold/wet conditions on the farm during winter-spring

Graphic depicting hot/dry, hot/wet, cool/dry, cool/wet conditions on the farm during summer-fall

What have we learned?

The key climate drivers were consistent across all focus groups: temperature and precipitation, ranging from below average to above average. In order to best capture the impacts, the participants separated winter/spring and summer/fall.

This method of using focus groups as our initial interaction with producers on climate change was well received. Most all farmers love to talk about the weather, so discussing historical trends and their experiences with it as well as being upfront with the uncertainties in future projections, while emphasizing the need for proactive planning seemed to resonate.

With so many competing interests for producers’ time, as well as a new programming area, it was critical to have trusted local educators to invite participants. Getting participants to the second round of focus groups was also more difficult, so future efforts should considering hosting a single, full day focus group, or allowing the participants to set the date for the second focus group, providing more motivation to attend.

Future Plans

The scenarios and related management options will be used to develop and enhance Extension programming and resources as well as inform new research efforts. The goal is to provide a suite of robust management options and tools to help producers make better decisions for their operation.

Corresponding author, title, and affiliation

Crystal Powers, Extension Engineer, University of Nebraska – Lincoln

Corresponding author email

Other authors

Rick Stowell, Associate Professor at University of Nebraska – Lincoln

Additional information

Crystal Powers


155 Chase Hall, East Campus

Lincoln, NE 68583


Thank you to the project team:

University of Nebraska – Lincoln: Troy Walz, Daren Redfearn, Tyler Williams, Al Dutcher, Larry Howard, Steve Hu, Matthew Luebbe, Galen Erickson, Tonya Haigh

South Dakota State University: Erin Cortus, Joseph Darrington,

This project was supported by the USDA Northern Plains Regional Climate Hub and Agricultural and Food Research Initiative Competitive Grant No. 2011-67003-30206 from the USDA National Institute of Food and Agriculture.

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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Talking Climate with Animal Agriculture Advisers

Proceedings Home W2W Home w2w17 logo


The Animal Agriculture in a Changing Climate (AACC) project was established to leverage limited Extension expertise across the country in climate change mitigation and adaptation, with the goal of building capacity among Extension professionals and other livestock advisers to address climate change issues.

What did we do? 

The Animal Agriculture in a Changing Climate project team created a suite of educational programs and products to build capacity across the United States. Key products of the project:

  • Online courses: 363 participants registered with a 35% completion rate (Whitefield et al., JOE, 2016)
  • National and regional symposia and workshops: 11 face-to-face conferences with approximately 1,350 attendees.
  • Website: Over 5,900 users with over 21,100 total views. Project videos have received nearly 8,900 views.
  • Social media: AACC weekly blog (990 subscribers); daily Southeast Climate Blog (38,506 site visits); regional newsletters (627 subscribers); Facebook & Twitter (280 followers)
  • Ready-to-use videos, slide sets, and fact sheets
  • Educational programming: 390 presentations at local, regional, and international meetings
  • Collaboration with 14 related research and education projects

What have we learned? 

A survey was sent out to participants in any of the project efforts, in the third year of the project and again in year five. Overall, participants found the project resources valuable, particularly the project website, the online course, and regional meetings. We surveyed two key measures: abilities and motivations. Overall, 60% or more of respondents report being able or very able to address all eight capabilities after their participation in the AACC program. A sizeable increase in respondent motivation (motivated or very motivated) existed after participation in the program, particularly for helping producers take steps to address climate change, informing others about greenhouse gases emitted by agriculture, answering client questions, and adding new information to programs or curriculum.

The first challenge in building capacity in Extension professionals was finding key communication methods to engage them. Two key strategies identified were to: 1) start programming with a discussion of historical trends and agricultural impacts, as locally relevant as available, and 2) start the discussion around adaptation rather than mitigation. Seeing the changes that are already apparent in the climatic record and how agriculture has adapted in the past and is adapting to more recent weather variability and climatic changes often were excellent discussion starters.

Another challenge was that many were comfortable with the science, but were unsure how to effectively communicate that science with the sometimes controversial discussions that surround climate change. This prompted us to include climate science communication in most of the professional development opportunities, which were then consistently rated as one of the most valuable topics.

Future Plans    

The project funding ended on March 31, 2017. All project materials will continue to be available on the LPELC webpage.

