«Washington State Department of Agriculture October 2011 For more information or additional copies of this report, please contact: Washington State ...»
Washington Dairies and Digesters
Washington State Department of Agriculture
For more information or additional copies of this report, please contact:
Washington State Department of Agriculture
Dairy Nutrient Management Program
Nora Mena, Program Manager
P.O. Box 42560
Olympia, WA 98504-2560
WSDA Web site: http://agr.wa.gov
Dairy Nutrient Management on the WSDA Web site:
http://agr.wa.gov/FoodAnimal/Livestock-Nutrient/ Cover photos: Dairy cows at Werkhoven Dairy/Washington Dairy Products Commission; In-ground digester at Farm Power Lynden/WSDA; 750 kW engine-generator at Farm Power Lynden/WSDA This report would not have been possible without the knowledgeable, thorough work of Margaret Drennan in collecting, organizing and articulating the information presented.
AGR PUB 602-343 (N/10/11) Do you need this publication in a different format? Contact the WSDA Receptionist at (360) 902-1976 or TTY (800) 833-6388.
Washington Dairies and Digesters, October 2011 Table of Contents Introduction
Facts about Washington’s Dairy Farms
Dairy Digesters in Washington: An Overview
Washington’s Dairy AD Systems
Biogas Treatment and Use
Effluent Processing and Use
Dairy Digester Profiles
Profile: FPE Renewables
Profile: George DeRuyter & Sons Dairy
Profile: Qualco Energy
Profile: Farm Power Rexville
Profile: Farm Power Lynden
Profile: Van Dyk-S Holsteins
The Importance of Nutrient Management and Recovery
Nutrient Recovery in Washington
Washington Dairy Digestion Potential
Dairy Size and Anaerobic Digestion
Potential Growth in Digesters by 2020
Information for Future Digester Operators
Other Types of Anaerobic Digestion in Washington
References and Endnotes
Introduction For over the past decade, anaerobic digestion (AD) on U.S. dairy farms has been promoted as a technology with both environmental and economic benefits. As one of the nation’s top ten dairy states, Washington is considered a prime market for dairy digesters.
Today’s dairy AD systems take advantage of a naturally-occurring process in which microbes feed on dairy manure and other biodegradable materials, producing biogas and nutrient-rich effluent that can be separated into solid and liquid portions for different uses.
• The biogas is about 60% methane and 40% carbon dioxide, with trace amounts of other constituents, and is typically used to generate electricity and heat.
• The digested solids are often used as bedding for cows, or processed into compost, peat moss substitute, or other soil amendments.
• The liquid effluent is generally applied to agricultural land to support crop production.
At a production rate of 27 tons of manure per cow per year, Washington’s commercial dairies produce more than 6.9 million tons of manure annually 1. Dairy producers typically use flush or scrape systems to collect the manure into lagoons where it’s stored until applied to fields. The manure provides nutrients, particularly nitrogen and phosphorus, needed for crop production.
Anaerobic digestion enhances this manure management system, providing both environmental and economic benefits. On the environmental side, digesters produce renewable energy and reduce greenhouse gas emissions, odor, and pathogens in manure. On the economic side, digester owners can profit from renewable energy sales, tipping fees for taking other organic wastes, and sales of digested solids, carbon credits, Renewable Energy Credits (RECs), and potentially other co-products.
Participating dairies may save on bedding costs while still getting nutrients for crop production.
This report includes information about the dairy industry and dairy nutrient management in Washington, as well as brief profiles of the anaerobic digesters installed in Washington that use dairy manure as the primary feedstock. As of July 2011, there were six operating dairy AD systems in Washington using manure from more than eight dairy farms.
This information is presented to provide a resource to those interested in the status of dairy digesters in Washington. Information was compiled in June and July 2011 by the Washington State Department of Agriculture (WSDA). WSDA administers the state’s Dairy Nutrient Management Act (Chapter
90.64 RCW), which requires all commercial dairy farms to develop and implement nutrient management plans to protect surface and ground water quality.
Facts about Washington’s Dairy Farms Source: USDA National Agricultural Statistics Service, WSDA Dairy Nutrient Management Program Milk is Washington’s second most valuable agricultural commodity (after apples), with a farmgate value of $950 million in 2010. More than 690 million gallons of milk were produced at Washington dairy farms in 2010, making Washington 10th in the nation in milk production.
Based on 2010 registration data from the WSDA Dairy Nutrient Management program, Washington has 443 commercial cow dairy farms, with more than 250,000 mature dairy cows. Of these, 175 dairies, or 40 percent, are small, with 1-199 mature cows; 165 dairies, or 37 percent, are medium in size, with 200-699 mature cows; and 103 dairies, or 23 percent, are large, with 700 or more mature animals, including 16 dairies that have 2,500 or more cows (Figure 1) 2.
There are commercial dairy farms in 28 of Washington’s 39 counties, but most of the dairies are concentrated in a few areas. Whatcom County is home to the most dairy farms (125 farms and 46,588 mature cows), and Yakima County has the most dairy cows (67 farms and 93,606 mature cows). Most of the large dairies (70 percent) are located in the Yakima Valley and the Columbia Basin; small and medium-sized dairies are typical in western Washington’s dairy areas.
The trend in Washington and across the U.S. has been towards fewer, larger commercial dairies, while the total number of dairy cows has remained relatively stable. Here in Washington, the annual average number of dairy cows has ranged between 237,000 and 264,000 head for the last 20 years.
All of Washington’s commercial dairies are Grade A dairies, producing milk that is eligible for sale as fluid milk. Milk from Washington’s dairy farms is sold as fluid milk and cream or processed into butter, cheese, ice cream, dry milk powder or other products and primarily marketed in Washington and Alaska, and exported to east Asia.
