Overview of the U.S. Agricultural Biogas Industry and AgSTAR Technical Resources

AgSTAR is a voluntary program coordinated by the U.S. Environmental Protection Agency (EPA), in cooperation with the U.S. Department of Agriculture (USDA), that supports farmers and industry in the development and adoption of anaerobic digester (AD) systems. In addition to producing biogas, AD systems can help achieve other social, environmental, agricultural and economic benefits. AgSTAR offers a variety of resources and tools to assist those interested in exploring the use of AD systems, including:

    • Outreach materials addressing system design, selection, and use and project development tools that help assess digester feasibility.
    • Events including workshops and webinars to promote sharing of knowledge, information, and experiences.
    • Website information on operating digesters, including nationwide statistics as well as in-depth project profiles that provide details on digester system design, biogas use, and benefits realized.

AgSTAR’s presentation will provide a market overview of agricultural biogas projects in the United States, including trends and outlook for the future of this sector, and highlight two resources currently under development for industry stakeholders.

What did we do?

AgSTAR’s mission is to educate and inform stakeholders on biogas production in the United States and support the development of new projects. AgSTAR has developed a number of market studies, technical tools and outreach resources for agricultural biogas projects over the years. The AgSTAR national database for digester projects contains a wealth of information on digester projects in the United States. As of January 2019, there are 248 anaerobic digesters operating on livestock farms in the US.  AgSTAR estimates that in 2018, digesters helped reduce 4.27 million metric tons of CO2 equivalent (MMTCO2e). Since 2000, digesters on livestock farms have reduced direct and indirect emissions by an estimated 39.3 MMTCO2e.

The biogas industry in the livestock sector has a lot of room to grow. AgSTAR estimates that biogas recovery systems are technically feasible at more than 8,000 large dairy and hog operations. These farms could potentially generate nearly 16 million megawatt-hours (MWh) of energy per year and displace about 2,010 megawatts (MWs) of fossil fuel-fired generation.

To meet this massive opportunity, innovation is needed.  Several policies and business models that are driving the growth in this sector include:  

    • Policies:  
      • Food Waste Diversion from Landfills
      • Renewable Natural Gas (RNG) Incentives
    • Business Models:  
      • RNG to vehicle fuel
      • Third-party owned and operated systems
      • Eco-markets for co-products

AgSTAR continues to educate stakeholders on these industry trends and encourage new opportunities.

New and Updated products coming soon!

The AgSTAR program pleased to announce two resources coming in 2019 to help facilitate the implementation of AD-biogas projects:

    • AgSTAR Project Development Handbook (3rd Edition) – The Handbook is intended for agriculture and livestock producers, farm owners, developers, investors, policymakers, implementers, and others working in agriculture or renewable energy who are interested in AD/biogas systems as a farm manure management option.  The handbook is being substantially redesigned for this 3rd edition to help users gain insight into AD and current state-of-the-art discussions on project development, economics, co-digestion feedstocks, manure management issues, including agronomic application, potential carbon impacts, and financing/operational/ownership options.  The document provides basic information about biogas production and outlines many of the considerations and questions that should be addressed when evaluating, developing, designing and implementing a farm-based digester project.
    • AgSTAR Anaerobic Digester Operator Guidebook – The Operator Guidebook is a new resource to assist on-farm AD/biogas system operators to increase operational uptime and performance and efficiency as well as to help prevent common pitfalls that can lead to system shutdown and neighbor complaints.  The Guidebook spans nearly every part of the AD and biogas production process, providing industry expert experience and advice on dealing with potential issues within an AD/biogas system. The Guidebook is designed to answer fundamental questions about what it takes to successfully operate and maintain an AD/biogas system on an agricultural operation and it can be used as a resource to maximize profitability by increasing biogas yield, improve biogas quality, and minimize operating and maintenance expenses.  It is intended for use as a training tool for AD/biogas system owners, managers, operators, and other project stakeholders.

What we have learned?

Anaerobic digesters on livestock farms can provide many benefits compared to traditional manure management systems, including:

    • Diversified Farm Revenue
    • Rural Economic Growth
    • Conservation of Agricultural Land
    • Energy Independence
    • Sustainable Food Production
    • Farm-Community Relationships

While technology choices are important when implementing AD projects, a viable business model is critical.  

Future plans

The AgSTAR Program intends to continue working with its government, academia, industry, and non-profit organization stakeholders to promote the use of biogas recovery systems to reduce methane emissions from livestock waste.  This includes sharing information on industry trends; promoting and conducting events and webinars; and preparing outreach materials and project development tools, such as the AgSTAR Project Development Handbook and Anaerobic Digester Operator Guidebook.


Nick Elger, Program Manager, U.S. EPA AgSTAR & Global Methane Initiative, Elger.Nicholas@epa.gov

Additional information

Additional information and resources can be found on the AgSTAR Program website at: https://www.epa.gov/agstar.