Corresponding author, title, and affiliation        

Crystal Powers, Extension Engineer, University of Nebraska – Lincoln

Corresponding author email

Other authors   

Rick Stowell, University of Nebraska – Lincoln

Additional information


Thank you to the project team:

Rick Stowell, Crystal Powers, and Jill Heemstra, University of Nebraska – Lincoln

Mark Risse, Pam Knox, and Gary Hawkins, University of Georgia

Larry Jacobson and David Schmidt, University of Minnesota

Saqib Mukhtar, University of Florida

David Smith, Texas A&M University

Joe Harrison and Liz Whitefield, Washington State University

Curt Gooch and Jennifer Pronto, Cornell University

This project was supported by Agricultural and Food Research Initiative Competitive Grant No. 2011-67003-30206 from the USDA National Institute of Food and Agriculture.


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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

How Well Do We Understand Nitrous Oxide Emissions from Open-lot Cattle Systems?

Proceedings Home W2W Home w2w17 logo


Nitrous oxide (N2O) emissions from concentrated animal feeding operations, including cattle feedyards, have become an important research topic. However, there are limitations to current measurement techniques, uncertainty in the magnitude of feedyard N2O fluxes, and a lack of effective mitigation methods. There are uncertainties in the pathway of feedyard N2O production, the dynamics of nitrogen transformations in these manure-based systems, and how N2O emissions differ with changes in climate and feedyard management.

What Did We Do?

A literature review was conducted to assess the state-of-the-science of N2O production and emission from open-lot beef cattle feedyards and dairies. The objective was to assess N2O emission from cattle feedyards, including comparison of measured and modeled emission rates, discussion of measurement methods, and evaluation of mitigation options. In addition, laboratory, pilot-scale, and field-scale chamber studies were conducted to quantify and characterize N2O emissions from beef cattle manure. These studies led to new empirical model to predict feedyard N2O fluxes as a function of temperature and manure nitrate and water contents. Organic matter stability/availability was important in predicting manure-derived N2O emissions: inclusion of data for dissolved organic carbon content and Ultraviolet-visible (UV-vis) spectroscopic indices of molecular weight, complexity and degree humification improved model performance against measured data.

What Have We Learned?

Published annual per capita flux rates for beef cattle feedyards and open-lot dairies in arid climates were highly variable and ranged from 0.002 to 4.3 kg N2O animal-1 yr-1. On an area basis, published emission rates ranged from 0 to 41 mg N2O m-2 h-1. From these studies and the Intergovernmental Panel on Climate Change emission factors, calculated daily per capita N2O fluxes averaged 18 ± 10 g N2O animal-1 d-1 (range, 0.04–67 g N2O animal-1 d-1). Some of this variability is inherently derived from differences in manure management practices and animal diets among open-lot cattle systems. However, it was proposed that other major causes of variation were inconsistency in measurement techniques, and irregularity in N2O production due to environmental conditions.

For modeling studies, N2O emissions were measured during 15 chamber studies (10 chambers per study) on commercial Texas feedyards, where N2O emissions ranged from below detection to 101 mg N2O m-2 h-1. Numerous feedyard and manure data were collected and regression analyses were used to determine key variables involved in feedyard N2O losses. Based on these data, two models were developed: (1) a simple model that included temperature, manure water content, and manure nitrate concentration, and (2) a more complex model that included UV-vis spectral data that provided an estimate of organic matter stability. Overall, predictions with both models were not significantly different from measured emissions (P < 0.05) and were within 52 to 61% agreement with observations. Inclusion of data for organic matter characteristics improved model predictions of high (>30 mg m-2 h-1) N2O emissions, but tended to overestimate low emission rates (<20 mg N2O m-2 h-1). This work represents one of the first attempts to model feedyard N2O. Further refinement is needed to be useful for predicting spatial and temporal variations in feedyard N2O fluxes.

Future Plans

This work clearly identified that neither the magnitude nor the dynamics of N2O emissions from open-lot cattle systems were well understood. Five primary knowledge gaps/problem areas were identified, where current understanding is weak and further research is required. These include: (i) the need for accurate measurement of N2O emissions with appropriate and more standardized methods; (ii) improved understanding of the microbiology, chemistry, and physical structure of manure within feedyard pens that lead to N2O emissions; (iii) improved understanding of factors that influence feedyard N2O emissions, including manure H2O content, porosity, density, available nitrogen and carbon contents, environmental temperatures, and use of veterinary pharmaceuticals; (iv) development of cost-effective and practical mitigation strategies to decrease N2O emissions from pen surfaces, manure stockpiles, composting windrows, and retention ponds; and (v) improved process-based models that can accurately predict feedyard N2O emissions, evaluate mitigation strategies, and forecast future N2O emission trends.

