On-farm Evaluation and Demonstration of Small-scale Biogas Technology

Final Report for FW06-325

Project Type: Professional + Producer
Funds awarded in 2006: $20,000.00
Projected End Date: 12/31/2009
Region: Western
State: Washington
Principal Investigator:
Chad Kruger
Washington State University
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Project Information


This project supported the development, fabrication and demonstration of a biogas technology application for small farms. Biogas technology has been used globally for decades, with primary applications for large-scale, high-tech commercial systems in Europe (and limited penetration in the US) and small-scale, low-tech “household” scale systems in Asia. The potential for application of biogas technology on small-scale farms in the US is great for providing alternative means for managing on-farm organic wastes (manure, on-farm food processing) and providing a clean, renewable source of energy for on-farm applications (thermal energy for water heating, food processing, etc.). Making biogas technology a viable option for small farms requires the development of reliable, effective biogas reactors that can be readily fabricated and maintained by farmers. This project evaluated existing designs, developed design recommendations that would overcome performance problems with existing designs, and fabricated three demonstration units for experimentation on farm. The final design selected for fabrication was a simple “plug-flow” reactor that combined elements to improve feedstock mixing and flow and retention of bacteria over the existing designs while maintaining simplicity for fabrication with readily available materials.


Rapidly rising costs for energy and agricultural inputs produced from non-renewable sources pose a critical threat to the economic viability of US farms. Small diversified and organic farms, while more insulated than chemically intensive farms, are still not immune to the effects of volatile energy markets and stand to gain considerably from the use of renewable energy technologies on farm. In particular, energy technologies focused on waste biomass – or bioenergy technologies – hold great promise for efficiently and inexpensively treating organic farm wastes, reducing odor and methane emissions (a powerful greenhouse gas), providing nutrient-rich material for land application, as well as producing renewable energy for use on farm. Biogas technology, also known as anaerobic digestion, is a natural, biological process that has been used worldwide for the treatment of wet, organic wastes and the production of biogas which is a form of renewable energy. Currently, less than 100 US farms use the technology.

Eighty seven percent of Washington’s farmers are classified as “small farms.” Many of these farms have shown a significant interest in the adoption of small-scale on-farm technologies for production and use of bioenergy and related co-products. These farmers are underserved by existing biogas technology providers as no commercially available technologies are suited to small-farm applications in the northern latitudes of the US. Currently available commercial biogas technologies of US or European design have limited applicability on small farms – they are primarily designed for digesting manure from large Confined Animal Feedlot Operations (CAFO’s) – and do not meet the technical or economic needs of the majority of small farmers in Washington State. Several small-scale biogas technologies are currently available from Asia. Three primary technologies are the Chinese fixed dome digester (Figure 1), the Indian floating cover digester (Figure 2), and the Taiwanese polyethylene tubular digester (Figure 3). Each of these technologies has been used successfully by subsistence farmers in the developing world, but could be improved with additional research and development. Furthermore, commercial application of these technologies in northern latitude, cold-climate regions such as Washington State will require improvements in engineering and design as these existing technologies were developed for tropical and sub-tropical application. Washington’s small farmers have requested research, education, and technology development in regard to small-scale biogas technology.

Refinement of small-scale biogas technology will improve the resiliency of small farms in the Western region to volatile energy prices and ultimately improve their sustainability. Key challenges for deploying commercially appropriate biogas technology on small-scale farms in the region include developing climate appropriate applications of the technology and financially appropriate turn-key packages, evaluating the role of biogas technology in the farming systems (including trade-offs with other waste-management practices, such as composting), education on use and maintenance of the systems, and identification of technologies for making the most valuable uses of the biogas (i.e. water heaters and stoves, small generators, liquid fuel conversions, etc.). The development of successful, small-scale biogas technology has tremendous application for farms throughout the Western region for improved waste management and as a substitute for non-renewable sources of energy. For example, the average cost/person for heating water in California in 2003 ranged from $163 (natural gas) to $488 (electricity) (California Energy Commission). As prices for non-renewable energy continue to rise, the use of on-farm biogas could provide a significant financial savings.

Project Objectives:
  • to introduce farmers to the potential opportunities of small-scale biogas technology applications

    to develop an improved/modified design based on the various Asian technologies

    to deploy and evaluate pilot plants on three farms.


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  • Lora Lea Misterly


Materials and methods:

Literature and design reviews of existing small-scale biogas systems were completed to determine the current state of available design and barriers to successful deployment of these systems. A workshop with participating producers, followed by a site visit were used to assess the types of materials and additional local design challenges that would need to be addressed. A conceptual design was developed by collaborating engineers in the WSU Department of Biological Systems Engineering and designs were drafted in CAD. The conceptual design was submitted as an invention disclosure to the WSU Office of Intellectual Property per university policy described in the WSU Faculty Manual. The conceptual design was shared with a biogas engineering and fabrication company (Andgar Corporation, Ferndale, Washington) who made additional recommendations for improvements and simplicity in the design for fabrication of pilot reactors. A final design and engineering drawings were developed in CAD and provided to Andgar Corporation to fabricate three pilot units for demonstration and experimentation on farm.