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

Revenue Streams from Poultry Manure in Anaerobic Digestion (AD)

DUCTOR Corp. has developed a biological process that separates and captures nitrogen (ammonia) from organic waste streams. The biogas industry is a natural platform for this biotechnology as it solves the problem of ammonia inhibition, which has long bedeviled traditional anaerobic digestion (AD) processes. DUCTOR’s technology allows for stabilized and optimized biogas production from 100% high nitrogen feedstocks (such as poultry manure) and significantly strengthens the economics of biogas facilities: relatively inexpensive inputs, optimized gas production as well as new, higher value revenue streams from the organically produced byproducts—a pure Nitrogen fertilizer and a high Phosphorus soil amendment. DUCTOR’s mission is to promote biogas as a renewable energy source while securing efficient waste management and sustainable food & energy production, supporting the development of circular economies.


Figure 1. High Nitrogen Feedstock-molecular structure
Figure 1. High Nitrogen Feedstock

High concentrations of ammonia in organic waste streams have been a perpetual challenge to the biogas industry as ammonia is a powerful inhibitor of biogas production. In typical methanogenic communities, as ammonia levels exceed 1500mg/L Ammonia-N, the inhibition of methane production begins until it reaches toxic levels above 3000mg/L. Traditionally, various mechanical and chemical methods have been deployed to lower ammonia concentrations in high nitrogen organic feedstocks prior to or following biodigestion (Figure 1). These methods have proven cumbersome and operationally unstable. They either require dilution with often costly supplemental feedstocks, are fresh water intensive, waste valuable nutrients, or require caustic chemicals injurious to the environment. Without the application of these methods, nitrogen levels will build up in the digester and negatively affect the efficiency of biogas (methane) production. DUCTOR’s proprietary process revolutionizes ammonia removal with a biological approach, which not only optimizes the operational and economic performance of biogas production, it also allows for the ammonia to be recaptured and recycled as an organic fertilizer product (a 5-0-0 Ammonia Water). This biotechnical innovation represents a significant advancement in biogas technology.  

What did we do?

DUCTOR’s innovation is the invention of a fermentation step prior to the classic anaerobic digestion process of a biogas facility (Figure 2).  During this fermentation step in a pre-treatment tank, excess nitrogen is biologically converted into ammonia/ammonium and captured through a physical process involving volatilization and condensation of the liquid portion of the digestate.


Typical DUCTOR facility layout
Figure 2. Typical DUCTOR facility layout

We ran a demonstration biogas facility with these two steps in Tuorla, Finland for 2000 hours using 100% poultry litter as fermenter feedstock without experiencing ammonia inhibition of the methanogenesis process. While the control, a single-stage traditional digester, showed increased buildup of toxic ammonia, the fermented material coming out of the first stage of the DUCTOR process (having ~50-60% of its nitrogen volatilized and removed) exhibited uniform levels of nitrogen below the inhibition threshold (Figure 3). This allowed a stable and efficient digestion by the methanogenic microbial community in the second stage digester. The fermentation step effectively eliminates the need for co-digestion of poultry manures with other higher C/N ratio substrates.

Figure 3: Ammonium concentration & Methane quantities in treated and untreated substrates
Figure 3: Ammonium concentration & Methane quantities in treated and untreated substrates

What we have learned?

In addition to solving the problem of ammonia inhibition, DUCTOR’s innovation realizes the separation of valuable recycled nutrients in a manner that can produce additional revenue streams. The result of the fermentation process in the first stage digestion tank is an organically produced non-synthetic ammonia (NH4OH), which is condensed and collected. This ammonia water product can be marketed and sold as an organic fertilizer as it is the result of a completely biological process with no controlled chemical reactions. The non-synthetic ammonia produced comes from the digestion of poultry litter by ammonifying microorganisms in anaerobic conditions. Furthermore, this ammonia water is in a plant available form that can be metered onto fields based on crop demands and thus reduce the amount of excess nitrates leaching into the water table and surrounding watershed.

The solids byproduct that results from the completion of the anaerobic digestion process has a large fraction of phosphorus and potash. This digestate can be dried and pelleted to produce a high-phosphorus soil amendment. While recognizing demand for this product would vary by region based on existing phosphorus levels in the soil, it offers a transportable & storable way to return these valuable elements to the nutrient cycle.

nutrient life cycle

Finally, the importance of gas production as a form of sustainable, renewable energy cannot be understated. With 2/3rds of the world’s greenhouse gas emissions coming from the burning of fossil fuels for energy or electricity generation,1 biogas derived from anaerobic digestion can displace some of those processes and reduce environmental greenhouse gas emissions.2 Currently, there are many state and federal policies focusing on renewable energy credits and low carbon fuel standards to incentivize this displacement.3 With the ability to unlock poultry litter as an additional AD feedstock, biogas facilities can offer greater volumes of biogas production per ton of manure than either dairy or swine.

Future plans

We have several commercial projects that will feature the DUCTOR technology at various stages of development in North America. The demonstration facility at Tuorla has been disassembled and shipped to Mexico where it will be reassembled as part of a larger commercial project there. In cooperation with our Mexican partner, we will demonstrate successful operations under a new set of conditions, including different climate and a new source of poultry litter from different regional growing practices. We further intend to demonstrate the highly efficient water use of the process in a drought-prone area.