Given the potential for future regulation of N2O emissions, feedyard managers, nutritionists, and researchers may play increasingly important roles in on-farm nitrogen management. Current management practices may need modification or refinement to balance production efficiency with environmental concerns. There is a need for data derived from both large-scale micrometerological measurement campaigns and small-scale chamber studies to assess the overall magnitude of feedyard N2O emissions and to determine key factors driving its production and emission. Refined empirical and process-based models based on manure physicochemical properties and weather could provide a dynamic approach to predict N2O losses from open-lot cattle systems.

Corresponding author (name, title, affiliation):

Heidi Waldrip, Research Chemist, USDA-ARS Conservation and Production Laboratory, Bushland, TX

Corresponding author email address

Other Authors

Rick Todd, Research Soil Scientist, USDA-ARS Conservation and Production Laboratory, Bushland, TX

David Parker, Agricultural Engineer, USDA-ARS Conservation and Production Research Laboratory, Bushland, TX

Al Rotz, Agricultural Engineer, USDA-ARS Pasture Systems and Watershed Management Research Unit, University Park, PA

Andy Cole, Animal Scientist, USDA-ARS Conservation and Production Research Laboratory (retired), Bushland, TX.

Ken Casey, Associate Professor, Texas A&M AgriLife Research, Amarillo, TX

Additional Information

“Nitrous Oxide Emissions from Open-Lot Cattle Feedyards: A Review”. Waldrip, H. M., Todd, R. W., Parker, D. B., Cole, N. A., Rotz, C. A., and Casey, K. D. 2016. J. Environ. Qual. 45:1797-1811. Open-access article available at:…

USDA-ARS Research on Feedyard Nitrogen Sustainability:…


This research was partially funded by the Beef Checkoff:

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. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Estimating the Economic Value of the Greenhouse Gas Reductions Associated with Dairy Manure Anaerobic Digestion Systems Located in New York State

Proceedings Home W2W Home w2w17 logo


There is a worldwide concern in controlling the anthropogenic emissions of greenhouse gas (GHG) emissions. GHGs pertinent to this paper, include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) and are measured in CO2 equivalents (CO2 eq.). On a 100-year basis, CH4 is 34 times as potent as CO2, while N2O is 298 times as potent as CO2 (IPCC, 2013); CO2 eq. is referred to as the global warming potential (GWP) of these gases. The carbon from feed used on a dairy farm originally comes from CO2 recently removed from the atmosphere during photosynthesis and so has a neutral impact on climate change. However, carbon that is converted to CH4 and N2O is a significant concern since their GWPs are much higher. Dairy farms create GHG emissions when they use fossil fuel-based sources to provide energy for the farm, when importing fertilizer to grow crops and to harvest milk. However, emissions from the animals in the form of enteric CH4 and GHGs from manure management ! are much more significant due to the GWP. While every farm is different, estimates from Thoma et al. (2012) show that of the 34.9 Tg of CO2 eq. in the US dairy supply chain, 19% comes from feed production and 53% comes from milk production. Of the milk production, CO2 eq., 49% is from enteric emissions while 44% is from manure management, predominately from CH4 emissions from manure storages.

New York State, the third largest dairy state in the nation (NASS, 2015), has established ambitious overall renewable energy goals including incorporating 50% renewable energy in the electricity used in the State by 2030 (Energy to Lead, 2015) and reducing GHG emissions 40% by 2040 based on 1990 year baseline values (Executive Order, 2009). The New York State Public Service Commission (PSC) is charged with the responsibility of developing a system that encourages utilities to help meet these goals. This includes reforming the energy vision, a new clean energy standard that is being developed to value electric products from distributed energy sources that includes an economic value for the environmental attributes (E).

An attempt at quantifying the environmental benefits of AD (E) might be expressed as follows:

Etotal=∑▒〖Eghg+Eair quality+Ewater quality+Esoil quality+E…〗

As the State’s renewable energy goals are realized, there needs to be a way for the process to include special provisions for those renewable energy sources that have extra societal benefits, including economic and environmental, and that support the rural character of upstate NY. The dairy industry is New York’s leading agricultural sector, accounting for more than one-half of the state’s total agricultural receipts. The increased milk supply has been very important in helping to meet the tremendous growth in the production of yogurt in NYS. However, the margin between the cost of producing milk and the price received for milk sales, is shrinking. Investing in farm facilities like ADSs will need to be analyzed carefully to ensure a return on investment that merits their implementation. An economic value for the environmental attributes of electricity produced from an ADS would aid in the analysis, showing a more positive overall benefit.