Research results and discussion:
  • More than 200 individuals (producers and others) in the Pacific Northwest have been introduced to the potential for small-scale applications of biogas technology as an alternative waste management/energy technology.

    A website with resources related to small-scale biogas has been created: http://csanr.wsu.edu/CFF/smallscalebiogas/smallscalebiogas.html

    A group of several producers have learned specific information about small-scale biogas technology and are prepared to fabricate and deploy a pilot biogas plant on their farms.

    An improved design has been developed that will provide far superior performance for applications of biogas technology in the US (and around the world).

    Three pilot biogas units were fabricated for on-farm demonstration and experimentation.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:
  • All materials produced for this project (as well as other relevant resources) are available at http://csanr.wsu.edu/CFF/smallscalebiogas/smallscalebiogas.html.

    Presentations were made at the Washington Tilth Producer’s Conference and the Regional Harvesting Clean Energy Conference. Farm demonstration sites were featured on Tilth Farm Walks. A demonstration model biogas reactor will be featured at the 2009 Washington Tilth Conference.

    A simple enterprise assessment tool useful for guiding initial plans for a biogas plant.

    An invention disclosure was filed with the WSU Office of Intellectual Property, according to university policy for inventions in the WSU Faculty Manual. At this time, the inventors anticipate that this invention will not be patented, but will be left in the public domain.

    Detailed CAD drawings for fabricating the pilot biogas units.

    The project director and collaborating scientists are developing a series of Extension Fact Sheets on various anaerobic digestion topics that have relevance to small-scale biogas (such as co-digestion of manure and food waste, land application of digestates, etc.) but are a separate activity from this project.

Education and Outreach Outcomes

Recommendations for education and outreach:

Potential Contributions

This project contributed a viable design for small-scale biogas applications for small, integrated farm operations in the northern latitudes. Detailed description of the engineering process and designs for the biogas reactor are attached in the WSU Invention Disclosure, which is also available on our small-scale biogas website: http://csanr.wsu.edu/CFF/smallscalebiogas/smallscalebiogas.html.

Highlights of the new design include:

1. A greenhouse and underground construction based strategy is proposed to preserve small scale digester temperature in cold climate.

2. A fermentation broth auto-recirculation mechanics is designed to introduce mixing and continuous inoculation with zero energy input

3. A high specific inner digester wall structure is designed to retain biomass

4. An arc baffle is specially designed to prevent influent short-circuit and dead zones formation

5. A hydrolysis chamber especially tailored for degradation of stalk materials separately from animal manure so as to avoid inner digester clogging

6. A slopefloor is designed to facilitate smooth desludge in cooperation with fermentation broth auto-recirculation mechanics

7. The arc baffle height is designed in such a way to crush any crust formed at water/liquid interface

A detailed CAD drawing of the pilot units that were fabricated follows in Figure 4

Four images of the fabricated pilots units are below.

Future Recommendations

It will be desirable for most small, integrated farms to “co-digest” manure with other available feedstocks, such as cheese whey (food processing wastes) and vegetative wastes. These wastes are generally much more volatile than manure and will produce more biogas. However, co-digestion can significantly increase the complexity of a biogas project, affecting both reactor sizing/design and management. Co-digestion is a rapidly emerging subject of research, and scientists have recently made significant contributions to the ability to assess the potential benefits of co-digestion (Zaher, et.al. 2009). A simplified publication of “standard feedstock mixes” for small farm applications would be extremely useful for improving small-scale biogas design, application and management.

Since the goal of small-scale biogas reactors is to keep them inexpensive and reliable, the likelihood is that users will want multiple material options for fabrication (ie. steel, concrete, brick, fiberglass, plastic, etc.) – including existing cast-off materials (ie. plastic tanks, barrels, etc.). Further experimentation by materials scientists and engineers on options for fabricating reactors is warranted.

Electricity is a very costly option for utilizing biogas (Bishop and Shumway, forthcoming) and a primary remaining barrier to widespread use of small-scale biogas. Current uses of biogas for small farms include thermal energy for water heating, cooking and food processing. Chengdu Biogas Institute has developed numerous “household scale” appliances for biogas utilization. However, higher value uses for biogas (ie. transportation fuel, tractor fuel, improved thermal recovery systems, flame-based weed control) would speed the adoption of biogas technology.

Bishop, C.P. and C.R. Shumway. Forthcoming. The Economics of Dairy Anaerobic Digestion with Co-Product Marketing. Review of Agricultural Economics.

Water Heaters, Consumer Energy Center, California Energy Commission http://www.consumerenergycenter.org/homeandwork/homes/inside/appliances/waterheaters.html

Zaher, Usama, et.al. 2009. A Procedure to Estimate Proximate Analysis of Mixed Organic Wastes. Journal of Water Environment Research 81:4.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.