Additionally, we have received approval from the North Carolina Utilities Commission for entry into their pilot program for injecting biomethane into North Carolina’s natural gas pipelines. Our first project there is expected to begin construction in Spring 2019 to be completed and operational by early 2020. These projects, and others in development, will bring a very attractive and new manure management option to poultry farmers, while recycling nutrients from the waste stream and returning them to the soil in a measurable and sustainable manner.


Bill Parmentier, Project Development, DUCTOR Americas


Additional information



1Global Greenhouse Gas Emissions Data, US Environmental Protection Agency (EPA), https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data

2Sources of Greenhouse Gas Emissions, US Environmental Protection Agency, https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions

3Methane is a potent greenhouse gas that is over 20 times more damaging on the environment than carbon dioxide. Anaerobic digestion stops the release of methane into the environment by capturing it and using it for energy production or transportation fuel.

Federal incentives include the Rural Energy for America Program (REAP), Alternative Fuel Excise Tax Credit, & Federal Renewable Energy Production Tax Credit to name a few. Examples of state level incentives include various states Renewable Portfolio Standards (RPS) as well as California’s Low Carbon Fuel Standard (LCFS) or Oregon’s Clean Fuels Standard (CFS).


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

Renewable Energy Set-asides Push Biogas to Pipeline

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Deriving the most value from the harvesting of organic wastes, particularly waste produced through farming operations, can be quite challenging. This paper describes an approach to overcome the challenges of realizing the best value from harvested farming wastes through aggregation. Included in this description is an overview of the first swine waste-to-energy project in North Carolina based on aggregation of the value stream rather than aggregation of the feedstock, or manure. Also included in the description are an overview of the challenges encountered, approaches to overcome these challenges, and the solutions developed for this breakthrough approach that will foster further development of successful ventures to maximize the value derived from recycled farming wastes.

What did we do?

Increasingly, our civilization is turning to bioenergy sources as an environmentally-friendly, sustainable alternative to harvesting long-buried fossil fuel sources to supply our energy needs. As the land that farmers have cultivated for years becomes encroached more and more by non-farming land uses, society seeks innovations to address its concerns for our future food needs produced in a manner that addresses environmental concerns associated with modern food production, including nutrient recovery, water conservation and reuse, and controlling odors and emissions from agricultural wastes and manures. Collectively, these innovations have been described as ‘sustainable farming’ approaches.

North Carolina is a significant agricultural producer, and as such, a large producer of agricultural wastes. This state also became the first state in the Southeast to adopt a Renewable Energy Portfolio Standard, and is the only state in the U.S. to require a certain percentage of that renewable energy must be generated from agriculture waste recovery, with specific targets for swine and poultry waste. Naturally, the plentiful resources coupled with a regulatory driver for renewable energy worked together to create attention and efforts toward cost-effective and efficient means of supplying our energy needs through organic waste recovery, or bioenergy approaches.

We are only beginning to see a surge in commercial development for the recovery of additional value stream from the waste, such as through the recovery of nutrients, enzymes, and monetized environmental attributes associated with pollution abatement. While manyOptima-KV swine waste to pipeline RNG project forward-thinking farmers have learned that their waste is valuable for supplying renewable energy, it has been unfortunately difficult for an individual farmer to implement and manage advanced value recovery systems primarily due to costs of scale. Rather, it seems, success may be easier achieved through the aggregation of these products from several farms and through the collaborative efforts of project developers, product offtakers, and policy. A shining example of such aggregation and collaboration can be observed from the Optima-KV swine waste to pipeline renewable gas project, located in eastern North Carolina in an area of dense swine farm population.

The Optima-KV project combines, or aggregates, the biogas created from the anaerobic digestion of swine waste from five (5) adjacently located farms housing approximately 60,000 finishing pigs. The Optima-KV project includes the construction of an in-ground anaerobic digester at each farm. The resulting biogas is captured from each farm, and routed to an adjacent, centralized biogas upgrading facility, or refinery, where the biogas undergoes purification and cleaning to pipeline quality specifications. The renewable natural gas produced from this system will be sold to an electric utility subject to the requirements of the North Carolina Renewable Energy Portfolio Standards, and will result in reduced emissions from both the receiving electricity generating unit and the farms, reduced emissions of odors from the farms, and reduced fossil fuel consumption for the production of electricity. The upgraded biogas (RNG) will be transmitted to the electricity generating unit through existing natural gas pipeline infrastructure.

What have we learned?

The innovative design, permitting, and financing for the project is very different than a conventional feedstock aggregation approach, and thus much has been learned. To deliver the RNG to the end user, in this case, multiple contracts with multiple utilities wereGraphic showing how it works required, which presented challenges of negotiating multiple utility connections and agreements. This learning curve was steepened as, at the time of the inception of Optima KV, the state of North Carolina lacked formal pipeline injection standards, so the final required quality and manner of gas upgrading was established through the development of the project.

The project is currently in the beginning stages of construction, and completion is expected by the end of 2017. Given this schedule, the Optima KV project will provide the first pipeline injection of gas – from any source – in the state of North Carolina (all natural gas presently consumed in the state is sourced from out of state).

