DANE COUNTY
COMMUNITY DIGESTER

Waunakee, Wl

Meet An Anaerobic Digester

Operator

Let's Meet-

Norman Doll. Chief Operating Officer for Clear Horizons

Anaerobic Digester Type: Complete Mix
Operating Since: Late 2010 (filled digesters)

Is the digester serving its intended purpose(s)?

The project helps manage waste from three dairy farms,
as well as some food wastes, restaurant waste grease,
and glycerin. The digester meets two of the project's
primary goals: protecting water quality, and growing
crops sustainably. The Wisconsin Department of Natural
Resources (DNR) and Dane County also recognized the
project's potential to control and export phosphorous;
they proposed paying for the digester through the sale of
byproducts and energy produced by the system. So far,
the digester and advanced phosphorous removal system
have allowed the capture and export of about 90 metric
tons of phosphorous from the watershed.

What challenges have you have had with your
system?

Farms using sand bedding - As sand accumulated over
time, digester vessels lost up to half of their capacity.

Unplanned liquid recirculation - Liquid digestate,
saturated with phosphorous, was unexpectedly coming
back from the farm and negatively affecting the process
and skewing nutrient recovery numbers. The 30,000
gallons per day of digestate in the raw manure input
stream led to phosphorous precipitating out in the forms
of struvite and vivianite, causing problems in the pipes
and vessels.

Technologies -The project added nets (nylon cord
baseball netting) to the tops of digester tanks as growth
media for bacteria. These nets improve growth of
the bacteria that are the primary means of removing
hydrogen sulfide from tank gas. We need to continue to
keep up with improving technologies.

What is limiting the development of more
digesters with this business model?

The business model under which these (Crave Brothers
and Dane County Community Digester - Vienna) were
built is no longer workable in Wisconsin. When these
were built we had the encouragement of government;

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access to grants; and a utility mandate for a 15%
renewable portfolio (i.e., requirement to generate
15% of energy from renewable sources). That's gone.
Utilities will no longer provide favorable power purchase
agreements (PPA). Going forward, developers will need
to find a new model to make these systems financially
viable. Even with our existing systems, when the current
PPAs run out, we will need a new revenue source to
keep them operating.

How would you respond if asked by the public
about safety issues with AD systems?

There are a lot of safety issues with these types of
systems and with livestock operations in general.

But the potential for explosion-related injury is small,
especially for those outside the facility (because of how
the digesters are designed, an explosion would actually
go up, not outward). On site, there is a lot of truck traffic
that must be managed properly; we do not allow people
on the site unescorted. Agricultural work around tanks
and lagoons can be dangerous, but made safe with a
good safety program and proper management. We have
had no problems in this area.



"Madison lakes are in trouble, and Lake Mendota is on the

DNR watch-list. It is clear that nonpoint phosphorous is the problem

coming from urban runoff and farms. DeCFQdSllig phOSpflOFOUS 111 SOllS

IS 3 priority for Dane County and DNR and to do this they need to export it
out of the watershed. The mdnUFG processing systems used at the
Dane County Vienna digester enable them to do that, and also allow expansion of
farming in the watershed without increasing problems with water quality."

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