Dairy Digesters in Washington: An Overview Although anaerobic digestion can be used to process any livestock or poultry manure, all six of the agricultural digesters operating in Washington are located on or associated with dairy farms.
These dairy digesters process manure from about 11,000 cows from Washington’s commercial dairy farms and, with the addition of other organic waste, are producing a steady output of up to 4,150 kilowatts of electricity, enough to power more than 2,700 homes, as well as generating other valuable products and benefits. On an annual basis, Washington’s dairy digesters capture 2,500 tons of methane, equivalent to more than 50,000 tons of carbon dioxide that would otherwise be released during conventional manure management.
Nationally, EPA AgSTAR 3 estimates that, as of July 2011, there are 142 dairy digesters operating in 26 states, with 88 digesters (62 percent) in the major dairy states of Wisconsin, New York, Pennsylvania, California and Vermont. EPA data shows Washington as 9th in the U.S. in number of dairy digesters.
The first of Washington’s dairy digesters started operating in 2004 and, since then, five others have been built. These digesters regularly receive manure from eight Washington dairy farms ranging in size from about 300 mature animals to more than 3,000 mature animals. Five digesters are located in northwest Washington and one is in eastern Washington, in the Yakima Valley. Three digesters are owned and operated by dairies, two are owned and operated by a local private company, and one is a public-private partnership. Figure 2 shows the location of the state’s dairies and dairy digesters.
Figure 2. Location of commercial cow dairy farms and dairy digesters, July 2011 Page 4 Washington State Department of Agriculture Washington Dairies and Digesters, October 2011 Washington’s dairy digesters all add varying amounts of other organic materials to the dairy manure in the digester and operate under a regulatory framework that was put in place by state legislation enacted in 2009 4.
This regulatory framework allows dairy digesters to receive pre-consumer, organic waste-derived materials without obtaining a solid waste handling permit if they meet certain conditions. To be eligible for the permit exemption, the feedstock for the digester must be, by volume, at least 50 percent livestock manure and no more than 30 percent pre-consumer, organic wastederived materials. Non-manure agricultural waste from the dairy can also be used.
In addition, the law specifies the handling and use of the organic waste, digested solids, and liquid effluent so as to address nutrient management, public health and other potential concerns. The permit exemption requires digester design and operation to be consistent with federal standards 5.
Table 1 summarizes some of the key characteristics of the state’s dairy digesters. More detailed information about each digester and the partner dairies is provided in the subsequent profiles.
Although all operate under the same framework, each digester has different characteristics because of local circumstances and the needs of the digester owners, contributing dairies and other partners.
Washington’s Dairy AD Systems A wide range of different technologies can be used in anaerobic digestion systems. Generally, for dairy digesters, manure and other biodegradable feedstocks are collected in a vessel where conditions are controlled to maximize the growth of a variety of naturally-occurring microorganisms. Under these conditions (which include controlled temperatures and the exclusion of oxygen), the microorganisms feed on these biodegradable materials and, as a byproduct, produce biogas. This biogas is captured and usually used to generate power and/or heat. Typically, the material exiting the digester is separated into solid and liquid streams.
Figure 3 shows the different steps and products found in varying combinations in the dairy AD systems in Washington. Each of these is discussed in more detail on the following pages.
Figure 3. Dairy AD system with added feedstocks and potential nutrient recovery
CNG = Compressed natural gas Digester Types There are two different digester designs currently in use in Washington. A hybrid plug-flow complete mix digester (designed by GHD, Inc. and installed by Andgar) is in use at five of Washington’s digesters. The other design is a complete mix digester installed by DariTech. The first full-scale system using the DariTech design began operating in June 2011. Both of these digester designs operate in the mesophilic temperature range, at about 100˚F, which supports good microbial activity and biogas production. There are other options for operating temperature, both higher (thermophilic) and lower (psychrophilic), which have different advantages and disadvantages for biogas production, system stability, and development and operation costs. The vast majority of digesters at U.S. dairies are mesophilic, according to EPA AgSTAR.
Page 6 Washington State Department of Agriculture Washington Dairies and Digesters, October 2011 Feedstocks In Washington, all of the operating dairy digesters use a combination of manure and some quantity of pre-consumer, organic waste-derived materials. This co-digestion has a number of advantages. The addition of pre-consumer waste can significantly increase biogas production over dairy manure alone.
The increase varies depending on the type and amount of waste used; in one study of a Washington digester, the addition of 20% high-energy pre-consumer waste resulted in a 100% increase in biogas production 6. Other research on feedstock addition to dairy digesters has shown biogas increases ranging from 25% to 400% 7,8. In addition to increased biogas production, the operator can collect fees, known as “tipping fees,” for receiving these wastes. In some cases, these tipping fees are a digester’s single largest revenue source. For the waste generator or collector, contracting with a digester may mean lower tipping fees compared to landfill disposal, reduced transportation costs, and a home for materials that are difficult to dispose of, such as grease trap waste.
Different organic wastes have different potential for biogas production, with manures at the low end of the spectrum. Washington’s dairy digesters process a wide range of pre-consumer waste, including whey, eggs, grease trap waste, fish and shellfish processing waste, chicken processing waste, cattle blood, wood processing pulp, cereal wastewater, and unsalable beverages. All these materials produce significantly higher amounts of biogas than dairy manure. Currently, the percentages of pre-consumer waste co-digested at Washington’s dairy digesters range from about 5% to close to 30% by volume.
Biogas Treatment and Use The biogas produced from anaerobic digestion usually consists of 55-70% methane (CH4) and 30-45% carbon dioxide (CO2). The biogas also contains trace amounts of ammonia, hydrogen, and hydrogen sulfide. The methane in the biogas can be used to produce electricity and heat, compressed natural gas (CNG), or pipeline gas.