Future Plans

North Carolina’s potential for agricultural waste-to-energy projects is enormous, given its vast agricultural resources. Combining the potential from agriculture with the bioenergy potential from wastewater treatment plants and landfills, it is estimated to be third in capacity behind only California and Texas. The unique approach to aggregation of value streams from multiple sources, as exhibited by this project, will open the doors for similar aggregation strategies, including the anaerobic digestion of mixed feedstocks such as food waste, poultry and swine waste, animal mortality, fats, oils and grease and energy crops.

Corresponding author, title, and affiliation

Gus Simmons, P.E., Director of Bioenergy, Cavanaugh & Associates, P.A.

Corresponding author email


Additional information





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.

Aeration to Improve Biogas Production by Recalcitrant Feedstock

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Why aerate biogas digesters?

Most agricultural waste is largely composed of polymers such as lignin and complex carbohydrates that are slowly or nearly completely non-degradable in anaerobic environments. An example of such a waste is chicken litter in which wood chips, rice hulls, straw and sawdust are commonly employed bedding materials.  This makes chicken litter a poor candidate for anaerobic digestion because of inherently poor digestibility and, as a consequence, low gas production rates.

Previous studies, however, have shown that the addition of small amounts of air to anaerobic digestates can improve degradation rates and gas production. These studies were largely performed at laboratory-scale with no provision to keep the added air within the anaerobic sludge.

What Did We Do?

Picture of 4 digesters with sprayer tanksFour digesters were constructed out of 55 gallon sprayer tanks. The digestate was 132 L in volume with a dynamic headspace of 76 L. At the bottom of each tank a manifold was constructed from ½” PVC pipe in an “H” configuration and with a volume of approximately 230 mL. The bottom of the manifold had holes drilled in it to allow exchange with the sludge. Tanks were fed 400 g of used top dressing chicken litter (wood shaving bedding) obtained from a local producer (averaging 40% moisture and 15% ash) in 2 L of water through a port in the tank [labeled “1” in figure]. Two hundred mL of air were fed to the manifold through a flow meter [2] 0, 1, 4, or 10 times daily in 15-minute periods at widely spaced intervals by means of an air pump and rotary timer [4]. A gas port [3] at the top of the tank allowed for sampling and led to a wet tip flow meter (wettipflowmeters.com) to measure gas production. Digestate samples were taken out of a side port [5] for measurement of water quality and dissolved gases and overflow was discharged from the tank by means of a float switch wired in line with a ½” PVC electrically actuated ball valve.

Seven dried and weighed tulip poplar disks were added to each tank at the beginning of the experiment. At the end of the experiment, the disks were cleaned and dried for three days at 105 0C before re-weighing. Dissolved and headspace gases were measured on a gas chromatograph equipped with FID, ECD, and TCD detectors. Water quality was measured by standard APHA methods.

What Have We Learned?

Graph of chemical oxygen demand per liter and graph of liters of biogas per day

Adding 800 mL of air daily increased biogas production by an average of 73.4% compared to strictly anaerobic digestate. While adding 200 mL of air daily slightly increased gas production, adding 2 L per day decreased gas production by 16.7%.

Aerating the sludge improved chemical oxygen demand (COD) with the greatest benefit occurring at 2,000 mL added air per day. As noted, however, this decreased gas production in the control indicating toxicity to the anaerobic sludge.

The experiment was stopped after 148 days. When the tanks were opened, there was widespread fungal growth both on the surface of the digestate and the wood disks in the aerated tanks [left], whereas non-aerated tanks showed little evidence of fungal growth [right]. While wood disks subjected to all treatments lost significant mass (t-test, α=0.05), disks in the anaerobic tank lost the least amount of weight on average (6.3 g) while all other treatments lost over 7 g weight on average.

Picture of widespread fungal growth on the surface of the digestate and the wood discs in aerated tanks

Future Plans

Research on other feedstocks and aeration regimes are being conducted as are 16s and 18s community analyses.

Chart of grams dry weight pre experiment and post experiment

Corresponding author (name, title, affiliation)

John Loughrin, Research Chemist, Food Animal Environmental Research Systems, USDA-ARS, 2413 Nashville Rd. B5, Bowling Green, KY 42104

Corresponding author email address


Other Authors

Karamat Sistani, Supervisory Soil Scientist, Food Animal Environmental Research Systems. Nanh Lovanh, Environmental Engineer, Food Animal Environmental Research Systems.

Additional Information



We thank Stacy Antle and Mike Bryant (FAESRU) and Zachary Berry (WKU Dept. of Chemistry) for technical assistance.

Inclusion of the Environment Bottom Line in Waste to Worth: The Interaction Between Economics, Environmental effects, and Farm Productivity in Assessment of Manure Management Technology and Policy

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In a global context, the pork industry constitutes a huge economic sector but many producers operate on very thin margins. In addition, pork is one of the largest and most important agricultural industries in North Carolina and the United States but faces a number of challenges in regards to waste management and environmental impacts.On more local scales, swine producers face a number of additional constraints including land availability, waste management options (technical and regulatory), nutrient management costs, profits, risk, and return on investment. In the face of increasingly stringent environmental regulations, decreasing land availability, and higher costs for fertilizer, it is necessary to consider alternative technologies with the potential for improving environmental conditions and creating value added products. Technology assessments generally focus on technical performance as the measure of “utility” or usefulness. Primary physical performance measures such as efficiency, production rate, and capacity, while necessary may not be sufficient for capturing the overall value of a technology. A significant amount of research has evaluated the feasibility of technology adoption based on traditional economic measures but far less research has attempted to “value” environmental performance either at farm-scale or in the larger context (e.g. supply chain response to changes in technology or policy and regulation). Considering response over time, the extent to which environmental and economic policies and regulations positively or negatively affect technology innovation, emission and nutrient management, competitiveness, and productivity, remains largely unknown.

