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Dairy Component: Anaerobic Digester
Bioproducts
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About 65% of the methane in the atmosphere is attributable
to agriculture (Duxbury, 1994), with a significant portion arising
from dairy cows. Methane is about 23 times more potent as a greenhouse
gas than CO2. Most modern dairies utilize a lagoon system
for animal waste treatment, a practice that leads to large emissions
of methane and nitrous oxide. Closed-system anaerobic digestion
(AD) of the manure has the potential to eliminate most of the lagoon
emissions while conserving more nutrients and also producing a renewable
energy source. In Washington State alone, if half of the 250,000
dairy cows were on a farm with AD, as much as 100 million pounds
of methane could be captured each year (about 3.15 million tons
C equivalent). Currently, however, only one dairy in the state and
less than 100 in the nation utilize anaerobic digestion. While capital
costs are a major barrier to this technology, producers need more
impartial comparisons of the available systems and a realworld demonstration
of their performance in order to consider adoption of this technology.
Also, a dairy with anaerobic digestion is better able to achieve
nutrient balance and protect water quality by exporting excess nutrients
through the sale of the fiber, a by-product of the digester.
Complete mix and plug-flow digesters are two existing
representative technologies. The most suitable commercially available
system and one new system designed by our anaerobic digester research
team are being compared for their performance and the ability to
optimize manure treatment, energy production, greenhouse gas mitigation,
and by-product quality.
Dairy farms in Whatcom County will be monitored
over two years to generate baseline data on greenhouse gas emissions,
C and N Cycling, energy flows, input costs, and management and labor
costs. This will provide the quantitative starting point against
which environmental improvements can be measured.
We are collaborating in the design and construction
of a farm-scale digester. We will montior the greenhouse gas mitigation
potential, methane yield, and operational costs of the digester,
as well as the characteristics and quantities of energy, fiber and
nutrient water by-products. Nutrient budgets will be developed and
economic analysis conducted to determine the viability of nutrient
exports from the farm. Socioeconomic analysis will examine farm
profitability, regional economic impacts, and policy needs. Market
research and development will be initiated for the energy and fiber.
Benchtop scale in the laboratory, pilot scale in
WSU's Dairy Center, and a mobile prototype of the new AD system
is under construction for the comparison with current commercially
available AD systems. The new system is being developed by Dr. Shulin
Chen's research group. Features of the new system include: additional
enzymatic hydrolysis steps to prmote high efficiency fiber digestion,
mechanisms for bacterial biomass enhancement, and an innovative
digester configuration. Work will also be conducted to improve and
evaluate the new system design.
In addition, research and demonstration of AD co-products
from the fiber and liquid effluent of the digester is being undertaken.
These two co-products will provide several key benefits to animal
feeding operations including 1) facilitating export of excess nutrients
off farms, 2) creating additional revenue streams to provide adequate
returns on investment for ADs, which 3) helps to enhance both the
economic and environmental sustainability of dairy farms across
rural America. The specific objectives are to: (1) establish fiber
quality criteria and evaluate the fiber products from existing AD,
(2) evaluate management practices and modify designs that improve
the quality of AD fiber in order to satisfy high-value markets,
such as using the fiber as a peat moss replacement in the horticultural
industry (see article by WSU Horticultural Scientist Linda
Chalker-Scott on the sustainability of peat moss), (3) demonstrate
and improve the struvite production process from the AD effluent,
(4) conduct market and cost/benefit analysis of the fiber and struvite
co-products in addition to methane, and (5) disseminate the technology
and information.
Much of the potential value from anaerobic digestion
of dairy manure will come from the development of bioproducts
developed to complement energy production.
Monitoring of dairies began in Summer 2004. Construction
of farm scale digester on the Vander Haak Dairy is completed
and the digester is now producing 285 kw of electricity from 1,200
cows..
For more information on the dairy component of
the project, contact Shulin Chen,
WSU Biological Systems Engineering and Craig
MacConnell, Whatcom County Extension.
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Updated
July 18, 2006
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