Dairy farms are also under increasing pressure to improve conditions environmentally. The New York State Department of Environmental Conservation (NYSDEC) proposed revisions for the CAFO state permit, regulating the water quality impact of farms with more than 300 cows, will require manure storages to be built to limit spreading on at-risk fields during the winter and early spring seasons. These are farm sizes where manure-based ADSs have been built in the past and where many more could be implemented, given a reasonable rate of return. Manure storages are an important best management practice (BMP) to reduce the potential for water pollution by allowing farms to avoid manure spreading during inappropriate times. Unfortunately, if the manure system does not have a way to capture the GHGs produced, they are released into the atmosphere. Manure-based ADSs installed on farms would be a win-win-win to capture and reduce GHGs and to produce renewable energy from the captured! CH4, fur thermore helping to meet the NYS renewable energy and GHG reduction goals. ADSs installed on farms would stimulate the rural economy and also provide the farm and rural community with all the additional benefits contained in Appendix A.

This paper presents an analysis of the GHG reduction potential for a NYS dairy manure management system that includes AD, post-digestion solid-liquid separation (SLS) and long-term manure storage of SLS liquid effluent. This system is representative of almost all of the 27 ADSs currently operating on-farm in NYS today.


The mass of GHG emission reductions (i.e., the mass of carbon dioxide equivalents [MT CO2 eq.]) associated with AD (in this analysis, AD followed by SLS with liquid effluent stored long-term) located in New York State (NYS), was quantified and is discussed in this paper. The following protocols were used: IPCC (2006), AgSTAR (2011), and EPA (Federal Register, 2009) combined with reasonable input values that are representative of a farm’s baseline condition (long-term manure storage with no pre-treatment by ADS). The reductions quantified include: 1) the replacement of fossil fuel-based electrical energy by using AD produced biogas to operate an on-site engine-generator set, and 2) GHG emissions from CAFO required (for water quality purposes) long-term manure storages. The difference between the baseline condition and the conditions post-implementation of an ADS yields the farm’s net GHG emission associated with manure storage. To quantify the economic value! of the G HG emission reductions, the EPA social cost of carbon (SC-CO2) was used (EPA, 2016).

What did we do? *


The baseline condition is represented in Figure 1. Typical liquid/slurry long-term manure storages have manure that consists of urine plus feces, solid bedding and milking center washwater, added continuously as is produced on the farm. A natural crust may form as lighter organic material floats to the surface. The storages are constructed as a designed earthen storage with 2:1 side slopes or fabricated from concrete or steel. The fabricated structures have straight sides so less surface area is exposed. A few storages have a SLS prior to storage, while very few have a manure storage cover. Without a cover, they are exposed to rainfall from both annual precipitation and from extreme storms. To determine the baseline condition, storage with no SLS and with a natural crust was considered.

Figure 1. Baseline emissions from dairy farm with no renewable energy system (per cow, per year)

Figure 1. Baseline Emissions from Dairy Farm with No Renewable Energy System (Per cow per year)

Establish Long-Term Manure Storage Baseline Emissions

Part I – Estimating typical CH4 emissions from a long-term manure storage

An independent panel of experts agreed (USDA, 2014) that GHG emission reductions are best estimated using the Intergovernmental Panel on Climate Change (IPPC) Tier 2 method. For long-term manure storages, the daily methane emissions can be calculated by using Equation 1.

Equation 1. ECH4 = VS x Bo x 0.67 x (MCF/100)


ECH4 = Mass of CH4 emissions (kg CH4/cow-day)

VS = Mass of volatile solids in manure going to storage (kg/cow-day)

Bo = Maximum volume of CH4 producing capacity for manure (m3 CH4/kg VS)

= 0.24 m3 CH4/kg VS (for dairy cow manure)

0.67 = Conversion factor for m3 CH4 to kg CH4

MCF = CH4 conversion factor for the manure management system

Yearly CH4 emissions (kg CH4/cow-yr.) can be estimated by summing the daily emissions (or multiplying an average representative daily emission by 365 days). The MCF is largely dependent on the temperature and the type of manure management system. The MCF will change throughout the year as the manure storage temperature changes. Using a summer ambient temperature representative of Upstate New York, of 18°C (64°F) and a winter ambient temperature of < 10°C (< 50°F), a farm can limit the amount stored and the time in storage during the warmer months to reduce the average yearly MCF. Different manure systems also have a different MCF based on the oxygen levels, interception of CH4 gases, and moisture content.

The two variables that can be controlled by the farm management are the VS loading per cow and the methane conversion factor (MCF). The VS loading rate can be reduced by any pre-manure storage treatment process that reduces the storage organic loading rate; fine tuning the diet to reduce VS in the manure and SLS are examples of two methods used to control the VS.