The purpose of this study is to evaluate the environmental and economic tradeoffs between current swine waste management practices in North Carolina and alternative scenarios for future on-farm decision making that include new technologies for waste removal, treatment, and nitrogen recovery. In addition, we begin to understand these economic and environmental tradeoffs in the context of various environmental policy and regulation scenarios for markets of carbon, electricity, and mineral fertilizer.

What did we do?

Using waste samples from swine finishing farms in southeastern NC, laboratory and bench scale experiments were conducted to determine the quantity and quality of biogas generation from anaerobic digestion and nitrogen recovery from an ammonia air stripping column. Based on these data as well as information from literature, six trial life cycle assessment scenarios were created to simulate alternatives for annual manure waste management for one finishing barn (3080 head) on the farm. Materials, energy, and emissions were included as available for all system components and processes including but not limited to waste removal from barns (flushing or scraping), treatment (open air lagoon or covered lagoon digester), nitrogen recovery (ammonia air stripping column), and land application (irrigation). A description of the scenarios as well as processes that are included/excluded for each can be found in Table 1. All scenarios were modeled over a one year operational period using a “gate to gate” approach where the mass and energy balance begins and ends on the farm (i.e. production of feed is not included and manure is fully utilized on the farm). It was assumed that each scenario included an existing anaerobic treatment lagoon with manure flushing system (baseline, representative of NC swine farms). In the remaining scenarios, the farm had an option of covering the lagoon and using it as a digester to produce biogas (offsetting natural gas); covering the digester and ammonia air stripping column for nitrogen recovery (offsetting mineral ammonium sulfate); installing a mechanical scraper system in the barn (replaces flushing); and/or different combinations of these. Open LCA, an open source life cycle and sustainability assessment software, was used for inventory analysis and the Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI 2.0) was used to characterize environmental impacts to air, water, and land. From Table 2 preliminary results indicate that all scenarios had a similar pattern in terms of impact for the assessed categories. The open air lagoon had the highest overall environmental impact followed by scraping manure with digestion and recovery and scraped slurry digestion with no nutrient recovery. Flushed manure to the digester with nutrient recovery had the lowest overall environmental impact, followed closely by scraped whole slurry to the digester with nutrient recovery.

Table 1. Life cycle assessment scenarios with waste management processes included in evaluation

Table 2. Relative impact of scenarios for selected environmental indicators

Using energy and emissions data from the initial life cycle assessment on alternative scenarios for swine waste management systems we have started to characterize the environmental and economic outcomes arising from selected on farm technologies. More specifically we began to examine the regulatory, institutional, and market barriers associated with technology adoption within the swine industry. We provide a theoretical model to support quantification of the change in revenues and expenses that result from changes in three major markets connected to swine production – carbon, electricity, and fertilizer. We examine some of the economic characteristics of environmental benefits associated with changes to farm practices. Finally, we discuss implications for innovation in technology and policy.

What have we learned?

Preliminary results are somewhat mixed and further research is needed to see how sensitive the life cycle assessment inputs and outputs are to system components. While there is a clear indication that covering lagoons, with or without additional nutrient recovery, reduces environmental impact – farm scale systems can be quite expensive and no further determination can be made until a full economic analysis has been conducted. Modeling secondary effects, such as increased ammonia emissions in barns from flush water recirculated from digesters, remains to be included. Besides farm level cost and returns, review of literature has pointed to additional barriers to adoption of reduced environmental impact technologies. Examples of barriers include deficient or non-existent markets for environmental benefits, and various state and federal regulations and policies related to renewable energy, carbon offsets, new farm waste management technology, etc. Solutions such as better cooperation between energy firms, regulatory agencies, and farmers as well as increased financial incentives such as carbon credits, renewable energy credits, net metering options, and enabling delivery of biogas to natural gas pipelines can greatly increase the profitability and implementation of this technology on NC hog farms.

Future Plans

As this is an ongoing multi-disciplinary project, future plans include the expansion of existing data to form a more comprehensive life cycle inventory with options for both new and existing swine farms, which include additional options for waste treatment, nutrient recovery, and land application/fertilizer methods, etc. Energy and emissions data from the life cycle model will continue to be utilized as inputs into a more fully integrated model capable of reflecting the true “cost” and “values” associated with waste management treatment systems. In addition, it is expected that the integrated model will include the flexibility to simulate overall costs and returns for various sizes of operations within the county, region, and if possible state-wide.

Corresponding author, title, and affiliation

Shannon Banner, Graduate Student, North Carolina State University

Corresponding author email


Other authors

Dr. John Classen, Dr. Prince Dugba, Mr. Mark Rice, Dr. Kelly Zering


Funding for this project was provided by a grant from Smithfield Swine Production Group

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.

