Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments
3.0 Renewable Energy Technology
Options
In addition to wastewater and agricultural residues, Los Angeles Department of
Water has announced a new agreement to purchase power from a 40 MW anaerobic
digestion facility that will process 3,000 tons per day of municipal green waste (such as
landscape trimmings and food waste) to produce biogas for power production. The
facility is scheduled to be on-line by 2009. This facility would be the largest of its kind
in the world. There are various other high-solids digestions systems installed world wide.
These are primarily in Europe and Japan and use municipal solid waste and green waste
as feedstocks.
Biogas produced by anaerobic digestion can be used for power generation, direct
heat applications, and/or absorption chilling. Reciprocating engines are by far the most
common power conversion device, although trials with microturbines and fuel cells are
underway. (For further discussion of conversion technology options see Section 3.10.)
Agricultural digesters frequently satisfy the power demands for the farm on which they
are installed, but do not provide significant exports to the grid. Municipal sewage sludge
digesters generally produce enough gas to satisfy about half the wastewater treatment
plant electrical load. Power production is typically a secondary consideration in digestion
projects. Increasingly stringent agricultural manure and sewage sludge management
regulations are the primary drivers.
Resource Availability
For on-farm manure digestion, the resource is readily accessible and only minor
modifications are required to existing manure management techniques. In some cases,
economies of scale may be realized by transporting manure from multiple farms to a
central digestion facility. For central plant digestion of manure from many farms, the
availability of a large number of livestock operations within a close proximity is
necessary to provide a sufficient flow of manure to the facility. However, the larger size
of regional facilities does not necessarily guarantee better economics because of high
manure transportation costs. For anaerobic digestion of municipal sewage wastes the
resource is readily available at the wastewater treatment plant.
Cost and Performance Characteristics
Table 3-6 provides typical characteristics of farm-scale dairy manure anaerobic
digestion systems utilizing reciprocating engine technology.
21 March 2005 3-16 Black & Veatch