Typically in NYS, manure is stored both in the summer and winter in a liquid/slurry system with no natural crust. Using average typical winter and summer manure storage temperatures, average MCF values can be used in Equation 1 to estimate average methane emissions for these 6-month storage periods. The MCF values are shown in Table 1.

Table 1. Typical Long-Term Manure Storage Methane Conversion Factors for Storage Periods in NYS1

Storage Period



Average Manure Storage Temperature (°C)






1These numbers are based on liquid/slurry storage without a natural crust cover.  (Source:  IPCC, 2006)

Using these MCF values shown in Table 1 and a per-cow VS excretion rate of 7.7 kg/cow-day (representative of high producing NY dairy cows – ASABE, 2006), manure storages could be estimated to produce 38 kg CH4/cow (for the winter storage period) and 79 kg CH4/cow (for the summer storage period) or an average of 4 metric tons (MT) of CO2 eq. per cow per year since 1 kg of CH4 = 34 kg CO2 eq.

Part II – Estimating typical N2O emissions from a long-term manure storage

There could be N2O emissions from a raw manure storage facility. The CO2 equivalent from N2O emissions can be estimated by using Equation 2.

Equation 2. CO2eq = 298 CO2/N2O GWP x EF3 x N x44 N2O/28 N2O-N


CO2eq = Equivalent global warming potential expressed as carbon dioxide

298 CO2/N2O = GWP factor for N2O

EF3 = Emission Factor for N2O-N emissions from manure management

N = Mass of N excreted per cow per day = 0.45 kg/cow-day (ASAE, 2005)

Using an EF3 value of 0.005 (USEPA, 2009) for long-term storage of slurry manure with a crust and multiplying it by 0.45 kg of N/cow-day and by 365 days per year yields an additional 0.38 MT of CO2 eq. per cow per year from N2O emissions from a long-term manure storage facility.

Summary of long-term storage GHG emissions

Combining both the CO2 eq. per cow per year from CH4 emissions and the CO2 eq. per cow per year from N2O emissions from a manure storage facility provides a baseline emission of 4.38 MT of CO2 eq. per cow per year from the manure storage systems that the NYS CAFO permit requires. These emissions can be mitigated by implementing a renewable energy system including an ADS with SLS of the digestate before storage.

Establish GHG Emissions and Emission Reductions for an ADS

If a manure-based ADS was installed on a farm, it could reduce the GHG emissions from manure management as well as replace fossil fuel use or energy for both the farm and other users. By capturing the CH4 produced, and combusting it for energy or simply flaring the excess, CH4 releases are converted back to the neutral CO2 originally consumed by the animals in the form of feed products. The ADS could help to meet NYS renewable energy and GHG reduction goals, however, farms with an ADS would need to manage the system to minimize leaks. With no incentives to control leaks, the CH4 produced potentially could add to overall farm GHG emissions.

Part I – Estimating typical CH4 emissions and emission reductions

There are a number of factors that need to be taken into consideration when estimating the GHG reductions that an ADS will provide. Leaks in the ADS can be very detrimental as more methane is produced in an ADS than is emitted naturally from a manure storage facility in the baseline condition. In addition, there are uncombusted CH4 losses from flares and even some from the engine as well. Although every farm system is different, typical values can be determined from the literature, on-farm measurements, and experience.

ADSs designed and built to supply only the quantity of electricity consumed on-farm and to reduce odors may not be as effective as systems designed specifically to reduce GHG emissions. The conservative values in Table 2 could be used to describe these types of systems. ADSs built specifically to reduce GHG emissions in addition to maximizing the renewable energy produced would achieve significantly better GHG reductions. The optimum numbers are achievable, while the obtainable values are based on ADSs that consider GHG emissions and are built to optimize CH4 production.

Table 2. ADS variables that can be controlled by the system equipment, operation, and management





Leaks from system (% CH4)




AgSTAR (2011) and on-farm
Flare Efficiency (%)




AgSTAR (2011) and on-farm
Engine capacity factor (decimal)




On-farm measurements
Engine efficiency (%)




On-farm measurements
ADS Parasitic load





On-farm measurements
Biodegradability post-digestion (%)




On-farm measurements
VS left after SLS (%)




On-farm measurements

The additional societal benefit of this technology can be calculated using EPA’s SC-CO2 of $47.82 as the 2017-2019 average SC CO2 value per metric ton of C02 eq. (at a 3% discount rate) for the methane and nitrous oxide emissions (EPA, 2016).

Part II – Estimating typical N2O emissions and emission reductions for an ADS

An EF3 value of 0 (IPCC, 2006) for an uncovered liquid manure storage describes the typical emission factor from an ADS with SLS since post-digestion there would be no free oxygen, and after solids removal, there would not be a crust forming.