Assessment of Coordinated Anaerobic Digestion of Dairy Manure

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Improving the economic feasibility of anaerobic digestion projects for processing dairy manure.

What did we do? 

We completed a study that evaluated the economics of dairy manure granulation as means to export phosphorus from P-sensitive watersheds. To achieve this goal we developed a techno-economic optimization model that considers all dairy farms within the watershed simultaneously to determine the minimum break-even price for the granulated manure.

A second study was developed to assess the economics of anaerobic digestion using a techno-economic optimization model. We incorporated different revenue sources (power sale, methane destruction credits, renewable energy certificates (RECs) and tipping fee (if co-substrate is available). The model evaluated the project feasibility over ranges of values for technical and economic parameters to quantify the project resilience to uncertainty in process conditions.

What have we learned? 

The results from the first study indicated that multi-farm participation can significantly improve feasibility and overall economics of manure granulation. Herd sizes were found to be a critical parameter in deciding whether a farm can economically participate in coordinated management. For manure granulation projects, liquid-solid separation followed by transportation of separated solids was always more economical than transporting raw manure from satellite farm to central processing facility. In the second study, electricity sale price was found to be the key parameter that determines the feasibility of anaerobic digesters. The hub-spoke configuration, where a large central farm hosts the digester and smaller surrounding farms contribute to it was found to be the most favorable arrangement. The size of the hub farm was critical to the feasibility of the project. Similarly, transportation distance was a critical factor that constrained the extent of cooperative digesters.

Future Plans    

The information generated from these studies is being written into peer-review publications and factsheets to share insights of collaborative manure management with a wider audience.We are currently expanding the model by adding the option for manure transportation via pipelines. Furthermore, we are also incorporating additional biogas utilization technologies,i.e., natural gas sale over pipelines and also the utilization of power/heat on-site in manure upgrading and processing.

Corresponding author, title, and affiliation        

Troy M. Runge, Associate Professor, University of Wisconsin-Madison

Corresponding author email    


Other authors   

Mahmoud A. Sharara, Rebecca Larson

Additional information

1. http://www.are.wisc.edu/

2. Sharara, Mahmoud, Apoorva Sampat, Laura W. Good, Amanda S. Smith, Pamela Porter, Victor M. Zavala, Rebecca Larson, and Troy Runge. “Spatially explicit methodology for coordinated manure management in shared watersheds.” Journal of Environmental Management 192 (2017): 48-56.

3. Sharara, Mahmoud, Qiang Yang, Thomas L. Cox, and Troy Runge. “Techno-economic assessment of dairy manure granulation.” In 2016 ASABE Annual International Meeting, p. 1. American Society of Agricultural and Biological Engineers, 2016.


This work is based on research supported by the USDA National Institute of Food and Agriculture for its financial support (USDANIFABRDI Grant No. 2012-10006-19423) and funding from Dane County, Wisconsin under Award Number 12486.

Innovative Business Models for On-farm Anaerobic Digestion in the U.S.

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AgSTAR is a collaborative voluntary program of the Environmental Protection Agency (EPA) and United States Department of Agriculture (USDA). AgSTAR promotes the use of anaerobic digestion (AD) systems to advance economically and environmentally sound livestock manure management. AgSTAR has strong ties to industry, government, non-profit and university stakeholders and assists those who enable, purchase or implement anaerobic digesters by identifying project benefits, risks, options and opportunities.

Anaerobic digestion (AD) continues to be a sustainable manure management opportunity with growing interest in innovative business models for project development.   AD systems provide a number of benefits, including improved nutrient management, locally sourced renewable energy, and diversified revenue streams for farmers.   As energy prices remain low across the country, and interest grows in managing food waste and organics outside of landfills, new business models have been implemented to make these on-farm AD projects viable. This presentation will provide a national overview of the livestock AD sector, explore new AD projects across the U.S., and highlight successful projects with innovative business models.

The presentation will cover several case studies of AD projects on topics including:

  • Third-party ownership and development of projects;
  • Food waste collection and boosting project profitability through tip fees and increased biogas production;
  • Eco-market products from dairy manure fibers; manure-based alternatives to peat moss for the horticulture industry; and
  • Biogas to vehicle fuel; opportunities and financial considerations.

With only 244 operating on-farm AD projects across the U.S., there exists a great opportunity for market share growth at the approximately 8,000 farms that could support a project. This, coupled with the desire for alternative management of organic waste streams, provides a unique opportunity for this sector to grow in the near future.

Pigs in a fieldCows in a field

Corresponding author, title, and affiliation

Nick Elger

Program Manager

AgSTAR & Global Methane Initiative

U.S. Environmental Protection Agency

1201 Constitution Ave NW, Mail code: 6207J

Washington, D.C. 20460

Phone: 202.343.9460

Email: elger.nicholas@epa.gov



Small to Mid-Sized Dairies: Making Compact Anaerobic Digestion Feasible

Why Consider Small or Medium Digester Projects?

Anaerobic digestion (AD) is an environmentally-friendly manure management process that can generate renewable energy and heat, mitigate odors, and create sustainable by-products such as bedding or fertilizer for dairies and farmers. However, due to economics, a majority of commercially available AD technologies have been implemented on large farming operations. Since the average herd size of dairies across the country is below 200 head of milking cows, there is a need for small-scale AD systems to serve this market.

eucolino allen farmsWhat did we do?

