merrillgould – Livestock and Poultry Environmental Learning Community

Purpose

The online Bioenergy Training Center provides educational training resources for Extension educators focused not only on the technical feasibility of bioenergy generation, but also on approaches and processes that assist communities in understanding the comprehensive implications of bio-based alternative energy. The intended outcome of the courses is to bring viable bioenergy projects into communities by providing Extension educators with tools and knowledge they can use to make this happen.

What Did We Do?

Developed three peer-reviewed, research-based online modular courses. Content was developed by experts from across the North Central Region. Included in one of the modules is a bioenergy and renewable energy community assessment toolkit.

Screen shot of the front page of the Bioenergy Training web site.

What Have We Learned?

The curriculum went live on the web in February 2013. We have not received any feedback on it to date. However, based on the reviews of individuals who used the bioenergy and renewable energy community assessment toolkit in 2012, it does a very good job of helping developers and communities objectively assess renewable energy projects.

Acknowledgements

Curriculum materials and training programs of ‘The Bioenergy Training Center’ were made possible through a grant from the National Water Resources Program, National Institute of Food and Agriculture, U.S. Department of Agriculture. NIFA/USDA Agreement No. WISN-2007-03790. Project Title: “Energy Independence, Bioenergy Generation and Environmental Sustainability: The Role of a 21st Century Engaged University”.

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. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

Anaerobic Digestate Pile at Scenic View Dairy in Fennville, MI

Anaerobic Digestate Pile, Scenic View Dairy, MI. Photo: M.C. Gould, MSU Extension

Anaerobic digestion generates a wide range of byproducts that farmers can use in their farming operations or sell. Beyond biogas used to generate electricity or as fuel, and liquids used for fertilizer or soil amendments, there are solid byproducts, which have a wide range of applications.

Value-added opportunities for fiber from digesters

Closeup of digestate. Photo: M.C. Gould, MSU Extension

Undigested biomass (referred to as digestate solids, fiber or biofiber) contained in the effluent (digestate) of anaerobic digesters provides opportunities for value-added byproducts. Organic fertilizer, livestock bedding, compost, fuel pellets, and construction material (medium density fiberboard and fiber/plastic composite materials) are a few examples of value-added byproducts that could be created from digestate solids.

Separating solids from the digestate

Solids can be extracted from the digestate using solid-liquid separation technologies such as slope screens, rotary drum thickeners and screw-press separators. Common solid-liquid equipment can produce digestate solids with a moisture content of 18 to 30%. The volume and the moisture content of the separated solids will vary depending on the technology used. Digestate solids are high in fiber, consisting mainly of fibrous undigested organic material (lignin and cellulose), microbial biomass, animal hair, and nutrients.

Fertilizer

During the anaerobic digestion process, nutrients contained in the feedstock are mineralized. Mineralized nutrients are easily used by a crop. Digestate solids contain higher concentrations of plant-available nitrogen and phosphorus compared to as-excreted manure, according to research. The high carbon content of digestate solids adds organic matter to the soil and improves the water holding capacity of the soil. Actual nutrient content of digestate solids will vary depending on feedstocks, digester type, management, and solid-liquid separation technology. Digestate solids as a fertilizer source can be used “as separated” (wet), blended with other materials and composted or dried and pelletized.

Anaerobic Digester Fiber - Freestall Bedding

Digestate Solids used in freestall at Crave Brothers Dairy, WI Photo: M.C. Gould, MSU Extension

Livestock bedding

Bedding for livestock is another opportunity for putting digestate solids to use. Utilizing digestate solids for bedding provides a significant cost offset to dairy and livestock farms. In addition, excess solids may be sold to neighboring farms for bedding or soil amendment, creating a revenue stream and route for nutrient export. Bedding with digestate solids requires intensive management to ensure that a healthy environment, with low pathogen concentrations, is provided for the animals.

Other value added products using digestate solids

Digestate solids can also be used as substrate in compost, providing sources of carbon and nutrients. Solids can be dried and pelletized for use as fertilizer or fuel. The maximum energy content of livestock manure is 8,500 Btu per pound; however ash and moisture content reduce the energy potential. As excreted, livestock waste typically has an energy content between 1,000 and 2,000 Btu per pound.

Another developing opportunity for digestate solids is as a renewable construction material. Medium-density fiberboard and wood/plastic composite material have emerged as important engineered construction materials. These engineered materials can also be created using digestate solids without sacrificing mechanical or aesthetic properties, research indicates.

Organic potting soil made with digestate as medium. Photo: M.C. Gould, MSU Extension

References & Additional Resources

Gould, M.C. and M.F. Crook. 2009. On-farm Anaerobic Digester Operator Handbook. Michigan State University. East Lansing, MI.

Kammel, D.W. 2004. Bedded Pack Housing for Dairy Cows. Minnesota/Wisconsin Engineering Notes.

Matuana, L. and M.C. Gould. 2006. Promoting the Use of Digestate from Anaerobic Digesters in Composite Materials: Final Report. Community Energy Project Grant No. PLA-06-42.