The resulting calculations from the conservative, optimum and obtainable ADS values are shown in Table 3. The fossil fuels avoided are based on the kilo-Watt hours (kWh) produced minus the parasitic load. The uncombusted CH4 from the engine is based on a rich burn engine. The CO2 equivalents from the system leaks and the digestate storage are the major emissions in the conservative scenario, the uncombusted emissions from the flare and the digestate storage are minor emissions from the optimum scenario, while storage contributes the most to the continuing emissions from the obtainable scenario.

Table 3. GHG Emissions from electric production converted with a $47.82 SC-CO2 into a value of E for conservative, optimum and obtainable ADS with solid separation of the digestate before storage.

Units Conservative Optimum Obtainable
Fossil Fuels Avoided
MT CO2 eq/cow-yr




Engine uncommuted CH4 MT CO2 eq/cow-yr

2.5 x 10-3

3.2 x 10-3

3.1 x 10-3

Flare uncommuted CH4 MT CO2 eq/cow-yr




System Leaks CH4 MT CO2 eq/cow-yr




Storage emissions CH4 MT CO2 eq/cow-yr




ƩCO2eq emitted – FF avoided MT CO2 eq/cow-yr




Baseline MT CO2 eq/cow-yr




Reduction in CO2eq MT CO2 eq/cow-yr




SC-CO2 Benefit $/cow-yr




Gross Electricity produced kWh/cow-yr




Value of E $/kWh




Summary of long-term storage GHG emissions

The obtainable value of E $0.081/kWh, for an ADS with SLS of the digestate could be used to better determine the value of renewable energy in meeting NYS’s goals of reducing GHG emissions, increasing renewable energy, and supporting the dairy industry and the upstate NY economy.

More specific values for each individual ADS could be determined as a more granulated value (i.e., a value based on a more detailed/thorough analysis) through the implementation of NYS’s renewable energy vision. By using a value of E that reflects the actual environmental benefit of an ADS, this would incentivize dairy farms with an ADS to improve their CH4 production to produce more electrical energy. This would also increase the interest of more dairy farms in controlling GHG emissions and producing renewable energy by investing in ADS on their farms.

What have we learned?

ADSs can be used to reduce the manure management generated GHG emissions from dairy farms. With careful management, 3.32 MT of CO2 eq. per cow-year can be credited to the ADS. Using EPA’s SC-CO2 average price during 2017-2019 of $47.82, this could amount to a GHG benefit of over $140/cow-year. At this time, the benefit to society is unrewarded and high costs for ADSs both to construct and to operate, discourage farms from installing them. Working towards New York State’s renewable energy goals, as well as the reduction in GHG emission goals by compensating farms for the societal value of $0.081 per kWh of electricity produced from a well-run ADS would better incentivize farms to both install and operate ADSs to the advantage of the State.

Future Plans


ADSs can provide additional GHG reductions by utilizing organic wastes that currently go to landfills or aerobic waste treatment facilities. Some landfills may be able to capture a portion of the CH4 that the organic waste produces as renewable energy, but typically the leaks from a landfill gas recovery system are greater than those of farm-based ADS. NYS has some interest in diverting organic waste from landfills to reduce: the fill rate, the potential GHG emissions, and O&M costs in landfills. The value of the diverted organic waste can be best recovered by society if the energy is recovered through manure-based AD since the nutrients would also be recovered by mixing the food waste with manure, digesting it and recycling the nutrients in the effluent to the land for growing crops.

Nutrients to grow crops that are currently utilized in the form of commercial fertilizer, could be offset by the nutrients contained in a post-digested liquid, which would also reduce the energy and accompanying fossil fuel emissions now emitted when manufacturing commercial nutrients.

Aerobic treatment of organic wastes requires additional energy that adds to the fossil fuel-based carbon dioxide emissions and typically does not recover nutrients. While anaerobic digestion creates renewable energy and preserves nutrients.

Typical ADSs produce a large portion of energy from CH4 as waste heat from the engine(s). Operating a Combined Heat and Power (CHP) system in conjunction with an enterprise that would utilize the heat produced, would enable the system to harvest even more renewable energy.

ADSs could improve GHG mitigation efforts if the effluent storage was covered and if the gas collected was included in the biogas utilization system, eliminating any emissions from the effluent storage while producing even more renewable energy.

