Economic Feasibility Study of Colorado Anaerobic Digester Projects ...

Low Moisture
Manure and
Other
Waste
Organics
High Organic Leachate
High Rate
Anaerobic Digester
Methane Gas
Figure 3.1 Two-Stage Anaerobic Digestion Process
B. Appropriate Volume and Mix of Feedstock: Interviews with both technology
providers and producers affirmed that a consistent, chemically balanced level of
feedstock is necessary in order to sustain the chemical reaction required to produce
bio-methane over time and to reduce AD system maintenance 2 . Several technology
providers noted that volume and mix of feedstock is one of the most important factors
in determining whether or not an AD project will be successful. Furthermore,
technology providers noted that feedstock issues make it challenge to maintain a
properly functioning digester at a single farm. One technology provider estimated
that a scale of 4,000-5,000 tons of feedstock is required in order to create a
sophisticated AD system with industrial controls capable of ensuring smooth
operation. Stated the provider, “Single-farm based systems are not sophisticated
enough to guarantee consistent operation.” Cooperatives, community digesters, and
co-digestion offer greater promise for consistent feedstock than independent, farmlevel
systems, and suggestions for optimal Colorado locations have recently been
identified by Stewart Environmental (2008).
C. Reducing the Administrative Burden of Cogeneration: Nearly all technology
providers noted that co-digestion and relationships with other industries (such as
food processing facilities), are critical make projects profitable and ensure a
consistent level of feedstock. This is particularly when an AD operator is able to
collect a tipping fee from feedstock providers. Other industries can also benefit from
the low odor, reduced emissions, and environmental benefits that can be facilitated
2 One technology provider, reluctant to provide proprietary financial data, provided the threshold of
“3,500 dairy cows” as the minimum level required to justify installation of a system in the state of
Colorado. The technology provider estimated that feedlot levels should be a 25,000-30,000 head,
considerably higher due to animal dietary needs. Another reference, the 2008 Stewart Environmental
report, uses 5,000 dairy cows as an estimated threshold for profitability.
Economic Feasibility Study of Colorado Anaerobic Digester Projects
Prepared by Dr. Catherine Keske, Colorado State University
August 2009
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