The University of Wisconsin-Oshkosh, in collaboration with BIOFerm™ Energy Systems, installed the EUCOlino—a small-scale, mixed, plug-flow digester—onto on a 136 milking head Wisconsin Dairy. The system is pre-manufactured, containerized and requires very limited on-site construction.   This includes grading, pouring a concrete pad for the containers and electrical services installation.

Start-up and commissioning were performed after the delivery of the 64 kWe combined heat and power (CHP). The input materials consist of bedded-pack dairy manure (corn or bean stover and straw), parlor wash water, and minor additional substrates such as lactose or fats, oils, and grease.

Solid materials are dumped via bucket tractor into a hopper feeder system that uses an auger to feed substrate into the anaerobic digestion tank. Additional parlor water is piped directly into the anaerobic digestion tank and mixed with the solids to make a feedstock of approximately 13% total solids. The solids are fed hourly, which is controlled by the PLC system.

The digester has a ~30-day retention time and the biogas produced is stored in a bag above the fermenters. Biogas produced is conditioned and combusted in a CHP mounted on a separate skid. Effluent from the system is pumped directly to an open pit lagoon for storage and subsequently land applied as fertilizer. The system produces approximately 25 – 33 m3/hour of biogas, with a raw biogas quality of 52-60% CH4 and less than 700 ppm H2S.

concrete pads for installation

What have we learned?

This project has been an important step forward in developing future small-scale anaerobic digesters across the U.S.  Notably, our installation has given us insight into balancing system economics with the size of small-scale models; the energy output of the system must exceed pre-processing energy requirements and the digester must still be large enough for the designed residence time. Our experience has shown that, while reducing the size of a digester, these requirements remain essential for an installation to economically make sense.

Additionally, challenges involved in AD at the small-scale are related to pre-processing or feedstock conveyance. Once suitable consistence or size for conveyance, anaerobically digesting the organic fraction can be relatively easy. Inconsistency of incoming feedstocks is very detrimental to the system’s stability. Additionally, exterior feedstock storage and above ground piping can limit processing potential when severe cold weather settles in. While all of these are challenges that are easily overcome with engineering, they come at a cost and that can make or break the economics at this scale.

Future Plans

For the small-scale EUCOlino to be effective in the United States, it is key to establishing a U.S.- based manufacturing location. Pre-processing needs to be well-suited to the incoming feedstock. Post-digestion products need established off-takers, for electricity generation, bedding, fertilizer, etc.


Steven Sell, Manager Application Engineer, BIOFerm™ Energy Systems beaw@biofermenergy.com

Whitney Beadle, Marketing Communications, BIOFerm™ Energy Systems

Additional information

The following publications offer additional information on the Allen Farms digester:

Readers interested in this topic can also visit our website for more information on the Allen Farms digester and other BIOFerm projects. We can also be found on Facebook, Twitter, and LinkedIn.

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. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

The Great Biogas Gusher

Why Pursue Bio-Energy?

The great Texas Oil Boom, also referred to as the Gusher Age, provided for dramatic economic growth in the US in the early 20th century, and ushered in rapid development and industrial growth. Although we typically think of the Middle East when we consider the impacts of oil discoveries on local economies (reference Dubai), at the time of its discovery, the oil finds in Texas were unprecedented; and the US quickly became the world’s top producer of petroleum.

As we all know, the rest of the world came to the party, and the US was soon falling in the ranks of top petroleum producers. Though the US oil reserves are vast, increasing concerns over the environmental impacts of finding, mining, extracting, refining, and consuming fossil fuels has incentivized the development of renewable energy resources, such as solar, wind, hydro, and bioenergy. Of these forms of renewable energy, bioenergy holds the promise for replacement of fossil fuels for transportation use.

a biogas collection systemWhat did we do?

Bioenergy may be described as fuels derived from organic materials, such as agricultural wastes, through processes like anaerobic digestion. The US has even more organic resources above the Earth’s surface than are identified in the petroleum and natural gas deposits yet to be exploited, yet the development of agricultural bioenergy systems seems to be progressing at a snail’s pace, as compare to the great Oil Boom. There is enormous potential in producing biogas from agricultural, industrial, municipal solid waste, sewage and animal byproducts which can be used to fuel vehicles. The EPA estimates that 8,200 US dairy and swine operation could support biogas recovery systems, as well as some poultry operations. Biogas can be collected from landfills and used to power natural gas vehicles or to produce energy. Wastewater treatment plants are estimated by the EPA to have the potential of about 1 cubic foot of digester gas per 100 gallons of wastewater, this energy could potentially meet 12% of the US electricity demand. Industrial, commercial and institutional facilities provide another source of biogas, in particular supermarkets, restaurants, and educational facilities with food spoilage.

What have we learned?

This presentation compares and contrasts the historical development of fossil fuel reserves with the potential for development of bioenergy from agricultural sources, such as animal wastes and crop residues. The US energy potential from these sources is grossly quantified, and current development inhibitions are identified and discussed. Opportunities for gathering biogas and bioenergy from multiple regional sources, similar to the processes used in the Texas oil fields, are discussed. The presentation offers insight into overcoming these obstacles, and how the US may once again rise to the top of the energy development rankings through efficient use and stewardship of our organic resources.

