BioCycle May 2010, Vol. 51, No. 5, p. 53
Mark Jenner

The American Biogas Council was launched last month and the commercial biogas industry is off and running! For most of the last 40 years, the incremental progress of the small biogas subsector of U.S. manure digesters has been like watching cold molasses run. After significant advances in technology design, market delivery options, and innovative policies, digesters will succeed as a commercial asset for industry and agriculture.
The U.S. EPA AgSTAR program has been a long-time champion of the evolution of the farm-manure digester industry. In early May, EPA and USDA announced a new interagency agreement to promote renewable energy generation and slash greenhouse gas emissions from livestock operations by expanding the work of the AgSTAR program. The collaboration will provide up to $3.9 million over the next five years. Another significant manure digester development has been the Innovation Center for U.S. Dairy’s Sustainability Initiative. They have charted an aggressive course to reduce the dairy industry greenhouse gas footprint by 12 percent by 2020.
Large-scale dairies continue to announce digester projects. These larger projects have a better chance of generating digester revenue than smaller projects. A feasible commercial project takes the following: 1) Proven technology; 2) Principal revenue market (electric or gas); 3) Secondary markets for heat and nutrients; 4) Credits and benefits from carbon markets; and 5) Access to public funding. Economic success requires most of these.
Large dairies and other high-volume waste streams are the low-hanging fruit. They have the greatest chance of success with the lowest risk of failure. Public funds spent on high volume waste streams reduce the greatest emissions for each public dollar spent. Efficiency and public policy give an advantage to large farms.
Farming is a serious business. Everyone who has been successful has earned every penny. The commercialization of large-scale digesters is exactly what is necessary. Small-scale digesters are just not as economically feasible as larger digesters. However, this does not mean that digesters cannot fit on smaller farms.

OPTIONS FOR SMALLER MANURE DIGESTERS
Large farm manure digester economics do not scale down at the same rate as an equivalent decrease in physical size. Larger digesters work well because each developer has invested decades in perfecting their biological ecosystems to run well at consistent, high volumes. Their intellectual knowledge has great value.
Larger, more productive digesters must generate enough revenue to pay back their high capital costs. Expensive components of a commercial digester include the intellectual property rights embedded in a proven technology, and the cost of the container. Fees for connecting to a power grid and/or the cost of cleaning the biogas for marketing off site in a pipeline can be high enough to kill the feasibility of a project. All three of these can be managed with smaller systems.
The cost of the anaerobic digester container is not easy to ignore. Fortunately, fewer animals require a smaller container. Earthen anaerobic lagoons of the Midwest and Southeast are cost-effective containers. These ambient temperature digesters only work well in areas without cold winters.
Wisconsin is funding a project for a local container company, USEMCO, to develop an inexpensive container for anaerobic digesters for as few as 100 cows. This is a good investment. Another factor that influences the container size is how much water is added to the system. Water is an excellent tool for moving manure away from the animals. It is only later – during treatment of all that water – when the costs of using all that water begin to add up. Additional water means a bigger digester container.
The egg-layer industry is a great example of manure handling systems that moved from flush/lagoon systems 40 years ago, to wet stacks, and now to manure that is so dry the nitrogen remains in the manure instead of venting into the exhaust fans. This not only improves human and animal breathing ability, but there is almost no water to haul to the field and the manure is higher in nitrogen. To get from lagoons to dry manure, water had to quit being added.
Generating electricity from a small digester unit still has the high overhead of needing generation and interconnect equipment. That makes on-farm use of raw biogas a very cost-effective proposition.
Recently EPA announced a student-team winner in the People, Prosperity, and Planet contest (P3) from Clarkson University in New York for their project in analyzing digester feasibility for 50 or fewer dairy cows in cold winter climates. In addition, the New York State Energy Research and Development Authority (NYSERDA) announced funding for a digester demonstration project on a dairy operation with 100 dairy cows. This kind of support is required to move digester technologies to smaller farms.
A note of caution before diving into a small-scale digestion project. Methane is explosive and if it is collected and not flared, it can escape the container a bit too close to sparking electric motors. We all handle explosive gasoline, but take precautions to avoid hazard. Digesters require the same precaution.
Farm-scale digesters look to ride the growth of the larger commercial biogas industry. Large commercial digesters can generate off-site energy more easily than the smaller digesters, but there are still benefits to be gained.

Mark Jenner, PhD, and Biomass Rules, LLC, has joined the California Biomass Collaborative. Burning Bio News and other biomass information is available at www.biomassrules.com.