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MANURE MANAGEMENT
FEASIBILITY STUDY - DANE COUNTY, WI
Dane County is one of Wisconsin’s most populous counties and one
of the leading agricultural counties in a largely agricultural
state. Like many other places, the number of farms has
decreased in the last decade, while the number of animal units (A.U.’s)
per dairy farm has increased. Dane County is also home to
significant surface water resources, including the Yahara chain
of lakes in the greater Madison area. The lakes, however, are
experiencing significant eutrophication because of high nutrient
loads. Based on some estimates, more than 75 percent of the
nutrients discharged to the Yahara River system are from
agricultural land in the county, and a significant portion of
those nutrients are derived from land application of manure.
This project
involved investigation of manure management alternatives to land
application of raw manure. These alternatives considered
single-farm systems as well as clusters of farms in the portion
of the Lake Mendota watershed located west, northwest, and north
of the lake (referred to as the “Upper Mendota Watershed” in
this study). The major objective was to remove at least 40
percent of the phosphorus (P) loading to the land. We were
retained by the County to conduct a feasibility study to
evaluate alternatives for manure management solutions. The
overarching goal of the study was to strengthen the livestock
industry in Dane County while protecting water quality as
related to manure management, considering the P, nitrogen, and
potassium requirements for land application.
The study began with a survey of the farmers in the Upper
Mendota Watershed, which includes the portions of Dane County
that have the highest P concentrations in the soil and the most
excess nutrients from manure. Farmers provided information on
current and future anticipated herd sizes, the quantity and
disposition of the manure, current and anticipated challenges in
manure management, and their level of interest in participating
in the study. The surveys were also used to select two clusters
of farms for evaluation of community systems.
The study examined the technical, logistical, financial, and
environmental factors related to implementing alternative manure
management approaches to accommodate the manure from two farm
clusters in the Upper Mendota Watershed. Alternatives were
evaluated using monetary and nonmonetary factors, with
sensitivity analyses completed for several critical monetary
factors.
This study was unique in that most of the similar manure
management studies in this country have focused on the economic
feasibility of anaerobic digestion, while the main driver for
this study was protection of water quality through reduction in
manure nutrient loadings, particularly P. The technologies
considered, with the exception of anaerobic digestion, have only
been used at a handful of farms in the United States, which made
evaluating their use particularly challenging. Because there
are no community facilities in operation in the Midwest and
nationally, there are only a limited number of examples. Issues
such as permitting, potential ownership models, and funding
alternatives needed to be considered as part of the feasibility
study.
The feasibility
study was completed in late 2007 and a final draft of the report
is available on the Dane County Internet site. Some of the
major conclusions of the study are as follows:
• Cluster manure management strategies appear to offer
significant economies of scale with respect to capital costs
compared to the individual farm systems. In general, while
comparing similar manure management strategies, the capital cost
projections of the cluster systems are approximately 50 to 75
percent of the capital cost of the individual farm systems when
compared on a “per A.U.” basis.
•
Some of the cluster management strategies have significantly
lower annual O&M cost projections (per A.U. basis) than the
existing annual O&M costs at the farms as well as the individual
farm manure management strategies. In particular the cluster
alternatives related to anaerobic digestion and incineration
could significantly reduce annual O&M costs and may generate net
revenues for the farms.
From a nonmonetary standpoint, the alternatives that
incorporated anaerobic digestion had the most favorable scores.
Anaerobic digestion is also projected to reduce greenhouse gas
emissions significantly when compared to current farm practices,
and such a project would potentially generate carbon credit
revenues for the farmers. Also, very importantly, all of the
alternatives evaluated resulted in significant reductions in
phosphorus loadings to the land when compared to current farming
practices, as summarized in the figure below.
We were recently retained by Dane County to prepare a facility
plan and preliminary design criteria for a cluster anaerobic
digestion system with phosphorus removal and biogas utilization
for energy production.
Summary of projected Phosphorous reductions.
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