Farm Disadvantages

Managing a complex and expensive ADS requires dedication and a sophisticated management effort that clearly competes for time with other tasks on the farm. There is the potential to emit excess CH4 if: 1) leaks are not properly controlled, 2) the engine generator, boiler and/or flare are not efficient or 3) if the effluent storage continues to produce uncontained CH4. These can all be compounded if off-site organics are imported to the farm. The existing NYS net metering program makes the current price paid for exported electricity, very low. This reduces the motivation to produce and capture the maximum amount of CH4 from the ADS.

Planning and installing an on-farm ADS takes time to consider the benefits and costs so that a business decision can be reached. Capital costs of ADSs vary, but can range from $4,000 to $5,500 per kW of generation capacity. Operating costs have been estimated at $0.02 to $0.03 per kWh. Much of the capital investment is considered lost capital by lenders. The existing manure management system should be examined to determine any disadvantages from extra solids, contaminants, or dilution. If the successful operation of the ADS depends on tipping fees from imported organics, the reliability and quality of these sources needs to be determined. If electricity is to be sold, the utility should be consulted to determine how/if the distribution lines to the farm can handle what is expected to be generated.

Corresponding author, title, and affiliation

Peter Wright, Agricultural Engineer, Cornell University

Corresponding author email

Other authors

Curt Gooch, Dairy Environmental Systems and Sustainability Engineer, Cornell University

Additional information

Early Stage Economic Modeling of Gas-permeable Membrane Technology Applied to Swine Manure after Anaerobic Digestion


Proceedings Home W2W Home w2w17 logo


The objective of this study was to conduct cost versus design analysis for a gas-permeable membrane system using data from a small pilot scale experiment and projection of cost versus design to farm scale.

What did we do?

This reported work includes two major steps. First, the design of a small pilot scale batch gas-permeable membrane system was scaled to process effluent volumes from a commercial pig farm. The scaling design maintained critical process operating parameters of the experimental membrane system and introduced assumed features to characterize effluent flows from a working pig farm with an anaerobic digester. The scaled up design was characterized in a spreadsheet model. The second step was economic analysis of the scaled-up model of the membrane system. The objective of the economic analysis was to create information to guide subsequent experiments towards commercial development of the technology. The economic analysis was performed by introducing market prices for components, inputs, and products and then calculating effects on costs and on performance of changes in design parameters.

What have we learned?

First, baseline costs and revenues were calculated for the scaled up experimental design. The commercial scale design of a modular gas-permeable membrane system was modeled to treat 6 days accumulation of digester effluent at 16,300 gallons per day resulting in a batch capacity of 97,800 gallons. The modeled large scale system is 19,485 times the capacity of the 5.02 gallon experimental pilot system. The installation cost of the commercial scale system was estimated to be $903,333 for a system treating 97,800 gallon batches over a 6 day period.

At $1/linear ft. and 7.9 ft./gallon of batch capacity, membrane material makes up 86% of the estimated installation cost. Other installation costs include PVC pipes, pumps, aerators, tanks, and other parts and equipment used to assemble the system, as well as water to dilute the concentrated acid prior to initiating circulation. The annual operating cost of the system includes concentrated sulfuric acid consumed in the process. Using limited experimental data on this point, we assume a rate of 0.009 gallons (0.133 pounds) of acid per gallon of digester effluent treated. At a price of $1.11 per gallon ($0.073/lb) of acid, acid cost per gallon of effluent treated is $0.010. Other operating costs include electric power, labor, and repairs and maintenance of the membrane and other parts of the system estimated at 2% of investment cost for non-moving parts and 6% of investment for moving parts. Potential annual revenue from the system includes the value of ammonium sulfate produced. Over the 6 day treatment period, if 85% of the TAN-N in the digester effluent is removed by the process, and if 100% of the TAN-N removed is recovered as ammonium sulfate, and given the TAN-N concentration in digester effluent was 0.012 pounds per gallon (1401 mg/l), then 0.01 pounds of TAN-N are captured per gallon of effluent treated. At an ammonium sulfate fertilizer price of $588/ton or $0.294/pound and ammonium sulfate production of 0.047 pounds (0.01 pounds TAN-N equivalent), potential revenue is $0.014 per gallon of effluent treated. No price is attached here for the elimination of internal and external costs associated with potential release to the environment of 0.01 pounds TAN-N per gallon of digester effluent or 59,073 pounds TAN-N per year from the system modeled here.

Several findings and questions, reported here, are relevant to next steps in experimental evaluation and commercial development of this technology.

1. Membrane price and/or performance can be improved to substantially reduce installation cost. Membrane material makes up 86% of the current estimated installation cost. Each 10% reduction in the product of membrane price and length of membrane tube required per gallon capacity reduces estimated installation cost per gallon capacity by 8.6%.