Percentage of waste water treatment plants that send solids to anaerobic digestion broken out by state

Future Plans

Biogas and bioenergy resources present an enormous opportunity for renewable energy development, and progression toward energy independence for the U.S. The U.S. currently has more than 2,000 active biogas harvesting sites, but claims more than 11,000 additional sites can be developed in the U.S., with the potential to power more than 3 million American homes if used to fuel electricity generating power plants. The USDA, EPA and DOE recently created a US Biogas Opportunities Roadmap which is off to a good start, which hopefully will initiate biogas programs, and foster investment in biogas systems to improve the market vitality in each state. To move the process forward, policy-makers, investors and the public need to have improved collaboration and communication on the state level. We need to develop a clear plan and strategy for developing these valuable biogas resources to promote environmental sustainability and economic growth of our b ioenergy sector.


Gus Simmons, P.E., Director of Bioenergy, Cavanaugh & Associates, P.A. gus.simmons@cavanaughsolutions.com

Additional Information           

http://www.cavanaughsolutions.com 1-877-557-8924



USDA/DOE/EPA US Bioenergy Roadmap

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. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

Money to Burn: How to Capitalize on BioCNG at Your Wastewater Plant


Across the globe, units of government are struggling with the balance of deriving clean energy with economics and environmental protection. This struggle has led to the development of many renewable energy innovations and inventions, such as rapid improvement in the cost and efficiencies of photovoltaic solar (PV) systems and the development of large off-shore wind turbine systems. The challenges imposed on energy utilities associated with managing grid variability leads emphasis on the development of ‘baseload’ alternative energy systems, like bioenergy systems. We should recognize, however, that we have a bounty of organic wastes generated by society each day, and systems that are able to recycle these organic resources into energy are capable of more consistent energy generation, as compared to the intermittency of solar and wind. In this regard, such bioenergy systems hold promise for balancing our energy needs.

Waste to worth mtb figure 1.What did we do?  

Bioenergy systems based on the utilization of organic wastes, such as municipal wastes, food wastes, and crop residues provide the additional benefits of supporting improved pollution prevention and waste treatment systems.

Of the organic wastes available for us in bioenergy systems, one may be directly correlated to the increasing energy needs and clean energy desires of the global population – waste organics associated with municipal wastewater treatment. Municipal wastewater treatment strategies vary by geography, climate, and level of development across our globe. However, in all cases, opportunities exist to utilize these waste as feedstocks for the creation of biogas that may be used to fuel electricity generators, farm implements, and the transportation needs of our population.

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What have we learned?  

Many municipal and industrial wastewater treatment plants (WWTP) across the U.S. already utilize anaerobic digestion as a primary treatment process to reduce sludge or reduce organic loading, expressed as Biochemical Oxygen Demand (BOD), to subsequent aerobic treatment processes. However, most of these facilities presently flare the biogas that is produced from the digestion process. Most often, these managers report the following reason for lack of implementation of energy harvesting. WHAT REASON???

We continue to seek clean, renewable energy sources across the globe to reduce our dependency on fossil fuels for improved air quality and economic stability. While solar, wind, and other renewable energy sources play a vital role in a diversified energy strategy, the development of bioenergy systems that continuously operate in ‘base load’ fashion is very important for grid stability. Additionally, unlike solar and wind, bioenergy systems that convert organic wastes into fuels have opportunities to positively impact transportation fuel needs. The development of systems that harvest biogas from anaerobic digesters employed at municipal wastewater plants can serve to fill a portion of this need, and create improved revenues for the wastewater treatment utility. Often, anaerobic digesters serving municipal wastewater treatment plants are operating well under their optimum capacity, creating opportunities for municipalities to engage in partnerships with private sector waste generators, such as food and beverage processors, restaurants, and farmers.

Many commercial fleets are converting to natural gas fuel to realize the cost savings and participate in programs that reward cleaner air quality through reduced emissions. Each commercial waste truck that is converted to natural gas from diesel has a comparable impact to removing 325 cars from the road. Currently the costs of natural gas-fueled vehicles are slightly higher (10-15%) than conventionally-fueled vehicles. However, as the costs of fossil fuels rise, and more CNG vehicles are manufactured, the costs are likely to become very similar.


****An explanation of the table below would be useful.. You should use this document to outline how you conducted the study and what you found, most of the information contained is introductory in nature.

Table 1.

Table 2.Future Plans    

Unlike fossil fuels, which are finite in quantity, bioenergy and biogas systems convert the organic wastes that are generated each day into fuel; often in only a few days’ time. In this regard, bioenergy systems offer a truly infinite resource for renewable energy, while providing the added benefit of pollution reduction and additional revenues to support existing wastewater treatment infrastructure systems.


Gus Simmons, Director of Bioenergy, Cavanaugh & Associates, P.A. gus.simmons@cavanaughsolutions.com

Additional information




Clean Water Needs Survey, 2008

Loyd Ray Farms, Yadkinville, NC

Duke University Carbon Offsets Initiative

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. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.