2. The longevity and maintenance requirements of the membrane in this system were not examined in the experiment. Installation cost recovery per gallon of effluent decreases at a declining rate with longevity. For example, Cost Recovery Factors (percentage of initial investment charged as an annual cost) at 6% annual interest rate vary with economic life of the investment as follows: 1 year life CRF = 106%, 5 year life CRF = 24%, 10 year life CRF = 14% . Repair costs are often estimated as 2% of initial investment in non-moving parts. In the case of the membrane, annual repair and maintenance costs may increase with increased longevity. Longevity and maintenance requirements of membranes are important factors in determining total cost per gallon treated.

3. Based on experimental performance data (TAN removal in Table 1) and projected installation cost for various design treatment periods ( HRT = 2, 3, 4, 5, or 6 days), installation cost per unit mass of TAN removal decreases and then increases with the length of treatment period. The minimum occurs at HRT = 4 days when 68% reduction of TAN-N in the effluent has been achieved.

Table 1. Comparison of installation cost and days of treatment capacity

4. Cost of acid relative to TAN removal from the effluent and relative to fertilizer value of ammonium sulfate produced per gallon of effluent treated are important to operating cost of the membrane system. These coefficients were beyond the scope of the experiment although some pertinent data were generated. Questions are raised about the fate of acid in circulation. What fraction of acid remains in circulation after a batch is completed? What fraction of acid reacts with other constituents of the effluent to create other products in the circulating acid solution? What fraction of acid escapes through the membrane into the effluent? Increased efficiency of TAN removal from the effluent per unit of acid consumed will reduce the cost per unit TAN removed. Increased efficiency of converting acid to ammonium sulfate will reduce the net cost of acid per gallon treated.

5. Several operating parameters that remain to be explored affect costs and revenues per unit of effluent treated. Among those are parameters that potentially affect TAN movement through the membrane such as: a) pH of the effluent and pH of the acid solution in circulation, b) velocity of liquids on both sides of the membrane, and c) surface area of the membrane per volume of liquids; effluent and acid solution, in the reactor. Similarly, the most profitable or cost effective method of raising pH of the digester effluent remains to be determined, as it was beyond the scope of the current study. Aeration was used in this experiment and in the cost modeling. Aeration may or may not be the optimum method of raising pH and the optimum is contingent on relative prices of alternatives as well as their effect on overall system performance. Optimization of design to maximize profit or minimize cost requires knowledge of these performance response functions and associated cost functions.

6. Management of ammonium sulfate is a question to be addressed in future development of this technology. Questions that arise include: a) how does ammonium sulfate concentration in the acid solution affect rates of TAN removal and additional ammonia sulfate production, b) how can ammonium sulfate be removed from, or further concentrated in, the acid solution, c) can the acid solution containing ammonium sulfate be used without further modification and in which processes, d) what are possible uses for the acid solution after removal of ammonium sulfate, e) what are the possible uses for the effluent after removal of some TAN, and f) what are the costs and revenues associated with each of the alternatives. Answers to these questions are important to designing the membrane system and associated logistics and markets for used acid solution and ammonium sulfate. The realized value of ammonium sulfate and the cost (and revenue) of used acid solution are derived from optimization of this p art of the system.

7. LCA work on various configurations and operating parameters of the membrane system remains to be done. Concurrent with measurement of performance response functions for various parts of the membrane system, LCA work will quantify associated use of resources and emissions to the environment. Revenues may arise where external benefits are created and markets for those benefits exist. Where revenues are not available, marginal costs per unit of emission reduction or resource extraction reduction can be calculated to enable optimization of design across both profit and external factors.

Future Plans

A series of subsequent experiments and analyses are suggested in the previous section. Suggested work is aimed at improving knowledge of performance response to marginal changes in operating parameters and improving knowledge of the performance of various membranes. Profit maximization, cost minimization, and design optimization across both financial and external criteria require knowledge of performance response functions over a substantial number of variables. The economic analysis presented here addresses the challenge of projecting commercial scale costs and returns with data from an early stage experimental small pilot; and illustrates use of such preliminary costs and returns projections to inform subsequent experimentation and development of the technology. We will continue to refine this economic approach and describe it in future publications.

Corresponding author, title, and affiliation

Kelly Zering, Professor, Agricultural and Resource Economics, North Carolina State University

Corresponding author email

Other authors

Yijia Zhao, Graduate Student at BAE, NCSU; Shannon Banner, Graduate Student at BAE, NCSU; Mark Rice, Extension Specialist at BAE, NCSU; John Classen, Associate Professor and Director of Graduate Programs at BAE, NCSU


This project was supported by NRCS CIG Award 69-3A75-12-183.